NASA/TP–2015–218482

Experimental and Computational Sonic 

Boom Assessment of Boeing N+2 Low 

Boom Models 

Donald A. Durston*

 

Alaa A. Elmiligui†

Susan E. Cliff*

Courtney S. Winski†

Melissa B. Carter†

Eric L. Walker†

* NASA Ames Research Center, Moffett Field, California 

† NASA Langley Research Center, Hampton, Virginia 

February 2015 

 
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NASA/TP–2015–218482

Experimental and Computational Sonic 

Boom Assessment of Boeing N+2 Low 

Boom Models 

Donald A. Durston*

 

Alaa A. Elmiligui†

Susan E. Cliff*

Courtney S. Winski†

Melissa B. Carter†

Eric L. Walker†

* NASA Ames Research Center, Moffett Field, California 

† NASA Langley Research Center, Hampton, Virginia 

National Aeronautics and 

Space Administration

Ames Research Center 

Moffett Field, California

February 2015 
i

Acknowledgements 

The authors would like to thank Linda Bangert, the Technical Lead in the High Speed Project 

overseeing this work, for her support and valuable input throughout the course of this work. We are 

grateful for the work done by the Boeing Seattle and Huntington Beach teams for their design of the 

QEVC concept and the wind tunnel models, for their leadership in the testing, and their CFD analyses. 

We appreciate the untiring efforts of the crews at the Ames 9- by 7-Foot Supersonic Wind Tunnel and the 

Glenn 8- by 6-Foot Supersonic Wind Tunnel for running the tests that provided all the experimental data 

herein. We are thankful for the CFD support of Mike Park and Michael Aftosmis, for adjoint-based 

solution adapted analyses with Cart3D, and we thank Edward Parlette, Sudheer Nayani, and Norma Farr 

for developing Euler and Navier-Stokes surface and volume grids. 

This report is available in electronic form at

http:// www.sti.nasa.gov/
ii 

Summary 

Near-field pressure signatures were measured and computational predictions made for several sonic 

boom models representing Boeing’s Quiet Experimental Validation Concept (QEVC) supersonic 

transport, as well as three axisymmetric calibration models. Boeing developed the QEVC under a NASA 

Research Announcement (NRA) contract for Experimental Systems Validations for N+2 Supersonic 

Commercial Transport Aircraft, which was led by the NASA High Speed Project under the Fundamental 

Aeronautics Program. The concept was designed to address environmental and performance goals given 

in the NRA, specifically for low sonic boom loudness levels and high cruise efficiency, for an aircraft 

anticipated to enter service in the 2020 timeframe. Wind tunnel tests were conducted on the aircraft and 

calibration models during Phases I and II of the NRA contract from 2011 to 2013 in the NASA Ames 9- 

by 7-Foot and NASA Glenn 8- by 6-Foot Supersonic Wind Tunnels. Sonic boom pressure signatures 

were acquired primarily at Mach 1.6 and 1.8, and force and moment data were acquired from Mach 0.8 to 

1.8. 

The sonic boom test data were obtained using a 2-in. flat-top pressure rail and a 14-in. round-top 

tapered “reflection factor 1” (RF1) pressure rail. Both rails capture an entire pressure signature in one data 

point, and successive signatures at varying positions along or above the rail were used to improve data 

quality through spatial averaging. The sonic boom data obtained by the rails were validated with highfidelity numerical simulations of off-body pressures using the CFD codes USM3D, Cart3D, and 

OVERFLOW. The test results from the RF1 rail showed good agreement between the computational and 

experimental data when a variety of testing techniques including spatial averaging of a series of pressure 

signatures were employed, however, reflections off the 2-in. flat-top rail caused distortions in the 

signatures that did not agree with the CFD predictions. The 9x7 and 8x6 wind tunnels generally produced 

comparable data. 

 
iii

Table of Contents 

Acknowledgements ........................................................................................................................................ i

Summary ....................................................................................................................................................... ii

List of Figures ............................................................................................................................................... v

List of Tables ................................................................................................................................................. x

Nomenclature ............................................................................................................................................... xi

1. Introduction ............................................................................................................................................ 1

2. Test Objectives and Overview ............................................................................................................... 3

3. Facilities ................................................................................................................................................. 4

3.1. Ames 9- by 7-Foot Supersonic Wind Tunnel ................................................................................. 4

3.2. Glenn 8- by 6-Foot Supersonic Wind Tunnel ................................................................................ 6

4. Full Scale Configuration and Wind Tunnel Models ............................................................................ 10

4.1. Quiet Experimental Validation Concept (QEVC) ....................................................................... 10

4.2. Wind Tunnel Models .................................................................................................................... 11

4.2.1. Performance Model ............................................................................................................... 11

4.2.2. Boom1 Model ........................................................................................................................ 16

4.2.3. Boom2 Model ........................................................................................................................ 19

4.2.4. Boom3 Model ........................................................................................................................ 20

4.2.5. Axisymmetric Models AS1, AS2, AS3 ................................................................................. 25

5. Instrumentation and Model Positioning ............................................................................................... 26

5.1. RF1 (14-in.) Pressure Rail ............................................................................................................ 26

5.2. 2-in. Pressure Rail ........................................................................................................................ 28

5.3. Pressure Transducers .................................................................................................................... 29

5.4. Model Balance and Additional Instrumentation ........................................................................... 29

5.5. Roll Mechanism ............................................................................................................................ 30

5.6. Linear Actuator ............................................................................................................................. 30

6. Wind Tunnel Flow Quality and Test Techniques ................................................................................ 31

6.1. Wind Tunnel Flow Quality ........................................................................................................... 31

6.1.1. Schlieren and Shadowgraph Imaging .................................................................................... 32

6.1.2. Lift, Angle of Attack, and Pitching Moment Variations During Sweeps ............................. 36

6.2. Corrections for Reference Runs ................................................................................................... 41

6.3. Test Technique Improvements ..................................................................................................... 44

6.3.1. Spatial Averaging and Error Analysis ................................................................................... 45

6.3.2. Tunnel Pressure ..................................................................................................................... 50

6.3.3. Humidity Levels .................................................................................................................... 50

6.3.4. Sampling Duration ................................................................................................................ 50

7. Experimental Results ........................................................................................................................... 53

7.1. Composite Plots of X- and Z-Sweep Individual and Averaged Signatures .................................. 53

7.2. Repeatability ................................................................................................................................. 60

7.3. Effect of Adjusting Height During X Sweeps .............................................................................. 63

7.4. Effect of Model Height ................................................................................................................. 64

7.5. Comparison of X vs. Z Sweeps ..................................................................................................... 66

7.6. Effect of Ram Position for Z Sweeps ........................................................................................... 70

7.7. Rail Comparisons — 14-in. (RF1) vs. 2 in. Rails ........................................................................ 72

7.8. Effect of Mounting Strut on Boom Model Signatures ................................................................. 77
iv 

7.9. Effect of Nacelles and Vertical Tails ............................................................................................ 79

7.10. Effect of Mach Number ............................................................................................................... 82

7.11. Effect of Total Pressure ............................................................................................................... 86

7.12. Effect of Angle of Attack ............................................................................................................. 87

7.13. Effect of Off-Track Angle ........................................................................................................... 89

7.14. Comparisons of Boom1 Model Signatures from 9x7 and 8x6 Tunnels ...................................... 92

7.15. Reference Run Comparisons and Effects of Humidity ................................................................ 95

7.15.1. Reference Run Repeatability at Constant and Varying Humidity ....................................... 95

7.15.2. Reference Pressure Changes Due to Swapping of Window Blanks .................................. 103

7.15.3. Comparison of Reference Pressures in 9x7 and 8x6 Tunnels Using 14-in. Rail ............... 104

7.15.4. Comparison of Reference Pressures in 9x7 and 8x6 Tunnels Using 2-in. Rail ................. 107

7.15.5. Comparison of Reference Pressures in 9x7 Parametric and TBC4 Tests Using 14-in. 

Rail ..................................................................................................................................... 109

7.15.6. Comparison of Reference Pressures for 14-in. and 2-in. Rails in 9x7 Parametric Test ..... 111

7.15.7. Comparison of Reference Pressures for 14-in. and 2-in. Rails in 8x6 TBC3 Test ............ 113

8. Computational Methods ..................................................................................................................... 115

8.1. Flow Solvers ............................................................................................................................... 115

8.1.1. USM3D ............................................................................................................................... 115

8.1.2. Cart3D / AERO ................................................................................................................... 115

8.1.3. Overflow ............................................................................................................................. 116

8.1.4. sBOOM ............................................................................................................................... 116

8.2. Grid Generation .......................................................................................................................... 116

8.2.1. Grid Extrusion Method: Mach Cone Aligned Prism ........................................................... 116

8.2.2. Grid Extrusion Method: Boom Grid (BG) .......................................................................... 117

8.2.3. Solution-Adaptive Cartesian Grids ..................................................................................... 118

8.2.4. Initial and Boundary Conditions ......................................................................................... 118

9. Comparison of Experimental Data and Computational Simulations ................................................. 118

9.1. AS2 Body of Revolution ............................................................................................................ 118

9.2. Boeing Boom1 Model ................................................................................................................ 122

9.3. Boeing Boom3 Model ................................................................................................................ 125

9.4. Performance Model .................................................................................................................... 128

10. Propagated Signatures to Ground Level ............................................................................................ 131

10.1. Repeatability .............................................................................................................................. 131

10.2. Effect of Mach Number ............................................................................................................. 131

10.3. Effect of Off-Track Angle ......................................................................................................... 133

11. Performance Model Drag Comparisons ............................................................................................ 133

12. Concluding Remarks ......................................................................................................................... 137

13. References ......................................................................................................................................... 138

Appendix A ............................................................................................................................................... 142

Appendix B ............................................................................................................................................... 145
v 

List of Figures 

Figure 1–1. Artist’s concept of Boeing N+2 QEVC supersonic transport ................................................... 2

Figure 3–1. Boeing Performance model installed in Ames 9x7-ft wind tunnel .......................................... 4

Figure 3–2. Boeing Performance model in Ames 9x7-ft wind tunnel with NASA (N) and Boeing 

(B) research and test staff ........................................................................................................ 5

Figure 3–3. Boeing Boom1 model installed in Glenn 8x6-ft wind tunnel .................................................. 7

Figure 3–4. Boeing Performance model in 8x6-ft wind tunnel, with view of porous window 

blank in upstream window frame and Schlieren window in downstream frame 

during week 1 of test ................................................................................................................ 8

Figure 3–5. Boeing Boom1 model in Glenn 8x6-ft wind tunnel, with view of porous window 

blank in downstream window frame and Schlieren window in upstream frame 

during week 2 of test ................................................................................................................ 8

Figure 3–6. Variation of total pressure and total temperature versus Mach number in 9x7 and 

8x6 wind tunnels (actual values from tests indicated by symbols) .......................................... 9

Figure 4–1. Boeing QEVC supersonic transport three-view drawing ....................................................... 10

Figure 4–2. Phase I Performance model top- and side-view drawings ..................................................... 11

Figure 4–3. CAD views of Performance model components .................................................................... 12

Figure 4–4. CAD views of Performance model modular parts ................................................................. 12

Figure 4–5. Photographs of assembled Performance model with sting can at aft end .............................. 13

Figure 4–6. Photograph of Performance model and interchangeable parts .............................................. 13

Figure 4–7. CAD views of Performance model, interchangeable parts, and sting with tailored 

dummy sting covers ............................................................................................................... 14

Figure 4–8. Photograph of Performance model new parts, and tailored sting covers ............................... 14

Figure 4–9. Boeing Performance model installed in Ames 9x7-ft wind tunnel ........................................ 15

Figure 4–10. Boeing Performance model installed in Glenn 8x6-ft wind tunnel ....................................... 16

Figure 4–11. Boom1 model top and side view drawings ............................................................................ 17

Figure 4–12. CAD views of VS1 strut (left) and Boom1 model with VS2 strut (right) ............................. 17

Figure 4–13. CAD views of Boom1 model modular parts .......................................................................... 18

Figure 4–14. Photographs of assembled Boom1 model .............................................................................. 19

Figure 4–15. Photographs of Boom1 model with VS2 strut mounted in 9x7 wind tunnel ......................... 19

Figure 4–16. Photograph of Boom1 (left) and Boom2 (right) models with interchangeable parts, 

VS1 and VS2 struts, balance adapter, and adapter fins ......................................................... 20

Figure 4–17. CAD views of Boom3 model, interchangeable parts, and VS3 and VS4 struts .................... 20

Figure 4–18. Photograph of Boom3 model, interchangeable parts, and VS3 and VS4 struts .................... 21

Figure 4–19. Photographs of Boom1, Boom2, and Boom3 (left to right) models ...................................... 22

Figure 4–20. Drawings of VS1, VS2, VS3, and VS4 struts ........................................................................ 23

Figure 4–21. Photographs of Boom1, Boom2, and Boom3 models with VS1, VS2, VS3, and VS4 

struts ....................................................................................................................................... 24

Figure 4–22. Photograph of AS2 model ...................................................................................................... 25

Figure 4–23. Photograph of AS2 model in 9x7 wind tunnel with RF1 rail mounted on forward 

window blank ......................................................................................................................... 25

Figure 5–1. Cross section of RF1 rail (dimensions in inches) ................................................................... 26
vi 

Figure 5–2. CAD views of RF1 14-in. rail mounted on forward window blank of 9x7 wind 

tunnel ...................................................................................................................................... 27

Figure 5–3. CART3D-AERO computation of the Seeb-ALR model, RF1 rail, and tunnel wall 

Mach = 1.6, α = 0 deg, h = 17.68 in. ..................................................................................... 28

Figure 5–4. CAD view of 2” pressure rail on aft window blank of 9x7 wind tunnel ............................... 28

Figure 5–5. Photographs of 2-in pressure rail on aft window blank of 9x7 wind tunnel .......................... 29

Figure 5–6. Fouling strip, cavity pressure tubes, and thermocouple wires attached to sting behind 

Performance model ................................................................................................................ 29

Figure 5–7. Fouling strip, cavity pressure tubes, and thermocouple wires on sting behind balance 

adapter .................................................................................................................................... 30

Figure 5–8. View of linear actuator and roll mechanism in 9x7 wind tunnel, with Boom1 model 

mounted on blade strut and balance adapter and RF1 pressure rail in background ............... 31

Figure 6–1. Schlieren images of Boeing Models in NASA Glenn 8x6 wind tunnel, taken through 

aft Schlieren windows ............................................................................................................ 33

Figure 6–2. RBOS images of Boeing Boom1 Model with VS2 strut in 9x7 wind tunnel, taken 

through the forward south side Schlieren window ................................................................ 34

Figure 6–3. Shadowgraph images of empty 9x7 wind tunnel, taken through forward Schlieren 

windows ................................................................................................................................. 35

Figure 6–4. Boom1 VS2 model lift, angle of attack, and pitching moment variations during X

sweeps, 9x7 parametric test ................................................................................................... 37

Figure 6–5. Boom1 VS2 model lift, angle of attack, and pitching moment variations during X

sweeps, 8x6 TBC3 test ........................................................................................................... 38

Figure 6–6. Boom1 VS2 model lift, angle of attack, and pitching moment variations during Z

sweeps, 9x7 parametric test ................................................................................................... 39

Figure 6–7. Boom1 VS2 model lift, angle of attack, and pitching moment variations during Z

sweeps, 8x6 TBC3 test ........................................................................................................... 40

Figure 6–8. Layout of reference and data runs in 9x7 wind tunnel for Boom1 VS2 model (view 

as from floor of tunnel looking up) ........................................................................................ 42

Figure 6–9. Layout of highest possible position of Performance model in 9x7 wind tunnel ................... 42

Figure 6–10. Layout of reference and data runs in 8x6 wind tunnel for Boom1 VS2 model ..................... 43

Figure 6–11. Differencing technique to isolate model pressure signature on the rail 9x7 

Parametric test, Boom1 VS2 model, M = 1.60, PT = 2292 psf, HumidAvg = 314 ppm ......... 44

Figure 6–12. Non-aligned and aligned waterfall plots for 9x7 parametric test X sweeps for AS2 

model ...................................................................................................................................... 45

Figure 6–13. Temporal and spatial uncertainty for the 9x7 and 8x6 wind tunnels ..................................... 48

Figure 6–14. Individual and averaged signatures for AS2 model runs 1010-1043 processed with 

either beginning or ending reference runs, 9x7 parametric test, 14-in. fwd rail, M = 

1.6 ........................................................................................................................................... 49

Figure 6–15. Averaged signatures for runs 1080 to 1105 processed with beginning and ending 

reference runs. 9x7 Parametric test, AS2 model, 14-in. forward rail, M = 1.60, α = 

0°, hNose = 30 in. ..................................................................................................................... 51

Figure 6–16. Beginning and ending reference run comparisons for run series 1080 to 1105 9x7 

Parametric test, AS2 model, 14-in. forward rail, M = 1.60, α = 0°, hNose = 50 in. ................. 51

Figure 7–1. AS2 model aligned waterfall plot and averaged signature plots for Z sweep from 

26” to 34” at XRam = 16 in., 9x7 parametric test, M = 1.6, 14-in. forward rail ....................... 55
vii

Figure 7–2. AS2 model aligned waterfall plot and averaged signature plots for X sweep from 0” 

to 8” at hNose = 59 in., 8x6 TBC3 test, M = 1.56, 2-in. rail ..................................................... 56

Figure 7–3. Boom1 VS2 model aligned waterfall plot and averaged signature plots for X sweep 

from 0” to 16” at hNose = 60 in., 9x7 parametric test, M = 1.6, 14-in. aft rail ......................... 57

Figure 7–4. Boom3 VS3 model aligned waterfall plot and averaged signature plots for Z sweep 

from 59” to 65”, 9x7 TBC4 test, M = 1.6, 14-in. aft rail ....................................................... 58

Figure 7–5. Performance model aligned waterfall plot and averaged signature plots for Z sweep 

from 59” to 65”, 9x7 TBC4 test, M = 1.6, 14-in. aft rail ....................................................... 59

Figure 7–6. Repeatability, X and Z sweeps 9x7 parametric test, AS2 model, 14-in. forward rail, 

M = 1.60 ................................................................................................................................. 61

Figure 7–7. Repeatability, X sweeps (0” to 16”) 9x7 parametric test, Boom1 VS2 model, 14-in. 

aft rail, M = 1.60 .................................................................................................................... 61

Figure 7–8. Repeatability, Z sweeps (59” to 64”) 9x7 TBC4 test, Performance sting+contour 

model, 14-in. aft rail, M = 1.60 .............................................................................................. 62

Figure 7–9. Repeatability, Z sweeps (59” to 64”) 9x7 TBC4 test, Performance sting+contour 

model, 14-in. aft rail, M = 1.80 .............................................................................................. 62

Figure 7–10. Effect of adjusting height in X sweeps (8” to 24”) 9x7 parametric test, Boom1 VS2 

model, 14-in. fwd rail, M = 1.60, HumidAvg=314 ppm ........................................................ 63

Figure 7–11. Effect of adjusting height in X sweeps (8” to 24”) 9x7 parametric test, Boom1 VS2 

model, 14-in. fwd rail, M = 1.80, HumidAvg=306 ppm ........................................................ 64

Figure 7–12. Effect of model height, X sweeps (8” to 24”, 0” to 16”) 9x7 parametric test, Boom1 

VS2 model, M = 1.60, HumidAvg = 301 ppm ....................................................................... 65

Figure 7–13. Effect of model height, X sweeps (8” to 24”, 0” to 16”) 9x7 parametric test, Boom1 

VS2 model, M = 1.80, HumidAvg = 295 ppm ....................................................................... 65

Figure 7–14. X vs Z sweep comparisons 9x7 parametric test, AS2 model, 14-in. forward rail, M

= 1.60, HumidAvg = 306 ppm ................................................................................................ 67

Figure 7–15. X vs Z sweep comparisons 9x7 parametric test, Boom1 VS2 model, 14-in. fwd rail, 

M = 1.60, HumidAvg=308 ppm ............................................................................................. 67

Figure 7–16. X vs Z sweep comparisons 9x7 parametric test, Boom1 VS2 model, 14-in. fwd rail, 

M = 1.80, HumidAvg=307 ppm ............................................................................................. 68

Figure 7–17. X vs Z sweep comparisons 9x7 parametric test, Boom1 VS2 model, 2-in. fwd rail, 

M = 1.60, HumidAvg = 321 ppm ........................................................................................... 68

Figure 7–18. X vs Z sweep comparisons 9x7 parametric test, Boom1 VS2 model, 2-in. fwd rail, 

M = 1.80, HumidAvg = 317 ppm ........................................................................................... 69

Figure 7–19. Effects of ram position for Z sweeps (26” to 34”) 9x7 parametric test, AS2 model, 

14-in. fwd rail, M = 1.60, HumidAvg = 306 ppm .................................................................. 70

Figure 7–20. Effects of ram position for Z sweeps (26” to 34”) 9x7 parametric test, Boom1 VS2 

model, 14-in. fwd rail, M = 1.60, HumidAvg=304 ppm ........................................................ 71

Figure 7–21. Effects of ram position for Z sweeps (26” to 34”) 9x7 parametric test, Boom1 VS2 

model, 14-in. fwd rail, M = 1.80, HumidAvg=306 ppm ........................................................ 71

Figure 7–22. Rail comparisons, X sweeps (8” to 24”) 9x7 parametric test, AS2 model, M = 1.60, 

HumidAvg = 302 ppm ............................................................................................................ 74

Figure 7–23. Rail comparisons, Z sweeps (26” to 34”) 9x7 parametric test, AS2 model, M = 

1.60, HumidAvg = 301 ppm ................................................................................................... 74

Figure 7–24. Rail comparisons, Z sweeps (26” to 34”) 9x7 parametric test, Boom1 VS2 model, 

M = 1.60, HumidAvg = 313 ppm ........................................................................................... 75
viii 

Figure 7–25. Rail comparisons, X sweeps (8” to 24”) 9x7 parametric test, Boom1 VS2 model, M

= 1.60, HumidAvg = 319 ppm ................................................................................................ 75

Figure 7–26. Rail comparisons, X sweeps (0” to 8”) 8x6 TBC3 test, Boom1 VS2 model, M = 

1.56, HumidAvg = 111 ppm ................................................................................................... 76

Figure 7–27. Rail comparisons, X sweeps (0” to 8”) 8x6 TBC3 test, Boom1 VS2 model, M = 

1.78, HumidAvg = 77 ppm ..................................................................................................... 76

Figure 7–28. Boom model mounting strut effects, X and Z sweeps 14-in. aft rail, M = 1.60, 

HumidAvg = 245 ppm ............................................................................................................ 78

Figure 7–29. Boom model mounting strut effects, X and Z sweeps 14-in. aft rail, M = 1.80, 

HumidAvg = 243 ppm ............................................................................................................ 78

Figure 7–30. Effects of Boom1 model nacelles and vertical tails, X sweeps (0” to 12”, 0” to 8”) 

8x6 TBC3 test, 14-in. rail, M = 1.56, HumidAvg = 181 ppm ................................................ 80

Figure 7–31. Effects of Boom1 model nacelles and vertical tails, X sweeps (0” to 8”) 8x6 TBC3 

test, 14-in. rail, M = 1.78, HumidAvg = 81 ppm .................................................................... 80

Figure 7–32. Effects of Boom3 model nacelle variations(N1, N3, N4), Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 225 ppm ........................................... 81

Figure 7–33. Effects of Performance model nacelle variations (N1, N3, N4), Z sweeps (59” to 

65”) 9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 220 ppm ................................. 81

Figure 7–34. Effects of Performance model nacelle variations (N1, NI4-NN3, NI3-NN4) Z

sweeps (59” to 65”), 9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 236 ppm ......... 82

Figure 7–35. Effect of Mach number for Boom1 VS2 model, X sweeps (8” to 24”) 9x7 

parametric test, 14-in. forward rail, h = 30 in., HumidAvg = 308 ppm .................................. 83

Figure 7–36. Effect of Mach number for Boom1 VS2 model, X sweeps (8” to 24”) 9x7 

parametric test, 2-in. forward rail, h = 30 in., HumidAvg = 320 ppm .................................... 83

Figure 7–37. Effect of Mach number for Boom1 VS2 model, X sweeps (0” to 16”, 0” to 24”) 

9x7 parametric test, 14-in. aft rail, h = 60 in., HumidAvg = 287 ppm ................................... 84

Figure 7–38. Effect of Mach number for Boom3 VS3 model, Z sweeps (59” to 65”) 9x7 TBC4 

test, 14-in. aft rail, HumidAvg = 227 ppm .............................................................................. 84

Figure 7–39. Effect of Mach number for Performance sting+contour model, Z sweeps (59” to 

65”) 9x7 TBC4 test, 14-in. aft rail, HumidAvg = 292 ppm .................................................. 85

Figure 7–40. Effect of total pressure for Boom1 VS2 model, Z sweeps (26” to 34”) 9x7 

parametric test, 14-in. forward rail, M = 1.6, HumidAvg = 298 ppm .................................... 86

Figure 7–41. Effect of angle of attack for Boom3 VS3 model, Z sweeps (59” to 65”) 9x7 TBC4 

test, 14-in. aft rail, M = 1.60, HumidAvg = 230 ppm ............................................................. 87

Figure 7–42. Effect of angle of attack for Performance sting+contour model, Z sweeps (59” to 

65”) 9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 278 ppm ................................. 88

Figure 7–43. Effect of angle of attack for Performance sting+contour model, Z sweeps (59” to 

65”) 9x7 TBC4 test, 14-in. aft rail, M = 1.80, HumidAvg = 237 ppm ................................. 88

Figure 7–44. Effect of off-track angle for Boom1 VS2 model, X sweeps (8” to 24”), hNose = 30.1 

in. 9x7 parametric test, 14-in. forward rail, M = 1.80, HumidAvg = 306 ppm .................... 89

Figure 7–45. Effect of off-track angle for Boom3 VS3 model, Z sweeps (59” to 65”) 9x7 TBC4 

test, 14-in. aft rail, M = 1.60, HumidAvg = 226 ppm ............................................................. 90

Figure 7–46. Effect of off-track angle for Performance sting+contour model, Z sweeps (59” to 

65”) 9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 265 ppm ................................. 90

Figure 7–47. Effect of off-track angle for Performance sting+contour model, Z sweeps (59” to 

65”) 9x7 TBC4 test, 14-in. aft rail, M = 1.80, HumidAvg = 237 ppm ................................. 91
ix 

Figure 7–48. Comparison of Boom1 VS2 model signatures from 9x7 and 8x6 wind tunnels 14-

in. rail, M = ~1.6, hNose = 60 in. .............................................................................................. 93

Figure 7–49. Comparison of Boom1 VS2 model signatures from 9x7 and 8x6 wind tunnels 14-

in. rail, M = ~1.8, hNose = 30 to 60 in. ..................................................................................... 93

Figure 7–50. Comparison of Boom1 VS2 model signatures from 9x7 and 8x6 wind tunnels 2-in. 

rail, M = ~1.6, hNose = 30 to 60 in. .......................................................................................... 94

Figure 7–51. Comparison of Boom1 VS2 model signatures from 9x7 and 8x6 wind tunnels 2-in. 

rail, M = ~1.8, hNose = 30 to 50 in. .......................................................................................... 94

Figure 7–52. 9x7 reference run comparisons, 14-in. rail, M = 1.60, constant humidity ............................. 96

Figure 7–53. 9x7 reference run comparisons, 14-in. rail, M = 1.60, varying humidity .............................. 97

Figure 7–54. 9x7 reference run comparisons, 14-in. rail, M = 1.80, constant humidity ............................. 98

Figure 7–55. 9x7 reference run comparisons, 14-in. rail, M = 1.80, varying humidity .............................. 99

Figure 7–56. 8x6 reference run comparisons, 14-in. rail, M = 1.56, varying humidity ............................ 100

Figure 7–57. 8x6 reference run comparisons, 14-in. rail, M = 1.78, constant humidity ........................... 101

Figure 7–58. 8x6 reference run comparisons, 14-in. rail, M = 1.79, varying humidity ............................ 102

Figure 7–59. 8x6 reference run comparisons, 14-in. rail, M = 1.79 Schlieren windows 

downstream (week 1, runs up to 605), Schlieren windows upstream (week 2, runs 

630 and after) ....................................................................................................................... 103

Figure 7–60. 9x7 and 8x6 reference run comparisons, 14-in. rail, M = ~1.6 ............................................ 105

Figure 7–61. 9x7 and 8x6 reference run comparisons, 14-in. rail, M = ~1.8 ............................................ 106

Figure 7–62. 9x7 and 8x6 reference run comparisons, 2-in. rail, M = ~1.6 .............................................. 107

Figure 7–63. 9x7 and 8x6 reference run comparisons, 2-in. rail, M = ~1.8 .............................................. 108

Figure 7–64. 9x7 parametric test and TBC4 test reference run comparisons, 14-in. aft rail, M = 

1.60 ....................................................................................................................................... 109

Figure 7–65. 9x7 parametric test and TBC4 test reference run comparisons, 14-in. aft rail, M = 

1.80 ....................................................................................................................................... 110

Figure 7–66. 14-in. and 2-in. forward rail reference run comparisons, 9x7 parametric test, M = 

1.60 ....................................................................................................................................... 111

Figure 7–67. 14-in. and 2-in. forward rail reference run comparisons, 9x7 parametric test, M = 

1.80 ....................................................................................................................................... 112

Figure 7–68. 14-in. and 2-in. rail reference run comparisons, 8x6 TBC3 test, M = 1.57 ......................... 113

Figure 7–69. 14-in. and 2-in. rail reference run comparisons, 8x6 TBC3 test, M = 1.79 ......................... 114

Figure 9–1. Symmetry plane CART3D adjoint-adapted grid for AS2 model, M = 1.6, α = 0° ............... 119

Figure 9–2. Symmetry plane pressure contours for AS2 model, Cart3D, M = 1.6, α = 0° ..................... 119

Figure 9–3. Experiment/CFD comparisons for AS2 model 9x7 parametric test, 14-in. forward 

rail, M = 1.60, hNose = 30 in., α = 0° ..................................................................................... 120

Figure 9–4. Experiment/CFD comparisons for AS2 model 8x6 TBC3 test, 2-in. rail, M = 1.56 

(WT), 1.60 (CFD), hNose = 60 in., α = 0° .............................................................................. 121

Figure 9–5. Surface pressure contours for Boom1 VS2 model, USM3D laminar results, M = 1.6, 

α = 3.4° ................................................................................................................................ 122

Figure 9–6. Symmetry plane pressure contours for Boom1 VS2 model, Cart3D, M = 1.6, α = 

3.4° ....................................................................................................................................... 122

Figure 9–7. Experiment/CFD comparisons for Boom1 VS2 model 9x7 parametric test, 14-in. 

forward rail, M = 1.60, hNose = 30 in., α = 3.4° ..................................................................... 123
x 

Figure 9–8. Experiment/CFD comparisons for Boom1 VS2 model 9x7 parametric test, 14-in. 

aft rail, M = 1.60, hNose = 60 in., α = 3.4° ............................................................................. 124

Figure 9–9. Surface pressure contours for Boom3 VS3 model, USM3D laminar results, M = 1.6, 

α = 3.1° ................................................................................................................................ 125

Figure 9–10. Symmetry plane pressure contours for Boom3 VS3 model, USM3D laminar results, 

M = 1.6, α = 3.1° .................................................................................................................. 125

Figure 9–11. CFD predictions for effect of off-track angle for Boom3 VS3 model, USM3D SA 

turbulent results, M = 1.6, hNose = 60 in., α = 3.1° ............................................................... 126

Figure 9–12. Experiment/CFD predictions for Boom3 VS3 model at various off-track angles 9x7 

TBC4 test, 14-in. aft rail, M = 1.60, hNose = ~60 in., α = ~3.1° ............................................ 127

Figure 9–13. Surface pressure contours for Performance model, USM3D SA turbulent results, 

M=1.6, α=3.4° ...................................................................................................................... 128

Figure 9–14. Symmetry plane pressure contours for Performance model, USM3D SA turbulent 

results, M=1.6, α=3.4° ......................................................................................................... 128

Figure 9–15. CFD predictions for effect of off-track angle for Performance model, USM3D SA 

turbulent results, M = 1.6, hNose = 60 in., α = 3.1° ............................................................... 129

Figure 9–16. Experiment/CFD predictions for Performance model at various off-track angles 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, hNose = ~60 in., α = 3.1° to 3.6° ........................... 130

Figure 10–1. Repeatability of sBOOM-extrapolated signatures for Performance model 9x7 

TBC4 test, 14-in. aft rail, M = 1.60, hNose = ~62 in., α = 3.3° .............................................. 132

Figure 10–2. Effect of Mach number in sBOOM-extrapolated signatures for Boom1 VS2 model 

9x7 parametric test, 14-in. forward rail, M = 1.60, hNose = 30 in., α = 3.4° ......................... 132

Figure 10–3. Effect of off-track angle in sBOOM-extrapolated signatures for Boom3 VS3 model 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, hNose = ~62 in., α = ~3.0° ..................................... 133

Figure 11–1. Experiment/CFD comparisons of drag polars for Performance model, M = 1.6, α = 

2.75o ..................................................................................................................................... 134

Figure 11–2. Experiment/CFD comparisons of turbulence models for Performance model, M = 

1.6, α = 2.75o ........................................................................................................................ 134

Figure 11–3. Grid convergence study for Performance model, M = 1.6, α = 2.75o .................................. 136

Figure 11–4. Effect of gridding style on drag prediction for Performance model, M = 1.6, α = 

2.75o ..................................................................................................................................... 136

List of Tables 

Table 1. N+2 Supersonic Transport (2020) Goals ................................................................................. 2

Table 2. Tunnel Operational Characteristics .......................................................................................... 9

Table 3. Boeing QEVC N+2 Flight Vehicle Attributes ....................................................................... 11

Table 4. Wind Tunnel Model Geometry .............................................................................................. 26

Table 5. Average ranges of variations of lift, angle of attack, and pitching moment during X

or Z sweeps ............................................................................................................................ 36

Table 6. Combinations of Boom Models and Struts Tested ................................................................ 77
xi 

Nomenclature 

bRef Model reference span, in. 

CAD Computer-Aided Design 

CFD Computational Fluid Dynamics 

CoR Center of Rotation 

CRef Model reference chord length, also mean aerodynamic chord, in. 

Duration Sampling duration for single data point (sequence number), sec 

EI NOx Emissions index of NOx (nitrogen oxides), grams of NO2 per kg of fuel 

EPNdB Effective perceived noise level in decibels 

h, h_nose Model altitude at model nose, in.

h/L, h_nose_L Model altitude non-dimensionalized by model length 

HumidAvg Average humidity from wind tunnel sensors, ppm by weight 

LRef Model reference length, in. 

LM Lockheed-Martin 

L/D Lift-to-drag ratio 

M Mach number 

MAC Mean Aerodynamic Chord, in. 

NaN Not a Number 

P Rail static pressure or ground overpressure (increment over ambient pressure), psfa 

P∞ Free stream static pressure, psfa 

PT Free stream total pressure, psfa 

PLdB Perceived sound level in decibels 

psfa Pounds/square foot absolute 

q Dynamic pressure, psf 

QEVC Quiet Experimental Validation Concept 

Re Reynolds number, non-dimensional, ρVL/μ

Re_L Reynolds number per unit length, 1/foot 

RF1 Reflection Factor 1, name of 14-in. pressure rail 

RBOS Retro-reflective Background-Oriented Schlieren 

SRef Model reference area, sq ft 

SWT Supersonic Wind Tunnel 

X Longitudinal coordinate, positive aft, in. 

XRam Longitudinal extension of linear actuator ram, in. 

Z Coordinate in tunnel angle-of-attack plane: lateral in 9x7, vertical in 8x6, positive “above” rail, in. 

