NASA Technical Memorandum 4791

Evaluation of High-Speed Civil

Transport Handling Qualities

Criteria With Supersonic

Flight Data

Timothy H. Cox and Dante W. Jackson

Dryden Flight Research Center

Edwards, California

National Aeronautics and

Space Administration

Office of Management

Scientific and Technical

Information Program

1997

ABSTRACT

Most flying qualities criteria have been developed from data in the subsonic flight regime. Unique characteristics

of supersonic flight raise questions about whether these criteria successfully extend into the supersonic flight regime.

Approximately 25 years ago NASA Dryden Flight Research Center addressed this issue with handling qualities

evaluations of the XB-70 and YF-12. Good correlations between some of the classical handling qualities parameters,

such as the control anticipation parameter as a function of damping, were discovered. More criteria have been

developed since these studies. Some of these more recent criteria are being used in designing the High-Speed Civil

Transport (HSCT). A second research study recently addressed this issue through flying qualities evaluations of the

SR-71 at Mach 3. The research goal was to extend the high-speed flying qualities experience of large airplanes and

to evaluate more recent MIL-STD-1797 criteria against pilot comments and ratings. Emphasis was placed on

evaluating the criteria used for designing the HSCT. XB-70 and YF-12 data from the previous research

supplemented the SR-71 data. The results indicate that the criteria used in the HSCT design are conservative and

should provide good flying qualities for typical high-speed maneuvering. Additional results show correlation

between the ratings and comments and criteria for gradual maneuvering with precision control. Correlation is shown

between ratings and comments and an extension of the Neal/Smith criterion using normal acceleration instead of

pitch rate.

NOMENCLATURE

ADI

bw

c.g.

CAP

CH

g

HSCT

IVSI

KEAS

Lct

LOES

Ny

Nz a

Pmax

PIO

s

SAS

0

Oc

_r

attitude direction indicator

bandwidth

center of gravity

control anticipation parameter, g-1 sec-2

Cooper-Harper (rating)

acceleration due to gravity

High-Speed Civil Transport

instantaneous vertical speed indicator

knots equivalent airspeed

dimensional lift curve slope, lb

low-order equivalent system

lateral acceleration, g

slope of normal acceleration as a function of angle of attack, g/rad

maximum roll rate, deg/sec

pilot-induced oscillation

Laplace operator

stability augmentation system

sideslip, deg

pitch attitude, deg

pitch attitude command, deg

bandwidth time delay parameter, sec

roll mode time constant, sec
x¢

_2talsoo

CObw_,

O_bwO

03dr

Osp

(0180 o

time delay of bank-angle-to-stick deflection frequency response, msec

bank angle, deg

phase angle at twice the phase crossover frequency, rad/sec

flightpath bandwidth parameter, rad/sec

pitch attitude bandwidth parameter, rad/sec

dutch roll frequency, rad/sec

short-period frequency, rad/sec

frequency of the second-order zero in the roll-rate-to-stick deflection transfer function, rad/sec

phase crossover frequency, rad/sec

dutch roll damping

damping of the second-order zero in the roll-rate-to-stick deflection transfer function

INTRODUCTION

Good handling qualities are essential for aircraft performance and can be predicted during the design process.

Handling qualities criteria used to evaluate aircraft designs are defined by experiential data obtained from previous

aircraft. A problem exists, however, when an aircraft flies in a new flight regime. Airplanes cruising at speeds greater

than Mach 2 or beyond exemplify this problem.

Since flying qualities criteria are based on subsonic data, they do not address some of the unique

characteristics of high-speed flight. For example, many of the current criteria assume that good flightpath response

follows from good pitch attitude response. For the high-speed case, however, this assumption may not be valid. As

Mach number increases, an aircraft's lift curve slope (Lct) decreases proportionally, thereby increasing the lag

between flightpath and pitch attitude response. Figure 1 compares responses from a step input in an SR-71

simulator at Mach 0.6 and 3.0, illustrating the increase in lag between flightpath and pitch attitude. For both

8 B

6

Mach 0.6

response, 4

deg

2

Pitch attitude

------ Flightpath

3 m

2

Mach 3.0

response,

deg

1

0 2 4 6 8 10 12

Time, sec 970048

Figure 1. Comparison of the lag between pitch attitude and flight path responses at Mach 0.6 and 3.0.
responsestheinputis appliedat0 secof time.Forthesubsonicasetheflightpathlagsthepitchattitudeby 1to

2sec,whereasfor theMach3.0casetheflightpathlagsby 4 to 5 sec.If thislagcharacteristicis too large,the

pilot'sabilityto controlflightpathis impaired.

Figure2 illustratesanotheruniquecharacteristicof high-speedflight,whichcomparestheresponsesof the

SR-71simulatortoalongitudinalstepinputatMach0.6and3.0.Thecomparisonrevealsthatasthespeedincreases,

thepitchattitudechangerequiredtoacquirethesamerate-of-climbdecreases. Thischaracteristic,ausedprimarily

by thelargevelocityterm,impliesthatasspeedincreasesthepilot mustmaintainmoreprecisecontrolof pitch

attitudetoestablishthedesiredrate-of-climbresponse. Unlessaccuratepitchattitudeorrate-of-climbinformationis

fedbackto thepilot,thischaracteristiccouldpotentiallycausethepilot to overcontroltheaircraft.Nevertheless

flyingqualitiescriteriaarebasedonsubsonicdata,wheretherequirementforprecisepitchattitudecontrolis more

relaxedthanit isforthehigh-speedcase.

6

Pitch

attitude, 4

deg

2

0

-- Mach 0.6

_ Mach 3,0 _-

75--

50--

Rate of

climb,

fVsec

25

I

0 2 4 6 8 10 12

Time, sec 970049

Figure 2. Comparison of pitch attitude changes at Mach 0.6 and 3.0 required to generate equivalent rates of climb.

Approximately 25 years ago NASA Dryden Flight Research Center researchers applied MIL-F-8785B criteria

to YF-12 and XB-70 data (ref. 1). The military specification defined criteria for four classes of airplanes:

• Class I, general aviation.

• Class II, medium weight.

• Class III, transports.

• Class IV, fighter aircraft.

Each criterion defined boundaries for three levels of handling qualities:

• Level 1, satisfactory handling qualities.

• Level 2, acceptable handling qualities.

• Level 3, controllable handling qualities.
Thecriteriaareapplied,dependingontheclassof airplane,forthreeflightcategories:

• CategoryA, rapidmaneuveringandprecisiontracking(air-to-aircombat).

• CategoryB,gradualmaneuveringwithoutprecisiontracking(cruiseflight).

• CategoryC,gradualmaneuveringwithprecisionflightpathcontrol(approachandlanding).

Thelongitudinaltasksfor theYF-12andXB-70,classHI aircraft,in up-and-awayflight includedprecise

flightpathtrackingwithoutgrossmaneuvering, whichwasconsideredcategoryC flight.Theresearchersshowed,

for boththeYF-12(refs.2,3,and4) andXB-70(refs.2and5),positivecorrelationbetweencategoryC criterion

oncontrolanticipationparameter(CAP)andpilotcommentsandratings.Theresearchersalsoindicatedthatthe

requirementsfor short-periodampingmayberelaxed,althoughtheseresultswerenot consideredconclusive

(refs.4 and5). Sincethat time severalmorecriteriahavebeendeveloped,someof whicharedescribedin

MIL-STD-1797(ref.6).TheHigh-SpeedCivil Transport(HSCT)programevaluatedtheflyingqualitiesof their

designbasedonsomeof thesecriteria(ref.7).Thismemorandumaddresseshowthesecriteriaapplyto airplanes

flyingin theregionof Mach2andbeyond.

