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NASA TECHNICAL NOTE
N A S A TN D-802J, C o /
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FLIGHT EVALUATION OF THE M2-F3
LIFTING BODY HANDLING QUALITIES
AT MACH NUMBERS FROM 0.30 TO 1.69
I
Robert W. Kempel, Willium H . Dana, and Alex G. Sim
/
Flight Reseurch Center *&& "
Edwurds, Culzy 93523 g
% .i* ''7.6 1976 3 .
N A T I O N A L A E R O N A U T I C S A N D SPACE A D M l ~ - H R A T l O f l W A S H I N G T O N , D. C. l J U ( X - b 7 5 c- J ' TECH LIBRARY KAFB, NM
I Illill l l U l l u l l lllY l i l t 1 1 1 1 II llll Ill
01338b3-- -- - .- I 2. Government Accession No. 3 . Recipient's Catalog No.
1. Report No.
NASA TN D-8027 I I
5. Report Date '4. Title and Subtitle July 1975 FLIGHT EVALUATION OF THE M2-F3 LIFTING BODY HANDLING 6. Performing Organization Code QUALITIES AT MACH NUMBERS FROM 0.30 TO 1 . 6 1
I
8. Performing Organization Report No.
7. Authorls) Robert W. Kempel , William H . Dana, and Alex G . Sim H-852 10. Work Unit No.
9. Performing Organization Name and Address
I 521-71-01
NASA Flight Research Center 11. Contract or Grant No.
P. 0. Box 273 Edwards, California 93523
i
13. Type o f Report and Period Covered 1 2 . Sponsoring Agency Name and Address Technical Note - National Aeronautics and Space Administration
I 14. Sponsoring Agency Code
Washington, D . C . 20546 I 5. Supplementary Notes - . . .
16. Abstract Percentage distributions of 423 pilot ratings obtained from 27 flights are used to indicate the general level of handling qualities of the M2-F3 lifting body. Eighty percent of the ratings were 3.5 or better, and 20 per- cent were 4 . 0 to 7 . 0 . Percentage distributions are compared on the basis of longitudinal and lateral-directional handling qualities, control system, control system status, and piloting task. Ratings of longitudinal han- dling qualities at low speed (subsonic configuration) were slightly better than those for transonic and supersonic speed (transonic config- uration) ; however, the ratings of lateral-directional handling qualities were unaffected by speed and configuration.
Specific handling qualities problems are discussed in detail, and com- parisons are made with pertinent handling qualities criteria.
~~ 17. Key Words (Suggested by Author(s1) 18. Distribution Statement Handling qualities Lifting bodies Stability and control Unclassified - Unlimited Category: 08 ___ .. - . - . . - . . , . . .- - .
20. Security Classif. (of this page) 19. Security Classif. ( o f this report) Unclassified Unclassified *For sale b y the National Technical Information Service, Springfield, Virginia 22151 FLIGHT EVALUATION OF THE M2-F3 LIFTING BODY HANDLING QUALITIES AT MACH NUMBERS FROM 0.30 TO 1.61
Robert W . Kempel, William H . Dana, and Alex G . Sim
Flight Research Center INTRODUCTION
The National Aeronautics and Space Administration and the U .S . A i r Force
jointly investigated the flight characteristics of several lifting body configurations to develop a reentry vehicle that could be maneuvered along a variety of atmos- pheric entry paths. The first configuration tested in flight was the lightweight M2-Fl (ref. 1). These tests were followed by flights of the heavyweight M2-F2 (refs. 2 and 3) , the HL-10 (ref. 4) , and the X-24A (ref. 5) lifting bodies at sub- sonic, transonic, and low supersonic speeds.
The M2-F2 lifting body was extensively damaged during a gear-up landing.
The vehicle was rebuilt and a fixed center fin was added. The modified vehicle was designated the M2-F3.
Twenty-seven flights were made in the M2-F3 flight test program. The num- bering sequence of the flights began with flight 17. (Flight 16 was the last M2-F2 flight .) During the program, the M2-F3 reached a maximum Mach number of 1 . 6 1 and a maximum altitude of 2 1 794 meters ( 7 1 501 feet).
This report discusses the M2-F3 handling qualities in general and the longi- tudinal and lateral-directional handling qualities in detail. Comparisons are made between the stability and control characteristics of the basic unaugmented vehicle and the augmented vehicle (stability augmentation and command augmentation sys- tems on). Pilot ratings of the vehicle's handling qualities during specific tasks are e v e n together with pilot comments. Flight stability and control characteris- tics determined from the data of reference 6 are compared with pilot evaluations where possible.
.
SYMBOLS Physical quantities in this report are given in the International System of
Units (SI) and parenthetically in U . S . Customary Units All measurements were
taken in U .S . Customary Units. Conversion factors are included in reference 7 .
a normal acceleration, g n a lateral acceleration, g Y b reference body span, m (ft) Rolling moment
rolling-moment coefficient, -
cQ
qSb
acQ
, per deg aileron-effectiveness parameter - cQ6 a Pitching moment pitching-moment coefficient, - ‘ m q s c aCm
longitudinal static stability parameter, -
Y per deg ‘ m aa a Yawing moment yawing-moment coefficient, - ‘ n qSb acn yawing moment due to aileron parameter, - C per deg a - C reference longitudinal length, m (ft) F longitudinal stick force, N (lb) es h altitude, m (ft) roll stability augmentation system gain deg/deg/ sec K P K roll command augmentation system gain, deg/deg/sec P C pitch stability augmentation system gain, deg/deg/sec K pitch command augmentation system gain , deg/deg/sec K 4 C yaw stability augmentation system gain , deg/deg/sec side stick gain, deg/sec/deg angle-of-attack hold gain, deg/deg dimensionalized aileron-effectiveness parameter, L6
-
a
q S b c , per see2
Rolling moment of inertia Q6 a M Mach number roll rate, deg/sec pitch rate, deg/sec dynamic pressure, hN/m2 (lb/ft2 ) yaw rate, deg/sec reference planform area, m2 (ft2 S Laplace transform operator, rad/sec t time, sec V velocity, m/sec (ft/sec) a angle of attack, deg or rad angle of sideslip, deg P aileron deflection, 6u - ' u , deg ' a left right (in. ) longitudinal stick deflection, cm lower flap deflection, deg
lateral stick deflection, cm (in .)
rudder deflection, 6r + ' r , deg left right 6 rudder pedal deflection, cm (in .)
r P longitudinal side stick deflection , deg lateral side stick deflection, deg upper flap position, $ 6 + 6u
( Uleft right
Dutch roll damping ratio roll-spiral damping ratio longitudinal short-period damping ratio pitch attitude angle, deg roll mode time constant , sec angle of bank, deg bank-angle-to-sideslip-angle ratio of the Dutch roll mode damped natural Dutch roll mode frequency , rad/sec undamped natural Dutch roll mode frequency, rad/sec undamped natural longitudinal short-period mode frequency, radjsec undamped natural roll-spiral mode frequency , rad/ sec Subscripts: QV average m a x maximum SAS stability augmentation system The sign convention used in this report to define the positive direction of forces, moments , velocities , angular displacements , and angular velocities is related to a is at the right-hand orthogonal body fixed-axis system. The origin of this system vehicle center of gravity. Positive directions , as viewed from the pilot's location , are forward , to the right , and down. Positive rotations are clockwise as viewed in the positive directions. By definition, right aileron and up normal acceleration are considered positive.
r
TEST VEHICLE The M2-F3 vehicle (figs. l(a) and l(b)) is a 13O, blunt, half cone with a boat- tailed afterbody and three aft vertical fins. The vehicle was powered by a four- chambered X L R l l rocket engine. Each chamber produced approximately 9786 new- tons (2200 pounds) of vacuum thrust. Liquid oxygen was used as the oxidizer and water alcohol as the propellant.
( a ) Side v i e w . E-21535 Horizontal Q reference Center fin, I r R i g h t rudder line I 6.77 (22.2)
-*
I 1 3 \ O
Lower ’ ‘XLR11 rocket engine
6 2 (9.63)
(four chambers) ( b ) Three-view drawing. Dimensions in meters (feet) .
Figure 1 . M2-F3 lifting body vehicle.
Reference The physical characteristics of the vehicle are presented in table 1.
dimensions used in the data analysis are included in the table.
TABLE 1 .- PHYSICAL CHARACTERISTICS O F M2-F3 VEHICLE
B o d y -
P l a n f o r m area, m2 (ft 1: 14.49 (156.0) A c t u a l . . . . . .
R e f e r e n c e . . . . . . . . . . 14.86 (160.0)
L o n g i t u d i n a l length, m (ft): 6.77 (22.2) A c t u a l and r e f e r e n c e . . .
Span, m (ft):
A c t u a l . . . . . . 2.93 (9.63)
3.03 (9.95) R e f e r e n c e . . . . .
L e a d i n g - e d g e sweep, deg . .
L o w e r flap - 1 . 4 2 (15.25) A r e a , m (ft2) . . . . .
1.65 (5.42) Span, m (ft) . . .
0.86 (2.81) C h o r d , m (ft) . . .
7570 (67 000) D e s i g n hinge m o m e n t , m-N (in-lb) .
U p p e r flaps, t w o - 0.85 (9.20) A r e a , each, m 2 (ft ) . . . .
