Robert F. Handschuh

Glenn Research Center, Cleveland, Ohio

Michael J. Hurrell

TFOME—Jacobs Technology, Inc, Cleveland, Ohio

Initial Experiments of High-Speed Drive System 

Windage Losses

NASA/TM—2011-216925

November 2011
NASA STI Program . . . in Profi le

Since its founding, NASA has been dedicated to the 

advancement of aeronautics and space science. The 

NASA Scientifi c and Technical Information (STI) 

program plays a key part in helping NASA maintain 

this important role.

The NASA STI Program operates under the auspices 

of the Agency Chief Information Offi cer. It collects, 

organizes, provides for archiving, and disseminates 

NASA’s STI. The NASA STI program provides access 

to the NASA Aeronautics and Space Database and 

its public interface, the NASA Technical Reports 

Server, thus providing one of the largest collections 

of aeronautical and space science STI in the world. 

Results are published in both non-NASA channels 

and by NASA in the NASA STI Report Series, which 

includes the following report types:

• TECHNICAL PUBLICATION. Reports of 

completed research or a major signifi cant phase 

of research that present the results of NASA 

programs and include extensive data or theoretical 

analysis. Includes compilations of signifi cant 

scientifi c and technical data and information 

deemed to be of continuing reference value. 

NASA counterpart of peer-reviewed formal 

professional papers but has less stringent 

limitations on manuscript length and extent of 

graphic presentations.

• TECHNICAL MEMORANDUM. Scientifi c 

and technical fi ndings that are preliminary or 

of specialized interest, e.g., quick release 

reports, working papers, and bibliographies that 

contain minimal annotation. Does not contain 

extensive analysis.

• CONTRACTOR REPORT. Scientifi c and 

technical fi ndings by NASA-sponsored 

contractors and grantees.

• CONFERENCE PUBLICATION. Collected 

papers from scientifi c and technical 

conferences, symposia, seminars, or other 

meetings sponsored or cosponsored by NASA.

• SPECIAL PUBLICATION. Scientifi c, 

technical, or historical information from 

NASA programs, projects, and missions, often 

concerned with subjects having substantial 

public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientifi c and 

technical material pertinent to NASA’s mission.

Specialized services also include creating custom 

thesauri, building customized databases, organizing 

and publishing research results.

For more information about the NASA STI 

program, see the following:

• Access the NASA STI program home page at 

http://www.sti.nasa.gov

• E-mail your question via the Internet to help@

sti.nasa.gov

• Fax your question to the NASA STI Help Desk 

at 443–757–5803

• Telephone the NASA STI Help Desk at

 443–757–5802

• Write to:

 NASA Center for AeroSpace Information (CASI)

 7115 Standard Drive

 Hanover, MD 21076–1320
Robert F. Handschuh

Glenn Research Center, Cleveland, Ohio

Michael J. Hurrell

TFOME—Jacobs Technology, Inc, Cleveland, Ohio

Initial Experiments of High-Speed Drive System 

Windage Losses

NASA/TM—2011-216925

November 2011

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

International Conference on Gears

cosponsored by the (CO) BGA, CMES, FVA, GCOE, IMechE, JSME, KIVI-NIRIA, and GTE

Garching, Germany, October 4–6, 2010
Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2011-216925 1 

Initial Experiments of High-Speed Drive System Windage Losses 

Robert F. Handschuh 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Michael J. Hurrell 

TFOME—Jacobs Technology, Inc. 

Cleveland, Ohio 44135 

Abstract 

High speed gearing performance is very important to the overall drive system efficiency. Certain 

losses such as gear meshing and bearing drag can be minimized by design changes such as pressure angle 

of the gears and the geometry and type of bearings being used. One component that can have a large 

effect on the overall performance of high-speed drive systems is the parasitic drag known as gear 

windage. This loss mechanism is not well understood and minimizing this component is usually 

accomplished through much trial and error. The results presented in this paper will document some of the 

design parameter effects on the amount of windage losses. A new test facility at NASA Glenn has been 

assembled to systematically study the design variables. Results from recent tests will be presented. The 

tests are for a single gear, with and without lubricants, and some initial studies using shrouds. 

