Flight Evaluation of Advanced Controls and Displays for Transition and Landing on the NASA V/STOL Systems Research Aircraft April 1996

NASA Technical Paper 3607

James A. Franklin, Michael W. Stortz, Paul F. Botchers, and Ernesto Moralez III

National Aeronautics and Space Administration

NASA Technical Paper 3607

Flight Evaluation of Advanced Controls and Displays for Transition and Landing on the NASA V/STOL Systems Research Aircraft 1996

James A. Franklin, Michael W. Stortz, Paul F. Borchers, and Ernesto Moralez III, Ames Research Center, Moffett Field, CaliJornia

National Aeronautics and Space Administration Ames Research Center Moffett Field, California 94035-1000

Contents

Page

Nomenclature ...... V

Summary ...... 1 Introduction ...... 1

Description of the V/STOL Systems Research Aircraft ...... 2

Flight Experiment ...... 9

Results ...... 13

Flying Qualities Assessment ...... 13

Control System Performance ...... 66

Design Recommendations ...... 74 Conclusions ...... 82

References ...... 83

Appendix ...... 84

iii

Nomenclature _yrcs yaw reaction control deflection, percent pitch attitude, deg ay lateral acceleration, ft/sec 2 0 commanded pitch attitude, deg D x, Dy stick complementary filter inverse time 0c constant, sec -1 0j thrust vector angle, deg acceleration due to gravity, ft/sec 2 g (YU, (Yv, _w longitudinal, lateral, and vertical quickening h altitude, ft inverse time constants, sec -I

fi, Vz inertial vertical velocity, ft/sec bank angle, deg

vertical velocity command, ft/sec heading, deg

NF fan revolutions per minute (rpm), percent f2o control input quickening inverse time constant, sec -1 P roll rate, deg/sec flightpath inverse time constant, sec -1 q pitch rate, deg/sec Acronyms qbar dynamic pressure, lb/ft 2 BW bandwidth r yaw rate, deg/sec FCC flight control computer s Laplace operator GPS Global Positioning System Vaf filtered airspeed, ft/sec HQR handling-qualities rating Vcas calibrated airspeed, knots HUD head-up display gtl ground speed with lower limit of 100 ft/sec IGE in ground effect Vx heading reference inertial longitudinal velocity, ft/sec IMC instrument meteorological conditions inertial navigation unit Vy heading reference inertial lateral velocity, INU ft/sec I/O input/output

sideslip angle, deg JPT jet pipe temperature

T flightpath angle, deg POT potentiometer

quickened flightpath angle, deg RCS reaction control system

8A aileron deflection, deg RLG ring laser gyro

61at, 8¢ lateral stick deflection, in. RMDU remote multiplexer/demultiplexer unit

80T lateral stick trim servo, in. rms root mean square

_long, _0 longitudinal stick deflection, in. SAS stability augmentation system

_0 T longitudinal stick trim servo, in. SKP station-keeping point

_p, 8_g pedal deflection, deg STOL short takeoff and landing

8s stabilator deflection, deg STOVL short takeoff/vertical landing

_Stw longitudinal stick thumbwheel, percent TRC translational-rate command

8T throttle lever or nozzle angle, deg VMC visual meteorological conditions

5hw throttle thumbwheel, percent VMS Vertical Motion Simulator

8x longitudinal proportional thumb controller, VSRA V/STOL Systems Research Aircraft

percent V/STOL vertical/short takeoff and landing 8y lateral proportional thumb controller, percent XMTR transmitter

Flight Evaluation of Advanced Controls and Displays for Transition and Landing on the NASA V/STOL Systems Research Aircraft

JAMES A. FRANKLIN, MICHAEL W. STORTZ, PAUL F. BORCHERS, AND ERNESTO MORALEZ III

Ames Research Center

Summary Introduction

Flight experiments were conducted on Ames Research For many years Ames Research Center has conducted a Center's V/STOL Systems Research Aircraft (VSRA) to program on advanced control and display technology assess the influence of advanced control modes and applied m the low-speed, precision flight operations of head-up displays (HUDs) on flying qualities for precision short takeoftTvertical landing (STOVL) aircraft in adverse approach and landing operations. Evaluations were made weather. This work is m_ativated by the control require- for decelerating approaches to hover followed by a merits for these aircraft that are predicated on the opera- vertical landing and for slow landings for four control/ tional environment to which they are exposed. For display mode combinations: the basic YAV-8B stability military use, these aircraft are required to operate from augmentation system (SAS); attitude command for pitch, conventional airfields, austere sites, aircraft carriers, or roll, and yaw; flightpath/acceleration command with small aviation-capable vessels. The capability for hover translational rate covnmand in the hover; and height-rate and low-speed flight and l`or rapidly transitioning between damping with translational-rate command. Head-up wing- and propulsion-borne flight permits STOVL aircraft displays used in conjunction with these control modes to operate into confined spaces associated with austere provided flightpalh tracking/pursuit guidance and decel- sites and decks of small ships. In principle, STOVL eration commands for the decelerating approach and a aircraft should be able to accomplish these operations mixed horizontal and vertical presentation for precision under weather conditions that would be prohibitive l'or hover and landing. Flying qualities were established and conventional aircraft. However, these operations demand control usage and bandwidth were documented t`or precision of control of position, velocity, and attitude, the candidate control modes and displays for the approach ability to quickly arrest closure rates in limited confines, and vertical landing. Minimally satislactory bandwidlhs and the capability to do so under challenging conditions were determined lot the translational-rate command of winds, turbulence, and low visibility. Such require- system. Test pilo| and engineer teams from the Naval Air ments exceed those imposed on conventional fixed-wing Warfare Center, the Boeing Military Airplane Group, counterparts to a considerable degree. Currently, the I,ockheed Martin, McDonnell Douglas Aerospace, shipboard capability of STOVL aircraft involves a Northrop Grumman, Rolls-Royce, and the British Defence constant-speed stabilized descent in instrument meteoro- Research Agency participated in the program along with logical conditions (IMC) to a minimum altitude of 300 ft NASA research pilots from the Ames and Lewis Research with a visual range of I mi, lbllowed by deceleration to Centers. The results, in conjunction with related ground- hover in visual meteorological conditions (VMC). based simulation data, indicate that the flightpath/ Recovery to the ship is restricted to landing areas at least longitudinal-acceleration command response type in the size provided by amphibious assault ships (LPH or conjunction with pursuil tracking and deceleration LHA) on the order of 50 x 50 ft and in sea state 3 or less. guidance on the HUD would be essential ['or operation to The impediment to routine vertical flight operations of instrumcn! mininmms significantly lower than the mini- this class of aircraft in adverse weather and low-visibility mums for the AV-SB. It would also be a superior mode conditions stems from poor flying qualities that are a for performing slow landings where prccise control to an consequence of the complex interaction of kinematics, austere landing area such as a narrow road is demanded. aerodynamics, and propulsive forces and moments during The translational-rate command system would reduce the transition from wing- to propulsion-borne flight and pilot workload for demanding vertical landing tasks during propulsion-borne operations. The pilot's control aboard ship and in confined land-based sites. problem is aggravated by an additional control requirement related to the transition (e.g., thrust vectoring and startup and control of lift-augmenting devices). The challenge to the designer is to determine the appropriate control response types and the associated cockpit displays experiment to evaluate control and display modes, the and inceptors that will provide the desired operational results of the pilots' evaluations, and modifications capability with the associated precision and minimum recommended for application to new STOVL aircraft. pilot effort required to perform the requisite tasks. Of equal importance is the requirement for and ability to integrate the STOVL aircraft's flight and propulsion Description of the V/STOL Systems controls that will provide the desired level of controlla- Research Aircraft bility over the full range of STOVL operations. The VSRA is the sole remaining aircraft from the This research program has involved analytical studies and YAV-8B Prototype Demonstration Program of the late ground-based simulation experiments to develop and 1970s. It has been highly modified tot its role as a evaluate control response types and associated displays research aircraft. The basic aircraft, shown in hover in with general applicability to STOVL operations. It has figure 1, is a single-seat, high-pertormance, transonic, yielded numerous promising concepts lor control aug- light attack vertical/short takeoff and landing (V/STOL) mentation systems and cockpit displays for decelerating aircraft. It is characterized by a shoulder-mounted, transition to hover under IMC and landing in confined supercritical, swept wing and swept stabilator, both with and austere sites and aboard small aviation-capable ships marked anhedral. It has a single vertical fin and rudder, (refs. 1-5). During the past several years, selected con- under-fuselage lift-improvement devices, and a large cepts have been developed further, applied to STOVL engine inlet with a double row of inlet doors. The aircraft fighter aircraft designs, and evaluated in moving-base is powered by a single Rolls-Royce Pegasus turbofan simulations on the Ames Vertical Motion Simulator engine that provides lift thrust for takeoff and landing, (refs. 6-8). Results of this body of ground-based simula- cruise thrust lor conventional wing-borne flight, deflected tion experiments indicate that a high degree of precision thrust lor V/STOL and in-flight maneuvering, and com- of operation for recovery aboard small ships in heavy seas pressor bleed air tbr the reaction control system (RCS). and low visibility with acceptable levels of pilot effort can Four exhaust nozzles, two on each side of the fuselage, be achieved by integrating the aircraft flight and propul- direct the engine thrust [Yom fully aft to 98.5 deg below sion controls to significantly improve the basic aircraft the thrust line that is inclined 1.5 deg above the fuselage response to pilot commands for attitude, height, and reference line. position control. The response types that elicited the most The flight control system consists of conventional favorable ratings and comments were those that provided aerodynamic surfaces that are hydraulically powered, dircct command of the aircraft responses associated with except for the rudder, which is completely mechanical, the task being performed. Thus tbr the decelerating and reaction control jets at the extremities, which are approach to hover, the favored responsc type was pressurized by compressor bleed air when the exhaust decoupled flightpath and longitudinal-acceleration nozzles are lowered. The reaction controls are mechani- command with the ability to independently control pitch cally linked to the respective aerodynamic control attitude without perturbing the longitudinal or vertical surfaces. Aircraft attitude is controlled by the reaction response. The preferred lateral-directional controls were control jets in hovering flight and by conventional the roll-rate command with bank-angle hold and yaw aerodynamic surfaces in wing-borne flight. Both systems damping with turn coordination. In hover, decoupled contribute to control during transition between wing- and control of the orthogonal translational velocities was most propulsion-borne flight. Longitudinal control is through sought. The availability of digital fly-by-wire control, downward-blowing front and rear fuselage reaction precision inertial sensors for attitudes, rates, and position, control jets and an all-moving stabilator; lateral control is and electronic displays makes it feasible to implement an through wing-tip-mounted reaction jets that thrust up and integrated control and display design of this sophistication down and outboard ailerons; and directional control is to achieve and demonstrate in flight the operational through a sideways-blowing reaction jet located in thc aft bcncfits promiscd by the simulation experiencc and to fuselage extension and through the rudder. Hydraulically cstablish their value for advanced STOVL aircraft powered control surface actuators are integrated with an dcsigns. electronically controlled, limited-authority stability Flight cxpcriments wcrc conducted on Ames Rcscarch augmentation system that provides pitch- and roll-rate Center's V/STOL Systems Research Aircraft (VSRA) to damping bclow 250 knots and yaw-rate damping only assess the influence of these advanced control modes and through the yaw RCS. head-up displays (HUDs) on flying qualitics for precision approach and landing. This rcport describcs thc VSRA and its research systems, the elements of the flight i

