Factors affecting handling qualities of a lift-fan aircraft during steep terminal area approaches

TM X- 62,424 NASA

NASA TECHNICAL

MEMORANDUM

N75-22313 FACTORS AFFECTING (NASA-TM-X-62424) AIRCRAFT HANDLING QUALITIES OF A LIFT-FAN DURING STEEP TERMINAL AREA APPROACHES (NASA) 01C Unclas CSCL 26 p HC $3.75 G3/05 19477 X z FACTORS AFFECTING HANDLING QUALITIES OF A LIFT-FAN AIRCRAFT DURING STEEP TERMINAL AREA APPROACHES Ronald M. Gerdes and S. Hynes Charles Ames Research Center-NASA Moffett Field, Calif. 94035 April 1975 2. Government Accession No. 3. Recipient's Catalog No.

1. Report No.

NASA TMX-62,424 and Subtitle 5. Report Date 4. Title Factors Affecting Handling Qualities of a Lift-Fan 6. Performing Organization Code Area Approaches Steep Terminal Aircraft During No.

8. Performing Organization Report 7. Author(s) Ronald M. Gerdes and Charles S. Hynes A-6016 10. Work Unit No.

9. Performing Organization Name and Address 760- 63-04-05 NASA Ames Research Center 11. Contract or Grant No.

Moffett Field, Calif. 94035 Type of Report and Period Covered 13.

12. Sponsoring Agency Name and Address Technical Memorandum National Aeronautics and Space Administration 14.Sponsoring Agency Code Washington, D. C. 20546 15. Supplementary Notes 16. Abstract The XV-5B lift-fan aircraft was used to explore the factors affecting handling qualities in the terminal area. A 100 ILS approach task was selected to explore these problems. Three major phases of the approach were considered: (1) interception of the glide slope at 457.2 m (1,500 ft), (2) glide slope tracking, (3) deceleration along the glide 'slope to a spot hover. Variations in airplane deck angle, deceleration schedule, and powered-lift management were studied to assess their effects on handling qualities. The overall descent performance envelope was identified on the basis of such operational limitations as fan stall, maximum comfortable descent rate, and controllability restrictions. The "collective-lift" stick pro- vided precise glide slope tracking capability through direct control of fan lift, but the pilot tended to "chase" glide slope if engine power (throttle) was modulated. The pilot preferred a deck-parallel (to glide slope) attitude for which he used powered lift (collective) to control glide slope and pitch attitude (stick) to keep the angle of attack near zero, which minimized his workload. This technique also provided a greater angle-of-attack margin fron fan stall.

Workload was reduced when the deceleration schedule was delayed until the aircraft was well established on the glide slope, since thrust vector changes induced flight path disturbances.

18. Distribution Statement 17. Key Words (Suggested by Author(s)) V/STOL Unclassified-Unlimited Lift Fan Terminal Area Handling Qualities STAR Category 05 22. Price* 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages Unclassified Unclassified 26 $3.75 *For sale by the National Technical Information Service, Springfield, Virginia 22151 FACTORS AFFECTING HANDLING QUALITIES OF A LIFT-FAN AIRCRAFT DURING STEEP TERMINAL AREA APPROACHES Ronald M.

Gerdes Aerospace Engineer & Pilot Charles S. Hynes Aerospace Engineer Ames Research Center-NASA, Moffett Field, California 94035 SUMMARY The XV-5B lift-fan aircraft was one of four NASA V/STOL research vehicles recently used to explore the factors affecting handling qualities in the terminal area. The objectives of the program were to define the limitations of powered-lift VTOL aircraft that prevent full exploitation of their low-speed capabilities, and to develop operationally feasible techniques for performing simulated precision instrument landing approaches.

A 100 ILS approach task was selected as representing a typical steep-angle approach with which to explore these problems.

Three major phases of the approach were considered: (1) interception of the glide slope at 457.2 m (1,500 ft), (2) glide-slope tracking, (3) deceleration along the glide slope to a spot hover. Variations in airplane deck angle, deceleration schedule, and powered-lift management were studied to assess their effects on handling qualities.

The overall descent performance envelope was iden- tified on the basis of such operational limitations as fan stall, maximum comfortable descent rate, and controllability restrictions.

The "collective- lift" stick provided precise glide-slope tracking capability (to within ±6.1 m (20 ft) through direct control of fan lift, but the pilot tended to "chase" glide slope if engine power (throttle) was modulated.

The pilot preferred a deck-parallel (to glide slope) attitude, for which he used powered lift (collective) to control glide slope and pitch attitude (stick) to keep the angle of attack near zero, which minimized his workload.