1.0 Introduction 

Power loss in high-speed gear systems due to windage can be a substantial portion of the total losses 

of the drive system. In the open literature this topic has not been investigated to the levels of other 

important gear research topics. However, in high speed gearing this loss mechanism is very important. 

When pitch line velocity is above 125 m/s (25000 ft/min), windage losses can be half or more of the 

total losses from the drive system. The rest of the losses can be summarized as that due to the gear 

meshing, bearings, and seals in the drive system under study (Refs. 1and 2). 

In prior work (Ref. 3) the gear windage effect on drive system power loss was extrapolated from 

work done on gas turbine disk power loss. Using this approach, the results were found from a few simple 

calculations and were dependent on the diameter and rotational speed. For a spur gear, the losses were 

found to be related to the gear size to the 3rd power and rotational speed to the 5th power. 

In the studies of Dawson (Refs. 4 and 5), a more gear-like representation was provided. Many typical 

gear features were varied such as gear helix angle, diameter to face width ratio, enclosure factor, and 

environmental quantities (viscosity and density). Power loss was found by the decelerated of the system. 

The data was then used to generate a calculation procedure for a single gear. A further refinement on the 

dependencies of gears and rotational speed were found. 

Winfree (Ref. 6) presented windage issues for intersecting axis gearing (spiral bevel). Gears were 

operated in a manner that the windage driven fluid could be observed. In this study, shrouding location, 

clearance, and shroud exit locations were investigated. Also, the power to drive the system was measured 

and therefore the most efficient arrangements were found. Shrouds on the gears helped reduce the losses 

on the order of 70% on test run to 25,000 ft/min (127 m/s). Also it was found that the closer the shrouding 

the lower the power loss. 

The work of Diab et al. (Ref. 7) also investigated the windage losses of a single gear that was rotated 

in an ambient (air) environment. Their data was then compared to prior methods and their own 

formulation to predict the windage loss behavior. 
NASA/TM—2011-216925 2 

In some recent work (Refs. 8 to 12), analytical and experimental studies on gear windage have been 

accomplished. The use of computational fluid dynamic (CFD) methods has begun to be applied to this 

very difficult problem. Not only is the modelling difficult, especially through the meshing zone, but also 

many other aspects such as two-phase flow and shrouding can further complicate the process to provide 

and accurate assessment of the power losses. 

The objective of this initial study was to investigate the windage behavior of a single, fairly large spur 

gear. Tests were conducted from low to very high rotational speed—where windage losses can be the 

dominant source. Tests were conducted with and without lubricant present, and/or using shrouding. The 

data that has been generated in this study can be used for analytical model validation or empirical model 

verification for very high-speed conditions. 

2.0 Test Facility 

The test facility used in this study is the newly operational Gear Windage Test Facility at NASA 

Glenn Research Center. A sketch of the test facility is shown in Figure 1. The facility has a 112 kW 

(150 hp) DC drive motor that is connected to a 5.7:1 speed up gearbox. The output of the speed-up 

gearbox then is connected to a torque meter prior to coupling connection of the input shaft to the test 

gearbox. The input and output shafts have hydraulically operated clutches that allow the facility (in single 

or dual shaft mode) to be disconnected from the power applier and/or magnetic brake attached to the 

output shaft. With the speed capability of the drive motor and speed increasing gearbox and the 

dimensions of the test specimen, the pitch line velocity can be taken to 280 m/s (~55,000 ft/min). 

Figure 1.—Overview sketch of the NASA Glenn Research Center 

Gear Windage Rig. 

 
NASA/TM—2011-216925 3 

The test gears can be run in the gearbox with or without shrouding. The shrouding clearance can be 

adjusted radially and axially. In the data presented in this paper, only results from a single spur gear will 

be discussed. The gear under test in this report is given in Table 1 and the maximum and minimum 

shroud clearances are provided in Table 2. A sketch of the shrouding arrangement is shown in Figure 2. 

Due to the high-speed conditions of the facility, safety precautions were taken to provide safe 

operation at the extremely high rotational speed. A photograph of the facility with containment shield in 

place is shown in Figure 3. 