33.33 ft The major components of the research system are indi- translational-rate command provides for control of the cated in the layout drawing and system architecture of longitudinal, latcral, and vertical axes. The fourth figure 2. They consist of dual flight computers that configuration is a variant of Configuration 3, in which the contain sensor conditioning and state estimation, control, vertical axis is simply direct thrust control during guidance, navigation, and display laws and response transition and incorporates a limited-authority series monitors; inertial navigation units (INUs) that are used height-rate command in hover. to provide attitudes, body angular rates, linear velocities, The cockpit layout of the aircraft is shown in figure 3. and accelerations; radio altimeters; a differential Global The cockpit interface was dictated by the VSRA's single- Positioning System (GPS); a programmable symbol cockpit configuration. For safe recovery from any generator used to drive the HUD; a multipurpose display research control system anomaly, the default configura- that provides for system command inputs as well as a tion is the basic YAV-8B hydromechanical system. moving map display; a servo control unit that provides Therefore, it is necessary to retain the normal functioning monitoring and servo drive signals; production pitch, roll, of the stick, throttle, and nozzle lever, even when the and yaw series stability augmentation servos, pitch and research system is engaged. For this reason, in the case of roll trim servos, and limited-authority, high-rate series and Configuration 3, two thumbwheels were chosen as control full-authority, low-rate parallel servos to drive the throttle inceptors for the longitudinal-acceleration and flightpath and nozzles. The HUD is a modified AV-SA production unit. command response types and a proportional thumb controller was chosen tor the translational-rate command Control modes thai were implemented in the flight response type. The hmgitudinal-acceleration command computers lor this experimental program are listed in thumbwheel is mounted on the stick and has a zero detent table 1. The control laws are described in the appendix. but no centering; it is the inceptor of choice for this The four configurations listed span control technologies response type except that the preferred location would bc that range from that of current generation operational on the throttle. The flightpath command thumbwheel with V/STOL aircraft to the most advanced applications similar mechanical characteristics is mounted on the envisaged, based on the extensive simulation experience throttle and, when it is in use, the pilot must allow the noted previously. As listed in table I, their features are: throttle to be back driven as necessary by the flight Configuration l-basic YAV-8B angular-rate damping; control computers (FCCs). The use of a thumbwheel for Configuration 2-pitch- and roll-attitude stabilization; flightpath command is a major compromise to accom- Configuration 3-flightpath and longitudinal-acceleration modate the default constraints noted previously. Given command during transition combined with three-axis design freedom, the inceptor of choice for flightpath translational-rate command in hover; and Configuration command would be the throttle, since it best integrates 4-longitudinal-acceleration command during transition the control of engine thrust in conventional flight with with translational-rate command in the horizontal plane flightpath and vertical-velocity control in powered-lift and height-rate damping in hover. More specifically, in operations. The proportional thumb controller functions the first configuration, angular-rate damping is provided like a joy stick in that it provides proportional control in in pitch, roll, and yaw, with simple turn coordination and two axes; it is mounted on the stick next to the trim Dutch roll damping also available during transition. button, has spring centering, and produces a velocity Thrust and thrust deflection are controlled manually proportional to displacement in the direction of actuation. through the aircraft's throttle and nozzle levers. For the The use of this inceptor is also a compromise, as the second configuration, pitch-attitude command/attitude preferred inceptor (indicated by considerable cxpcricncc hold is available for transition and hover control modes. in simulation) would be the control stick itself. Configu- Roll-rate command/attitude hold is employed during rations I and 2 were able to use the basic aircraft's stick, transition, switching to attitude command/attitude hold in pedal, throttle, and nozzle inceptors for the attitude, thrust, hover. The yaw axis provides turn coordination during and thrust-deflection control functions. Configuration 4 transition and yaw-rate command in hover. Again, thrust allowed tbr use of the throttle as the flightpath and and thrust deflection are controlled manually. For the vertical-velocity inceptor; the acceleration control third configuration, the pitch, roll, and yaw axes controls thumbwheel was then relocated to the throttle handle. remain the same as for the second configuration during Thus these two inceptors were representative of an transition with the addition of flightpath and longitudinal- eventual operational configuration. A complete listing acceleration command. In hover, pitch attitude can be of the cockpit inceptor and responsc type pairings is adjustcd through the pitch trim control. Otherwise, the prescnted in table 1. Angular accelerometer analog notch filters GPS receiver Engine life recorder and JPT limiter

Tacan and conve_er Transformer, deutch strip and relay installation EC amplifier RMDU Pressure transducers

Programmable VHF tranceiver symbol generator 4096 transponder Servo control unit Air data computer Flight control computer - A Flight control computer - B Dual angular and linear accelerometers

Roll reaction control pressure tap

Throttle series servo

Throttle parallel servo No. 1 radio altimeter

Hybrid sliding/ Instrumentation ball-bearing cable signal conditioners Stick top Roll reaction control Hud camera and \ pressure tap downlink XMTR

Mode-menu panel -._ Cold nozzle position pot Forward reaction control eervo Nozzle series servo and coupling pin Nozzle parallel servo Throttle top

No. 2 .radi° altimeter ",_._1_ INU battery No. 2 ring laser gyro _ .,,,,.,,_I_ / inertial navigation unit

No. 1 ring laser gyro INU cooling blowers inertial navigation unit

(a) System layout.

Figure 2. VSRA research system. YAV-8B © SAS computer

Programmable Deflection _. Head-updisplay symbol generator mplifier

=' 1Color unitdisplay ]

IBM-AT I Telemetry microcomputer

Flight computer A Mode/menu IJ - Data I/O m switches - Self test

- Sensor scaling GPS _--- - Sensor compares Servo control unit - Navigation - Guidance - Clock Laser track __ uplink - Display laws - Telemetry synchronizer - Control laws - FCC cmd compares - Response monitors - Servo drivers Dual RLG INUs _- - Servo loop monitors Flight computer B - Failure annunciation Air data _- I Throttle - Data I/O - Engage logic j parallel - Self test _--___...._ Th rottle ] - Sensor scaling - Sensor compares Dual radio II i se.esI - Navigation altimeters - Guidance I I _] Nozz,eI - Display laws Pilot cmds -I parallel I Dual angular - Control laws / . I Nozzle accel. - Response monitors v series

(b) System architecture.

Figure 2. Concluded. Table I. Flight control modes

Inceptor Transition Configuration 1 Configuration 2 Configuration 3 Configuration 4

Longitudinal stick Pitch-rate damping Pitch-attitude N/A Pitch-attitude command/attitude command/attitude hold hold

Longitudinal trim Trim rate Pitch attitude Pitch attitude Pitch attitude Lateral stick Roll-rate damping Roll-rate command/ Roll-rate command/ Roll-rate command/ attitude hold attitude hold attitude hold Lateral trim Trim rate Roll attitude Roll attitude Roll attitude Pedals Yaw damper Yaw damper Yaw damper Yaw damper Throttle lever Thrust magnitude Thrust magnitude NIA Thrust magnitude Nozzle lever Thrust deflection Thrust deflection N/A N/A Throttle thumbwheel N/A N/A Flightpath command Longitudinal- (vertical velocity acceleration for V < 60 knots) command/ velocity hold Stick thumbwheel N/A N/A Longitudinal N/A acceleration command/ velocity hold Proportional thumb N/A N/A N/A N/A controller

lnceptor Hover Configuration 1 Configuration 2 Configuration 3 Configuration 4

Longitudinal stick Pitch-rate damping Pitch-attitude N/A N/A command/attitude hold

Longitudinal trim Trim rate Pitch attitude Pitch attitude Pitch attitude Lateral stick Roll-rate damping Roll-attitude Roll-attitude Roll-attitude command/attitude command/attitude command/attitude hold hold hold Lateral trim Trim rate Roll attitude Roll attitude Roll attitude Pedals Yaw damper Yaw-rate command Yaw-rate command Yaw-rate command Throttle lever Thrust magnitude Thrust magnitude N/A Thrust with height- rate damper Nozzle lever Thrust deflection Thrust deflection N/A N/A Throttle thumbwheel N/A N/A Vertical velocity N/A command/altitude hold Stick thumbwheel N/A N/A N/A N/A Proportional thumb N/A N/A Longitudinal- and Longitudinal- and controller lateral-velocity lateral-velocity command command 1. Nozzle handle 2. Throttle handle 3. Throttle thumbwheel 4. Stick thumbwheel 5. Proportional thumb controller 6. Control display unit 7, Head-up display Figure 3. Cockp# layout HUD modes are associated with the transition from predicted velocity symbol over the intended hover posi- conventional flight to hover and with the precision hover tion, typically the landing pad, and keep it there as the and vertical landing. They are tailored to the charac- aircraft and pad symbols converge. The height of the teristics of the control mode selected by the pilot. aircraft above the landing pad is represented by the References 9-12 present details of the design of the landing surface bar, which is displaced at a scaled vertical display formats and content. The two HUD modes are distance below the aircraft symbol. Predicted vertical depicted in figure 4. For the transition phase (fig. 4(a)), velocity is displayed by a diamond, which is referenced to the display is flightpath centered and presents the pilot the right leg of the aircraft symbol and to a ribbon that with a pursuit tracking task for following the intended represents the allowable range of sink rate. To maintain transition and approach guidance to a final hover point. altitude, the pilot keeps the vertical-velocity diamond Course and glideslope guidance are provided in the form adjacent to the right leg of the aircraft symbol, indicating of a leader (ghost) aircraft that follows the desired flight zero sink. To initiate the vertical landing and to maintain profile at a specified distance ahead of the VSRA. The the desired closure rate to the pad, the pilot commands the pilot's task is to maneuver the VSRA's flightpath diamond to the desired sink rate within the allowable vertically and laterally to track the ghost aircraft, a task limits. Attitude, radar altitude, airspeed, ground speed, similar to a gunsight tracking task. Deceleration guidance distance to the hover point, engine rpm and JPT, thrust is presented by an acceleration error ribbon on the left vector angle and flap deflection, heading, and vertical- side of the flightpath symbol, which the pilot nulls to velocity limits are provided as situation information. achieve the deceleration required to bring the aircraft to a hover at the initial hover station-keeping point. Situation Flight Experiment information that accompanies the flightpath and ghost aircraft symbology includes aircraft attitude, barometric The operational task for evaluation was a curved altitude (radar altitude below 400 ft), airspeed, reference decelerating approach to hover, followed by a vertical angle of attack and angle-of-attack warning, engine rpm, landing on the landing pad (fig. 5) or by a slow landing jet pipe temperature (JPT), thrust vector angle, flap on the runway. For evaluation purposes, the decelerating deflection, longitudinal acceleration, heading, distance to approaches were divided into two phases that reflect the the hover point, and flight control mode annunciation. principal aspects of the decelerating transition to hover as well as the precision instrument approach to decision During the latter stages of the deceleration, as the aircraft height. The first phase was initiated on the downwind leg approaches the intended point of hover, selective changes in level flight at pattern altitudes from 1000 to 1500 ft at are made to the approach display to provide guidance for approximately 120 knots in the powered approach config- the hover-point capture. Specifically, the longitudinal- velocity vector, predicted longitudinal velocity, and uration. This phase entailed capture of a 3-deg glideslope, initiation of a 0.1 g nominal deceleration, a left turn to station-keeping cross appear referenced to the flightpath base leg and then to align with the final approach course, symbol (fig. 4(a)). The pilot controls the predicted and, on short final at a range of 1000 ft, a change in the velocity toward the position of the station-keeping cross nominal deceleration rate to 0.05g. Desired perlbrmance and adjusts velocity to bring the cross to rest at the refer- was defined as keeping the center of the ghost aircraft ence hover point (the point at which the cross is adjacent within the circular element of the flightpath symbol, with to the flightpath symbol). Once the aircraft is stabilized in only momentary excursions permitted. Adequate perfor- this condition, the pilot is ready to perform the vertical mance was achieved when tracking excursions were landing. significant, but not divergent. The initial phase of the For the vertical landing, the HUD format superimposes approach was considered complete at the change in horizontal (plan) and vertical views and provides com- deceleration rate corresponding to the final closure to the mand and situation information in a pursuit tracking hover point. presentation (fig. 4(b)). The aircraft symbol, centrally The second and final phase of the approach involved located and fixed in the display, presents the relative completion of the deceleration and acquisition of the locations of the landing gear and nose boom in plan view. hover point 50 ft above the landing surface. This phase Also in the plan view is the landing-pad symbol, repre- included an initial station-keeping hover 100 ft to the right senting a 40- × 64-ft landing area scaled in proportion to and 100 ft aft of the landing spot. Desired performance the landing gear of the aircraft symbol. The aircraft's was defined as acquisition of the hover with minimal horizontal-velocity vector is represented by a line emanat- overshoot and altitude control within +5 ft. Adequate ing from the aircraft symbol. A horizontal-velocity predic- performance was achieved when overshoot did not result tor symbol indicates the magnitude and direction of the in loss of the landing-pad symbol from the display field of pilot's velocity commands. The pilot's task is to place the Magnetic heading (deg) -

Heading scale----

Control system engaged -- ' 13S21 ' Radar altitude indicator Waterline symbol-- '"A 8/ ---- Airspeed (kt) Altitude (ft) Groundspeed (kt)--_ 1ii9] i 140]----_-- I Rate of climb (ft/min) STOL runway ---- __G 118 Hover position_ Ghost aircraft Predictor ball_ 4 Longitudinal velocityt_ Range to hover t(below 25 kt) position (n. mi.)