Theflying qualitiesof theSR-71at Mach3 areevaluatedusingthreewell-definedmaneuversconsidered

typicalfor a supersonictransport:asteadylevelturn,anascendingturn,andaverticalplanealtitudechange.Pilot

ratingsandcommentsof themaneuversaredocumentedandreasonsareidentifiedforcaseswherelevel2 ratings

weregiven.Thegoalof thisresearchwastoextendthehigh-speedflyingqualitiesexperienceoflargeairplanesand

to evaluatesomeof themorerecentMIL-STD-1797criteriaagainstpilot commentsandratings.TheXB-70and

YF-12datafrom researchconductedapproximately25yearsagosupplementtheSR-71data.Evaluationof the

criteriafocusesoncomparingterminalflightphaseboundariesfortheHSCT(ref.7) withcategoryC boundaries

fromMIL-STD-1797.ThesupersonicflightdataarenotcomparedwiththeHSCTnonterminalboundariesbecause

theseboundarieswereundefinedwhenreference7waspublished.Thefollowinglongitudinalcriteriaareevaluated:

low-orderequivalentsystems(LOES)(ref. 8), pitchbandwidth(ref. 9), flightpathbandwidth(ref. 10),and

Neal/Smith(ref.11).Additionallythememorandumevaluatesthefollowinglateral-directional criteria:LOESand

lateralaccelerationatthepilot station(ref.6).

AIRCRAFT DESCRIPTION

The SR-71 (fig. 3) is a twin-engine, delta wing airplane that was designed to cruise at Mach 3.2 above 80,000 ft

(fig. 4). The SR-71 is powered by two Pratt & Whitney J-58 afterburner engines with axisymmetric, variablegeometry, mixed compression inlets. Centerbody spikes and bypass doors on the forward part of the nacelle

are automatically modulated to control the oblique and normal shock positioning associated with flying at

high supersonic speeds. The data discussed in this memorandum were gathered with doors and inlets in this

automatic configuration.

Most of the cockpit contains conventional instrumentation. Some of the main cockpit instruments used during

this evaluation include a pressure-driven, instantaneous vertical speed indicator (IVSI) and a triple-display indicator

that shows altitude, knots equivalent airspeed (KEAS), and Mach number in a digital format. The resolution of the

IVSI is 100 ft/min. The resolutions of the triple-display indicator parameters are 50 ft, 1 knot, and 0.01 Mach,

respectively. Because a lag in the response of the IVSI exists at high altitude, a horizontal needle on the attitude

direction indicator (ADI) displaying inertial vertical speed provides a reference for climb/descent rates. With this,

the SR-71 pilots get a more precise and reliable vertical speed indicator than from the IVSI. A vertical needle on the

ADI displays the error between the actual and desired bank angle based on the navigation system. Thus, the SR-71

pilots have a reference bank angle for following a ground track.

Wing trailing edge elevons are used symmetrically as elevators and differentially as ailerons to provide

longitudinal and lateral control, while twin, all-movable vertical tails supply directional control. The pilot controls
Figure3.SR-71researchaircraftshortlyafterrefueling.

EC9442883-04

90 m

80-

70-

60-

50-

Altitude,

-1000 ft

40--

30--

'°F

lO

o

S,S "'0K''c"m''°'r"°'"m

/1,5..jK.As c,,. <.,.n...,.

I I zo' I 1 I I I I I

.4 .8 1.2 1.6 2.0 2.4 2.8 3.2 3.6

Mach number

970050

Figure 4. SR-71 flight envelope.
consistof a conventionalstick for pitchandroll inputs,andrudderpedalsfor yawinputs.TheSR-71hasa

conventional responsewithangle-of-attackandnormalaccelerationchangescommandedby thepitchstick.The

controlsareirreversibleandfullypoweredbytwoindependent, 3000lb/in2hydraulicsystemsthatoperateactuating

cylindersateachcontrolsurface.

TheSR-71usesanautomaticflightcontrolsystemthat provides stability augmentation or increased damping

about all three axes. This damping is accomplished with conventional feedback of roll rate, pitch rate, and yaw rate.

In addition, lateral acceleration is used in the yaw axis to reduce the severity of engine unstarts.

An autopilot is available to reduce the workload involved in flying the SR-71. The autopilot includes attitude

hold in pitch and roll, Mach hold, and KEAS hold. Normal aircraft maneuvering is executed by pitch and roll attitude

inputs through thumbwheels, while acceleration/deceleration to and from Mach 3 are performed with the KEAS

hold engaged on the autopilot. The autopilot mode is used routinely in the climb, cruise, and descent portions of the

flights. However, for the handling qualities evaluations all autopilot modes were disengaged, and the maneuvers

were performed manually with the stick.

TASK DESCRIPTION

Three maneuvers were flown at Mach 3.0 to evaluate the handling qualities characteristics of the SR-71 aircraft:

a steady level turn, an ascending turn, and a vertical plane altitude change. These maneuvers are considered typical

of maneuvers to be flown by a large, supersonic transport aircraft. Each maneuver had two variations, and is

discussed more fully in the following sections.

Pilot comments evaluating the maneuvers against the adequate and desired performance margins were collected

immediately after performing each task and during postflight briefings. Adequate margins for all three maneuvers

were +300 ft deviation from target altitude and +10 KEAS deviation from target airspeed. Desired margins for all

three maneuvers were -t-100 ft deviation from target altitude and +5 KEAS deviation from target airspeed.

Vertical Plane Altitude Change

The vertical plane altitude change at constant KEAS entailed a wings-level pullup to capture a 2000 ft altitude

increment at a climb rate of 1000 ft/min. After the target altitude was established, it was held for 10 sec. Constant

airspeed was maintained throughout the maneuver. The pilots evaluated this maneuver with two variations: one

using the IVSI and another using the inertial vertical speed.

Steady Level Turn

The first variation of the steady level turn involved rolling the aircraft to a constant bank angle of 30 ° and

turning through a specified heading change while maintaining constant KEAS and altitude. After acquiring the final

heading, a rollout to wings level was performed followed by holding constant altitude and airspeed at the final

heading for 10 sec. For the second variation, instead of rolling to a constant bank angle, the pilot was required to

follow the vertical ADI bank angle needle, which was commanded by the navigation computer to follow a specified

ground track. At Mach 3.0 bank angles of around 30 ° were commanded.

Ascending Turn

The first variation of the ascending turn involved rolling the aircraft to a constant bank angle of 30 °. After 10°

of heading change the pilot began an ascent at a rate of 500 ft/min. This state was held for an additional 30 ° of

heading change, where the pilot leveled off in altitude. Constant airspeed was maintained throughout the whole

maneuver. As with the steady level turn the second variation of the maneuver was performed with the pilot following

the vertical ADI bank angle needles.
PILOT EVALUATIONS

This section summarizes pilot comments for the three maneuvers described in the previous section. Two pilots

flew the maneuvers, and their Cooper-Harper (CH) ratings and comments were recorded. Figure 5 presents the

CH ratings for these maneuvers; it should be referred to throughout the discussion. Pilot comments for steady and

ascending turns were consistent with each other, and are presented together in the following discussion. CH ratings

are split into three handling qualities levels according to the following definitions:

• Level 1 = CH < 3.5

• Level 2 = 3.5 < CH <6.5

• Level 3 =6.5 < CH < 9.5

10

9

8

7

6

Cooper-Harper

rating

Shaded symbols: maneuver flown

with inertial vertical speed

Open symbols: maneuver flown

with IVSI

B

-- []

D

5 --

4 --

3 -- I

2 --

1 I

Vertical plane

altitude change

[] Pilot A

o Pilot B

Level 3

Level 2

/Follow ground

track

\-;

Level 1

II _ Constant 1_ jill

I I

Steady Ascending

level turn turn

970051

Figure 5. Pilot ratings for the vertical plane altitude change, steady level turn, and ascending turn maneuvers.

Vertical Plane Altitude Change

Comments from both pilots are summarized below for both variations of the vertical plane

change maneuvers.

