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&A FLIGHT RESWCH CENTER HANDLING-QUALITIES __.-- P R O G R A M
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ON GE3JERAL-AVIATION AIRCF&FT
By W J l l i a m E. Gray, -_-- Jr. f i q ~ y ] p . ?
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178 O b 2%SA 'Flight Re seare h Cent e 5
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(M F) ff 653 Julv65 h_ AIAA (@era1 &viation A i r c r a f t Design and ODerations Meeting,
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April 21, 1964
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NASA FLIGHT RESEARCH CENTER HANDLING-QUALITIES P R O G R A M ON GENERAL-AVIATION AIRCRAFT William E. Gray, Jr.
Executive Transport Handling Q u a l i t i e s Section Head, NASA Flight Research Center c Edwards, California Introduction An additional program objective i s t h e assess- ment of p r a c t i c a l design changes that can be made t o improve IFR rough-air handling q u a l i t i e s .
For many years the NACA and the NASA have maintained a research e f f o r t devoted t o the study During t h i s phase of the program, NASA ground-based simulators w i l l be used t o evaluate p o t e n t i a l of aircraft handling q u a l i t i e s . This research, opinion with primarily on contemporary m i l i t a r y a i r c r a f t and design changes by correlating p i l o t contemporary m i l i t a r y problems, proved t o be a varying f l i g h t c h a r a c t e r i s t i c s .
fruitful source of infomation during t h e design and development stages of successive generations It i s expected that f i v e or s i x t y p i c a l l a t e - model a i r c r a f t w i l l be evaluated i n the f l i g h t of a i r c r a f t . Although many of the r e s u l t s of the m i l i t a r y research a r e applicable t o c i v i l a i r c r a f t , program. Both single and twin-engine a i r c r a f t , representative of current production by d i f f e r e n t some problems a r e unique and require specific solutions. Research on c i v i l a i r c r a f t , however, manufacturers, w i l l be studied. Tests on an indi- has been given only minimal a t t e n t i o n since before vidual a i r c r a f t should be completed i n less than
World W a r 11, primarily because of concentration on 4 months. -
w a r years and t h e m i l i t a r y a i r c r a f t during t h e Instrumentation and D a t a Processirq e f f o r t devoted t o the X-series of research a i r c r a f t .
I n implementing t h i s f l i g h t program, t h e use I n recent years, the increasing use of c i v i l a i r c r a f t i n instrument-weather conditions by p i l o t s of r e l i a b l e instrumentation t o measure airplane who a r e frequently solo and who sometimes have f l i g h t parameters f o r correlation with p i l o t opin- I n s t a l l a t i o n of such minimal experience has given r i s e t o an operating ion i s of primary importance.
problem of s u f f i c i e n t importance t o warrant study. instrumentation i s a time-consuming phase of any f l i g h t - t e s t program and assumes p a r t i c u l a r impor- The NASA F l i g h t Research Center has, therelore, recently i n i t i a t e d pertinent handling-qualities tance i n t h e scheduling of t h i s program, since research. several a i r c r a f t a r e being studied i n a short time.
The purpose of t h i s paper i s t o b r i e f t h e general-aviation industry on t h e program objec- A significant development that w i l l make it possible t o maintain a rapid pace i s t h e design and con- t i v e s , t o discuss the general approach that i s s t r u c t i o n of an instrumentation "package" ( f i g . 1) being taken toward solving the operating problem, and t o s o l i c i t comments from t h e industry a t t h i s by Flight Research Center personnel.
e a r l y stage i n the program.
Prime considerations i n the design of the instrumentation package were size, weight, ease of Program Objectives i n s t a l l a t i o n i n a v a r i e t y of a i r c r a f t , methods of recording data, and a self-contained power supply.
The primary QbJeetive of t h i s research pro- These requirements a r e d i c t a t e d by the limited gram i s t o formulate updated handling-qualities space, payload, and e l e c t r i c a l parer a v a i l a b l e i n c r i t e r i a , with p a r t i c u l a r emphasis on rough-air some a i r c r a f t plus t h e need t o minimize manpower instrument-flight operations with general-aviation requirements f o r instrument i n s t a l l a t i o n , m i n t e - aircraft.