Span, each, m (ft) . . . 1.26 (4.21)
0.68 (2.23) C h o r d , m (ft) . . . . .
3390 (30 000) D e s i g n hinge m o m e n t , each, m-N (in-lb) .
V e r t i c a l s t a b i l i z e r s , two - 1.50 (16.10) A r e a , each, m 2 (ft2) .
1.16 (3.79) H e i g h t , trailing edge, m (ft) .
C h o r d , m (ft): 2.24 (7.36) Root .
0.79 (2.58) Tip .
62.3 L e a d i n g - e d g e s w e e p , deg .
C e n t e r f i n - 1 . 1 2 (12.02) A r e a , m 2 (ft') .
1 . 2 6 (4.13) H e i g h t , trailing edge, m (ft) .
C h o r d , m (ft): 1 . 5 9 (5.21) Root, at h o r i z o n t a l r e f e r e n c e plane .
0.30 (1.00) Tip . . .
L e a d i n g - e d g e s w e e p , deg .
R u d d e r s , two -
. . 0.49 (5.27)
A r e a , each, m 2 (ft ) . .
Span, each, m (ft) . . . . 1 . 2 8 (4.20)
0.38 (1.25) C h o r d , m (ft) . . .
2600 (23 000) D e s i g n hinge m o m e n t , each, m-N (in-lb) .
C e n t e r of gravity, r e f e r e n c e - 0.496 Decimal f r a c t i o n of chord .
Aerodynamic Control and Vehicle Configurations Aerodynamic control was provided by a lower flap (pitch control), a differen- tial upper flap (roll control), and rudders (on the outboard surfaces of the out- board vertical fins) (figs. 1 and 2 ) . The rudders could be deflected in unison to The center vertical fin was fixed.
serve as speed brakes.
M 2 - F 3 rear quarter view showing lower E -21 533 Figure 2 .
f l a p , upper f l a p , r u d d e r , and fixed center f i n .
Two vehicle upper flap configurations-transonic and subsonic-were used.
The transonic configuration provided stability at transonic speeds; the subsonic configuration provided low drag (increased lift-to-drag ratio) for approach and landing. Upper-flap positions of - 1 1 . 8 O and - 2 O O were used for the subsonic and transonic configurations, respectively.
Reaction Control Rocket System In addition to the aerodynamic control surfaces, small hydrogen-peroxide- fueled rocket motors were installed to study their use as a means of vehicle con- trol and damping augmentation in the atmosphere. This system consisted of four 400-newton- (go-pound-) thrust rockets which were fired in pairs. These rockets were on the aft base area of the vehicle.
FLIGHT CONTROL SYSTEM The selection of M2-F3 flight control system characteristics was initially based on M2-F2 glide flight experience; however, extensive analysis of the M2-F3 ve- hicle was later required because of changes in aileron characteristics resulting from the fixed center fin and the rapid Mach envelope expansion planned for the vehicle.
Changes in control system characteristics were made by using a piloted hy- brid simulation to verify optimum damper gains and compensation time constants.
This simulation included rate and authority limits, a nonlinear longitudinal aero- dynamic model, and a linear lateral-directional aerodynamic model. In addition to the piloted simulation, linear analyses, including root loci and time response, were performed before the first flight and during the flight test program as aero- dynamic data were updated. Open- and closed-loop studies with various control systems, augmentation damper gains, compensation parameters, flight conditions, and aerodynamic derivative variations were made. Pilot evaluation of system sta- bility and performance was the final criterion upon which parameter selection was based. The llbestllestimate of the M2-F3 aerodynamic derivatives, mass charac- teristics, and open-loop dynamics is presented in reference 6 .
Manual Controls Primary s y s t e m . -The characteristics of the center stick, rudder pedals, and corresponding control surfaces are presented in table 2 . The pilot was provided with center stick and rudder pedal force feel by the use of coil-spring bungees, which provided force proportional to stick or rudder pedal position. Fine pitch trim was accomplished by biasing the center stick neutral no-load position of the coil-spring bungee to the desired commanded lower flap trim position. Roll trim was accomplished by biasing the individual upper flap aileron position.
TABLE 2 .-CENTER STICK, RUDDER PEDAL, AND CONTROL SURFACE CHARACTERISTICS - A u t h o r i t y , I A u t ; : ? , d e g l c m G e a r i n g , (deglin. ) Rate limit, Control c m ( i n . ) N l c m ( l b l i n . ) N (Ib) deglsec 12.19 ( 4 . 8 ) 1 Lower 10
I 13.35 (3)
1.67 ( 4 . 2 3 ) 25 4 8 . 5 flap ~~ ~~
I 4, I 2 7 . 1 1 (22.8) I , 7 . 8 8 ( 4 . 5 ) I 5 . 5 6 (1.25) f 2 0
A i l e r o n 2 . 8 2 ( 7 . 1 5 ) 30 I I I !
I 6 p p I t 1 1 . 1 8 ( f 4 . 4 ) I 41.33 (23.6) I 2 2 . 2 4 (5) R u d d e r 2 4 . 5 0 . 4 0 ( 1 . 0 2 ) ~- ~ The pilot made fine trim commands through a two-degree-of-freedom "beep" switch at the top of the center stick. Coarse longitudinal trim and configuration change were accomplished by means of a trim wheel on the left console which biased the upper flap. Rudder trim was through the rudder trim switch on the left console.
Secondary s y s t e m . --Speed brake commands were made through a switch on the X L R l l rocket throttle handle. Maximum speed brake authority was 20° and could be commanded from zero to maximum at approximately 2 . 9 degrees per second.
Two hydrogen-peroxide rockets were provided for use in landing the vehicle if energy became low during the final approach. Each of the rockets could provide approximately 2224 newtons (500 pounds) of thrust. The landing rockets were also controlled through a switch on the X L R l l rocket throttle handle.
The landing gear was deployed by pneumatic actuators controlled through a lever on the left of the instrument panel.
Cockpit d i s p l a y s . -The cockpit instrument display included indicators of air- speed, altitude, angle of attack, normal acceleration, and control surface position.
A three-axis attitude indicator provided attitude and angle-of-sideslip information.
Figures 3(a), 3(b), and 3(c) show the left console, instrument panel, and right console, respectively.
( a ) Left console. E-22387 Figure 3 . Arrangement of M2-F3 cockpit controls.
( b ) Instrument panel. E-25141 ( c ) Right console.
E -251 40 Figure 3 . Concluded.
Automatic Controls StabiZity augmentation system. -A limited authority, rate feedback stability aug- mentation system (SAS) provided damping augmentation about all three axes. A simplified block diagram of the flight control system is shown in figure 4 . The feed- back signals were provided by conventional rate gyros. The pilot selected system gains ranging from 0 to 1 in increments of 0 . 1 in terms of degrees of surface deflec- tion per degree per second of angular rate. The gains were fixed unless the pilot changed the position of the SAS control switch, which was on the left console in the
cockpit (fig. 3 (a)) . The yaw rate signal was modified by an electronic high-pass
(washout) filter so that the rudder returned to zero deflection as the yaw rate approached steady state. This kept constant-rate turns from being impeded by a SAS-commanded rudder input which would resist the steady yaw rate.
Rate gyro and Series
- Kr -= -
washout filter washout filter servo , U U 1 -
I I
Series - -
- Rategyro
KP -= servo Lateral 1 I , P Power Aileron
L ! - r *
stick actuator -cp L - P Rudder Power ~ 2 + 3 -' actuator dynamics
ray
--e Longitudinal Power - - stick
- i ' 9
actuator i - a servo q Figure 4 . Simplified block diagram of M2-F3 flight control system
Command augmentation system . -After flight 29 a rate command augmentation
system (CAS) was added to the vehicle. A simplified block diagram of the system is shown in figure 5 . This system made use of the basic M2-F3 control system hard- ware. Vehicle rate damping in the CAS mode was provided through the pitch and roll rate gyros and the existing SAS series servo actuators. Control was also pro- vided through the limited authority SAS servos. To provide adequate longitudinal control over the entire range of angle of attack a trim follow-up system was in- stalled. (CAS trim follow-up ranged from O o to 52O of lower flap .) The CAS aileron
authority was the same as the SAS aileron authority, + l o o or half the pilot authority
Series Rate gyro and
-
Kr -
servo washout filter
I
Rate gyro
=I
Latera I -P
Power Aileron - -
Stick gain and K - Series -
side stick - - c r
* compensation P C servo actuator - r p ' 0 = a Rudder Rudder M2-R Y
- Power -
-!- peda I
- dynamics
- actuator
-
= an Longitudinal CAS Stick gain and Series side stick- --(I
. compensation I compensation I
--a a6ack hold T r i m
I CAS
Angle-of- attack hold Ka and Angle-of-attack compensation vane
Et- Rate gyro
Figure 5. Simplified block diagram of M2-F3 command augmentation system. CAS engaged; angle-of-attack hoZd disengaged.
in the SAS mode. A selectable angle-of-attack hold mode was included as part of the CAS. Cockpit control of the CAS was through a side stick (table 3 ) . The CAS was mechanized in the pitch and roll axes only.