This technique also provided a greater angle-of-attack margin from fan stall.

Workload was reduced when the deceleration schedule was delayed until the aircraft was well established on the glide slope, since thrust vector changes induced flight path disturbances.

INTRODUCTION After about 15 years of being relegated to proof-of-concept testbed duties, it now appears that VTOL aircraft may very well be placed into service to solve some of our most pressing military and commercial air Presented at the 27th Annual National Forum of the American Helicopter Society.

May 1971.

(Include Forum credit in all cases).

-1- of limited numbers of transportation problems. The introduction Harriers into U.S. Marine Corps service, and the Hawker-Siddeley AV-8A NASA to development of a VTOL high priority assigned by the DOT and support this viewpoint. Such vehicles transport for service in the 1980's that assure the acceptance of both pilots and must have characteristics from high speed passengers throughout the entire operational spectrum a pre- cruise to hover touchdown. Satisfactory handling qualities are Past experience with VTOL requisite for safe and profitable operations.

qualities were optimized for research vehicles has indicated that handling the cruise and hover regimes, and it was left up to the pilot to struggle through the transition from one to the other. Instrument flight in this!

"in between" region was found to be very difficult, if not altogether impos- sible. The terminal area instrument approach, therefore, has been identi- fied as one of the most demanding problems the VTOL transport pilot and the designer both face.

Present V/STOL handling quality criteria and specifications, such as references 1 and 2, contain only "guideline" information relative to opera- and more complete definition will tions in the terminal area. Further the depend on operational experience as well as a clearer understanding of which affect the handling factors peculiar to powered-lift aircraft qualities of these vehicles.

This paper describes some of the preliminary results of the terminal area study conducted at the Ames Research Center with the XV-5B lift-fan research airplane. Its purpose is to identify some of the operational a han- factors that the pilot considered to be of major significance from The factors described, especially the dling qualities point of view.

management of powered lift and thrust vector control have caused handling - difficulties on several other powered-lift vectored-thrust aircraft difficulties so severe as to limit their practical usefulness. The details the of the pilot's criticism of handling qualities depend, of course, on as in peculiarities of each aircraft (especially control mechanization), the case of the XV-5B. However, these differences are seen in more general perspective when it is realized that no vectored-thrust powered-lift vehicle yet flown by the NASA has solved these handling problems well enough to take full advantage of vectored-thrust performance during termi- nal area operations.

In the XV-5B program, an ILS approach along a 100 glide slope was selected as the terminal area mission. Three.major piloting tasks were considered: (1) glide-slope interception, (2) glide-slope tracking, (3) deceleration along the glide slope to a spot hover. Variations in airplane deck angle, deceleration schedule, and powered-lift management were studied in terms of handling qualities and associated pilot workload. The overall descent performance envelope was explored to identify operational limita- axis maneu- tions. The scope of this paper is restricted to longitudinal vering about the glide slope in the fan mode of flight only, and does not treat the jet (or conventional) mode of flight or the conversion from jet mode to fan mode operations prior to the approach.

-2- OF THE AIRCRAFT DESCRIPTION the XV-5B, shown in hovering flight in Fig. 1, Pertinent details of of the limited detail to provide a basic understanding are described in that affect fan-mode approach. Only controls systems used to perform the of the are described. A more detailed description the longitudinal axis The XV-5B is the XV-5A aircraft XV-5B is contained in reference 3.

landing gear.

modified to incorporate outboard fixed 2.

system can be seen in figure The major elements of the propulsion the thrust-to-weight ratio is For flight from 100 knots down to hover, the J-85 hot gas efflux to drive increased from 0.5 to 1.25 by diverting A similar the tip turbines of the two 1.5 m (5-ft) diameter lift fans.

m (3-ft) fan, located in the nose, provides pitch control through 0.91 located below the nose fan. Movable vanes two thrust reversing doors of each wing fan vector the located in the exit plane ("exit louvers") to 450 aft of the vertical, and can spoil as much as thrust from 70 forward to provide lift control.

25% of fan thrust by pinching action helicopter controls (stick, The pilot is provided with conventional quadrant-mounted throttles. The pedals, and collective) and conventional move with the cockpit controls conventional aerodynamic control surfaces stick and pedals to the at all times. A mechanical mixer links the cockpit Pitch attitude is con- fan exit-louver and thrust-reverser-door actuators.

reverser doors. The trolled by longitudinal stick which actuates the by spoiling thrust collective stick provides height control during hover actuating the wing fan exit louvers. Turbojet RPM is controlled inde- by which are locked together and mechanically pendently by the throttles, on the collective. Wing fan RPM is neither connected to a twist grip con- governed (like the gas turbine-powered helicopter) nor independently of gas power input to trolled, but rather is determined by the combination flow, which is the fan from the gas generators and the loading due to fan thus uses J-85 sensitive to flow conditions at the fan inlets. The pilot RPM as a direct reading reference for power settings.