The shroud arrangement used in this study is shown in Figures 4 to 6. In Figure 4 the shroud is shown 

adjusted at the minimum conditions for the gear used in this study. The outer housing provided support 

and kept the shroud in alignment via circumferentially machined groves. The radial clearance was 

maintaining via grooves machined on the sides of the shrouds. 

Table 1.—Basic Gear Dimensions 

Number of teeth 52 

Pitch / module, 1/in. (mm) 4 (6.35) 

Face Width in. (mm) 1.12 (28.4) 

Pitch Diameter, in. (mm) 13.0 (330.2) 

Pressure Angle, deg. 25 

Outside Diameter, in. (mm) 13.49 (342.65) 

Table 2.—Shroud to Gear Clearances Used in Testing 

 Minimum Maximum 

Radial, in. (mm) 0.034 (0.864) 0.656 (16.66) 

Axial, in. (mm) 0.05 (1.27) 1.19 (30.23) 

Figure 2.—Shrouding assembly for the test facility. 
NASA/TM—2011-216925 4 

Figure 3.—Photograph of the test gearbox with containment 

shield in place. 

Figure 4.—Shroud before installation in test 

facility, showing adjustability of clearance 

radially and axially. 

Figure 5 shows the support and bottom shroud fastened inside the test gearbox at the minimum radial 

and axial conditions for the gear used in this study. Figure 6 shows the entire shroud arrangement for a 

single gear with a block off plate for the instrumentation and lubrication jet. If there were another gear 

meshing, then the meshing zone would be in this region occupied by the block-off plate. 
NASA/TM—2011-216925 5 

Figure 5.—Bottom shroud installed with closest axial and 

radial clearances. 

Figure 6.—Shroud installed in test facility in minimum axial and radial 

clearances. 

3.0 Test Procedure and Data Acquisition 

The facility was operated at a series of increasing drive motor speeds. At each of these conditions 

several different data were collected. The drive motor speed, torque applied to rotate the test hardware, 

internal shroud (fling-off) temperature, and internal shroud static pressure data were taken at steady drive 

motor speed conditions. Data was taken and then the speed was incremented up a given drive motor speed 

from 500 to 3125 RPM (or 2587 to 16168 RPM of the gear shaft). The data was taken from motor 

controller speed, a commercially available torque meter for torque, thermocouple for inside shroud 

temperature (fling-off), and a manometer. 
NASA/TM—2011-216925 6 

4.0 Test Results 

In order to determine the effects of the gear-only windage a separate test was conducted with the 

entire system in place minus the gear. The data from that test is shown in Figure 7. The losses from this 

test were mainly the support bearing and seal losses from the input shaft. Since the data to be presented in 

this paper were for a single gear, this test was sufficient to determine these facility support losses over the 

speed range of the tests to be discussed. The data from Figure 7 was used to remove these facility losses 

from the total losses measured when conducting tests. 

4.1 Closed Shroud Results 

One of the environmental-facility test conditions that was conducted included running the gear in the 

shroud system without a drain hole (slot) in the shrouding. This test could only be conducted in an air 

only environment since there would be no circumferential drain holes in the shroud to allow for 

evacuation of the lubricating oil. This data was used in the modeling effort conducted in Reference 12. 

This was done with the shrouding at minimum and maximum conditions for the shrouds (Table 2). The 

data with the tare losses removed is shown in Figure 8. From this figure the shroud losses are much more 

for the case of large clearance and becomes much more efficient when the shrouding is pulled in close to 

the gear at the minimum radial and axial clearances. The data indicates that the radial clearance affects are 

more important than the axial clearance. The windage loss was reduced by over 50 percent by minimizing 

the radial and axial clearance as compared to the shrouds in the maximum radial and axial clearance 

configuration. 

Also, during these tests data was taken from a thermocouple and static pressure probe on the outer 

circumference of the shroud at the mid point across the gear tooth face width. The thermocouple and 

static pressure probes enabled the shroud internal temperature and pressure to be tracked during the 

stepped increase of rotational speed of the gear-shaft assembly. The data from these two sensors are 

shown in Figures 9 and 10, respectively. 

The data shown in Figure 9 was not a steady state value (thermally), but more an indicator of shroud 

pitch line velocity effects. Once again the minimum axial and radial clearance produced the lowest flingoff temperatures. 

Figure 7.—Input shaft only results. 