Horizon line ---- - Alpha reference bracket I >_L2-___----i Longitudinal acceleration 45N _----__ Fan rpm (%) Engine nozzle angle (deg) Jet pipe temp (deg C)-- 5Sb - Flap angle (deg)

-- Sideslip indicator Decel guidance ribbon i -- Flightpath ---8 Pitch ladder Glideslope reference / -- Alpha warning bar

(a) Transition.

Figure 4. Head-up display formats. Magnetic heading (deg)-- \ 88 Heading scale 35 \ I I Control system engaged - ' Iss8' Radar altitude indicator Waterline symbol------H-- 8/ Airspeed (kt) Altitude (ft) Groundspeed (kt) 58j_J--J-- J Rate of climb (ft/sec) J --_G 8 -3 j Hover position -- J Landing pad Predictor ball -- --- Distance to hover position (ft) Velocity vector "0 -- Aircraft trident symbol Horizon line --_ I I -- Predicted vertical velocity 8ZN__ _R 8Z Engine nozzle angle (deg) Fan rpm (%) \ 62F -- Flap angle (deg) Jet pipe temp (deg C) -- ...... d673 #

-- Allowable vertical velocity Landing surface bar -- -- Pitch ladder

(b) Hover.

Figure 4. Concluded. System engaged 120 knots Final hover Initial 45 ° nozzles and landing hover \ Level flight Initiate segment deceleration

100 1500 ft 3° Glideslope Hover/vertical intercept landing _:_'%_

Approach

Figure 5. Approach profile.

view and the altitude control was safe. This segment was defined as landing within 500 ft at a sink rate no greater complete when a stable hover was established at the initial than 8 ft/sec. station-keeping point. Five pilots with V/STOL and powered-lift aircraft The vertical landing was initiated at the initial station- experience performed as evaluation pilots in this experi- keeping point with a constant altitude translation to a ment. Pilot ratings and comments were obtained, based on hover over a 40- × 64-ft landing pad marked on the the Cooper-Harper scale (ref. 13). Detailed commentaries taxiway, followed by a descent to touchdown on the pad. are provided in table 2 (p. 104). Time histories of data Desired landing performance was defined as touchdown were processed in real time or post run to document the within a 5-ft radius of the center of the pad with a sink behavior of the aircraft and pilot performance. rate of 3-5 ft/sec. Adequate perlbrmance was a touch- The tbur configurations described in table I were used down within the confines of the pad at a sink rate less than 12 ft/sec and with minimal lateral drift. in the evaluations. These configurations were chosen to represent control and display technologies ranging from Slow landings were performed under VMC to the main those of the AV-8B Harriers to response types providing runway. Runs were initiated downwind in level flight in direct command of aircraft response most directly asso- the landing pattern, as for the decelerating approach, and ciated with the task at hand. They can be generally were flown to a visual aim point displaced approximately defined as the basic YAV-8B SAS, the attitude command, 1000 ft from the runway threshold. Deceleration to the the flightpath/acceleration and translational-rate com- pilot's selected approach speed was performed in suffi- mand, and the acceleration command with height-rate cient time to be stabilized on speed during the final damper and translational-rate command. Each configura- straight-in segment of the approach. No guidance was tion had a specific combination of transition and hover provided by the ghost airplane on the HUD during the control modes. All operations were conducted under final segment; instead, the pilot aimed the flightpath VMC in the winds and turbulence of the day. For the symbol at the desired touchdown spot. This procedure translational-rate command system, variations were made presented a repeatable task from which touchdown in the bandwidth of the longitudinal-, lateral-, and precision could be determined. Desired performance was vertical-velocity controls by changing their individual considered to be landing within 100 ft of the aim point lbrward-loop gains. Each of these system variants was with a sink rate of 3-5 ft/sec. Adequate performance was evaluated for the hover positioning and vertical landing

12 tasktodeterminetheboundarybetweensatisfactoryand qualities for the basic YAV-8B with stability augmenta- adequateflyingqualitiesforthistask. tion (Configuration 1) are only adequate, principally because of the workload associated with control of pitch attitude in the presence of trim changes with thrust and Results thrust deflection and with poor directional control. Sixty-five flights were flown during the evaluation Workload during the initial stages of the approach was for the four configurations, including 120 decelerating low, but it increased steadily as the aircraft decelerated approaches and 158 vertical landings. Operations gener- and approached the initial hover point. With three control ally occurred in light and variable winds with no signifi- inceptors in the longitudinal axis (stick, throttle, and cant turbulence component. On one occasion, noted in the nozzle lever) and two hands available to operate them, the following discussion, moderate winds and turbulence general strategy was to set the nozzle position open loop prevailed, providing an opportunity to assess the effects of and then regulate pitch and throttle. This technique helped significant disturbances on performance of the flightpath reduce the workload that would otherwise have been and acceleration command control mode. associated with continuous manipulation of thrust vector angle during the deceleration. Flightpath control was Results of the flight experiments are presented first as accomplished during the initial stages of the approach by pilot assessments of ['lying qualities in the form of changes in pitch attitude. When the aircraft is configured Cooper-Harper pilot ratings and qualitative commentary with the thrust deflected to the hover setting and the supporting these ratings. Time histories of selected phases aircraft decelerates to speeds at which flightpath is not of the operation are used to illustrate task performance responsive to changes in pitch attitude, the throttle (thrust and activity of the individual controls. Implications of magnitude) becomes the primary flightpath or vertical- these results for control system and display design are velocity controller. Pitch attitude was adjusted to follow covered in following subsections. the deceleration profile as presented to the pilot by the deceleration guidance ribbon on the HUD. Results of Flying Qualities Assessment earlier simulation evaluations on the Ames Research Center's Vertical Motion Simulator (VMS; see refs. 2 A discussion of results is presented lor the individual and 11) of the basic YAV-8B for the transition task, segments of the approach and landing that were explained shown by the vertical brackets on the figure, indicate an previously in the evaluation criteria, that is, the transition, assessment of adequate flying qualities for the task similar hover-point acquisition, and vertical landing. to that obtained in the flight program. Transition- Results of the pilots' evaluations tbr the decelerating approach are presented in figure 6. Flying

Pilot Cooper-Harper Rating • A 10 • B Inadequate 9 C improvement • D 8 Simulation results required • E 7

Adequate 6 improvement 5 warranted 4 I Bo& Ko& 3 Satisfactory 2

1 I I I YAV-8B Attitude Flightpath Thrust control SAS command acceleration acceleration command command

Figure 6. Pilot evaluations of the decelerating transition.

13 Example time histories in figure 7 show the aircraft nozzle-flap interconnect, were sufficient to induce response and control effector behavior during the transi- coupling with the thrust control. This coupling introduced tion. The basic YAV-8B is typified by continuous throttle perturbations in flightpath that prevented achievement of and stick inputs, oscillatory flightpath response, and the desired tracking performance. Pitch trim was also frequent pitch-attitude perturbations. At the point the continuously active to counter the trim changes due to nozzle lever is moved to the hover stop, a large and variations in thrust and thrust deflection. Ratings for continuous throttle advance to the hover setting is approach-path tracking at constant speed prior to the required as the aircraft decelerates. A large trim change deceleration were only adequate. Some pilots chose to accompanying the nozzle deflection and thrust increase is ignore this behavior, once its cause was understood, and evident in the stick trace. Bank-angle control during the instead concentrated on achieving the most precise turn to final approach required continuous stick inputs tracking during the latter stage of the approach. This stage with few rudder inputs until the latter stage of the consisted of the deceleration and descent to the nominal approach, when the rudder was required for heading decision height of 100 ft, followed by capture of the hover control at low speed. altitude and the final deceleration to the hover. By this point, nozzle deflection had increased such that the When pitch and roll attitudes are stabilized (Configura- hysteresis diminished significantly and the flaps reached tion 2) by the attitude command system, flying qualities show some improvement. Favorable pilot comments their final setting of 62 deg. It was possible to achieve the desired tracking performance with minimal workload. reflected the improved stability of pitch attitude as a consequence of decoupling the pitch axis from the Flightpath control was considered satisfactory for this final stage. Flightpath control was considered satisfactory controls used for flightpath and deceleration. Other also for the case of moderate wind and turbulence comments indicated an improved ability to follow the (15-knot winds with 3-ft/sec root mean square (rms) deceleration profile. Otherwise, control of flightpath with pitch or throttle and deceleration with thrust deflection gusts). Decoupling of flightpath control from control of the deceleration was a major factor in workload reduction. and pitch attitude were similar to Configuration I. For both the YAV-8B SAS and the attitude command system, Further, the HUD offered excellent path guidance for the significant attention to flightpath control and compensa- curved approach through the ghost aircraft and also provided effective commands for the deceleration to tory throttle inputs was required to compensate for heave disturbances when the thrust vector was deflected hover. Pilots consistently noted the ease of tracking the initially, and for the lift loss that occurs during the final ghost aircraft throughout the approach and the essentially open-loop nature of the deceleration. phase of deceleration. Consistent with current AV-8 operational limitations, these characteristics would not The mechanical characteristics and the sensitivities of permit decelerating approaches to be made in IMC. both of the thumbwheels were issues for most of the pilots. The stick thumbwheel appeared to be too sensitive As can be seen in figure 8, Configuration 2 required less in the airspeed range of 110-120 knots and then very continuous stick activity other than occasional trimming when the nozzle was deflected or thrust was increased. noticeably undersensitive as the aircraft decelerated below 110 knots. The throttle thumbwheel was flush in its Commanded changes in pitch attitude are evident toward mounting, providing poor feel, which made small, precise the end of the approach to control the deceleration to inputs difficult. The throttle thumbwheel was also too hover. Throttle activity is similar to that for the YAV-8B SAS, including large continuous thrust changes through- sensitive in the 110-120-knots range, adequate below 110 knots, and far too low at hover. Were it not ['or these out the deceleration. Pitch attitude and flightpath are mechanical deficiencies and the opinion that the throttle noticeably more steady than for the YAV-SB SAS shown thumbwheel was not the desired choice lbr flightpath in figure 7. Control of the lateral-directional axes was control, the decelerating transition would have been rated comparable to that for the YAV-SB SAS. satisfactory by the pilots. Results from the earlier When flightpath and longitudinal-acceleration command simulations also reflect the borderline satisfactory/ were employed (Configuration 3), the pilots' ratings were adequate ratings observed in these flight tests. still borderline satisfactory/adequate as a consequence of Representative time histories for Configuration 3 are objectionable wandering in the flightpath response early presented in figure 9. They are characterized by an initial in the approach (100-120 knots) and deficiencies in the oscillatory flightpath response, then by precise tracking of thumbwheel inceptors. This flightpath wandering is the ghost aircraft and a smooth and continuous decelera- attributed to hysteresis in the nozzle control system tion. Corrections with the throttle and stick thumbwheels (+4.5 deg). Nozzle variations within the hysteresis band, for control of flightpath and deceleration were small and accompanied by variations in flap position through the infrequent. The low workload is evident in the infrequent

14 pitch attitude, deg _

F|ightpath angle, deg i o

¢Q

<3 F_ C> _Q

5 7- @

_0 ,< Co

C_ _3

o 100 100

8O u 5 -- 8O

"0 0 L.- O_ c 60 -- _ 0-- 0 .12 C o z I,L

4O -- --5 -- 4O

20 -- -10 -- 20 I /

80 -- 5

l _ J ill I 1) ! o ...... -i "a .i ... . 4O

20 -- -5 t t 0 50 1O0 151 Time, sec (b) Longitudinal inceptors and control effectors.