Thrust vector angle is controlled electrically by "beep" switches located on the right throttle handle and on the collective grip. Because of the drag characteristics of the airplane in forward flight, airspeed closely follows vector angle changes. Transition to control by the conven- tional aerodynamic surfaces at the higher fan-mode speeds is effected by mechanical washout within the mixer of louver response to cockpit controls at vector angles exceeding 200, which corresponds to speeds above 50 knots in fuselage-level flight. At vector angles exceeding 300 (70 knots in level flight), louver response to collective stick inputs is entirely fan thrust only indirectly by setting washed out, and the pilot can control turbojet RPM with the throttles.

roll A stability augmentation system provides limited-authority pitch, servos.

and yaw rate damping through the fan-mode control -3- FACTORS CONTRIBUTING TO PILOT WORKLOAD Powered-Lift Management The high workloads required to manage the powered-lift system are for the major difficulties affecting handling qualities of responsible a proof of concept research vehicle, the this aircraft. Designed as the fan-mode regime as XV-5B was intended to be transitioned through conditions. Controllability rapidly as possible in level flight in VFR In contrast, the terminal was optimized for hover and jet-mode flight.

area approach requires precision instrument flying during transition through a region of "aerodynamic overlap" where the pilot must adapt to a complex set of controls. Factors contributing to pilot workload during terminal area maneuvering are discussed below. Although this paper dis- cusses XV-5B characteristics, experience has shown that very similar factors have influenced the handling qualities of other vectored-thrust aircraft, such as the DO-31, P.1127 and XC-142A.

Magnitude Control - Lift magnitude, or fan thrust, can be con- Lift louver (and reverser door) modulation trolled by two independent methods: RPM by modulation of J-85 power with collective stick and changes in fan is immediate with the throttles. Fan thrust response to collective input is required. When engine since only louver and reverser door movement throttles are used for height control, the pilot must cope with a combi- the order of 1.5 seconds. A decel- nation of engine-plus-fan thrust lag of eration schedule which commences with vector angles above 300 requires that pilot not only switch from one method of glide slope control to the the other but also compensate for the change in response characteristics with airspeed.

One problem was identified with using collective stick for glide slope control. Angle-of-attack increases as collective stick is lowered to increase descent rate. The resultant build-up in aerodynamic lift reduces collective downward control power to the point where the collective often ends up on the bottom stop with the pilot complaining about "running out of collective." The only alternative is to reduce power and/or drop the nose.

Lift Vector Control - Lift vector angle provides a very effective means of controlling velocity along the glide slope, but the resulting lift and thrust component transients cause flight path disturbances which require pilot compensation to maintain glide slope tracking. Lift component dis- turbances must be countered with collective stick, throttle, or longitu- dinal stick. Thrust (or velocity) transients are less of a problem and require retrimming to.the new airspeed. Changing vector angle by "beeping" the control instead of constant rate steps allows the pilot to compensate easily.

for the resultant flight path disturbances more Fan Stall - Avoiding fan stall is the major angle-of-attack restriction attitude) considered because it limits the maximum deck-level (zero pitch -4- glide-slope angle capability of the airplane. Full-scale wind-tunnel tests stall occurs at about 150 angle of attack and is charac- indicate that fan in fan thrust, and an downward pitching moment, a loss terized by a gradual the fan stall was encountered during increase in fan speed. An approach to the pilot was correcting for a "fly several deck-level approaches when felt to be the A 100 approach angle was therefore down" glide slope error.

from the stall in the deck-level limit, allowing a 5* maneuver margin approach.

Stability and Control Longitudinal were found to deficiencies in the longitudinal control system Serious overall terminal area be responsible for a general degradation in the was to maintain a The primary longitudinal control task maneuverability.

(either deck-level or deck-parallel to the glide slope) prescribed attitude decelerated along the glide slope from about 70 knots as the aircraft was affecting longitudinal control, which to hover. Two characteristics a continuously demanding task together made controlling pitch attitude from were: (1) large changes in static longitudinal stability ranging 75 and 55 knots) to positive (at negative (at airspeeds between about (2) inadequate nose-down pitch speeds between about 55 and 25 knots) and longitudinal sta- trim authority in the 30 to 75 knot speed range. Static is the is presented in figure 3. Since maintaining deck attitude bility longitudinal control task, it is evident that much of the pilot's primary be required to contend with these adverse characteristics.

attention may artificial attitude stability has worked well with other VTOL Providing aircraft. The pilot cannot manage a powered-lift system effectively if controlling aircraft attitude demands excessive attention.