All handling q u a l i t i e s w i l l Ire evaluated, nance, and data reduction. The instrumentation and s p e c i a l a t t e n t i o n w i l l be given t o those that package provides permanent records of airspeed, are found t o be problems. It i s anticipated that some handling q u a l i t i e s w i l l assume great impor- a l t i t u d e , angle of attack, angle of sideslip, bank tance t o a s o l o p i l o t i n instrument weather and/or angle, three-axes l i n e a r and angular accelerations, three-axes angular velocity, and a l l control forces turbulent air, such as s p i r a l i n s t a b i l i t y , phu- re- and positions. It a l s o has provisions f o r goidal o s c i l l a t i o n s , l a t e r a l - d i r e c t i o n a l osc i l l a - cording other q u a n t i t i e s i f the need a r i s e s .
tions, adverse yaw, rapid speed-increase tendencies, Information i s recorded on photographic film, as control-system f r i c t i o n , and l a r g e t r i m changes i l l u s t r a t e d i n figure 2. Quantitative measurement * = r e s u l t i n g from a i r c r a f t configuration changes.
of t h e various parameters i s accomplished by measuring the displacement of the individual t r a c e s IFR handling-qualities c r i t e r i a w i l l be based The periodic v e r t i c a l on t h e c o r r e l a t i o n of quantitative aerodynamic o r from the reference l i n e .
l i n e s provide time c o r r e l s t i o n a t 0.1-second response c h a r a c t e r i s t i c s with opinions expressed by p i l o t s who have flown t y p i c a l instrument missions. i n t e r v a l s . In addition t o t h e recorded informa- tion, continuous visual i n f o r m t i o n on airspeed, The i n i t i a l f l i g h t tests on each a i r c r a f t w i l l be made by NASA research p i l o t s experienced i n the a l t i t u d e , control forces and positions, and norm1 acceleration i s displayed t o a f l i g h t - t e s t engineer.
p a r t i c u l a r techniques required f o r quantitative The visual display has been extremely valuable i n documentation of s t a b i l i t y c h a r a c t e r i s t i c s . To enabling i n - f l i g h t data reduction with the associ- i n s u r e that the p i l o t opinions represent r e a l i s t i c operational viewpoints, p i l o t s with experience in ated a b i l i t y t o determine during t h e f l i g h t t e s t whether t h e data a r e adequate.
general a v i a t i o n w i l l then be invited t o p a r t i c i - pate with t h e NASA p i l o t s i n evaluating the a i r - c r a f t handling q u a l i t i e s during t y p i c a l instrument An appreciable portion of t h e data processing missions. involves analysis of t h e information recorded on photographic film. Processing of t h e s e data a t t h e of stick-fixed and s t i c k - f r e e s t a b i l i t y a r e i n d i - F l i g h t Research Center i s f a c i l i t a t e d by t h e use of cated, respectively, by l a r g e changes of e l e v a t o r mechanized film-reading equipment, electronic angle and elevator force with airspeed.
d i g i t a l computers f o r performing necessary calcula- tions, and automatic p l o t t i n g of t h e f i n a l curves. Stick-fixed s t a t i c s t a b i l i t y g r e a t l y i n f l u - ences dynamic longitudinal s t a b i l i t y , since t h e Discussion tendency t o r e t u r n t o a given angle of a t t a c k o r airspeed following a disturbance i s d i r e c t l y re- Handling q u a l i t i e s a r e defined as t h e c o r r e l a - l a t e d t o t h e degree of stick-fixed s t a b i l i t y .