TABLE 3 .-SIDE STICK A N D CONTROL SURFACE CHARACTERISTICS G e a r i n g , A u t h o r i t y , F o r c e g r a d i e n t , B r e a k o u t f o r c e , A u t h o r i t y , Control S u r f a c e d e g of s u r f a c e / N l d e g ( l b / d e g ) N (1b) d e g d e g of s t i c k Lower 1 . 2 1 ( 0 . 2 7 2 ) 9 . 3 1 ( 2 . 0 9 ) i 7 . 5 0 . 3 flap
I I
230 1 . 3 1 (0.293) 6 . 4 6 (1.45) A i l e r o n f10 0.333 6sP s Figures 6 (a) 6 (b) and 6 (c) illustrate the operation of the longitudinal SAS , CAS, and angle-of-attack hold modes, respectively. The SAS provided only angular rate damping, the CAS provided rate command and angular rate damping, and the angle-of-attack hold provided rate damping. With the CAS in operation the cockpit angie-of-attack hold switch engaged, and the pilot's side stick i n the centered
Center stick T A j longitudinal Fa
q ( a ) SAS.
- M2-D -a
K (5 -+ 1.5) 61 longitudinal Side stick -
q C 5 dynamics - q i r I ~~
I
( b ) CAS.
( c ) Angle-of-attack hold.
Figure 6 . Simplified block diagram of M2-F3 longitudinal control system modes.
position, constant angle of attack was maintained. The side stick was provided with 'a centered position detent so that when the stick was out of center, angle-of-attack hold was disengaged and a rate was commanded until some new angle of attack was If the hold was reached. Centering the stick reengaged the angle-of-attack hold.
not desired, the cockpit switch was turned off and only rate command was operative.
A vernier was provided in the form of a switch on the side stick so that angle of attack could be changed without taking the stick out of detent. Center stick control with the SAS could be regained at any time by disengaging the CAS switch on the instrument panel or on the center stick.
Reaction Control Rocket System The four reaction control rockets were controlled either through the manual reaction control system (RCS) or the automatic rate feedback reaction augmentation
system (RAS) . From flight 2 3 to flight 29 the RCS and RAS were activated by the
pilot (about the roll axis only) through a simple toggle switch on the right console.
From flight 30 to flight 4 3 the pilot controlled the RCS through a side stick installed in the vehicle for use with the CAS. For these flights the system was mechanized to evaluate either the rolling or the pitching handling qualities, but not both. A sim- plified block diagram of the RCS and RAS mechanization is presented in figure 7.
Fixed
4-HFHFt gain
Deadband W . 5 deglsec) Figure 7 . Simplified block diagram of M2-F3 pitch o r roll RCS and RAS mechanization.
Two candidate rocket geometries (fig. 8) were established from wind-tunnel data on the basis of the yawing moment produced when the system was configured an outboard and to control the roll axis. Roll control was achieved by using opposite inboard rocket combination. The wind-tunnel data indicated that geom- etry 1 would provide proverse yaw during a roll maneuver; however, flight test results indicated that better handling qualities resulted when geometry 2 , which was predicted to produce no yawing moment, was used. Geometry 2 was thus used throughout most of the M2-F3 program. All longitudinal evaluations were made using geometry 2 . Wind-tunnel and flight-determined reaction control rocket data are presented in reference 6 .
k 0 . 8 8 9 ( 2 . 9 1 7 ) 4
L - 1.3446 (4.417) -
( a ) Geometry 1.
Left inboard Right inboard -15" 15" Right outboard ( b ) Geometry 2 .
Figure 8 . M 2 - F 3 reaction contro2 rocket geometries.
Dimensions in meters ( f e e t ) .
FLIGHT TESTS Flight Envelope The approximate operational flight envelope of the M2-F3 vehicle is shown in figure 9 in terms of altitude and Mach number. The flight envelope was bounded at the bottom by the dynamic pressure structural limit of 191.5 hN/m2 (400 lb/ft2 ) and at the top by an estimated minimum stability and control effectiveness boundary of
23.95 hN/m2 (50 lb/ft2 ) . The shaded area indicates the general envelope in which
the M2-F3 was flown.
Echvards altitude 0 .2 .4 .6 .8 1.0 1 . 2 1 . 4 1.6 1.8 M Figure 9. Approximate M2-F3 altitude and Mach number envelope.
Test Procedures The M2-F3 vehicle was launched from a B-52 airplane at an altitude of approxi- mately 13 720 meters (45 000 feet) and a Mach number of 0.67. Because of the exten- sive M2-F2 glide flight experience, only three glide flights were necessary for pilot checkout and to investigate the M2-F3 vehicle's aerodynamics with the center fin installed.
Figure 10 shows typical ground tracks for the terminal approach and landing pattern of an M2-F3 flight. During flight, ground radar tracked the vehicle and Distance, n. mi.
0 2 4 6 8 10 12 14 16 Ground track I I I I I 1 - I _ _ _ _ Low-energy track 2 5 :1d I High -energy track 12 Configuration change - (transonic to subsonic) (20000ft) - Distance, Distance, m ti n. mi.
0 5 10 15 20 25 30xld Distance, m Figure 10. Typical M2-F3 flight ground tracks f o r the terminal approach and landing pattern.
rxovided mission control with ground track and altitude information. Deviations k o m the planned profile, because of such €actors as high or low energy, were radioed to the pilot so he could take corrective action. The low-key point on the ground track was the point at which 180° were left to turn to final approach. A s shown, low key occurred at an altitude of approximately 6100 meters (20 000 feet).
A typical powered flight (fig. 11) began with launch in the transonic configura- tion at an altitude of 13 720 meters (45 000 feet). The launch point was approx- imately 74 kilometers (40 nautical miles) southwest of Rogers Dry Lake. Ten sec- onds after launch, the vehicle was rotated to an angle of attack of 14O as the engine was ignited. Vehicle rotation was then continued to a pitch attitude of approx- The vehicle climbed to an altitude of imately 40° , which was held for 19 seconds.
16 150 meters (53 000 feet) and attained a Mach number of 0.82 , where it was pushed over to O o angle of attack and accelerated to Mach 1.36 at 94 seconds after launch. Maximum Mach number was reached at rocket engine burnout. Vehicle configuration change from transonic to subsonic occurred at approximately 255 sec- onds at Mach 0.6. At this point the pilot visually navigated to the downwind leg 180° turn to the and into the landing pattern. The final phase of the flight was a final approach and landing. The powered portion of the flight averaged 92 seconds and the unpowered portion averaged 301 seconds, for a total average flight time of 393 seconds.
I Figure 1 1 . Typical M2-F3 powered flight profile.
Several landings were made at an alternate dry lake when conditions were unfavorable at Rogers Dry Lake. No problems were encountered on these landings.
PILOT RATINGS The in-flight handling qualities of the M2-F3 vehicle were assessed by four research pilots. The pilots all had lifting body experience although most of their experience was with fighter-type aircraft. On each flight the pilots were asked to evaluate selected maneuvers and tasks at specified angles of attack and Mach num- bers. Some of the tasks were part of the basic flight profile, such as the powered Narrative and numerical evaluations of the vehicle's boost, turns and flare.
handling qualities and response characteristics were obtained immediately after each flight. The numerical pilot ratings were based on the modified Cooper-Harper 8) shown in table 4(a). Table 4(b) presents levels of flying rating scale (ref.
qualities from Military Specification MIL-F-8785B (ref. 9 ) . A s shown level 1 corresponds to pilot ratings from 1.0 to 3.5, level 2 from 3.5 to 6.5 and level 3 from 6.5 to 9.5. For comparison with the Military Specification the M2-F3 vehicle was considered to be a Class I1 vehicle, that is a mediumweight aircraft with low- to-medium maneuverability. The flight phases considered to be applicable were
nonterminal (Category B) and terminal (Category C) . The nonterminal flight phase
is defined as being normally accomplished by using gradual maneuvers with no precision tracking although a requirement for accurate flightpath control may exist. A terminal flight phase is defined as being accomplished by using gradual maneuvers that usually require accurate flightpath control.
DISCUSSION General Handling Qualities QveraZZ stabizity and controz .-Figure 1 2 shows the percentage distribution of the 423 pilot ratings obtained during the 27 flights of the M2-F3 vehicle. The most frequently assigned rating of 3.0 constituted approximately 31 percent of those ob- tained. Eighty percent of the ratings were 3.5 or better; that is, the handling qual- ities were considered to be satisfactory without improvement. Twenty p.ercent of the ratings were from 4.0 to 7.0. (Only one rating of 7.0 was given. ) Figures 13 and 14 present the percentage distribution of the pilot ratings of the longitudinal and lateral-directional handling qualities , respectively. The data are presented as an implicit function of speed, in that results are presented for both the subsonic and transonic configurations.
13 (a) and 13 (b)) the ratings for For the longitudinal handling qualities (figs.
the lower speeds (subsonic configuration) were slightly better than those for the
transonic and supersonic speeds (transonic configuration) . For the subsonic con-
figuration 87.6 percent of the ratings were 3.5 or better y and for the transonic configuration 69.8 percent were 3.5 or better.
TABLE 4 . -MODIFIED COOPER-HARPER HANDLING QUALITIES RATING SCALE AND MILITARY SPECIFICATION DEFINITION OF FLYING QUALITIES LEVELS (b) Military Specification definition of (a) Modified Cooper-Harper rating scale (from ref. 8) levels of flying qualities (from ref. 9) DEMANDS ON THE PILOT AOEWACY FOR SELECTED TPSK OR A " Y + F ~HARACTER~ST~CS ' IN SELECTED TASK OR REOUIREO OPERATIC^ RAT REWIRED OPERATION* - Eacellent Pilaf compensation not o foclor for I( Hlghly desirable desired performance I Good Pilot compensation no1 o foctw for
. Flying qualities clearly adequate for
v * desired performance Neqllgible ckficimies 1 1 the mission flight phase.