FOR INVESTIGATION SELECTION OF APPROACH PROCEDURES Operational Criteria The approach procedures for this investigation were based on the following operational criteria: (1) The approach should make use of a high of descent and rapid deceleration to hover to conserve fuel and reduce rate congestion; (2) The approach should be along a steep glide slope traffic reduce propulsion system noise and and make maximum use of wing lift to to conduct safe operations in IFR fuel consumption; (3) One should be able the pilot's workload and with reasonable conditions without increasing passenger comfort.

Selection of Deck Angle Two deck angles (pitch attitudes) were evaluated as limiting cases from an operational point of view: (1) deck-parallel and, (2) deck-level.

In the deck-parallel case, the fuselage is alined parallel to the glide -5- a technique now approach, angle-of-attack in a near-zero slope, resulting of course, provides deck-level approach, STOL aircraft. The used with some for this technique the it was hoped that lift. In addition, more wing a constant level attitude be reduced since workload would attitude-control and 4(b)). A deck- (see figs. 4(a) the approach is maintained throughout for passenger comfort.

would also be preferable level attitude Schedule Selection of Deceleration proce- compared to conventional area approach, when The VTOL terminal glide must be decelerated along the dures, is unique in-that the aircraft presents a very touchdown. This requirement slope to a hover before the be sig- was found that pilot workload could piloting task, and it demanding of a deceleration scheme. Initially, nificantly reduced by proper selection by programming thrust schedules, were devised such schemes, or devector two (1) gradual of indicated pressure altitude: angle as a function vector angle (and thus the deceleration. The vector and (2) terminal deceleration in the gradual with altitude was decreased gradually resultant airspeed) was as the hover spot and was decreased rapidly deceleration case, thus pilot's task was case. The the terminal deceleration approached in of the around the periphery schedule printed "track" the devector simply to Figure 5 is an a pointer-reference.

100-foot needle as altimeter using the on the its placement schedule, showing of a typical devector example altimeter.

Descent Performance was determined for flight descent capability of the XV-5B The fan mode of the investigation.

the initial phases as steep as 200 during path angles angle the deck-parallel (zero descent performance for both A summary of the in figs. 6(a) and 6(b) and deck-level approaches is presented of attack) rate along a given between airspeed and descent and shows the relationship were vector angles. These relationships flight path angle at various and in determining various approach procedures found useful in establishing operational limitations.

and flight path variations of rate of descent Figure 6(a) shows the pitch attitude is that result when radial lines) with airspeed angle (solid vector angle is procedure) and thrust held fixed at zero (the deck-level The by the broken contours.

one of the five values illustrated fixed at contours shows that in fuselage-level vertical slope of these nearly independent vector angle and is depends only on thrust flight the airspeed without change thus the descent angle can be controlled of descent angle; level while keeping the fuselage regulating thrust magnitude of airspeed by the cross-hatched boundary shows vector angle fixed. The and the thrust the onset of fan stall at angles descent angles to 15* due to limitation of and flight path the fuselage level, angle of attack of attack near 150; with equal.

angle are, of course, numerically angle and variations in descent illustrates the resulting Figure 6(b) attack fixed at is varied to keep angle of when pitch attitude airspeed -6- attitude coincides procedure); thus pitch (or deck) zero (the deck-parallel of thrust vector The slope of the broken contours with flight path angle.

angle downward and to the right shows that when descent is steepened by to reduction in vector angle is required lowering the nose, a compensating in speed; furthermore, the magnitude of the vector angle avoid an increase in flight path angle. For is very nearly equal to the change reduction flight at 70 knots when a 10* descent is initiated from level example, angle must be reduced the nose 100, the thrust vector (point A) by lowering knots in the 100 300 to 200) to maintain a speed of 70 about 100 (from rotates the thrust (point B). Since rotating the aircraft in pitch descent exit louvers remain fixed, compensating changes in vector as well when the inclination of thrust vector angle (exit louver position) simply cause the Exact equal- the thrust vector to remain fixed with respect to the earth.

angular increments in thrust vector angle and flight path ity of these at angle would be expected at constant speed when angle of attack is fixed of zero, since.aerodynamic lift then remains constant. The near-equality the chart of figure 6(b) shows that such increments as may be read from the flight results with surprising accuracy.