With Instantaneous Vertical Speed Indicator

altitude

Sluggish initial response and excessive delay between the stick input and a reaction in the IVSI gauge made

establishing and maintaining the desired rate of climb very difficult. The altitude change could be performed, but not

without high concentration and some loss of performance. The pilot's ability to hold airspeed was difficult because

of the excursions in rates of climb. These problems warranted CH ratings between 5 and 7 (levels 2 to 3).

7
With Inertial Vertical Speed Indicator

Achieving desired performance was relatively easy. The rate of climb was easy to establish and maintain when

using inertial vertical speed as feedback. As long as enough range in throttle motion in afterburner was available, the

airspeed was easily maintained as well. The only difficulty arose when searching to establish rate of climb and when

leading the aircraft as it approached the target altitude. This minor compensation required in establishing flightpath,

added to the basic concentration necessary to fly this airplane, warranted a CH rating of 3 (level 1).

Steady Level and Ascending Turns

Both levels 1 and 2 ratings were assigned for the steady level and ascending turns (fig. 5). The level 1 ratings

were associated with the maneuver flown at constant bank angle, whereas the level 2 ratings were associated with the

maneuver flown while following the bank angle steering bar for constant ground track. The following is a summary

of both pilots' comments.

Turns Following Ground Track

For the turns where the ground track or bank angle steering bar was followed, the level of concentration required

to perform the task was quite high, although the task was performed to within desired performance. Three sources

exist for this concentration level:

• The high degree of baseline concentration required to fly the aircraft normally.

• Simultaneously maintaining small vertical speed and bank angle errors, which was of paramount concern

because large errors were difficult to correct and manage.

• Maintaining airspeed, which was considered easy but still contributed to the level of concentration required.

The concentration from each of these sources was minimal when considered separately. When combining all the

sources simultaneously, however, the required concentration level drove the CH ratings to level 2. Keeping the

vertical speed error small was more demanding than following the bank angle command needle. Lags inherent in the

aircraft's flightpath response made it more difficult to maintain a precise vertical speed than a precise bank angle.

Although the roll response was a little abrupt, it was easy to acquire and maintain desired bank angle.

Turns With Constant Bank Angle

Flying the turn with a constant bank angle reduced the concentration required to perform the maneuver when

following the bank angle needle. Because no problems existed with bank angle control, establishing the required

bank angle was relatively easy with only a few minor adjustments required to maintain it. Therefore, less attention

was placed on the lateral-directional axis. The reduction in the required concentration was enough for CH ratings

of 2 and 3 (level 1).

Pilots' General Comments

Trimming the aircraft could be a tedious task because of poor resolution in the vertical speed indicator or lack

of vertical acceleration feedback. The airplane would appear to be trimmed but many seconds later the inertial

vertical speed would have drifted off and require further adjustments. This characteristic could be related to the

lightly damped phugoid mode (ref. 12).

Although control harmony was a significant problem due primarily to heavy longitudinal forces, it became only

a minor influence on the handling qualities when the longitudinal trim button was used to cancel stick forces. The

pilots did not consider control harmony when giving the ratings and comments.
Summary for Comparison With Criteria

Longitudinal handling qualities were level 1 when using the inertial vertical speed as a feedback parameter.

Vertical speed was an important feedback, as the pitch attitude display on the ADI did not provide enough resolution

to be useful. Lags existed in the flightpath response; however, the aircraft was predictable and solid. These comments

were based on gentle maneuvering, which is typical of the types of missions flown with this aircraft. Because of the

inherent lags of the vehicle at high speeds aggressive maneuvering was not possible without control difficulties.

Although airspeed response was sluggish, it was easy to maintain. An average CH rating of 3 for the vertical plane

altitude change maneuvers using the inertial vertical speed indicator as feedback will be used to compare with the

longitudinal criteria.

Specific lateral-directional axis ratings were not obtained during the SR-71 handling qualities evaluations.

However, certain inferences could be made about these ratings. First, the vertical plane altitude change maneuvers

were rated by both pilots as CH = 3. Because this maneuver was mainly a longitudinal one, these ratings represented

the longitudinal task. Pilot comments indicate that lateral-directional dynamics had a "slightly abrupt, but

predictable response" that was less demanding than the response in the longitudinal axis. Because the ratings of the

longitudinal dynamics were CH = 3 for both pilots, it can be inferred that the ratings for the lateral-directional

dynamics were CH = 3 or better.

The turns performed with the pilot following the bank angle steering bar on the ADI received CH ratings of 4

and 4.5. The comments indicate that the increase in ratings for this maneuver was caused by the increase in attention

and concentration required to "juggle" the altitude task, bank task, speed task, and normal aircraft functions. These

comments imply that a better estimate of lateral-directional dynamics alone would come from the constant bank

angle turns. The averaged rating of these maneuvers, CH = 2.5, also fits within the requirement for CH = 3 or better.

Thus, ratings for the steady level turn flown with constant bank angle will be used when comparing SR-71 data with

the lateral-directional criteria.

LONGITUDINAL CRITERIA EVALUATION

Longitudinal criteria evaluated are LOES, bandwidth (pitch and flightpath), and Neal/Smith. These criteria were

emphasized because they are identified as design criteria for the HSCT (ref. 7). To increase the value of this

investigation, the LOES criteria were also applied to high-speed flying qualities data from the XB-70 (ref. 5) and

YF-12 (ref. 3). Because the flight conditions where the data were collected were not recorded in the XB-70 report,

the application of this data to the other criteria was not possible. However, enough information existed in the YF- 12

report to extract the test condition of the data. Because of the similarity of the YF- 12 and SR-71 in the longitudinal

axis, a flight-validated linear simulation of the SR-71 supplemented as a model of the YF-12 data. The other

longitudinal criteria were then applied to this model.

Evaluation of the criteria focuses on comparing terminal flight phase boundaries for the HSCT with category C

boundaries from MIL-STD- 1797. Comparison of the supersonic flight data with HSCT nonterminal boundaries was

not done because these boundaries were undefined when reference 7 was published. Although category C is typically

associated with approach and landing, the high-speed maneuvers for the SR-71, XB-70, and YF-12 were considered

category C because precise flightpath control without rapid maneuvering was required (ref. 5). Flying qualities

ratings from the previous research correlated well with the category C borders. To further investigate this

assumption, comparisons between category A and B criteria from MIL-STD-1797 were conducted as well. If the

flying qualities ratings and comments continue to correlate best with category C across all the criteria, HSCT criteria

used for the terminal flight phase may be appropriate for the high-speed flying qualities design as well.

Low-Order Equivalent System

The LOES technique was developed to apply classical boundaries of handling qualities to higher order aircraft.

The technique fits second-order transfer function models of pitch rate and normal acceleration from stick deflection

9
tohigherordermodelsorflightdata.A timedelaymodelisaddedtothesecond-order transferfunctionstoaccount

for differencesinphaseanglebetweenthelowerandhigherordermodels.As aresult,LOESestimatesof shortperiodfrequency,damping,andthelift curveslope(Let)canbeappliedto classicalcriteriaontheseparameters. A

criterionforthetimedelayestimatehasalsobeendeveloped.

ALOESfit wasperformedusingaFastFourierTransformof anSR-71flightdatafrequencysweep.TheLOES

fit wasperformedwithsimultaneouspitchratefromstickdeflectionandnormalaccelerationfromstickdeflection

frequencyresponses. Figure6showsanexampleofthefitusingthenormalaccelerationneartheinstantaneouscenter

ofrotation.Agoodfit withacostofapproximately50wasobtained.Inaddition,aLOESfitwasperformedwithjust

thepitchratefrom stickdeflectionfrequencyresponse,wherethefirst-orderzerowasfixedat thevalueof Let

calculated from flight data. The frequency, damping, and time delay estimated from this fit and the simultaneous fits

were within 10 percent.