α Angle of attack, degrees 

β Angle of sideslip, degrees 

ΔP/P Overpressure coefficient, (P – P∞)/P∞

φ Off-track angle, or model roll angle relative to the rail, degrees 

Subscripts 

 Data Data run, where model pressure signature was measured on the rail 

 Ref Reference run “empty” tunnel measurement, where model pressure signature was not on the rail; 

 also a reference parameter for model geometry 

∞ ambient, or freestream, flow conditions 
1 

1. Introduction 

Flight at speeds greater than the speed of sound is currently not permitted over land, primarily 

because of the sonic boom annoyance and potential structural damage caused by sonic boom pressure 

waves generated by supersonic aircraft. Mitigation of the sonic boom is a key focus area of the High 

Speed Project under NASA’s Fundamental Aeronautics Program. The project is focusing on technologies 

to enable future civilian aircraft to fly efficiently with reduced sonic boom, engine and aircraft noise, and 

emissions. One major objective is the improvement of both computational and experimental capabilities 

for design of low boom aircraft. NASA and industry partners are developing improved wind tunnel 

testing techniques and new pressure instrumentation to measure the weak sonic boom pressure signatures 

of modern vehicle concepts. In parallel, computational methods are being developed to provide rapid 

design and analysis of supersonic aircraft with improved meshing techniques that provide efficient, 

robust, and accurate off-body pressures at several body lengths from vehicles with very low sonic boom 

overpressures. The maturity of these critical parallel efforts is necessary before low-boom flight can be 

demonstrated and commercial supersonic flight can be realized. 

The measurement of the sonic boom pressure signatures of modern low-boom supersonic vehicles in 

wind tunnels is challenging. Historically, these signatures were measured in a wind tunnel using needlelike conical probes that measure static pressure at a single point in the flow-field.1

 This technique requires 

axial translation of the model past the probe to obtain a complete pressure signature of the model (or 

translation of the probe past the model). Traditional methods used a move-pause data acquisition 

technique requiring between 40-60 minutes per signature, although a recent effort2

 has shown that near 

continuous model translation with environmentally-controlled pressure transducers and shortened 

pressure lines can significantly speed up data acquisition time using a probe. However, the single-probe 

technique is still prone to reduced data accuracy because of small changes in tunnel flow conditions even 

over short data acquisition times. Humidity, turbulence, ambient pressure variations and stream angle 

changes during model translation all contribute to reduced data quality. 

Unlike single-point conical probes, pressure rails with hundreds of closely-spaced pressure orifices 

measure a model’s entire sonic boom pressure signature at one location of the model in the tunnel. Rails 

offer significant gains in efficiency and precision compared with conventional conical probe testing. 

Several rails with different cross-sectional shapes have been investigated in the 9- by 7-Foot Supersonic 

Wind Tunnel at NASA Ames Research Center since 2008.3

 Initial rail concepts had flat or large-diameter 

rounded tips that resulted in unknown and inconsistent reflection (i.e., amplification of the pressure signal 

due to the shock reflection off the surface) of a model’s pressure signature. A pressure rail that effectively 

eliminates shock reflection and boundary layer growth effects on the tip of rail was designed in 2010 

using CFD analyses.3

 This rail, designated the “reflection factor 1” (RF1) rail, is 14-in. tall and tapered 

toward the tip to a 0.05-in. radius, and was used in some of the tests discussed in this report. Another rail 

used in these tests was a 2-in. tall flat-top rail, but reflection of the model shocks off the surface of this 

rail caused some parts of the model signature to be amplified. 

When NASA first used pressure rails for sonic boom testing in 2008, it was envisioned that model 

translation would be unnecessary since the rails capture an entire model signature at once. However, 

further testing with rails showed that spatially averaging a series of pressure signatures from a number of 

model positions significantly improved measurement accuracy.4,5 Small ambient pressure oscillations and 

disturbances caused by small shocks emanating from the tunnel structure are nearly eliminated by spatial 

averaging techniques. 

In 2009, NASA published a NASA Research Announcement (NRA)6

 requesting proposals for 

“System-Level Experimental Validations for Supersonic Commercial Transport Aircraft Entering Service 
2 

in the 2018–2020 Time Period.” The aircraft concepts were to be designed to second generation “N+2” 

supersonic vehicle technology with a focus on providing system-level solutions capable of overcoming 

the efficiency, environmental, and performance barriers to practical supersonic flight. The N+2 

environmental and performance goals are given in Table 1. 

Table 1. N+2 Supersonic Transport (2020) Goals 

Environmental Goals

Sonic Boom 85 PLdB up to 20° off-track 

Airport Noise (cumulative below stage 3) 10–20 EPNdB 

Cruise Emissions < 10 EI NOx 

Performance Goals

Cruise Speed Mach 1.6–1.8 low-boom flight 

Range 4000 nm 

Payload (passengers) 35–70 passengers 

Fuel Efficiency (passenger-nm per lb of fuel) 3.0 

The NRA contractors were to independently design N+2 concepts to meet these goals, and then build 

and test wind tunnel models to validate the sonic boom and aerodynamic performance estimates. Two 

companies were awarded the NRA contracts: Lockheed-Martin Aeronautics Company (LMAC) and The 

Boeing Company (TBC). This report covers the experimental measurements and CFD predictions for the 

concepts developed by Boeing, and a companion report covers the same for the concepts developed by 

Lockheed-Martin.7 

The contracts with both companies were executed in two phases, each concluding with wind tunnel 

test validation of the sonic boom characteristics of their design efforts. The first phase8,9 of Boeing’s 

efforts was focused on design of a low boom airliner (Figure 1–1), the reduction of on-track (directly 

below aircraft in straight-and-level flight) sonic boom signatures, and assessment of aerodynamic 

performance in light of the environmental and performance goals specified in the NRA. The second 

phase10-12 focused on nacelle integration with the airframe in terms of its effects on the boom signatures 

and aerodynamic performance, as well as inlet performance. 

 NASA provided Computational 

Fluid Dynamics (CFD) predictions of 

sonic boom pressure signatures of test 

articles prior to wind tunnel testing so 

that the experimentalists would have a 

firm understanding of the expected 

wind tunnel test results. Predicting 

accurate sonic boom pressure signatures 

of weak signals is challenging and 

significant improvements in the 

accuracy of sonic boom characteristics 

have been realized during the High 

Speed Project. Accurate CFD 

simulations can be obtained in many 

ways. One is by providing dense 

meshes within the sonic boom pressure 

disturbance along with mesh rotation 

Figure 1–1. Artist’s concept of Boeing N+2 QEVC 

supersonic transport 

Courtesy of The Boeing Company 
3 

techniques to align the mesh with the Mach angle.13 Another is to provide unstructured mesh adaptation 

with effective refinement criterion but without cell alignment.14 A clever method that provides dense 

unstructured meshes, by grid sourcing and stretching at the Mach angle, tends to align the cells through 

the stretching and shearing process.15 Solution-adaptive techniques using node-centered unstructured 

mixed-element meshes,16-18 or Cartesian-adaptive refinement methods with domain rotation for Euler 

solutions19-21 have proven successful. A method that provides anisotropic adapted unstructured mesh 

optimization for shock capturing has also been successfully used for the compressible Euler equations.22 

Also, structured overset grid methods,23 or hybrid methods24-26 that utilize an unstructured flow solutions 

in the near-field and structured grid solutions in the far-field can also provide accurate on-track 

calculations. Grid generation tools that allow stretching of the mesh in addition to alignment to the Mach 

cone angle27-30 offer smaller meshes that maintain density in the axial direction and reduce the effects of 

dissipation along characteristic lines. The CFD computations provided here use Mach cone aligned prism 

meshes.27 Some solution-adaptive (Cartesian and tetrahedral) results18-21 and new overset grid 

computations will also be shown. 

2. Test Objectives and Overview 

There were three primary objectives for conducting the tests in this experimental validations program: 

1. Obtain data to evaluate sonic boom and aerodynamic performance of the Boeing 

configurations, including the effects of nacelle changes and varying mass flows 

2. Improve wind tunnel test techniques for acquiring such data 

3. Provide a large, high-quality experimental validation database for CFD tool development and 

improvement of low-boom design methods 

The overall purpose of the experimental validations program was to design a viable low-boom 

supersonic transport aircraft that would meet the NRA environmental and performance goals. Boeing 

designed their N+2 transport to meet these goals, but needed high-quality experimental data to evaluate 

the merits of their design. Boeing worked with NASA in developing a wind tunnel test program that 

would meet their needs. Past experience and lessons learned were applied to the test program to get the 

best data possible, and additional valuable experience was gained for further improvement of the test 

techniques. The result was a large dataset that Boeing used to assess their multidisciplinary design and 

analysis methods for their Phase I transport design,8

 and their final N+2 design at the completion of Phase 

II of the NRA contract.10 These data also provided NASA and industry the information needed to 

validate their CFD codes. 

A total of five tests were conducted with The Boeing Company (TBC) in pursuit of the NRA goals: 

Phase I: 

1. TBC1: Ames 9x7-ft wind tunnel, April 2011, Test 97-0229 

2. TBC2: Ames 11x11-ft wind tunnel, June 2012, Test 97-0249 

3. TBC3: Glenn 8x6-ft wind tunnel, September 2012, Test 86-12-002 

Phase II: 

4. TBC4: Ames 9x7-ft wind tunnel, April 2013, Test 97-0259 

5. TBC5: Glenn 8x6-ft wind tunnel, March 2013, Test 86-13-001 

This report will cover data only from the TBC3 and TBC4 tests, where the data were spatially 

averaged, and also from a 9x7 “parametric” test (April 2012, Test 97-0250, also referred to herein as 

“97p”). No spatial averaging was done in TBC1, so this test will not be covered herein because the data 

quality is poorer without spatial averaging. TBC2 data were compromised by high lateral dynamics in the 

11x11-ft wind tunnel, and TBC5 data were acquired for inlet performance and recovery, which is not the 
4 

subject of this report. Various combinations of the Boeing N+2 “Boom” models, a “Performance” model, 

and axisymmetric calibration models were run in the above tests, which will be described in detail in the 

Models section below. 

3. Facilities 

Wind tunnel tests for the data presented herein were conducted at the NASA Ames 9- by 7-Foot and 

the NASA Glenn 8- by 6-Foot Supersonic Wind Tunnels. Brief descriptions of the wind tunnel facilities 

are presented in this section. 

3.1. Ames 9- by 7-Foot Supersonic Wind Tunnel 

The Ames 9- by 7-Foot Supersonic Wind Tunnel is part of the Unitary Plan Wind Tunnel31,32

complex at NASA Ames Research Center at Moffett Field, California. It is a continuous-flow, closedcircuit, variable-density tunnel equipped with an asymmetric sliding-block nozzle for setting Mach 

number. The floor of the wind tunnel test section is part of the nozzle block. It translates axially 

(streamwise) to vary the nozzle throat area while the contoured tunnel ceiling remains stationary. This 

combination provides a Mach number range from 1.55 to 2.5. The sidewalls are flat and parallel through 

the nozzle and test section. The asymmetric nozzle results in slightly larger stream angle variations in the 

vertical plane, on the order of 0.25 to 0.5 degrees, whereas stream angle in the horizontal plane is 

generally less than 0.2 degrees. The angle-of-attack plane is therefore horizontal, and the model support 

strut at the rear of the test section is oriented this way. Models are thus normally mounted wings vertical, 

and the strut’s side-to-side heave compensation keeps the model in the center of the tunnel as the pitch 

angle is changed. The forward end of the strut centerbody pivots by means of a mechanical joint 

Figure 3–1. Boeing Performance model installed in Ames 9x7-ft wind tunnel 

RF1 Rail
5 

(knuckle-sleeve system) to achieve any combination of angle of attack or sideslip within a 15° cone angle. 

Throughout this report, the model distance from the rail on the sidewall of the tunnel is referred to as 

“height,” even though in reality it is a horizontal distance in the 9x7 wind tunnel. 

The tunnel is driven by an 11-stage axial compressor powered by four wound-rotor motors totaling 

216,000 hp. The tunnel operates at total pressures between 634 and 3600 psfa with corresponding unit 

Reynolds numbers between 0.8 and 5.7 million per foot. For the subject series of sonic boom tests, the 

Mach number and total pressure have been prescribed in the tunnel control system, rather than Mach and 

Reynolds number, because it is more productive for the 9x7 to run in constant-pressure mode, allowing 

temperature to float. 

Figure 3–2. Boeing Performance model in Ames 9x7-ft wind tunnel with NASA (N) and Boeing (B) 

research and test staff 

Kneeling L–R: Eric Adamson (B), Michael Treese (N), Ross Flach (N), Don Durston (N) 

Standing L–R: Courtney Winski (N), Laura Kushner (N), Eric Walker (N), Ed Schairer (N), Nicole 

Mendoza (B), Spencer Fugal (B), Tom Romer (N), Susan Cliff (N), Stephen Shaw (B), Alaa Elmiligui (N)

Most types of testing in the 9x7 wind tunnel do not require very low humidity and fine control of it, 

but sonic boom testing is an exception because static pressure measurements are sensitive to humidity. 

Humidity is normally brought down to operational levels (less than 500 ppm by weight, depending on test 

requirements) by purging the tunnel of wet air and pumping back up with dry air, but for best data quality 

in sonic boom testing, this purging is supplemented by continuously injecting dry, high-pressure air to 

keep the humidity below ~300 ppm. Modulation of this dry-air injection has proven capable of 
6 

maintaining humidity within ±5 ppm, which has allowed more consistent static pressure measurements 

relative to earlier tests where humidity was not so tightly controlled. 

An installation photograph of the Boeing Performance model in the 9x7 tunnel is shown in Figure 3–

1. The model, RF1 pressure rail, strut and centerbody are visible in the photograph (the model is shown 

rolled approximately 60° from its normal wings-vertical orientation to better show the model’s upper 

surface features). The RF1 pressure rail is mounted on the north sidewall of the test section to measure 

the pressure signatures below the model. The wind tunnel strut movement controls the distance from the 

model to the top of the rail. 

A similar photograph of the Performance model in the tunnel surrounded by many (but not all) of the 

NASA and Boeing research and test staff associated with this test is shown in Figure 3–2. 

3.2. Glenn 8- by 6-Foot Supersonic Wind Tunnel 

The Glenn 8- by 6-Foot Supersonic Wind Tunnel33,34 is an atmospheric facility with a test section 

Mach number range from 0.25 to 2.0 (at discrete Mach numbers). It has dual-cycle operation in that it 

can operate closed-loop in an aerodynamic cycle, or open-loop in a propulsion cycle when combustion 

products are being introduced into the air stream. The tunnel is driven by a 7-stage axial compressor 

powered by three wound-rotor motors totaling 87,000 hp. Total pressure in the tunnel is a function of 

Mach number and temperature since the tunnel is not pressurized. High temperatures from the heat of 

compression are cooled by a heat exchanger on the leg of the tunnel opposite to the compressor and 8x6 

test section, but with the test section being immediately downstream of the compressor, temperatures in 

the 8x6 typically reach 200° F at speeds of Mach 1.8 and higher. The range of total pressure from 

minimum to maximum Mach number is roughly 2150 to 3625 psfa, with corresponding unit Reynolds 

numbers between 1.7 to 5.1 million per foot. A balance chamber surrounds the test section and is used to 

provide boundary layer and Mach number control of the airflow in the test section through slanted holes 

in the walls. 

Humidity is controlled by an air dryer in the tunnel circuit that consists of activated alumina in 

multiple beds. Each bed is two feet thick, through which all the wind tunnel air is continuously passed 

when not in bypass mode. On days when the outside humidity is high, the dryer beds can reach saturation 

during or by the end of an operating shift in the tunnel. At this point, they can no longer maintain a low 

dew point (upper limit is typically -15° F, an approximate humidity of 320 ppm by weight) to continue 

running without sacrificing data quality. The time it takes to reach saturation is dependent on the 

humidity of the outside air, as the tunnel is an atmospheric tunnel. During multiple-day test operations, 

the dryer beds are put through a heating and cooling cycle on a non-running shift to remove the excess 

moisture, as there is no active humidity control other than the dryer beds. 

The test section of this facility is 8 ft. high by 6 ft. wide and 23.5 ft long. The nozzle upstream of the 

test section consists of flexible walls that are moved inward by hydraulic jacks for supersonic flow, and 

the floor and ceiling of the tunnel through the nozzle and test section areas are flat and parallel. The test 

section is divided into two sections: a supersonic section, 9.08 ft long starting from the end of the nozzle, 

and a transonic section 14.42 ft long from the end of the supersonic section. The walls around the 

supersonic section are solid, and they are porous around the transonic section with 1-in. diameter holes at 

60° angles through the walls. 

Several different strut arrangements are available for the tunnel, but the one used in sonic boom 

testing is a supersonic strut that raises and lowers through the tunnel floor with a pitch capability of -5° to 

20°. Models are mounted wings-horizontal since the angle-of-attack plane is vertical. 
7 

Figure 3–3. Boeing Boom1 model installed in Glenn 8x6-ft wind tunnel 

For the TBC3 test, the RF1 pressure rail was mounted on the top wall of the transonic (porous wall) 

section to measure the pressure signatures of the models, which were thus required to be mounted upsidedown on the strut so the rail would see the model lower-surface pressures. The distance from the model to 

the rail was controlled by adjusting the height of the wind tunnel strut. A photograph of one of the Boeing 

Boom models in the 8x6 tunnel and the RF1 rail on the ceiling is shown in Figure 3–3. 

Two additional photographs of the 8x6 wind tunnel are shown in Figures 3–4 and –5 that show the 

positions of the windows in the tunnel side walls. In the first week of the TBC3 test, the tunnel was 

configured with porous window blanks in the upstream window frame and Schlieren windows in the 

downstream frames (Figure 3–4). This was done to accommodate Schlieren imaging of the models, as the 

strut and model mounting hardware positioned the models in line with the downstream windows. For the 

second week of testing, it was desired to have smoother flow at the model and over the pressure rail, so 

the Schlieren windows were moved forward and the porous blanks moved aft (Figure 3–5). The impacts 

of this move on the data will be discussed later. 

A short table summarizing the operational characteristics of the Ames 9x7 and the Glenn 8x6 wind 

tunnels is given in Table 2, and a plot of the pressure and temperature conditions experienced during the 

subject tests is presented in Figure 3–6. Throughout this report, data from the 9x7 are presented at Mach 

numbers of 1.6 and 1.8, but the corresponding Mach numbers obtained in the 8x6 were 1.56 and 1.78, 

respectively, because the tunnel only operates at discrete Mach numbers. These slight differences in 

Mach number are believed to be not significant for the comparisons made in this report. 

RF1 

Rail

RF1 

Rail

Boom1 VS2 

Model
8 

Figure 3–4. Boeing Performance model in 8x6-ft wind tunnel, with view of porous window 

blank in upstream window frame and Schlieren window in downstream frame 

during week 1 of test 

Figure 3–5. Boeing Boom1 model in Glenn 8x6-ft wind tunnel, with view of porous window 

blank in downstream window frame and Schlieren window in upstream frame 

during week 2 of test 

RF1 

Rail

Boom1 VS2 

Model

Boom1 VS2 

Model

RF1 

Rail
9 

Table 2. Tunnel Operational Characteristics 

 Ames 9x7-Ft Supersonic Wind Tunnel Glenn 8x6-Ft Supersonic Wind Tunnel 

Mach Range 1.55 – 2.5, continuously variable 0.36 – 2, discrete 

Pressure Control Range of 634 to 3600 psf Atmospheric; PT varies with Mach 

Temperature 

Control 

Heat exchanger removes most heat of 

compression 

Heat exchanger partially effective, 

TT dependent on Mach number 

Humidity 

Control 

Humidity control continuously available 

by make-up air and high-pressure air 

Humidity controlled by dryer beds, run 

time dependent on weather 

Nozzle Design Asymmetric sliding block (floor) nozzle Symmetric vertical flex walls 

Figure 3–6. Variation of total pressure and total temperature versus Mach number in 9x7 and 8x6 

wind tunnels (actual values from tests indicated by symbols) 
10 

4. Full Scale Configuration and Wind Tunnel Models 

4.1. Quiet Experimental Validation Concept (QEVC) 

The Boeing Quiet Experimental Validation Concept (QEVC) supersonic transport configuration was 

developed during Phase I of the Supersonic Experimental Validations NRA contract with Boeing. It was 

designed to the NASA N+2 goals (Table 1) for low sonic boom loudness levels and high cruise efficiency 

as an airliner feasible for entry into service in the in the 2018 to 2020 timeframe. It was designated by 

Boeing as their 6007 configuration after an extensive design study, and its design cruise flight conditions 

were Mach 1.8, CL = 0.104, and an angle of attack of 3.28 degrees. 

A three-view drawing of the configuration is shown in Figure 4–1, and the flight vehicle attributes are 

given in Table 3. It is a twin-engine design with the nacelles on top of the wing, and V-tails mounted 

outboard of the nacelles. The nacelles were placed on the upper surface to minimize their effect on the 

sonic boom signature, but this location creates potential problems with inlet recovery and distortion. The 

inlet performance, the effects of nacelles on the sonic boom, and the aerodynamic performance were 

investigated in Phase II of the study contract. 

Figure 4–1. Boeing QEVC supersonic transport three-view drawing 

88.6’ 

202.0’ 

10otail strike

19.3’ 

20.3’ 45°

59.5’ 

86.1’ 

Courtesy of The Boeing Company 
11 

Table 3. Boeing QEVC N+2 Flight Vehicle Attributes 

Length (ft) 202.0 

Span (ft) 86.1 

Reference area (sq ft) 2,592 

Flight altitude (ft) 47,500 

Cruise Mach number 1.8 

Cruise L/D 11.6 

Aspect ratio 2.86 

Taper ratio 0.17 

LE sweep angles (inbd/mid/outbd) 80°/71°/52° 

MAC (ft) 34.1 

4.2. Wind Tunnel Models 

4.2.1. Performance Model 

The Performance model is a 43.31-in.-long, 1.79%-scale model of the QEVC. This model was sized 

primarily for good resolution in measuring aerodynamic performance, with some reduced capability to 

measure off-body sonic boom pressure signatures as its length sometimes prevented fitting the entire 

signature on the rail, depending on position. It is sting-mounted, with a 1-in. diameter six-component 

Figure 4–2. Phase I Performance model top- and side-view drawings 

30.93” (balance center)

43.31”

43.31”

18.49”

36.96” model break (aft deck flap)

33.50” model break (nacelle)

20.05” model break (nose)

20.05”

2.96”

NASA 1”

Diameter 

Balance

1.57” 1.4”

7.49” 9.46”

Courtesy of The Boeing Company 
12 

balance located in the center of the model. To accommodate the sting and the balance, the aft body of the 

model had to be made with a constant cross section, thus unavoidably compromising the boom signature 

from this part of the model. In addition, the edges of the wings, V-tails, and nacelle inlets and nozzles 

were thickened to a minimum of 0.004 in. at model scale for manufacturability and durability. Other 

changes from the full-scale configuration necessitated by model manufacturing requirements were that the 

nacelles had to be moved inboard 5 in., the support pod thickness needed to be increased by 50%, and the 

V-tail wing tips and winglet thicknesses needed to be increased from an original t/c = 3% to 4.5%. 

Figure 4–3. CAD views of Performance model components 

Figure 4–4. CAD views of Performance model modular parts 

Courtesy of The Boeing Company 

Courtesy of The Boeing Company 
13 

Figure 4–5. Photographs of assembled Performance model with sting can at aft end 

Top- and side-view drawings of the model with sting are shown in Figure 4–2, and color-coded CAD 

representations of the model components are shown in Figures 4–3 and –4. The parts of the model that 

have interchangeable options are the wings, V-tails, and nacelles, and there are also three different sets of 

nacelle inlet plugs that can be inserted in the flow-through nacelles. Photographs of the assembled 

Performance Model are shown in Figure 4–5, and the model with all of its interchangeable parts and a 

check-loading frame is shown in Figure 4–6. 

Figure 4–6. Photograph of Performance model and interchangeable parts 

Courtesy of The Boeing Company 

Courtesy of The Boeing Company 
14 

Figure 4–7. CAD views of Performance model, interchangeable parts, and sting with tailored 

dummy sting covers 

Figure 4–8. Photograph of Performance model new parts, and tailored sting covers 

EXISTING MODEL PARTS

NOSE, CENTERBODY, BAL ADAPTER & COVER

VTAIL, INBD FLAP, STING

SPLIT CAN

INLET NI3

INLET DECK

INLET NI4

NOZZLE NN3

NOZZLE NN4

CENTER SECTION NC3

LOCK PLUG

TAILORED DUMMY STING

Courtesy of The Boeing Company 

Courtesy of The Boeing Company 
15 

As previously stated, Phase II of the NRA contract focused on (1) nacelle effects on the sonic boom 

signatures, (2) aerodynamic performance of the vehicle, and (3) inlet performance. New parts were made 

for the Performance model that would allow these investigations, namely, inlet sections NI3 and NI4 and 

nozzle sections NN3 and NN4. These are shown in the CAD views in Figure 4–7 and in a photograph in 

Figure 4–8. New nacelle center sections were also made so that parametric inlet and nozzle sections 

could be tested in various combinations. The primary differences between the new nacelle parts and the 

nacelles used in Phase I are that the new parts have contoured lower inside surfaces, simulating the inlet 

and nozzle throats. All of the nacelle options for this model and the Boom models are strictly flowthrough—no external suction or blowing was applied in the tests to the inlets and nozzles to simulate 

propulsion effects. 

The model is shown in Figures 4–2, –3, –5, and –6 with a “sting can” at the rear of the model, which 

extends the cylindrical body 6-in. aft to minimize the influence of the sting on the sonic boom pressures 

and the aerodynamic performance. It was found during the TBC1 and TBC3 tests, however, that the aftfacing cavity area between the sting can and the sting was adversely affecting the aft part of the pressure 

signature, so sting covers (two clamshell halves) were made prior to the TBC4 test to replace the sting can 

and continue the cylindrical cross section of the aft body as far back as possible along the sting, to the 

point where it tapers up in size to meet strength requirements. The assembly of these sting covers on the 

sting is referred to as the “tailored dummy sting,” and this, along with the sting can (in a split view), are 

shown in the exploded CAD views in Figure 4–7. A lock plug was inserted into the back end of the 

model just ahead of the dummy sting to prevent the model from rotating about the balance and causing 

steps and gaps when deflecting under aerodynamic loads. Note that this plug and the attachment of the 

dummy sting to the model bridge the balance, thus rendering the balance readings invalid. During the 

TBC4 test, the Performance model was run with the tailored dummy sting for all boom signature 

measurements, and with the sting can for force and moment measurements. 

Various views of the Performance model installed in the 9x7 and 8x6 wind tunnels are provided in 

Figures 4–9 and –10. 

Figure 4–9. Boeing Performance model installed in Ames 9x7-ft wind tunnel 
16 

 

Figure 4–10. Boeing Performance model installed in Glenn 8x6-ft wind tunnel 

4.2.2. Boom1 Model 

The Boom1 model is a 15.748-in.-long model of the QEVC at 0.65% scale. It has the same 

aerodynamic lines as the Performance model (which is 2.75 times the size of the Boom models) aside 

from the differences for the mounting provisions. Boeing sized the Boom1 model to provide the best 

compromise of model fidelity and the ability to measure off-body sonic boom pressure signatures in a 

large wind tunnel. The small size was selected to measure the full signature of model on the pressure rail 

with room to spare for various sting or strut mounting configurations at various positions and sweeps 

relative to the rail. As with the Performance model, the sharp edges of the wings, V-tails, and nacelle 

inlets and nozzles had to be thickened relative to their true scaled-down thicknesses to a minimum of 

0.004 in. 

Drawings of the model are shown in Figure 4–11, which show that the model was attached to the 

balance by a swept blade strut and a balance adapter. The same 1-in. diameter six-component balance 

that was used for the Performance model was also used for this and all the other Boeing models. Two 

blade struts were made in Phase I of the NRA study for this model and the Boom2 model (discussed in 

next section): a short one, VS1 (10.028-in. long), and a long one, VS2 (11.652-in. long). VS1 is the one 

shown in Figure 4–11, and also in the left-side view of the colored model components in Figure 4–12. 

VS2 is shown in the right-side view of Figure 4–12. They both attach to the model at the same mounting 

location, so the longer length of VS2 places the model nose 1.625 in. further forward in the tunnel than 

VS1. The longer strut was preferred for minimizing strut effects on the model signature, but the shorter 
17 

Figure 4–11. Boom1 model top and side view drawings 

Figure 4–12. CAD views of VS1 strut (left) and Boom1 model with VS2 strut (right) 

 

15.75”

6.71”

15.75”

15.80”

22.77” 2.46” 7.83”

3.21”

7.29” model break (nose)

7.29” model break (nose)

12.18” model break (nacelle)

1.81”

Balance 

Adapter

27.72” (balance center)

Modular (~.0065 Scale) QEVC Small Boom Model

Courtesy of The Boeing Company 

Courtesy of The Boeing Company
18 

one was tested first to determine whether the cantilevered model would have high lateral dynamics in the 

wind tunnel. After this was determined to be a non-issue, VS2 was run with the Boom1 model from then 

on with no significant dynamics. The large fins attached to the rear of the balance adapter, shown in the 

right-side image of Figure 4–12, were built just as a standby measure in case the lateral dynamics were 

too severe with either strut, but they were never needed. 

Color-coded CAD representations of the Boom1 model components are shown in Figure 4–13, where 

an alternate nacelle/V-tail (one-piece) part is shown, as well as a nacelle-off/V-tail-only part. The small 

teardrop-shaped mass flow plug is shown in the nacelle inlet, but a flat-bottomed fully-open nacelle 

component was also available. Photographs of the assembled Boom1 Model are shown in Figure 4–14, 

and two views of this model with the VS2 strut in the 9x7 wind tunnel are shown in Figure 4–15. 

Figure 4–13. CAD views of Boom1 model modular parts 

Courtesy of The Boeing Company 
19 

Figure 4–14. Photographs of assembled Boom1 model 

 

Figure 4–15. Photographs of Boom1 model with VS2 strut mounted in 9x7 wind tunnel 

4.2.3. Boom2 Model 

The Boom2 model is an alternate low-boom design with the same breakdown and general features as 

the Boom1 model. It was designed for a free stream Mach number of 1.6 and CL = 0.14, and the focus in 

the design was more on drag and pitching moment rather than on the near-field signature shape. It did 

result in significantly lower drag than Boom1, with a lower pitching moment and an under-track signature 

comparable to Boom1. The off-track signatures were somewhat worse for Boom2, however. 

The differences between Boom1 and Boom2 are in minor tweaks of the OML, particularly on the 

underside body contours which will be discussed in the next section. The two models with their interchangeable parts, the VS1 and VS2 struts, balance adapter, and adapter fins, are shown in Figure 4–16. 

Courtesy of The Boeing Company 
20 

Figure 4–16. Photograph of Boom1 (left) and Boom2 (right) models with interchangeable parts, 

VS1 and VS2 struts, balance adapter, and adapter fins 

4.2.4. Boom3 Model 

The Boom3 model was made during Phase II of the NRA contract, and has nearly the same 

aerodynamic lines as the Boom1 model aside for provisions for mounting on the new VS3 and VS4 struts. 

CAD views of the Boom3 model with its alternate nacelles and VS3 and VS4 struts are shown in Figure 

4–17, and a photograph of this model and parts are shown in Figure 4–18. 

Figure 4–17. CAD views of Boom3 model, interchangeable parts, and VS3 and VS4 struts 

EXISTING NOSE

B1 BODY

AFT FUSE

UPPER SWEPT STRUT TAPERED SOCKET

TAILORED STING STRUT

TAILORED STING

N4 NACELLE

N3 NACELLE

TAIL

Courtesy of The Boeing Company 

Courtesy of The Boeing Company 
21 

Figure 4–18. Photograph of Boom3 model, interchangeable parts, and VS3 and VS4 struts 

 

Courtesy of The Boeing Company 
22 

Figure 4–19 shows side-by-side comparison photographs of all three Boom models, both upright and 

inverted. The models-upright photo (a) shows the mounting interface pylon for the VS1/VS2 struts at the 

rear of the Boom1 and Boom2 (left and center) models in between the nacelles. The mounting interface, 

in the rear fuselage cut-away area, for the VS3/VS4 struts on the Boom3 (right) model extends further 

forward than on the other two models since the VS3 strut was made to attach near the center of the 

Boom3 model. The VS4 strut has a straight sting that covers this mounting interface from the rear up to 

the center section of the body. 

A subtle difference among the undersides of the three models is evident in Figure 4–19(b). Boom1 

and Boom3 are intended to be aerodynamically similar aside from the mounting strut location, and a 

slightly raised area under the aft fuselage between the wings can be seen on these models that is much 

flatter on Boom2. This shape difference is likely the main contributor to the small drag and pitching 

moment differences between Boom2 and the other models. 

(a) Models upright 

(b) Models inverted 

Figure 4–19. Photographs of Boom1, Boom2, and Boom3 (left to right) models 

Drawings of the VS1 through VS4 struts are provided in Figure 4–20, and photographs of the three 

Boom models mounted on these struts are provided in Figure 4–21. VS3 is a forward-swept strut similar 

to VS1 and VS2, but it is significantly longer than VS2 (14.365 vs 11.652 in.), though its attachment 

location is closer to the center of the model so that the nose remains the same distance from the balance 

center as with VS2. VS4 is an aft-swept strut that supports a straight, rear-entry sting for the Boom3 

model. As with VS3, it too is designed to place the model nose at the same station as the VS2 strut. 
23 

Figure 4–20. Drawings of VS1, VS2, VS3, and VS4 struts 

(+"*-,#

('"')/#

)",*'#

*"//-#

(+"*-,#









*".*/#

(("-,)#

*"+-/#
24 

Figure 4–21. Photographs of Boom1, Boom2, and Boom3 models with VS1, VS2, VS3, and VS4 

struts 

##&(!

#" %&





		

	


##&(!

##&(!

!%'$(

!&"%

!%'$(

!%'$(

!%'$(
25 

4.2.5. Axisymmetric Models AS1, AS2, AS3 

Three axisymmetric calibration models were tested to calibrate the pressure rail signature and provide 

data for CFD validation. The three models were designated AS1, AS2, and AS3. Boom results will only 

be presented for the AS2 model in this report because it was used as the common calibration body in the 

various Boeing tests, and data from AS1 and AS3 are not pertinent to this report. The attributes of the 

AS2 model are provided in Table 4, where the diameter listed is that of the long cylindrical portion of the 

model. A close-up photograph of the AS2 model is given in Figure 4–22, and a photograph of it mounted 

in the 9x7 tunnel is shown in Figure 4–23. The AS-2 model is a true “Seeb” configuration designed after 

the work of George, Seebass, and Darden.35,36 It was designed without alteration of the aft signature and 

was designed to produce a sonic boom pressure signature with a small 2-in. flat pressure region behind 

the nose shock. 

Figure 4–22. Photograph of AS2 model 

Figure 4–23. Photograph of AS2 model in 9x7 wind tunnel with RF1 rail mounted on forward 

window blank 
26 

Important geometry parameters for all of the Boeing models are given in Table 4. 

Table 4. Wind Tunnel Model Geometry 

Model AS2* Boom Models 

on VS1 

Boom Models 

on VS2,3,4 Performance 

Scale — 0.65% 0.65% 1.79% 

LRef (in) 18.611 15.748 15.748 43.307 

SRef (sq in) — 15.322 15.322 115.891 

CRef (in) — 2.6714 2.6714 7.3465 

bRef or Dia. (in) 0.965 6.7111 6.7111 18.4555 

XRef (in) — 11.4706 11.4706 31.5441 

ZRef (in) — 0 0 0 

XNose to BMC (in) 24.024 26.854 28.478 31.345 

ZNose to BMC (in) 0 3.201 4.139 1.053 *

 Reference parameters for AS models were set equal to those for Boom models for consistency 

in test data reduction; actual AS2 model dimensions are given here 

5. Instrumentation and Model Positioning 

Sonic boom pressure signatures in the various tests were measured using either the tapered RF1 (14-

in.) pressure rail or the flat-top 2-in. pressure rail, and a few selected signatures were measured on both 

rails (one at a time) in a given test for direct comparisons. 

5.1. RF1 (14-in.) Pressure Rail 

The RF1 rail, also known as the 14-in. rail, has a small 

rounded tip and is blade-like with a small 3.5° angle from the 

tip to the base. A cross sectional cut through the pressure 

measuring center section of the rail is shown in Figure 5–1 

and a CAD drawing of the design is shown in Figure 5–2. The 

rail is shown attached to two window blanks (54-in. diameter 

steel plates that replace the windows in the 9x7 wind tunnel) 

in the drawing. The rail stands off the wall 14 in., has a 0.05-

in. radius tip, and a 1-in. base width, and is 90 in. long with an 

instrumented section 66 in. long. The rail height was selected 

to prevent contamination of the aft part of a model’s signature 

measured on the rail by reflections off the tunnel wall of 

model shock waves from the forward part of the model. The 

height of 14 in. provides reflection-free data for model lengths 

of 35 and 43 in. at Mach 1.6 and 1.8, respectively. 