Figure 7. Continued.

16 1,5 -- 150

100 ,v o I r- ¢: J¢ d "o "o =3 0. ,< < 50

, L I O-- 0

200 15 _ 50

100 _

It,,.

0 -5 -50 0 50 1O0 150 Time, sec

Figure 7. Continued.

17 100-- 5

5O -- 0 -- _A

O'} .o E} "D Q.

o rr" 8yrcs

-5O -- -10

-100 -- -15 I I

1 -- I

.5 --

ra 0 -- ID 0 ,, , ¢D a.

_p w.5 --

-I -- -1 I I 0 50 I00 150 Time, sec

(d) Lateral-directional inceptors and control effectors.

Figure 7. Concluded.

18 1.5-- 150

Vcas

1 -- £ 100 0 I C

"0 "O

Q. ,¢ .5 -- <[ 50

I r ..... 0 -- 0

15 --

10 -- 0 -- st

"0 k _ _

"O e- / 5 -- ¢u --2 =. m t- o r. a. ,'7 0 -- -4

-5-- --6 I 0 50 100 150 Time, sec

(a) Longitudinal response.

Figure 8. Decelerating transition time history for attitude command (Configuration 2).

19 100 -- 10 -- 100

80 -- 5 m 8O

"0 @ d P & c 60-- o 0 -- 0= e= E-e_ _= ._ r- o or) I1= z I 40 -- 4O I 20 - -10 -- 2O I I I

80 --

I p / a el .,

01 U 4) "0 p o" _o o "0 r- ,-! I-- D1 f- 0 J

8long

20 -- -s I I 0 50 100 150 Time, sec

(b) Longitudinal inceptors and control effectors.

Figure 8. Continued.

2O 1.5 -- 150

100

O ¢- 0; _5 "O

D. == °-- .5 50 I

I """"i ..... 0

200 15 -- 5O :\ 150 10-- 25

¢D "O "0 10 i \ o .t 100 r- 1D ca e" "T- 00 nn

50 0-- -25 J -5 -- -50 0 50 100 150 Time, sec

Figure 8. Continued.

21 Yaw RCS, percent Pedal,in. i I 0 ol o o o 0 o I I I I I I

Lateral stick, in. Aileron, deg i o o 01 I

°<:

o 1.5 -- 150

100 0 C

Q. <.w

< 50

I I 0 --

15-- 2

10-- 0 -- O_ 01 10 "0

01 "0 t'- 5-- J_

¢- .,C

13. ._m

0 -- -4--

-5 -- 0 50 100 150 Time, sec

(a) Longitudinal response.

Figure 9. Decelerating transition time history for flightpath/acceleration command (Configuration 3).

23 0 .5 - _'v-- _Stw

/u 0_-- 0 - ....•...... :i_j!...... "" "- it I pl t .... ! t tI i

-1.0 _ -.5 - _ttw -1.5 -5 -1.0 0 5O 4 100 Time, se¢ 151

(b) Longitudinal inceptors and control effectom.

Figure 9. Continued.

24 1.5 -- 150

100

O f-

"O --t Q. ¢¢ < 50

I I 0 --

200 -- 15 -- 5O \ 150 -- 10-- 25

O_ 03 "O "0 "0 \ o 100 -- d. 5-- == 0 U) "10 o0 ¢0 "O =.. ¢o -f- m

50 -- 0 I -25

0 -- --5 -- -50 0 5O 100 150 Time, sec

Figure 9. Continued.

25 100 -- 5

5O -- 0

o O3 ¢D "0 Q. o_ -- _ -5 o cE V 5yrc s 3: ¢Q >- -5O -- -10

-100 -- -15 I I

1.0 -- 1.0

.5 .5

e- ._u

'lO _D a.

-1.0 -1.0 I I 0 50 1O0 150 Time, sec

(d) Lateral-directional inceptors and control effectors.

Figure 9. Continued.

25 2O

.= 0 r-

"_10 "=_ "10 (u

"I"

0 I I I 8O 100 120 140 160 Time, sec

(e) Head- wind component.

0 C

.¢: 10

0 [ [ I 80 100 120 140 160 Time, sec

(f) Cross-wind component.

Figure 9. Continued.

27 °5 t i°

80 100 120 140 160 Time, sec

(g) Vertical-wind component.

Figure 9. Concluded.

command inputs and the stable pitch attitude. The smooth tion with the thumbwheel (Configuration 4), the throttle decrease in speed and altitude support the pilot commen- inceptor was considered to be a more favorable control. tary regarding high precision. This combination of low Even without flightpath command and stabilization, two workload and high precision would enable instrument of the pilots rated the control of the decelerating approach approaches to achieve very low minimums with a high as satisfactory. It should be noted that these data were degree of confidence. Lateral-path tracking was also obtained under calm wind conditions, and the lack of precise and required only minor bank-angle changes to flightpath stabilization in disturbances could have caused correct small lateral errors with respect to the ghost. The these ratings to degrade. One pilot rated the approach data shown in figure 9 are from an approach flown in a adequate because the HUD flightpath symbol quickening 10-15-knot head wind with an 8-10-knot cross-wind was not optimized and the thumbwheel controller on the component and turbulence of 2-3 ft/sec rms. throttle did not have favorable mechanical characteristics. Except for these unfavorable characteristics, he would The objectionable effects of nozzle hysteresis are shown have rated the system satisfactory. in figure 10, where the +4.5-deg band is apparent at nominal nozzle deflections of approximately 45 deg. For The longitudinal time histories of figure 12 show a the thrust levels associated with this stage of the approach, smooth deceleration to near hover comparable to that 4.5 deg of hysteresis translates into about 0. Ig of normal of the flightpath and acceleration command system. acceleration. This acceleration acts as a disturbance to Flightpath control was accomplished using both pitch the vertical axis and couples into the throttle control laws attitude and thrust, depending on which was the most to cause an oscillatory response in engine thrust, as effective. Early in the approach, attitude was used while illustrated in figure ! 1. Once the nozzles are deflected wing lift was effective. Then, as the aircraft slowed to jet- below 50 deg, restoring torque from the deflected thrust borne speeds, a large throttle advance was required to acts as a preload on the nozzles, reducing the hysteresis to replace wing lift. Thumbwheel usage for the deceleration more tolerable levels (I-i.5 deg). For example, it can be was nearly open loop since the system controls precisely seen in figure 10 that, once the nozzles have deflected to the deceleration profile. beyond 50 deg, the oscillatory nozzle and throttle Hover-Point Acquisition- As shown in figure 13, control response, and hence the oscillatory flightpath response, of the closure to hover at the initial station-keeping point diminish significantly. was rated adequate lor the basic YAV-8B configuration. With the throttle employed as the thrust magnitude With the low level of pitch augmentation, it was difficult controller and with direct control of longitudinal accelera- to control closure rates to establish hover at the desired

28 1.5 m 150

1.0 -- 100

0 C ¢- ,X 10 .._= 4-"

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__"'"-...... i.... __...i.._ "......

-- 0

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¢- O3 10 ..'--.,",,,."-,,.; "'"_I.-"',---.,",....,....:.'A--"",I,-,. 5 __ 0_ --2 %_ i J:: iI. t _ t i ,I - 0_ ¢- J_

LL -- -4

I I -5 -- -6 0 5O 100 150 Time, sec

(a) Longitudinal response.

Figure 10. Example of nozzle hysteresis for Configuration 3.

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Figure 10. Concluded.

31 Normal acceleration, g Rpm, percent Nozzle angle, deg I o ¢D ¢,_ ,_ ¢,n 0 o 0 0 0

c_ C)

C_ 0_

o 1.5 -- 150

Vcas

1.0 -- _ 100 v o c

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-- 0

15 -- 2

03 "o T

d t b "o _' • .t I', I ._=

J_ .o_ Q. -- _'--4 T

--5 - 4 I [ 0 50 1O0 150 Time, sec

(a) Longitudinal response.

Figure 12. Decelerating transition time history for thrust control/acceleration command (Configuration 4).

33 100 -- 15 -- lO0

75 -- 10-- 8O l f_,n f-

L2 01 & c 50 -- m -- l_ 60 _¢ C 0 ffl Z U.

25 -- 0 -- 40

0 m -5 -- 2O

.5 -- 5 m

0 m

i 7O ,IC d - : ',, Q E .-,1 I ..... ;,_.., _"h p_.,...,jr-'--. " --.5 - "._ o-- F- 0 2 £ ffl I-- 5O

-1.0

I I -1.5 D _5 -- 3O 50 1 O0 150 Time, sec

(b) Longitudinal inceptors and control effectors.

Figure 12. Concluded.

34 Pilot Cooper-Harper Rating • A • B 10 C Inadequate 9 • D improvement 8 A E required 7

Adequate 6 improvement 5 O& • warranted 4 • L¢ O&

Satisfactory

I I I I I YAV-8B Attitude Flightpath Thrust control SAS command acceleration acceleration command command

Figure 13. Pilot evaluations of hover-point acquisition.

point. Concentration on any single task element usually between attitude and height control when large attitude resulted in the deterioration o1 another element. Use of the changes are used for deceleration. An oscillatory bank closure guidance (controlling the predictor ball to the angle and roll-control response appear during an abrupt station-keeping-point cross) was difficult for some pilots, lateral correction approaching hover. A residual small- and they would resort to external visual references to amplitude oscillation in the lateral control persists during complete the deceleration to hover at the station-keeping the initial hover, reflecting the high roll-loop gain for the point. Height control was also difficult with thrust control attitude command control. The pilot's control of bank alone because of low vertical damping and a tendency to angle was not impacted by this oscillation. Its absence in wander away from an established hover height. Coordi- the lateral stick indicates that it was not induced by the nation of throttle and pitch-control inputs was required pilot. Simulator experience indicates that the roll gain when making attitude changes to adjust the deceleration. could be reduced to eliminate the oscillation without degrading bank-angle control for the pilot. Representative time histories of hover-point acquisition are shown in figure 14. The YAV-SB was typified by Flightpath and deceleration command (Configuration 3) oscillatory vertical-velocity control and frequent throttle made the task fully satisfactory for most pilots because of manipulations. Several attitude adjustments were made to the improvement in height control. Some pilots found it control closure to the hover point during the final stage of difficult to use the longitudinal-velocity vector and the deceleration. The pedals were active to maintain horizontal-position symbology in conjunction with the heading. stick thumbwheel to control the final deceleration to the hover point; other pilots found the task easy to accom- With the inclusion of attitude stabilization (Configura- plish. Vertical-velocity control was precise and height tion 2), flying qualities improved slightly to borderline hold was open loop. Desired performance was generally adequate/satisfactory. The closure symbology was still achieved with minimal workload. Time histories in difficult for some pilots to use, and the difficulty with figure 16 are characterized by a smooth capture of the height control remained. Some pilots used a technique of hover altitude and a gradual deceleration to the hover making gross changes in deceleration with thrust vector station-keeping point. Control activity with the thumb- angle while making minor adjustments with pitch attitude. wheels was minor, and lateral precision was good with Height control remained the predominant contributor to little lateral-control activity evident. workload |br the same reasons noted previously. The time histories in figure 15 exhibit large transients in vertical For manual control of thrust with the deceleration velocity and a particularly large throttle input in conjunc- command (Configuration 4), the ratings were borderline tion with a large pitch-attitude excursion as the aircraft satisfactory/adequate with the principal deficiencies being reaches hover. This behavior reflects the strong coupling the control of the final closure to the hover point and the

35 5 100 --

75_ i°I ¢: o_ o 0 50 -- >

25_

-5 0

20 -- 30

is - _ 20

0 d o "ID

J= _3 0

155 -1o L_ _ _ i 0 L- 140 145 150 135 Time, sec

(a) Longitudinal response.

Figure 14. Station-keeping point acquisition time histories for YA V-8B SAS (Configuration 1).