Figure 8.—Closed shroud windage power loss as a 

function of pitch line velocity. 
NASA/TM—2011-216925 7 

Figure 9.—Closed shroud fling-off temperature as a function 

of pitch line velocity. 

Figure 10.—Closed shroud static pressure as a function 

of pitch line velocity. 

Figure 11.—Windage power loss for single gear with 

1-in. circumferential drain, with and without 

lubricant present. 

Finally in Figure 10 for the closed shroud data, the static pressure at the shroud wall is presented as a 

function of pitch line velocity. The minimum axial and radial clearance had a reduced static pressure 

when compared to the other arrangements. 

4.2 Shroud With Drain Slot 

Another series of tests were run with the single gear inside a shroud with a single drain slot, with and 

without the lubricating oil present. The tests were first conducted in air to ensure that no lubricant was 

inside the shroud, and then the lubricant would be turned on and the test sequence repeated. The 

lubricating jet temperature was maintained near the ambient conditions. 

The data for the windage power loss is shown in Figure 11. The shrouding was positioned as shown 

in Table 2 for the minimum and maximum radial and axial positions. The lubricant, when present, was 

injected radially at the mid-face width location at a pressure of ~100 psi and with a flow rate of ~0.4 gpm. 

The lubricant then drains out of the shroud (1 in. rectangular slot) located at the bottom. As can be seen 
NASA/TM—2011-216925 8 

from Figure 11, the minimum axial and radial shroud locations produced the lowest power loss. When 

compared to the maximum-maximum conditions (Table 2), the minimum clearances had at least a 4X 

decrease in power loss. 

The fling-off temperature and static pressure data are shown in Figures 12 and 13 for the same tests as 

already discussed in Figure 11. For all cases the “air and lube” condition immediately followed the “air 

only” condition. The residual heat from the “air only” test resulted in an elevated initial fling-off 

temperature for the “air and lube” test. With the introduction of the relatively cooler lubricant (~room 

temperature) at the beginning of the test, the “air and lube” fling-off temperature exhibited a negative 

trend with increasing speed. However, the work on the air-lube mixture from the rotating gear and shaft 

assembly eventually reversed this trend in fling-off temperature as shown in this figure. 

As mentioned in the earlier discussion, the temperature data shown was not a steady state value. Data 

was taken relatively quickly as the speed and torque data stabilized. For the data shown in Figures 12 and 

13, the minimum radial, maximum axial clearance shrouding produced the lowest fling-off temperature 

and static pressure. The maximum radial clearances produced the highest fling-off temperatures and static 

pressures. 

Figure 12.—Fling-off temperature for single gear, 1-in. 

circumferential drain, with and without lubricant present. 

Figure 13.—Static pressure for single gear, 1-in. circumferential 

drain, with and without lubricant present. 
NASA/TM—2011-216925 9 

Figure 14.—No shroud windage power loss. 

4.3 No Shroud Results 

Finally the data from the same gear operating with and without lubricant flowing and without a 

shroud is presented. This arrangement produced the largest losses from a windage standpoint as compared 

to any of the other shrouded conditions discussed in this paper. The data for the no-shroud conditions is 

shown in Figure 14 for windage power loss. For the highest speed conditions the losses were 3 to 5 times 

greater than that of the worst performing shrouded conditions. 

Conclusions 

A study was conducted to determine the windage power loss from a single gear. The gear was 

operated from 8800 to 55000 ft/min (44.7 to 279.5 m/s) pitch line velocity. The gear was run in an 

enclosed shroud, a shroud with a single drain slot and completely without shrouds. For the shroud with a 

drain and no shroud conditions the gear was run with and without a lubricating jet present. 

The following conclusions can be drawn from this preliminary study: 

1. For very high pitch line velocities shrouding, even loosely fitting to the rotating gear is extremely 

beneficial in reducing windage power losses. 

2. Minimum axial and radial clearance between the shrouding and the gear tips and gear sides 

produced the lowest windage power losses. 

3. For the closed shroud tests (air only), the fling-off temperature and static pressure followed the 

same trends as the windage power loss. 

4. For the data taken with drained shrouds, the minimum axial and radial clearance conditions 

produced the lowest windage power loss, fling-off temperatures, and lowest static pressure. 