these simple ideas predict Selection of Approach Angle and Initial Speed was selected as a For the present study an approach angle of 100 of the deck-parallel and reasonably steep approach which enabled comparison could be flown without deck-level techniques. Deck-parallel approaches approaches could be uncomfortably steep nosedown attitudes, and deck-level of flown with safe (50) angle-of-attack margins. An initial approach speed and was chosen as providing a good combination of descent rate 70 knots the effectiveness. The vector angle was 200 at 70 knots during collective deck-parallel approach and 30* at 70 knots during the deck-level approach a 6(a) and 6(b)). Two operational considerations dictated that (see figs.

be (70 knots) rather than a common thrust vector angle common airspeed of the two approaches. If the deck-level chosen for the initial conditions vector angle, so as to provide col- approach had been initiated with a 200 the velocity and descent rate would have been lective stick authority, both out" approach requiring slightly reduced considerably, yielding a "dragged angle and 90-knot approach speed increased fuel reserves. A 300 vector approach, but complete phase-out could have been used for the deck-parallel rate would have been too of collective control and an excessive descent With the approach angle fixed detrimental to pilot tracking performance.

procedures at 100 and the initial speed fixed at 70 knots, detailed flight were developed for the approach evaluations.

Area Approach Procedures Terminal procedures (see fig. 4) were Two operationally promising approach would have chosen for this investigation, although flexibility of control made possible the selection of many other combinations of parameters. A and termina- 10* ILS approach with a 457.2 m (1,500 ft) intercept altitude tion to a spot hover was specified as the basic guidance task. All approaches were conducted in VFR conditions with an initial airspeed of -7- to IFR about 70 knots. An attempt was made to extrapolate observations conditions. Deck-parallel and deck-level approaches were evaluated inter- for direct comparison. The deck-parallel approach required a changeably 100 nose-down pitch change upon glide-slope intercept, followed by a return to a near level attitude just prior to coming to a hover. Pitch.

attitude remained nearly constant throughout the deck-level approach. In each case, the vector angle was systematically reduced according to a selected deceleration schedule in order to slow the aircraft to a hover Both gradual and terminal at about 6.1 to 7.6 m (20 - 25 ft) altitude.

deceleration schedules were evaluated.

can thus be summarized as follows: The glide The piloting task slope was intercepted at 457.2 m (1,500 ft) and an airspeed of about 70 knots and was either deck-parallel or deck-level. The pilot tracked the glide slope as closely as possible while decelerating the aircraft to an eventual hover over the touchdown spot.

HANDLING QUALITIES CRITERIA Handling qualities described in this investigation were judged to be poor when an approach task required pilot compensation for vehicle deficiencies which significantly increased pilot workload. Pilot assess- ment of handling qualities in terms of compensation and workload are clearly described in reference 4. Definition of some of the major terms pertaining to handling qualities contained in this reference are repro- duced in figure 7 to help clarify the reader's understanding of the handling qualities factors described below.

RESULTS OF FLIGHT EVALUATION Deck-Parallel Approach Handling Qualities The initial approach speed of 70 knots required a vector angle of 300 in level flight before the glide path was intercepted (see fig. 6(b)- point A). Early attempts to intercept the glide slope at constant vector angle (of 200) by merely "dropping the nose" 100 was found to be undesir- able because there was a tendency to "balloon" through the glide slope.

In addition, initial glide slope tracking was hindered somewhat by the requirement to retrim to the new airspeed (from 50 to 70 knots). A tech- nique which was found to work well, was to approach the glide slope at a 30* vector angle and perform a constant airspeed pitch-over by reducing vector angle 100 (to 20*) simultaneously with pitch attitude (from point A vertically downward to point B on fig. 6(b)).

Collective stick was found to be extremely effective for tracking the glide slope. Response to this "direct lift control" was precise and quick.

During on-course tracking, J-85 power was set through experience to place the collective somewhere in its midrange. The piloting task was simply to -8- somewhere and keep the angle of attack glide slope with collective track Once glide slope was established pitch attitude (stick).

near zero with this task was found to be pleasant and easy. If very at constant speed, J-85 power had to glide-slope errors were encountered, large "fly-down" "running out of collective."

be adjusted to avoid schemes were evaluated. The and gradual deceleration Both terminal unacceptable because of the deceleration technique was judged terminal in coping with the ensuing attitude and flight path intolerable workload was felt to the ground. This "quick stop" maneuver disturbances close as an instrument approach procedure.