The rail has 420 pressure orifices of 0.015-in. diameter, 

spaced 4 mm (approximately 0.1575 in.) apart along its tip. 

Prefabricated ferrules were used to accommodate the small 

orifice size, and were connected to metal pressure tubes that 

Figure 5–1. Cross section of RF1 

rail (dimensions in inches) 
27 

were routed through seven machined grooves on one side of the rail. Covers over these grooves are shown 

in purple in the CAD images of Figure 5–2, which lead the tubes through the rail footpads mounted in the 

9x7 window blanks. The mounting location of the rail in this figure is referred to as the forward location, 

since most of the pressure orifices are over the forward window blank, and all the pressure tubing runs 

through this blank. The rail can also be mounted on the aft window blank, where the aft end of the rail is 

secured to the tunnel wall downstream of the aft blank. In the 8x6 tunnel, the rail was just mounted in 

one position in the ceiling, so no “forward” or “aft” designation is given for the mounting position in the 

8x6 in the figures presented herein. 

Figure 5–2. CAD views of RF1 14-in. rail mounted on forward window blank of 9x7 wind tunnel 

A flow field simulation of the rail with shocks generated by the Lockheed Seeb body-of-revolution 

model37 (similar to AS2 but with a longer nose) is shown in Figure 5–3. Shocks from the nose of the 

model (the small red tip in the center of the figure, indicating compression) pass over the rail surface and 

reflect off the tunnel wall to the region indicated as the reflected signature. The computation was 

performed with Cart3D19-21,38 in conjunction with the Adjoint Error Optimization (AERO) module. The 

computation utilized mesh adaptation to minimize errors along a line sensor placed 0.1 in. above the tip of 

the RF1 rail. The simulation provides visualization of the pressure field in the symmetry plane of the rail. 

The mesh is colored by pressure coefficient and was rotated to nearly align with the Mach angle of the 

flow. The model is one body length (17.68 in.) from the rail in the computation. Here it is evident that the 

model’s leading shock reflects from the wall far downstream of the model pressure signature on the rail. 

The figure marks the model’s signature and reflected signature regions on the rail, and it is clear that there 

are nearly two body lengths behind the model’s signature that offer no contamination from reflected 

model shocks. Details of the computational assessment of the rail are provided by Cliff.3 

The RF1 rail was used in conjunction with the 2-in. rail during the TBC3 and 9x7 parametric tests and 

exclusively during the TBC4 test. 

18” 66” 6”

14”

18” 66” 6”

14”
28 

Figure 5–3. CART3D-AERO computation of the Seeb-ALR model, RF1 rail, and tunnel wall 

Mach = 1.6, α = 0 deg, h = 17.68 in. 

5.2. 2-in. Pressure Rail 

The RF1 rail was used in the Lockheed Phase I test before the first Boeing test in the 9x7 wind tunnel, 

but it was desired to build and test a more conventional 2-in. pressure rail for the Boeing TBC1 test. 

Instead of a tapered cross section like the RF1 rail, it has a rectangular cross section, being 1.5 in. wide 

and 2 in. tall with a flat top. The flat surface of the rail caused shock reflections that were known to 

artificially amplify some parts of the model signatures. The rail is 96 in. long with a 72-in. instrumented 

section used for boom signature measurement. The leading- and trailing-edge sections, 18 in. and 6 in. 

long, respectively, are wedge-shaped as shown in the CAD view of the rail on the aft window blank in 

Figure 5–4. The rail consists of 458 pressure orifices spaced 4 mm (approximately 0.1575 in.) apart, each 

with an internal diameter of 0.015 in. Pressure tubes from the orifices were routed from the rail through 

the rail foot pads and tunnel window blank to the 64-port PSI modules located just outside of the test 

section. Photographs of the rail installation in the 9x7 test section are shown in Figure 5–5. 

Figure 5–4. CAD view of 2” pressure rail on aft window blank of 9x7 wind tunnel 
29 

The 2-in. rail was used exclusively during the TBC1 test, and in conjunction with the RF1 rail during 

the TBC3 and 9x7 parametric tests. 

 

Figure 5–5. Photographs of 2-in pressure rail on aft window blank of 9x7 wind tunnel 

5.3. Pressure Transducers 

The rail pressures were measured using a series of 64-port, 5-psid ESP electronic pressure scanners 

deranged to 1.67 psid. The ESP pressure scanners are miniature electronic differential pressure 

measurement units that contain an array of 64 pressure sensors, one for each of 60 rail ports plus 4 

monitor ports (not plumbed to the rail). Seven ESP scanners were used with the RF1 rail (420 orifices), 

and eight scanners were used with the 2-in. rail (458 orifices). The accuracy of these scanners was 

determined to be 0.08% of the deranged value, which equates to about 0.0013 psi or 0.187 psf. The 

measured pressures are converted to pressure coefficients using the tunnel freestream static pressure 

computed from the Mach number and freestream total pressure measured in the plenum upstream of the 

test section. 

5.4. Model Balance and Additional Instrumentation 

All Boeing models run in the Phase I 

and II tests used the Ames 1.0-in. Task Mk 

XIV-C six-component force balance. 

Upright and inverted runs were conducted 

in the first test (TBC1) to correct the 

angles of attack and sideslip for tunnel 

flow angularity. These angle corrections 

turned out to be not significant in their 

impact on the sonic boom data, so the flow 

angularity was not measured or applied in 

subsequent tests. 

In the Performance model the balance 

was located inside the model close to the 

center, but for the Boom and axisymmetric 

models the balance was located in a 

balance adapter with one of the VS1 

Figure 5–6. Fouling strip, cavity pressure tubes, and 

thermocouple wires attached to sting behind 

Performance model 
30 

through 4 struts in between. The axisymmetric models were directly attached 

to the balance adapter. The use of the 

adapter was required because there was 

insufficient room for a balance inside the 

smaller models without compromising the 

outer mold lines, but the downstream 

location of the balance meant that the 

resolution of the model forces was not as 

good. The recorded force data were not 

adjusted for aerodynamic tares from the 

blade strut or balance adapter. 

A fouling strip was wrapped around 

the forward end of the model sting to 

detect fouling from the back end of the 

Performance model, or the balance adapter 

when the Boom or axisymmetric models 

were being run. An exception, however, in the use of the fouling strip was with the Performance model in 

the TBC4 test, where the tailored dummy sting covers were attached to the rear of the model and the 

sting. Since this cover was attached both to the sting and to the model, the balance was fouled and the 

force measurements were not reliable, so the fouling strip was not used. The model angle was therefore 

set only by angle of attack and not by lift coefficient for the sonic boom measurements. 

Cavity pressure measurements were recorded just inside the aft end of the Performance model and the 

aft end of the balance adapter for the other models in order to make cavity drag corrections. A 

thermocouple was also installed at the forward end of the sting just behind the balance to measure balance 

temperature at its back end. A photograph showing the fouling strip, cavity pressure tubes, and 

thermocouple wires attached to the sting behind the Performance model is shown in Figure 5–6, and the 

same behind the balance adapter is shown in Figure 5–7. 

5.5. Roll Mechanism 

The Ames small model roll mechanism (SMRM) was used for off-ground-track boom signature 

measurements in the 9x7 parametric and TBC4 tests, but not at the 8x6 in the TBC3 test. The SMRM has 

a fixed 7.5° bend in it to further accommodate offset angle-of-attack and -sideslip ranges desired by 

particular tests. This bend has been useful in sonic boom tests in that it allows a model to be moved 

closer to the rail (mounted on the north wall) or further from the rail (toward the south wall) than would 

be possible without it, though the bend has not been required for some of the recent sonic boom testing in 

the 9x7. 

5.6. Linear Actuator 

A linear actuator was used in the 9x7 parametric and TBC3 tests to translate the model longitudinally 

in the wind tunnel. This allowed acquisition of multiple pressure signatures at small increments in the X 

direction over a specified distance, such as 26 positions spaced 0.63 in. apart (~4 rail orifices) in a typical 

X sweep conducted in the 9x7 parametric test. In the TBC4 test, the linear actuator was not installed, so 

the only sweeps were in the Z direction, accomplished by translating the tunnel strut. Both X and Z 

sweeps in the various tests were successfully used in improving the quality of the signatures through 

spatial averaging. 

Figure 5–7. Fouling strip, cavity pressure tubes, and 

thermocouple wires on sting behind balance adapter 
31 

The linear actuator is remotely controlled and its ram translates forward and aft at a rate of 0.7 in. per 

second over a 24-in. traverse distance. The minimum and maximum (retracted and extended) lengths of 

the linear actuator plus ram are 44 in. and 68 in., respectively. The linear actuator mounts into the roll 

mechanism with a 2.875-in. diameter male taper, and accommodate the model sting in the linear actuator 

with a 1.05-in. diameter female taper. 

Figure 5–8. View of linear actuator and roll mechanism in 9x7 wind tunnel, with Boom1 model 

mounted on blade strut and balance adapter and RF1 pressure rail in background 

A photograph showing the linear actuator and exposed portion of the roll mechanism in the 9x7 wind 

tunnel is provided in Figure 5–8. The ram of the actuator is shown in its retracted position, where the 

minimum of 2.625 in. of it is exposed at the front end of the actuator. The tilted-cone-shaped head of the 

roll mechanism is visible between the primary adapter (at right, partially hidden) and the rear of the linear 

actuator. The non-rotating cylindrical body of the roll mechanism is secured in the forward end of the 

primary adapter. 

6. Wind Tunnel Flow Quality and Test Techniques 

6.1. Wind Tunnel Flow Quality

Ideally, a wind tunnel flow field surrounding a model would be completely uniform and steady for all 

model positions in the tunnel. However, this is rarely the case in supersonic wind tunnels, and in the 9x7 

wind tunnel, there are spatial variations in terms of undesired flow angularity and Mach number variation 

throughout the test section, as well as temporal variations. These variations are caused in large part by the 

asymmetric sliding-block nozzle, and the fixed nozzle contours of the floor and ceiling, which result in a 

design that is optimized for one Mach number and not ideal for the others. Therefore, it is not surprising 

that unsteady characteristic waves emanate from the nozzle through the test section, affecting flow angles, 

Linear Actuator

ll h i i 9 7 i d l i h

Roll Mechanism (exposed portion)
32 

Mach number, and steadiness of the flow. It is not possible to completely correct for these issues, but 

spatial and temporal averaging have been used to minimize their effects on the sonic boom signatures. To 

illustrate some of these flow features in the tunnel, Schlieren and shadowgraph images of the flow in the 

9x7 and some plots of the variation of model forces and angle of attack will be presented. 

6.1.1. Schlieren and Shadowgraph Imaging 

Undesired facility-generated shock waves within a wind tunnel become significant in a sonic boom 

test when the shock waves from a low-sonic-boom design are generally weaker than those from the 

facility. This is evident in viewing Schlieren images that reveal both the ambient tunnel pressure waves 

and the model shock waves. Figure 6–1 presents Schlieren images of three Boeing models (AS2, Boom1, 

and Performance) in the Glenn 8x6 wind tunnel. The red arrows point to some of the facility-generated 

shock waves in the tunnel, which, in some cases, appear as strong if not stronger than the model shocks. 

The effect of these shocks on the model forces or boom characteristics could not be measured however, 

because there was insufficient flexibility in placement of the model to allow gathering data with the 

model clear of the tunnel-generated shock waves. Figure 6-1 shows the facility shock waves visible 

through the windows; it is very likely that such shocks persist downstream of the tunnel nozzle and 

through the entire test section.39

In the AS2 model image at Mach 1.8 (Figure 6–1(a)), the nose shocks are clearly visible against the 

background, and do appear stronger and more clearly defined than the tunnel ambient shocks. However, 

in the Boom1 model image at the same Mach number (Figure 6–1(b); the model is mounted upside-down 

for reasons stated above), the nose shock is much less visible than in the AS2 image, primarily because 

the nose tip is more slender. Additional shocks along the length of the model are very weak and difficult 

to see, with the exception of the shocks emanating from the vertical blade strut where it attaches near the 

rear of the upper surface of the model. For the Performance model at Mach 1.6 (Figure 6–1(c)), the nose 

shocks appear a little stronger than those of the Boom1 model, as expected because of the almost 3x 

larger model size. The rest of the Performance model behind the nose is not visible in the RBOS image 

because it is too large for the viewing window. 

Schlieren-like images of the Boeing Boom1 model in the Ames 9x7 wind tunnel are shown in Figure 

6–2. These were not made with the conventional through-tunnel Schlieren technique, but with a 

technique known as retro-reflective background-oriented Schlieren (RBOS).40 This technique is used 

when optical access is limited, such as in sonic boom tests where window blanks are installed on one side 

of the tunnel to accommodate the pressure rail. For the tests of the Boeing models in the 9x7, cameras 

and lights were placed on the south side of the tunnel, and a highly reflective material (3M Scotchlite 

brand film 900X) was placed on the north side window blanks behind the model. This was then speckled 

with ink in order to provide a background against which image-processing techniques would highlight 

density gradients in the field of view, due to the apparent movement of the speckles between wind-on and 

wind-off images. 

In the Boom1 model RBOS images in Figure 6–2, the first image is at Mach 1.6 and the model is 

shown in the wings-horizontal orientation. The second image is at Mach 1.8 and the model is shown 

wings-vertical. The RF1 rail is the black horizontal band across each of the images, and the model and 

strut are also masked out. At first glance, it appears that the background shocks in the 9x7 are much 

stronger than in the 8x6, but this is not necessarily the case. The darkness of the 9x7 images are a result 

of higher contrast obtained in the RBOS technique, as the gray scale was compressed to make the model 

shocks stand out more. 
33 

 (a) AS2 model, Mach 1.8 (b) Boom1 model, Mach 1.8 

(c) Performance model, Mach 1.6 

Figure 6–1. Schlieren images of Boeing Models in NASA Glenn 8x6 wind tunnel, taken through aft 

Schlieren windows 

Facility shocks

Facility shocks

Facility shocks
34 

 (a) Mach 1.6 (b) Mach 1.8 

Figure 6–2. RBOS images of Boeing Boom1 Model with VS2 strut in 9x7 wind tunnel, taken 

through the forward south side Schlieren window 

In the Mach 1.6 9x7 image, it is apparent that there is a pair of strong facility-generated shock waves 

that cross the model nose from the lower left to the upper right, along with quite a few weaker shocks and 

Mach lines throughout the window view. The source of these waves was not able to be determined 

during the test as there were no steps or bumps on the tunnel floor in line with these waves—they could 

be characteristic waves from the nozzle bouncing between the floor and ceiling. A shadowgraph image 

through the forward windows of the 9x7 in Figure 6–3(a) taken with the tunnel empty shows the same 

strong shock waves, confirming that they are independent of the presence of the model. The Mach 1.8 

images in Figure 6–2(b) and 6–3(b) also show similar background shock wave patterns. 

The Boom1 model nose shock is very difficult to see in Figure 6–2(a) because both above and below 

the nose the shock is nearly coincident with facility shocks, which may or may not be at the same 

spanwise position in the tunnel as the model. Shock waves further aft on the model are more evident in 

both the Mach 1.6 and 1.8 images, such as those coming off the wings, tails, and nacelles. Also, the wake 

coming off the back of the model in the streamwise direction is clearly evident. Note that the shocks from 

the model appear as dark bands going upward and light bands going downward; this is because the 

density gradients resolved by the RBOS technique are measured by the vertical deflection of the light 

path, equivalent to a horizontal knife edge in conventional Schlieren. 

All of these images show the shock wave patterns in the tunnel at an instant in time, but time-resolved 

video (not shown herein) using Schlieren, shadowgraph, and RBOS reveals that the tunnel ambient 

pressure waves randomly shift positions by small amounts. This shifting covers distances on the order of 

one-quarter of an inch on the average, and occurs both in short-term temporal variations (at frequencies 

on the order of 100 Hz or more) and in long-term variations (several seconds or more). The short-term 

variations are averaged out in the data samples, but the long-term variations cause differences to be seen 

in the force and pressure data for the short data samples (~2 second durations).
35 

 (a) Mach 1.6 (b) Mach 1.8 

Figure 6–3. Shadowgraph images of empty 9x7 wind tunnel, taken through forward Schlieren 

windows
36 

6.1.2. Lift, Angle of Attack, and Pitching Moment Variations During Sweeps 

The Ames 9x7 and the Glenn 8x6 wind tunnels have stream angle variations throughout the test 

sections which result in variations in the model forces, moments, and angles when the model is moved in 

the X or Z direction to acquire multiple signatures. Figures 6–4 through –7 show plots of lift, angle of 

attack, and pitching moment variations during selected X and Z sweeps for the Boom1 VS2 model in the 

9x7 and 8x6 tunnels, and Table 5 lists the average ranges of these variations among the all the curves on 

each of the plots. Data at nominal Mach numbers of 1.6 and 1.8 are presented in the first three figures, 

but only at Mach ~1.8 (1.78 in 8x6) in the last figure since no Z sweeps were acquired for the Boom1 

model in the 8x6 wind tunnel at Mach ~1.6 (1.56 in 8x6). 

Note that for some of the runs, the configuration is the Boom1 VS2 model with nacelles and vertical 

tails off (“n/v off”) since valid comparison runs with these components on the model were not available in 

some cases. While the nacelles and verticals do affect the lift and pitching moment, the focus in this 

section is just on the variation of these coefficients over the ranges of the sweeps conducted, and the 

effect of the nacelles and verticals on the average variation is believed to be small. 

Table 5. Average ranges of variations of lift, angle of attack, and pitching moment 

during X or Z sweeps 

9x7 X Sweeps 8x6 X Sweeps 9x7 Z Sweeps 8x6 Z Sweeps

Figure 6–4 6–5 6–6 6–7 

CL 0.019 0.004 0.011 0.004 

α 0.030 0.055 0.007 0.018 

CM 0.057 0.017 0.056 0.021 

One of the notable differences among the four sets of plots is that the angle of attack increased by an 

average of more than 0.030° over the length of the various X sweeps in the 9x7 and 8x6 wind tunnels, 

while it varied extremely little during Z sweeps. This is a clear indication that the stream angle in the 

angle-of-attack plane varies with longitudinal position in both tunnels, and thus could be expected to 

cause small differences in the pressure signatures over the length of the X sweeps. In the 9x7 Z sweeps, 

the average angle-of-attack variation was only 0.007°, indicating that the α stream angle is fairly uniform 

across the width of the tunnel within the range of heights tested: 26- to 34-in. “above” the rail, or 40- to 

48-in. horizontally away from the north wall. 

Very few Z sweeps were run in the 8x6 test (Figure 6–7) because it was learned early in the test that 

moving the tunnel strut vertically had an intolerable effect on the rail pressures. The strut was located 

directly under the aft part of the rail, and while any shocks from the strut fell behind the rail at the Mach 

numbers tested, the porous walls in the transonic part of the test section (where the rail was located) 

allowed changes in the air exiting through the tunnel walls due to strut movement, and this had a 

significant effect on the rail pressures. The three curves shown in Figure 6–7 for Z-sweep runs in the 8x6 

tunnel at Mach 1.78 show some angle-of-attack variation with model height, but it is not consistent as it 

was for X sweeps in either tunnel or for Z sweeps in the 9x7. 

In regards to the fairly uniform angle-of-attack variation observed in X sweeps in both tunnels, it is 

interesting to note that there are generally not the commensurate uniform changes in lift or pitching 

moment that one would expect with the α changes. The lift or pitching moment curves are mostly flat 

over the ranges of ram positions tested, with the exception of a few of the sweeps in the 9x7 tunnel 

(signature “sig” sets 53, 45, and 51). 
37 

Figure 6–4. Boom1 VS2 model lift, angle of attack, and pitching moment variations during 

X sweeps, 9x7 parametric test 

.08

.10

.12

.14

CL .08

.10

.12

.14

CL 3.35

3.37

3.39

3.41

3.43

3.45

_

3.35

3.37

3.39

3.41

3.43

3.45

_

0 2 4 6 8 10 12 14 16 18 20 22 24 

XRam

-.15

-.10

-.05

0

.05

.10

C

M

Sig Set 

53

45

61

51

38

60

Runs

1724—1749

1472—1497

2047—2072

1662—1687

1247—1272

2006—2044

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Rail

2-in Fwd 

14-in Fwd 

14-in Aft 

2-in Fwd 

14-in Fwd 

14-in Aft 

hNose

30.5

30.5

60.0

30.0

30.1

60.2

_

3.40

3.40

3.40

3.40

3.41

3.39

Mach

1.60

1.60

1.60

1.80

1.80

1.80

HumidAvg

321

311

288

320

305

284

0 2 4 6 8 10 12 14 16 18 20 22 24 

XRam

-.15

-.10

-.05

0

.05

.10

C

M

Sig Set 

53

45

61

51

38

60

Runs

1724—1749

1472—1497

2047—2072

1662—1687

1247—1272

2006—2044

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Rail

2-in Fwd 

14-in Fwd 

14-in Aft 

2-in Fwd 

14-in Fwd 

14-in Aft 

hNose

30.5

30.5

60.0

30.0

30.1

60.2

_

3.40

3.40

3.40

3.40

3.41

3.39

Mach

1.60

1.60

1.60

1.80

1.80

1.80

HumidAvg

321

311

288

320

305

284
38 

Figure 6–5. Boom1 VS2 model lift, angle of attack, and pitching moment variations during 

X sweeps, 8x6 TBC3 test 

.14

.15

.16

.17

.18

CL .14

.15

.16

.17

.18

CL 3.35

3.37

3.39

3.41

3.43

3.45

_

3.35

3.37

3.39

3.41

3.43

3.45

_

16 17 18 19 20 21 22 23 24 

XRam

-.44

-.42

-.40

-.38

-.36

-.34

C

M

Sig Set 

93

66

77

81

61

70

Runs

1060—1085

863—888

966—991

1008—1033

818—843

912—937

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 n/v off 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 n/v off 

Rail

2-in

14-in

14-in

2-in

14-in

14-in

hNose

59.3

59.5

59.3

49.1

49.2

49.3

_

3.39

3.38

3.41

3.43

3.38

3.40

Mach

1.56

1.56

1.56

1.78

1.78

1.78

HumidAvg

129

75

287

81

70

92

16 17 18 19 20 21 22 23 24 

XRam

-.44

-.42

-.40

-.38

-.36

-.34

C

M

Sig Set 

93

66

77

81

61

70

Runs

1060—1085

863—888

966—991

1008—1033

818—843

912—937

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 n/v off 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 n/v off 

Rail

2-in

14-in

14-in

2-in

14-in

14-in

hNose

59.3

59.5

59.3

49.1

49.2

49.3

_

3.39

3.38

3.41

3.43

3.38

3.40

Mach

1.56

1.56

1.56

1.78

1.78

1.78

HumidAvg

129

75

287

81

70

92
39 

Figure 6–6. Boom1 VS2 model lift, angle of attack, and pitching moment variations during 

Z sweeps, 9x7 parametric test 

.08

.09

.10

.11

.12

CL .08

.09

.10

.11

.12

CL 3.35

3.40

3.45

3.50

3.55

_

3.35

3.40

3.45

3.50

3.55

_

25 27 29 31 33 35 

h_nose

-.15

-.10

-.05

0

.05

.10

C

M

Sig Set 

52

44

43

48

37

36

Runs

1690—1722

1437—1469

1401—1433

1567—1599

1213—1245

1179—1211

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Rail

2-in Fwd 

14-in Fwd 

14-in Fwd 

2-in Fwd 

14-in Fwd 

14-in Fwd 

XRam

24.0

16.0

24.0

24.0

16.0

24.0

_

3.41

3.40

3.41

3.40

3.50

3.51

Mach

1.60

1.60

1.60

1.80

1.80

1.80

HumidAvg

321

312

296

315

308

303

25 27 29 31 33 35 

h_nose

-.15

-.10

-.05

0

.05

.10

C

M

Sig Set 

52

44

43

48

37

36

Runs

1690—1722

1437—1469

1401—1433

1567—1599

1213—1245

1179—1211

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Rail

2-in Fwd 

14-in Fwd 

14-in Fwd 

2-in Fwd 

14-in Fwd 

14-in Fwd 

XRam

24.0

16.0

24.0

24.0

16.0

24.0

_

3.41

3.40

3.41

3.40

3.50

3.51

Mach

1.60

1.60

1.60

1.80

1.80

1.80

HumidAvg

321

312

296

315

308

303
40 

Figure 6–7. Boom1 VS2 model lift, angle of attack, and pitching moment variations during 

Z sweeps, 8x6 TBC3 test 

.14

.15

.16

.17

.18

CL .14

.15

.16

.17

.18

CL 3.35

3.37

3.39

3.41

3.43

3.45

_

3.35

3.37

3.39

3.41

3.43

3.45

_

35 40 45 50 55 60 65 

h_nose

-.44

-.42

-.40

-.38

-.36

-.34

C

M

Sig Set 

31

36

40

Runs

367—391

443—467

500—536

Model

Boom1 VS2 

Boom1 VS2 n/v off 

Boom1 VS2 n/v off 

Rail

14-in

14-in

14-in

hNose

41.9

42.0

55.0

_

3.40

3.40

3.38

Mach

1.78

1.78

1.78

HumidAvg

345

123

139

35 40 45 50 55 60 65 

h_nose

-.44

-.42

-.40

-.38

-.36

-.34

C

M

Sig Set 

31

36

40

Runs

367—391

443—467

500—536

Model

Boom1 VS2 

Boom1 VS2 n/v off 

Boom1 VS2 n/v off 

Rail

14-in

14-in

14-in

hNose

41.9

42.0

55.0

_

3.40

3.40

3.38

Mach

1.78

1.78

1.78

HumidAvg

345

123

139
41 

What these variations in the model data during X or Z sweeps mean for the boom signature data is that 

not all of the signatures measured in a sweep are at constant model conditions, resulting in a somewhat 

incorrect averaging of the signature data. It is possible to reprocess the data using only those X or Z 

positions where the model conditions are fairly constant, but that has not been done as of the writing of 

this report, since it would reduce the number of signatures used in the average and could reduce data 

quality more so than any improvement due to consistent model and tunnel conditions.

6.2. Corrections for Reference Runs 

The standard technique for acquiring sonic boom data using a pressure rail is to subtract a reference 

run from a data run, so that the difference yields only the model’s signature and none of the ambient 

freestream signature from the tunnel flow. The reference run is taken in a “clean” tunnel, where the 

model shocks (if the model is present) are either off the rail or behind where they will be in the data run. 

Truly clean-tunnel runs can also be used, where the model and support components are physically out of 

the tunnel, but this is usually not necessary as long as the model shocks from the reference run do not 

overlap with those from the data run. 

Model locations for typical reference and data runs in the 9x7 wind tunnel are illustrated in Figure 

6–8, where the Boom1 VS2 model and test set up are shown schematically using an Excel-based layout 

diagram. The red model is in the reference run position (nose 52 in. above rail, alpha 3.4°, ram retracted), 

and its shocks (dashed lines drawn at the Mach line angle as an approximation) pass just behind the rail at 

the 14-in. height of the rail orifices above the wall. For the data runs (a sweep from XRam = 8 to 24 in.), 

the blue model is 30 in. above the rail at an alpha of 3.4°. Note that the model shocks for these data runs 

fall on the instrumented section of the rail—from tunnel station -84 to -116 in. It is clear from this figure 

that the data-run model shocks are far enough ahead of those from the reference run to produce valid 

measurements, given that in supersonic flow there is no appreciable influence ahead of a model leading 

shock wave, aside from miniscule influences that might feed forward through the thin boundary layer of 

the rail tip. 

In contrast to the reference run for the small Boom model, the 43-in. Performance model is too long 

to acquire a reference run and leave enough room ahead of the nose shock for data runs to be acquired. 

Figure 6–9 shows a layout for this model with it positioned as far from the rail as possible (while leaving 

adequate clearance—at least 6 in.—between the model and the south wall of the tunnel, at the top of the 

figure), and even with the model tail shock aft of the rail orifices, the nose shock falls just 30-in. behind 

the first orifice on the rail. This clearly does not leave a sufficient length of uncontaminated orifices to 

get a clean signature for this model, so in the TBC4 test, reference runs were acquired at the beginning of 

the test without the model installed, each of the two Mach numbers, 1.6 & 1.8. A simple cone fairing was 

attached to the male taper at the front of the tunnel strut for these runs, which, with positioning away from 

the rail, assured that no shock waves from anything attached to the strut fell anywhere close to the rail. 

A typical layout diagram for the Boom1 VS2 model in the 8x6 wind tunnel is shown in Figure 6–10. 

As stated in Section 3.2, the model was mounted upside down since the rail was mounted on the ceiling to 

allow use of the tunnel strut which translates up and down through the floor and pitches about a center of 

rotation below the floor. Throughout this report, the height of the model “above” the rail in the 8x6 is 

physically a vertical distance upward from the nose of the model to the rail tip. The rail position shown is 

the only position used in the 8x6 test; it was not moved to either a forward or aft position as it was in the 

9x7 test. The rail position in the 8x6 tunnel was determined by assuring that the model shocks would fall 

on the rail when the model was positioned between the pair of downstream Schlieren windows in the side 

walls of the tunnel (refer to Figures 3–3 through –5). 
42 

Figure 6–8. Layout of reference and data runs in 9x7 wind tunnel for Boom1 VS2 model 

(view as from floor of tunnel looking up) 

Figure 6–9. Layout of highest possible position of Performance model in 9x7 wind tunnel
43 

 

Figure 6–10. Layout of reference and data runs in 8x6 wind tunnel for Boom1 VS2 model

The reference run shown in the layout of Figure 6–10 is positioned as low as possible in order to keep 

the model shocks as far back as possible on the rail so that they would not interfere with the rail pressure 

measurements for the data run. A number of runs were acquired this way, but it was observed in the data 

that the reference run pressures were strongly dependent on the exposed height of the tunnel strut above 

the floor. The decision was therefore made to use in-line reference runs only; that is, the strut height for 

the reference run was selected to be at the same height as for the data run, even though there would likely 

be some signature overlap on the rail for the reference and data runs. This probably caused some 

compromise in data quality relative to using reference and data runs without any overlap, though it was 

not entirely clear in the data. Comparisons of various signatures from the 9x7 and 8x6 wind tunnels will 

be presented in the Experimental Results section. 

Pressure signatures measured on the RF1 rail for the Boom1 model reference and data runs of the 

layout in Figure 6-8 are shown in Figure 6–11. In the top of the plot, the reference and data runs are 

plotted as ΔP/P, where ΔP = P – P∞, and the P in the denominator is P∞. The red curve is the reference 

run, which is the tunnel’s ambient pressure signature on the rail. The variance of the pressures over the 

length of the rail is due to the non-uniformity of the tunnel flow (including various facility shocks as 

discussed above) and the influence of the rail on the ambient flow as it passes over the 18-in. leadingedge section of the rail and establishes itself over the instrumented section. The black curve is the 

signature from a single data run (XRam = 8 in.), visible mostly in the region where the model shocks fall on 

the rail at tunnel stations approximately from -84 to -105 in. Where the black curve appears slightly 

separated from the red curve ahead of the model shocks is indicative of small temporal variations in the 

tunnel flow between the reference and data runs. The corrected pressure signature of the model is shown 

in the figure as the blue curve (offset in the plot by -0.04 in ΔP/P for clarity), obtained by subtracting the 

reference signature from the data signature. 
44 

Figure 6–11. Differencing technique to isolate model pressure signature on the rail 

9x7 Parametric test, Boom1 VS2 model, M = 1.60, PT = 2292 psf, HumidAvg = 314 ppm

 

6.3. Test Technique Improvements 

NASA and its NRA contract partners found that some changes employed in the current tests to some 

former test techniques resulted in improved accuracy and repeatability of the sonic boom pressure data. 

These changes included: 

• Spatially average the data over limited model movements in the X or Z direction 

• Operate the 9x7 tunnel at a higher total pressure (2300 psf) than in previous sonic boom tests 

• Reduce the freestream humidity to less than 250 ppm and maintain within 4 ppm 

• Position the model upstream of the leading edge shocks from the rails 

• Optimize the sampling duration of the reference and data runs 

Details of these changes and their effects on the data are discussed in the following sections. 

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

1500

1499

1500

hNose

29.9

52.4

29.9

_ ̊

3.38

3.36

3.38

XRam

8

0

8

Data Run 

Reference Run 

Data Run - Reference Run 

-150 -140 -130 -120 -110 -100 -90 -80 

XOrifice

-.06

-.05

-.04

-.03

-.02

-.01

0

.01

.02

6P/P

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

1500

1499

1500

hNose

29.9

52.4

29.9

_ ̊

3.38

3.36

3.38

XRam

8

0

8
45 

6.3.1. Spatial Averaging and Error Analysis 

The spatial averaging technique was developed to reduce the effect of tunnel flow field spatial 

distortions on the data at single model positions during supersonic wind tunnel testing.4,5 In sonic boom 

testing in the 9x7 wind tunnel, the non-uniform flow field causes pressure signatures on the rail to be 

different for different model positions in the test section. To enable the spatial averaging technique, the 

model is typically translated a short distance longitudinally (X direction) or vertically (Z direction, away 

from the rail), and a number of sonic boom signatures are acquired at multiple positions as shown in the 

waterfall plot in Figure 6–12(a). The X locations at each point on the individual signatures need to be 

aligned in order to enable averaging of the signatures. For an X sweep, the X values of the rail orifice 

locations are aligned by simply adding the ram position, as shown in Figure 6–12(b): 

XAligned = XOrif + XRam 

For a Z sweep, the X values of the rail orifice locations are adjusted by subtracting the height of the 

model nose at each Z position multiplied by the Mach number beta parameter: 

XAligned = XOrif − hNose M 2 −1

 (a) Model signatures not aligned (b) Model signatures aligned 

Figure 6–12. Non-aligned and aligned waterfall plots for 9x7 parametric test X sweeps for AS2 

model 

An individual signature after alignment is represented by the function fi(XAligned ), and the grand 

averaged signature f (X), is obtained by summing individual temporally averaged signatures, 

fi(XAligned ), at each port XOrif and dividing by N, the number of positions: 

−140 −130 −120 −110 −100 −90 −80

0.0

0.1

0.2

0.3

0.4

0.5

XOriginal

(ΔP/P)data−(ΔP/P)ref + offset

X−Sweep Runs, RefRun 1079

1080 1105

−50 −40 −30 −20 −10 0 10 20

XAligned

X−Sweep Runs, RefRun 1079

1080 1105

Average
46 

f (X) =

f i(XAligned )

i=1

N

∑

N 

where 

fi(XAligned ) =

fij(XOrif )

j=1

k1

∑

k1

− f Ref (XOrif )

f Ref (XOrif ) =

f0 j(XOrif )

j=1

k2

∑

k2

and 

 i is the counter for the ram positions 

 j is the counter for data point samples (acquired over the sampling duration) 

 fi is the i

th temporal average at rail position XOrif 

 XRam is the i

th position of the linear actuator 

is the temporal average of the reference signature(s) 

 are the intervals of the temporal average for the data run signatures, fi, and reference run 

signatures, fRef, respectively 

Theoretically, the mean signature is obtained at each port where the shifted signatures align perfectly. 

In practice, interpolation is required between the port measurements on the rail to properly align the 

signatures with minimal setpoint error. Figure 6–12(b) shows aligned pressure signatures for the run 

series, which are the result of adjusting for the linear actuator position or X shift from the model nose 

height to each pressure signature. 

To begin estimation of uncertainties for the spatial averaging technique, it is necessary to compute 

several components of variation from the test data. For the purpose of understanding the behavior of the 

test technique a relative uncertainty analysis is performed. This analysis is useful for the comparison of 

spatially averaged signatures and is not necessarily indicative of the total uncertainty of the final averaged 

signature. 