36 85-- ,°°I 99 NF O) ej 1D

O1 el ,_ eo - 98

,ID C O Z

--4 97

75 -- --6 96 J J J

90-- 5

8O m

O1 O q) ,m 1D --_ 70 -- _ 0 2 e- _long l-- t- O 60

5O -5 135 140 145 150 155 Time, sec

(b) Longitudina/ inceptors and contro/ effectors.

Figure 14. Continued.

37 100 -- 20

75 m 15 u/

O1 Q "O

"O 5O 2 -- .t 10 h <¢ 4) "!"

25 -- 5

m 0 I I I

10 -- 10

Vy 0 B 5 O

O1 @

-lo m

> ¢ C I1o

-20 -- -5

-,30 -10 t I I 135 140 145 150 155 Time, sec

Figure 14. Continued.

38 100 -- 10

5O -- 5

@ O_ u_ i °

-5O -- -5

-100 -- -10 I I I

1.0 -- 1.0

.5-- .5

r- °- 81at J¢ ._c o m 0 F ¢n "O m

a. (a .J , ,

_o5 -- -.5

I I I -1.0 -- -1.0 135 140 145 150 155 Time, sec

(d) Lateral-directional inceptors and control effectors.

Figure 14. Concluded.

39 100 -- 5

75 m 0

0 qD ,._=5O -- o 0 > i¢ 0 "E 0 25

0 m --5 r i i

20 -- 30

I I I 120 130 140 150 Time, sec

(a) Longitudinal response.

Figure 15. Station-keeping point acquisition time histories for attitude command (Configuration 2).

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25 5 --

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Figure 15. Continued.

42 100 -- 10

50 --

_yrcs P

¢Z 0 -- n-

o= >-

-50 --

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-100 -- -_0 l I I

1.0 -- 1.0

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i s I J --.5 -- -.5 5p

-1.0 -- -1.0 I 1 I 110 120 130 140 150 Time, sec

(d) Latera/-directiona/ inceptors and control effectors.

Figure 15. Conc/uded.

43 100-- 5

75 B O

-- o 0 i 50 E h

O I:: O 25

I I O m -5

10 -- 3O

_ o 20

'ID d "ID 0 '-! s-_ lo

_._o

C --_9 o

0 __ -10 I I 130 140 150 160 Time, sec

(a) Longitudina/ response.

Figure 16. Station-keeping point acquisition time histories for flightpath/acceleration command (Configuration 3).

44 Stick thumbwheel Nozzle angle, deg 00 co b c_ o u1 o I I I I

Stick trim, in. Stabilator, deg I u1 o u1 I I I I I

Throttle thumbwheel Fan rpm, percent

.._0 (D 0

r_ c) 9

c_ J _b

c_ cb

c) 0 1 J

3_ w

J_ _J1 100 --

75 --

-5

'ID

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25 -- -2O

0 -- -25

10 -- lO

"" ...... - My

0 -- 5 0 0

0 d U o -10 -- _ 0 0 ca >

ell II1

-20 -- -5

--,3O -lO I L 130 140 150 160 Time, sec

Figure 16. Continued.

46 100 10

o O_ 1D 0...... o.. vyrcs c5 " 0 L) o n- _¢

>- 8A -5O -5

-100 -10 I I

1.0 -- 1.0

_ 51at .5 -- .5

r- ;o o g.

.J 5p

-.5 D --,5

I I -1.0 -- -1.0 130 140 150 160 Time, sec

(d) Lateral-directional inceptors and control effectors.

Figure 16. Concluded.

47 throttle thumbwheel mechanical characteristics. One pilot from translational control in the horizontal plane was sought more deceleration authority with the thumbwheel. considered to be the principal source of the reduction in Otherwise, the transition from the approach to hover workload. Position control was accomplished with desired control was easy. As can be seen in figure 17, the final precision and generally with minimal compensation by deceleration is smooth and the hover point is captured using the proportional thumb controller. One pilot experi- with a final adjustment with the thumbwheel. No throttle enced a tendency to drift off the hover point rearward manipulation was required for altitude control. and to the left, requiring moderate effort to compensate. Aggressive longitudinal maneuvers could lead to Vertical Landing- Figure 18 shows that the pilot ratings objectionable discrepancies between the longitudinal- of the vertical landing with the basic YAV-8B system fall velocity vector and predictor ball because of a lag in the in the adequate range. Pilots considered the principal aircraft's response to the translational-rate command. deficiency to be the considerable attention and compensa- Bank-angle excursions to provide lateral translational tion required to control sink rate during the descent in the control were generally considered to be reasonable and presence of ground effect. Stabilization of pitch and roll comfortable. On one occasion during hover in a steady attitude during translational maneuvers and in the pres- wind, the lack of integral control to provide trim into the ence of thrust changes also made the task difficult with the basic aircraft. As can be seen from the brackets in wind caused the pilot to hold a steady command on the proportional thumb controller to maintain position. This figure 18, the range of previous simulation ratings situation points to the need to include integral control to compare reasonably well with these flight results. relieve the pilot of this demand. With the exception of Representative time histories of the vertical landing, concerns about longitudinal drift, the translational-rate shown in figure 19, are typified by wandering height control was also a significant source of reduced workload control, with frequent throttle corrections made in an since horizontal positioning could be accomplished with attempt to establish a steady hover altitude. Numerous fewer control inputs and lower pilot concentration. pitch-attitude adjustments were necessary during the Finally, the hover display, in combination with the translation to the hover point and during the descent to translational-rate command control, gave the pilot the landing. Roll and yaw controls were also very active tbr ability to achieve excellent hover and landing precision, controlling the lateral translation and maintaining a steady with touchdowns consistently inside a 5-ft-radius circle. heading. The hover display format did not pose a problem for the pilots; they accommodated readily to the mixed presenta- No significant improvement was provided by the attitude tion of horizontal and vertical information. Simulation command system (Configuration 2) because of annoying data represented by the brackets show the same fully features associated with the limited range of authority satisfactory ratings as were obtained in flight. afforded by the pitch and roll series servos. Specifically, when the servos reached their limits, the aircraft reverted Vertical velocity is set precisely and maintained during from an attitude-stabilized response to an acceleration the descent to landing (fig. 21). Only minor adjustments response. At that point, the attitude response to the stick show on the throttle thumbwheel. Minor adjustments are became too sensitive. Furthermore, height and sink-rate evident with the proportional thumb controller for control remained difficult tasks. Assessments of position longitudinal and lateral position, with corrections made holding during the descent varied from easy to accomplish smoothly and precisely. to having an annoying tendency to drift off the point. With the height-rate damper and translational-rate Figure 20 illustrates the same difficulty with hover-height command (Configuration 4), the hover positioning and control that was evident for the basic YAV-8B. Pitch landing task was also fully satisfactory. Height control excursions and stick activity were similar to those of the was easy and essentially the same as with vertical-velocity YAV-8B. Lateral-stick activity for the lateral offset command. Minor compensation was required with the correction to the hover point was reduced somewhat from throttle during aggressive longitudinal or lateral maneu- that for the YAV-8B, as was pedal activity for heading vers when the thrust vector was displaced significantly control. Again, the oscillatory control response is reflec- from the vertical. The throttle was considered to be the tive of the high-gain attitude control system performance. natural control for the vertical axis. As shown in figure 22, hover positioning with the height-rate damper When vertical-velocity command was introduced with the and translational-rate command was smooth and height translational-rate system (Configuration 3), the landing hold and vertical-velocity control were accomplished with ratings improved to satisfactory. Height and sink-rate minimal throttle adjustment. control became very precise and were performed with little effort. The resulting decoupling of height response

48 6_

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t.n Pilot Cooper-Harper Rating • A • B Inadequate • C improvement • D &E required I78 ,ionresu,,s Adequate improvement 'IT". warranted st-,4 ., _ ° OA Satisfactory 23 II • T I_oA• 1 I I I YAV-8B Attitude Translational Height rate damper SAS command rate command translational rate command

Figure 18. Pilot evaluations of vertical landing.

51 100-- 5

75 m tJ t, 0

0 "0 5O -- o 2 >

0 'E -5 > 25

- -10 I I I ",

10 3O

4 t • x t l

L" t 20 -- | _t • i • i "0 b s_ ii t d 0 "0 0 m II I -- 5 - >_lO-- Ii t m V x t_ ¢13 r- .__

,-,i a.

C _9 o--

-- -10 I I 140 160 180 20( Time, sec

(a) Longitudinal response.

Figure 19. Hover and vertical-landing time histories for YA V-8B SAS (Configuration 1).

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O-- m

C m IB m "_-2o

zOO 180 --,3O -10 160 140 Time, sec

Figure 19. Continued.

54 100 -- 10

5O -- 5

il ir _

P O_ 'ID ,,'1 - _ o _ , _ .j _ _'- /.. " j'. _,,- ,, rr %._ o ° r L -w _A -50 -- -5

-100 -- -10 I I

1.0 -- 1.0

.5 -- .5--

¢J o- "_ o- "O __Slat ,..

I I_ IL • _ t tl i i

-.5 -- B5 -- ir /

-1.0 B1.0 I I 140 160 180 200 Time, sec

(d) Lateral-directional inceptors and control effectors.

Figure 19. Concluded.

55 100

75 D 0 @

¢:

d 0 "O 50 -- o fp- .= 4) >

¢= 0 t:: Q 25

-5

10 3O ,.,.,, ,, ,',', / ;,

o 20 Jt - ,_ 0"}

"0 1 I "0 .,_=5 -- _> 10 .H ¢= $ -- _,,'" e r-

o 0

o - -lo I I 140 160 180 2O0 Time, sec

(a) Longitudinal response.

Figure 20. Hover and vertical-landing time histories for attitude command (Configuration 2).

56 Nozzle angle, deg

'M 0 cn 0 O_ 0 I L I I I

Throttle, deg Stabilator, deg CO o o o o j= i I I I I [ I I I L

Longitudinal stick, in. Fan rpm, percent

I (D ¢0 ._LU1 Q O_ ¢o c.O 0

E_ i .5 C_ PO

C_ -- i C_

CL i CJ G_ C)

i -g Cj

t ;2_'- ="

-__-_-_= .F'

0 0

t_ 100 -- 2O

75 -- 15

"O "" h so -- .t 10 'lO

G) "r

25 -- 5

J "t- -- 0

10 -- 10

0 -- 5 " - ...... My

"tD

0 o -10 -- _ o

> B ¢- m II1

-20 -- -5

I I -30 -- -10 140 160 180 20O Time, sec

Figure 20. Continued.

58 100

5O 5 ,°l _)yr cs

o ¢P "ID I i i (p u_ 2 o 0 / -' ...... ,z..-.'..."'.""',,-, ..- ....",, 'J,. !.

-5O

-5 J 8A

-100 -10 i i

1.0 -- 1.0

_ 81at .5-- .5

O ,,,,,., 0-- 1D

O,. m S',r ,,-I 5p

-.5

I I -1.0 -- -1.0 140 160 180 2OO Time, sec

(d) Lateral-directional inceptors and control effectors.

Figure 20. Concluded.

59 C_ 0

Pitch attitude, deg Altitude, ft r_

L I 1 1 I

_b Longitudinal velocity, ftJsec I Vertical velocity, ft/sec

_o o o o ol o o I , "'_ ,

cb _. __ _

c_ o - _

o Longitudinal proportional thumb controller Nozzle angle, deg ..L .I •_1 CO CO (JD _D 0 u_ o _n 0 O_ 0 01 O 01 I I I I I I I I I

Stick trim, in. Stabilator, deg I I ol o 01 I I D I I I I

Throttle thumbwheel Fan rpm, percent I ,.L ..b 0 "_1 OO _0 O I I

5" .______-_', --_ ¢3 o_ PO c_ C) o

(1) -

¢) C_

oq X 0 -- 0

0 100 -- -10

-15 m

o_ -20 i,° _ -2s

--,3O

-35

-- --4O

10 -- 10

Vy 0 ¢)

¢J o -10 IU > t-

II1

-20 -5

-3O -10 I I 160 180 200 220 Time, sec

Figure 21. Continued.