Fa~r - Some mildly . Minimol pilot capcnsalion reqwred fw
unpleasonl deficiencies dewred performonce
YtS c \ J M l M but amoylng . Desired performonce requires maderolc 7
j pilot compensotion deflClenCles plish the mission flight phase, but
Moderolely ck~ctiorable . Adequole perlormonce requires
Level 2 some increase in pilot workload or deflClencles consideroble pilol compensotion degradation in mission effectiveness very objectloraMe bul Adequole performonce requires exlensive IdnoMe deficiencies ' pl~ol compensation or both, exists.
/ r Adequole performance nd olloinable wllh I Flying qualities such that the air-
M o p deflclencies . moilmum tolerable pilal compensation. 7
Controllobilily not in question plane can be controlled safely, but
Ma,or . Consideroble pilot compensalion is required
Level 3 pilot workload is excessive or for conlrol mission effectiveness is inadequate,
Malor def,c,encltS . Intense pilot cornpensolion is required lo
or both.
reloin control I J \ 'Definition of required operation involves designation of flight phose and/or subphoses wilh RlOf k l S l O n s accomponyinq conditions.
c
Occurrence of pilot ratings, 20 percent 4 5 6 7 P i lot r a t i n g Figure 12. Percentage distribution of pilot ratings. Total ratings, 423.
Satisfactory without 50 Sat i sfactory without improvement improvement CAS o r off Occurrence of pilot ratings, percent 2o 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Pilot r a t i n g Pilot r a t i n g ( a ) Subsonic speeds and subsonic ( b ) Transonic and supersonic speeds configuration. SAS or CAS o n , and transonic configuration. S A S or CAS o n , 111 ratings (93.3 percent); 94 ratings (83.2 percent); S A S o f f , S A S off, 8 ratings ( 6 . 7 percent); 19 ratings ( 1 6 . 8 percent); total ratings, 113. total ratings, 119.
Figure 13. Percentage distribution of longitudinal pilot ratings for subsonic, SAS on and off; total ratings, 232.
transonic, and supersonic speeds.
For the lateral-directional handling qualities (figs. 14(a) and 14(b)), speed and configuration had little effect on the ratings. For the subsonic configuration 87.3 per- cent of the ratings were 3 . 5 or better, and for the transonic configuration 76.4 per- cent of the ratings were 3 . 5 or better.
Satisfactory without r = +Satisfactory without
i - 4 / improvement
r improvement
Occurrence of pilot ratings, 20 percent 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Pilot r a t i n g Pilot rating ( a ) Subsonic speeds and subsonic ( b ) . Transonic and supersonic speeds configuration. S A S or CAS o n , and transonic configuration. S A S or 90 ratings (88.2 percent); SAS o f f , CAS o n , 83 ratings (93.3 percent); 12 ratings (11.8 percent); total SAS off, 6 ratings (6. 7 percent); ratings, 102. total ratings, 89.
Figure 1 4 . Percentage distribution of lateral-directional pilot ratings for sub- sonic, transonic, and supersonic speeds. SAS o n and off; total ratings, 191.
Approximately 10 percent of the 423 ratings were for SAS-off conditions. The handling qualities of the M2-F3 vehicle under these conditions were considered to be generally satisfactory. Although many maneuvers were performed with the SAS off, most of the pilot ratings were better than 5 . 0 . The SAS-off conditions (K = 0) or the lateral-directional evaluated were either in the longitudinal axis axis ( K = K r = 0 ) , but not both. The damping ratio for the longitudinal short- P period mode and the Dutch roll mode with the SAS off was generally 0 . 1 or less.
The roll mode time constant with the SAS off was generally greater than 5 seconds.
The M2-F3 vehicle was typical of vehicles with very low aspect ratios, in that the natural roll damping was low, resulting in aileron control that was very sensitive with the roll and yaw SAS off. Longitudinal SAS-off characteristics were generally satisfactory at the flight conditions selected. Conditions at which stability was marginal were not investigated in this mode.
Although the vehicle's SAS-on handling qualities were considered to be gener- ally satisfactory, SAS-on handling qualities problems did occur in some portions of the flight envelope. Two particular problems-the powered boost constant-high- angle-of-attack longitudinal task, and a SAS-induced lateral-directional transonic instability-are discussed later.
2 1 Comparison of stability augmentation system and command augmentation s y s - tem ratings. -Figures 15(a) and 15m) compare pilot ratings for the SAS and the (Pitch and roll tasks were CAS for the subsonic and transonic configurations.
combined .) For this comparison , only ratings which evaluated the SAS and the CAS
for the same task are included. For the subsonic configuration only 10.9 percent of the ratings were for the CAS mode; no significant difference in handling qual- ities is indicated with the CAS on. For the transonic configuration almost half of the ratings were for the CAS mode; an improvement of 0.5 in pilot ratings ( 3 . 0 to 2.5) is indicated with the CAS on.
Satisfactory without Satisfadory without
/- 1 improvement /-I improvement
Occurrence of
- r n
p i lot ratings, percent 1 2 3 4 5 6 7 L 2 3 4 5 6 7 Pilot r a t i n g P i lot rating ( b ) Transonic and supersonic ( a ) Subsonic speeds and subsonic speeds and transonic configura- configuration. SAS , 90 ratings tion. S A S , 58 ratings ( 5 6 . 8 per- (89.1 percent); CAS, 11 ratings ( 1 0 . 9 percent); total ratings, 101. cent); CAS, 44 ratings ( 4 3 . 2 per- cent); total ratings, 102.
Figure 15. Comparison of SAS and CAS pilot ratings for subsonic, transonic, and supersonic speeds. Total ratings, 203; pitch and roll tasks.
Reaction rocket control and damping augmentation. -In the lateral axis , reaction rocket control was adequate for maneuvering as well as for stability augmentation , although in the manual or RCS mode , control sensitivity resulted in "jerky" attitude changes and received a pilot rating of 5.0. In the rate feedback or RAS mode, with normal pilot aileron control , the damping augmentation was rated 2 . 0 .
In the longitudinal axis, the RCS mode could not compensate for aerodynamic trim. In the RAS mode , however , damping augmentation was considered to be good.
Pilot ratings for the pitch RAS mode were generally 2 . 0 to 2.5 when only minimal damping was required. For more demanding situations, such as when the vehicle's natural damping was low, the rate damping requirements exceeded the RAS capability, and pilot ratings were 4.0 to 4.5. On one flight an asymmetrical dead- band existed so that the RAS was activated when the nose-down rate was 1 deg/sec and the nose-up rate was 5 deg/sec. This resulted in pilot ratings from 5.0 to 6.0.
Even though the RAS was not optimized, the proof-of-concept was established.
The results of this study are particularly significant in light of the RAS damping with aerodynamic trim proposed for the space shuttle vehicle.
Longitudinal Handling Qualities Longitudinal stability and control. -Generally, the longitudinal static stability
characteristics of the M2-F3 vehicle were satisfactory (ref. 6) . The linear longitu-
dinal static stability characteristics were satisfactory throughout the flight envelope, In this range the pitching-moment coefficient charac- except from Mach 0.86 to 1.05.
teristics became nonlinear, as illustrated in figure 16 in which pitching-moment
.03 r
I -4 -2 0 2 4 6 8 10 12 14 16 18 a, deg Figure 16. Pitching-moment curve from wind-tunnel data ( r e f . 6 ) .
= -2OO; center of gravity = 0 . 4 9 6 c .
M = 0.95; 6 U Figure 1 7 presents the wind-tunnel and coefficient is plotted against angle of attack.
flight-determined static stability parameter, Cm , as a function of Mach number for a several angles of attack. A s shown, the static stability at transonic speeds was low.
Lower flap control effec- Consequently, the handling qualities were relatively poor.
tiveness remained at an acceptable level throughout the flight envelope.
0 Flight Wind tunnel ---- Interpolation -.003
r
I- a = 3.6"
f I I I I I I
0 -------
_ # - -
-_
IO--' c, I Per deg a a = 5 . 1 "
-
-.003 - -.002
c, . Per deg
-- - / *-.MA
a -n.
c c - c -.001 \ \ .I a = 7.2" 'IL--.
I I I 1 1 I .86 .90 .94 .98 1.02 1.06 1.10 M Figure 17. Comparison of static stability parameter obtained from flight data i n the transonic speed region with wind-tunnel predictions ( r e f . 6 ) .
6 = - Z O O ; 6Q as required for trim.
U The flight-determined longitudinal stability boundary is shown as a function of Trim limits are included. It is evi- angle of attack and Mach number in figure 18.
dent that, between Mach 0 . 7 and 0 . 9 6 , the vehicle could enter an unstable region.
The unstable region was never penetrated with the SAS off, although flight in this region was necessary during the powered boost. A maximum SAS-on limit of 15O .. .. . . .
. . . . . ... .- - ...
I angle of attack was established, but was exceeded occasionally. This limit was a compromise between the angle of attack required for satisfactory SAS-on longitudinal stability and that required to promptly attain the powered boost flightpath angle.