t i o n of s t a b i l i t y and control c h a r a c t e r i s t i c s of an Further, t h e tendency t o r e s i s t a disturbance and a i r p l a n e with t h e p i l o t ' s impression of t h e ease of t o remain a t a given angle of a t t a c k i s ificreased f l y i n g t h e a i r p l a n e . The r e s u l t of handling- with increasing stick-fixed s t a b i l i t y . High l e v e l s q u a l i t i e s research i s the formulation of c r i t e r i a of s t i c k - f i x e d s t a b i l i t y a r e d e s i r a b l e from t h e i n terms of q u a n t i t i e s t h a t may be measured i n standpoint of dynamic s t a b i l i t y ; however, s t i c k - f l i g h t o r predicted from wind-tunnel t e s t s and fixed s t a b i l i t y should not be s o high that it w i l l t h e o r e t i c a l analyses. References 1 t o 3 contain i m p a i r a i r p l a n e maneuverability. Similarly, s t i c k - numerous examples of a i r c r a f t design c r i t e r i a t h a t f r e e s t a t i c s t a b i l i t y i s important t o dynamic a r e based on conclusions from handling-qualities longitudinal s t a b i l i t y because it a l s o increases research programs. When a i r c r a f t a r e designed t o t h e tendency t o r e t u r n t o t r i m airspeed a f t e r a such c r i t e r i a , it i s reasonably c e r t a i n t h a t they speed deviation. It should be noted, however, t h a t w i l l have d e s i r a b l e q u a l i t i e s from t h e p i l o t ' s s t i c k - f r e e s t a b i l i t y provides only minimal i n i t i a l standpoint. r e s i s t a n c e t o a disturbance; t h e s t a b i l i z i n g re- If a c t i o n occurs only a f t e r t h e speed has changed.
Evaluation of p i l o t opinion i s an important, l o w s t i c k - f r e e s t a b i l i t y i s combined with low though often d i f f i c u l t , p a r t of any handling- s t i c k - f i x e d s t a b i l i t y , t h e a i r c r a f t may e x h i b i t an q u a l i t i e s study. Occasionally, t h e opinions ex- appreciable response as a r e s u l t of gust d i s t u r b - pressed by t h e various p i l o t s vary widely. It has ances and a slow r a t e of r e t u r n t o t r i m speed a f t e r been found t h a t these differences can be consid- t h e disturbance i s removed. I f t h e s t i c k - f r e e erably reduced by c a r e f u l l y specifying t h e opera- s t a b i l i t y i s increased and t h e s t i c k - f i x e d s t a b i l i t y t i o n a l viewpoint t o be considered, by devising a remains low, t h e r e t u r n from a speed deviation may r a t i n g s c a l e f o r t h e expression of broad categories be a t such a rapid r a t e t h a t t h e t r i m speed w i l l be of q u a l i t a t i v e opinions, and by choosing t h e fewest overshot. Consequently, t h e r e t u r n t o t r i m speed r a t i n g s t o describe s i g n i f i c a n t differences i n i s achieved only a f t e r a s e r i e s of o s c i l l a t i o n s .
operational s u i t a b i l i t y . During t h i s research Such slow, continuous speed o s c i l l a t i o n s represent program, each important f l i g h t c h a r a c t e r i s t i c w i l l poor dynamic s t a b i l i t y c h a r a c t e r i s t i c s , which w i l l be r a t e d by each p i l o t f o r s o l o f l i g h t i n both be aggravated by turbulent a i r .
smooth and rough air i n both IFR and VFR f l i g h t .
The r e l a t i o n s h i p of s t i c k - f i x e d and s t i c k - f r e e Most handling-qualities s t u d i e s and many s t a t i c longitudinal s t a b i l i t y t o dynamic longitu- handling-qualities c r i t e r i a have not d i f f e r e n t i a t e d d i n a l s t a b i l i t y w i l l be studied on a l l of t h e air- between VFR and IFR handling q u a l i t i e s . There a r e c r a f t used i n t h e program. It i s expected t h a t indications t h a t s a t i s f a c t o r y VFR handling q u a l i - t h i s research w i l l r e s u l t i n recomendations on IFR t i e s do not necessarily imply s a t i s f a c t o r y means of improving t h e dynamic longitudinal- handling q u a l i t i e s . For example, f i g u r e 3 i l l u s - s t a b i l i t y c h a r a c t e r i s t i c s of general-aviation t r a t e s a Dutch r o l l motion t h a t was evaluated by a i r c r a f t .