10

0

Magnitude,

dB - 10

- 20

- 30

LOES fit

------ Flight data

Phase,

deg

100--

-100

-20o I I I I I I I II I I I I I I I I I

.1 .2 .3 .4 .5 .6 .7.8.91.0 2 3 4 5 6 7 8 910

Frequency, rad/sec

970052

Figure 6. Typical LOES fit of the pitch rate from stick deflection frequency response.

Figures 7, 8, and 9 show the CAP, damping, and time delay of the XB-70,YF-12, and SR-71, respectively. CAP

was approximated using equation (1) between the short-period frequency (O_sp) and the change in normal

acceleration with angle of attack Nz, _ •

2

CAP = c°sp

N z a

(1)

Data are compared with the criterion on CAP from the MIL-STD-1797 for categories A, B, and C, and from

HSCT design guidelines. The HSCT criterion for CAP is equivalent to the category A, level 1 region of

MIL-STD- 1797. The traditional CAP as a function of damping format was not presented to be consistent with the

previous XB-70 and YF-12 analysis. The solid line in figure 7 is faired through the XB-70 data and came from

reference 5. The shaded region shows where the data should fall if the criteria correlate with pilot ratings.

10
Cooper-Harper

rating

6

.05

[] O

.10 .15

Level 2

[]

0 XB-70

[] YF-12

X SR-71

MIL-STD-1797

category C

I I I I I I I

.20 .25 .30 .35 .40 .45 .50

CAP, g -1 eec - 2

970053

(a) Category C criteria.

3

Cooper-Harper

ratlng

.05

[]

Level 2

0 XB-70

_] [] YF-12

X SR-71

MIL-STD-1797

category B

I I I I I I I I I

.10 .15 .20 .25 .30 .35 .40 .45 .50

CAP, g -1 aec - 2

970054

0

[]

(b) Category B criteria.

Figure 7. LOES estimates of CAP compared with categories A, B, and C criteria from MIL-STD- 1797 and HSCT

criteria.

II
Cooper-Harper

rating

[] 3

LevelI

Level2

4

[]

O

s

ooo o

[]

o

6

.05 .10 .15 .20 .25 .30 .35

CAP,g-1 sec- 2

(c) HSCT and category A criteria.

Figure 7. Concluded.

[]

0 XB-70

[] YF-12

X SR-71

HSCTandMIL-STD-1797

categoryA criteria

I I I

.40 .45 .50

970055

From figure 7 CAP correlates better with category C guidelines from MIL-STD- 1797 than it does with the HSCT

and category B guidelines. Reference 5 noted this correlation with category C for XB-70 data. The addition of the

YF- 12 data from reference 3 supports this conclusion, and the SR-71 point falls within the level 1 region as expected.

A total of 83 percent of all the data falls within the boundaries predicted by category C criterion on CAP. The HSCT

criterion appears too stringent for the type of altitude-tracking maneuvers flown because several level 1 ratings fall

outside that region. Only 33 percent of the level 1 ratings fall within the HSCT guidelines, whereas 79 percent of the

level 1 ratings fall within the category C, level 1 criterion. For the MIL-STD-1797 category B criterion, 60 percent

of the data fall within the predicted boundaries, worse than the 83 percent estimated by the category C criterion.

Figure 8 shows the XB-70, YF-12, and SR-71 short-period damping estimates. MIL-STD-1797 criteria for

category A and C and the HSCT criterion are superimposed on the data. The shaded region shows where the data

should fall if the criteria correlate with pilot ratings. All the criteria for damping appear to be too restrictive for the

high-speed maneuvers, even if category B requirements on damping (0.3) were considered. Short-period damping is

less significant as a flying qualities parameter in high-speed flight than in low-speed flight. A relaxation of the

allowable damping limits for high-speed flight might be possible, although other factors not accounted for in the

XB-70 and YF-12 ratings, such as turbulence, may increase the damping requirement. However, references 4 and 5

noted that aircraft response due to turbulence may be reduced at high Mach number because of the reduced La.

In figure 9 the MIL-STD- 1797 and HSCT criteria for equivalent time delay are superimposed on the SR-71 and

YF-12 equivalent system time delay estimate. The shaded regions show where the data should fall if the criteria

correlate with pilot ratings. The HSCT criteria predict level 1 for time delays less than 200 msec. No distinctions are

made among categories A, B, and C in the time delay criterion of MIL-STD- 1797. The military standard states that

although not enough time delay data exist for class III (transport) aircraft to be conclusive, it is apparent that a

relaxation in the time delay criterion is in order. This is because the standard's criteria are based on class IV (fighter)

airplanes. Class III aircraft data have shown that delays as much as 250 msec have been evaluated as level 1 (ref. 6).

Thus, the HSCT criterion appears reasonable. The single SR-71 data point supports a criterion less restrictive than

MIL-STD-1797, but is obviously not enough to be conclusive.

12
Cooper-Harper

rating

1 --

2 --

3

4

5

O

Level 1

Level 2 []

[]

[]

o x(

_-//

,.//

.2 .3

_ 0

0

0

0 XB-70

[] YF-12

X SR-71

MIL-STD-1797

HSCT

e I I II I I I I I

0 .I .4 .5 .6 .7 .8 .9 1.0 1.1

Short period damping

970056

Figure 8. LOES estimates of short-period damping compared with HSCT and MIL-STD-1797 criteria.

Cooper-Harper Level 1

rating Level 2

I I I

6(_ 50 100 150 200 250 300 350

Time delay, maec

970057

Figure 9. LOES estimates of time delay compared with MIL-STD-1797 and HSCT criteria.

13
Bandwidth Criterion

The bandwidth criterion as defined in MIL-STD-1797 was used to analyze both the SR-71 and (reproduced)

YF-12 data. The gain-limited bandwidth (defined as the frequency at the magnitude that is 6 dB more than the

magnitude at the phase crossover frequency) and phase-limited bandwidth (defined as the frequency where 45 °

phase margin exists) were calculated from a pitch attitude from stick deflection frequency response. The lesser of the

two frequencies was considered the bandwidth frequency. The criterion places limits on the bandwidth frequency as

a function of the time delay (Xp), which is estimated from the phase at twice the phase crossover frequency

((I)2(o180o), and phase crossover frequency (0)180o) :

(1)2(_lSOo + 180 °

_p = 57.3(20)180o )

(2)

The calculation of the bandwidth frequency for SR-71 and YF-t2 data with the stability augmentation system

(SAS) turned on proved straightforward. However, the YF-12 data included four test points where the SAS was

turned off. Figure 10 shows a typical example of the pitch attitude bandwidth calculation for low damped, YF-12

data. The calculation of the phase bandwidth value, the frequency where the phase is -135 ° , is straightforward.

However, the calculation of the gain bandwidth value is more confusing. Applying the definition of the gain-limited

bandwidth to the data in figure 10 results in three possible gain bandwidth values: 1.8, 0.8, and 0.19 rad/sec. Note

that a slightly increased phase crossover frequency, (o180o, would prevent this phenomenon from occurring. If the

value of 1.8 rad/sec is considered the gain bandwidth value, then the phase bandwidth value would be compared

with the criterion because it is less than 1.8 rad/sec. However, if either the 0.8 or 0.19 rad/sec values are the

appropriate gain bandwidth value, then these would be compared with the criterion because they are less than the

phase bandwidth value.

This phenomenon results mainly from the large, "shelf-like" characteristic created by the large difference

between Lct and the short-period frequency and the low short-period damping. The low short-period damping

characteristic produces the three possible gain bandwidth values. Standard procedure for this situation would be to

Magnitude,

dB

Phase,

deg

20--

0--

- 20 --

- 40 --

- 60

O)bw, gain = 1.8-_

O)bw, gain = 0.8-_

_- °_bw, gain =0.19

I I I I II II

- 100

- 200

B

-- __ /- ¢ =- 1as

__ 6 dB

1 I I I IIIII

_- co180 °

__._0 =- 180

1, I

°)bw, phase = I" -_ l l l l I l l l II l l l l l I II

-300.1 .2 .3 .4 .5 .6.7.8.91 2 3 4 5 6 7 8 910

Frequency, rad/sec

970058

Figure 10. Example pitch attitude bandwidth calculation typical of a low damped YF-12 test point.