Unstable (SAS off), \ Limits of trimmed flight/\\\ I 1 - 0 .2 .4 .6 .8 1.0 1.2 1.4 1.6 M Figure 18. M2-F3 trimmed flight envelope and the longitudinal SAS-off stability boundary. 6 = - Z O O ; center of gravity = 0 . 4 9 6 c .
U Powered boost. -The powered boost portion of the flight profile consisted of three distinct tasks: maintaining a constant high angle of attack ( 1 5 O limit) to the desired pitch attitude , maintaining a constant pitch attitude to the desired altitude , and pushing over to a low angle of attack to attain maximum Mach number. For the powered flights the vehicle was launched with the center of gravity at the approxi- mate aft limit ( 5 0 . 5 percent c ) , which resulted in static instability with the SAS off of attack and subsonic speed. With the SAS on, the stability was at high angle marginal, resulting in a demanding handling qualities task in which precise con- trol of angle of attack was required. Indicative of the magnitude of this problem was a situation which occurred on one flight. With the SAS on , the pilot inad- vertently allowed the angle of attack to reach 21° when his attention was directed to the rocket engine ignition sequence.
Figure 19 shows the distribution of pilot ratings for the longitudinal powered boost task in which the SAS and the CAS were used. These ratings are significantly worse than those for other tasks. Of these ratings 5 1 . 6 percent were between 4 . 0 and 6 . 5 ; the most common rating was 5 . O ( 2 2 . 6 percent).
To improve the handling qualities in this portion of the flight profile an angle-of- attack hold mode option was included as part of the CAS. Early experiences with the angle-of-attack hold were disappointing, as indicated by the frequent pilot rating . ..
.. . . ..
Satisfactory without improvement
: i z (angle-of-attack hold)
Occurrence of p i lot ratings, percent 1o 1 2 3 4 5 6 Pilot rating Figure 1 9 . Percentage distribution of longitudinal transonic speed and transonic configuration pilot ratings for powered boost. Total ratings, 3 1 .
of 5.0. This rating was given primarily because of the difficulty in engaging the angle-of-attack hold , as a result of the poor side stick characteristics (for example, In addition, it was necessary for the the narrow detent and low breakout force).
pilot to wear a pressure suit while he performed dynamic maneuvers , which aggra- vated the effect of the low breakout force, narrow detent, and force gradient of the side stick. Another problem which distracted the pilots was the approximately +0.5O angle-of-attack drift associated with the angle-of-attack hold system. Modifications to the breakout force and the width of the detent combined with increased pilot ex- perience indicated that the CAS could be made to function as intended.
Figure 20 is an example of the use of the SAS and the CAS with angle-of-attack hold to perform the powered boost. The pilot indicated that when the SAS was on he could not stabilize angle of attack. He rated the task at 6 . 0 . On the following flight he used the CAS with the angle-of-attack hold. H i s comments concerning this task were as follows: Longitudinal damping was significantly improved in comparison with normal SAS-on boost. Angle-of-attack control was positive and apparently better than indicated during simulation. The 1 4 O angle of attack was easily established during rotation and the angle-of-attack hold was especially effective after engagement at 1 4 O angle of attack, and wander was almost nonexistent. At no time did I observe more than 0.5O angle-of-attack excur- sion from the desired 14O. Pilot rating during boost was 2 . 0 .
An improvement in pilot rating from 6 . 0 to 2 . 0 was realized from one flight to the next. It should be pointed out that this improvement was not typical.
The constant-pitch-attitude portion of the boost was much improved by using the CAS. Pilot comments concerning this task were as follows: A s the aircraft reached 40° theta, the angle-of-attack hold was disen- gaged. With no pilot input, and thus a zero pitch rate commanded, the CAS held the aircraft at precisely 40° theta. The rate command loop This appeared to be much tighter than the angle-of-attack hold loop.
portion of the flight was given a pilot rating of 2 . 5 , which compared to a pilot rating of 5.0 for the same task using SAS .
The CAS with the angle-of-attack hold was a welcome addition to the vehicle, and Some of the its potential was recognized even though difficulties were encountered.
discrepancies which prevented realization of the full potential included the following: (1) In the angle-of-attack hold mode , during high pitching rates , the desired angle of attack was attained and, as the stick was centered to engage the hold, the pitch rate decayed, thus reducing the angle of attack from the desired value.
(2) The low total system gain permitted an angle-of-attack deviation of more than 0.5O at high angles of attack.
(3) The generally poor side stick characteristics could not be changed without affecting the overall integrity of the controller (e. g. , force gradient , deadband, and breakout force).
C A S and angle-of-attack hold on 9, deglsec I I U -10 r '11 d@ 30 10 20 30 40 50 t, sec ( a ) SAS, Mav = 0 . 8 5 , = 89.47 hN/m2 ( b ) CAS and angle-of-attack hold, - a v = 0 . 8 0 , qav = 84. 76 hN/m2 (190 l b / f t 2 ) , power on, K = 1 d e g / d e g / M a v q = 1 d e g / (180 lb/ft2 ) , power on, K s e e , pilot rating = 6 . 0 .
9, d e g / s e c , pilot rating = 2 . 0 .
Figure 20. Comparison o f M2-F3 powered boost using SAS and CAS w i t h angle-of-attack hold.
2 7 Short-period mode characteristics. -Table 5 shows representative M2-F3 short-period mode characteristics and pilot ratings for selected flight co:iSI tions .
TABLE 5 .-REPRESENTATIVE M2-F3 LONGITUDINAI R E S P O N S E CH/:T? iCTERI' 11C S AND PILOT RATINGS FOR SELECTED FLIGHT CONDITIONS - K n ' a n l a , 9 .
M
I Configuration Pilot r a t i n g a , deg q ' S P
hN/m2 (lb/ft2 ) C S P degldeglsec radlsec glrad 1 . 0 2.96 2.23 7.45 0.70 128.8 (269) 1 . 7
k S u b s o n i c 2 . 5
1 4 1 . 3 (295) 1 . 3 0 . 4 2.89 1 . 2 5 7.64 3 . 0 0 . 5 1 Subsonic 1 . 0 1 . 4 5 1 . 3 1 2.43 0.67 4 2 . 6 (89) 1 . 0 Transonic 3 . 0 8 . 5 0 . 4 2 . 7 0 0.988 4.87 Transonic 3 . 0 0.89 1 1 0 . 1 (230) 1 . 0 2 . 5 1.10 4 3 . 1 (90) 4 . 6 2 . 2 1 0.738 2.10 Transonic 5 7 . 0 (119) 4 . 1 0 2.48 0.083 2.25 Transonic 3 . 0 1 . 0 9 .~ Frequency, damping ratio, and acceleration sensitivity were computed by using the flight data of reference 6 . These data are typical of those obtained throughout the flight test program, except in the powered boosts.
Longitudinal stability and damping for the flight con- ditions shown in the table were relatively good. The frequency and acceleration 6 sensitivity characteristics are compared in figure 2 1 W n Q I ,-,..,.I I m with the current Military On 9 Specification for piloted SP 2 radlsec airplanes (ref. 9 ) . The data for the M2-F3 vehicle were generally within the .8 level 1 boundary.
.6 .4 Longitudinal trim. - Changes in longitudinal trim I I I I - - I I 1 1 1 associated with shifts in the 2 4 6 8 10 20 40 60 80100 center of pressure and aero- anla, glrad dynamic center encountered during the M2-F3 flight test program were caused by Figure 2 1 . Comparison o f M2-F3 longitudinal changing transonic Mach num- short-period mode frequency and acceleration ber, configuration change sensitivity characteristics w i t h Category B from transonic to subsonic, requirements from reference 9. M = 0 . 5 1 to speed brake deployment, and a = l . O o to 8.5O; K = 0 to 1 . 0 d e g / d e g / 1.10; landing gear extension. 4 s e c .
The transonic speed range (M = 0.88 to 1.04) power-on and power-off trim curves are summarized in reference 6 . Changes in trim angle of attack varied from 3 O to 4 O in a nose-down direction. The pilots generally believed that this t r i m change was easily controlled and that the transient longitudinal characteristics were not a problem. This pitch-down tendency did however, cause a lateral- directional instability which is discussed later.
The configuration change on each of the three lifting bodies (M2-F3, HL-10, and X-24A) was approached cautiously. One pilot made the following comments about a flight on which the SAS was operating: Of the three lifting bodies the M2-F3 exhibited the least troublesome
characteristics [during configuration change] . This was due in large
part to the training provided by excellent simulation of this maneuver.
The pilot rating for this maneuver was 3 . 5 .
The same pilot made the following comments for a flight on which the CAS was used: A "hands off" configuration change was performed utilizing alpha- hold. It held angle of attack better than the simulator. The pilot rating for this maneuver using CAS was 2 . 5 .
A large nose-down pitching moment was associated with speed brake deploy- ment. Simulation indicated that when full speed brake was deployed maximum elevator deflection could be reached in the landing flare. To avoid this problem the pilots returned the speed brakes to the zero position before starting the flare.