62 100 -- 10

(_yrcs ,_I[ P O_ "O Q. u_ - o,o,r --_ .... _ J ,o r--._ ., r,J| ILL. u 2 rr ,<

-5O -5

I I -100 -- -10

1.0 -- 1.0

0 .5 -- c .5 0 U .12 E _c

e.. o Q. o o. 2 -.5 - _ -.5

-1.0 -1.0 I I 160 180 200 220 Time, sec

(d) Lateral-directional inceptors and control effectors

Figure 21. Concluded.

63 100 -- 5

75 0 0 # 0 'ID= 50 -- o 0

-- -5

10 _ 30

tJ e • 20 I i O1 4) i "O i ! U "O _o

•-- 5 t I Lj I (0 III .f C e-

C _ o

0 - -10 I I I 120 140 160 180 200 Time, sec

(a) Longitudinal response.

Figure 22. Hover and vertical-landing time histories for height-rate dampertranslational-rate command (Configuration 4).

64 Longitudinal proportional thumb controller Nozzle angle, deg

I I I I l I

• Stick trim, in. ! Stabilator, deg ..=

Throttle, 1 deg I I Fan rpm, I percent I _.o _, o= _ == _ _g °_ I I I I I

_ ___.-_ --_

¢3 E-

_| _

,; "_-______Effects of control bandwidth: Variations in was of insufficient authority to counter the nose-down translational-rate control system bandwidth produced the moment, thus forcing the pilot to intervene to avoid a results shown in figures 23-25. The value of the band- nose-gear strike at touchdown. Another pilot complained width of the control system is defined as the frequency of a sluggish flightpath response in the landing flare; for a 45-deg phase margin for longitudinal-, lateral-, he desired additional descending flightpath authority. or vertical-position response to the respective cockpit However, the flightpath command system was considered controller. It was determined from frequency response to be a superior mode for performing slow landings where data obtained using the method described in reference 14. precise control to an austere landing area, such as a Examples of these frequency responses for the baseline narrow road, is demanded. translational-rate command configurations are presented Example time histories for the flightpath/acceleration in the appendix. command system, shown in figure 26, illustrate a slow Longitudinal-velocity control results, presented in landing from a visual approach along a descending turn to figure 23, indicate that a borderline satisfactory/adequate the runway. The turn was completed to line up with the bandwidth is 0.33 rad/sec. The baseline longitudinal runway at an altitude of about 150 ft. After the initial stick translational-rate control evaluated in the program had a thumbwheel input to decelerate to the target approach bandwidth of 0.36 rad/sec and was considered to be fully speed of 100 knots, no further action was required of the satisfactory, as noted previously. For the lateral controller, pilot for speed control. Speed held steady in the presence the borderline bandwidth is 0.25 rad/sec, as shown in of flightpath corrections about a nominal 4-deg path figure 24. The baseline lateral translational-rate control throughout the approach and during the flare to touch- with a bandwidth of 0.29 rad/sec was rated satisfactory. down. Nearly full aft throttle thumbwheel was required For both longitudinal- and lateral-position control, at the for a descent of 5 deg. The initial action to reduce sink lower bandwidths the pilots complained about a sluggish rate prior to touchdown was performed with the throttle response to their commands through the proportional thumbwheel. thumb controller and poor predictability in translating to, and establishing a precise hover over, the intended point. Control System Performance The satisfactory/adequate boundary for vertical-position control bandwidth is 0.6 rad/sec, as shown in figure 25. In Control Utilization- Figures 27 through 40 show comparison, the baseline height-rate command bandwidth minimum, maximum, and mean control activity for the was determined to be 0.64 rad/sec and was rated solidly VSRA during approach, station-keeping-point acquisition, satisfactory. Complaints about height control for the lower hover, vertical landing, and slow landing, collected over bandwidths concerned a sluggish response to vertical- the course of more than 100 flights. The data are cate- velocity commands and poor holding of a steady vertical gorized by the control mode used for each flight and velocity as the aircraft entered ground effect, causing the arranged from left to right in order of increasing mean pilot to adjust the sink-rate command to complete the control activity. The variation in mean control activity is landing. At the lowest bandwidth tested, positive ground associated with variations in aircraft trim due to changes cushion upon entering ground effect caused sufficient in loading and winds among the individual runs. Maxi- fluctuations in sink rate to arrest the descent momentarily. mum and minimum excursions about the mean reflect For all three axes, the basic aircraft with no translational- control authority used for maneuvering. It should be noted rate augmentation was rated only adequate (handling- that most data were obtained for light winds and qualities rating (HQR) 4 to 5) for the hover-position turbulence. control task. Pitch control: Figures 27-30 illustrate pitch-control Slow Landing- Pilots' evaluations for the attitude activity for the different tasks and response types. During command system revealed some improvement over the the decelerating approach (fig. 27), there is no apparent basic YAV-8B; the improvement was achieved by influence of control response type on peak control decoupling the attitude response in the presence of thrust excursions about the mean. The excursions are on the modulation for path control. Control of flightpath was order of +2.5 to 4 deg out of a total stabilator authority of precise during the approach. The flightpath command -10.25 to 11.25 deg, and they represent 23 to 37 percent system was rated satisfactory during the approach as a of total authority. Variations in the mean stabilator consequence of the precise path control and the ability to deflection reflect changing longitudinal trim associated easily set and hold speed. However, one pilot rated the with variations in center of gravity with fuel remaining for flare to touchdown borderline satisfactory/adequate different approaches. For the task of capturing the station- because of the need to compensate for a tendency to pitch keeping point, response type impacts control usage to down when entering ground effect. The pitch series servo some degree. As noted previously, for the YAV-8B SAS

66 Cooper-Harper Rating Pilot 10 •D Inadequate 9 AE improvement 8 required 7 Adequate 6 improvement 5 warranted 4 & • 3 Satisfactory 2 1 I I I I .1 .2 .3 .4 Longitudinal position control bandwidth, rad/sec

Figure 23. Pilot evaluations of longitudinal-position control bandwidth.

Cooper-Harper Rating Pilot 10 •D &S Inadequate 9 improvement 8 required 7

Adequate 6 improvement 5 warranted 4 3 & e& Satisfactory 2 1 I I I I 0 .1 .2 .3 .4 Lateral position control bandwidth, rad/sec

Figure 24. Pilot evaluations of lateral-position control bandwidth.

Cooper-Harper Rating Pilot •D 10 •E Inadequate 9 improvement 8 required 7 Adequate 6 improvement 5 warranted 4 eL Satisfactory I I I I 0 .2 .4 .6 .8 Vertical position control bandwidth, rad/sec

Figure 25. Pilot evaluations of vertical-position control bandwidth.

67 1000 100

O_ @ "0

:= 50 soo ¢= 0

0 Z

0 t I I

150 100

Q e-o 100

"O E" 50 Q. ._ so P ¢B U.

I t J I I

J¢

.Q 0 E

-lo 0 J¢ o_ ¢/) U.

-2O I I I -1 I I I 0 20 40 60 8O Time, sec 1 !o !

-1 0 20 40 60 8O Time, sec

(a) Longitudinal response.

Figure 26. Time histories for Configuration 3 in a slow landing.

6B 5O

r i i I I -50

1.0

c .5 .5

t- 0

0 r_._- 0 "O

(g -.5 -.5

I I I -1.0 -1.0 0 20 40 60 80 2O 4O 6O 8O Time, sec Time, sec

(b) Lateral response.

Figure 26. Concluded.

75 -- 8 m • Mean • Maximum • Minimum

P ¢P GI.

r- .o 25

_L. nww • J_ • • BIB • O9 • ,, '.%"- BIB EB mR -2 --B m n • • •m 'b Om •

-4 -- .P YAV-8B Attitude Flightpath acceleration Thrust control SAS command command acceleration -50 -- command

Figure 27. Pitch-axis control activity during approach.

69 5.0 m 40 -- • Mean • Maximum 4.0 • Minimum _k _k i 20-_ • ", %,,,,, • Q. •& -,:,: • • •_ am" °

0 _ 2.0 _'bl_• dml,•m m_ • mm • -%- m_mlLm'm • m• d" m"'rm_mu'_•-num mu • • • a. • • • 1.0 -20 --

YAV-SB Attitude Flightpath acceleration Thrust control SAS command command acceleration command

Figure 28. Pitch-axis control activity during hover-point acquisition.

o ., • mll-- - m. r- o o r- m• .o -20 m • • • OmPdmlmm in mmmm • • • mmlmn.. :;...,.,,...'. (0 o • --- -_ • [] mm P • • J_ • • mlmm -4o m a. m • • Mean • Maximum -6O • Minimum ---3--

-80 -- -4 --

YAV-SB Attitude Translational rate Height rate damper SAS command command translational rate command

Figure 29. Pitch-axis control activity during hover and vertical landing.

?0 6 -- 50

4 m • • • • •

25 "0 2 -- & c- O t- .D o o 0 0 "0

"13

-2-- .q -25 • •

--4 -- • Mean • Maximum • Minimum -50 --6-- YAV-8B Attitude Flightpath acceleration SAS command command

Figure 30. Pitch-axis control activity during slow landing.

and the attitude command system, the pilot adjusts pitch Roll control: Control activity for the roll axis is attitude to decelerate to the hover, whereas for the two presented in figures 31-34 for the various tasks. Response systems with longitudinal-acceleration command working types do not influence the level of roll-control activity for through thrust deflection, the pitch attitude is held any of the tasks, even though attitude stabilization is constant. The data in figure 28 show that peak control provided for all except the YAV-SB SAS and the lateral- excursions for the YAV-SB SAS and the attitude velocity command is available for two of the modes in command system exceed those for the flightpath/ hover. In figure 31, data for the approach show peak acceleration command and thrust control with acceleration excursions about the mean from 0.5 deg right wing command systems. For the former two response types, down to 1 deg left wing down, with many cases of sub- excursions range from 0.7 to 1.7 deg. It should be noted stantially lower magnitude. Of a total aileron authority that, for hover or near-hover conditions, reaction controls of +16.8 deg, these larger excursions still reach only rather than the stabilator supply the control moments, and 6 percent of maximum aileron. The airplane shows a the RCS authority (in terms of equivalent stabilator consistent left-wing-down trim requirement of 1 deg. position) ranges from -3.3 to 10 deg. Thus the excursions During acquisition of the station-keeping point (fig. 32), noted represent 10 to 25 percent of total pitch reaction occasional peaks in control utilization are as large as those control authority. For the latter two response types, for the approach, but the predominance of data show excursions range from 0.4 to 1 deg of the equivalent small excursions of about 0.2 deg. For hover or near- stabilator and represent 6 to 16 percent authority. This hover conditions, control authority is based on the maxi- contrast between response types holds for the hover and mum available reaction control, which in this case is vertical landing task as well. In figure 29, peak excursions +11.5 deg of equivalent aileron. Thus, the range of peak for the YAV-SB SAS and attitude command range from roll control excursions for this task is from 2 to 9 percent I to 3 deg (up to 45-percent authority), whereas those for of the reaction control capability for all the response the two longitudinal-acceleration command systems range types. For hover and vertical landing (fig. 33), the from 0.4 to 2 deg (up to 30-percent authority). Rather magnitude of peak excursions is similar to those for the sparse data exist for slow landings and do not reveal any station-keeping-point acquisition. Again, the control influence of response type. Figure 30 indicates excursions usage is from 2 to 9 percent of maximum reaction control. from 1.5 to 3 deg, or about 28 percent of total stabilator Peak aileron excursions for the slow landing (fig. 34) are authority for this task for all the systems. again from 0.2 to as large as 1 deg, and in this case they

71 0-- 0

Q P -.5 • O. • & •A • • • _' F. • AA_A • _• .== t- O _ m 4-. O _¢ o-1.0

10 _. -m nnm_" t- mm-nm-- • • -- _ -- O • • • Q -1.5 _-II • _o m -10 0B 4.. a- "_ -2,0 -- mill• • a m • • m mimmlmmllmu a • Mean • • -2.5 -- -15 -- • Maximum • Minimum

-3.0 -- YAV-8B Attitude Flightpath acceleration Thrust control SAS command command acceleration command

Figure 31. Roll-axis control activity during approach.