14
choosethelesservalue,0.19rad/sec,asthegainbandwidth.Therationaleisthatif thepilottriestoclosetheloopat

thehighergainbandwidthvaluesatendencyto oscillatewill occurbecauseof thelightlydampedpeak.Thelarge,

shelf-likecharacteristicresultsina largeseparationbetweenthethreegainbandwidthvalues.Theexistenceof a

largeshelfis generallyanindicationof poorhandlingqualities,becausethegainmarginisverysensitiveto slight

changesin phase(ref.6).In thefollowingdiscussionthepitchattitudebandwidthforthecaseswhentheSASwas

off will bebasedonthephasebandwidthvalue,unlessotherwisementioned.Somecomparisonwiththecriterion

will alsobedoneusingthelowestvalueof gainbandwidth,representedby0.19rad/secinfigure10.

Figure11showstheresultsusingcategoriesA andC criteriafromMIL-STD-1797.All thedataratedlevel1

fallswithinthelevel2regionfor thecategoryA criterion.ThecategoryA criterionappearstoostringentonpitch

.2O

.15

l:p, .10

lie(:

.O5

_ x,/v 3.0 Level 2

.'x_ ¢ 4.:.9 374 x

Z" ,.%0 o.-

3._'; 8

-

I I I

2 4 6 8 10

O YF-12

X SR-71

o_0, rad!sec

I

12

970059

(a) Category A.

.35

O YF-12 phase bandwidth

O YF-12 gain bandwidth

X SR-71

.30 --

.25 --

Level 3

,15 --

4.9 \

4-3- -30 "3.8 -'+

.°5 V _ Level 1

I I I I ",4 I

0 .5 1.0 1.5 2.0 2,5 3,0

ml_e, rad/s_

970060

(b) Category C.

Figure 11. MIL-STD-1797 pitch bandwidth criteria for categories A and C flight.

15
attitudebandwidth.However,thecategoryC criterion reduces the restriction on pitch attitude bandwidth. For the

category C criterion the ratings and comments correlate better with the border between the level 1 and 2 regions.

Overplotted on the category C criterion is the gain-limited pitch attitude bandwidth values for the four YF-12 test

points that were conducted with the SAS off. As is expected the pitch attitude bandwidth is drastically reduced to

around 0.25, near the level 3 border. Correlation with pilot comments and ratings appears better with the phaselimited bandwidth values than the gain limited value, although the reason behind this phenomenon is unknown.

Although good correlation was obtained with the phase bandwidth values, it may be a misleading result. A large

shelf exists in the pitch attitude frequency response, which is normally associated with poor pitch attitude control.

However, the large shelf is actually the cause of good flightpath control. Figure 12 compares the magnitude of pitch

attitude and flightpath frequency responses. For the frequency range where the large shelf is prevalent in the pitch

attitude frequency response, the flightpath frequency response has a "l/s" characteristic. The 1/s characteristic is

typical of airplanes with good flying qualities. Thus, pilot control of flightpath should be better than pitch attitude

control. A flightpath command control is approximated with a conventional aircraft because pitch attitude deviations

are small in supersonic flight. Other types of control systems, such as pitch rate command systems, could remove the

shelf making pitch attitude control good, but would cause flightpath control to deteriorate.

50

Magnitude, 0

dB

Pitch attitude

.... Slope of 1Is

Flightpath

- 5O

.01 .02 .04 .06 .08.10 .2 .4 .6 .8 1 2 4 6

Frequency, rad/sec

Figure 12. Comparison of pitch attitude and flightpath from stick position frequency response.

8 10

970061

Figure 13 presents the pitch bandwidth using the HSCT criterion (ref. 7). The HSCT criterion is based on the

terminal flight phase, which is equivalent to a category C flight phase. Note that the HSCT criterion is less restrictive

on level 1 pitch attitude bandwidth than the MIL-STD- 1797, category C criterion. Although there is some correlation

with the HSCT criterion, less correlation exists using the HSCT criterion compared with the category C criterion

from MIL-STD-1797 because level 2 ratings fall within the level 1 region. Either the criterion is not restrictive

enough in pitch attitude bandwidth, or other factors are creating the level 2 ratings that this criteria does not account

for. As was mentioned before, many of the flying qualities criteria, based on subsonic data, place restrictions on pitch

attitude and assume that a good flightpath response follows. This assumption works in subsonic flight, where the

criteria were defined. However, in supersonic flight, unique flightpath characteristics might invalidate the criteria.

Flightpath control could be the factor not accounted for in the HSCT criterion presented in figure 13.

A criterion comparing flightpath bandwidth with pitch attitude bandwidth, presented in figure 14, had also been

identified by the HSCT program. Again this criterion was based on the terminal flight phase or category C flight

phase. At first glance good correlation exists between the ratings and the HSCT criterion. The three level 2 ratings

that were predicted to be level 1 in figure 13 are now predicted to be level 2/3. However, a closer scrutiny of the data

reveals some problems. This criterion sets requirements on the amount of lag between pitch attitude and flightpath

response. The flightpath bandwidth values in figure 14 are above the level 1 region. This finding implies that the

flightpath response lags the pitch attitude not by too much, as is expected, but by too little. This result is counter

intuitive because physically the lag between pitch attitude and flightpath increases with Mach number.

16
Xp,

sec

.35 --

.30 --

.25 --

.20 --

.15 --

.10 -

.05 --

Level 3 2 Level 1

0 o

"_ 3.0 3.8

\

\

I I " I I I I

.5 1.0 1.5 2.0 2.5 3.0

O)bwe, rad/sec

970062

O YF-12

X SR-71

\

Figure 13. HSCT criteria on pitch bandwidth.

O X

3.4 3.0

1.4

1.2

1.0

.8

.6

.4

.2

4.93(_ ._ O YF-12

3.0 \_ "_" X SR-71

4.3 7./

0 3.0

x

J.¢. ....,1

,.._ \\

_" Level 2

_\\\\\\\\\\\\\\\\\\\\

Level 3

I I I I I I

0 .5 1.0 1.5 2.0 2.5 3.0

O)bwO, re(:I/eec

970063

Figure 14. HSCT criteria on pitch bandwidth as a function of flightpath bandwidth.

17
One possible explanation for this data is that the upper limit on flightpath bandwidth was set based on precision

approach and landing. In this flight phase both pitch attitude and fiightpath response are controlled by the pilot. For

the data of figure 14 the pilot ratings and comments were based on cruise flight during a vertical plane altitude

change using an inertial vertical speed feedback. The requirement for consonance between flightpath and pitch

attitude response may not be as important for these conditions. The pilot simply may not care as much about the

smaller pitch attitude response in cruise flight compared with landing, especially if vertical speed is fed back. As a

result, adjustment of the level 1 upper borders may be required for precision flightpath control at cruise conditions.

Neal/Smith Criterion

The Neal/Smith criterion involves closing the loop around a pitch attitude to stick deflection transfer function

and a lead-lag compensator, modified by the addition of pure time delay, to meet specific closed-loop characteristics.

The characteristics of the closed-loop frequency response are defined as -90 degrees of phase at the bandwidth

frequency and no less than -3 dB of droop (fig. 15). The bandwidth frequency represents the piloting task that is

being conducted and is generally chosen based on flight phase. Criteria are established based on the lead required of

the compensator to meet the characteristics and the maximum amplitude, or resonant peak, of the frequency

response of the closed-loop (i.e., the compensator and airplane) system.