to be completely unsuitable of 50 vector scheme, consisting of a series A gradual deceleration to be unsat- ft) down the glide slope, was found changes every 76.2 m (250 isfactory. Starting the devector schedule immediately upon intercepting task of getting established slope resulted in a dual piloting the glide Workload was intensified slope while following the schedule.

on glide (see fig. 8(a)). The and glide slope tracking performance deteriorated to be too small in that devector increments of 5* were also considered time to compensate completely for the flight path there was insufficient it was time to devector by one vector change before disturbances produced was oscillatory.

once more to the next one. The resulting flight profile to improve on the A revised or delayed devector schedule intended Initiation of of the first two was found to work very well.

deficiencies changes, was the vector schedule, consisting of two nominal 100 vector on the glide slope at delayed until the aircraft was well established were actually made in a series about 152.4 m (500 ft). The vector changes (instead of 50 steps) to reduce the sever- of smaller increments or "beeps" the pilot an opportunity to ity of the resulting disturbances and give oscillatory behav- with collective stick inputs. The resulting compensate The use of 100 increments allowed ior was greatly reduced (see fig. 8(b)).

schedule scan tracking time and reduced the required vector for increased already set reducing pilot workload. With the vector angle rate, thus at the hover position of -3o, transition to (below 61 m (200-ft) altitude) to a level executed at about 21.3 m (70 ft) by a gradual rotation hover was of final sink rate with collective stick.

attitude and a check Deck-Level Approach Handling Qualities of 300 (70 was initiated with a vector angle The deck-level approach track- the use of J-85 thrust modulation for glide-slope knots) to evaluate comparison with the deck-parallel method.

ing and as a basis for direct of collective authority at the vector Because of the complete phase-out glide slope cap- angle of 300, a power reduction was required to initiate and after ture. J-85 RPM was reduced as the glide slope was approached, smooth constant- some experience, the pilot was able to achieve a relatively the glide slope, however, he was speed capture. When the pilot overshot during the "fly down" to avoid the fan forced to reduce pitch attitude that throughout the entire stall boundary. It should be emphasized -9- whenever to the pilot proximity was a major concern approach, fan stall itself.

a large "fly down" situation presented was reduced the vector angle technique before Glide-slope tracking to correct modulating J-85 RPM consisted of 300 for the deceleration below the glide- pilot tended to chase As expected, the hold "on course."

to and as flight path inducing as oscillatory with the throttles, slope needle the order of 1.5 sec time constant of in figure 9. Engine-plus-fan shown and this behavior cause of this high workload, felt to be the primary was glide slope with ease of controlling contrast to the relative was in sharp the deck-parallel approach.

collective during task per- pilot workload and a deterioration in In general, increased Some of the to the deck-parallel case.

evident as compared formance were and fuel Although power, noise for this are not fully understood.

reasons that the addition of aerodynamic reduced, indications were consumption were by reducing the aircraft's the pilot's tracking performance lift hindered lift controls. This effect has displacement response to powered vertical angles precise flight path control at high not yet been clearly defined but used the collective reduced whether the pilot of attack was significantly and stated that "the approaches were wormy or the throttles. The pilot disturbances uncomfortable." (Some lateral-directional felt generally complaint based on deck- pilot opinion.) One specific also influenced powered-lift reductions was that larger than expected parallel experience Even at vector when responding to "fly down" commands.

were required J-85 power was sometimes forced to reduce angles below 200, the pilot workload point of down-collective." From a pilot because of "running out stick for glide- advantage of using collective of view, this meant that any was forced to make additional engine.

slope control was lost when the pilot the necessity of having a adjustments. This problem points to power control.

integrated powered-lift single in order to of the deceleration schedule Delaying the initiation well estab- the glide slope capture and get the pilot time to complete give in the deck-parallel case. Terminal lished reduced cockpit workload as Termination to be completely unacceptable.

deceleration was again found by increasing power by the executed at about 21.3 m (70 ft) to hover was the glide slope.

amount it had been reduced to capture AND RECOMMENDATIONS PILOT PREFERENCE Preferred Approach Profile schedule employing a delayed deceleration A deck-parallel approach, judged to be the most preferable from a with 100 vector increments, was view. Major considerations were safety, track-.

handling qualities point of (ride quality). The following ter- ing performance, workload, and comfort was preferred for a 100 ILS task: minal area approach technique -10- 1. Line up on the localizer in level flight at a vector angle of (in the with J-85 power set for a mid-collective position 30* approach).

vector Upon approaching the glide slope, simultaneously reduce 2.