NASA research p i l o t s as not being objectionable i n e i t h e r smooth o r rough a i r during VFR f l i g h t . It Control-System F r i c t i o n was a l s o s a t i s f a c t o r y during IFR f l i g h t i n smooth air, b u t was considered t o be objectionable i n IFR Control-system f r i c t i o n i s a l s o a n t i c i p a t e d f l i g h t when combined with rough a i r .
The p i l o t t o be a problem that w i l l warrant s p e c i a l a t t e n - opinions support comments from numerous sources t i o n . The ways i n which f r i c t i o n a f f e c t s t h e t h a t t h e program discussed i n t h i s paper should be p i l o t ' s opinion of a i r c r a f t handling q u a l i t i e s a r e oriented toward IFR and rough-air handling t o o numerous t o d e t a i l , b u t it should be noted that q u a l i t i e s .
It is t h e e f f e c t i s almost i n v a r i a b l y adverse.
r e a l i s t i c t o expect that any d e t e r i o r a t i o n of Dynamic Longitudinal S t a b i l i t y handling q u a l i t i e s w i l l compound t h e p i l o t ' s prob- lem i f t h e a i r p l a n e i s operated IFR, p a f i i c u l a r l y It is a n t i c i p a t e d that t h e dynamic when t h e p i l o t i s solo.
l o n g i t u d i n a l - s t a b i l i t y c h a r a c t e r i s t i c s of general- a v i a t i o n a i r c r a f t w i l l p se problems i n t h e IFR Figure 5 i l l u s t r a t e s t h e type of problem that
rough-air environment .4-g The r e l a t i v e l y l o w mass
can occur when f r i c t i o n prevents a c o n t r o l from and moments of i n e r t i a s of these a i r c r a f t imply l o w returning t o an aerodynamically centered position.
l e v e l s of physical damping of dynamic motions.
When a p i l o t r e l e a s e s t h e a i l e r o n s a f t e r having Thus, various aerodynamic c h a r a c t e r i s t i c s may d e f l e c t e d them, they may assume a p o s i t i o n anywhere g r e a t l y influence t h e dynamic motions i n rough air.
within 2' from t h e n e u t r a l p o s i t i o n . The resulting Although many f a c t o r s a r e involved i n dynamic : , r a t e of roll may be as high as 2.5 deg/sec (shaded ~ longitudinal s t a b i l i t y , t h i s discussion i s l i m i t e d area, upper p l o t ) . Normally, t h i s r o l l rate would t o two of t h e more important: stick-fixed and not b e considered high; however, If a p i l o t d i v e r t s stick-free s t a t i c longitudinal s t a b i l i t y .
h i s a t t e n t i o n f o r only 10 seconds, t h e bank angle can be as high as 25' (shaded area, lower p l o t ) .
as t h e v a r i - Stick-fixed s t a b i l i t y i s defined The seriousness of t h i s s i t u a t i o n i s obvious.
a t i o n of elevat,or angle with airspeed, and s t i c k - f r e e s t a b i l i t y i s defined as t h e v a r i a t i o n of e l e v a t o r f o r c e with airspeed ( f i g . 4 ) .
High l e v e l s ..
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b S p i r a l S t a b i l i t y extensive changes on the a i r c r a f t . The simulator research i s expected t o provide information from The s p i r a l mode, which i s of no consequence which recommendations on r e a l i s t i c means of i m - r during VFR f l i g h t , becomes important during s o l o proving IFR rough-air handling qualities can be IFX f l i g h t . Thus, considerable emphasis i s being formulated.