Using the method described by Walker41 for developing a dispersion relationship for equations with 

multiple levels of variation, the dispersion σ2

 of the grand averaged signature can be written as 

σ2

f (x) =

σ sp

2 +σ f i( ) XOrif

2 +σ f ref( ) XOrif

⎡ 2

⎣⎢ ⎤⎦⎥ i=1

N

∑

N

where 

σ sp

2 = σ ar2 −σ f i(XOrif )

2

σ ar

2 = 1

N f ⎡

i( ) XOrif − f ( ) X ⎣ ⎤

⎦ i=1

N

∑

2

 

σ sp

2 is the spatial standard deviation of the i

th model position at rail position XOrif

fref f0 j

k1,k2

f (x)
47 

σ f i(XOrif )

2 is the temporal standard deviation of the i

th model position at rail position XOrif

σ f Ref (XOrif )

2 is the temporal standard deviation of the reference run at rail position XOrif

σ ar

2 is the spatial standard deviation across runs of the i

th model position at rail position XOrif, 

where a run is a measurement of rail pressures at a given model position i 

The reported uncertainty band applied to the grand mean sonic boom pressure signature is 2σ2

f (x)

. 

Since the primary application of the uncertainty band was to compare signatures, no fossilized uncertainty 

(from tunnel or instrument calibration errors) was included in the uncertainty buildup. Some of the 

fossilized uncertainty due primarily to calibration of the pressure measurement devices may also be 

mitigated by subtraction of the reference signatures. At best, the uncertainty bands or intervals provided 

should be deemed to represent a minimum level of uncertainty. The interval is set to a width of four 

standard deviations with no statement of the associated distribution. This corresponds to 95 percent 

coverage for a normal distribution. However, given the low sample sizes for the experimental data it is 

best to not assume a distribution. 

Some assumptions are made for the uncertainty calculations of the RF1 rail. It is assumed that the 

average performance of the ports across the rail are similar. While this may be a valid assumption, the 

experimental data show that different regions of the signature have different levels of variation. It is not 

known if these differences are caused by non-uniformities in the rail surface (unlikely) or just fixed nonuniformities in the tunnel flow in the vicinity of the rail (more likely). The uncertainty calculations 

currently do not include the variation due to reproducibility of the signature.3 

Temporal variance is the variance of the reference run pressures (each reference run includes a 

number of 2-second points which are used in the reference uncertainty calculations) multiplied by the 

duration of the reference points. Spatial variance is the difference between the variance of the averaged 

data run and the average variance of the reference run data. The total variance is the data run variance 

divided by the number of points included in the run variance added to the reference run variance divided 

by the number of points. The square root of the total variance is taken to get the standard deviation, and 

multiplied by two, for the two-sigma uncertainty. 

Figure 6–13 shows the temporal and spatial uncertainty components and the total composite 

uncertainty for the 9x7 and 8x6 wind tunnels, where σ is shown as ΔP/P. The center plot represents 8x6 

data and the left and right plots are of the 9x7 data. Each of the three run series are shown with the 

X sweep data processed by the beginning reference runs (a; top) and the ending reference runs (b; 

bottom). The temporal uncertainties are almost the same for all three cases. These would be higher if 

computed from single runs or just a few runs each, but the data were averaged over 26 runs in each of the 

X sweeps. The spatial uncertainties increase substantially from left to right with height of the model above 

the rail (30, 49, and 60 in.), which makes sense because the pressure gradients are weaker at the greater 

distances from the model, and they have traveled through more of the wind tunnel turbulent flow field on 

their way to the rail. The total composite uncertainties for the three cases are fairly similar, though 

slightly higher for the 9x7 and definitely higher for the 60-in. model height case. 

The computed uncertainty and/or the scatter observed among the individual pressure signatures 

computed with a given reference run are often used as figures of merit to determine the best reference run 

to use. Reference runs were usually taken just before and just after each series of data runs for an X or Z 

sweep. When deciding which reference run to use in forming the spatially averaged signature, the one 

with the least scatter or smallest average standard deviation over the entire signature is typically selected. 

Figure 6–14 shows the individual, average, and ±1σ signatures for an AS2 model X sweep from runs
48 

(a) Sweep data processed using beginning reference runs 

(b) Sweep data processed using ending reference runs 

Figure 6–13. Temporal and spatial uncertainty for the 9x7 and 8x6 wind tunnels 

−40 −20 0 20

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

0.0045

0.0050

9x7 Parametric

Runs 1080−1105, Ref 1079

XAligned

1 Standard Deviation 

Δ P/P

Mean Temporal Component

Spatial Component

Total Composite

140 160 180

8x6 TBC3

Runs 818−843, Ref 817

XAligned

−40 −20 0 20 40

9x7 Parametric

Runs 2006−2044, Ref 1989

XAligned

−40 −20 0 20

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

0.0045

0.0050

9x7 Parametric

Runs 1080−1105, Ref 1106

XAligned

1 Standard Deviation 

Δ P/P

140 160 180

8x6 TBC3

Runs 818−843, Ref 844

XAligned

−40 −20 0 20 40

9x7 Parametric

Runs 2006−2044, Ref 2045

XAligned

AS2 model 

14” forward rail

Mach 1.6

h = 30”

X sweep

Boom1 VS2 model 

14” rail

Mach 1.78

h = 49”

X sweep

Boom1 VS2 model 

14” aft rail

Mach 1.8

h = 60”

X sweep
49 

(a) Beginning reference run 1079 

(b) Ending reference run 1106 

Figure 6–14. Individual and averaged signatures for AS2 model runs 1010-1043 processed with 

either beginning or ending reference runs, 9x7 parametric test, 14-in. fwd rail, M = 1.6

−50 −40 −30 −20 −10 0

−0.005

0.000

0.005

0.010

0.015

XAligned

(ΔP/P)data−(ΔP/P)ref

Average

+/− 1σ X−Sweep Runs, RefRun 1079

1080 1105

−50 −40 −30 −20 −10 0

−0.005

0.000

0.005

0.010

0.015

XAligned

(ΔP/P)data−(ΔP/P)ref

Average

+/− 1σ X−Sweep Runs, RefRun 1106

1080 1105
50 

1080 to 1105 of the 9x7 parametric test, where the signatures computed from the before reference run 

(1079) are shown in (a), and those computed from the after reference run (1106) are shown in (b). While 

the amount of scatter of the individual signatures, and the spread of the ±1σ signatures around the 

average, appear to be about the same between the two plots, the average curve in (b) drops slightly below 

the ΔP/P = 0 line well forward of the model nose shock, indicating that in this case, the before reference 

run is probably the better choice. This can be seen a little more clearly in Figure 6–15, where the plot of 

just the two averaged curves shows the separation in the leading zero points. Note, however, that the 

curves for the model signatures lie right on top of each other. A plot of the two reference runs, 1079 and 

1106, by themselves is shown in Figure 6–16, and the differences between them are very slight, 

essentially insignificant. This was the case with most reference runs taken within a short period of time 

throughout the tests, with the exceptions being among those which were taken at substantially different 

humidity levels. 

6.3.2. Tunnel Pressure 

Operating the 9x7 wind tunnel slightly above atmospheric condition at a total pressure of 2300 psf 

rather than 1450 psf as was used in some earlier tests has significant advantages. At Mach 1.6 a higher 

Reynolds number per foot of 4.5×106

 is obtained compared with 2.8×106 at 1450 psf. Testing at a higher 

Reynolds number reduces the likelihood of flow separation from the model or blade mounting surfaces. 

Also, the settling time of the rail static pressures is reduced by nearly a factor of two compared with 

operation at 1450 psf. And operating at 2300 psf also reduces the quantity of dry (~50 ppm) highpressure air needed to stabilize the humidity, and lower humidity levels are more easily obtained, thus 

reducing time to get on condition. 

6.3.3. Humidity Levels 

Maintaining a reasonably low humidity level for data and reference runs is of utmost importance to 

obtain high quality sonic boom data. Higher levels of humidity can cause rounding of the shocks in the 

signatures, shifts in the overall ΔP/P level, and also random variations in the pressure data. The effects of 

humidity on sonic boom single probe data as well as pressure rail data in a 2008 test in the 9x7 wind 

tunnel, and methods to correct for these effects, are discussed by Durston1

 and Cliff.3 In sonic boom tests 

in the 9x7 since 2008, very dry high-pressure air has been pumped into the wind tunnel to reduce and 

stabilize the humidity levels. Typically, approximately 5 to 10 lbs/sec of dry air is continuously pumped 

into the tunnel via a single pipe exiting through the bottom of the wind tunnel strut and pointed 

downstream. Humidity levels in the tests reported herein have been set generally below 300 ppm by 

weight and stabilized to within about 4 ppm within each run series (between reference runs). This has 

resulted in significantly higher-quality data in that there are almost no variations of the pressures due to 

humidity differences. 

6.3.4. Sampling Duration 

Short-, medium-, and long-term variations in the wind tunnel flow cause temporal uncertainties in the 

measured signatures. In the present work, short-term is defined as the time required to take one data point 

(aka one “sequence” in Ames wind tunnels), which is often just one or two seconds, but longer if more 

temporal averaging is desired. Medium-term is defined here as periods of minutes, in which multiple data 

points are taken, and large-scale flow structures or turbulence have had a chance to move around the wind 

tunnel circuit at least several times. Long-term refers to intervals of hours or days, where a repeat run 

may be taken after completing several run series, model changes, and/or tunnel stops and starts since the 
51 

Figure 6–15. Averaged signatures for runs 1080 to 1105 processed with beginning and ending 

reference runs. 9x7 Parametric test, AS2 model, 14-in. forward rail, M = 1.60, α = 0°, hNose = 30 in.

Figure 6–16. Beginning and ending reference run comparisons for run series 1080 to 1105 

9x7 Parametric test, AS2 model, 14-in. forward rail, M = 1.60, α = 0°, hNose = 50 in.

Sig Set 

33

33

Runs

1080—1105

1080—1105

Ref Run 

1079: Beginning 

1106: Ending 

Mach

1.60

1.60

PT'

2293

2293

HumidAvg

306

306

-60 -50 -40 -30 -20 -10 0 10 

XAligned (in.) 

-.005

0

.005

.010

.015

(6P/P)Data - (

6P/P)Ref

Sig Set 

33

33

Runs

1080—1105

1080—1105

Ref Run 

1079: Beginning 

1106: Ending 

Mach

1.60

1.60

PT'

2293

2293

HumidAvg

306

306

Run

1079

1106

Seq

52

52

Duration

60

60

Mach

1.60

1.60

PT'

2293

2293

HumidAvg

308

304

-150 -140 -130 -120 -110 -100 -90 -80 

Tunnel Station (in.) 

-.03

-.02

-.01

0

.01

.02

(6P/P)Ref

Run

1079

1106

Seq

52

52

Duration

60

60

Mach

1.60

1.60

PT'

2293

2293

HumidAvg

308

304
52 

original run being repeated was acquired. The present discussion regarding sampling duration pertains to 

the short- and medium-term flow variations only. 

The spatial averaging technique described above helps to reduce the uncertainties due to the longterm variations by having multiple signatures acquired over a period of five or ten minutes. For each 

individual signature (one “run” as defined for the present studies), multiple data points are normally 

taken, each of which has its own sampling duration. In the series of sonic boom wind tunnel tests 

conducted for Boeing and Lockheed-Martin in support of their NRA contracts, various combinations of 

number of seconds of sampling duration per data point and number of data points per run were 

implemented during various X and Z sweeps and reference runs to determine which would give the best 

results while maintaining good productivity. Factors contributing to “best” results were 1) allowing 

sufficient lag time for the pressures passing through the tubing from the rail to settle at the measurement 

transducers, and 2) taking a number of data points over a specified time interval that could be averaged to 

give a final result for a run. 

In the 9x7 parametric test in particular, a number of sampling studies were done, with reference run 

durations from 10 to 90 seconds and data run (for signature sweeps) sampling durations from 2 to 16 

seconds. In the TBC3 test, durations of 16 seconds were used for both reference and data runs, allowing 

for 6 seconds of pressure lag in which data were not acquired and 10 seconds of data recording. In TBC4, 

durations of 8 seconds were used for most reference runs and all data runs, but the empty-tunnel reference 

runs acquired in the beginning of the test for the Performance model (including runs 116, Mach 1.8, and 

119, Mach 1.6 used for the data plotted herein) had durations of 30 seconds. The sampling durations in 

each test eventually converged to those used in TBC4 as the best compromise between data quality and 

productivity. 
53 

7. Experimental Results 

Selected experimental data from the Boeing AS2, Boom1, Boom3, and Performance models run in 

the 9x7 wind tunnel parametric and TBC4 tests and in the 8x6 wind tunnel TBC3 test are presented in this 

section. Sample composite plots of individual pressure signatures taken during X or Z sweeps and their 

resulting averages are given first to illustrate the averaging procedure. Then the remainder of the plots—

up to but not including the reference run plots—consisting only of the averaged signatures will be shown 

to isolate various comparisons among the data, such as repeat runs, rail comparisons, X vs. Z sweeps, 

model variations, Mach effects, angle-of-attack effects, etc. Note that a “sig set” (signature set) number is 

included in the listing and in the legends of the plots—this is a sequential count of the X or Z sweeps 

(referring to a run range) within a test, and the sig set numbers were restarted at 1 for each test. 

A listing of all of the run sweeps plotted in this section and the figure numbers in which they appear 

is given in Appendix A, and a listing of all of the reference runs plotted and the figure numbers in which 

they appear is given in Appendix B. 

7.1. Composite Plots of X- and Z-Sweep Individual and Averaged Signatures 

Sample composite plots of selected X and Z sweeps for three Boeing models (AS2, Boom1, and 

Performance) are shown in Figures 7–1 through –5. Each composite plot consists of four plots: an aligned 

waterfall plot (upper left) showing individual pressure signatures (offset in small ΔP/P increments, in 

various colors) obtained within a sweep, along with the spatially-averaged signature (in black, at the 

bottom); a similar plot of the individual and averaged signatures but collapsed to the same ΔP/P scale 

(lower left); a zoomed-in plot of just the average model signature (lower right); and a small layout 

diagram showing the reference and sweep positions for the model (upper right). Average values and 

ranges of the model parameters for the sweep represented by the plots are given in the table at the top of 

each plot. 

The waterfall plots are shown after alignment of the signatures. Prior to alignment, the ends of the 

signatures line up vertically in the waterfall plot (as in Figure 6–12(a); representing the first and last 

orifices on the rail at their fixed X positions in the tunnel), and the locations of the model shocks vary 

throughout the sweep. The alignment allows the signatures to be averaged together, but note that the ends 

of the averaged signature do not use all of the individual signatures in computing the average because of 

the forward-sweeping (in viewing from bottom to top) signature edges in the aligned waterfall plot. The 

goal in the testing was to keep the model shocks far enough from the ends of the rail orifices so that as 

many as possible, if not all, of the signatures in the sweep could be used in the average. This was 

generally easy to do for the smaller models, but the large 43-in.-long Performance model required careful 

planning to make sure its signature was sufficiently centered on the rail. The dynamic layout diagrams 

shown on these composite plots and in Figures 6–8 through –10 were created in Excel by the author to 

permit the researchers to estimate shock locations on the rail for any given model and position in the 

tunnel. 

The variation of the corrected pressures from one model position to the next can be seen in the 

waterfall plot (albeit at a very compressed vertical scale). These variations are seen at their normal scale 

in the plot below the waterfall plot. The ambient flow upstream of the wind tunnel model should produce 

a pressure signature of exactly zero as a result of subtracting the reference run from the data run. The 

cause of these corrected pressures not being zero is due to temporal variations in the wind tunnel flow 

between the reference and data runs. The flatness of these “leading zero” pressures upstream of the 

model is a good indication of the quality of the pressure signature of the model—if the tunnel flow 

variations are small enough that these leading zero pressures are close to zero, then the temporal effects 
54 

on the model signature will be slight. Other contributors to errors in the model signature measurements 

are tunnel turbulence (temporal variations that are short term and small scale) and model vibration. Also, 

the discrete spacing (4 mm) of the pressure taps on the rail can lead to rounding of the model signatures if 

the shock peaks mostly fell between the rail orifices during the sweeps. 

Figure 7–1 shows the experimental pressures for the AS2 model from the 9x7 parametric test 97-0250 

for the run series 1010–1043. A Z sweep was conducted in this series, consisting of an 8-in. vertical 

traverse with 0.25-in. spacing in the Z direction (roughly equivalent to 2-orifice, 0.31-in., spacing in X). 

Within the whole range of rail pressures shown, the AS2 model pressure signature runs from the first 

shock wave at approximately X = -12, followed by a short flat region, then a recovery at negative ΔP/P

and back to ambient pressure at X = 2, before the large shock wave from the balance adapter aft of that 

point. The signatures show slight pressure variations at each Z position in the tunnel due to nonuniformities in the tunnel flow, and some of these can be identified by small bumps or spikes in the 

signatures at constant orifice locations on the rail. 

Figure 7–2 shows the aligned pressure signatures for an X sweep from the 8x6 TBC3 test, in run 

series 1162–1187, consisting of an 8-in. horizontal traverse with 0.31-in. (2 orifices) spacing. Note that 

with this X sweep, the ends of the signatures in the waterfall plot sweep aft from the bottom to the top, in 

contrast to the forward-swept edges of the Z sweep in the previous figure. As model height above the rail 

is increased, the model shocks move aft on the rail, whereas in an X sweep, the model shocks move 

forward on the rail, and the alignment process shifts the edges of the signatures on the waterfall plots in 

the opposite direction to get the model shocks to line up at constant X values. 

The portion of the rail pressures showing the AS2 model signature is from approximately X = 143 to 

155 (the X values are different for the 8x6 wind tunnel because the origin is at the forward end of the test 

section). The model signature in this figure looks similar to that in the previous figure, though the flat 

region behind the nose shock is lower in magnitude, primarily because the model is twice as far from the 

rail (60 in. vs. 30 in.). 

Composite signature plots for the Boom1 and Boom3 models in the 97p and TBC4 tests are shown in 

Figures 7–3 and –4, respectively. Note that the entire Boom1 model signature (X = -15 to 7) was captured 

for every position in the X sweep in Figure 7–3, allowing a number of leading zero points before the start 

of the model signature at approximately X = -12, but in Figure 7–4 the front of the model signature was 

not even captured until higher in the Z sweep. This caused enough smearing of the model nose shock that 

it is not even recognizable in the averaged signature, rendering this data set unusable as a full signature. 

This run series was chosen to show here to illustrate the importance of positioning the model properly in 

the wind tunnel in order to acquire usable signatures. It is likely that this position was believed to be 

acceptable at the time of the running, but the missing front of the signature was noticed only after the data 

were taken. 

Performance model data from the 9x7 TBC4 test are shown in Figure 7–5. These data are at a 

nominal height of 60 in., and the model signature covers an X range from approximately -32 to 15. 

Significant variations among the individual signatures are evident in the waterfall plot, and the average 

curves show some unexpected undulations between the nose shock and the highest peak from the wing 

shock. These are most likely the result of the large (60-in.) distance from the model to the rail. The 

spatial and temporal tunnel flow irregularities affect the shock wave patterns coming from the model to 

the rail, and make it difficult to consistently acquire high-quality data at these distances. 
55 

Figure 7–1. AS2 model aligned waterfall plot and averaged signature plots for Z sweep from 

26” to 34” at XRam = 16 in., 9x7 parametric test, M = 1.6, 14-in. forward rail 

0.10

0.20

0.30

0.40

0.50

0.60

0.70

(ΔP/P)data−(ΔP/P)ref + offset

Average

−50 −40 −30 −20 −10 0 10 20

−0.01

0.00

0.01

0.02

0.03

0.04

XAligned

(ΔP/P)data−(ΔP/P)ref

+/− 1σ

−15 −10 −5 0 −0.010

−0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

XAligned

Z−Sweep Runs, RefRun 1009

1010 1043

Xram, in ________ _____ h/L h, in ___

16.00 (16.00−16.00) 30.02 (26.02−34.01) 1.61 (1.40−1.83)

______

α, deg ______ β, deg ______ φ, deg

0.04 (0.04−0.04) 0.01 (0.01−0.01) −0.15 (−0.18− −0.13)

C

___L C___D C___M

0.006 (−0.003−0.010) 0.04470 (0.04180−0.04972) −0.021 (−0.052−0.047)
56 

Figure 7–2. AS2 model aligned waterfall plot and averaged signature plots for X sweep from 

0” to 8” at hNose = 59 in., 8x6 TBC3 test, M = 1.56, 2-in. rail 

0.10

0.20

0.30

0.40

0.50

(ΔP/P)data−(ΔP/P)ref + offset

Average

130 140 150 160 170 180 190 200

−0.06

−0.04

−0.02

0.00

0.02

0.04

XAligned

(ΔP/P)data−(ΔP/P)ref

+/− 1σ

145 150 155 −0.010

−0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

XAligned

X−Sweep Runs, RefRun 1188

1162 1187

Xram, in ________ _____ h/L h, in ___

19.94 (16.00−23.88) 59.15 (59.12−59.18) 3.76 (3.75−3.76)

______

α, deg ______ β, deg ______ φ, deg

−0.02 (−0.04−0.00) 0.00 (0.00−0.00) 0.00 (0.00−0.00)

C

___L C___D C___M

0.070 (0.069−0.071) 0.03953 (0.03933−0.03986) 0.130 (0.129−0.132)
57 

Figure 7–3. Boom1 VS2 model aligned waterfall plot and averaged signature plots for X sweep 

from 0” to 16” at hNose = 60 in., 9x7 parametric test, M = 1.6, 14-in. aft rail 

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

(ΔP/P)data−(ΔP/P)ref + offset

Average

−30 −20 −10 0 10 20 30 40

−0.06

−0.04

−0.02

0.00

0.02

0.04

XAligned

(ΔP/P)data−(ΔP/P)ref

+/− 1σ

−15 −10 −5 0 5 −0.010

−0.005

0.000

0.005

0.010

0.015

0.020

XAligned

X−Sweep Runs, RefRun 2073

2047 2072

Xram, in ________ _____ h/L h, in ___

7.87 (−0.00−15.75) 59.59 (59.10−60.08) 3.78 (3.75−3.82)

______

α, deg ______ β, deg ______ φ, deg

3.40 (3.38−3.42) 0.21 (0.20−0.22) 0.39 (0.34−0.43)

C

___L C___D C___M

0.100 (0.090−0.104) 0.07165 (0.06711−0.07379) −0.019 (−0.028−0.000)
58 

 

Figure 7–4. Boom3 VS3 model aligned waterfall plot and averaged signature plots for Z sweep 

from 59” to 65”, 9x7 TBC4 test, M = 1.6, 14-in. aft rail 

0.05

0.10

0.15

0.20

0.25

(ΔP/P)data−(ΔP/P)ref + offset

Average

−10 0 10 20 30 40 50 −0.04

−0.03

−0.02

−0.01

0.00

0.01

0.02

0.03

0.04

XAligned

(ΔP/P)data−(ΔP/P)ref

+/− 1σ

−15 −10 −5 0 5 −0.010

−0.005

0.000

0.005

0.010

0.015

0.020

XAligned

Z−Sweep Runs, RefRun 1624

1628 1652

Xram, in ________ _____ h/L h, in ___

 (−) 61.66 (58.63−64.69) 3.92 (3.72−4.11)

______

α, deg ______ β, deg ______ φ, deg

2.57 (2.55−2.57) 0.23 (0.23−0.23) 0.19 (0.18−0.20)

C

___L C___D C___M

0.060 (0.054−0.065) 0.06502 (0.06397−0.06554) 0.005 (−0.010−0.028)
59 

Figure 7–5. Performance model aligned waterfall plot and averaged signature plots for Z sweep 

from 59” to 65”, 9x7 TBC4 test, M = 1.6, 14-in. aft rail

0.05

0.10

0.15

0.20

0.25

(ΔP/P)data−(ΔP/P)ref + offset

Average

−30 −20 −10 0 10 20 30

−0.02

−0.01

0.00

0.01

0.02

0.03

0.04

XAligned

(ΔP/P)data−(ΔP/P)ref

+/− 1σ

−30 −20 −10 0 10

−0.010

−0.005

0.000

0.005

0.010

0.015

0.020

0.025

XAligned

Z−Sweep Runs, RefRun 119

795 819

Xram, in ________ _____ h/L h, in ___

 (−) 60.87 (57.87−63.88) 1.41 (1.34−1.48)

______

α, deg ______ β, deg ______ φ, deg

3.40 (3.39−3.40) −0.19 (−0.20− −0.19) 45.46 (45.03−45.85)

C

___L C___D C___M

0.064 (0.063−0.066) 0.01109 (0.01044−0.01166) −0.014 (−0.014− −0.014)
60 

7.2. Repeatability 

The plots in the remainder of the report showing experimental model signature data will now consist 

only of the spatially averaged pressure signatures, as opposed to those of the previous subsection which 

included the individual signatures that were used to generate the average. It should be noted that the 

Mach, total pressure, and humidity values in the second title lines of each of the following plots are the 

average values of those parameters for all of the runs shown in the plots. On plots where these 

parameters vary among the runs, the plot legends will show those values for each set of runs. 

Short-term repeatability of signature measurements for several models in the 9x7 tests are shown in 

Figures 7–6 through –9. (Long-term repeat runs were not acquired because of limitations on test time.) 

Back-to-back Z sweeps followed by X sweeps from the 9x7 parametric test for the AS2 model at heights 

of 30 and 31.8 in. are shown in Figure 7–6, where the four signatures are almost identical except for a 

roughly 10% difference in the ΔP/P levels in the flat part of the signatures behind the nose shock. This 

difference could be due to the slight differences in model height or due to the type of sweep (more on 

these effects later), but considering the variation in individual signatures seen in Figures 7–1 and –2, it 

could also be considered within the scatter of the data. Boom1 VS2 model signatures in Figure 7–7 show 

similar very good repeatability. 

Repeatability for various Z sweeps with the Performance model in the TBC4 test are shown in 

Figures 7–8 and –9. The agreement in the forward part of the signatures, aside from the nose shock, is 

quite good ahead of X = -65 in., but aft of that it is worse in the vicinity of wing, nacelle, and tail shocks 

(in particular, at X = -61, -55, and -41 in.), with differences up to ~0.0025 in ΔP/P. Average humidity for 

the three runs is displayed in the legend to see if there is any correlation between any humidity differences 

and the data mismatches, but the trends are not consistent. The humidity for runs in sig set 2 is over 100 

ppm higher than in the other sig sets, and yet it is sig set 4 that has the greatest deviations among the runs. 

(Average humidity differences between each pair of runs in Figures 7–6 and –7 were within 2 ppm, so 

humidity is likely not the cause of the slight differences in those repeat runs.) 

The other comparison of repeat runs for the Performance model is shown in Figure 7–9. In these 

runs, the entire model signature was captured, and the repeatability is only slightly better than in the 

previous figure—there are several places with differences up to ~0.0020 in ΔP/P. The deviations in both 

of these plots are probably a fair representation of the repeatability that can be expected for sonic boom 

measurements in the 9x7, and are most likely due to model fluctuations or variations in tunnel flow 

conditions over time. 
61 

Figure 7–6. Repeatability, X and Z sweeps

9x7 parametric test, AS2 model, 14-in. forward rail, M = 1.60 

Figure 7–7. Repeatability, X sweeps (0” to 16”) 

9x7 parametric test, Boom1 VS2 model, 14-in. aft rail, M = 1.60 

Sig Set 

31

32

33

34

Runs

1010—1043

1045—1078

1080—1105

1107—1132

Ref Run 

1044

1079

1106

1133

Sweep

Z

Z

X

X

hNose

30.0

30.0

30.0

31.8

_

0.04

0.04

0.04

0.04

HumidAvg

305

307

306

304

-100 -95 -90 -85 -80 -75 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

31

32

33

34

Runs

1010—1043

1045—1078

1080—1105

1107—1132

Ref Run 

1044

1079

1106

1133

Sweep

Z

Z

X

X

hNose

30.0

30.0

30.0

31.8

_

0.04

0.04

0.04

0.04

HumidAvg

305

307

306

304

Sig Set 

61

62

Runs

2047—2072

2074—2099

Ref Run 

2073

2100

hNose

60.0

60.0

_

3.40

3.39

HumidAvg

288

290

-65 -60 -55 -50 -45 -40 -35 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

61

62

Runs

2047—2072

2074—2099

Ref Run 

2073

2100

hNose

60.0

60.0

_

3.40

3.39

HumidAvg

288

290

Mach 1.6

Mach 1.6
62 

Figure 7–8. Repeatability, Z sweeps (59” to 64”) 

9x7 TBC4 test, Performance sting+contour model, 14-in. aft rail, M = 1.60 

Figure 7–9. Repeatability, Z sweeps (59” to 64”) 

9x7 TBC4 test, Performance sting+contour model, 14-in. aft rail, M = 1.80 

Sig Set 

2

3

4

Runs

199—222

224—247

249—273

Ref Run 

119

119

119

_

3.33

3.33

3.32

HumidAvg

348

238

233

-80 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

2

3

4

Runs

199—222

224—247

249—273

Ref Run 

119

119

119

_

3.33

3.33

3.32

HumidAvg

348

238

233

Sig Set 

9

12

Runs

401—425

476—500

Ref Run 

116

116

_

3.32

3.25

HumidAvg

238

237

-70 -60 -50 -40 -30 -20 -10 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

9

12

Runs

401—425

476—500

Ref Run 

116

116

_

3.32

3.25

HumidAvg

238

237

Mach 1.6

Mach 1.8
63 

7.3. Effect of Adjusting Height During X Sweeps 

All of the Boeing models were mounted on the struts/balance adapter/balance at zero incidence angle; 

that is, the model was “level” when the balance was “level” (speaking of the Z, or “height” orientation). 

The linear actuator was colinear with the balance, so in order to run the Boom models at a positive angle 

of attack, the wind tunnel strut had to be pitched up by this angle. This meant that as the ram of the linear 

actuator was extended, it was driving the model higher, away from the rail during X sweeps. For a model 

angle of attack of 3.4° and a 16-in. X sweep, the model nose would move up in Z by 0.95 in. There was 

concern during the test as to whether this height change would affect the pressure signature, so some 

comparison runs were obtained in the 9x7 to investigate this. 

The model height for the Boom1 VS2 sig set 45 was adjusted to try to keep the height within 0.33 in. 

of the target value, and in sig sets 46 and 47, the height was not adjusted but allowed to drift. The 

resulting signatures are shown in Figure 7–10 at Mach 1.6, where the changes in height for the three run 

sets, designated by ΔhNose, were 0.42 in., 0.96 in., and 0.97 in., respectively. The three signatures are 

nearly identical, and the very minor variations among them are well within the repeatability of the data. 

A similar comparison of runs where the heights were and were not adjusted is presented in Figure 7–

11 at Mach 1.8. The model height during the X sweep was adjusted for sig set 38 (ΔhNose, = 0.21 in.), but 

allowed to drift up for sig set 39 (ΔhNose, = 0.97 in.). As on the previous plot, the signatures are very 

close, but the one which was allowed to drift is very slightly lower overall than the adjusted one, though 

within expected repeatability. 

Figure 7–10. Effect of adjusting height in X sweeps (8” to 24”) 

9x7 parametric test, Boom1 VS2 model, 14-in. fwd rail, M = 1.60, HumidAvg=314 ppm 

Sig Set 

45

46

47

Runs

1472—1497

1500—1525

1526—1551

Ref Run 

1498

1499

1552

Adjust h 

Adjust

Drift

Drift

hNose

30.30—30.72

29.89—30.85

30.41—31.38

6hNose

0.42

0.96

0.97

_

3.40

3.40

3.40

-100 -95 -90 -85 -80 -75 -70 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

45

46

47

Runs

1472—1497

1500—1525

1526—1551

Ref Run 

1498

1499

1552

Adjust h 

Adjust

Drift

Drift

hNose

30.30—30.72

29.89—30.85

30.41—31.38

6hNose

0.42

0.96

0.97

_

3.40

3.40

3.40

Mach 1.6
64 

Figure 7–11. Effect of adjusting height in X sweeps (8” to 24”) 

9x7 parametric test, Boom1 VS2 model, 14-in. fwd rail, M = 1.80, HumidAvg=306 ppm 

These two plots clearly indicate that adjusting model height during an X sweep has essentially 

negligible effects on the measured signatures—the differences appear to be well within the expected 

uncertainty, and these plots can be considered as repeatability plots, which show very good repeatability. 

7.4. Effect of Model Height 

For a given rail and mounting position on the wall of the 9x7 tunnel, there are allowable ranges of 

model X and Z positions where the model shocks stay within the instrumented section of the rail (refer to 

Figure 6–8 for a typical layout). For the Boom1 model with the VS2 strut at Mach 1.6, α = 3.4° in the 

9x7 tunnel, with the rail on the forward window blank, the model height range (estimated by the Excel 

layout) that allows for at least an 8-in. X sweep without overlap between the reference and data runs is 

from 10 to 38 in. With the rail on the aft window blank, the model height range that allows for at least an 

8-in. X sweep is from 52 to 68 in. The rail could also be mounted to span the two window blanks to cover 

the middle range, but this position was not used in any of the tests in the interest of time. 

In the 9x7 parametric test, the RF1 rail was run in both the forward and aft window blank positions, 

and signature measurements of the Boom1 VS2 model were acquired at heights of 30 and 60 in. 

Comparisons of these signatures from X sweeps at Mach 1.6 and 1.8 are shown in Figure 7–12 and –13, 

respectively. The signatures at both Mach numbers at 30 in. have much more clearly defined shock peaks 

than those at 60 in., and the magnitude of the overall pressure levels are higher at 30 in., as one would 

expect. At 60 in., the small shocks aft of the primary expansion have already coalesced. 

Sig Set 

38

39

Runs

1247—1272

1274—1299

Ref Run 

1273

1300

Adjust h 

Adjust

Drift

hNose

30.00—30.21

29.55—30.52

6hNose

0.21

0.97

_

3.41

3.42

-95 -90 -85 -80 -75 -70 -65 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

38

39

Runs

1247—1272

1274—1299

Ref Run 

1273

1300

Adjust h 

Adjust

Drift

hNose

30.00—30.21

29.55—30.52

6hNose

0.21

0.97

_

3.41

3.42

Mach 1.8
65 

Figure 7–12. Effect of model height, X sweeps (8” to 24”, 0” to 16”) 

9x7 parametric test, Boom1 VS2 model, M = 1.60, HumidAvg = 301 ppm 

Figure 7–13. Effect of model height, X sweeps (8” to 24”, 0” to 16”) 

9x7 parametric test, Boom1 VS2 model, M = 1.80, HumidAvg = 295 ppm 

Sig Set 

46

61

Runs

1500—1525

2047—2072

Ref Run 

1499

2073

Rail

14-in Fwd 

14-in Aft 

hNose

30.4

60.0

_

3.40

3.40

-5 0 5 10 15 20 25 30 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

46

61

Runs

1500—1525

2047—2072

Ref Run 

1499

2073

Rail

14-in Fwd 

14-in Aft 

hNose

30.4

60.0

_

3.40

3.40

Sig Set 

39

60

Runs

1274—1299

2006—2044

Ref Run 

1300

2045

Rail

14-in Fwd 

14-in Aft 

hNose

30.0

60.2

_

3.42

3.39

-5 0 5 10 15 20 25 30 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

39

60

Runs

1274—1299

2006—2044

Ref Run 

1300

2045

Rail

14-in Fwd 

14-in Aft 

hNose

30.0

60.2

_

3.42

3.39

hNose = 60”

hNose = 30”

hNose = 60”

hNose = 30”

Mach 1.8

Mach 1.6
66 

7.5. Comparison of X vs. Z Sweeps 

Spatial averaging of model pressure signatures can be accomplished by moving the model over small 

ranges in either the X or Z direction such that the signatures fall on different regions of the pressure rail. 

The first sweeps done to accomplish this in the series of tests were in the X direction, and were made 

possible by extension of the ram of the linear actuator. At the time of the 9x7 parametric test, it was 

anticipated that a future test might not include the linear actuator, but it needed to be established first that 

Z sweeps over small ranges would give equally valid data as X sweeps. Hence a few direct comparisons 

of signatures obtained with both types of sweeps for the AS2 and Boom1 VS2 models were run in both 

the 9x7 parametric and the 8x6 TBC3 tests. 