100 nose down.

angle to 200 and pitch Track the glide slope with collective stick and keep angle of 3.

near zero with pitch attitude.

attack Select a delayed devector schedule which allows sufficient 4.

prior to start of deceleration.

glide-slope tracking time increments employing a "beeping" technique and 5. Use 10* devector to correct for resultant flight path collective adjustment disturbances.

6. Make final deceleration to hover by simply pitching up to a rate with collective.

hover attitude and adjusting final sink Recommended Vehicle Improvements It is felt that some of the major handling qualities characteristics which caused unacceptable levels of pilot workload during the terminal area approach in the XV-5B can be improved by the following modifications to the powered-lift and control systems. These are listed for considera- tion in future designs.

Power Management - This system would integrate and 1. Integrated automatically schedule engine power and fan-lift controls in such a way as to give the pilot a single powered-lift control as in the present day turbine-powered helicopter. It, should also reduce the changes in effectiveness of the longitudinal controls during terminal area approach maneuvering.

2. Automatic Devector Control - This system would eliminate the piloting tasks of following a devector schedule. For example, vector angle could be automatically programmed as a function of height above the touchdown spot.

- This system would relieve the 3. Attitude Stability Augmentation disturbances. It is pilot of the task of coping with attitude VTOL aircraft will require generally agreed that any operational attitude stability for IFR missions.

CONCLUSIONS An evaluation of steep terminal area approaches along a 100 ILS approach path was performed in the XV-5B lift-fan aircraft in VFR condi- tions to ascertain the major operating factors that affect its handling qualities. The following conclusions were drawn as a result of this investigation: 1. The XV-5B exhibited a broad descent capability which was gener- ally suited for steep terminal area approach profiles. The major source of handling problems was found to be in the management of the powered-lift systems.

-11- 2. For glide-slope tracking, control of powered lift with the collective stick was preferred over engine power modulation.

When engine power was used, lags in propulsion system response the glide slope with throttle movement.

caused the pilot to chase 3. Changing thrust vector angle was a very effective means of con- tracking perfor- trolling velocity along the glide slope, but schedule mance deteriorated if the deceleration (or devector) was initiated immediately upon glide-slope intercept. Pilot workload was significantly reduced when the devector schedule was delayed until the airplane was well established on the glide slope.

4. Changing thrust vector angle induced flight path disturbances during deceleration, but the pilot was able to cope with them if vector changes were "beeped" in 100 increments.

5. The deck-parallel (to glide slope) approach was preferred over the deck-level approach because it allowed a greater fan stall maneuver margin and minimized aerodynamic lift effects. In the deck-level case, aerodynamic lift supplemented powered lift, but aerodynamic lift effects hindered glide-slope tracking performance.

6. Control of pitch attitude was found to cause a high workload because of disturbances induced by maneuvering, adverse longitu- dinal static stability, and inadequate pitch trim authority.

7. Terminal area approach handling qualities could have been improved if the XV-5B had been modified to include integrated power management, automatic devector control, and attitude stabi- lization augmentation.

-12- REFERENCES 1. NATO AGARD Report 577-70, V/STOL HANDLING I - CRITERIA AND Group for DISCUSSION, North Atlantic Treaty Organization - Advisory Aerospace Research and Development, 1970.

OF 2. MIL-F- (Proposed draft) MILITARY SPECIFICATION-FLYING QUALITIES PILOTED V/STOL AIRCRAFT, July 1970.

3. USAAVNTA PROJECT NO. 62-72, ENGINEERING FLIGHT RESEARCH EVALUATION OF THE XV-5A LIFT FAN AIRCRAFT, Finnesteda, R., Ferrell, K., Welter, Army Aviation Test Activity, Edwards Air W., and Anderson, W., U.S.

Force Base, California, August 1966.

4. NASA TN D-5153, THE USE OF PILOT RATING IN THE EVALUATION OF AIR- CRAFT HANDLING QUALITIES, Cooper, G. and Harper, R., National Aero- Administration, Washington, D.C., April 1969.

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0 10 20

30 40 50 60

70 80 90

CALIBRATED

AIRSPEED, knots

Figure 3.- XV-5B static longitudinal stability.

1,500

ft (457.2

m)

(a)

DECK-PARALLEL

APPROACH

MAJOR

APPROACH PHASES

GLIDE

SLOPE CAPTURE

DECELERATION

SCHEDULE

HOVER

1, 500 ft (457.2

m)

(b) DECK-LEVEL

APPROACH

Figure 4.-Terminal area procedures.

