'NASA TN D-84

TECHNICAL NOTE D-841

HOVERING FLIGHT INVESTIGATION OF TWO METHODS OF

CONTROLLING A MAN-CARRYING DUCTED-FAN VEHICLE

OF THE FLYING-PLATFORM TYPE

By Lysle P. Parlett

Langley Research Cente Langley Field, Va.

JUL '7 1961 SPACE FLIGHT

LANGLEY FIELD, VIRGINIA *

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

WASHINGTON June 1961

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

TECHNICAL NOTE D-841

HOVERING FLJGHT INVESTIGATION OF TWO METHODS OF

C O N T R O U N G A MAN-CARRYING DUCTED-FAN V E H I C U

OF THE FLYING-PLATFORM TYPE

By Wsle P. Pa r l e t t

Full-scale hovering f l i g h t t e s t s have been made t o compare two methods of controlling a ducted-fan vehicle of the flying-platform type. The vehicle had counterrotating fans, 4 f e e t i n diameter, operating i n a duct 20 inches long. The thrus t of the duct-fan assembly was supple- mented by f o u r a i r jets, directed para l le l t o the axis of fan rotat ion and spaced equally around the outer circumference of the duct inlet l i p . One control method tes ted w a s the kinesthetic method, i n which the p i l o t stood on the vehicle and furnished control moments by sh i f t ing his body weight. control moments by moving an airplane-type control s t i ck linked t o valves which d i f fe ren t ia l ly varied the thrus t of the four air je t s .

The other method was one i n which the p i l o t , seated, produced

The investigation consisted only of hovering f l i gh t t e s t s i n which a slack overhead safety cable was provided t o prevent crashes and i n which an outside operator controlled the thrus t and azimuth of the vehicle. During the course of the investigation, the machine was flown by 10 men. This group included men of no previous f l i g h t experience, men prof ic ient i n light-plane operation, and men with extensive experi- ence i n f lying mil i tary jets and helicopters. made by a l l men, although some practice time (seldom exceeding about 10 minutes) w a s occasionally required before reasonable proficiency was attained. A l l but one of the s i x men who flew the machine with both control systems preferred the control-stick method o f control.

Successful f l i g h t s were

INTRODUCTION

The f lying platform i s one of the proposed types of a i r c r a f t intended primarily t o give ground troops a degree of mobility unattain- able by any existing mode of surface transportation. The mission of

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the flying platform would be t o provide one man with short-range trans- portation, unrestr ic ted by t e r r a i n obstacles. great pract ical value, t he machine would have t o be very simple i n construction and so easy t o operate that only a re la t ive ly low degree of p i l o t s k i l l and t ra in ing would be required. simplicity of construction and ease of control seemed t o be met by a configuration which w a s basical ly a r e l a t ive ly low-powered ducted fan on which a man could stand and control the machine i n p i t ch and ro l l by simply shif t ing h is body weight. I n t h i s method of control, cal led the kinesthetic method, the p i l o t senses accelerations and applies control moments using the same reflexes and muscles normally used t o maintain equilibrium while simply standing on a surface fixed re l a t ive t o the earth. This control system has been used successfully on a number of one-man l i f t devices of various configurations. (See refs. 1 t o 3. )

I n order t o be of any

The requirements of

Although the kinesthet ic control seemed t o represent nearly the

The ultimate i n mechanical simplicity, no tes ts had been performed t o compare i t s ease of mastery with t h a t of other control systems. qua l i t i es of an airplane-type s t i c k control, f o r instance, had not been investigated i n t h i s application. Administration therefore undertook the construction and t e s t ing of a man-carrying ducted-fan vehicle equipped w i t h a removable seat and con- t r o l s t ick so tha t d i rec t comparisons could be made, i n ac tua l hovering f l i g h t , of the handling qua l i t i e s of t he kinesthet ic and s t i c k control systems.