AS2 body of revolution signatures from one X sweep and two Z sweeps at nominally 30-in. heights 

above the 14-in. rail in the 9x7 are shown in Figure 7–14. The agreement is generally excellent among all 

three signatures, though slight differences appear, unexpectedly, between the two Z sweeps, where the 

latter one (sig set 32) with XRam = 24 in. has a slightly higher initial shock peak and the aft flat area before 

the main expansion is higher. It is possible that the 8-in.-further-forward position in the tunnel (XRam = 24 

in. vs. 16 in.) for the second Z sweep could account for this difference, if there was a slightly different 

flow angle or static pressure in the tunnel for this position. Or the differences could be just random 

scatter in the data as they are not atypical in light of the measured repeatability. 

Four different X vs. Z sweep comparisons for the Boom1 VS2 model in the 9x7 are shown in Figures 

7–15 through –18, two with the 14-in. rail and two with the 2-in. rail, all at nominally 30-in. heights 

above the rails. The first comparison, at Mach 1.6 in Figure 7–15, shows very good agreement over the 

entire length of the signatures, with minor differences in various positions along the signatures. The next 

comparison, at Mach 1.8 in Figure 7–16, shows that the Z sweep has an overall slightly higher pressure 

level than the X sweep, ranging from 0 to 0.001 ΔP/P difference. This difference exists even in the 

leading zero points, though very small, and if the leading zero points just ahead of the model’s front 

shock were made to align by an overall lowering of the Z sweep curve, then the two sweeps would have a 

more favorable comparison. The Z sweep curve has a little more rounding, or smearing, of the shock 

peaks relative to the X sweep curve. Nonetheless, it seems that there must have been some variation in 

the tunnel flow between these two sets of runs to cause the differences that are apparent. 

The other two comparisons of sweep types with the Boom1 VS2 model are in Figures 7–17 and –18, 

with the 2-in. rail. The two signatures at Mach 1.6 in Figure 7–17 show good agreement up to (X = -88) 

but not including the highest pressure peak, where the differences from this point through the aft 

expansion (X = -82) are fairly significant, up to 0.003 in ΔP/P. At Mach 1.8, Figure 7–18, the differences 

between the two sweeps are more in line with those at the same Mach number from the 14-in. rail (Figure 

7–16). However, at this Mach number, the Z sweep pressures are higher than those from the X sweep in 

the 14-in. rail data, but lower in the 2-in. rail data at both Mach numbers. 

The reasons for the pressure signature differences between the two types of sweeps are not 

understood, but from these data and data from other tests not reported herein the two types of sweeps 

were considered equally valid for acquiring sonic boom data for spatial averaging. 
67 

Figure 7–14. X vs Z sweep comparisons

9x7 parametric test, AS2 model, 14-in. forward rail, M = 1.60, HumidAvg = 306 ppm 

Figure 7–15. X vs Z sweep comparisons 

9x7 parametric test, Boom1 VS2 model, 14-in. fwd rail, M = 1.60, HumidAvg=308 ppm 

Sig Set 

33

31

32

Runs

1080—1105

1010—1043

1045—1078

Ref Run 

1106

1044

1079

XRam

8—24

16

24

hNose

30

26—34

26—34

Sweep

X

Z

Z

-100 -95 -90 -85 -80 -75 -70 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

33

31

32

Runs

1080—1105

1010—1043

1045—1078

Ref Run 

1106

1044

1079

XRam

8—24

16

24

hNose

30

26—34

26—34

Sweep

X

Z

Z

Sig Set 

46

44

43

Runs

1500—1525

1437—1469

1401—1433

Ref Run 

1499

1470

1434

XRam

8—24

16

24

hNose

30

26—34

26—34

Sweep

X

Z

Z

-100 -95 -90 -85 -80 -75 -70 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

46

44

43

Runs

1500—1525

1437—1469

1401—1433

Ref Run 

1499

1470

1434

XRam

8—24

16

24

hNose

30

26—34

26—34

Sweep

X

Z

Z

Z sweep

Z sweep

X sweep

Z sweep

Z sweep

X sweep

Mach 1.6

Mach 1.6
68 

Figure 7–16. X vs Z sweep comparisons 

9x7 parametric test, Boom1 VS2 model, 14-in. fwd rail, M = 1.80, HumidAvg=307 ppm 

Figure 7–17. X vs Z sweep comparisons 

9x7 parametric test, Boom1 VS2 model, 2-in. fwd rail, M = 1.60, HumidAvg = 321 ppm 

Sig Set 

39

37

Runs

1274—1299

1213—1245

Ref Run 

1300

1246

XRam

8—24

16

hNose

30

26—34

Sweep

X

Z

-95 -90 -85 -80 -75 -70 -65 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

39

37

Runs

1274—1299

1213—1245

Ref Run 

1300

1246

XRam

8—24

16

hNose

30

26—34

Sweep

X

Z

Sig Set 

53

52

Runs

1724—1749

1690—1722

Ref Run 

1750

1723

XRam

8—24

24

hNose

30

26—34

Sweep

X

Z

-100 -95 -90 -85 -80 -75 -70 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

53

52

Runs

1724—1749

1690—1722

Ref Run 

1750

1723

XRam

8—24

24

hNose

30

26—34

Sweep

X

Z

Z sweep

X sweep

Z sweep

X sweep

Mach 1.8

Mach 1.6
69 

Figure 7–18. X vs Z sweep comparisons 

9x7 parametric test, Boom1 VS2 model, 2-in. fwd rail, M = 1.80, HumidAvg = 317 ppm 

Sig Set 

51

49

Runs

1662—1687

1601—1633

Ref Run 

1688

1634

XRam

8—24

16

hNose

30

26—34

Sweep

X

Z

-95 -90 -85 -80 -75 -70 -65 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

51

49

Runs

1662—1687

1601—1633

Ref Run 

1688

1634

XRam

8—24

16

hNose

30

26—34

Sweep

X

Z

Z sweep

X sweep

Mach 1.8
70 

7.6. Effect of Ram Position for Z Sweeps 

It is well known that the flow in the 9x7 test section is curved in the vertical plane due to the 

asymmetric nozzle, and this impacts the measurement of sonic boom data because the model is in 

different flow environments in different locations in the test section. The subtraction of an ambient 

pressure signature on the rail from a data run is intended to reduce or eliminate the effects of the different 

flow environments, but that is not always a given. 

In the 9x7 parametric test, a few runs were conducted with the AS2 and Boom1 VS2 models to 

investigate these possible effects. Z sweeps centered on a 30-in. height for the AS2 model were run at 

XRam positions of 16 and 24 in., and the signatures for these sweeps taken at Mach 1.6 are shown in Figure 

7–19. There are some minor differences in the nose shock peak and the aft flat area, but these differences 

are no greater than those observed in Figure 7–8 showing repeatability and in Figure 7–15 showing the 

comparison of X vs. Z sweeps. 

Similar insignificant differences between Z sweeps at XRam positions of 16 and 24 in. for the Boom1 

VS2 model are seen in Figures 7–20 and –21 at Mach 1.6 and 1.8, respectively. There are some minor 

variations among the curves, but not any greater than those observed in the plots showing repeatability or 

comparison of sweep types. Perhaps greater differences could have been seen between sweeps at the 

extremes of the ram positions—0 and 24 in.—but there were other higher-priority test objectives that 

precluded getting additional comparable signatures at XRam = 0 in. 

Figure 7–19. Effects of ram position for Z sweeps (26” to 34”) 

9x7 parametric test, AS2 model, 14-in. fwd rail, M = 1.60, HumidAvg = 306 ppm 

Sig Set 

31

32

Runs

1010—1043

1045—1078

Ref Run 

1044

1079

XRam

16.0

24.0

-115 -110 -105 -100 -95 -90 -85 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

31

32

Runs

1010—1043

1045—1078

Ref Run 

1044

1079

XRam

16.0

24.0

XRam = 24

XRam = 16

Mach 1.6
71 

Figure 7–20. Effects of ram position for Z sweeps (26” to 34”) 

9x7 parametric test, Boom1 VS2 model, 14-in. fwd rail, M = 1.60, HumidAvg=304 ppm 

Figure 7–21. Effects of ram position for Z sweeps (26” to 34”) 

9x7 parametric test, Boom1 VS2 model, 14-in. fwd rail, M = 1.80, HumidAvg=306 ppm 

Sig Set 

44

43

Runs

1437—1469

1401—1433

Ref Run 

1470

1434

XRam

16.0

24.0

-115 -110 -105 -100 -95 -90 -85 -80 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

44

43

Runs

1437—1469

1401—1433

Ref Run 

1470

1434

XRam

16.0

24.0

Sig Set 

37

36

Runs

1213—1245

1179—1211

Ref Run 

1246

1212

XRam

16.0

24.0

-105 -100 -95 -90 -85 -80 -75 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

37

36

Runs

1213—1245

1179—1211

Ref Run 

1246

1212

XRam

16.0

24.0

XRam = 24

XRam = 16

XRam = 24

XRam = 16

Mach 1.8

Mach 1.6
72 

7.7. Rail Comparisons — 14-in. (RF1) vs. 2 in. Rails 

In this section various comparisons of data from the 14-in. and 2-in. rails for the AS2 and Boom1 

models are presented. Two primary differences in the effects of the rail on the data were expected 

between the two rails: 

1) Reflection factor: The 14-in. RF1 rail was expected to not amplify the measured pressures at all, 

whereas the 2-in. rail was expected to cause amplifications between a factor of 1 and 2 (would be 

2 for an infinitely-wide flat plate, but lower for this 1.5-in.-wide rail). 

2) Contamination of the aft part of the signatures from shock reflections off the wall: The 14-in. 

height of the RF1 rail was chosen to eliminate this possibility for models up to 33-in. long at a 

Mach 1.6 (51°) Mach line angle, whereas on the 2-in. rail, the reflected shock passes back over the 

surface of the rail about 5 in. aft of the incident shock location at Mach 1.6, or possibly less 

distance aft if the lower Mach line angle closer to the tunnel wall (due to the boundary layer) is 

taken into account. 

Flat-top rails like the 2-in. rail have been used in many sonic boom tests outside of NASA, and users 

of those rails have developed methods or calibration factors for correcting the data. These corrections are 

usually based on CFD analyses and/or experience with models of different sizes whose signatures are 

well known. However, in the present NASA studies discussed herein, no such corrections have been 

generated, and the data from both rails will be presented as they were taken, with the exception of 

reflection factors for the 2-in. rail data computed to get the best overall match of the whole signature with 

the 14-in. rail data. 

Figure 7–22 shows a comparison between the sonic boom signatures acquired with the 14-in. rail and 

2-in. rail for the AS2 body of revolution in X sweeps at a height of 30 in. at Mach 1.6 and α = 0°. The 2-

in. rail data with no reflection factor correction (RF = 1) is quite high relative to the data acquired with the 

14-in. rail, probably as one would expect. But the aft “flat” portion of the signature, which is fairly 

horizontal in the 14-in. data, is sloped upward in the 2-in. data, which may be due to a reflection of the 

nose shock off the tunnel wall that is contaminating the aft portion of the signature. 

To see what the 2-in. rail data would look like with a correction, a reflection factor of 1.7 (ΔP/P / 1.7) 

was applied to match the nose shock strength of the 14-in. rail—see the second sig set 54 curve, with RF 

1.7. The nose shock strength now matches that of the 14-in. rail data, but the correlation with the 14-in. 

data in the aft flat area is poor. From these data and other sources, it is surmised that the correction for 

reflection factor should not be applied evenly over the entire signature, but a thorough study of how it 

should be applied has not been conducted by the authors, and so the data will remain as presented herein 

for now. Similar data for the AS2 model obtained with Z sweeps shown in Figure 7–23 shows similar 

results. 

Rail comparisons for data from the Boom1 VS2 model from both tunnels at various heights are 

shown in Figures 7–24 through –27. Data from the 9x7 tunnel for Z and X sweeps at a model height of 

30 in. and Mach 1.6 are shown in the first two figures. In the Z sweep data in Figure 7–24, as with the 

AS2 data, the unadjusted signatures from the two rails show similar trends, though the 2-in. rail data 

shows more rounding and less definition of the pressure waves between the shocks. The adjustment of 

the 2-in. rail data for a reflection factor of 1.7 brings that data down to the level of the 14-in. rail data for 

the front half of the signature, but in the rear half (after ΔP/P crosses zero), the adjusted 2-in. rail data 

have significantly higher pressure levels than the 14-in. data. This could be due to the shock reflections 

off the wall contaminating the rear part of the signature, but as stated earlier, based strictly on the shocks 

following the Mach line angle, one might expect the contamination to start about 5 in. aft of the nose 
73 

shock. The 2-in. rail data shows no or very little deviation from the 14-in. data at 5 in. back (around 

X = -110), but the major differences start around 11 in. back (X = -104). 

In the X sweep data in Figure 7–25, there are slightly greater differences between the magnitudes of 

the pressure data for the two rails, even after applying the reflection factor of 1.7 to the 2-in. rail data. All 

other run parameters (M, h, α) are the same in these data versus those in the previous figure aside from 

the sweep type, but it doesn’t seem likely that sweep type would account for these differences given the 

findings in Section 7.5. 

Rail comparisons for the same model from X sweeps in the 8x6 wind tunnel are shown in Figures 7–

26 and –27 for heights of 59 and 49 in. and at Mach numbers of 1.56 and 1.78, respectively. In both 

figures, the adjusted 2-in. data with RF = 1.7 applied match up fairly well with the 14-in. rail data, though 

better at the lower height (49 in.). Also, the leading zero pressures for all of the runs in these two figures 

are below the zero ΔP/P line, indicating that there were probably some significant differences in the 

tunnel flow between the reference and data runs. All of the data from the 8x6 tunnel presented in this 

report were acquired during the second week of testing, after the smooth windows (no holes) were moved 

to the forward part of the test section and the Mach number was being held to a tighter tolerance, so the 

poorer data quality issues encountered during the first week are not a factor in these plots. 

 
74 

Figure 7–22. Rail comparisons, X sweeps (8” to 24”) 

9x7 parametric test, AS2 model, M = 1.60, HumidAvg = 302 ppm 

Figure 7–23. Rail comparisons, Z sweeps (26” to 34”) 

9x7 parametric test, AS2 model, M = 1.60, HumidAvg = 301 ppm 

Sig Set 

33

54

54

Runs

1080—1105

1759—1784

1759—1784

Ref Run 

1106

1785

1785

hNose

30.0

30.1

30.1

Rail

14-in Fwd 

2-in Fwd 

2-in Fwd 

RF

1.0

1.0

1.7

-100 -95 -90 -85 -80 -75 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

33

54

54

Runs

1080—1105

1759—1784

1759—1784

Ref Run 

1106

1785

1785

hNose

30.0

30.1

30.1

Rail

14-in Fwd 

2-in Fwd 

2-in Fwd 

RF

1.0

1.0

1.7

Sig Set 

32

55

55

Runs

1045—1078

1786—1818

1786—1818

Ref Run 

1079

1819

1819

XRam

24.0

24.0

24.0

Rail

14-in Fwd 

2-in Fwd 

2-in Fwd 

RF

1.0

1.0

1.7

-120 -115 -110 -105 -100 -95 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

32

55

55

Runs

1045—1078

1786—1818

1786—1818

Ref Run 

1079

1819

1819

XRam

24.0

24.0

24.0

Rail

14-in Fwd 

2-in Fwd 

2-in Fwd 

RF

1.0

1.0

1.7

2-in. Rail

Adjusted for RF = 1.7

2-in. Rail

14-in. Rail

2-in. Rail

Adjusted for RF = 1.7

2-in. Rail

14-in. Rail

Mach 1.6

Mach 1.6
75 

Figure 7–24. Rail comparisons, Z sweeps (26” to 34”) 

9x7 parametric test, Boom1 VS2 model, M = 1.60, HumidAvg = 313 ppm 

Figure 7–25. Rail comparisons, X sweeps (8” to 24”) 

9x7 parametric test, Boom1 VS2 model, M = 1.60, HumidAvg = 319 ppm

Sig Set 

43

52

52

Runs

1401—1433

1690—1722

1690—1722

Ref Run 

1434

1723

1723

XRam

24.0

24.0

24.0

Rail

14-in Fwd 

2-in Fwd 

2-in Fwd 

RF

1.0

1.0

1.7

-120 -115 -110 -105 -100 -95 -90 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

43

52

52

Runs

1401—1433

1690—1722

1690—1722

Ref Run 

1434

1723

1723

XRam

24.0

24.0

24.0

Rail

14-in Fwd 

2-in Fwd 

2-in Fwd 

RF

1.0

1.0

1.7

Sig Set 

46

53

53

Runs

1500—1525

1724—1749

1724—1749

Ref Run 

1499

1750

1750

hNose

30.4

30.5

30.5

Rail

14-in Fwd 

2-in Fwd 

2-in Fwd 

RF

1.0

1.0

1.7

-100 -95 -90 -85 -80 -75 -70 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

46

53

53

Runs

1500—1525

1724—1749

1724—1749

Ref Run 

1499

1750

1750

hNose

30.4

30.5

30.5

Rail

14-in Fwd 

2-in Fwd 

2-in Fwd 

RF

1.0

1.0

1.7

2-in. Rail

Adjusted for RF = 1.7

14-in. Rail

2-in. Rail

2-in. Rail

Adjusted for RF = 1.7

2-in. Rail

14-in. Rail

Mach 1.6

Mach 1.6
76 

Figure 7–26. Rail comparisons, X sweeps (0” to 8”) 

8x6 TBC3 test, Boom1 VS2 model, M = 1.56, HumidAvg = 111 ppm 

Figure 7–27. Rail comparisons, X sweeps (0” to 8”) 

8x6 TBC3 test, Boom1 VS2 model, M = 1.78, HumidAvg = 77 ppm 

Sig Set 

66

93

93

Runs

863—888

1060—1085

1060—1085

Ref Run 

889

1086

1086

hNose

59.2

59.3

59.3

Rail

14-in

2-in

2-in

RF

1.0

1.0

1.7

190 195 200 205 210 215 220 225 230 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

66

93

93

Runs

863—888

1060—1085

1060—1085

Ref Run 

889

1086

1086

hNose

59.2

59.3

59.3

Rail

14-in

2-in

2-in

RF

1.0

1.0

1.7

Sig Set 

61

81

81

Runs

818—843

1008—1033

1008—1033

Ref Run 

844

1034

1034

hNose

48.9

49.1

49.1

Rail

14-in

2-in

2-in

RF

1.0

1.0

1.7

190 195 200 205 210 215 220 225 230 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

61

81

81

Runs

818—843

1008—1033

1008—1033

Ref Run 

844

1034

1034

hNose

48.9

49.1

49.1

Rail

14-in

2-in

2-in

RF

1.0

1.0

1.7

14-in. Rail

2-in. Rail

Adjusted for RF = 1.7

14-in. Rail

2-in. Rail

2-in. Rail

Adjusted for RF = 1.7

2-in. Rail

Mach 1.56

Mach 1.78
77 

7.8. Effect of Mounting Strut on Boom Model Signatures 

The four different mounting struts, VS1 through VS4, were used with the Boom models (Boom1 or 

Boom2 with VS1 or VS2, and Boom3 with VS3 or VS4) in the various tests (see Figures 4–20 and –21), 

but the VS1 strut was only used in the 9x7 TBC1 test. This test was conducted before X or Z sweeps were 

employed to permit spatial averaging, therefore, the Boom1 model with VS1 will not be included in the 

comparisons with the other three struts since the individual signature data does not have the tunnel spatial 

flow variations removed, and thus is of poorer quality. The Boom1 model was run only with the VS2 

strut in the TBC1, 9x7 parametric, and the 8x6 TBC3 tests, and the Boom3 model was run with both the 

VS3 and VS4 struts in the 9x7 TBC4 test—see Table 5 for the combinations of boom models and struts 

tested. Recall from the model description section that the Boom3 model has the same aerodynamic lines 

as the Boom1 model aside for provisions for mounting on the new VS3 and VS4 struts, so comparing the 

Boom3 model with its struts with the Boom1 model with its struts is valid for illustrating strut effects. 

Boom1 VS2 data from the 8x6 test will not be included because such data are available from the 9x7 

parametric test. 

Table 6. Combinations of Boom Models and Struts Tested 

Test Model Strut Strut shape Spatial averaging*

9x7 TBC1 Boom1 VS1 Swept forward, short No 

9x7 TBC1 Boom1 VS2 Swept forward, mid No 

9x7 TBC1 Boom2 VS2 Swept forward, mid No 

9x7 Parametric Boom1 VS2 Swept forward, mid Yes 

8x6 TBC3 Boom1 VS2 Swept forward, mid Yes 

9x7 TBC4 Boom3 VS3 Swept forward, long Yes 

9x7 TBC4 Boom3 VS4 Swept aft, straight sting Yes 

*

 Red text: No spatial averaging done in TBC1 test 

Black text: Spatial averaging done in 9x7 Parametric and TBC4 tests 

Blue text: Spatial averaging done in 8x6 TBC3 test

Signature comparisons for the Boom1 VS2, Boom3 VS3, and Boom3 VS4 models are made in 

Figures 7–28 and –29 at Mach 1.6 and 1.8, respectively, at model heights of approximately 60 in. The 

three signatures for each Mach number are very similar, as expected, in the forward parts up to near the 

maximum overpressure point, and aft of that there are differences as influenced by the struts. It seems odd 

though, that in the expansions just aft of the peaks in the Mach 1.6 data, the pressures from the VS3 and 

VS4 struts look very similar, while the pressures from VS2 are lower; it is VS2 and VS3 that are the 

upper swept struts, which allow the underside and back ends of the models to remain clean, so they 

should be more similar. The VS3 strut is longer than VS2 because it has a more forward mounting point 

on the model, and thus it probably has less influence on the pressure signature below the model, resulting 

in a cleaner signature that is likely more representative of the real airplane signature. 

The VS4 strut has a straight sting that compromises the lower aft end of the Boom3 model, but 

apparently the effects due to this compromise are not seen in this part of the signature at Mach 1.6. The 

strongest effect of the VS4 strut is in the large shock at X = -60 in the Mach 1.6 plot, and at -46 in the 

Mach 1.8 plot, which is from the swept section of the strut that supports the sting. It was learned in the 

testing that this swept section was not far enough aft to keep its shock from overtaking the signature from 

the aft end of the model by the time the pressure field reached the rail, thus this strut was deemed 

unusable. 
78 

Figure 7–28. Boom model mounting strut effects, X and Z sweeps 

14-in. aft rail, M = 1.60, HumidAvg = 245 ppm 

Figure 7–29. Boom model mounting strut effects, X and Z sweeps 

14-in. aft rail, M = 1.80, HumidAvg = 243 ppm 

Test

9x7 Parametric 

9x7 TBC4 

9x7 TBC4 

Sig Set 

61

50

43

Runs

2047—2072

1562—1586

1365—1389

Ref Run 

2073

1612

1390

Model

Boom1 VS2 

Boom3 VS3 

Boom3 VS4 

hNose

60.0

61.8

62.5

_

3.40

3.54

3.43

-85 -80 -75 -70 -65 -60 -55 -50 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Test

9x7 Parametric 

9x7 TBC4 

9x7 TBC4 

Sig Set 

61

50

43

Runs

2047—2072

1562—1586

1365—1389

Ref Run 

2073

1612

1390

Model

Boom1 VS2 

Boom3 VS3 

Boom3 VS4 

hNose

60.0

61.8

62.5

_

3.40

3.54

3.43

Test

9x7 Parametric 

9x7 TBC4 

9x7 TBC4 

Sig Set 

60

57

47

Runs

2006—2044

1755—1779

1473—1497

Ref Run 

2045

1728

1523

Model

Boom1 VS2 

Boom3 VS3 

Boom3 VS4 

hNose

60.2

61.9

61.8

_

3.39

3.52

3.15

-70 -65 -60 -55 -50 -45 -40 -35 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Test

9x7 Parametric 

9x7 TBC4 

9x7 TBC4 

Sig Set 

60

57

47

Runs

2006—2044

1755—1779

1473—1497

Ref Run 

2045

1728

1523

Model

Boom1 VS2 

Boom3 VS3 

Boom3 VS4 

hNose

60.2

61.9

61.8

_

3.39

3.52

3.15

Mach 1.8

Mach 1.6

Boom1 VS2

Boom3 VS3

Boom3 VS4

h/L (all) = ~3.9 (~61”)

h/L (all) = ~3.9 (~61”)

Boom1 VS2

Boom3 VS3

Boom3 VS4
79 

7.9. Effect of Nacelles and Vertical Tails 

The Boom1 model was run with nacelles and vertical tails off (abbreviated “n/v off” herein) only in 

the 8x6 TBC3 test—refer to Figure 4–15 for CAD views of these components with the model. 

Comparison plots of these components on and off are presented in Figures 7–30 and –31 with 14-in. rail 

data at Mach 1.56 and 1.78 and at heights of 59 and 49 in., respectively. In the first figure, the n/v-off 

signature has an overall higher pressure level than the signature for the full configuration, but this is 

believed to be just an artifact of the tunnel flow variations between these sets of runs, since there is no 

reason why the model signature should be different ahead of the vertical tails, and many of the 8x6 runs 

had similar offsets. The shock from the verticals is apparent near the rear of the signature at X = 217 in 

the full-configuration curve. This shock is considered to be primarily from the verticals and not the 

nacelles, since the latter are shielded by the wing. In the second figure, at Mach 1.78, the fullconfiguration and n/v-off curves do overlap for most of the signature until the shock from the tails at X = 

216. 

The Boom3 model was run with baseline N1 nacelles and alternate nacelles N3 and N4 in the 9x7 

TBC4 test at Mach 1.6, and a comparison plot of these three nacelle configurations is shown in Figures 7–

32. The significant differences among the nacelles are visible around X = -60. The shocks for the 

alternate nacelles occur a little earlier in the signature relative to the shock for the baseline nacelles.

Alternate nacelles N3 and N4 of the same design were also fabricated for the Performance model, and 

a comparison plot of these with the baseline nacelle N1 is given in Figure 7–33. The primary effect of the 

nacelles is very subtle in this figure—the N3 and N4 nacelles create slight rises in pressure in the main 

expansion region (X = -54 to -46), and possibly have continued effects aft of this, but the differences 

among the signatures forward of this region are not likely due to the nacelle variations. 

In the following figure, 7–34, the inlet and nozzle portions of the N3 and N4 nacelles are switched: 

one combination (sig set 24) has the inlet (NI4) for the N4 nacelle with the nozzle (NN3) for the N3 

nacelle, and the other (sig set 37) has the opposite combination, NI3 NN4. The plot shows the same 

baseline N1 nacelle runs as in the previous figure for reference. The latter combination of inlet and 

nozzle sections, NI3 NN4, did not make much difference relative to a pure N4 nacelle configuration 

(compare to Figure 7–33), but the NI4 NN3 combination did cause a significant rise in pressure along the 

main expansion, particularly near X = -52. This rise, having been measured at roughly 60 in. from the 

rail, was probably a small shock wave coming from some part of the nacelle, which would be seen if a 

closer measurement had been taken (all the signatures in the TBC4 test were measured at nominally 60 

in.). 
80 

Figure 7–30. Effects of Boom1 model nacelles and vertical tails, X sweeps (0” to 12”, 0” to 8”) 

8x6 TBC3 test, 14-in. rail, M = 1.56, HumidAvg = 181 ppm 

Figure 7–31. Effects of Boom1 model nacelles and vertical tails, X sweeps (0” to 8”) 

8x6 TBC3 test, 14-in. rail, M = 1.78, HumidAvg = 81 ppm 

Sig Set 

66

77

Runs

863—888

966—991

Ref Run 

889

957

Model

Boom1 VS2 

Boom1 VS2 n/v off 

hNose

59.2

59.1

_

3.36

3.38

190 195 200 205 210 215 220 225 230 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

66

77

Runs

863—888

966—991

Ref Run 

889

957

Model

Boom1 VS2 

Boom1 VS2 n/v off 

hNose

59.2

59.1

_

3.36

3.38

Sig Set 

61

70

Runs

818—843

912—937

Ref Run 

844

911

Model

Boom1 VS2 

Boom1 VS2 n/v off 

hNose

48.9

49.0

_

3.35

3.37

190 195 200 205 210 215 220 225 230 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

61

70

Runs

818—843

912—937

Ref Run 

844

911

Model

Boom1 VS2 

Boom1 VS2 n/v off 

hNose

48.9

49.0

_

3.35

3.37

N/V ON N/V OFF

N/V ON N/V OFF

Mach 1.56

Mach 1.78
81 

Figure 7–32. Effects of Boom3 model nacelle variations(N1, N3, N4), Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 225 ppm 

Figure 7–33. Effects of Performance model nacelle variations (N1, N3, N4), Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 220 ppm 

Sig Set 

50

60

65

Runs

1562—1586

1843—1867

1980—2004

Ref Run 

1535

1816

1953

Config

N1

N3

N4

_

3.54

3.49

3.49

-85 -80 -75 -70 -65 -60 -55 -50 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

50

60

65

Runs

1562—1586

1843—1867

1980—2004

Ref Run 

1535

1816

1953

Config

N1

N3

N4

_

3.54

3.49

3.49

Sig Set 

3

17

32

Runs

224—247

612—636

1043—1067

Ref Run 

119

119

119

Config

N1

N3

N4

_

3.33

3.36

3.34

-80 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

3

17

32

Runs

224—247

612—636

1043—1067

Ref Run 

119

119

119

Config

N1

N3

N4

_

3.33

3.36

3.34

N4

N3

N1

N4

N3

N1

Mach 1.6

Mach 1.6
82 

Figure 7–34. Effects of Performance model nacelle variations (N1, NI4-NN3, NI3-NN4) 

Z sweeps (59” to 65”), 9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 236 ppm 

7.10. Effect of Mach Number 

The effect of Mach number (1.6 and 1.8) on the sonic boom signatures of Boom1 VS2, Boom3 VS3, 

and Performance models from the two 9x7 tests are presented in Figures 7–35 through –39. The first 

three figures are from X sweeps of the Boom1 model in the 9x7 parametric test on the three different rail 

configurations run in this test: the 14-in. forward rail, the 2-in. forward rail, and the 14-in. aft rail. All of 

these figures show the overall higher pressure levels and shock peaks in the Mach 1.8 data as expected. 

The latter two figures are from Z sweeps of the Boom3 and Performance models in the 9x7 TBC4 test 

on the 14-in. aft rail. The Boom3 data in Figure 7–38 show higher pressure peaks for Mach 1.8, but the 

overall level difference between the two Mach numbers is not present as it is in the three previous figures. 

One might be led to believe that the higher model height (60 in., vs. 30 in. for Figures 7–35 and –36) 

would be the reason why there is not a greater difference in overall pressure levels, but the last previous 

figure (7–37) for the Boom1 model is also at 60-in. height above the rail, so it is puzzling as to why the 

Boom3 model did not show a similar distinction. 

Sig Set 

3

24

37

Runs

224—247

830—854

1180—1204

Ref Run 

119

119

119

Config

N1

NI4 NN3 

NI3 NN4 

_

3.33

3.55

3.33

-80 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

3

24

37

Runs

224—247

830—854

1180—1204

Ref Run 

119

119

119

Config

N1

NI4 NN3 

NI3 NN4 

_

3.33

3.55

3.33

NI3 NN4

NI4 NN3

N1

Mach 1.6
83 

Figure 7–35. Effect of Mach number for Boom1 VS2 model, X sweeps (8” to 24”) 

9x7 parametric test, 14-in. forward rail, h = 30 in., HumidAvg = 308 ppm 

Figure 7–36. Effect of Mach number for Boom1 VS2 model, X sweeps (8” to 24”) 

9x7 parametric test, 2-in. forward rail, h = 30 in., HumidAvg = 320 ppm 

Sig Set 

45

38

Runs

1472—1497

1247—1272

Ref Run 

1498

1273

Mach

1.60

1.80

XRam

8—24

8—24

hNose

30.5

30.1

_

3.40

3.41

-100 -95 -90 -85 -80 -75 -70 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

45

38

Runs

1472—1497

1247—1272

Ref Run 

1498

1273

Mach

1.60

1.80

XRam

8—24

8—24

hNose

30.5

30.1

_

3.40

3.41

Sig Set 

53

51

Runs

1724—1749

1662—1687

Ref Run 

1750

1688

Mach

1.60

1.80

XRam

8—24

8—24

hNose

30.5

30.0

_

3.40

3.40

-100 -95 -90 -85 -80 -75 -70 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

53

51

Runs

1724—1749

1662—1687

Ref Run 

1750

1688

Mach

1.60

1.80

XRam

8—24

8—24

hNose

30.5

30.0

_

3.40

3.40

Mach 1.8

Mach 1.6

Mach 1.8

Mach 1.6
84 

Figure 7–37. Effect of Mach number for Boom1 VS2 model, X sweeps (0” to 16”, 0” to 24”)

9x7 parametric test, 14-in. aft rail, h = 60 in., HumidAvg = 287 ppm 

Figure 7–38. Effect of Mach number for Boom3 VS3 model, Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, HumidAvg = 227 ppm 

Sig Set 

62

60

Runs

2074—2099

2006—2044

Ref Run 

2100

2045

Mach

1.60

1.80

XRam

0—16

0—24

hNose

60.0

60.2

_

3.39

3.39

-65 -60 -55 -50 -45 -40 -35 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

62

60

Runs

2074—2099

2006—2044

Ref Run 

2100

2045

Mach

1.60

1.80

XRam

0—16

0—24

hNose

60.0

60.2

_

3.39

3.39

Sig Set 

49

56

Runs

1537—1561

1730—1754

Ref Run 

1612

1728

Mach

1.60

1.80

hNose

59—65

59—65

_

3.02

2.99

-70 -65 -60 -55 -50 -45 -40 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

49

56

Runs

1537—1561

1730—1754

Ref Run 

1612

1728

Mach

1.60

1.80

hNose

59—65

59—65

_

3.02

2.99

Mach 1.8

Mach 1.6

Mach 1.8

Mach 1.6
85 

Figure 7–39. Effect of Mach number for Performance sting+contour model, Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, HumidAvg = 292 ppm 

Sig Set 

2

12

Runs

199—222

476—500

Ref Run 

119

116

Mach

1.60

1.80

hNose

59—65

59—65

_

3.33

3.25

-70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

2

12

Runs

199—222

476—500

Ref Run 

119

116

Mach

1.60

1.80

hNose

59—65

59—65

_

3.33

3.25

Mach 1.8

Mach 1.6
86 

7.11. Effect of Total Pressure 

Figure 7–40 shows the effect of total pressure in the 9x7 wind tunnel on the sonic boom signatures of 

the Boom1 VS2 model at a Mach number of 1.6 and a nominal height of 30 in. from the 14-in. forward 

rail. Data at pressures of 1450 and 2300 psf are shown. Overall, the agreement between the two 

signatures is very good, though the higher-pressure run does show slightly higher shock peaks throughout 

the signature. As discussed in Section 6.3.2, the higher pressure gives a higher Reynolds number, and in 

general, less flow separation, so it seems reasonable that these would be the causes of the higher shock 

peaks. 

Figure 7–40. Effect of total pressure for Boom1 VS2 model, Z sweeps (26” to 34”) 

9x7 parametric test, 14-in. forward rail, M = 1.6, HumidAvg = 298 ppm 

Sig Set 

35

36

Runs

1144—1176

1179—1211

Ref Run 

1177

1212

PT'

1446

2297

XRam

24.0

24.0

hNose

26—34

26—34

_

3.42

3.51

-115 -110 -105 -100 -95 -90 -85 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

35

36

Runs

1144—1176

1179—1211

Ref Run 

1177

1212

PT'

1446

2297

XRam

24.0

24.0

hNose

26—34

26—34

_

3.42

3.51

PT = 2300 psf

PT = 1450 psf
87 

7.12. Effect of Angle of Attack 

Figures 7–41 through –43 show the effects of angle of attack on the sonic boom signatures of the 

Boom3 and Performance models from Z sweeps (59–65 in.) in the 9x7 TBC4 test. Angles from 2.5° to 4° 

are shown for the Boom3 model at Mach 1.6 in the first figure, and the trends of the overall pressure 

levels and shock peaks for the lifting parts of the model (i.e., aft of the nose shock) are consistent with the 

increasing lift causing stronger sonic boom signatures. Also note that the small shock at the bottom of the 

main expansion (X = -61) for the lowest angle of attack grows in strength and moves forward in the 

signature as the angle is increased. 