DECK -PARALLEL DEVECTOR

SCHEDULE-IO00 ILS

INDICATED

ALTITUDE, VECTOR

ANGLE, DESIRED

AIRSPEED,

deg knots

m ft

(457.2) 1500 20 70

(381.0) 1250 15 62

(304.8) 1000 10 51

(228.6)

750 5 42

(152.4)

500 0 32

(76.2) 250 -3 25--0

7 ALT 3

PILOT'S INDICATOR ON ALTIMETER

Figure 5.- Typical deceleration devector schedule - deck-parallel approach.

m/min

ft/min

INDICATED

AIRSPEED~

knots

(121.9)

400 -

z (243.8)

. (365.8)

-

1FAN

STALL

-(487.7)

-

BOUNDARY

F-(609.6)

(731.6)

THRUST

VECTOR

ANGLE

--

(853.4)

FLIGHT

PATH

ANGLE

OR

ANGLE

OF ATTACK

(a) Deck level.

Figure 6.- Descent performance.

m/min

ft/min

INDICATED

AIRSPEED~

knots

.0

60 80

A

(121.9)

400 -

W (243.8)

800 -

W (365.8) 1200

0 (487.7) 1600-

S(609.6)

2000-

(731.6)

-

(853.4) 2800

- THRUST VECTOR ANGLE

18*

FLIGHT

PATH

ANGLE

OR

DECK ATTITUDE

ANGLE

(b) Deck parallel.

Figure 6. - concluded.

FROM TN-D-5153

DEFINITIONS

PERFORMANCE

COMPENSATION

respect to

pilot effort The precision'of control with

The measure of additional

aircraft movement that a pilot is able to

attention required to maintain a

and

a task. (Pilot-

face of achieve in performing

4given level of performance in the

performance is a measure of

vehicle characteristics. vehicle

deficient

performance. Pilot perform-

handling

HANDLING QUALITIES ance is a measure of the manner or

pilot moves the

with which a

of an efficiency

or characteristics

Those qualities

in performing a task.)

and preci- principal controls

aircraft that govern the ease

which a pilot is able to perform

sion with

ROLE

an air-

tasks required in support of

the

craft role.

The function or

purpose that defines the

aircraft.

of an

use

primary

MISSION

The composite

of pilot-vehicle functions

TASK

that must be performed

to fulfill opera-

of or as repre-

tional requirements. May be specified for performed in completion

flight, flight phase, or

a role, complete

a designated flight segment.

sentative of

flight subphase.

WORKLOAD

The integrated physical and mental effort required

task.

piloting

a specified

to perform

Figure 7.- Handling qualities evaluation terms from reference 4.

m ft

(487.7)

1600 -

p

= THRUST VECTOR

ANGLE

v

z (426.7) 1400

°

0 (365.8) 1200 -=3°° 20

I 15o

(304.8) 1000

w (243.8) 800 -

-

(182.9)

m

400 -

9)

(121

(121.9)

400 ARROWS INDICATE WHERE

WAS INITIATED

L ,0v CHANGE

-

S(61.0) 200

_-

- 2

ft XO 96 80 64 48 32 16 0

- 2

mX10 (29.3) (24.4) (19.5) (14.6) (9.8) (4.9)

DISTANCE FROM TOUCHDOWN

(a) Gradual deceleration schedule.

of a'deck-parallel approach.

Figure 8.- Radar profile

m ft

(487.7)

-

V =

THRUST

VECTOR

ANGLE

Z

(426.7)

-

0 = 300 200

0 (365.8)

1200 -

(304.8) 1000

w (243.8)

m (182.9) 600

200 -40100

I (121 .9) 400 -

(121.9)

400 ARROWS INDICATE WHERE

S(61

.0) 200v CHANGE WAS INITIATED O

-

S(61 .0) 200

-0

- 30

ft 96

80 64 48 32

16 0

mxlo

(29.3) (24.4)

(19.5) (14.6)

(9.8) (4.9)

DISTANCE FROM TOUCHDOWN

(b) Delayed deceleration schedule.

- concluded.

Figure 8.

m

ft

(487.7)

/v

= THRUST

VECTOR

ANGLE

z (426.7)

8v = 30*

a

(365.8)

- (START)

(304.8) 1000

w (243.8)

m (182.9) 600

I

(12 . 9) 400 -

(121.9)

400 ARROWS

INDICATE WHERE

Lv CHANGE WAS INITIATED 8v=30*1200

r (61.0)

200 100

f100 - -130

- 2

ftX10

96 80

48 32

- 2

mxlO

(29.3) (24.4)

(19.5)

(14.6)

(9.8) (4.9)

DISTANCE

FROM

TOUCHDOWN

Figure 9.- .Radar profile of a deck-level approach - delayed deceleration schedule.