References 

1. Handschuh, R., and Kilmain, C.: “Preliminary Investigation of the Thermal Behavior of High-Speed 

Helical Gear Trains,” International Conference on Gears, Munich, Germany, March 2002, 

NASA/TM—2002-211336, ARL TR–2661. 

2. Handschuh, R. and Kilmain, C.: “Operational Influence on Thermal Behavior of High-Speed Helical 

Gear Trains, “American Helicopter Society, Forum 62, Phoenix, AZ, May 9–11, 2006. 

3. Townsend, D.: Dudley’s Gear Handbook, 2nd Edition, McGraw-Hill, Inc., 1992. 
NASA/TM—2011-216925 10 

4. Dawson, P.H.: “Windage Loss in Larger, High-Speed Gears,” Proc. Instn Mech Engrs, Vol. 198A, 

No. 1, 1984, pp. 51–59. 

5. Dawson, P.H.: “High Speed Gear Windage,” GEC Review, Vol. 4(3), 1988, pp. 164–167. 

6. Winfree, “Reducing Gear Windage Losses from High Speed Gears,” ASME Power Transmission 

and Gearing Conference, Baltimore, MD, Sept. 2000. 

7. Diab, Y., Ville, F., Velex, P., and Changent, C.: “Windage Losses in High Speed Gears—

Preliminary Experimental and Theoretical Results,” Journal of Mechanical Design, Vol. 126, Sept. 

2004, pp. 903–908. 

8. Al-Shibl, K., Simmons, K., and Eastwick, C.: ”Modeling Windage Power Loss from an Enclosed 

Spur Gear,” Journal of Power and Energy, Vol. 221, 2007, pp. 331–341, Proc. IMechE Part A. 

9. Marchesse, Y., Changenet, C., Ville, F., and Velex, P.: “Investigations on CFD Simulation for 

Prediction Windage Power Losses in Spur Gears,” 3rd International Conference on Integrity, 

Reliability and Failure, Porto, Portugal, July 2009. 

10. Imai, H., Goi, T., Arisawa, H., and Nishmimura, M.: “Reduction in Gear Windage and Churning 

Loss by Optimum Shroud Design with Aid of CFD,” JSME International Conference on Motion and 

Power Transmission, JSME, Matsushima Isles Resort, Japan, May 2009. 

11. Hill, M., Kunz, R., Noack, R., Long, L., Morris, P., and Handschuh, R.: “Application and Validation 

of Unstructured Overset CFD Technology for Rotorcraft Gearbox Windage Aerodynamics 

Simulation, “AHS Forum 64, Montreal, Canada, April 2008. 

12. Hill, M., Kunz, R., Medvitz, R., Handschuh, R., Long, L., and Noack, R.: “CFD Analysis of Gear 

Windage Losses: Validation and Parametric Aerodynamic Studies,” Presented at the AHS Forum 66, 

Phoenix, AZ, May 2010. 
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the 

data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this 

burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. 

Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB 

control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 

1. REPORT DATE (DD-MM-YYYY)

01-11-2011 

2. REPORT TYPE

Technical Memorandum 

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

Initial Experiments of High-Speed Drive System Windage Losses 

5a. CONTRACT NUMBER

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Handschuh, Robert, F.; Hurrell, Michael, J. 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

WBS 877868.02.07.03.01.01.01 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-17421-1 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2011-216925 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Category: 37 

Available electronically at http://www.sti.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

High speed gearing performance is very important to the overall drive system efficiency. Certain losses such as gear meshing and bearing 

drag can be minimized by design changes such as pressure angle of the gears and the geometry and type of bearings being used. One 

component that can have a large effect on the overall performance of high-speed drive systems is the parasitic drag known as gear windage. 

This loss mechanism is not well understood and minimizing this component is usually accomplished through much trial and error. The 

results presented in this paper will document some of the design parameter effects on the amount of windage losses. A new test facility at 

NASA Glenn has been assembled to systematically study the design variables. Results from recent tests will be presented. The tests are for a 

single gear, with and without lubricants, and some initial studies using shrouds.

15. SUBJECT TERMS

Gears; Efficiency; Power transmission 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

16 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

U 

19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18