IOlOcl,

dB

dog

-10

0

- 9O

- 180

0

I

Frequency,

I

Frequency,

rad/eec

Bandwidth

frequency

970064

Figure 15. Illustration of application of Neal/Smith criteria.

For the data presented here, the time delay of the compensator was chosen to be 0.3 sec. Three bandwidths

ranging from 1.0 to 2.5 were analyzed to represent increases in the demands of the task. Figure 16 presents the

results from applying this criterion to SR-71 data. From this figure the compensator requires large amounts of lag,

which drives the ratings into the level 2 region. These results would be consistent with the large shelf in the pitch

attitude from stick position frequency responses. Data in this region of the Neal/Smith plane predict pilot comments

of abruptness in the initial response with tendencies to bobble. Pilot comments from flight data are contrary to this

prediction. One pilot commented during the vertical plane altitude change maneuver that "a great deal of lead is

required (to acquire the target altitude) in terms of time." This comment suggests that the Neal/Smith analysis should

18
Resonant

peak,

dB

Level 3

Level 2

-2--

-4 I I

- 40 0 20 40 60 80

Pilot lead, deg

970065

key

Figure 16. Neal/Smith analysis of the pitch attitude to stick deflection frequency response.

yield results on the lead side of the plane, where pilot comments of sluggish initial responses are predicted. However,

the pilot later commented that "the workload for this maneuver is acceptable because of the low rates of change

involved," and gave the aircraft a CH of 3, which implied that the workload was not significant. Thus, one would

expect the Neal/Smith analysis to yield results within the level 1 region.

A contradiction exists between the pilot ratings and comments and the Neal/Smith analysis. The solution to this

contradiction may be found through closer examination of the instrumentation available to the pilot for the

evaluations. Typically a pilot uses pitch attitude as a primary feedback to his commanded inputs to the stick.

However, the SR-71 and YF-12 had inertial vertical speed displayed through needles on the ADI and driven by an

inertial navigation system. This display allowed direct feedback to the pilots on vertical speed without the lags of a

pressure-driven vertical speed display. The pilots on both the SR-71.and YF-12 took advantage of this feature by

flying these maneuvers using these needles as their primary feedback parameter. Reference 3 described the

advantage of using the inertial vertical speed indication. If this is the case, perhaps the Neal/Smith results would

correlate better with ratings and comments if the integral of normal acceleration, or vertical speed, would be used in

the analysis instead of pitch attitude.

The Neal/Smith analysis was repeated for the SR-71 data, this time using the integral of normal acceleration at

the center of gravity (c.g.) and normal acceleration at the pilot station to approximate vertical speed. Figure 17

presents the results for bandwidth frequencies of 1.0, 1.5, and 2.0 rad/sec. The data fall on the lead side of the

Neal/Smith plane as expected. Superimposed on the results are the MIL-STD-1797 criterion and the HSCT criterion.

Note that the level 1/2 HSCT border is nearly equivalent to the MIL-STD-1797 border, but that the level 2/3 border

is more restrictive. Quite a bit of difference exists between the results using c.g. and pilot station vertical speed. The

rate of flying qualities degradation as a function of increasing bandwidth is much higher for the vertical speed at the

c.g. than for the vertical speed at the pilot station. The inertial system used to calculate the vertical speed that is fed

back to the pilot is located close to the pilot station. Therefore, using the vertical speed calculated for the pilot station

in the Neal/Smith analysis is more representative of the actual vertical speed indicator than the vertical speed at the

c.g. The Neal/Smith results using vertical speed calculated at the pilot station also indicate that there can be a

beneficial effect in modifying the c.g. vertical speed with, in this case, pitch acceleration lead.

19
16

14

12

10

8

Resonant

peak, 6

dB

4

2

0_

i

-2_--

-4

- 40

m

B

_\\\\\\\\-

w

//////////

- 20

bw=2.0 X

bLeVel 2

Lov°ll I I _ I I

0 20 40 60 80

Pilot lead, deg

970066

O vertical speed at pilot

station

X Vertical speed at c.g.

HSCT borders

MIL-STD-1797 borders

MIL-STD-1797 end

HSCT borders

Figure 17. Neal/Smith analysis of the vertical speed at the c.g. and the vertical speed at the pilot station from stick

deflection frequency response.

As described previously, the aircraft was rated level 1, with noticeable lead required. As the bandwidth increases,

the c.g. vertical speed results enter the level 2 region with relatively low levels of lead required, whereas the pilot

station vertical speed results enter the level 2 region with significant amounts of lead. Thus, using the vertical speed

at the pilot station correlates better with ratings and comments than using the c.g. vertical speed. Bandwidths within

the 1.0 to 1.5 rad/sec range correlate best with SR-71 pilot comments and ratings.

Both MIL-STD-1797 and HSCT criteria use 1.5 rad/sec as the bandwidth for the terminal, or category C, flight

phase. From figure 17 the use of this value of bandwidth correlates well with the ratings and comments from highspeed flight, although the 1.5 rad/sec bandwidth is at the high end of bandwidths that correlate. Thus, as long as

the vertical speed at the pilot station transfer function is used instead of the pitch attitude transfer function, the

category C requirement should provide a conservative analysis for normal maneuvering in high-speed flight.

To further examine the Neal/Smith criterion figure 18 shows the reproduced YF-12 data along with the SR-71

data for a bandwidth of 1.0 rad/sec. Two of the test points correlate well with the level 1 region. However, the rest

of the points predict a great deal of oscillatory characteristics. The oscillatory prediction is great enough to be pilotinduced oscillation (PIO) prone and level 3. Pilot comments in no way suggest these characteristics. All the test

points that do not correlate well were gathered without the SAS. Short-period damping was reduced from

approximately 0.5 to 0.15 by turning off the SAS. Increases in the oscillatory tendency of the aircraft would be

expected, as well as a large sharp peak in the magnitude and a large phase dropoff in the frequency response used in

the Neal/Smith analysis. These frequency response characteristics would result in higher calculations of resonant

peak in the Neal/Smith analysis.

Because the data from figure 18 show that level 2 ratings exist in the level 3 region because of large values of

resonant peak, the Neal/Smith criterion may be too restrictive in short-period damping and may require adjustment

of the border between the level 1 and 2 regions. This finding is supported by the short-period damping analysis in

figure 8. From this data it was shown that a relaxation of the damping criterion was necessary to define the border

between the level 1 and 2 regions for normal maneuvering in high-speed flight.

20
816

14

E

12

10-

Resonant 8-

peak,

dB 6--

4--

2--

0

-2 --

-4

- 40

m

\\\\

- 20

8 0 YF-12

.000 X SR-71

3.8

Level 3

\\\_\ ..

Level 1

I 1 I I

0 20 40 60 80

Pilot lead, deg 970067

Figure 18. Neal/Smith analysis of the vertical speed at the pilot station from stick deflection frequency response

using 1.0 rad/sec bandwidth.

LATERAL-DIRECTIONAL CRITERIA EVALUATION

Lateral-directional criteria were evaluated using the LOES technique and lateral acceleration at the pilot station.

These criteria were used in the design of the HSCT. The SR-71 flight data were compared with MIL-STD-1797 and

HSCT criteria. Unfortunately, test conditions of previous XB-70 and YF-12 lateral-directional evaluations were not

available. Therefore, it was not possible to reproduce any of this data, as was done in the longitudinal axis. Pilot

evaluations did exist for the XB-70, and these results were compared with the criterion on dutch roll damping.

Low-Order Equivalent System

The LOES technique was developed to apply classical boundaries for handling qualities to higher order aircraft.

The technique fits fourth-order transfer function models of roll attitude from stick deflection and sideslip from rudder

pedal to higher order models or flight data. A time delay model is added to the fourth-order transfer functions to

account for differences in phase between the lower and higher order models. As a result, LOES estimates of dutch

roll frequency (t.Odr) and damping (_dr), roll mode (Xr), and spiral mode can be applied to classical criteria on these

parameters. An additional criterion on the time delay estimate has also been developed.