placed on measuring t h i s mode. I n - f l i g h t measure- ment i s d i f f i c u l t , and i s a l s o an i n t e r e s t i n g Autopilot Considerations L research problem, since t h e s p i r a l motion depends upon t h e net result of t h e relationship of four It should be noted that handling qualities not d i f f e r e n t s t a b i l i t y derivatives: 3 dihedral effect, only influence p i l o t opinion but can a l s o a f f e c t d i r e c t i o n a l s t a b i l i t y , r o l l due t o y a w , and y a w t h e design of autopilot and s t a b i l i t y augmentation damping. systems. I n general, the simplicity and associated cost of an autopilot depend on t h e handling quali- Figure 6 shows t h e s p i r a l motions t h a t can t i e s of t h e vehicle being controlled. For example, occur when t h e controls are released from a Steady consider divergent, neutral, and damped long-period bank angle. Whether t h e bank angle decreases, a l t i t u d e o s c i l l a t i o n s . Any of these types of increases, o r remains the same, depends on whether o s c i l l a t i o n s a r e possible, depending on control- is, respectively, posi- system f r i c t i o n , the type of control-surface aero- t h e term
C z Cnr - C z r C v
B dynamic balance, and the phugoidal mode.? Even t i v e , negative, o r zero, where: divergent o s c i l l a t i o n s a r e r a r e l y noticed by a human p i l o t (because of the long period and small C z B = e f f e c t i v e dihedral amplitude of the o s c i l l a t i o n s ) who automatically c o r r e c t s f o r the variations i n a l t i t u d e . Although Cnr = yawing moment due t o yawing velocity extremely simple autopilots w i l l be able t o c o n t r o l damped oscillations, they nay have trouble main- C z r = r o l l i n g moment due t o yawing velocity taining constant a l t i t u d e when controlling a i r c r a f i o r divergent o s c i l l a t i o n s . They may with n e u t r a l Cv = d i r e c t i o n a l s t a b i l i t y even operate out of phase with t h e o s c i l l a t i o n and, thus, increase t h e amplitude. Similarly, l i g h t l y Since p o s i t i v e s p i r a l s t a b i l i t y m y not be neces- damped l a t e r a l - d i r e c t i o n a l o s c i l l a t i o n s , when ex- sary f o r p r a c t i c a l IFR f l i g h t , t h e research prob- c i t e d by turbulent air, may be d i f f i c u l t t o control lem i s t o determine, by correlating measured r a t e s with simple autopilots and nay force t h e a u t o p i l o t of r o l l with p i l o t opinion, t h e m a x i m u m r a t e of Thus, manufacturer toward more complex designs.
s p i r a l divergence that can be tolerated. In addi- a i r c r a f t handling q u a l i t i e s not only influence tion, t o a s s e s s p o t e n t i a l design improvements, the p i l o t impressions but can a l s o a f f e c t t h e ease with s p i r a l mode must a l s o be correlated with f l i g h t which simple, low-cost a u t o p i l o t s can c o n t r o l an measurements of t h e pertinent aerodynamic deriva- Consideration i s being given i n t h i s airplane.
t i v e s . Such measurements involve specialized p i l o t research program t o t h e influence of a i r c r a f t techniques, accurate instrumentation t o record the handling q u a l i t i e s . o n t h e design of a u t o p i l o t a i r c r a f t response t o c o n t r o l inputs, detailed data systems.
analysis, and accurate determination of t h e moments of i n e r t i a about each axis of t h e a i r c r a f t .
Concluding Remarks Moments of I n e r t i a The primary research objective of t h e NASA
r n > _ L L n ------ I- , ? ^ . - A --,- ^P L-..,al<.... ".."li-
. c i i & . u b i\eaeaiLu ~ , c i i b c ' i D D ~ U U J VI ~u3uurrng %-LA- Accurate moments of i n e r t i a about t h e a i r c r a f t t i e s of general-aviation a i r c r a f t i s t o formulate axes a r e of s u f f i c i e n t importance that it i s handling-qualities c r i t e r i a pertinent t o operations d e s i r a b l e t o obtain experimental values r a t h e r than by solo p i l o t s i n an IFR rough-air environment. It t o r e l y on calculated e s t i n a t e s . The experimental i s expected t h a t the information obtained w i l l lead technique f o r determining moments of i n e r t i a i s t o r e a l i s t i c means of designing t o meet such c r i t e - i l l u s t r a t e d i n f i g u r e 7. Essentially, t h e a i r c r a f t r i a . The influence of a i r c r a f t handling q u a l i t i e s i s balanced ( r e s t r a i n e d only by springs) i n such a on t h e design of autopilots and s t a b i l i t y augmen- manner that it i s f r e e t o o s c i l l a t e around t h e t a t i o n systems i s a l s o being considered.