Similar trends of increasing pressure levels and shock peaks with angles of attack from 2.8° to 3.8° 

for the Performance model at Mach 1.6 are observed in Figure 7–42, and at Mach 1.8 in Figure 7–43 for 

angles from 3.3° to 3.8°. 

Figure 7–41. Effect of angle of attack for Boom3 VS3 model, Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 230 ppm 

Sig Set 

52

49

50

51

Runs

1628—1652

1537—1561

1562—1586

1587—1611

Ref Run 

1624

1612

1612

1612

_

2.57

3.02

3.54

4.01

-85 -80 -75 -70 -65 -60 -55 -50 -45 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Sig Set 

52

49

50

51

Runs

1628—1652

1537—1561

1562—1586

1587—1611

Ref Run 

1624

1612

1612

1612

_

2.57

3.02

3.54

4.01

α = 4.01°

α = 3.54°

α = 3.02°

α = 2.57°
88 

Figure 7–42. Effect of angle of attack for Performance sting+contour model, Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 278 ppm 

Figure 7–43. Effect of angle of attack for Performance sting+contour model, Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, M = 1.80, HumidAvg = 237 ppm 

Sig Set 

1

2

5

Runs

151—175

199—222

274—298

Ref Run 

119

119

119

_

2.84

3.33

3.83

-80 -75 -70 -65 -60 -55 -50 -45 -40 -35 -30 -25 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

1

2

5

Runs

151—175

199—222

274—298

Ref Run 

119

119

119

_

2.84

3.33

3.83

Sig Set 

9

10

Runs

401—425

426—450

Ref Run 

116

116

_

3.32

3.86

-70 -65 -60 -55 -50 -45 -40 -35 -30 -25 -20 -15 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

9

10

Runs

401—425

426—450

Ref Run 

116

116

_

3.32

3.86

α = 3.83°

α = 3.33°

α = 2.84°

α = 3.86°

α = 3.32°
89 

7.13. Effect of Off-Track Angle 

The boom loudness is not only critical for the ground track under the flight path, but also off to both 

sides of the ground track. Signatures at off-track angles up to 45° are compared to the 0° on-track 

signatures for the Boom1, Boom3, and Performance models in Figures 7–44 through –47. The first figure 

shows the signatures for the Boom1 model at a height of 30 in., Mach 1.8, for angles of 0°, 20°, 30°, and 

40°, where the off-track angle signatures all have higher maximum pressure peaks than the on-track 

signature, and the gradients in the main expansions after the maximum peaks are also steeper for the offtrack angles. Note also that the on-track signature shows small shocks just after the main expansion, 

probably for the nacelles and vertical tails, whereas none of the off-track signatures show these. 

Figure 7–45 shows signatures for the Boom3 model at a height of 60 in. (nominally), Mach 1.6, for 

angles of 0°, 15°, 30°, and 45°. Again, the off-track signatures have slightly higher maximum pressure 

peaks and do not show the small shocks just after the main expansion. 

On- and off-track signatures for the Performance model are shown for the same height and angles as 

for the Boom3 model, at Mach 1.6 and 1.8 in Figures 7–46 and –47, respectively. The same comments as 

for the other two models apply here as well, but in particular for the Mach 1.8 data, Figure 7–47, the 

maximum and minimum pressure peaks for the 30° and 45° off-track angles are substantially higher than 

those for the two lower angles, indicating that the boom loudnesses for these 30° and 45° angles are 

probably a bit higher also. 

Figure 7–44. Effect of off-track angle for Boom1 VS2 model, X sweeps (8” to 24”), hNose = 30.1 in. 

9x7 parametric test, 14-in. forward rail, M = 1.80, HumidAvg = 306 ppm

Sig Set 

38

40

41

42

Runs

1247—1272

1301—1326

1328—1353

1373—1398

Ref Run 

1273

1327

1354

1399

q ̊

-0.6

19.4

30.0

40.0

_

3.41

3.40

3.40

3.40

-95 -90 -85 -80 -75 -70 -65 

XAligned (in.) 

-.02

-.01

0

.01

.02

(6P/P)Data - (

6P/P)Ref

Sig Set 

38

40

41

42

Runs

1247—1272

1301—1326

1328—1353

1373—1398

Ref Run 

1273

1327

1354

1399

q ̊

-0.6

19.4

30.0

40.0

_

3.41

3.40

3.40

3.40

φ = 45°

φ = 30° φ = 15°

φ = 0°
90 

Figure 7–45. Effect of off-track angle for Boom3 VS3 model, Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 226 ppm 

Figure 7–46. Effect of off-track angle for Performance sting+contour model, Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, HumidAvg = 265 ppm 

Sig Set 

49

53

54

55

Runs

1537—1561

1653—1677

1678—1702

1703—1727

Ref Run 

1612

1624

1624

1624

q ̊

0.2

14.8

30.8

45.6

_

3.02

2.96

2.94

2.94

-5 0 5 10 15 20 25 

XAligned (in.) 

-.02

-.01

0

.01

.02

(6P/P)Data - (

6P/P)Ref

Sig Set 

49

53

54

55

Runs

1537—1561

1653—1677

1678—1702

1703—1727

Ref Run 

1612

1624

1624

1624

q ̊

0.2

14.8

30.8

45.6

_

3.02

2.96

2.94

2.94

Sig Set 

2

6

7

8

Runs

199—222

323—347

348—372

373—397

Ref Run 

119

119

119

119

q ̊

-0.1

14.9

30.2

45.7

_

3.33

3.39

3.39

3.38

0 10 20 30 40 50 

XAligned (in.) 

-.02

-.01

0

.01

.02

(6P/P)Data - (

6P/P)Ref

Sig Set 

2

6

7

8

Runs

199—222

323—347

348—372

373—397

Ref Run 

119

119

119

119

q ̊

-0.1

14.9

30.2

45.7

_

3.33

3.39

3.39

3.38

φ = 45° φ = 30°

φ = 15°

φ = 0°

φ = 45°

φ = 30° φ = 15°

φ = 0°
91 

Figure 7–47. Effect of off-track angle for Performance sting+contour model, Z sweeps (59” to 65”) 

9x7 TBC4 test, 14-in. aft rail, M = 1.80, HumidAvg = 237 ppm 

Sig Set 

12

13

14

15

Runs

476—500

501—525

526—550

551—575

Ref Run 

116

116

116

116

q ̊

-0.1

15.1

30.3

45.4

_

3.25

3.30

3.29

3.34

-70 -60 -50 -40 -30 -20 -10 

XAligned (in.) 

-.025

-.015

-.005

.005

.015

.025

(6P/P)Data - (

6P/P)Ref

Sig Set 

12

13

14

15

Runs

476—500

501—525

526—550

551—575

Ref Run 

116

116

116

116

q ̊

-0.1

15.1

30.3

45.4

_

3.25

3.30

3.29

3.34

φ = 45° φ = 30°

φ = 15°

φ = 0°
92 

7.14. Comparisons of Boom1 Model Signatures from 9x7 and 8x6 Tunnels 

A few comparison run series between the 9x7 and 8x6 wind tunnels for the Boom1 VS2 model are 

given in this section in Figures 7–48 through –51, though only in the first figure do the model heights 

above the rail match. In the latter three figures, the heights do not match so the comparisons presented 

are meant to be more qualitative, as the runs in these four figures are the only ones available for direct or 

quasi-direct comparisons between the two facilities for the Boeing models. The 14-in. rail was positioned 

longitudinally in the 8x6 tunnel such that Boom model heights from approximately 45 to 60 in. could be 

run while allowing for X or Z sweeps, so direct comparisons at a height of 30 in. as obtained in many 9x7 

runs were not possible. 

Figure 7–48 shows the only direct comparison of the Boom1 model signatures measured by the 14-in. 

rail at an approximate height of 60 in. at a nominal Mach number of 1.6 (1.56 in the 8x6 vs. 1.6 in the 

9x7). The 8x6 signature has a lot of waviness and small spikes that are not seen in the 9x7 signature, 

consistent with data from this rail shown in Figures 7–27 and –28 and others, but the overall shape of the 

8x6 curve is similar to that of the 9x7. With some of the leading-zero points of the 8x6 curve being below 

the zero ΔP/P line, one could argue that the entire curve could be shifted upwards a small amount, which 

would give a better match with the 9x7 data, but the leading-zero points are not consistent enough to 

justify this adjustment. 

In Figure 7–49, two curves from the 9x7 at heights of 30 and 60 in. are shown for comparison to the 

8x6 curve at 49 in. for the Boom1 model signature comparisons at a nominal Mach number of 1.8. Given 

these substantial height differences, one does not expect the data to match, but one would expect the 49-

in. data to lie roughly in between the 30- and 60-in. data. This is not the case, however, as it is generally 

lower in the front half of the signature than the two curves from the 9x7, although shifting it upward by 

the amount that the leading-zero points are low would put it in a more reasonable position (aside from the 

numerous small spikes in the curve). 

Comparisons of 9x7 and 8x6 data for the Boom1 model using the 2-in. rail are presented in Figures 

7–50 and –51 at nominal Mach numbers of 1.6 and 1.8, respectively. As previously stated, these are not 

direct comparisons at the same height for each tunnel: in the first figure, the 9x7 data are at a height of 30 

in. and the 8x6 at 60 in., and in the second figure, the 9x7 data are at a height of 30 in. and the 8x6 at 49 

in. Nonetheless, qualitative comparisons of the runs do show what appear to be reasonable reductions in 

signature and shock magnitudes from the 30-in. to greater heights, though the reductions here are greater

than those observed in Figures 7–12 and –13 for the 30- to 60-in. height comparisons from 9x7 data. This 

is consistent with the low overall levels of the 8x6 signatures in Figures 7–48 and –49 from the 14-in. rail 

data. 
93 

Figure 7–48. Comparison of Boom1 VS2 model signatures from 9x7 and 8x6 wind tunnels

14-in. rail, M = ~1.6, hNose = 60 in. 

Figure 7–49. Comparison of Boom1 VS2 model signatures from 9x7 and 8x6 wind tunnels 

14-in. rail, M = ~1.8, hNose = 30 to 60 in. 

Test

9x7 Parametric 

8x6 TBC3 

Sig Set 

62

66

Runs

2074—2099

863—888

Ref Run 

2100

889

Mach

1.60

1.56

Rail

14-in Aft 

14-in

_

3.39

3.36

hNose

60.0

59.2

-10 -5 0 5 10 15 20 25 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Test

9x7 Parametric 

8x6 TBC3 

Sig Set 

62

66

Runs

2074—2099

863—888

Ref Run 

2100

889

Mach

1.60

1.56

Rail

14-in Aft 

14-in

_

3.39

3.36

hNose

60.0

59.2

Test

9x7 Parametric 

8x6 TBC3 

9x7 Parametric 

Sig Set 

38

61

60

Runs

1247—1272

818—843

2006—2044

Ref Run 

1273

844

2045

Mach

1.80

1.78

1.80

Rail

14-in Fwd 

14-in

14-in Aft 

_

3.41

3.35

3.39

hNose

30.1

48.9

60.2

-10 -5 0 5 10 15 20 25 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Test

9x7 Parametric 

8x6 TBC3 

9x7 Parametric 

Sig Set 

38

61

60

Runs

1247—1272

818—843

2006—2044

Ref Run 

1273

844

2045

Mach

1.80

1.78

1.80

Rail

14-in Fwd 

14-in

14-in Aft 

_

3.41

3.35

3.39

hNose

30.1

48.9

60.2

8x6

hNose = 60

9x7

hNose = 60

Mach ~1.6

14-in. Rail

8x6

hNose = 49

9x7

hNose = 30

Mach ~1.8

14-in. Rail

9x7

hNose = 60
94 

Figure 7–50. Comparison of Boom1 VS2 model signatures from 9x7 and 8x6 wind tunnels 

2-in. rail, M = ~1.6, hNose = 30 to 60 in. 

Figure 7–51. Comparison of Boom1 VS2 model signatures from 9x7 and 8x6 wind tunnels 

2-in. rail, M = ~1.8, hNose = 30 to 50 in.

Test

9x7 Parametric 

8x6 TBC3 

Sig Set 

53

93

Runs

1724—1749

1060—1085

Ref Run 

1750

1086

Mach

1.60

1.56

Rail

2-in Fwd 

2-in

_

3.40

3.39

hNose

30.5

59.3

-10 -5 0 5 10 15 20 25 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Test

9x7 Parametric 

8x6 TBC3 

Sig Set 

53

93

Runs

1724—1749

1060—1085

Ref Run 

1750

1086

Mach

1.60

1.56

Rail

2-in Fwd 

2-in

_

3.40

3.39

hNose

30.5

59.3

Test

9x7 Parametric 

8x6 TBC3 

Sig Set 

51

81

Runs

1662—1687

1008—1033

Ref Run 

1688

1034

Mach

1.80

1.78

Rail

2-in Fwd 

2-in

_

3.40

3.43

hNose

30.0

49.1

-10 -5 0 5 10 15 20 25 

XAligned (in.) 

-.020

-.015

-.010

-.005

0

.005

.010

.015

.020

(6P/P)Data - (

6P/P)Ref

Test

9x7 Parametric 

8x6 TBC3 

Sig Set 

51

81

Runs

1662—1687

1008—1033

Ref Run 

1688

1034

Mach

1.80

1.78

Rail

2-in Fwd 

2-in

_

3.40

3.43

hNose

30.0

49.1

8x6

hNose = 60

9x7

hNose = 30

Mach ~1.6

2-in. Rail

8x6

hNose = 49

9x7

hNose = 30

Mach ~1.8

2-in. Rail
95 

7.15. Reference Run Comparisons and Effects of Humidity 

Up to this point, the data presented herein have mostly been the model signatures corrected with the 

reference run pressures, with the exception of the sample reference run shown in Figure 6–11 and the 

before- and after-reference-run comparisons shown in Figure 6–16. Various comparisons of reference 

runs will be shown in this section to quantify the magnitude of pressure variations due to the tunnel flow 

itself, as well as illustrating the effects of changing Mach number, humidity, porous window blank 

placement in the 8x6 tunnel, and comparisons between tunnels, tests, and rails. 

An ideal reference run signature in a wind tunnel would be flat, at zero ΔP/P, meaning no static 

pressure variation over the length of the rail. Then when a model is positioned such that its shock waves 

fall on the rail, the resulting pressure distribution would be that of just the model alone. The reference run 

would not contribute to any errors in the model signature, and this would yield the most consistent and 

reliable data sets. However, all wind tunnels have some amount of static pressure variation throughout 

the test section, and the presence of a rail itself causes further pressure variations due to its influence on 

the tunnel flow. If the reference pressure gradients along the rail are small, then the corrected model 

signatures will be more accurate than if these gradients are large. Large gradients over a small number of 

orifices adversely affect the model signatures in that various factors (tunnel Mach number variation, 

turbulence, humidity, and model vibration) cause the model shock waves to shift back and forth over 

small ranges of orifices during “constant” conditions. With a large reference pressure gradient, a shift of 

a model shock over a distance of just a few orifices can easily result in a corrected model pressure error 

on the order of 0.01 to 0.02 in ΔP/P. Clearly, this is highly undesirable when the typical magnitudes of 

the model shocks being measured are usually less than 0.005 ΔP/P. 

Plots of various reference runs are provided in Figures 7–52 through –69. The plots are all made to 

same ΔP/P scale so that relative magnitudes can be compared among plots, and the X scales are in tunnel 

station inches except when comparing the pressures between the 9x7 and 8x6 tunnels, where rail orifice 

numbers are used instead because of the different tunnel station origins used. 

7.15.1. Reference Run Repeatability at Constant and Varying Humidity 

The initial set of reference run plots is intended to show the repeatability of various reference runs 

and the effects of humidity where humidity varies among the runs. Figure 7–52 shows four reference 

runs from the 9x7 parametric test at Mach 1.6 with humidity essentially constant (296 to 301 ppm). The 

pressure profiles are all nearly identical (to within ~0.002 ΔP/P), indicating excellent repeatability. A 

small layout schematic below the plot shows the model and rail positions for these runs in the 9x7 wind 

tunnel, and the model nose shock is projected at the Mach line angle (51.3° for Mach 1.6) to strike the rail 

within a few inches aft of the line of rail orifices. Given that the shocks tend to spread slightly with 

distance from the model, and the uncertainty in shock location due to flow variations and model vibration, 

the model shocks are likely to fall on some of the aft orifices on the rail. Nonetheless, there is no 

apparent increase in the scatter of the reference run pressures toward the aft end of the signature. 

Note that a new model configuration, “LM 1021, blade,” is identified in the legend of Figure 7–52. 

This is the Lockheed-Martin 1021 configuration,37 mounted with a blade strut (as opposed to a sting 

mount) that was run in the 9x7 parametric test. The layout in the figure shows an outline of this model 

and its blade strut. Note also that the 9x7 window blank locations are shown as thick gray lines at the 

bottom of the layout image. The window blanks do not protrude into the tunnel as indicated by the gray 

lines, but the lines are shown merely to point out their locations in the tunnel north wall. 

Three runs from the 9x7 parametric test having a humidity spread from 199 to 512 ppm are plotted in 

Figure 7–53. In contrast to the previous figure, there is a definite, though slight, spread of the three 
96 

signatures, with the highest signature being the one with the highest humidity. A trend of higher 

pressures with higher humidity has also been reported in Reference 1. 

Figure 7–52. 9x7 reference run comparisons, 14-in. rail, M = 1.60, constant humidity 

 

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

862

883

904

1004

Model

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

Rail

14-in Fwd 

14-in Fwd 

14-in Fwd 

14-in Fwd 

hNose

52.3

52.0

52.0

52.0

_

3.3

2.2

2.3

2.1

Mach

1.60

1.60

1.60

1.60

PT'

2301

2293

2293

2292

HumidAvg

298

297

296

301

-150 -140 -130 -120 -110 -100 -90 -80 

Tunnel Station (in.) 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

862

883

904

1004

Model

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

Rail

14-in Fwd 

14-in Fwd 

14-in Fwd 

14-in Fwd 

hNose

52.3

52.0

52.0

52.0

_

3.3

2.2

2.3

2.1

Mach

1.60

1.60

1.60

1.60

PT'

2301

2293

2293

2292

HumidAvg

298

297

296

301

9 ft

Window blank 

locations
97 

Figure 7–53. 9x7 reference run comparisons, 14-in. rail, M = 1.60, varying humidity 

 

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

397

831

564

Model

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

Rail

14-in Fwd 

14-in Fwd 

14-in Fwd 

hNose

52.2

52.3

52.0

_

2.2

3.1

2.1

Mach

1.60

1.60

1.60

PT'

2299

2303

2282

HumidAvg

199

278

512

-150 -140 -130 -120 -110 -100 -90 -80 

Tunnel Station (in.) 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

397

831

564

Model

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

Rail

14-in Fwd 

14-in Fwd 

14-in Fwd 

hNose

52.2

52.3

52.0

_

2.2

3.1

2.1

Mach

1.60

1.60

1.60

PT'

2299

2303

2282

HumidAvg

199

278

512
98 

Reference runs at Mach 1.8 from the same 9x7 test are shown in Figure 7–54, where the humidity 

spread is only 3 ppm. The repeatability is excellent here too, though not quite as good (generally within 

~0.003 ΔP/P) as at Mach 1.6. A plot of runs at Mach 1.8 with humidity varying by 300 ppm is given in 

the next figure, 7–55, and here the humidity effect is dramatic: pressures vary by up to 0.015 ΔP/P

between the lowest- and highest-humidity runs, with the higher-humidity runs generally having the 

highest pressures. 

Figure 7–54. 9x7 reference run comparisons, 14-in. rail, M = 1.80, constant humidity 

 

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

1178

1327

1372

1399

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Rail

14-in Fwd 

14-in Fwd 

14-in Fwd 

14-in Fwd 

hNose

52.0

52.1

51.8

52.3

_

3.5

3.4

0.0

3.4

Mach

1.80

1.80

1.80

1.80

PT'

2299

2298

2302

2291

HumidAvg

305

307

305

304

-150 -140 -130 -120 -110 -100 -90 -80 

Tunnel Station (in.) 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

1178

1327

1372

1399

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 

Rail

14-in Fwd 

14-in Fwd 

14-in Fwd 

14-in Fwd 

hNose

52.0

52.1

51.8

52.3

_

3.5

3.4

0.0

3.4

Mach

1.80

1.80

1.80

1.80

PT'

2299

2298

2302

2291

HumidAvg

305

307

305

304
99 

Figure 7–55. 9x7 reference run comparisons, 14-in. rail, M = 1.80, varying humidity 

 

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

604

633

692

699

Model

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

Rail

14-in Fwd 

14-in Fwd 

14-in Fwd 

14-in Fwd 

hNose

52.1

53.2

53.4

53.4

_

2.6

2.6

2.7

2.7

Mach

1.80

1.80

1.80

1.80

PT'

2302

2299

2297

2297

HumidAvg

201

285

402

502

-150 -140 -130 -120 -110 -100 -90 -80 

Tunnel Station (in.) 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

9x7 Parametric 

Run

604

633

692

699

Model

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

LM 1021, blade 

Rail

14-in Fwd 

14-in Fwd 

14-in Fwd 

14-in Fwd 

hNose

52.1

53.2

53.4

53.4

_

2.6

2.6

2.7

2.7

Mach

1.80

1.80

1.80

1.80

PT'

2302

2299

2297

2297

HumidAvg

201

285

402

502
100

Similar sets of runs with constant and varying humidity from the TBC3 8x6 wind tunnel test are 

shown in Figures 7–56 through –58. The gray window outline shown in the left side of the wind tunnel 

layout inset image is the downstream window in the 8x6 tunnel; the upstream window is located further to 

the left relative to this image and is out of view. In the first figure, at Mach 1.56, four runs are plotted, 

where the first two have nearly identical humidity levels (73 and 78 ppm), and the latter two have higher 

levels (208 and 330 ppm). The constant- and varying-humidity runs were combined on one plot because 

it was found that there is almost no variation in pressure among them, indicating that for this set of runs, 

there seems to be essentially no effect of humidity. In the next figure, 7–57, two runs at Mach 1.78 at 

very close humidity levels show excellent repeatability. Runs with humidity levels ranging from 184 to 

687 ppm are shown in Figure 7–58 at Mach 1.78, and these runs do show an effect of humidity (up to 

~0.01 ΔP/P difference), though not as much an effect as observed in the 9x7 data at Mach 1.8 (Figure 7–

55). 

Figure 7–56. 8x6 reference run comparisons, 14-in. rail, M = 1.56, varying humidity 

 

Test

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

Run

862

889

957

992

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 n/v off 

Boom1 VS2 n/v off 

Rail

14-in

14-in

14-in

14-in

hNose

59.0

58.8

59.0

58.9

_

3.4

3.4

3.4

3.4

Mach

1.56

1.56

1.56

1.56

PT'

2911

2918

2919

2923

HumidAvg

73

78

208

330

170 180 190 200 210 220 230 240 250 

Tunnel Station (in.) 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

Run

862

889

957

992

Model

Boom1 VS2 

Boom1 VS2 

Boom1 VS2 n/v off 

Boom1 VS2 n/v off 

Rail

14-in

14-in

14-in

14-in

hNose

59.0

58.8

59.0

58.9

_

3.4

3.4

3.4

3.4

Mach

1.56

1.56

1.56

1.56

PT'

2911

2918

2919

2923

HumidAvg

73

78

208

330

8 ft
101

Figure 7–57. 8x6 reference run comparisons, 14-in. rail, M = 1.78, constant humidity 

 

Test

8x6 TBC3 

8x6 TBC3 

Run

815

816

Model

Boom1 VS2 

Boom1 VS2 

Rail

14-in

14-in

hNose

63.7

63.7

_

-0.1

-0.1

Mach

1.78

1.78

PT'

3309

3309

HumidAvg

91

87

170 180 190 200 210 220 230 240 250 

Tunnel Station (in.) 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

8x6 TBC3 

8x6 TBC3 

Run

815

816

Model

Boom1 VS2 

Boom1 VS2 

Rail

14-in

14-in

hNose

63.7

63.7

_

-0.1

-0.1

Mach

1.78

1.78

PT'

3309

3309

HumidAvg

91

87
102

Figure 7–58. 8x6 reference run comparisons, 14-in. rail, M = 1.79, varying humidity 

Test

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

Run

366

549

575

392

413

Model

Boom1 VS2 

AS2

AS2

Boom1 VS2 

Boom1 VS2 

Rail

14-in

14-in

14-in

14-in

14-in

hNose

63.8

67.9

67.9

63.7

63.8

_

0.1

0.0

0.0

0.0

0.0

Mach

1.79

1.79

1.79

1.79

1.79

PT'

3288

3254

3268

3294

3293

HumidAvg

184

209

342

453

687

170 180 190 200 210 220 230 240 250 

Tunnel Station (in.) 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

8x6 TBC3 

Run

366

549

575

392

413

Model

Boom1 VS2 

AS2

AS2

Boom1 VS2 

Boom1 VS2 

Rail

14-in

14-in

14-in

14-in

14-in

hNose

63.8

67.9

67.9

63.7

63.8

_

0.1

0.0

0.0

0.0

0.0

Mach

1.79

1.79

1.79

1.79

1.79

PT'

3288

3254

3268

3294

3293

HumidAvg

184

209

342

453

687

Boom1 VS2 AS2
103

7.15.2. Reference Pressure Changes Due to Swapping of Window Blanks 

The two prior figures containing 8x6 reference runs at Mach 1.78 show a shift in the pressure levels 

relative to each other. One run from each of the figures, runs 366 and 815, were selected to plot against 

each other in Figure 7–59 to clearly show these differences. The run conditions, model, and model and 

rail positions are identical, and though there is a 90 ppm difference in humidity between them, the 

differences between the curves are far greater than one would expect for this humidity difference. The 

major difference between these two runs is the window configuration of the wind tunnel. In Section 3, it 

was stated that the Schlieren windows were in the downstream position during the first week of the test, 

with the porous window blanks in the upstream position. Before the start of the second week, the 

Schlieren windows and the porous blanks were swapped. This is believed to be the cause of the 

difference between the two reference pressure signatures, as the air flow patterns in the test section would 

be expected to change with the repositioning of the porous blanks. There should be little or no effect of 

this on the model pressure signatures since the standard procedure in NASA sonic boom testing is to take 

a reference run either just before or just after a run series when possible. However, model signatures at 

the same conditions taken in the first and second weeks of the test are not available to enable a direct 

comparison. 

Figure 7–59. 8x6 reference run comparisons, 14-in. rail, M = 1.79 

Schlieren windows downstream (week 1, runs up to 605), Schlieren windows upstream 

(week 2, runs 630 and after) 

Test

8x6 TBC3 

8x6 TBC3 

Run

366

815

Model

Boom1 VS2 

Boom1 VS2 

Rail

14-in

14-in

hNose

63.8

63.7

_

0.1

-0.1

Mach

1.79

1.78

PT'

3288

3309

HumidAvg

184

91

170 180 190 200 210 220 230 240 250 

Tunnel Station (in.) 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

8x6 TBC3 

8x6 TBC3 

Run

366

815

Model

Boom1 VS2 

Boom1 VS2 

Rail

14-in

14-in

hNose

63.8

63.7

_

0.1

-0.1

Mach

1.79

1.78

PT'

3288

3309

HumidAvg

184

91
104

7.15.3. Comparison of Reference Pressures in 9x7 and 8x6 Tunnels Using 14-in. Rail 

Reference runs measured on the 14-in. rail installed in the two wind tunnels are compared in Figures 

7–60 and –61 for nominal Mach numbers of 1.6 and 1.8, respectively. Data at Mach ~1.6 from the rail in 

both forward and aft positions in the 9x7 are presented, as are the data for the rail mounted in the one 

position in the 8x6. The layout diagrams below the plot show that the three reference runs plotted were 

acquired with three different models: the LM 1021, Boom1, and the cone fairing. Shocks from the latter 

two models were predicted by the layouts to fall on the rear portion of the instrumented section of the rail, 

so the portion of the reference run signatures in the plot aft of where the most forward model shocks are 

(for the Boom1 model, in the vicinity of orifice number 300) are considered not valid for comparison. 

Ahead of this point however, the curves are considered valid representations of the empty-tunnel pressure 

signatures. The major points that can be drawn from this plot are 1) that the magnitudes of the pressure 

variations in the 9x7 tunnel are about twice as high for the aft rail position (±0.030) than for the forward 

position (±0.015), and 2) the magnitude of the variations for the 8x6 tunnel are significantly higher 

(±0.040) than either of the 9x7 rail positions. Note also that the 8x6 curve is mostly below the ΔP/P = 0 

line—this merely indicates that the static pressures of the rail were lower than the tunnel static pressure 

reference. In the 8x6 tunnel, this reference static is measured in the “balance house,” which is a large 

plenum chamber surrounding the test section. A choice of a different static pressure would shift the rail 

pressure curve up or down accordingly. 

Pressure data from the 14-in. rail in both tunnels at Mach ~1.8 are presented in Figure 7–61. Again, 

data from the same three models are used, except at this higher speed, the model shocks were predicted to 

mostly not fall on the instrumented section of the rail, though there is a large shock from the Boom1 

model toward the rear of the signature (at orifice number 400). The same general conclusions from the 

previous figure can also be drawn from this one: the 9x7 reference signature has more variation with the 

rail in the aft position than in the forward position, and the 8x6 signature variation is significantly higher 

than either of those from the 9x7. 

 
105

 

Figure 7–60. 9x7 and 8x6 reference run comparisons, 14-in. rail, M = ~1.6 

 

Test

9x7 Parametric 

9x7 Parametric 

8x6 TBC3 

Run

862

2100

771

Model

LM 1021, blade 

Boom1 VS2 

Cone fairing 

Rail

14-in Fwd 

14-in Aft 

14-in

hNose

52.3

80.0

68.1

_

3.3

-6.5

0.0

Mach

1.60

1.60

1.57

PT'

2301

2299

2923

HumidAvg

298

290

142

0 50 100 150 200 250 300 350 400 450 

Orifice # 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

8x6 TBC3 

Run

862

2100

771

Model

LM 1021, blade 

Boom1 VS2 

Cone fairing 

Rail

14-in Fwd 

14-in Aft 

14-in

hNose

52.3

80.0

68.1

_

3.3

-6.5

0.0

Mach

1.60

1.60

1.57

PT'

2301

2299

2923

HumidAvg

298

290

142

9x7 Run 862

9x7 Run 2100 8x6 Run 771
106

 

Figure 7–61. 9x7 and 8x6 reference run comparisons, 14-in. rail, M = ~1.8 

Test

9x7 Parametric 

9x7 Parametric 

8x6 TBC3 

Run

764

1989

738

Model

LM 1021, blade 

Boom1 VS2 

Cone fairing 

Rail

14-in Fwd 

14-in Aft 

14-in

hNose

52.1

80.0

68.1

_

2.5

-6.5

0.0

Mach

1.80

1.80

1.79

PT'

2298

2303

3309

HumidAvg

285

284

85

0 50 100 150 200 250 300 350 400 450 

Orifice # 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

8x6 TBC3 

Run

764

1989

738

Model

LM 1021, blade 

Boom1 VS2 

Cone fairing 

Rail

14-in Fwd 

14-in Aft 

14-in

hNose

52.1

80.0

68.1

_

2.5

-6.5

0.0

Mach

1.80

1.80

1.79

PT'

2298

2303

3309

HumidAvg

285

284

85

9x7 Run 764

9x7 Run 1989 8x6 Run 738
107

7.15.4. Comparison of Reference Pressures in 9x7 and 8x6 Tunnels Using 2-in. Rail 

A similar pair of plots comparing the 9x7 and 8x6 reference run signatures at nominal Mach numbers 

of 1.6 and 1.8 is presented in Figures 7–62 and –63 with data from the 2-in. rail. However, this rail was 

not run in the aft position in the 9x7 tunnel during the subject tests, so only one curve from the 9x7 is 

given in each of these figures. The results are similar to the prior two figures, except that the variation in 

the 9x7 forward rail position is slightly lower (±0.010 at both Mach numbers) than for the 14-in. rail, and 

that the variation in the 8x6 tunnel is a bit higher (roughly ±0.050 at Mach 1.56 to ±0.060 at Mach 1.78). 

Note that the Boom1 model shocks fall on the rail starting at about 2/3 of the length of the rail in the 8x6 

test, but the model signature is not discernable at all in the midst of the large peak-to-peak variations in 

both plots. 

 

Figure 7–62. 9x7 and 8x6 reference run comparisons, 2-in. rail, M = ~1.6 

 

Test

9x7 Parametric 

8x6 TBC3 

Run

1750

1103

Model

Boom1 VS2 

Boom1 VS2 

Rail

2-in Fwd 

2-in

hNose

52.0

58.9

_

3.4

3.4

Mach

1.60

1.56

PT'

2299

2910

HumidAvg

320

211

0 50 100 150 200 250 300 350 400 450 500 

Orifice # 

-.06

-.04

-.02

0

.02

.04

.06

.08

.10

.12

(6P/P)Ref

Test

9x7 Parametric 

8x6 TBC3 

Run

1750

1103

Model

Boom1 VS2 

Boom1 VS2 

Rail

2-in Fwd 

2-in

hNose

52.0

58.9

_

3.4

3.4

Mach

1.60

1.56

PT'

2299

2910

HumidAvg

320

211

9x7 Run 1750 8x6 Run 1103
108

 

Figure 7–63. 9x7 and 8x6 reference run comparisons, 2-in. rail, M = ~1.8

Test

9x7 Parametric 

8x6 TBC3 

Run

1688

1051

Model

Boom1 VS2 

Boom1 VS2 

Rail

2-in Fwd 

2-in

hNose

52.0

48.9

_

3.4

3.4

Mach

1.80

1.78

PT'

2299

3305

HumidAvg

320

77

0 50 100 150 200 250 300 350 400 450 500 

Orifice # 

-.06

-.04

-.02

0

.02

.04

.06

.08

.10

.12

(6P/P)Ref

Test

9x7 Parametric 

8x6 TBC3 

Run

1688

1051

Model

Boom1 VS2 

Boom1 VS2 

Rail

2-in Fwd 

2-in

hNose

52.0

48.9

_

3.4

3.4

Mach

1.80

1.78

PT'

2299

3305

HumidAvg

320

77

9x7 Run 1688 8x6 Run 1051
109

7.15.5. Comparison of Reference Pressures in 9x7 Parametric and TBC4 Tests Using 14-in. Rail 

Repeatability of rail pressures at constant conditions within a test has been shown in prior figures (7–

52, –54, 56, 57), but in the following two figures (7–64 and –65), repeatability from one test to another in 

the same tunnel will be shown. Two short-term repeat runs from each of the 9x7 parametric and TBC4 

tests are shown in Figure 7–64 at Mach 1.6, where the short-term repeatability within each pair of runs is 

excellent (note the dashed lines showing one curve on top of the other). From the parametric test, the 

Boom1 model shocks are on the rail aft of tunnel station -34, but ahead of this point the comparison with 

the tunnel strut cone data (where the cone shock is well aft of the rail) from TBC4 is valid. The test-totest repeatability (ahead of tunnel station -34) is fairly good, with differences up to 0.015 in ΔP/P that 

appear consistent with the slightly higher humidity of the parametric test runs (~290 ppm) versus that of 

the TBC4 test runs (~230 ppm). At Mach 1.8 in Figure 7–65, the differences in the reference run 

pressures between the two tests is greater overall, and more consistent through the length of the signature, 

than at Mach 1.6. The humidity differences are about the same as for the Mach 1.6 data, so this does not 

necessarily explain the greater differences here. It is interesting, and not obvious why, when the same 

hardware is put in the same tunnel, and run at almost identical test conditions, that the “empty” tunnel 

reference signatures are not more similar. There was about a year of separation between the two tests, but 

time should not be a factor in contributing to the differences unless some changes were made to the tunnel 

during the interim (and no changes were made which would affect the air flow). 

Figure 7–64. 9x7 parametric test and TBC4 test reference run comparisons, 14-in. aft rail, M = 1.60 

Test

9x7 Parametric 

9x7 Parametric 

9x7 TBC4 

9x7 TBC4 

Run

2046

2100

113

119

Model

Boom1 VS2 

Boom1 VS2 

Tunnel strut cone 

Tunnel strut cone 

Rail

14-in Aft 

14-in Aft 

14-in Aft 

14-in Aft 

hNose

80.0

80.0

4.0

4.0

_

-6.5

-6.5

-0.2

-0.2

Mach

1.60

1.60

1.60

1.60

PT'

2299

2300

2301

2300

HumidAvg

287

290

231

236

-80 -70 -60 -50 -40 -30 -20 -10 

Tunnel Station (in.) 