Landing gear deployment, as previously mentioned produced a relatively large nose-down pitching moment. Landing gear extension time was approximately 1 second, thus the pitching-moment transient was abrupt. No particular problems were reported by the pilots as a result of the magnitude or abruptness of the trim change. Pilot ratings were generally 2 . 5 . One pilot reported the following: I did notice a tendency for a slight pilot-induced oscillation after gear deployment, but not severe enough to be of concern. [Pitch damper setting was K = 0 . 4 deg/deg/sec. 1 F i n d a p p r o a c h , f l a r e , a n d Zanding. -Lifting body landing procedures and rationale are described in detail in reference 1 0 . The four phases of the landing consisted of: (1) a high-constant-speed ( 5 5 5 . 6 km/hr (300 knots)) final approach, starting at approximately 3050 meters (10 000 feet) altitude, (2) a 1.5g flare 305 meters (1000 feet) above ground level, (3) landing gear extension at 3 0 . 5 meters (100 feet) or less and (4) touchdown. All landings were unpowered with relatively steep final approach glidepath angles of approximately -3OO.
The CAS was never used during the final approach, flare and landing because of the lack of redundancy it w a s used up to the final approach.
in the automatic pitch trim system although Pilot comments indicated a tendency toward a longitudinal pilot-induced oscilla- tion (PIO) before touchdown as a result of the overly sensitive longitudinal center stick. To assist the pilot, the basic vehicle damping was improved by increasing the pitch SAS gain to 0 . 3 deg/deg/sec or, preferably, 0 . 4 deg/deg/sec before touch- down. The following pilot comment was made: I wouldn't want it any more sensitive. I felt that I was right on the threshold of a longitudinal PIO. [Pitch damper gain of K = 0 . 3 deg/
deg/sec. 1 q
Figure 22 (a) compares the computed short-period mode frequency and damping characteristics for landing flare and touchdown with the Military Specification of reference 9 . Data for the vehicle with the SAS on are within the level 1 boundary.
3.0
- Minimum for -
range 2.5 Kq' degldeglsec 0 0
y
2.0 0 0.1 / 0 0.2 / O n A 0.4 S P / radlsec 1.5 / 1.0 > 1 1 .I .2 .4 . 6 .8 1.0 2.0 zSP ( a ) Frequency and damping.
Figure 22. Comparison of M2-F3 subsonic configuration longitudinal short-period mode landing characteristics with minimum Category C levels from reference 9 . Landing flare: = 146.5 hN/m2 (306 Zb/ft2),
V = 162.2 m/sec (532 ft/sec) , M = 0.5; touchdown: < = 47.9 hN/m2
(100 l b / f t 2 ) , V = 106.7 m/sec (350 ft/sec), M = 0.35.
Figure 22 (b) shows that the short-period mode frequency and acceleration sensitiv- ity data are also within the level 1 boundary for the vehicle with the SAS on.
I a, deg 0 5 a 10 o 15 2 and 3 n i S P radlsec 1 I I l l I I I l l .2 2 4 6 8 10 20 40 60 80100 anla, glrad ( b ) Frequency and acceleration sensitivity, K = 0 . 4 d e g / d e g / s e c .
q Figure 22. Concluded.
Figure 23 compares the M2-F3 SAS-on longitudinal stick force and stick travel per unit normal load factor (for the short-period dynamics of fig. 22 (a)) with the des/an, in./g 0 .25 .50 .75 1.00 1 I I 0 .5 1.0 1.5 2.0 2.5 3.0 des/an, cmlg Figure 23. Comparison of the M2-F3 longitudinal stick force and stick travel p e r unit load factor (for the dynamics of f i g . 2 2 ( a ) ) w i t h the criterion of reference 11.
satisfactory low-altitude , high-speed flight boundary from reference 11. The longi- tudinal sensitivity of the M2-F3 vehicle is indicated by the shaded area, which approaches the P I 0 boundary. Although the M2-F3 vehicle was considered to be sensitive to longitudinal control and tended toward pilot-induced oscillations, its handling qualities were rated as satisfactory on the basis of the criterion of refer- ence 11.
The pilots considered the M2-F3 handling qualities and flight characteristics to be good during the landing approach. Figure 24 presents the pilot ratings for this task. Approximately 95 percent of the ratings were 3 . 5 or better. Typical pilot comments were as follows: The M2-F3 landing task was 50 - Satisfactory without
- /=I improvement
straightforward. There was am-
-
ple normal acceleration capability - available for the flare, and stick force per unit g was linear. A nose-down pitching moment did 30 - Occurrence of occur at landing gear extension pilot ratings, and was expected to cause a'han- - percent 2o - dling qualities problem, but in - fact was quite easily corrected for with back stick. Generally, - - there was adequate normal accel- eration capability after gear de- l l ployment , and most touchdowns 0 Over-the-deck vision out of the M2-F3 was quite good forward. To the sides , the deck blocked most downward vision, and field of vie'w was unsatisfactory. When navigating , it was necessary for the pilot to roll the vehicle considerably to see the ground abeam his position.
Also , just before touchdown , the deck blocked the pilot's view of the runway lines used for height reference.
To provide forward Vision at high deck angles, particularly at land- ing , there was a window in the M2-F3 nose. The right side of this win- dow was blocked approximately 50 percent by instruments and other equipment. The left side originally provided good vision for landing and was used extensively just prior to touchdown. When the CAS was added , switch panels encroached upon about three-quarters of the left nose window. This caused the final phases of landing to be much more challenging, and longitudinal control during landing was not as smooth after the CAS panel was installed. Pilots who checked out in the M2-F3, however , were warned that forward visibility at high deck angles was inadequate. Therefore, pilots compensated by looking obliquely over the deck during landing, and they indicated that this technique allowed good landing vision even with the CAS panel installed.
Lateral-Directional Handling Qualities Lateral-directional stability and control. -The M2-F3 lateral-directional sta- bility characteristics were dominated by aerodynamic characteristics unique to this class of lifting body vehicle. These included very high effective dihedral and low natural roll damping. In addition, the mass distribution was highly concentrated about the roll axis , resulting in a low rolling moment of inertia (ref. 6 ) . A s a re- sult of these characteristics, the Dutch roll mode exhibited relatively high fre- quency, and a coupled roll-spiral mode usually existed with the roll and yaw SAS off (ref. 3 ) .
Extreme adverse yawing moment due to aileron was a problem on the M2-F2 vehicle which necessitated large aileron-to-rudder crossfeed compensation. Wind- tunnel tests indicated that the yawing moment due to aileron would be favorable with the fixed center fin on the M2-F3 vehicle and would have little effect on other aerodynamic characteristics. With the improved aileron characteristics and proper selection of SAS and CAS gains , stability and control characteristics were generally satisfactory (refs. 3 and 6 ) . One exception was that at transonic speeds, low angle of attack, and certain SAS gain settings the Dutch roll mode was unstable, as is discussed later.
Powered boost. -The lateral-directional handling qualities in the powered boost were generally considered to be good. One pilot commented as follows: In general, during the launch, rotation, and climb phase of the flight, the lateral-directional axes were never a concern. Pilot ratings were consistently 2 . 5 or better. Because of the difficulty in performing the pitch task during the boost portion of the flight, very little time was allowed to assess lateral-directional handling qualities. A testimony to the excellent lateral-directional characteristics is the fact that they could be ignored while concentrating on the pitch task. I feel that this fact in itself warrants a pilot rating of at least 2 . 0 to 2 . 5 .
Wind-shear-induced disturbances. -During the powered boost portion of the flight , the pilots frequently commented about uncommanded lateral disturbances.
In an attempt to determine the cause of the disturbances, photographs of the M2-F3 contrail were made from a ground position directly below the vehicle. These photographs were correlated with the pilot's voice transmissions to observe the nature of the contrail whenever he stated that an uncommanded upset had occurred.
The photographs showed that parts of the contrail became increasingly displaced, with time , from the original contrail. Thus many of the disturbances were attrib- uted to wind shear. Although no serious problems occurred as a result of this phenomenon, it did complicate an already complex task.
Dutch roll and roll mode characteristics. -Table 6 presents representative M2-F3 Dutch roll and roll mode characteristics (computed from flight data of ref. 6) and pilot ratings together with task , configuration , and flight condition. Figure 25 compares the Dutch roll mode frequency and damping ratio with the criterion of reference 9. The data for the vehicle with the SAS on generally exceeded the level 1 requirement , which resulted in pilot ratings of 3 . 5 or better. For reduced SAS gains and with the SAS off, the data tended toward the minimum level bound- aries and in some instances were below the minimums. The associated pilot ratings were 3 . 5 or worse. With the yaw SAS off and the roll SAS on, the Dutch roll damp- ing became relatively light , as indicated by the pilot rating of 5 . 0 .
When evaluating lateral-directional handling qualities of lifting bodies , the Dutch roll mode cannot be evaluated independent of the roll mode. Figure 26 com- pares the lateral control power , L 6 , with the roll mode time constant criter- ' a 'max ion of reference 12 , and the minimum roll mode time constant requirements from reference 9 with the data of table 6 . A s shown in table 6 , a coupled roll-spiral mode was calculated to exist. These data are included in figure 2 6 . A s for the Dutch roll mode criteria comparison, the SAS-on data generally meet the level 1 requirements , with better pilot ratings , and the SAS-off data fall toward the lower level boundaries, with poorer pilot ratings. It is believed that the general agree- ment of the flight data with the criteria of references 9 and 1 2 is satisfactory. N o criteria , as such, exist for the coupled roll-spiral mode, except that the Military Specification does not permit its existence.