0 m

• Mean

m°5 D • Maximum -5-- _D • Minimum "O

e" ¢D O -1.0 D. O -10 -- O mm C O O -1.5 -- t- (%) O -15 -- O m '_ -2.0 --

Cg 0 -20 -- a -2.5 --

-25 -- -3.0 -- YAV-8B Attitude Flightpath acceleration Thrust control SAS command command acceleration command

Figure 32. Roll-axis control activity during hover-point acquisition.

72 • Mean • Maximum A• • • Minimum -50--- -.5 ot "E 1:) _t

r_ --" -10 o r "o • • • • O mmlm ¢) -1.5 • •

O -_ -15 U -2.0 • • mmlm • • O I1: -20 _ .=_ r,l -2.5 --

-25 -- -3.0 -- YAV-8B Attitude Translational-rate Height-rate damper SAS command command translational rate command

Figure 33. Roll-axis control activity during hover and vertical landing.

0 n 0

• Mean • Maximum _ -.5 m 0 • Minimum o .o -5 -- '*" A • _ -1.0 --& • • A •

C • • • • '- 2 II • • • • • o __ --_ "_ -1.5 --m -10 -- "m

_ -2.0 =_ ca Q • •

-15 -- -2.5 L_ YAV-8B Attitude Flightpath acceleration SAS command command

Figure 34. Roll-axis control activity during slow landing.

73 reflect up to only 6 percent of the total lateral control Control Frequency Content- Measures of the frequency available in forward flight. content of the pitch, roll, and yaw control effectors were obtained in transition for the flightpath/acceleration Yaw control" Figures 35-38 present yaw-control command system and in hover for these three controls; usage in the same format as for pitch and roll. As for the engine rpm was also measured for the translational-rate roll axis the response type has no effect on control command control. These results were obtained using the activity. During the approach, for all system variants frequency analysis method described in reference 14, and shown in figure 35, nominal peak excursions are about they are presented in the power spectral plots of figures 4 I 20 percent of yaw reaction control authority. Occasional to 43. The ordinate of these figures is the square of peak occurrences up to 50-70 percent can be observed, normalized control magnitude plotted on a decibel scale. but they are the exception. Control activity is shown as a Frequency bandwidth is defined analytically in this case percent of yaw reaction control since this is the only as the upper frequency that contains 0.707 of the energy control that includes inputs from both the pilot's pedal of the entire control response. In computing this band- and the series stability-augmentation system servo. width, the frequency response data were truncated at low Because virtually all the approaches were flown without frequency so as to disregard energy in the response pedal inputs during the approach, little or no rudder associated with trim control. activity is present, and the reaction control reflects total yaw control used. During acquisition of the station- For the decelerating transition, figure 41 presents the keeping point, figure 36 shows that peak utilization was pitch-, roll-, and yaw-control frequency content obtained from 40 to as high as 60 percent, although many of the from time histories from three approaches. Analytically cases indicate only about +20-percent excursions from the defined bandwidths are 5.5, 6.0, and 1.4 rad/sec for the mean. The 40- to 60-percent range also holds for the stabilator, aileron, and yaw reaction control, respectively. hover and vertical landing; however, some variations as A visual inspection of these plots indicates general large as 80 to 100 percent arc observed in the data in agreement with the analytical measure except for the figure 37. Slow landings (fig. 38) show excursions of stabilator, which shows a rolloff above 3.5 rad/sec. Given about 30 percent, which are more on the order of those the notch in the stabilator frequency response just above utilized during the approach. 2 rad/sec, the analytical measure of bandwidth may have Thrust control: In the case of thrust utilization, data been biased to a higher frequency than would have been the case if the frequency response were flat over the are presented only for acquisition of the station-keeping frequency band. point, hover, and vertical landing. During the approach, such large variations in thrust were required as the aircraft Results from four hover cases (fig. 42) show the band- decelerated that meaningful data cannot be presented. widths defined analytically for the data to be 5.3, 8.5, and Acquisition of the station-keeping point produced the 2.3 rad/sec for the pitch, roll, and yaw reaction controls, results shown in figure 39, revealing small differences respectively. The well-defined peak in the roll response between response types with manual thrust control and reflects the high-frequency oscillation in the roll control those with vertical-velocity command. In the case of the that is associated with the high forward-loop gain in this former, the YAV-8B SAS and attitude command, excur- axis. Engine rpm response for the vertical-velocity sions in engine power setting about the mean are on the command system and for manual control of thrust during order of 1 to 1.5 percent rpm. At high thrust settings hover are indicated in figure 43. Whereas engine response associated with hover, a l-percent change in rpm equates to the pilot's manual control for height rolls off above to 3 percent of the maximum available vertical thrust lor 0.6 rad/sec, the vertical-velocity command control does the Pegasus engine. Thus the rpm excursions noted are not begin to drop off until about 0.8 rad/sec, and it still equivalent to 3 to 4.5 percent of maximum thrust. For the shows appreciable response out to 3 rad/sec. vertical-velocity command systems, somewhat lower peak rpm excursions of 0.6 to 1 percent arc noted, amounting Design Recommendations to 2 to 3 percent of maximum thrust. For the hover and vertical-landing tasks (fig. 40), only a slight difference in Numerous suggestions were made by the participating rpm excursions exists between the manual thrust and pilots regarding improvements that could be made in the vertical-velocity command controls. Where the manual- system design that could resolve some of their concerns, thrust-control types show nominal excursions of about as well as alternate design approaches that should be 1.8-percent rpm (5.4-percent maximum thrust) during considered in contrast to those used in the VSRA. These hover, the vertical-velocity command systems are only comments, along with related experience of the VSRA marginally lower ( 1.5- to 1.8-percent rpm or 4.5- to design team, are separated into those related to the control 5.4-percent maximum thrust).

74 • Maximum 60 • • • • • Minimum •

80 I AAA_ _ _ , Mean & _- 20 •_ o

o -40 -- • h- e -60 >. =-80 f -100 YAV-8B Attitude Flightpath acceleration Thrust control SAS command command acceleration command

Figure 35. Yaw-axis control activity during approach.

• •• . k AA • • •_Uk '°40 f • • • •'= • •• ,,•k• •• 20 A-_-- , == =.= • •= == --• t == A • • • ••• • & j_ ._.,..

_o. _ %..:._.. -.., ;,..-;.; .- :_. • O • BiB • _ •

-40 >. • Mean • Maximum -60-- • Minimum

-80 m YAV-8B Attitude Flightpath acceleration Thrust control SAS command command acceleration command

Figure 36. Yaw-axis control activity during hover-point acquisition.

75 100- • Mean 80-- A Maximum • A• • Minimum 60 • • •A&••

. • &• . . . •& .•& •& •& • • • 4o-•• • ••A*,_* • _AA • ••• #A_ AA o < I I •• •rat a, ,_llm'• •

-40 -- l i I • mm • mm _ mmm mi %,,.,," >- BIB mm

•-60 -- [] • • • • -80--

-100 -- YAV-8B Attitude Translational-rate Height-rate SAS command command damper translational rate command

Figure 37. Yaw-axis control activity during hover and vertical landing.

60-- • Mean • Maximum • Minimum

4) P o 20 Q. c" O

O & • 0 lip • • O "O • • • U) • • • (J rr -20 --m >-

-40 --

-80 -- YAV-8B Attitude Flightpath acceleration SAS command command

Figure 38. Yaw-axis control activity during slow landing.

?6 106

104 • M%oum "

• Minimum AA 102 • & •=11 All 100 g 98 _ -

an • __="_= • ,1= 96 • _a=¢_. m minim • i" ...,- 94 iuR= u • •

92 U YAV-8B Attitude Flightpath acceleration Thrust control SAS command command acceleration command

Figure 39. Vertical-axis control activity during hover-point acquisition.

106

• Mean 104 • Maximum • Minimum 102

•& •,.,,',.,

g 98 • •,'=,,,",,',_,-,

• ,IP • U. 96 ,c=..o _ • _11 l• • •e,_ =P • •,P == 94 .V'. --O • •

92 YAV-8B Attitude Translational-rate Height-rate damper SAS command command translational-rate command

Figure 40. Vertical-axis control activity during hover and vertical landing.

77 20

Yaw

• ,---...... , _.. m "o d "O Roll ,_ ,\ -10 C O_ ¢1 Pitch "'"_ _,,

-2O

-30

-40 [ J I [ I ] I I .3 .4 .6 .8 1 2 4 6 8 10 Frequency, rad/sec

Figure 41. Control frequency content for the approach.

?8 2O

10 m

/r\ Pitch / \

m "o

"0 \ \ .._=-lo =,.,

"_ Yaw \

-20 _ \.

-30 --

L I I I I I L I I I I L I I -4O .3 .4 .6 .8 1 2 4 6 8 10 Frequency, rad/sec

Figure 42. Control frequency content for hover.

?9 2O

N.\ _'_ .Vertical-velocity command \\

rn "O

"0 \\\ \.. Manualthrottle control ¢.,. 0') \ =E

\ \

-2O

-30 -- \ \ \

-4O ! I I I I I I I I I I I I I .3 .4 .6 .8 1 2 4 6 8 10 Frequency, rad/sec

Figure 43. Engine rpm frequency content for hover.

8O system and those related to the HUD; they are noted as wing lift effectiveness is no longer adequate. From that follows. point on into hover, throttle alone would be used for vertical-speed control and pitch attitude would be set as Control System- Comments are presented with regard to desired for hover and landing. the individual control axes; they deal with the control inceptor and the attendant aircraft response. 10. Excessive hysteresis in the nozzle control excited flightpath disturbances for the tlightpath/acceleration 1. Location of the pitch trim button made its use command system. Hysteresis in the thrust-deflection- awkward; a central location on the stick would be control effectors needs to be minimized for both the preferable. transition and hover. 2. A few pilots considered roll-control sensitivity to be 11. A few pilots found the proportional thumb high with the rate command/attitude-hold mode; others controller to be too sensitive for control of longitudinal considered the sensitivity acceptable. and lateral translational rates. 3. Directional control during the approach was poor, 12. Several pilots expressed a preference tor using thc especially in turbulence. This characteristic is attributed to center stick instead of the proportional thumb controller the fact that the low-authority series servo works solely for translational-rate command. One pilot preferred the through the yaw reaction control. Further, the directional- proportional thumb controller lor this inceptor because of control law was not sufficiently high in gain to make full a concern for a reverse sense of application of the center use of the servo authority. stick to control the horizontal display elements in the 4. One pilot would have liked for the directional hover display. augmentation to point the aircraft's nose into the wind 13. Some pilots observed a lag in the longitudinal- when turning during low-speed air taxi. velocity response in the translational-rate command. 5. Several pilots stated a preference for using a throttle 14. One pilot preferred more lateral translational-rate lever as the inceptor to control flightpath and vertical command authority, particularly when translating into a velocity as opposed to the thumbwheel located on the cross-wind component. Quicker lateral-velocity response throttle. These comments were reinforced by three of the was also desired with the lateral system using bank angles pilots in the evaluation of Configuration 4. up to 10 deg.

6. Some pilots found it easy to confuse the use of the 15. Several pilots preferred a discrete manual switch by thumbwheels, in terms of both function and sense of the pilot between the transition and hover control modes. application. Instances of reverse control of flightpath with the throttle thumbwheel were noted for these pilots. A 16. The number of discrete selections of control mode, preferable set of inceptors, a throttle handle for flightpath display mode, and guidance when switching from as noted in item 5, and a thumbwheel mounted on the approach to hover was excessive, and the selections throttle for longitudinal acceleration were considered by should be integrated. these pilots to be a plausible solution to these objections. 17. Back-drive motion of the stick and throttle by the 7. A lag was noted in flightpath response to the parallel actuators could cause inadvertent inputs to the thumbwheel during the approach and during slow thumbwheels and proportional thumb controller. landings. It would be desirable to reduce this lag some- ]lead-up Display- Comments on the HUD format and what, although the control response characteristics were drive laws are associated with either the approach or the rated satisfactory. hover display modes.