An LOES fit was performed on a Fast Fourier Transform of a lateral stick frequency sweep performed during

flight. Unfortunately, a good measurement of sideslip was not available. Therefore, simultaneous fits of flight-datarecorded sideslip from rudder pedal and bank-angle-to-stick deflection frequency responses were not possible.

However, dutch roll damping and frequency estimates from flight data were still desired. To obtain these estimates

an LOES fit was performed on the bank-angle-from-stick deflection frequency response with the second-order

numerator zero fixed at a value estimated by the linear simulation model.

The LOES estimates of roll mode time constant, dutch roll frequency, time delay, and dutch roll damping are

plotted in figures 19 through 22, respectively, against categories A, B, and C criteria from MIL-STD-1797 and

21
againstHSCTcriteria.Theshadedregionsshowwhere the data should fall if the criteria correlate with pilot ratings.

Except for the time delay criterion, HSCT criteria are either the same as or more restrictive than MIL-STD-1797

criteria. For the roll mode time constant (fig. 19) and dutch roll frequency (fig. 20) both MIL-STD-1797 and HSCT

criteria predict level 1 flying qualities, which agrees with pilot ratings and comments. Time delay estimates (fig. 21)

fall outside the MIL-STD-1797 criterion. However, the MIL-STD-1797 criterion appears to be too restrictive,

especially for a class III vehicle (ref. 13). Although not enough data exist to be conclusive, the SR-71 data support

a less restrictive time delay criterion than MIL-STD-1797.

1

2

3

Cooper-Harper .

rating

41-

5 _

X SR-71

MIL-STD-1797

categodes A,

B, and C

HSCT

Level 1

Level 2

I

1.5 2.0 2.5 3.0

_r' sec

e' I I I

0 .5 1.0 3.5

970068

Figure 19. LOES estimates of roll mode time constant compared with HSCT and MIL-STD-1797 criteria.

1 -- X SR-71

_ MIL-STD-1797

and HSCT

2--

3--

Cooper-Harper

rating

4--

5--

60 .5 1.0 1.5 2.0 2.5 3.0 3.5

COdr, rad/sec

970069

Figure 20. LOES estimates of dutch roll frequency compared with MIL-STD- 1797 and HSCT criteria.

22
Cooper-Harper

rating

S m

Level 1

100 150 200

'_(_, msec

X SR-71

MIL-STD-1797

HSCT

Level 2

e i

0 50 250 300

I I I

350

970070

Figure 21. LOES estimates of time delay estimate compared with HSCT and reference 5 criteria.

The most interesting results are observed in the dutch roll damping ratio estimates presented in figure 22, which

have XB-70 data overplotted. The solid line in figure 22 is a fairing of the data. The shaded region shows where the

data should fall if the criteria correlate with pilot ratings. From this data it is obvious that the HSCT criterion is too

restrictive and that the categories B and C criteria from MIL-STD- 1797 are not restrictive enough. The data fit within

the category A criterion with nearly 100-percent correlation. This fit implies that either (1) the lateral-directional

tasks being flown by the XB-70 are better represented by the category A flight phase, or (2) that some other parameter

Cooper-Harper

rating

1 m

2 m

3 B

///

///

4 - ///

///

///

///

S - ///

///

///

///

6 0 "( /

(_//_oCO/0 0 0 XB-70

/o: X SR-71

MIL-STD-1797

categories B and C

[-_ HSCT

I I I I I I I

.1 .2 .3 .4 .5 .6 .7

_dr

970071

Levell

Level2

(a) HSCT, categories B and C criteria.

Figure 22. LOES estimates of dutch roll damping compared with HSCT criteria and criteria from categories A, B,

and C of MIL-STD- 1797.

23
3

Cooper-Harper

rating

4

Level 1

Level 2

O XB-70

5 X SR-71

MIL-STD-1797

category A

s I I I

0 .1 .2 .3 .4 .5 .6 .7

_dr

970072

(b) Category A criteria.

Figure 22. Concluded.

was affecting the flying qualities, which is not accounted for in this plot. Reference 5 mentioned that the ratings

were collected during sonic boom measurement runs, where precise heading was crucial to fly over sonic boom

equipment on the ground.

Two HSCT criteria were defined to evaluate the roll rate oscillations due to the dutch roll mode. These two

criteria are defined as (1) the cost of an LOES first-order fit to the bank-angle-to-stick deflection frequency response

must be less than 25, and (2) _¢ptg_/_rt.Odr must be between 0.95 and 1.05. Both criteria were applied to SR-71 flight

data. Application of an LOES first-order fit to the bank-angle-to-stick deflection frequency response resulted in a

cost of approximately 11. Thus, the SR-71 data are acceptable according to the first criterion. The second criterion

was applied through an LOES fit to the bank-angle-from-stick deflection frequency response with the second-order

numerator parameters fixed at values estimated by a linear model. The dutch roll parameters were then estimated in

the LOES fit. The results show that _¢O_/_drO_dr is equal to 0.90, just outside the acceptable range. Pilot comments

indicated no problems with roll rate oscillations because of the dutch roll mode.

Lateral Acceleration at Pilot Station

The next criterion addresses the acceptable level of lateral acceleration at the pilot station during a roll. The

criterion is based on a parameter calculated by dividing the lateral acceleration at the pilot station by the maximum

roll rate encountered during the first 2.5 sec of a lateral step input. The criterion is applied to SR-71 flight data and

presented in figure 23. HSCT and MIL-STD-1797 criteria are superimposed on figure 23. The shaded regions show

where the data should fall if the criteria correlate with pilot ratings. Note that the HSCT criterion is slightly more

restrictive than the MIL-STD-1797 criterion. The SR-71 data, although inconclusive because of their scarcity, do

support both HSCT and MIL-STD-1797 criteria.

24
Cooper-Harper 3

rating

X SR-71

MIL-STD-1797

HSCT

Level 1

.02 .03

Ny at pilot station, g/(deg/sec)

Pmax

Level 2

s I

0 .01 .04

970073

Figure 23. Criteria on lateral acceleration at the pilot station.

CONCLUSIONS

NASA Dryden Flight Research Center evaluated the flying qualities of the SR-71 at Mach 3 through three welldefined maneuvers: steady level turn, ascending turn, and a vertical plane altitude change. The flying qualities of the

SR-71 were documented and reasons were identified for cases where level 2 ratings were given. The goal of this

research was to extend the high-speed flying qualities experience of large airplanes and to evaluate some of the more

recent MIL-STD-1797 criteria against pilot comments and ratings. The XB-70 and YF-12 data from research

conducted approximately 25 years ago supplemented the SR-71 data. Emphasis was placed on evaluating the criteria

used for the design of the High-Speed Civil Transport (HSCT). The following longitudinal criteria were evaluated:

low-order equivalent system (LOES), pitch bandwidth, flightpath bandwidth, and Neal/Smith. Additionally, the

memorandum evaluated the following lateral-directional criteria: LOES and lateral acceleration at the pilot station.

The results indicate the following:

1. In general, MIL-STD-1797, category C, or terminal flight criteria on pitch bandwidth and control

anticipation parameter (CAP) correlate well with the evaluations of high-speed flying qualities. The tasks

flown are considered typical maneuvering for high-speed flight. Application of these category C criteria to

aircraft in high-speed fight should result in an accurate evaluation of the longitudinal flying qualities.

2. Evidence exists for relaxing the short-period damping criterion for high-speed flight. The relaxation of the

short-period damping requirement may also affect the Neal/Smith borders on resonant peak as well.

However, other factors not accounted for in the XB-70 and YF-12 ratings, such as turbulence, may increase

the damping requirement.