Few specific pilot comments concerning the SAS-off low Dutch roll mode damp- ing were received. However, numerous comments were made concerning the SAS- off roll damping and accompanying apparent aileron sensitivity. The ailerons pro- vided adequate roll control and damping augmentation. Because of the low level of natural roll damping, the ailerons with the roll SAS off appeared to command roll acceleration rather than rate. Consequently , when the pilots performed maneuvers in this mode, they accelerated to large roll rates in short periods of time and fre- quently commented that the vehicle was very sensitive in roll. In this configura- tion roll rate per unit stick was reported to have been too high. One pilot commented: The only surprise I had during the entire flight occurred after I had turned the roll damper off. I was asked [by mission control] to make a right turn for flightpath control. I put in considerable (initial) aileron , not remembering that K was at zero.
I was rewarded with a significant P amount of roll rate. A s soon as I remembered that I was at zero roll damp- ing, I adjusted my own control [technique] , and no further surprises occurred.
During this maneuver the vehicle rolled through approximately 66O of bank angle before recovery was made.
Generally, with the roll and yaw SAS off , modal response characteristics com- of reference 6 (table 6) indicated that a coupled roll- puted by using the flight data spiral mode would exist. Although the coupled roll-spiral mode was difficult to TABLE 6 .-REPRESENTATIVE LATERAL-DIRECTIONAL RESPONSE CHARACTERISTICS AND PILOT RATINGS OF THE M2-F3 LIFTING BODY VEHICLE ' 2.0 0.63 76.6 (160) 2.70 0 . 4 4.87 0.291 I 0.422 , - - - , - - - 10 0 . 4
3.14 1 iii 0 . 4 4.50 0.372 i 0.353 I - - -
i 2 . 0 0.46 8 9 . 1 (186) 6 . 7 0 . 4
7 3 . 5 " 0 . 6 6 . ' 42.6 (89) - 1 . 3 0 0 ' 2.19 0.042 F = % k ? 1.55
1.20 i 4 7 . 9 (100) 9 . 5 0 . 1 0 . 4 3.30 0.128 2.041 - _ _ , 1 . 0 3 3.2
3.0 0 . 8 1 3.2 8 . 5 0.1 1, 0.4 2.13 0.089 0.221 , 0.995 T r a n s o n i c 4.0 0.94 27.8 (58)
I 1 - - -
1 . 6 8 I 5.6
- 1 . 4 0 . 2 0 1 3.20 0.022 ! 0.;3; 1
5.0 1.32 ~ 8 0 . 9 (169) 0.131 0.793 2.19 0.042 - - - I Stability 1 4 . 5 ~ 0.66 42.6 (89) - 1 . 3 0 0 1.55 6 . 1 , a n d 2.14 4.4 0.52 3.48 0.062 - - - 0.264 0.687 ' 4 . 6 0 0 3 . 0 6 2 . 2 (130) control 0.60 0.236 0.414 3.62 0.112 - - - 4.0 95.8 (200) 0 . 4 0 0 3.37 5.7 evaluation 4 . 4 5 0.338 0.187 - - - - - - Subsonic 3.0 0.70 128.8 (269) 1 . 7 0 . 4 0 . 4 4.64 3.7 4.44 0.475 0.182 - - - - - - 2.5 0.52 143.6 (300) 2 . 5 0.4 0 . 4 5.06 4.2 4.30 0.248 0.143 - - - - - - 3 . 5 0.52 164.2 (343) 0 0 . 4 0 . 1 5.92 3.8 0.49 4.45 0.464 0.215 - - - - - - 2.0 128.3 (268) 3 . 6 0.4 0 . 4 4.46 4 . 3 W cn 6 P i lot rating 0 1.5 0 2.0 0 2.5 A 3.0 A 0 CD b 3.5 CI 4.0 n 4.5 o 5.0 u n ; 3 Open symbols denote r o l l and yaw SAS o n radlsec Solid symbols denote r o l l and yaw SAS off Half-solid symbol denotes r o l l SAS on, yaw S A S off .1 .2 .3 .4 .5 ‘d Figure 25. Comparison of M2-F3 Dutch roZZ mode frequency and damping ratio with criterion of reference 9 for Class II aircraft, Category €3.
3 > 20 ( r a d / s e c ) 2 .
( O n d ) I p I
20 P i lot rating 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Pilot opinion contours (ref. 12) Open symbols denote r o l l and yaw SAS o n Solid symbols denote r o l l and yaw SAS off Half-solid symbol denotes r o l l SAS on, rad/sec2 yaw S A S off .8 .6 .4 .2 1 J .I .1 .2 .4 .6 .8 1 2 4 6 8 10 20 T sec R ’ Figure 26. Comparison of M2-F3 lateral control power and roZZ mode time constant with criteria from references 9 and 12.
I
identify explicitly in flight, careful flight maneuver conditioning did reveal it on one flight. Pilot coupling with this mode was not a handling qualities problem as it was with the M2-F2 vehicle (ref. 3 ) . In an attempt to determine the pilot's ability to con- trol a vehicle with suspected coupled roll-spiral characteristics, a number of traffic patterns were flown with the roll and yaw SAS off. General pilot comments were as follows: Any roll maneuvering was accompanied by jerkiness and some over- control. However, the vehicle was entirely controllable and would receive a pilot rating of 4 . 0 .
Transonic Dutch roll mode instability. -Figure 27 presents data from the first and most severe Dutch roll mode instability experienced in the transonic flight region. A s shown, this oscillation was relatively severe, even though large bank angle excursions were not experienced. The SAS input and the total control input are shown. The pilot did not command rudder pedal during this time interval; therefore, rudder SAS is the total rudder input. The longitudinal transonic trim change occurred between 1 3 seconds and 17 seconds. Vehicle characteristics in this Mach range were not as repeatable as desired; however, the derivative extrac- tion routine described in reference 6 was used in an attempt to determine if any unpredicted derivative variations were occurring in the transonic speed region.
Figure 28 compares the aileron rolling- and yawing-moment coefficients ob- tained from flight data and wind-tunnel data. From Mach 0 . 9 to 1 .O consistent derivatives were extremely difficult to obtain. Flight data indicated that the aileron control effectiveness may have been greatly reduced at angles of attack below 5 O , but this was not clearly substantiated.
Figure 29 presents a theoretical root-loci analysis of the time history of fig- ure 2 7 . This type of analysis has limitations in that the system being analyzed is assumed to be linear, that i s , the angle of attack, dynamic pressure, and Mach number are assumed to be constant and the aerodynamic derivatives are assumed to be linear. It is obvious from figure 27 that the first three conditions are not met; however, flight-determined linear aerodynamic derivatives were used. Even though the first three conditions were violated, it was believed that an analysis of this type could aid in understanding the mechanism by which the instability was initiated and point to a possible solution. The approximate average flight angle of attack, dynamic pressure, and Mach number were selected for the analysis. For comparison, the approximate frequency and damping data obtained during the un- stable and stable portions of the time history of figure 27 are presented in figure 2 9 .
SAS gains The variable in this figure is roll or yaw SAS gain. At the flight (K = 0 . 4 deg/deg/sec and K r = 0 . 2 deg/deg/sec) the vehicle is predicted to be un- P stable, and as roll gain is increased from this point the vehicle becomes more un- stable. The most stable point is at a roll SAS gain of zero. A s the yaw SAS gain is increased, above Kr = 0 . 2 deg/deg/sec, stability is also achieved. Thus, increas- ing yaw gain is a stabilizing influence, but increasing roll gain is a destabilizing influence.
Illlll I I I I1 I I 1 I " w--- -20 I I I 1 I . l J 40 I- -20 - 4 0 L I I I I I I I LJ -10 -10 -10 1 . 1 I L I 4 k-Unstable*Stable-- -2
1.00 r + , L T r i m c h a n g e
Figure 27. M 2 - F 3 transonic SAS-on Dutch roll mode instability.
K = 0 . 4 deg/deg/sec; K r = 0.2 deg/deg/sec.
P L-- ,o 8 0 M = 0.94, 6" = -20" c, , Per deg
-
Trimmed, M = 0.95 -4 0 4 8 12 16 a, deg Figure 28. Comparison of aileron rolling-moment and yawing- moment effectiveness obtained from transonic flight data ( r e f . 6 ) and wind-tunnel data.
o t = 8 t o 1 8 s e c 4.0
1 Flight, fig. 27
,-Unstable flight t = 18 to 28 sec 0 P.8 - Variation of Kr at K = 0.4 degldeglsec . 6 / P x --- Variation of K at K r = 0.2 degldeglsec 3.5 2 , / K r = O P 4kFiight S A S gains 3.0 w , radlsec d 2.5 Unstable u 2.0 -.8 -.4 0 .4 .8 wn Cd, radlsec d Figure 29. Theoretical root loci of the M2-F3 Dutch roll mode instability of figure 27 using linear flight-determined deriva- tives from reference 6. a = 2. 7O; M = 0.93; V = 283.5 m/sec (930 f t / s e c ) ; = 57.5 hN/m2 (120 l b / f t 2 ) .
The primary cause of this instability was the combination of low aileron roll effectiveness, CR , and high favorable or proverse aileron yawing-moment , C , n6 6U characteristics. The ailerons thus produced a relatively low roll damping moment through the roll SAS while a relatively large proverse yawing moment proportional together with the high effec- to roll rate was being generated. This combination caused the divergence. A s a result of tive dihedral and low natural roll damping this analysis, it was decided to traverse the transonic region using a higher yaw SAS gain and a lower roll SAS gain. With this configuration no further problems were encountered with the Dutch roll mode transonic instability.