The National Aeronautics and Space

MODEL

A drawing and photographs of the model are presented i n figures 1 The duct was of aluminum construction, 4 feet i n and 2, respectively.

diameter, and 18 inches long, exclusive of t he i n l e t l i p . l i p radius w a s 2.5 inches. stand, was centered on the axis of revolution of t he duct about 5 inches above the plane of the top of t he i n l e t l i p . I n order t o provide an attachment point f o r t h e overhead safety cable, a simple framework of aluminum tubing extended upward about 6.5 feet from the plane of the i n l e t l ip . The fan system consisted of two two-blade counterrotating wooden propellers driven, through a reduction gear, by an induction motor; the fan speed was controlled by an operator on the ground who varied the frequency of the motor power supply. a i rcraf t , exclusive of the p i l o t , w a s about l3O pounds.

The i n l e t A l i g h t grating, on which the p i l o t could

The weight of the

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Approximately 50 pounds of t h rus t w a s provided by four air jets, 5/8 inch i n diameter, directed p a r a l l e l t o t he fan axis and spaced equally around the outer circumference of the i n l e t l i p . These jets

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were equipped with simple valves which were linked t o a spring-centered airplane-type control s t i ck which was gimbal-mounted near the center of the grating. Deflection of the control s t i ck caused the valves on dia- metrically opposed air j e t s t o be d i f fe ren t ia l ly deflected, which produced pi tch and r o l l control moments up t o about k5O foot-pounds each. A removable seat w a s provided fo r the p i l o t during the control- s t i ck t e s t s . For the kinesthetic control t e s t s , the s t i ck and seat were removed, and a hand bar, i n the form of a piece of aluminum tubing, was fastened horizontally i n front of the p i l o t about 4 f ee t above the grating. valves were held_hn-~--a~proximately neutral position. f e l t that the p i l o t could no%-rave"BMTtetl hfs OW center of gravity more than about 1 foot without moving h i s f ee t , the maximum control moment available under kinesthetic control could be considered t o be about l5O foot-pounds.

For the t e s t s of the kinesthetic control system the a i r - j e t Because it i s

-- __ For a l l t e s t s , four radial vanes i n the fan slipstream near the

e x i t of the duct provided yaw control. a pneumatic servo uni t , the input t o which was controlled by two sources. One of the sources, a r a t e gyroscope mounted on the vehicle, varied the input t o provide a r t i f i c i a l daxping i n yaw, while an operator, stationed

The yaw vanes were actuated by

I on the ground, remotely controlled the heading of the vehicle. - -. - -- --1

.. TESTS

The t e s t s consisted of hovering f l i gh t s and mild maneuvers over the area allowed by the scope of t he overhead safety cable, about 15 f ee t t rans la t ion i n any direction f r o m the center of the area. Almost all the t e s t s were conducted inside a building about 70 f ee t square with a 50-foot-high ceil ing. The air i n the building at the beginning of a t e s t w a s , of course, very s t i l l , but as the t e s t pro- gressed the air became f a i r l y rough because of random recirculation of the slipstream within the builaing. p i l o t t o fly with one control system u n t i l he had at ta ined a reason- able degree of proficiency. using the other control system. control and some began with the s t ick control. usually of about 3 minutes duration and were made at a l t i tudes of from about 4 t o 6 f ee t measured t o the duct ex i t .

The usual procedure was fo r a

Fl ights were then undertaken by the p i l o t Some p i l o t s began with the kinesthetic

Individual f l i g h t s were

RFSULTS AND DISCUSSION *)

A motion-picture f i l m supplement t o this paper has been prepared a d i s available on loan. A request ca rd form and a description of the

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fi lm wil l be found at the back of this paper, on the page immediately preceding the abstract page.

During the course of the investigation, the t e s t vehicle was flown by a to t a l of 10 "pilots." types of control systems. w a s represented by the members of the group. f i ve men with very l i t t l e o r no previous experience a t a l l . end were three men (one of whom was a helicopter p i l o t ) with extensive experience i n f ighter a i r c ra f t . l i g h t planes.