p e r t i n e n t axis. Analysis of information on t h e longitudinal and v e r t i c a l location of t h e center of It i s believed that t h i s handling-qualities gravity, l o c a t i o n of t h e center of rotation, program w i l l contribute s i g n i f i c a n t l y t o t h e r e s t r a i n i n g spring constant, and the period of solution of some of t h e operating problems asso- o s c i l l a t i o n y i e l d s experimental values of the The r e s u l t s c i a t e d with general-aviation a i r c r a f t .
moments of i n e r t i a .
of t h e program w i l l be published f o r use by t h e industry i n the design and developmental stages of Simulation future general-aviation a i r c r a f t . The Flight Research Center w i l l , on occasion, request t h e As a means of supplementing the information assistance and cooperation of individuals i n t h e obtained from f l i g h t t e s t s , NASA ground-based industry. Comnents from any segment of t h e air- e l e c t r o n i c analog simulators w i l l be used.
Fig- c r a f t industry w i l l be welcome during t h e program.
ure 8 i s a photograph of t y p i c a l simulator equip- ment that i s a v a i l a b l e f o r t h i s research. The Referemes simulator w i l l be mechanized t o provide input and response c h a r a c t e r i s t i c s corresponding t o those of 1. Gilruth, R. R. : Requirements f o r Satisfactory t h e a i r c r a f t being studied. Individual s t a b i l i t y Flying Qualities of Airplanes. NACA Rep. 755, C h a r a c t e r i s t i c s can be changed a t w i l l , and t h e 1943 * resulting f l i g h t c h a r a c t e r i s t i c s can be correlated with p i l o t opinion. Thus, desirable or undesirable 2. P h i l l i p s , W i l l i a m H.: Appreciation and Pre- combinations of s t a b i l i t y c h a r a c t e r i s t i c s can be d i c t i o n of Flying Qualities. NACA Rep. 927, quickly determined with simulators without making 1949.
3. Perkins, Courtland D., and Hage, Robert E.: N e w e l l , Fred, and Rhoads, Donald W.: Flight 5.
Airplane Performance, S t a b i l i t y and Control. Evaluations of the Effect of Variable Phugoid John Wiley & Sons, Inc., 1 9 4 9 . Damping i n a m - 2 6 ~ Airplane. WADC Tech.
Rep. 56-223, Wright A i r Dev. Center, U.S. Air \ 4. Greenberg, Harry, and Sternfield, Leonard: A Force, Dee. 19%. (Available from ASTIA a s Theoretical Investigation of Longitudinal AD NO. 118103.)
S t a b i l i t y of Airplanes With Free Controls Including Effect of Friction i n Control System. 6. Hunter, Paul A . : Flight Measurements of the NACA W R L-430, 1 9 4 4 . (Formerly NACA ARR 4B01.) Flying Qualities of Five Light Airplanes.
NACA !I" 1573, 1948.
INSTRUMENTATION
ACCELERATIONS DURING LONGITUDINAL OSCILLATION
Figure 2
?
A DUTCH ROLL RIGHT 20 RUDDER ANGLE, IO DEG RIGHT 4r SIDESLIP ANGLE, O [ [ .
DEG RIGHT I O r VELOCITY, 0 DEGBEC RIGHT 4 r
G T Y , OEG/SEC .Lp&p+=U-
ILLUSTRATION OF STICK-FIXED AND
STICK-FREE STABILITY
S T I C K FIXED
I
STICK FREE
Figure 4
EFFECT OF AILERON FRICTION
RIGHT 20r I I O ROLL VELOCITY, 0 DEGGEC IO
2sb ;2 0 4 b 4 . 8 ; 2
AILERON DEFLECTION. DEG SPIRAL MOOE POSITIVE SPIRAL STABILITY RIGHT r L NEUTRAL SPIRAL STABILITY L - NEGATIVE SPIRAL STABILITY
Figure 6
DETERMINATION OF MOMENTS OF INERTIA
AIRPLANE SLING YAW
n
5Z3iEf2 -WING JACK WlNT
PITCH ROLL