Final approach and landing. -The lateral-directional handling qualities during final approach and landing were considered to be satisfactory. The typical pilot rating for this task was 2 . 0 . One pilot reported the following: Lateral-directional control was excellent during landing. Roll con- trol response remained excellent down to minimum landing speed and was not noticeably coupled with yaw. Directional stability and damping remained satisfactory to touchdown.
On one flight a landing was made with the roll and yaw SAS off. The pilot rated this lateral-directional task 4 . 5 . Pilot comments concerning this landing were as follows: This landing was satisfactory, but I would not be enthusiastic to land in this condition again. This was due to the quickness of the roll control and the possibility that in the presence of turbulence short-term upsets close to the ground would be unsatisfactory.
With the exception of the wind shears during boost, all turbulence observed by the pilots occurred on the final approach, when a tight lateral tracking task was
being performed (lining up with the runway) . Generally, the turbulence was
sensed only in the lateral axis in the form of high roll rate and small amplitude up- sets. This type of response was due to the excessively high effective dihedral. At first, exposure to low-level turbulence made the pilots apprehensive because of the unusual nature of the vehicle's response. With experience, this apprehension decreased as the pilot became confident that the vehicle was not on the threshold of a divergent lateral oscillation. One pilot reported the following: Turbulence response was noticeable as a high frequency lateral oscillation. Upsets were not generally objectionable from either riding or handling qualities aspects.
In contrast to these comments another program pilot reported the following: The riding qualities of the M2-F3 in turbulence are better than in the other two lifting bodies (HL-10, X-24A). The response to turbulence was not nearly as quick as in the other two; instead it responded more like an F-104 in that it was manifested primarily as normal acceleration inputs rather than rapid roll inputs as in the X-24A.
Frequently, a wingman flying close escort in an F - 1 0 4 airplane would not detect any turbulence or perceptible motion of the M2-F3 vehicle as turbulence was penetrated.
To reduce pilot apprehension, a transport aircraft (with low wing loading) was flown through the M2-F3 approach corridor a few minutes before each flight of the M2-F3 vehicle and the M2-F3 pilot was informed of the location and severity of the turbulence. Turbulence was of continuing concern, as evidenced by the fact that launch ground rules throughout the n/I2-F3 flight program contained a constraint requiring low-altitude turbulence to be less than moderate. “Moderate” was con- sidered to be the maximum level of turbulence under which it would be acceptable to proceed with a launch. This term was agreed upon by the pilots in the lifting body program.
CONCLUDING REMARKS A flight study to assess the longitudinal and lateral-directional handling qual- ities of the M2-F3 lifting body vehicle indicated that the vehicle’s handling quali- ties were generally satisfactory. Eighty percent of the pilot ratings were 3 . 5 or better; 31 percent were 3 . 0 , the most frequently assigned rating, indicating that the handling qualities were fair; and 20 percent of the ratings were from 4 . 0 to 7 . 0 .
The longitudinal handling qualities at low speeds (subsonic configuration) were slightly better than at transonic and supersonic speeds (transonic configura- tion); 8 7 . 6 percent of the ratings for the subsonic configuration and 6 9 . 8 percent for the transonic configuration were 3 . 5 or better. The lateral-directional handling qualities were unchanged by speed and configuration; 8 7 . 3 percent of the ratings for the subsonic configuration and 7 6 . 4 percent for the transonic configuration were 3 . 5 or better. The pilot evaluations were generally for the vehicle with the sta- bility augmentation system (SAS) on; only 10 percent of the ratings were for the SAS off. Generally, the SAS-off handling qualities were satisfactory at the condi- tions selected for investigation.
The most difficult handling qualities task presented to the pilots was longitudinal control during the constant-high-angle-of-attack portion of the powered boost. The pilot ratings for this task were significantly worse than those for other portions of the flight or other tasks. Of these ratings 5 1 . 6 percent were between 4 . 0 and 6 . 5 ; the most frequently assigned rating was 5 . 0 . To improve the handling qualities an angle-of-attack hold mode was included with the installation of the command augmen- tation system. Because of the poor physical characteristics of the command augmen- tation system side stick and the requirement that the pilots wear a pressure suit, which aggravated the effect of the poor stick characteristics, the anticipated improve- ment with this system was never fully achieved. The potential of the command aug- mentation system was recognized, however, and the system was a welcome addition to the vehicle.
All other longitudinal handling qualities were considered to be satisfactory, although some tendencies toward pilot-induced oscillations were noted in the final approach and landing flare. Ninety-five percent of the pilot ratings for the aDDrn9”h anr’ - +-cr task were 3 . 5 or better.
The lateral-directional stability characteristics were dominated by aerodynamic characteristics unique to this class of lifting body. These included very high effec- tive dihedral, low natural roll damping, and a high concentration of mass about the roll axis. As a result of these characteristics , the M2-F3 vehicle was subject to roll-spiral mode coupling with the roll and yaw SAS off. However, pilot coupling with this mode was not a handling qualities problem, as it was with the M2-F2 vehicle.
At transonic speeds a Dutch roll mode instability occurred with the SAS on. A linear analysis revealed that this instability was induced by the roll SAS when the roll gain was higher than the yaw gain. The primary cause of this instability was the aileron aerodynamic roll effectiveness and yawing-moment effectiveness at transonic speeds. The problem was eliminated with the selection of higher yaw SAS gains and lower roll SAS gains at transonic speeds.
The lateral-directional handling qualities during the final approach were con- sidered to be satisfactory. The typical pilot rating for this task was 2.0. The aero- M2-F3 vehicle produced an unusual turbulence dynamic characteristics of the response, which the pilots observed as low-amplitude high-frequency lateral oscil- lations. No significant handling qualities problems were encountered as a result of the turbulence.
The reaction control rockets were generally satisfactory when used for damping augmentation. When used for control, they proved to be too sensitive in the roll axis and could not provide adequate trim control moment in the longitudinal axis.
Flight Research Center National Aeronautics and Space Administration Edwards, C a l i f . , April 16, 1975 REFERENCES 1. Smith, H a r r i e t J. : Evaluation of the Lateral-Directional Stability and Control C h a r a c t e r i s t i c s of the Lightweight M2-F1 Lifting B o d y at Low Speeds. NASA T N D-3022, 1965.
.: Stability and Control C h a r a c t e r i s t i c s of the M2-F2 Lifting
2. Holleman, E u c l i d C NASA TM X-1593, 1968.
Body M e a s u r e d D u r i n g 16 Glide Flights.
A n a l y s i s of a Coupled Roll-Spiral-Mode , Pilot-Induced 3. Kempel , R o b e r t W . : Oscillation E x p e r i e n c e d W i t h the M2-F2 Lifting B o d y . NASA T N D-6496, 1971.
4 . Kempel, R o b e r t W .; and Manke , John A . : Flight Evaluation of HL- 10 Lifting
B o d y H a n d l i n g Qualities at Mach N u m b e r s From 0.30 to 1.86. NASA T N D-7537, 1974.
NASA TM X-2101, 1970.
5 . Flight Test R e s u l t s P e r t a i n i n g to the Space S h u t t l e c r a f t .
Flight-Determined Stability and Control C h a r a c t e r i s t i c s of the 6 . Sim , Alex G. : M2-F3 Lifting B o d y V e h i c l e . NASA T N D-7511, 1973.
7. Mechtly , E . A.: The International S y s t e m of Units - P h y s i c a l C o n s t a n t s and C o n v e r s i o n Factors. Second R e v i s i o n . NASA SP-7012, 1973.
8 . C o o p e r , G e o r g e E . ; and H a r p e r , R o b e r t P . , Jr .: The Use of Pilot R a t i n g in the Evaluation of A i r c r a f t H a n d l i n g Qualities. NASA TN D-5153, 1969.
9 . Flying Qualities of Piloted A i r p l a n e s . Military Specification MIL-F-8785B (ASG) , A u g . 7 , 1969.
1 0 . D a n a , William H . ; and G e n t r y , J . R . : Pilot I m p r e s s i o n s of Lifting Body V e h i c l e s . Flight Test R e s u l t s Pertaining to the Space S h u t t l e c r a f t . NASA T M X-2101, 1970, pp. 73-88.
11. A ' H a r r a h , R a l p h C . : Low A l t i t u d e , H i g h - s p e e d H a n d l i n g and R i d i n g Qualities.
AGARD R e p . 443, A p r . 1963.
1 2 . C r e e r , B r e n t Y . ; Stewart, John D . ; Merrick, R o b e r t B . ; and D r i n k w a t e r , Fred J. 111: A Pilot Opinion Study of L a t e r a l Control R e q u i r e m e n t s f o r Fighter-Type A i r c r a f t . NASA Memo 1-29-59A, 1959.
4 3 NASA-Langley, 1975 H-852 NATIONAL AERONAUTICS A N D SPACE ADMINISTRATION- WASHINGTON, D.C. 20546 P O S T A G E A N D F E E S P A I D N h T I O N A L A E R O N A U T I C S hND SPACE A D M I N I S T R A T I O N OFF I C 1 A L BUS I N ESS
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