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

.10

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

9x7 TBC4 

9x7 TBC4 

Run

2046

2100

113

119

Model

Boom1 VS2 

Boom1 VS2 

Tunnel strut cone 

Tunnel strut cone 

Rail

14-in Aft 

14-in Aft 

14-in Aft 

14-in Aft 

hNose

80.0

80.0

4.0

4.0

_

-6.5

-6.5

-0.2

-0.2

Mach

1.60

1.60

1.60

1.60

PT'

2299

2300

2301

2300

HumidAvg

287

290

231

236

97p Runs 2046, 2100 TBC4 Runs 113, 119
110

Figure 7–65. 9x7 parametric test and TBC4 test reference run comparisons, 14-in. aft rail, M = 1.80 

 

Test

9x7 Parametric 

9x7 Parametric 

9x7 TBC4 

9x7 TBC4 

Run

1989

2045

110

116

Model

Boom1 VS2 

Boom1 VS2 

Tunnel strut cone 

Tunnel strut cone 

Rail

14-in Aft 

14-in Aft 

14-in Aft 

14-in Aft 

hNose

80.0

80.0

4.0

4.0

_

-6.5

-6.5

-0.2

-0.2

Mach

1.80

1.80

1.80

1.80

PT'

2303

2299

2302

2302

HumidAvg

284

285

231

233

-80 -70 -60 -50 -40 -30 -20 -10 

Tunnel Station (in.) 

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

.10

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

9x7 TBC4 

9x7 TBC4 

Run

1989

2045

110

116

Model

Boom1 VS2 

Boom1 VS2 

Tunnel strut cone 

Tunnel strut cone 

Rail

14-in Aft 

14-in Aft 

14-in Aft 

14-in Aft 

hNose

80.0

80.0

4.0

4.0

_

-6.5

-6.5

-0.2

-0.2

Mach

1.80

1.80

1.80

1.80

PT'

2303

2299

2302

2302

HumidAvg

284

285

231

233

97p Runs 1989, 2045 TBC4 Runs 110, 116
111

7.15.6. Comparison of Reference Pressures for 14-in. and 2-in. Rails in 9x7 Parametric Test 

9x7 parametric test data from the two pressure rails are compared in the next two figures, 7–66 and 

–67. The 14-in. and 2-in. rails were mounted in the same forward window blank location, and the 

reference runs were acquired at the same tunnel conditions for both Mach numbers, 1.6 and 1.8. The 

models were different (LM 1021 and Boom1) between the two runs in each figure, but with their shocks 

almost entirely off the rails, the use of the different models should not make a difference in the reference 

run comparisons. 

Qualitatively, there is very little difference between the data from the two rails at either Mach 

number, though the maximum ΔP/P variation is a little higher for the 14-in. rail (±0.02) than for the 2-in. 

rail (±0.012). 

Figure 7–66. 14-in. and 2-in. forward rail reference run comparisons, 9x7 parametric test, M = 1.60 

 

Test

9x7 Parametric 

9x7 Parametric 

Run

862

1689

Model

LM 1021, blade 

Boom1 VS2 

Rail

14-in Fwd 

2-in Fwd 

hNose

52.3

52.0

_

3.3

3.5

Mach

1.60

1.60

PT'

2301

2300

HumidAvg

298

321

0 50 100 150 200 250 300 350 400 450 500 

Orifice # 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

Run

862

1689

Model

LM 1021, blade 

Boom1 VS2 

Rail

14-in Fwd 

2-in Fwd 

hNose

52.3

52.0

_

3.3

3.5

Mach

1.60

1.60

PT'

2301

2300

HumidAvg

298

321

Run 862 Run 1689
112

Figure 7–67. 14-in. and 2-in. forward rail reference run comparisons, 9x7 parametric test, M = 1.80 

Test

9x7 Parametric 

9x7 Parametric 

Run

764

1688

Model

LM 1021, blade 

Boom1 VS2 

Rail

14-in Fwd 

2-in Fwd 

hNose

52.1

52.0

_

2.5

3.4

Mach

1.80

1.80

PT'

2298

2299

HumidAvg

285

320

0 50 100 150 200 250 300 350 400 450 500 

Orifice # 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

9x7 Parametric 

9x7 Parametric 

Run

764

1688

Model

LM 1021, blade 

Boom1 VS2 

Rail

14-in Fwd 

2-in Fwd 

hNose

52.1

52.0

_

2.5

3.4

Mach

1.80

1.80

PT'

2298

2299

HumidAvg

285

320

Run 764 Run 1688
113

7.15.7. Comparison of Reference Pressures for 14-in. and 2-in. Rails in 8x6 TBC3 Test 

The same rail comparisons are plotted from the 8x6 wind tunnel data in Figures 7–68 and –69, where 

the runs with the Boom1 model are in-line reference runs. The much larger peak-to-peak pressure 

variations in the 8x6 relative to the 9x7 are obvious, and so the differences in the pressures between the 

two rails are somewhat magnified. It is puzzling to observe, however, that in this tunnel, the 2-in. rail 

data show slightly greater variation (±0.06) than the 14-in. rail data (±0.05). 

 

Figure 7–68. 14-in. and 2-in. rail reference run comparisons, 8x6 TBC3 test, M = 1.57 

 

Test

8x6 TBC3 

8x6 TBC3 

Run

771

1103

Model

Cone fairing 

Boom1 VS2 

Rail

14-in

2-in

hNose

68.1

58.9

_

0.0

3.4

Mach

1.57

1.56

PT'

2923

2910

HumidAvg

142

211

0 50 100 150 200 250 300 350 400 450 500 

Orifice # 

-.10

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

(6P/P)Ref

Test

8x6 TBC3 

8x6 TBC3 

Run

771

1103

Model

Cone fairing 

Boom1 VS2 

Rail

14-in

2-in

hNose

68.1

58.9

_

0.0

3.4

Mach

1.57

1.56

PT'

2923

2910

HumidAvg

142

211

Run 771 Run 1103
114

 

Figure 7–69. 14-in. and 2-in. rail reference run comparisons, 8x6 TBC3 test, M = 1.79 

Test

8x6 TBC3 

8x6 TBC3 

Run

738

1051

Model

Cone fairing 

Boom1 VS2 

Rail

14-in

2-in

hNose

68.1

48.9

_

0.0

3.4

Mach

1.79

1.78

PT'

3309

3305

HumidAvg

85

77

0 50 100 150 200 250 300 350 400 450 500 

Orifice # 

-.08

-.06

-.04

-.02

0

.02

.04

.06

.08

.10

(6P/P)Ref

Test

8x6 TBC3 

8x6 TBC3 

Run

738

1051

Model

Cone fairing 

Boom1 VS2 

Rail

14-in

2-in

hNose

68.1

48.9

_

0.0

3.4

Mach

1.79

1.78

PT'

3309

3305

HumidAvg

85

77

Run 738 Run 1051
115

8. Computational Methods 

8.1. Flow Solvers 

Three high-fidelity NASA CFD codes where used to compute the flow around and sonic boom 

signatures for the Boeing models: USM3D, Cart3D, and OVERFLOW. USM3D was the default code used 

in this study, and selected cases were computed using the other two codes. Propagation of the sonic 

boom signatures to the ground was done using sBOOM. In this section a brief description of each of the 

CFD codes is given. 

8.1.1. USM3D 

USM3D42,43 is a tetrahedral cell-centered, finite volume Euler and Navier-Stokes (N-S) method. It 

provides a variety of options for solving the flow equations and several turbulence models for closure of 

the N-S equations. For the current study, Roe’s flux difference splitting scheme was used with a CFL 

number of 20. Flux limiters were used to preclude oscillations due to shocks and discontinuities by 

limiting the values of the spatial derivatives. For the present study, at the start of a new solution, the 

USM3D code ran with first order spatial accuracy for 10,000 iterations, and then ran for an additional 

20,000 iterations with second-order spatial accuracy. Obtaining a well converged, first-order accurate 

solution before switching to second order significantly improves the chance of convergence with the 

code, but it is sometimes not necessary. USM3D has been successfully used to compute sonic boom 

studies.28,29 The flow on the models is not expected to be a fully turbulent flow but in some transient state 

between laminar and fully turbulent flow. Thus, in addition to the turbulent simulations, some selected 

laminar flow computations were also made. Pointwise grid generation methods were used for inviscid 

flow simulations with USM3D, and VGrid methods were used for laminar and turbulent (using the 

Spalart-Allmaras turbulence model) viscous flow simulations. 

8.1.2. Cart3D / AERO 

Cart3D19-21,38 is a high-fidelity inviscid analysis package for conceptual and preliminary aerodynamic 

design. It allows users to perform automated CFD analysis on complex geometry. The package includes 

utilities for geometry import, surface modeling, mesh generation, flow simulation and post-processing of 

results. The main simulation code, FlowCart, runs in parallel both in shared memory (OpenMP) and 

distributed memory (MPI) with excellent scalability. The package is highly automated so that geometry 

acquisition, and mesh generation can usually be performed within a few minutes on current desktop 

computers. 

The Cart3D simulation package comes with an internal mesher called Cubes and geometric models 

are imported into the package as watertight surface triangulations. Cart3D uses adaptively-refined 

Cartesian grids to discretize the space surrounding the models, and cuts the geometry out of the set of 

"cutcells" which actually intersect the surface triangulation. Cubes then produces a topologicallyunstructured, adaptively-refined Cartesian grid. The Cart3D Adjoint Error Optimization (AERO) module 

was also used. This module uses the method of adjoint-weighted residuals to drive mesh adaptation. Once 

a user specifies outputs of interest, (lift, drag, etc.) with a corresponding error tolerance, this module 

automatically refines the mesh to drive the remaining numerical errors in the outputs below the requested 

tolerance. 

FlowCart is the current solver being released with Cart3D. It is a scalable, multilevel, linearly-exact 

upwind solver and uses domain-decomposition to achieve very good scalability. On most modern desktop 

machines it can converge well over 2 million cells-per-hour-per processor, and it does very well on multicore CPUs. FlowCart is very tightly integrated into Cart3D and all of the automation tools are built 
116

around it. Since it is a multilevel code, it converges very quickly and includes the state of the art work on 

low-dissipation approaches, solid wall boundaries, mesh interfaces and limiters. Both the parallelization 

and multigrid are completely transparent to the user and are turned on by simple command line arguments 

to encourage their use. In the present study, FlowCart used cell-centered, finite-volume, upwind 

differencing. The Barth–Jespersen limiter was used to preserve monotonicity. Time integration was 

performed by an unstructured, nested multigrid procedure. 

8.1.3. Overflow 

OVERFLOW44,45 is the OVERset structured grid FLOW solver that was used by Boeing for their 

inviscid and viscous simulations8

 presented in this paper. The turbulence model that was used was the 

Spalart-Allmaras (SA) model, and the dissipation scheme was TLNS3D. The simulation was run until the 

residuals reduced to near zero and this took approximately 5000 time steps.

8.1.4. sBOOM 

A recently-developed NASA sonic boom prediction code, sBOOM,

46 was used to propagate sonic 

boom signatures to the ground. sBOOM solves the augmented Burger’s equation numerically and takes 

into account effects such as non-linearity, molecular relaxation and thermo-viscous absorption into the 

propagation process. The thickness of the shocks is predicted analytically, which avoids artificial 

smoothing and empirical shock thickening during loudness calculation. sBOOM can predict on-track and 

off-track ground signatures with or without wind effects, along with consideration for aircraft maneuvers. 

Ground signatures extrapolated with sBOOM have been run in the present study through a loudness 

code based on the procedures laid out by Shepherd and Sullivan.47 The code estimates the boom loudness 

levels in PLdB, dBA, and dBC, but only the PLdB results will be presented herein since this metric is the 

perceived level as heard by humans. 

8.2. Grid Generation 

Customized off-body volume grids for supersonic flow are fundamental to the prediction of accurate 

sonic boom pressure signatures. The various grid generation methods—Mach cone aligned prism 

(MCAP) meshes, Boom Grid (BG) Generation Method, Inflate Generation Method, and a solution 

adaptive Cartesian method—are discussed in this section. 

8.2.1. Grid Extrusion Method: Mach Cone Aligned Prism 

The Mach Cone Aligned Prism (MCAP) collar grid method,3,27,28 was used with the USM3D flow 

solver for accurate sonic boom computations. MCAP appends geometrically-similar prism cell meshes to 

an interior tetrahedral mesh with cylindrical boundaries. The shearing angle of the appended prism mesh 

is adjusted for the angle of attack and Mach angle to allow for both on- and off-track aligned grids. The 

MCAP algorithm provides a mesh composed entirely of tetrahedral cells and an automated process to 

construct grids suited to obtain accurate sonic boom pressure signatures. Sonic boom pressure signatures 

can be obtained on configurations of any level of geometric complexity provided a refined volume grid of 

tetrahedra within the near body cylindrical boundary of surface triangles is supplied. The inner cylindrical 

meshes were developed using TetRUSS48 (GridTool and VGrid)

49 or Pointwise50,51 grid generation 

methods. Thin, anisotropic cells near the configuration surfaces were developed to support viscous 

computations at the wind tunnel Reynolds number. The mesh density was increased within the sonic 

boom zone of influence below the model to off-track angles of 90 degrees to accurately capture the sonic 

boom signature out to the cylindrical boundary. The inner cylindrical boundaries were then used as input 

to the MCAP software and projected in the radial direction and sheared to align with the Mach angle with 
117

a series of prism layers to the far field. The projected prism collar grid maintains the highly refined grid 

spacing in the axial direction of the inner cylindrical mesh to the far field. By simply increasing the 

distance of radial projection, as successive prism layers are appended to the grid, radial stretching of the 

cells is accomplished, and this greatly reduces the number of grid points required, while also reducing the 

effects of numerical dissipation. Shearing to align the prism cells with the Mach cone angle around the 

aircraft model improves the accuracy of both on- and off-track computations. When the angle of attack is 

non-zero, an additional asymmetrical shear is applied and a cosine function is used to smoothly transition 

the differences in shear angle from the lower to upper symmetry planes. 

8.2.2. Grid Extrusion Method: Boom Grid (BG) 

The Boom Grid (BG) method30 is similar to other “extrusion” grid generation approaches in that the 

new grid is created by extending lines from grid points on a boundary surface for an existing grid in a 

direction approximately normal to that surface. The Q2D (Quasi-two-dimensional) grid generation code, 

from which the BG code evolved, was developed using this approach to provide a rapid airfoil analysis 

capability. The Q2D method uses a point numbering system that automatically provides matching faces 

when the extruded prisms are split into tetrahedral cells, eliminating the need to post-process the cells to 

meet this requirement, and thus reducing grid generation times dramatically. 

The BG method utilizes the same efficient cell-splitting method used in Q2D, but has several 

requirements that resulted in it being developed as a separate code. First, instead of using the symmetry 

plane as the starting surface, the new cells are extruded through the outer, typically cylindrical, far-field 

boundary of an existing “core” 3-D grid around a configuration, creating a “collar” grid. The extension 

direction is approximately normal to the original surface points when viewed from the front, but the new 

grid lines are swept in the stream-wise direction. This grid line shearing, along with stretching of the 

distance between subsequent layers, creates high-aspect ratio cell faces that are closely aligned with the 

Mach angle so that the dissipation of the boom signature is reduced. Depending on the desired location 

for extracting a sonic boom signature, anywhere from 20 to more than 100 layers of cells may need to be 

generated. Another difference from Q2D is that these cells then need to be merged with the core grid, 

which requires converting the old outer boundary faces to field faces and renumbering the points, cells 

and faces to reflect flow solver requirements. 

The collar grid lines are often extruded normal to the original core grid outer boundary when viewed 

from the front. If the outer boundary is a cylinder, then all of the extruded grid lines meet at the center of 

the circle (front view of the cylinder) as a radial reference point. If the core grid has the configuration 

located at this reference point, then boom signature propagation lines will be approximately aligned with 

the radial grid lines, as desired. The weakness of this approach, however, is that in generating a core grid 

with the outer cylinder outside of the wing tip, there can be a significant distance from the bottom of the 

fuselage to the beginning of the collar grid. As the grid is not sheared and stretched in this region, the 

signal can get dissipated before reaching the collar grid. 

If only on-track signatures are needed, then the above problem can be resolved (though with some 

additional cost due to more grid cells) by simply increasing the size of the outer core grid circle to allow 

the configuration to be shifted down closer to the lower boundary. For off-track signatures, however, this 

approach gives poor alignment of the grid lines and signal propagation direction. The BG method 

attempts to address this problem by using a variable radial reference point instead of the standard center 

of the circle. This allows the configuration to be shifted down closer to the outer boundary, using either a 

larger circle or an arbitrary-shaped boundary, and still have the radial lines emanate from the 

configuration for better signal propagation. It has also been found that the location of the radial reference 

point can be calibrated to focus the grid lines in a desired off-track direction to provide good signal 

resolution with very little degradation of the on-track signature. 
118

8.2.3. Solution-Adaptive Cartesian Grids 

Solution-adaptive cartesian grids are used by Cart3D, and are generated by the Cubes and AERO 

modules as described above in section 8.1.2. 

8.2.4. Initial and Boundary Conditions 

For all viscous simulations, a no-slip viscous boundary condition (BC) was used on all solid surfaces 

of the models. A supersonic inflow BC was used at the domain inflow face and an extrapolation BC was 

used at the downstream outflow face of the domain. A characteristic inflow and outflow BC was used 

along the far field, lateral faces of the outer domain. For the inviscid flow simulation Cart3D used an 

inviscid aerodynamic surface BC on all solid surfaces. 

9. Comparison of Experimental Data and Computational Simulations 

Data from selected wind tunnel runs of the Boeing AS2, Boom1, Boom3, and Performance models 

are compared to predictions from the three CFD codes described above in this section. 

9.1. AS2 Body of Revolution 

All three CFD codes were used to compute the pressure signatures for the AS2 model at distances of 

30 and 60 in. below the model. As an example of an adapted grid and pressure contours from Cart3D, 

Figure 9–1 shows the adjoint-adapted grid at Mach 1.6 after 13 levels of adaptation, and the sensor lines 

are shown in orange at 30- and 60- in. heights. The refinement pattern is driven by the features of the 

adjoint solution. Figure 9–2 shows the symmetry plane pressure contours. 

Inviscid and viscous predictions of AS2 signatures are compared with 9x7 wind tunnel data in Figure 

9–3 at a height of 30 in., and with 8x6 wind tunnel data in Figure 9–4 at a height of 60 in. The data from 

the 9x7 were acquired at Mach 1.6 with the 14-in. rail, while the 8x6 data were acquired at Mach 1.56 

with the 2-in. rail. The CFD predictions were run at Mach 1.6 and a Reynolds number of 4.1 million per 

foot, which is a little lower than the 9x7 wind tunnel Reynolds number of 4.5 million per foot at M = 1.6 

and PT = 2300 psf. 

The wind tunnel data in these plots are shown in the dark gray curves with circle symbols, and the 

predictions are shown in the colored curves without symbols. Note that the y-axis labels, (ΔP/P)Data – 

(ΔP/P)Ref, apply exclusively to the experimental data; there is no need for “reference” runs in the CFD, 

so the labels for the CFD cases would be just ΔP/P. 
119

Figure 9–1. Symmetry plane CART3D adjoint-adapted grid for AS2 model, M = 1.6, α = 0° 

Figure 9–2. Symmetry plane pressure contours for AS2 model, Cart3D, M = 1.6, α = 0° 
120

Two inviscid CFD predictions, Cart3D and USM3D, and two viscous CFD predictions, Cart3D and 

USM3D SA (Spalart-Allmaras turbulence model) and OVERFLOW, are compared to AS2 model data 

from the 9x7 parametric test at a height of 30 in. above the rail in Figure 9–3. All of the codes predict 

nose shock peaks between 20% and 60% higher than the experimental data peak and much faster rise 

times. The experimental data are from the 14-in. RF1 rail, so there is no amplification of the measured 

shock peak by any reflection factor. There is good agreement of all three codes with experimental data in 

the flat region behind the nose shock, but all of the codes over-predict the main expansion in the aft 

portion of the signature. The reason for this discrepancy is not known, though the same discrepancy was 

noted for the Lockheed Seeb body-of-revolution model.3,37 It was surmised that the leading shock from 

the pressure rail striking the curved part of the AS2 model was the cause for the discrepancy, but upon 

further review of the 26 individual signatures in the X sweep for the 1080–1105 run series from the 9x7 

parametric test, it was determined that this is not the likely cause. For the first few inches of the 16-in. 

X sweep, the rail nose shock does pass over the curved nose section of the AS2 model, but the model 

pressures in the main expansion are nearly the same as those from the latter part of the X sweep, 

indicating that the rail shock does not significantly influence model signature. The two inviscid and 

viscous CFD results in Figure 9–3 match the flat portion of the signature fairly well, though the viscous 

OVERFLOW result (sig set 34) has a bit of an undershoot at the start of the shocks for the model nose 

(X = 1) and the balance adapter (X = 15.5).

Figure 9–3. Experiment/CFD comparisons for AS2 model 

9x7 parametric test, 14-in. forward rail, M = 1.60, hNose = 30 in., α = 0° 

Test

9x7 Parametric 

Cart3D Inv 

USM3D_PW Inv 

9x7 Parametric 

USM3D_PW SA 

B OVRFLW NS 

Sig Set 

33

3

11

33

17

34

Runs

1080—1105

CFD case 3 

CFD case 11 

1080—1105

CFD case 17 

CFD case 34 

Ref Run 

1106

—

—

1106

—

—

hNose

30.0

30.0

30.0

30.0

30.0

30.0

_

0.04

0.00

0.00

0.04

0.00

0.00

-10 -5 0 5 10 15 20 

XAligned (in.) 

-.005

0

.005

.010

.015

.020

.025

.030

.035

.040

(6P/P)Data - (

6P/P)Ref

Test

9x7 Parametric 

Cart3D Inv 

USM3D_PW Inv 

9x7 Parametric 

USM3D_PW SA 

B OVRFLW NS 

Sig Set 

33

3

11

33

17

34

Runs

1080—1105

CFD case 3 

CFD case 11 

1080—1105

CFD case 17 

CFD case 34 

Ref Run 

1106

—

—

1106

—

—

hNose

30.0

30.0

30.0

30.0

30.0

30.0

_

0.04

0.00

0.00

0.04

0.00

0.00

Experiment

Cart3D inviscid

USM3D inviscid

Experiment

USM3D viscous (SA)

OVERFLOW viscous (SA)
121

Figure 9–4 below shows experiment and inviscid/viscous CFD comparisons for the AS2 model at 

heights of 60 in. from the 2-in. rail in the 8x6 wind tunnel. In contrast to the prior figure with the 14-in.-

rail data, the nose shock peaks are substantially higher than the CFD-predicted peaks. This is consistent 

with the rail comparison findings in the earlier section, in which the reflection factor for the 2-in. rail 

abnormally amplifies the shock peaks. The experimental data in Figure 9–4 also show a slight bump in 

the flat portion of the signature around X = 3.5. It is possible that this bump could be the reflection of the 

nose shock off the tunnel wall, though it is just over 2 in. aft of the nose shock in this Mach 1.56 

signature, whereas a shock reflection in a Mach 1.6 flow is expected to affect the model signature a little 

less than 5 in. downstream of the incident shock as discussed above. 

Figure 9–4. Experiment/CFD comparisons for AS2 model 

8x6 TBC3 test, 2-in. rail, M = 1.56 (WT), 1.60 (CFD), hNose = 60 in., α = 0° 

Test

8x6 TBC3 

Cart3D Inv 

USM3D_PW Inv 

8x6 TBC3 

USM3D_PW SA 

B OVRFLW NS 

Sig Set 

111

4

13

111

19

35

Runs

1162—1187

CFD case 4 

CFD case 13 

1162—1187

CFD case 19 

CFD case 35 

Ref Run 

1188

—

—

1188

—

—

hNose

59.2

60.0

60.0

59.2

60.0

60.0

_

-0.02

0.00

0.00

-0.02

0.00

0.00

-10 -5 0 5 10 15 20 

XAligned (in.) 

-.005

.005

.015

.025

.035

(6P/P)Data - (

6P/P)Ref

Test

8x6 TBC3 

Cart3D Inv 

USM3D_PW Inv 

8x6 TBC3 

USM3D_PW SA 

B OVRFLW NS 

Sig Set 

111

4

13

111

19

35

Runs

1162—1187

CFD case 4 

CFD case 13 

1162—1187

CFD case 19 

CFD case 35 

Ref Run 

1188

—

—

1188

—

—

hNose

59.2

60.0

60.0

59.2

60.0

60.0

_

-0.02

0.00

0.00

-0.02

0.00

0.00

Experiment

Cart3D inviscid

USM3D inviscid

Experiment

USM3D viscous (SA)

OVERFLOW viscous (SA)
122

9.2. Boeing Boom1 Model 

The flow field around the Boom1 VS2 was computed using all three codes for a free-stream Mach 

number of 1.6, angle of attack of 3.4,o and Reynolds number of 4.1 million per foot. Figure 9–5 shows 

pressure coefficient contours on the surface of the Boom1 VS2 model as computed by USM3D with a 

laminar boundary layer, and Figure 9–6 shows the symmetry plane pressure contours below the model for 

a Cart3D solution after 14 levels of adaption. The refinement pattern is driven by the features of the 

adjoint solution. As with the AS2 model predictions, the sonic boom signatures were extracted at a 

distances of 30 and 60 in. below the model nose for comparisons with the wind tunnel data, as indicated 

by the orange lines in the figure. 

Figure 9–5. Surface pressure contours for Boom1 VS2 model, USM3D laminar results, 

M = 1.6, α = 3.4° 

Figure 9–6. Symmetry plane pressure contours for Boom1 VS2 model, Cart3D, M = 1.6, α = 3.4° 
123

Inviscid Cart3D and OVERFLOW predictions for Boom1 VS2 are compared with wind tunnel data in 

Figure 9–7 at α = 3.4° and hNose = 30 in. There is very good agreement between the CFD results and wind 

tunnel data along the flat portions of the signature, but both CFD codes predict stronger shocks at every 

location along the experimental data signature where there is some waviness or a rounded shock peak. 

The rounding is not surprising since the temporal and spatial variations in the wind tunnel flow cause 

individual pressure signatures in an X or Z sweep to have varying degrees of shock peak amplitudes that 

become somewhat washed out in the averaging. The greatest differences between the CFD and 

experimental data are aft of the main expansion, where the codes predict some very strong shocks from 

the region around the nacelles and vertical tails. The absence of a boundary layer is the cause of the 

discrepancy with experiment. 

Viscous OVERFLOW and USM3D laminar predictions for this model at the same conditions provide 

a better match with the wind tunnel data than the inviscid predictions, and the shock peaks are not nearly 

as amplified as for the inviscid predictions as well. Note that the OVERFLOW prediction captures more 

of the small-shock details than the USM3D prediction does just forward of the main expansion, but which 

are not seen in the experimental data. 

Figure 9–7. Experiment/CFD comparisons for Boom1 VS2 model 

9x7 parametric test, 14-in. forward rail, M = 1.60, hNose = 30 in., α = 3.4° 

Test

9x7 Parametric 

Cart3D Inv 

B OVRFLW Inv 

9x7 Parametric 

USM3D_VG SA 

B OVRFLW NS 

Sig Set 

44

44

36

44

62

40

Runs

1437—1469

CFD case 44 

CFD case 36 

1437—1469

CFD case 62 

CFD case 40 

Ref Run 

1470

—

—

1470

—

—

hNose

30.4

30.0

30.0

30.4

30.0

30.0

_

3.40

3.40

3.40

3.40

3.40

3.40

-5 0 5 10 15 20 25 

XAligned (in.) 

-.015

-.010

-.005

0

.005

.010

.015

.020

.025

.030

(6P/P)Data - (

6P/P)Ref

Test

9x7 Parametric 

Cart3D Inv 

B OVRFLW Inv 

9x7 Parametric 

USM3D_VG SA 

B OVRFLW NS 

Sig Set 

44

44

36

44

62

40

Runs

1437—1469

CFD case 44 

CFD case 36 

1437—1469

CFD case 62 

CFD case 40 

Ref Run 

1470

—

—

1470

—

—

hNose

30.4

30.0

30.0

30.4

30.0

30.0

_

3.40

3.40

3.40

3.40

3.40

3.40

Experiment

Cart3D inviscid

OVERFLOW inviscid

Experiment

Cart3D inviscid

USM3D viscous (SA)
124

Figure 9–8. Experiment/CFD comparisons for Boom1 VS2 model 

9x7 parametric test, 14-in. aft rail, M = 1.60, hNose = 60 in., α = 3.4° 

CFD/experiment comparisons at h = 60 in. are shown in Figure 9–8. One inviscid solution is given 

from Cart3D and one viscous turbulent solution is given from USM3D with the Spalart-Allmaras 

turbulence model. As with the comparisons at 30 in., the agreement is generally very good, with the 

shock peaks from the predictions being somewhat higher than those from the wind tunnel, especially for 

the inviscid solution. Note that the greatest discrepancies between the experimental and CFD data occur 

in the aft part of the signature, with the viscous solution being closer to the wind tunnel data than the 

inviscid solution. 

Comparing the overall pressure level between this figure and that of the previous two figures 

confirms that the CFD codes did very well in capturing the effects of model height. 

Test

9x7 Parametric 

Cart3D Inv 

USM3D_VG SA 

Sig Set 

61

45

63

Runs

2047—2072

CFD case 45 

CFD case 63 

Ref Run 

2073

—

—

hNose

60.0

60.0

60.0

_

3.40

3.40

3.40

-5 0 5 10 15 20 25 

XAligned (in.) 

-.015

-.005

.005

.015

.025

(6P/P)Data - (

6P/P)Ref

Test

9x7 Parametric 

Cart3D Inv 

USM3D_VG SA 

Sig Set 

61

45

63

Runs

2047—2072

CFD case 45 

CFD case 63 

Ref Run 

2073

—

—

hNose

60.0

60.0

60.0

_

3.40

3.40

3.40

Experiment

USM3D viscous (laminar)

OVERFLOW viscous (SA)
9.3. Boeing Boom3 Model 

Laminar and turbulent USM3D predictions were made for the Boom3 VS3 model at Mach 1.6, a 

Reynolds number of 4.1 million per foot, α = 3.1o, and off-track angles of 15°, 30°, and 45° in addition to 

the on-track angle of 0°. Figure 9–9 shows the surface pressure contours on this model for a USM3D

laminar solution, and the symmetry plane flow field pressure contours down to a height of 60 in. are 

shown in Figure 9–10. 

Figure 9–9. Surface pressure contours for Boom3 VS3 model, USM3D laminar results, 

M = 1.6, α = 3.1° 

Figure 9–10. Symmetry plane pressure contours for Boom3 VS3 model, USM3D laminar results, 

M = 1.6, α = 3.1° 
126

The experiment/CFD comparison plots that follow are for each of the on-track and off-track angles at 

a model height of 60 in., but first a plot of just the USM3D-SA predictions at the four track angles is given 

in Figure 9–11 to clearly illustrate the differences in the signatures at these angles. Note that the four 

signatures are very similar in the forward region (as expected since the geometry here is mostly a body of 

revolution), with the exception that the nose shock is predominant in the φ = 0° case and becomes smaller 

until flat in the φ = 45° case. The reason for this could be due to the flow field grid being of finer 

resolution below the model than off to the sides, but this is being looked into at the time of this writing. 

The primary differences in the signatures occur from the lifting surfaces of the model, from the wings aft. 

The main expansion becomes deeper and moves forward with off-track angle, and the aft shocks become 

stronger. The same is generally true for the experimental data at these four track angles shown in Figure 

33, but the nose shock signature shape stays very consistent with off-track angle, as would be expected. 

Figure 9–11. CFD predictions for effect of off-track angle for Boom3 VS3 model, USM3D SA 

turbulent results, M = 1.6, hNose = 60 in., α = 3.1° 

The four sets of curves in Figure 9–12 show comparisons between the experimental data and viscous 

CFD results (USM3D laminar and turbulent SA) for this model at the conditions specified above. Note 

the 0.02 ΔP/P offsets for the upper three sets of curves. In general there is good agreement between the 

experimental and CFD results in the front part of the signatures at all track angles, though not as good for 

capturing the nose and wing shocks at the 45° off-track angle. In the φ = 0° case, the laminar and 

turbulent USM3D results agree with each other from the front through the main expansion, but aft of this 

they differ. Both USM3D methods predict stronger nose shocks under track, which appears smeared in the 

experimental data, and they also overpredict the strength of some of the aft shocks under track after the 

main expansion. The 15° and 30° off-track CFD predictions match the wind tunnel data very well 

overall, with little difference between the laminar and turbulent solutions. 

Test

USM3D_VG SA 

USM3D_VG SA 

USM3D_VG SA 

USM3D_VG SA 

Sig Set 

113

115

117

119

Runs

CFD case 113 

CFD case 115 

CFD case 117 

CFD case 119 

hNose

60

60

60

60

_

3.1

3.1

3.1

3.1

q ̊

0

15

30

45

-5 0 5 10 15 20 25 

XAligned (in.) 

-.015

-.005

.005

.015

.025

(6P/P)Data - (

6P/P)Ref

Test

USM3D_VG SA 

USM3D_VG SA 

USM3D_VG SA 

USM3D_VG SA 

Sig Set 

113

115

117

119

Runs

CFD case 113 

CFD case 115 

CFD case 117 

CFD case 119 

hNose

60

60

60

60

_

3.1

3.1

3.1

3.1

q ̊

0

15

30

45

φ = 45° φ = 30°

φ = 15° φ = 0°
127

Figure 9–12. Experiment/CFD predictions for Boom3 VS3 model at various off-track angles 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, hNose = ~60 in., α = ~3.1° 

Test

9x7 TBC4 

USM3D_VG Lam 

USM3D_VG SA 

9x7 TBC4 

USM3D_VG Lam 

USM3D_VG SA 

9x7 TBC4 

USM3D_VG Lam 

USM3D_VG SA 

9x7 TBC4 

USM3D_VG Lam 

USM3D_VG SA 

Sig Set 

49

105

113

53

107

115

54

109

117

55

111

119

Runs

1537—1561

CFD case 105 

CFD case 113 

1653—1677

CFD case 107 

CFD case 115 

1678—1702

CFD case 109 

CFD case 117 

1703—1727

CFD case 111 

CFD case 119 

Ref Run 

1612

—

—

1624

—

—

1624

—

—

1624

—

—

hNose

61.8

60.0

60.0

61.7

60.0

60.0

61.6

60.0

60.0

61.0

60.0

60.0

_

3.02

3.10

3.10

2.96

3.10

3.10

2.94

3.10

3.10

2.94

3.10

3.10

q ̊

0.1671

0.000

0.000

14.84

15.00

15.00

30.80

30.00

30.00

45.64

45.00

45.00

q = 0 ̊

q = 15 ̊

q = 30 ̊

q = 45 ̊

-5 0 5 10 15 20 25 

XAligned (in.) 

-.01

0

.01

.02

.03

.04

.05

.06

.07

.08

(6P/P)Data - (

6P/P)Ref

Test

9x7 TBC4 

USM3D_VG Lam 

USM3D_VG SA 

9x7 TBC4 

USM3D_VG Lam 

USM3D_VG SA 

9x7 TBC4 

USM3D_VG Lam 

USM3D_VG SA 

9x7 TBC4 

USM3D_VG Lam 

USM3D_VG SA 

Sig Set 

49

105

113

53

107

115

54

109

117

55

111

119

Runs

1537—1561

CFD case 105 

CFD case 113 

1653—1677

CFD case 107 

CFD case 115 

1678—1702

CFD case 109 

CFD case 117 

1703—1727

CFD case 111 

CFD case 119 

Ref Run 

1612

—

—

1624

—

—

1624

—

—

1624

—

—

hNose

61.8

60.0

60.0

61.7

60.0

60.0

61.6

60.0

60.0

61.0

60.0

60.0

_

3.02

3.10

3.10

2.96

3.10

3.10

2.94

3.10

3.10

2.94

3.10

3.10

q ̊

0.1671

0.000

0.000

14.84

15.00

15.00

30.80

30.00

30.00

45.64

45.00

45.00

9x7 WT, 14” aft rail h = 61”, α = 3.0°

USM3D viscous (laminar) h = 60”, α = 3.1°

USM3D viscous (SA) h = 60”, α = 3.1°
128

9.4. Performance Model 

Similar laminar and turbulent USM3D predictions were made by NASA for the larger Performance 

model as for the Boom3 VS3 model, at the same conditions of Mach 1.6, a Reynolds number of 4.1 

million per foot, a height of 60 in., and for the track angles of 0°, 15°, 30°, and 45°. The angle of attack 

for these predictions though was 3.4° since this configuration is of the same design as the Boom1 model 

aside from the difference in mounting provisions. Figure 9–13 shows the surface pressure contours on 

this model for a USM3D turbulent solution, and the symmetry plane flow field pressure contours down to 

a height of 60 in. are shown in Figure 9–14. 