Of this group, s i x p i lo t s flew with both A very wide range of previous f l i g h t experience

A t one end of the range were A t the other

In between were two men experienced w i t h

The t e s t s demonstrated that all the men, regardless of previous experience, could operate the t e s t vehicle successfully with e i the r type of control system, although some pract ice time w a s occasionally required with one o r both systems. Without exception, the men with .any appreciable previous experience, e i the r i n l i g h t planes o r f igh ters , expressed a def ini te preference f o r the s t i ck control and flew smoothly w i t h it from the very first. Some, but not a l l , of these men experi- enced i n i t i a l d i f f i cu l t i e s w i t h the kinesthetic control. The only man who preferred the kinesthetic control o r who had any i n i t i a l trouble with t h e s t i ck control had prac t ica l ly no previous f l i gh t experience.

Kinesthetic Control

During the investigation of the kinesthetic control method, two variations of p i l o t technique were tes ted. I n one, no par t of the p i l o t ' s body, other than his f ee t , w a s i n contact with the machine. I n the other, the p i l o t stood on the machine and grasped the hand bar fixed t o the vehicle 's framework.

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The discussion of the kinesthetic balancing process presented i n reference 1 se t s for th the theory tha t a man supported by a thrust device attached only t o his f e e t w i l l unconsciously sense the need f o r a control application and w i l l inst inct ively apply the proper correc- t i v e control. The t e s t s presently under discussion indicated tha t although the direction of the applied control m a y be correct, some practice time may be necessary before the magnitude of the p i l o t ' s muscular reaction becomes adjusted t o the l eve l required t o avoid overshooting the equilibrium position: This overshooting tendency, which was never completely overcome by any of the p i l o t s , gave r i s e t o a continuous osci-aatory motion which was usually more pronounced longitudinally than l a t e r a l q . tude sufficient t o impair seribusly the p i l o t ' s control over the vehicle, but was somewhat t i r i n g t o contend with and caused some apprehension on the part of the p i l o t as t o whether the machine w a s rea l ly under control.

The osc i l la t ion was never of an ampl i -

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This osc i l la tory tendency was not so apparent i n the t e s t s of refer- ence 1, which may be due t o the differences i n aerodynamic and i n e r t i a character is t ics between the two test vehicles.

A l l the p i l o t s using the kinesthetic control f e l t tha t the osc i l la - t i on became l e s s bothersome when they placed t h e i r hands on the hand bar fixed t o the framework of the vehicle. Although the osc i l la t ions were thereby reduced, the f l i gh t s freduently became rougher as soon as.manual contact w a s made. Forces transmittea through the hands t o the vehicle seemed t o be frequently i n the wrong direction f o r cbrrect control and, although a l l the p i l o t s seemed t o f ee l more at ease while grasping the

his hands "follow" the bar and provide on* a steadying force, allowing his f e e t t o produce all control moments. attempts were made t o force the vehicle into a desired a t t i t ude by use of the hands were all very rough and occasionally ended i n complete l o s s of control over the vehicle. The feeling w a s expressed by a p i l o t of considerable experience, i n Jet- and p ropeller-driven f igh ter a i r c r a f t thZt previous conventional f l i g h t training was of negligible value i n f G i n g with kinesthetic control.

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I hand bar, no smooth f l i gh t s were made u n t i l the p i l o t learned t o l e t

Flights during which manual i

Stick Control *

Flights during which the airplane-type s t i ck control was used were, i n genex,l, considerabq smoother than those i n which the kinesthetic cont_r&- was -soyed:-%Angular motions were noticeably smaller, and the precision with wech the vehicle could be maneuvered and positioned seemed. greater than with the kinesthetic control method. A f a i r l y high sens i t iv i ty t o gusts w a s noted during f l i g h t s with the s t i ck control. It i s possible that the same sensi t ivi ty existed during the t e s t s of the kinesthetic control but may have been obscured by the p i l o t ' s unconscious application of corrective control. proficiency w a s a t ta ined w i t h the s t i c k control w a s worthy of note. A l l but one of the men flew well with it f r o m the first attempt. man who encountered any di f f icu l ty at a l l required only about 20 minutes pract ice t i m e t o develop the a b i l i t y to hover f a i r l y smoothly over a predetermined spot o r t o perform forward, rearward, or sideward f l i g h t at w i l l . control over the vehicle by hovering very smoothly o r by executing various f l i g h t patterns rapidly and precisely.