3. High-speed handling qualities data, in general, support the HSCT terminal phase criteria as sufficient to

provide a good flying qualities airplane for typical high-speed maneuvering. Borders in the criteria specified

for the design of the HSCT were more restrictive, or conservative, in nature than both the MIL-STD-1797

criteria and the high-speed flying qualities evaluations. Criteria on CAP and short-period damping proved

too restrictive. Application of the flightpath bandwidth criterion to the data did not predict the expected pitch

attitude and flightpath consonance characteristics.

25
4. ApplyingtheNeal/Smithcriteriawiththestandardpitchattitudefromstickdeflectionfrequencyresponse

yieldedresultsthatdid not matchpilot commentsof leadcompensation. To correlatethe Neal/Smith

analysiswithpilotratingsandcomments, anextensionof thetechniqueusingtheverticalspeedatthepilot

stationwasrequired.OnlytheNeal/Smithcriterionfor caseswith highdampingappearsconsistentwith

evaluationsof high-speedhandlingqualities.

5. EstimatesofdutchrolldampingfortheXB-70correlatewellwithcategoryAcriterionfromMIL-STD-1797.

However,categoryCandHSCTcriteriadonotcorrelatewell,whichisoppositeto therelationshipseenin

otherparameters.

6. Usinginertialverticalspeed,insteadof theinstantaneousverticalspeedindicator(IVSI),whichisdrivenby

pressure,isimportantinthepilotcontrolofflightpath.

Althoughnotenoughdataexistin high-speedflightto beconclusive,theresultsof thisstudyindicatethat

categoryCcriteriamaybeapplicabletothehigh-speedflightregime.Manyof thecriteriamatchedpilotratingsand

comments,withtheHSCTcriteriaontheconservativeside.

Dryden Flight Research Center

National Aeronautics and Space Administration

Edwards, California, January 27, 1997

26
REFERENCES

1. Anon., "Flying Qualities of Piloted Airplanes," MIL-F-8785B, Aug. 7, 1969, U.S. Military Specification.

2. Berry, Donald T., "Some Handling Qualities Problems of Supersonic Cruise Aircraft," in NASA Aircraft Safety

and Operating Problems Conference, Volume H, NASA SP-271, May 1971, pp. 25-38.

3. Berry, Donald T., "A Summary of YF-12 Handling Qualities," in YF-12 Experiments Symposium, Volume 2,

NASA CP-2054, Sept. 1978, pp. 31-57.

4. Berry, Donald T., Donald L. Mallick, and Glenn B. Gilyard, "Handling Qualities Aspects of the NASA YF-12

Experience," Proceedings of SCAR Conference, NASA CP-001, Nov. 1976, pp. 193-213.

5. Berry, Donald T. and Bruce G. Powers, "Flying Qualities of a Large, Supersonic Aircraft in Cruise and

Landing Approach," AIAA 70-566, AIAA Atmospheric Flight Mechanics Conference, Tullahoma, Tennessee,

May 13-15, 1970.

6. Anon., "Flying Qualities of Piloted Vehicles," MIL-STD-1797 (USAF), Mar. 31, 1987, U.S. Military Standard.

7. Princen, N. H., M. A. Page, and K. F. Rossitto, "High Speed Civil Transport Preliminary Controls Sizing and

Flying Qualities Issues and Requirements," MDC report 94K0269, May 16, 1994.

8. Hodgkinson, J. and W. J. LaManna, "Equivalent System Approaches to Handling Qualities Analysis and Design

Problems of Augmented Aircraft," AIAA 77-1122, Aug. 1977.

9. Hoh, Roger H., David G. Mitchell, and John Hodgkinson, "Bandwidth--A Criterion for Highly Augmented

Airplanes," AFWAL-CR-80-3604, Air Force Wright Aeronautical Laboratories, Wright-Patterson AFB, Ohio,

June 1982.

10. Hoh, Roger H., "Recommendations for Approach and Landing Flying Qualities," STI Working Paper 2361-1,

Dec. 1988.

11. Neal, T. Peter and Rogers E. Smith, "An In-Flight Investigation to Develop Control System Design Criteria for

Fighter Airplanes, Volume 1," AFFDL-TR-70-74, Air Force Flight Dynamics Laboratory, Wright-Patterson AFB,

Ohio, Dec. 1970.

12. Powers, Bruce G., Phugoid Characteristics of a YF-12 Airplane With Variable-Geometry Inlets Obtained in

Flight Tests at a Mach Number of 2.9, NASA TP-1107, Dec. 1977.

13. Meyer, Robert T., John R. Knox, and Stephen A. Tingas, "Suggested Revisions to MIL-F-8785C for Large

(Class III) Aircraft" AFWAL-TR-83-3015, Feb. 1983.

27
REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188

Public reporting burden for this collection of mformatlon 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 completingand reviewingthe collectionof information. Sendcommentsregardingthisburdenestimateor any other aspect ot this collectionof information,

includingsuggestions for reducingthisburden,to WashingtonHeadquartersServices,DirectorateforInformationOperationsand Reports,1215JeffersonDavis Highway,Suite 1204, Arlington,

VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3. REPORTTYPE AND DATES COVERED

April 1997 Technical Memorandum

4.TTTLE AND SUBTITLE S. FUNDING NUMBERS

Evaluation of High-Speed Civil Transport Handling Qualities Criteria

With Supersonic Flight Data

6. AUTHOR(S)

Timothy H. Cox and Dante W. Jackson

7.PERFORMINGORGANIZATIONAME(S)ANDADDRESS(ES)

NASA Dryden Flight Research Center

P.O. Box 273

Edwards, California 93523-0273

9. SPONSORING/MONITORINGAENCYNAME(S)ANDADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

WU 529-50-24

8. PERFORMING ORGANIZATION

REPORT NUMBER

H-2153

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM-4791

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified--Unlimited

Subject Category 08

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

Most flying qualities criteria have been developed from data in the subsonic flight regime. Unique characteristics of

supersonic flight raise questions about whether these criteria successfully extend into the supersonic flight regime.

Approximately 25 years ago NASA Dryden Flight Research Center addressed this issue with handling qualities

evaluations of the XB-70 and YF-12. Good correlations between some of the classical handling qualities parameters,

such as the control anticipation parameter as a function of damping, were discovered. More criteria have been developed

since these studies. Some of these more recent criteria are being used in designing the High-Speed Civil Transport

(HSCT). A second research study recently addressed this issue through flying qualities evaluations of the SR-71 at

Mach 3. The research goal was to extend the high-speed flying qualities experience of large airplanes and to evaluate

more recent MIL-STD-1797 criteria against pilot comments and ratings. Emphasis was placed on evaluating the criteria

used for designing the HSCT. XB-70 and YF-12 data from the previous research supplemented the SR-71 data. The

results indicate that the criteria used in the HSCT design are conservative and should provide good flying qualities for

typical high-speed maneuvering. Additional results show correlation between the ratings and comments and criteria for

gradual maneuvering with precision control. Correlation is shown between ratings and comments and an extension of the

Neal/Smith criterion using normal acceleration instead of pitch rate.

14. SUBJECTTERMS

Bandwidth criteria, Flightpath bandwidth, Flying qualities, High-speed civil transport,

Low-order equivalent systems, Neal/Smith criteria, SR-71 aircraft, Supersonic flying qualities

17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION

OF REPORT OF THIS PAGE OF ABSTRACT

Unclassified Unclassified Unclassified

NSN 7540-01-280-5500 Available from the NASA Center for AeroSpace Information, 800 E/kridge Landing Road,

Linthicum Heights, MD 21090; (301)621-0390

IS. NUMBER OF PAGES

31

16. PRICE CODE

A03

20.LIMITATIONOFABSTRACT

Unlimited

Standard Form 298 (Rev. 2-89)

Prescribed by ANSI SId Z39-18

298-102