Figure 9–13. Surface pressure contours for Performance model, USM3D SA turbulent results, 

M=1.6, α=3.4° 

Figure 9–14. Symmetry plane pressure contours for Performance model, USM3D SA turbulent 

results, M=1.6, α=3.4° 
129

Note that as shown in these figures, the configuration was modeled in CFD with the sting can at the 

aft end and not the tailored dummy sting (refer to Figures 4–6 and –7). As stated in Section 4.2.1, the 

experimental data presented herein were acquired with the tailored dummy sting, so this represents a 

configuration mis-match in the experiment/CFD comparisons to be presented. The dummy sting surface 

mesh was not available in time for preparation of those results for this report, so the comparisons are 

presented as they are to show the differences/similarities in the front halves of the signatures. 

A set of plots similar to those presented above for the Boom3 model showing the predicted effects of 

off-track angle and comparisons with experimental data are shown in Figures 9–15 and –16. The first 

plot, Figure 9–15, shows the USM3D-SA predictions at the four track angles from 0° to 45°. In this case, 

however, unlike the Boom3 model predictions, the shape and magnitude of the nose shock at all four 

angles are identical, and the signatures overlap up to the start of the wing shock, as one would expect. Aft 

of this point, similar to Boom3, the main expansion pressures become deeper and move forward with offtrack angle. 

Figure 9–15. CFD predictions for effect of off-track angle for Performance model, USM3D SA 

turbulent results, M = 1.6, hNose = 60 in., α = 3.1° 

Comparisons between the experimental data and CFD results (USM3D turbulent SA) for this model 

are presented in Figure 9–16, with the caveat as stated above that the tailored dummy sting was used in 

the experiment and the sting can was used in the CFD. The CFD predictions did not match the 

experimental data in the front half of the signature (ahead of the y0 point—where the mail expansion after 

the highest peak crosses the y = 0 line) nearly as well for this model as they did for the Boom3 model. In 

these Performance model plots, the experimental data show a lot of definition of the small shocks along 

the length of the model that the CFD did not capture. There may be too much variation, however, in the 

measured data for this model, in that the ramp from the nose shock to the wing shock is fairly smooth in 

the Boom1 and Boom3 signatures, leading to some questions about the validity of the data for this model. 

Test

USM3D_VG SA 

USM3D_VG SA 

USM3D_VG SA 

USM3D_VG SA 

Runs

CFD case 134 

CFD case 135 

CFD case 136 

CFD case 137 

hNose

60

60

60

60

_

3.4

3.4

3.4

3.4

q ̊

0

15

30

45

-10 0 10 20 30 40 50 

XAligned (in.) 

-.03

-.02

-.01

0

.01

.02

(6P/P)Data - (

6P/P)Ref

Test

USM3D_VG SA 

USM3D_VG SA 

USM3D_VG SA 

USM3D_VG SA 

Runs

CFD case 134 

CFD case 135 

CFD case 136 

CFD case 137 

hNose

60

60

60

60

_

3.4

3.4

3.4

3.4

q ̊

0

15

30

45

φ = 45° φ = 30°

φ = 15°

φ = 0°
130

Figure 9–16. Experiment/CFD predictions for Performance model at various off-track angles 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, hNose = ~60 in., α = 3.1° to 3.6° 

Test

9x7 TBC4 

USM3D_VG SA 

B OVRFLW NS 

9x7 TBC4 

USM3D_VG SA 

B OVRFLW NS 

9x7 TBC4 

USM3D_VG SA 

B OVRFLW NS 

9x7 TBC4 

USM3D_VG SA 

B OVRFLW NS 

Sig Set 

2

166

170

6

167

171

7

168

172

8

169

173

Runs

199—222

CFD case 166 

CFD case 170 

323—347

CFD case 167 

CFD case 171 

348—372

CFD case 168 

CFD case 172 

373—397

CFD case 169 

CFD case 173 

Ref Run 

119

—

—

119

—

—

119

—

—

119

—

—

hNose

61.8

60.0

62.0

62.3

60.0

62.0

61.2

60.0

62.0

61.8

60.0

62.0

_

3.33

3.40

3.60

3.39

3.40

3.60

3.39

3.40

3.60

3.38

3.40

3.60

q ̊

-0.1199

0.000

0.000

14.92

15.00

15.00

30.23

30.00

30.00

45.72

45.00

45.00

q = 0 ̊

q = 15 ̊

q = 30 ̊

q = 45 ̊

-10 0 10 20 30 40 50 

XAligned (in.) 

-.03

-.02

-.01

0

.01

.02

.03

.04

.05

.06

.07

.08

(6P/P)Data - (

6P/P)Ref

Test

9x7 TBC4 

USM3D_VG SA 

B OVRFLW NS 

9x7 TBC4 

USM3D_VG SA 

B OVRFLW NS 

9x7 TBC4 

USM3D_VG SA 

B OVRFLW NS 

9x7 TBC4 

USM3D_VG SA 

B OVRFLW NS 

Sig Set 

2

166

170

6

167

171

7

168

172

8

169

173

Runs

199—222

CFD case 166 

CFD case 170 

323—347

CFD case 167 

CFD case 171 

348—372

CFD case 168 

CFD case 172 

373—397

CFD case 169 

CFD case 173 

Ref Run 

119

—

—

119

—

—

119

—

—

119

—

—

hNose

61.8

60.0

62.0

62.3

60.0

62.0

61.2

60.0

62.0

61.8

60.0

62.0

_

3.33

3.40

3.60

3.39

3.40

3.60

3.39

3.40

3.60

3.38

3.40

3.60

q ̊

-0.1199

0.000

0.000

14.92

15.00

15.00

30.23

30.00

30.00

45.72

45.00

45.00

9x7 WT, 14” aft rail h = 62”, α = 3.4°

USM3D viscous (SA) h = 60”, α = 3.1°

B OVERFLOW (NS) h = 62”, α = 3.6°
131

Despite this, however, it is clear from the plots that the overall trends of the signature variations with offtrack angle; in particular, matching the main expansions quite well in the 30° and 45° off-track angle 

cases. 

The expansions and shocks aft of the y0 point show significant disagreements between the CFD and 

experimental data, as expected due to the sting can vs. tailored dummy sting differences, though it is 

surprising to see better agreement as the off-track angle is increased. 

10. Propagated Signatures to Ground Level 

Selected near-field pressure signatures from the measured data for the Boom1, Boom3, and 

Performance models were extrapolated to ground level by the sBOOM46 code and their loudnesses 

estimated using a code based on the procedure by Shepherd.47 Flight altitudes of 47,500 ft were assumed 

for all cases since that is the cruise altitude chosen by Boeing in their studies, and the signatures were 

scaled up in X by the inverse of the model scale before being processed in sBOOM. 

No adjustments were made to the measured signatures for input to sBOOM other than truncating them 

so that they began and ended at zero ΔP/P, and ensuring that none of the portions of the signature 

associated with the model support system were included. It is recognized that without correcting the 

signatures to a flight configuration—replacing the model aft end and support system flow field pressures 

with estimated pressures for the full airplane with propulsion system effects—the absolute levels of the 

predicted sonic boom loudnesses will not be right. The low experimental Reynolds number (1 million at 

Mach 1.6 based on Boom1 model chord) relative to that in cruising flight (72 million at Mach 1.6, 47,500 

ft) also contributes to errors in the loudness levels estimated from wind tunnel measurements. However, 

it is the intent in this report to show the estimated ground signatures for the various configurations and to 

highlight their differences both in terms of the signature shapes and the loudness levels. No inferences 

should be made about the PLdB levels quoted for the extrapolated signatures being the final levels 

expected for the selected configurations. Modeling the full-scale vehicle at flight conditions in CFD is 

required for more accurate estimation of the real sonic boom loudness levels. 

10.1. Repeatability 

Near-field signatures showing the repeatability of three Z-sweep run series acquired back-to-back for 

the Performance model in the TBC4 test were shown in Figure 7–8, and these signatures extrapolated to 

ground level are shown in Figure 10–1. The data were acquired at Mach 1.6 in the 9x7 wind tunnel, with 

the model approximately 62 in. from the 14-in. rail at 3.3° angle of attack. The small differences in the 

near-field signatures cause some differences in the ground signatures, particularly in the front ramp 

portions. The first curve, sig set 2, has the highest pressure peak and the greatest loudness by 3 dB over 

the other two curves, indicating the sensitivity of the loudness metric to the small shape differences 

among the repeat runs. 

10.2. Effect of Mach Number 

Two X-sweep run series for the Boom1 model in the 9x7 parametric test showing the signature 

differences between Mach 1.6 and 1.8 were presented in Figure 7–35, and the signatures extrapolated to 

the ground for these run series are presented in Figure 10–2. In the near-field signatures, there was a 

significant increase in the overall pressure levels and shock peaks at Mach 1.8 relative to Mach 1.6, and 

this is also true for ground signatures, where the higher-Mach-number case has a sound level 4.5 dB 

higher than at the lower Mach number. 
132

Figure 10–1. Repeatability of sBOOM-extrapolated signatures for Performance model 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, hNose = ~62 in., α = 3.3° 

Figure 10–2. Effect of Mach number in sBOOM-extrapolated signatures for Boom1 VS2 model 

9x7 parametric test, 14-in. forward rail, M = 1.60, hNose = 30 in., α = 3.4° 

Sig Set 

2

3

4

Runs

199—222

224—247

249—273

Model

Performance Sting+Contour 

Performance Sting+Contour 

Performance Sting+Contour 

Mach

1.60

1.60

1.60

hNose

61.8

61.9

62.5

_

3.3

3.3

3.3

PLdB

96.6

93.6

93.2

0 20 40 60 80 100 120 140 160 180 200 

Time (ms) 

-1.0

-.5

0

.5

1.0

1.5

(6P/P)Data - (

6P/P)Ref

Sig Set 

2

3

4

Runs

199—222

224—247

249—273

Model

Performance Sting+Contour 

Performance Sting+Contour 

Performance Sting+Contour 

Mach

1.60

1.60

1.60

hNose

61.8

61.9

62.5

_

3.3

3.3

3.3

PLdB

96.6

93.6

93.2

Sig Set 

45

38

Runs

1472—1497

1247—1272

Model

Boom1 VS2 

Boom1 VS2 

Mach

1.60

1.80

hNose

30.5

30.1

_

3.4

3.4

PLdB

91.5

96.0

0 20 40 60 80 100 120 140 160 180 200 

Time (ms) 

-1.0

-.5

0

.5

1.0

1.5

(6P/P)Data - (

6P/P)Ref

Sig Set 

45

38

Runs

1472—1497

1247—1272

Model

Boom1 VS2 

Boom1 VS2 

Mach

1.60

1.80

hNose

30.5

30.1

_

3.4

3.4

PLdB

91.5

96.0
133

10.3. Effect of Off-Track Angle 

Boom3 model pressure signatures at 60 in. from the rail at three different off-track angles, 15°, 30°, 

and 45°, as well as undertrack, 0°, were presented in Figure 9–12, and those signatures extrapolated to 

ground level are presented in Figure 10–3. The primary differences among the near-field signatures are in 

the highest pressure peaks just before the main expansions, and in the shocks right after the main 

expansions. In the ground signatures, these differences are apparent in the locations and magnitudes of 

the coalesced shocks toward the front and in the rear shocks. There is a spread of sound levels of around 

7 dB among these signatures, with the 30°- and 45°-angle data having the highest levels. 

Figure 10–3. Effect of off-track angle in sBOOM-extrapolated signatures for Boom3 VS3 model 

9x7 TBC4 test, 14-in. aft rail, M = 1.60, hNose = ~62 in., α = ~3.0° 

11. Performance Model Drag Comparisons 

As part of the evaluation of NASA in-house prediction capability for supersonic transports, CFD drag 

predictions were made for the Boeing Performance model (with the sting can at the rear, not the tailored 

dummy sting). The code used was USM3D, and the grids were generated using VGrid.49 The grid was 

optimized for drag prediction (thus with a viscous solution), and it was not stretched or extended to obtain 

a boom signature at some distance from the model. OVERFLOW predictions from Boeing were also 

included in the study for comparison. 

Drag polar comparisons of experimental data with the USM3D and OVERFLOW predictions are 

shown in Figure 11–1 for the Performance model at M = 1.6, α = 2.75o. The USM3D results compare 

well with the experimental and differ by a maximum of 6 counts of drag (0.0006). Additionally, the 

USM3D results are in closer agreement to wind tunnel data than the Boeing-supplied OVERFLOW

results. 

Sig Set 

49

53

54

55

Runs

1537—1561

1653—1677

1678—1702

1703—1727

Model

Boom3 VS3 

Boom3 VS3 

Boom3 VS3 

Boom3 VS3 

Mach

1.60

1.60

1.60

1.60

hNose

61.8

61.7

61.6

61.0

_

3.0

3.0

2.9

2.9

q ̊

0.2

14.8

30.8

45.6

PLdB

88.7

92.4

95.5

95.0

0 20 40 60 80 100 120 140 160 180 200 

Time (ms) 

-1.0

-.5

0

.5

1.0

1.5

(6P/P)Data - (

6P/P)Ref

Sig Set 

49

53

54

55

Runs

1537—1561

1653—1677

1678—1702

1703—1727

Model

Boom3 VS3 

Boom3 VS3 

Boom3 VS3 

Boom3 VS3 

Mach

1.60

1.60

1.60

1.60

hNose

61.8

61.7

61.6

61.0

_

3.0

3.0

2.9

2.9

q ̊

0.2

14.8

30.8

45.6

PLdB

88.7

92.4

95.5

95.0
134

Figure 11–1. Experiment/CFD comparisons of drag polars for Performance model, 

M = 1.6, α = 2.75o 

Figure 11–2. Experiment/CFD comparisons of turbulence models for Performance model, 

M = 1.6, α = 2.75o 

-0.150 

-0.100 

-0.050 

0.000 

0.050 

0.100 

0.150 

0.200 

0.020 0.021 0.022 0.023 0.024 0.025 0.026 0.027 0.028 

CL 

CD 

Experiment 

USM3D SA 

Boeing OVERFLOW 

-0.150 

-0.100 

-0.050 

0.000 

0.050 

0.100 

0.150 

0.200 

0.020 0.021 0.022 0.023 0.024 0.025 0.026 0.027 0.028 

CL 

CD 

Experiment 

USM3D SA 

Boeing OVERFLOW 

USM3D SST 

USM3D SA, No LimiterNOT CONVERGED 
135

A study of the standard turbulence models used for supersonic testing was also conducted. The bulk 

of the study was conducted with the Spalart-Allmaras (SA) turbulence model.48 Additionally, Menter's 

Sheer Stress Transport (SST) turbulence model48 has shown promise for supersonic predictions, so three 

runs using this model were also made. Figure 11–2 shows the effect of turbulence modeling on the 

computed drag polar. USM3D SA results were closer to the wind tunnel data than Boeing OVERFLOW

and USM3D SST results. For this case, the SST model did a poor job predicting the drag and was 

considerably different from all of the other results. Also included in the figure are the results from an SA

run with out the MINMOD limiter. This limiter is needed for most supersonic flow cases to avoid 

numerical oscillations that result in the code being unable to compute results (NaNs). Historically, the 

use of a limiter has incorrectly predicted the skin-friction drag. Several runs were conducted without the 

use of the limiter. However, none of the runs were fully successful in that the code reported errors and 

terminated. The furthest-processed data point (closest to convergence) is shown, and as can be seen, it 

further deviates from the experimental data than the USM3D SA case with the limiter. In all of the 

limiter-off cases, the drag value moved away from the USM3D results and closer to the Boeing 

OVERFLOW predictions. 

A grid convergence study using USM3D SA was conducted as part this computational analysis of the 

Boeing Performance model. The locations of the sourcing remained constant, although the size of the 

grid cell dictated by the source was altered both up and down by an overall scaling factor. Five grids 

were created ranging from 26.5 to 72.2 million grid cells. Figure 11–3 shows that as the grid size 

increased the code converged to a smaller drag number for the given point. The difference between the 

68.9- and 72.2-million-point grids was less that 0.1 percent. Consequently, the 68.9-million-point grid 

was used for the study (this was the original grid produced). 

Finally, a comparison of results from a grid designed for boom prediction and a grid designed for 

drag prediction was made. The boom-stretched grid was created by VGrid, then sourced by AUTOSRC

and SSGRID to stretch the grid. These methods were introduced in 2008 as part of the NASA 

Fundamental Aeronautics Program Sonic Boom Prediction Workshop.52 The grid had 34 million grid 

cells and was stretched for the case at Mach 1.6 with an angle of attack of 2.75°. The results are 

compared to the baseline 68.9-million-point grid in Figure 11–4 and differed by over 2.4 counts of drag 

although the lift coefficient did increase slightly. An additional grid was therefore made to try to reduce 

this difference. This new grid used the sourcing from the baseline case, but had a volume source inserted 

under the model (as AUTOSRC adds) and a smaller outer boundary. SSGRID was then used to stretch the 

grid for the same Mach 1.6, angle of attack 2.75° case. The resultant grid had approximately 67 million 

cells, and the drag results are much closer to the baseline results, differing by less than one-tenth of a drag 

count. 
136

Figure 11–3. Grid convergence study for Performance model, M = 1.6, α = 2.75o 

Figure 11–4. Effect of gridding style on drag prediction for Performance model, M = 1.6, α = 2.75o 

-0.100 

-0.050 

0.000 

0.050 

0.100 

0.150 

0.021 0.022 0.023 0.024 0.025 0.026 

CL 

CD 

26.5 mil 

30.2 mil 

43.8 mil 

68.9 mil Baseline 

72.2 mil 

-0.100 

-0.050 

0.000 

0.050 

0.100 

0.150 

0.021 0.022 0.023 0.024 0.025 0.026 

CL 

CD 

68.9 mil Baseline 

Boom-Stretched Grid 34 mil 

Stretched Grid 67 mil 
137

12. Concluding Remarks 

Near-field pressure signatures were measured and computational predictions made for three models 

representing Boeing’s Quiet Experimental Validation Concept (QEVC) supersonic transport as well as for 

an axisymmetric calibration model. Experimental sonic boom pressure signatures were acquired 

primarily at Mach 1.6 and 1.8 in wind tunnel tests conducted during Phases I and II of a NASA Research 

Announcement (NRA) contract for Experimental Systems Validations for N+2 Supersonic Commercial 

Transport Aircraft, which was led by the NASA High Speed Project under the Fundamental Aeronautics 

Program. 

The sonic boom test data were obtained using a 14-in. tapered “RF1” rail and a 2-in. flat-top rail. 

Both rails captured an entire pressure signature in one data point, and successive signatures at varying 

positions along or above the rail were used to improve data quality through spatial averaging. The sonic 

boom data obtained by the rails were validated with high-fidelity numerical simulations of off-body 

pressures. The test results generally showed good agreement between the computational and experimental 

data when a variety of testing techniques including spatial averaging of a series of pressure signatures 

were employed. The two wind tunnels generally produced comparable data. 

The spatially-averaged sonic boom test data generally showed good agreement with computational 

predictions. The use of the RF1 rail combined with spatial averaging of aligned signatures with different 

axial positions and constant altitude masked the wind tunnel distortions seen in the individual pressure 

signatures at most fixed model positions in the wind tunnel. The rail data were, as predicted, free from 

model shock reflections for the boom model. The data from these wind tunnel tests proved that accurate 

data with reasonable acquisition time is obtainable in the Ames 9x7 and Glenn 8x6 supersonic wind 

tunnels. 

In summary, the wind tunnel test provided validation data that provides the confidence in the CFD 

methods to predict the sonic boom pressures of complex vehicles. CFD, regardless of flow solver, with an 

Mach aligned mesh, is able to fairly accurately predict the sonic boom levels and the next step towards 

realization of civilian supersonic transportation would be the design and CFD evaluation of flight vehicles 

with vehicle flight demonstration testing with true atmospheric effects. 

The high-fidelity sonic boom pressure data from the recent tests will aid in the development of 

improved computational and grid generation techniques for sonic boom analysis in the future by 

providing the data and model geometries to the supersonic aircraft development community. 
138

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142

Appendix A 

Listing of Experimental Run Sweeps Plotted 

Test Model Rail Swp Mach hNose 

(in.)

XRam 

(in.) α° φ° Sig 

Set 

Run 

Sweeps* Figures 

97p AS2 14" 

Fwd 

X 1.6 30 7.9–

23.8 

0 0 33 1080–1105: 

1079 

6-12,13,14,15 

97p AS2 14" 

Fwd 

X 1.6 30 7.9–

23.8 

0 0 33 1080–1105: 

1106 

6-13,14,15; 

7-6,14,22; 9-3 

97p AS2 14" 

Fwd 

X 1.6 31.8 8–

23.8 

0 0 34 1107–1132: 

1133 

7-6 

97p AS2 14" 

Fwd 

Z 1.6 26–34 16 0 0 31 1010–1043: 

1009 

7-1 

97p AS2 14" 

Fwd

Z 1.6 26–34 16 0 0 31 1010–1043: 

1044

7-6,14,19

97p AS2 14" 

Fwd 

Z 1.6 26–34 24 0 0 32 1045–1078: 

1079 

7-6,14,19,23 

97p AS2 2" 

Fwd 

X 1.6 30 8–

23.8 

0 0 54 1759–1784: 

1785 

7-22 

97p AS2 2" 

Fwd 

Z 1.6 26–34 24 0 0 55 1786–1818: 

1819 

7-23 

97p Boom1 

VS2 

14" 

Fwd 

X 1.6 30 8–

23.8 

3.4 0 45 1472–1497: 

1498 

6-4; 7-10,35 

97p Boom1 

VS2 

14" 

Fwd 

X 1.6 30 8–

23.8 

3.4 0 46 1500–1525: 

1499 

7-10,12,15,25 

97p Boom1 

VS2 

14" 

Fwd 

X 1.6 30 8–

23.8 

3.4 0 47 1526–1551: 

1552 

7-10 

97p Boom1 

VS2 

14" 

Fwd 

X 1.8 30 8–

23.8 

3.4 0 38 1247–1272: 

1273 

6-4; 

7-11,35,44,49 

97p Boom1 

VS2 

14" 

Fwd 

X 1.8 30 8–

23.8 

3.4 0 39 1274–1299: 

1300 

7-11,13,16 

97p Boom1 

VS2 

14" 

Fwd 

X 1.8 30 8–

23.8 

3.4 20 40 1301–1326: 

1327 

7-44 

97p Boom1 

VS2 

14" 

Fwd 

X 1.8 30 8–

23.8 

3.4 30 41 1328–1353: 

1354 

7-44 

97p Boom1 

VS2 

14" 

Fwd 

X 1.8 30 8–

23.8 

3.4 40 42 1373–1398: 

1399 

7-44 

97p Boom1 

VS2 

14" 

Fwd 

Z 1.6 26–34 24 3.4 0 43 1401–1433: 

1434 

6-6; 

7-15,20,24 

97p Boom1 

VS2 

14" 

Fwd 

Z 1.6 26–34 16 3.4 0 44 1437–1469: 

1470 

6-6; 7-15,20; 

9-7 

97p Boom1 

VS2 

14" 

Fwd 

Z 1.8 26–34 24 3.4 0 35 1144–1176: 

1177 

7-40 

97p Boom1 

VS2 

14" 

Fwd 

Z 1.8 26–34 24 3.4 0 36 1179–1211: 

1212 

6-6; 7-21,40 

97p Boom1 

VS2 

14" 

Fwd 

Z 1.8 26–34 16 3.4 0 37 1213–1245: 

1246 

6-6; 7-16,21 

97p Boom1 

VS2 

14" 

Aft 

X 1.6 60 0–

15.8 

3.4 0 61 2047–2072: 

2073 

6-4; 

7-3,7,12,28; 

9-8 

97p Boom1 

VS2 

14" 

Aft 

X 1.6 60 0–

15.8 

3.4 0 62 2074–2099: 

2100 

7-7,37,48 
143

Test Model Rail Swp Mach hNose 

(in.)

XRam 

(in.) α° φ° Sig 

Set 

Run 

Sweeps* Figures 

97p Boom1 

VS2 

14" 

Aft 

X 1.8 60 0–

23.9 

3.4 0 60 2006–2044: 

2045 

6-4,13; 

7-13,29,37,49 

97p Boom1 

VS2 

2" 

Fwd 

X 1.6 30 8–

23.8 

3.4 0 53 1724–1749: 

1750 

6-4; 

7-17,25,36,50 

97p Boom1 

VS2 

2" 

Fwd 

X 1.8 30 8–

23.8 

3.4 0 51 1662–1687: 

1688 

6-4; 

7-18,36,51 

97p Boom1 

VS2 

2" 

Fwd 

Z 1.6 26–34 24 3.4 0 52 1690–1722: 

1723 

6-6; 7-17,24 

97p Boom1 

VS2 

2" 

Fwd 

Z 1.8 26–34 24 3.4 0 48 1567–1599: 

1600 

6-6 

97p Boom1 

VS2 

2" 

Fwd 

Z 1.8 26–34 16 3.4 0 49 1601–1633: 

1634 

7-18 

TBC3 AS2 2" X 1.56 59 16–

23.9 

0 – 111 1162–1187: 

1188 

7-2; 9-4 

TBC3 Boom1 

VS2 

14" X 1.56 59 0–7.9 3.4 – 66 863–888: 

862 

7-30 

TBC3 Boom1 

VS2 

14" X 1.56 59 0–7.9 3.4 – 66 863–888: 

889 

6-5; 7-26,48 

TBC3 Boom1 

VS2 

14" X 1.56 59 0–7.9 3.4 – 77 966–991: 

957 

7-30 

TBC3 Boom1 

VS2 

14" X 1.56 59 0–7.9 3.4 – 77 966–991: 

992 

6-5 

TBC3 Boom1 

VS2 

14" X 1.78 49 0–7.9 3.4 – 61 818–843: 

817 

7-31 

TBC3 Boom1 

VS2 

14" X 1.78 49 0–7.9 3.4 – 61 818–843: 

844 

6-5,13; 

7-27,49 

TBC3 Boom1 

VS2 

14" X 1.78 49 0–7.9 3.4 – 70 912–937: 

911 

7-31 

TBC3 Boom1 

VS2 

14" X 1.78 49 0–7.9 3.4 – 70 912–937: 

938 

6-5 

TBC3 Boom1 

VS2 

14" Z 1.78 39.5–

44.6 

0 3.4 – 36 443–467: 

468 

6-7 

TBC3 Boom1 

VS2 

14" Z 1.78 39.6–

44.5 

0 3.4 – 31 367–391: 

392 

6-7 

TBC3 Boom1 

VS2 

14" Z 1.78 46.1–

64 

0 3.4 – 40 500–536: 

499 

6-7 

TBC3 Boom1 

VS2 

2" X 1.56 59 0–7.9 3.4 – 93 1060–1085: 

1086 

6-5; 7-26,50 

TBC3 Boom1 

VS2 

2" X 1.78 49 0–7.9 3.4 – 81 1008–1033: 

1034 

6-5; 7-27,51 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 58.6–

64.7 

0 4 0 51 1587–1611: 

1612 

7-41 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 58.8–

64.8 

0 3 0 49 1537–1561: 

1612 

7-38,41,45; 

9-12 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 58.8–

64.8 

0 3.5 0 50 1562–1586: 

1535 

7-32 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 58.8–

64.8 

0 3.5 0 50 1562–1586: 

1612 

7-28,41 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 59–65 0 2.6 0 52 1628–1652: 

1624 

7-4,41 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 59–65 0 3 15 53 1653–1677: 

1624 

7-45; 9-12 
144

Test Model Rail Swp Mach hNose 

(in.)

XRam 

(in.) α° φ° Sig 

Set 

Run 

Sweeps* Figures 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 59–65 0 3 30 54 1678–1702: 

1624 

7-45; 9-12 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 59–65 0 3 45 55 1703–1727: 

1624 

7-45; 9-12 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 59–65 0 3.5 0 60 1843–1867: 

1816 

7-32 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.6 59–65 0 3.5 0 65 1980–2004: 

1953 

7-32 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.8 59.5–

64.5 

0 3 0 56 1730–1754: 

1728 

7-38 

TBC4 Boom3 

VS3 

14" 

aft 

Z 1.8 59.5–

64.5 

0 3.5 0 57 1755–1779: 

1728 

7-29 

TBC4 Boom3 

VS4 

14" 

aft 

Z 1.6 59.5–

65.6 

0 3.4 0 43 1365–1389: 

1390 

7-28 

TBC4 Boom3 

VS4 

14" 

aft 

Z 1.8 59.3–

64.3 

0 3.1 0 47 1473–1497: 

1523 

7-29 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 58.2–

64.3 

0 3.3 30 7 348–372: 

119 

7-46; 9-16 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 58.3–

64.3 

0 3.3 0 32 1043–1067: 

119 

7-33 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 58.7–

64.7 

0 3.8 0 5 274–298: 

119 

7-42 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 58.8–

64.9 

0 3.3 45 8 373–397: 

119 

7-46; 9-16 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 59.3–

65.4 

0 3.3 15 6 323–347: 

119 

7-46; 9-16 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 59.6–

64.1 

0 3.3 0 2 199–222: 

119 

7-8,39,42,46; 

9-16 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 59.6–

64.1 

0 3.3 0 3 224–247: 

119 

7-8,33,34 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 59.6–

65.5 

0 3.3 0 4 249–273: 

119 

7-8 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 59.6–

65.6 

0 3.3 0 37 1180–1204: 

119 

7-34 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 59.6–

64.4 

0 2.8 0 1 151–175: 

119 

7-42 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 59.7–

65.7 

0 3.3 0 17 612–636: 

119 

7-33 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.6 60.2–

66.3 

0 3.6 0 24 830–854: 

119 

7-34 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.8 58.1–

63.1 

0 3.3 30 14 526–550: 

116 

7-47 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.8 58.6–

63.7 

0 3.3 45 15 551–575: 

116 

7-47 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.8 59–

64.1 

0 3.3 0 9 401–425: 

116 

7-9,42 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.8 59.2–

64.2 

0 3.3 15 13 501–525: 

116 

7-47 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.8 59.2–

64.3 

0 3.9 0 10 426–450: 

116 

7-42 

TBC4 Perf sting 

+ contour 

14" 

aft 

Z 1.8 59.4–

64.5 

0 3.3 0 12 476–500: 

116 

7-9,39,47 

*

 Run sweeps nomenclature: sweep start–end: reference 
145

Appendix B 

Listing of Reference Runs Plotted 

Test Model Rail Mach hNose 

(in.)

XRam 

(in.) α° φ° Runs Figure 

97p Boom1 VS2 14" Fwd 1.8 52 0 3.4 0 1178 54 

97p Boom1 VS2 14" Fwd 1.8 52 0 3.4 20 1327 54 

97p Boom1 VS2 14" Fwd 1.8 52 0 3.4 30 1372 54 

97p Boom1 VS2 14" Fwd 1.8 52 0 3.4 40 1399 54 

97p Boom1 VS2 14" Aft 1.6 82 0 5 0 2100 60 

97p Boom1 VS2 14" Aft 1.6 82 0 5 0 2046 64 

97p Boom1 VS2 14" Aft 1.6 82 0 5 0 2100 64 

97p Boom1 VS2 14" Aft 1.8 82 0 5 0 1989 61 

97p Boom1 VS2 14" Aft 1.8 82 0 5 0 1989 65 

97p Boom1 VS2 14" Aft 1.8 82 0 5 0 2045 65 

97p Boom1 VS2 2" Fwd 1.6 52 0 3.4 0 1750 62 

97p Boom1 VS2 2" Fwd 1.6 52 0 3.4 0 1689 66 

97p Boom1 VS2 2" Fwd 1.8 52 0 3.4 0 1688 63 

97p Boom1 VS2 2" Fwd 1.8 52 0 3.4 0 1688 67 

97p LB 1021, blade 14" Fwd 1.6 52 0 2.3 0 862 52 

97p LB 1021, blade 14" Fwd 1.6 52 0 2.3 0 1004 52 

97p LB 1021, blade 14" Fwd 1.6 52 0 2.3 0 397 53 

97p LB 1021, blade 14" Fwd 1.6 52 0 2.3 0 831 53 

97p LB 1021, blade 14" Fwd 1.6 52 0 2.3 0 862 60 

97p LB 1021, blade 14" Fwd 1.6 52 0 2.3 0 862 66 

97p LB 1021, blade 14" Fwd 1.6 52 0 2.3 20 883 52 

97p LB 1021, blade 14" Fwd 1.6 52 0 2.3 30 904 52 

97p LB 1021, blade 14" Fwd 1.6 53 0 2.3 0 564 53 

97p LB 1021, blade 14" Fwd 1.8 52 0 2.3 0 764 61 

97p LB 1021, blade 14" Fwd 1.8 52 0 2.3 0 764 67 

97p LB 1021, blade 14" Fwd 1.8 53 0 2.3 0 604 55 

97p LB 1021, blade 14" Fwd 1.8 53 0 2.3 0 633 55 

97p LB 1021, blade 14" Fwd 1.8 53 0 2.3 0 692 55 

97p LB 1021, blade 14" Fwd 1.8 53 0 2.3 0 699 55 

TBC3 AS2 14" 1.8 67.86 0 0 — 549 58 

TBC3 AS2 14" 1.8 67.9 0 0 — 575 58 

TBC3 Boom1 VS2 14" 1.6 59 0 3.4 — 862 56 

TBC3 Boom1 VS2 14" 1.6 59 0 3.4 — 889 56 

TBC3 Boom1 VS2 14" 1.6 59 0 3.4 — 957 56 

TBC3 Boom1 VS2 14" 1.6 59 0 3.4 — 992 56 

TBC3 Boom1 VS2 14" 1.8 63.68 0 0 — 392 58 

TBC3 Boom1 VS2 14" 1.8 63.83 0 0 — 366 58 

TBC3 Boom1 VS2 14" 1.8 63.83 0 0 — 413 58 

TBC3 Boom1 VS2 14" 1.8 63.83 0 0 — 366 59 

TBC3 Boom1 VS2 14" 1.8 64 0 0 — 815 57 

TBC3 Boom1 VS2 14" 1.8 64 0 0 — 816 57 

TBC3 Boom1 VS2 14" 1.8 64 0 0 — 815 59 

TBC3 Boom1 VS2 2" 1.557 59 0 3.4 — 1103 62 

TBC3 Boom1 VS2 2" 1.557 59 0 3.4 — 1103 68 

TBC3 Boom1 VS2 2" 1.775 49 0 3.4 — 1051 63 

TBC3 Boom1 VS2 2" 1.775 49 0 3.4 — 1051 69 

TBC3 Cone fairing 14" 1.6 68 0 0 — 771 60 
146

Test Model Rail Mach hNose 

(in.)

XRam 

(in.) α° φ° Runs Figure 

TBC3 Cone fairing 14" 1.6 68 0 0 — 771 68 

TBC3 Cone fairing 14" 1.8 68 0 0 — 738 61 

TBC3 Cone fairing 14" 1.8 68 0 0 — 738 69 

TBC4 Strut cone 14" aft 1.6 58 0 -7.5 0 113 64 

TBC4 Strut cone 14" aft 1.6 58 0 -7.5 0 119 64 

TBC4 Strut cone 14" aft 1.8 58 0 -7.5 0 110 65 

TBC4 Strut cone 14" aft 1.8 58 0 -7.5 0 116 65