The rapidi ty with which

The one

Men with extensive previous experience demonstrated excellent

Ther? seem t o be several reasons w h y the machine w a s so easi ly controlled by the use of the s t i ck method. F i r s t , the center of gravity of the pilot-vehicle combination was approximately one-fourth of a fan diameter above the top of the i n l e t l ip . The tendency of a ducted-fan vehicle t o develop an unstable osci l la t ion i s reduced as the center of

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gravity i s raised re la t ive t o the i n l e t l i p , and although the center-of- gravity location tes ted i s probably not the ideal , it w a s high enough tha t the osci l la tory tendency so prominent i n some other ducted-fan configurations w a s never noted by any of the p i lo t s . A second factor which i s considered t o have contributed heavily t o the ease of control of the vehicle was the powerful, posi t ive control moment available t o th_e_p_ilot. nearly a pure couple, unaccompanied by a change i n net force on the vehicle. The third reason i s the f a c t that the yaw and power controls were operated remotely by men stationed on the f loo r of the t e s t area. This considerably simplified the p i l o t ' s task by leaving him f r e e t o devote h i s en t i r e a t tent ion t o p i tch and roll control. Another reason f o r the confidence of the p i l o t s and the rapidi ty with which they learned with either control system w a s the f a c t that they knew that the safety cable would save them i n the event of mistakes which caused them t o lose control of the a i r c ra f t .

The air-Tet-system produced a control moment which was

The or ig ina l intention had been t o give the p i l o t control over the vehicle i n yaw, as well as i n p i tch and roll. when early f l i g h t t e s t s revealed random torque fluctuations which, i n addition t o being completely unpredictable, were so powerful and sudden that the p i l o t frequently l o s t control of the model i n yaw. of large random fluctuation of torque and other forces and moments on propellers when operated indoors i n t h e i r own recirculated slipstream has been observed many times i n the past and has never been adequately explained. A system having heavy a r t i f i c i a l damping i n yaw, with a man on the f loor controll ing the trim required f o r a desired heading, elim- inated the problem and w a s used during all f l i g h t s discussed i n this paper.

T h i s plan was abandoned

T h i s type

CONCLUSIONS

A f l i g h t investigation comparing two methods of controll ing a man- carrying ducted-fan vehicle of the flying-platform type has yielded information which seems t o justify the following conclusions:

1, The kinesthetic and s t i c k control systems each represent work- able methods of controlling a vehicle of this type. previous f l i g h t experience are l i k e l y t o prefer the s t i c k control

P i l o t s having

system.

2. A vehicle having a sui tably high center-of-gravity location and a powerfU source of control moment may prove extremely easy t o f ly w i t h a s t i c k control system.

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3 . The i n e r t i a and aerodynamic character is t ics of a vehicle may inf luenceconsiderably i t s adaptability t o kinesthetic control.

4. Random torque variations may be encountered which would present a serious complication t o the problem of yaw control with e i the r the kinesthetic o r s t i c k control system when the vehicle i s operating i n gusty air o r near obstructions.

Langley Research Center, National Aeronautics and Space Administration,

Langley Field, Va . , March 22, 1961.

1. Z i m m e m , C. H., H i l l , Paul R. , and Kennedy, T. L.: Preliminary Experimental Investigation of the Flight of a Person Supported by a J e t Thrust Device Attached t o His Feet. NACA RM L52DlO, 1953.

2. H i l l , Paul R., and Kennedy, T. L.: Flight Tests of a Man Standing on a Platform Supported by a Teetering Rotor. NACA RM L54Bl2a, 1954

3. Townsend, M. W., Jr.: S tab i l i t y and Control of Unducted Stand-On Helicopters: Preliminary Theoretical and Flight Test Results. Rep. No. 404 (Contract DA &-177-TC-392), Dept. Aero. Eng. , Princeton Univ., Nov. 1957.

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Comoressed air t u b i n g .

S a f e t y f m e w o r k

Foot p l a t f o r m

Upper f a n

Lower ran -’

il C o n t r o l S t i c k

Figure 1.- Drawing of test vehicle as set up for stick-controlled flight. A l l dFmensions are in inches.

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NASA - La@ey Field, V..