8. Nonlinear sensitivity for the thumbwheels would 1. As noted previously, pitch-attitude cues were have been a better match for desired sensitivities over the considered by some pilots to be poor and in need of a low-speed range through approach to hover. For example, stronger pitch reference. the stick thumbwheel was considered to be overly sensitive at high speeds and insensitive at low speeds. 2. One pilot desired to see actual flightpath displayed along with the quickened flightpath symbol. 9. Concern was raised about throttle reduction at fixed- pitch attitude when controlling flightpath because of the 3. As reflected in earlier comments, some pilots had increase in angle of attack occurring at low speeds and difficulty using the longitudinal-velocity predictor ball low altitudes. Preference was stated for coordinated use and the station-keeping-point symbols to control closure of attitude and thrust for flightpath control while semi-jet- to the hover point. This comment applied to both the borne until the aircraft has decelerated to speeds where

81 attitudecommandandtheflightpath/accelerationcom- flightpath control and large trim changes with thrust and mandcontrolmodes.Onepilotchosetousetheapproach thrust deflection. The attitude command system improved display down to approximately a 100-ft altitude, then on the basic YAV-8B for the transition. It was considered switch to external visual cues to complete the deceleration marginally satisfactory because it eliminated the pilot's to the hover point. Whether this difficulty was fundamen- need to counter trim changes. However, the demands of tal to the display concept or due to training procedures is thrust control during the deceleration, as the loss of wing not clear. lift must be compensated by increasing thrust, were objectionable to the pilots. These findings, in conjunction 4. Symbol clutter in the hover display at the hover point with related ground-based simulation results, indicate was objectionable to most pilots. that the flightpath/longitudinal-acceleration command 5. Pilots preferred having the velocity-vector and response type would be an essential part of a system to predictor-ball symbols available on the approach display permit operation to instrument minimums significantly for speeds of 25 knots and below, instead of the speeds of lower than those achieved today for the AV-8B. It would 20 knots and below used in the initial display design. also be a superior mode for performing slow landings where precise control to an austere landing area, such 6. Workload would be reduced by having the display- as a narrow road, is demanded. The translational-rate mode switch triggered by the switch of the control mode. command system would reduce pilot workload for 7. It would be desirable to maintain higher speed in the demanding vertical landing tasks aboard ship and in early part of the approach, then to make an acceptably confined land-based sites. aggressive deceleration down to the final closure The HUD was generally felt to offer excellent path deceleration to the station-keeping point. guidance for the curved approach through the ghost aircraft as well as effective commands for the deceleration Conclusions to hover. It would be expected to significantly reduce pilot workload and improve precision for night shipboard Flight experiments were conducted on the Ames Research recovery for AV-8B operations or for operation to lower Center's V/STOL Systems Research Aircraft (VSRA) to visibility minimums than permissible for the AV-SB. In assess the influence of advanced control modes and combination with the translational-rate command control, head-up displays on flying qualities for precision the hover display gave the pilot the ability to achieve approach and landing operations. Evaluations were made excellent hover and landing precision, with touchdowns for decelerating approaches to hover followed by a consistently inside a 5-foot-radius circle. The hover vertical landing and for slow landings for four control/ display format did not pose a problem for the pilots; they display mode combinations: the basic YAV-8B SAS; accommodated readily to the mixed presentation ot' attitude command for pitch, roll, and yaw; flightpath/ horizontal and vertical information. acceleration command and translational-rate command; and height damper with translational-rate command. Control utilization and frequency content were docu- HUDs that could be used in conjunction with these mented for the control effectors in all axes. The only control modes provided flightpath tracking/pursuit significant effect of control response type on control guidance for the decelerating approach and a mixed activity was observed to be a reduction in pitch control horizontal and vertical presentation for precision hover used with the longitudinal-acceleration command during and landing. the approach to hover in comparison to that used for the basic YAV-8B or the attitude command system. This Flying qualities were established for candidate control reduction is attributed to the absence of pitch maneu- modes and displays for the approach and vertical landing. vering to control deceleration to the hover lbr the Results of the pilots' evaluations indicated that satisfac- longitudinal-acceleration command. Similar results were tory flying qualities could be achieved for the decelerating observed for the translational-rate command system transition to hover with flightpath/longitudinal- during hover and vertical landing; thrust deflection rather acceleration command systems and for precision hover than pitch attitude was used to maneuver longitudinally. and vertical landing with translational-rate command Otherwise, only minor differences in control activity or systems. Attitude command systems and the basic none at all were experienced for the different response YAV-8B stability-augmentation system provided only types for pitch, roll, yaw, and thrust control for the adequate flying qualities during hover and landing various tasks. Borderline satisfactory/adequate flying because they did not compensate for poor vertical- qualities associated with bandwidth of the translational- velocity control. The basic YAV-8B also was considered rate control were established for the hover and landing to be just adequate lbr the transition because of poor task for longitudinal and lateral position and for height

82 control.Thesebandwidthswere0.33,0.25,and 5. Merrick, V. K.: A Translational Velocity Command 0.6rad/sec,respectively. System for VTOL Low-Speed Flight. NASA TM-84215, Mar. 1982. Theuseofathrottle-mountedthumbwheelforflightpath controlin theapproachandforvertical-velocitycontrol 6. Franklin, J. A.; Stortz, M. W.; Engelland, S. A.; inthehoverwasasignificantlimitationtothepilotsand Hardy, G. H.; and Martin, J. L.: Moving Base hadanadverseeffectontheirratings.Furthermore,the Simulation Evaluation of Control System useofastick-mountedproportionalthumbcontroller Concepts and Design Criteria lor STOVL fortranslational-ratecommandinhoverwasnotideal. Aircraft. NASA TM-103843, June 1991. Prominentsuggestionsfordesignmodificationswere tousethethrottlcforflightpathandvertical-velocity 7. Chung, W. W. Y.; Borchers, P. F.; and Franklin, command;tousethecentersticklortranslational-rate J. A.: Moving Base Simulation of an ASTOVL Lift Fan Aircraft. NASA TM-110365, command;toallowflightpathcontroltoblendinanatural fashionasspeeddecaysfrompitchattitudetothrustas Sept. 1995. theprimarycontroller;toreducehysteresisinthethrust- 8. Franklin, J. A.; Stortz, M. W.; Gerdes, R. M.; Hardy, deflection-controleffectorstoaminimum;toimprove Gordon H.; Martin, James L.; and Engelland, directionalcontrolduringtransitionwithahigher Shawn A.: Simulation Evaluation of Transition authorityyaw-augmentationsystem;andtoswitchboth and Hover Flying Qualities of the E-7A STOVL controlanddisplaymodesfromapproachtohover Aircraft. NASA TM-101015, Aug. 1988. simultaneously. 9. Merrick, V. K.; Farris, G. G.; and Vanags, A.: A Head Up Display for Application to V/STOL References Aircraft Approach and Landing. NASA TM- 102216, Jan. 1990. 1. Foster, J. D.; Moralez, E.; Franklin, J. A.; and Schroeder, J. A.: Integrated Control and Display 10. Merrick, V. K: Some VTOL Head-Up Display Research for Transition and Vertical Flight on Drive-Law Problems and Solutions. NASA the NASA V/STOL Research Aircraft (VSRA). TM- 104027, Nov. 1993. NASA TM- 100029, Oct. 1987. 11. Dorr, D. W.; Moralez, E.; and Merrick, V. K.: 2. Moralez, E.; Merrick, V. K.; and Schroeder, J. A.: Simulation and Flight Test Evaluation of Head- Simulation Evaluation of an Advanced Control Up-Display Guidance lor Harrier Approach Concept for a V/STOL Aircraft. Journal of Transitions. AIAA Paper 92-4233, Aug. 1992. Guidance, Control, and Dynamics, vol. 12, 12. Merrick, V. K. and Jeske, J. A.: Flightpath Synthesis no. 3, May-June 1989, pp. 334-341. and HUD Scaling for V/STOL Terminal Area 3. Farris, G. G.; Merrick, V. K.; and Gerdes, R. M.: Operations. NASA TM- 110348, Apr. 1995. Simulation Evaluation of Flight Controls and 13. Cooper, G. E.; and Harper, R. P., Jr.: The Use ot" Pilot Display Concepts for VTOL Shipboard Rating in the Evaluation of Aircraft Handling Operations. AIAA Paper 83-2173, Aug. 1983. Qualities. NASA TN D-5153, Apr. 1969.

4. Merrick, V. K.: Simulation Evaluation of Two VTOL 14. Tischler, Mark B.: System Identification Methods Control/Display Systems in IMC Approach for Aircraft Flight Control Development and and Shipboard Landing. NASA TM-85996, Validation. NASA TM-! 10369, Oct. 1995. Dec. 1984.

83 Appendix the coupling gain to the ailerons. Proportional-plus- integral compensation was adjusted through the time Control Laws constant x_, similar to that for the pitch control. No VSRA control laws underwent extensive development in frequency sweeps were performed for the roll-attitude ground-based simulation followed by further refinement control system. The basic YAV-8B SAS (Configura- during the VSRA flight program. The final version of the tion 1) consisted simply of roll-rate feedback. pitch, roll, yaw, longitudinal-, lateral-, and vertical-axis Lateral-velocity control laws are shown in figure A-4. control laws that were flown on the VSRA during the Command inputs came through the lateral proportional flying qualities evaluation program is described in the thumb controller. Gain KVy c set the control sensitivity, following paragraphs. and gain KVy provided the desired control bandwidth and Frequency response characteristics of some of the associated roll response to the pilot's velocity command baseline control modes that were obtained during the inputs. The forward-loop gain Klgy coupled the velocity flight test program are noted in this discussion. These command to the roll-control laws. The lateral-velocity data were obtained from frequency sweeps generated by frequency response from frequency sweeps with the the pilot for the control axes and flight conditions of lateral proportional thumb controller for hover are shown interest and analyzed using the frequency response in figure A-5. The bandwidth for lateral-position control method described in reference 14. They are the basis for is based on the frequency for a 45-deg phase margin for definition of control bandwidth for the baseline control position response, which is equivalent to the frequency modes. Variations in bandwidth for the translational-rate for a 45-deg phase lag for lateral velocity. The position- command modes that were made around the baseline control bandwidth noted on figure A-5 is 0.29 rad/sec; for configurations were documented using the nonlinear lateral-velocity control the bandwidth for a 45-deg phase simulation model of the VSRA aircraft and system. margin is seen to be 0.73 rad/sec.

Pitch Control- For pitch control in transition or hover, Yaw Control- Yaw-control modes provided yaw an attitude-command/attitude-hold response type was damping during transition (fig. A-6(a)) and switched to implemented, as shown in figure A-1. The pilot's inputs yaw-rate command at low speed and in hover (fig. A-6(b)) were through the control stick and trim switch. Gain K0C for Configurations 2, 3, and 4. In transition, lead-lag established control sensitivity, while K0 and K0 deter- filtered lateral acceleration and washed-out yaw-rate mined system bandwidth and phase margin. Gain KI go feedbacks along with lateral-stick-position cross feed was the coupling gain to the stabilizer and was scheduled were used to improve turn coordination and Dutch roll in proportion to dynamic pressure. Scheduled cross feeds damping. In the hover control mode, yaw-rate feedback from engine rpm and nozzle position were used to reduce alone was used for yaw-rate command. No frequency the associated trim changes. The positive feedback of response data were obtained for the yaw control. servo command through the first-order filter was equiva- Longitudinal-Acceleration and Velocity Control- lent to proportional-plus-integral l_ed-forward compensa- The longitudinal-acceleration control is shown in tion, and their relative proportion was established by the figure A-7(a). During transition between forward flight first-order filter time constant x0. System gains and time and hover, the pilot commanded longitudinal acceleration constants are listed on the figure. In figure A-2, the pitch- using a thumbwheel on the control stick for Configura- attitude frequency response from frequency sweeps with tions 1, 2, and 3. For Configuration 4, the input came the longitudinal stick at 120 knots indicates a bandwidth from the thumbwheel on the throttle handle. Complemen- for attitude control of 3.8 rad/sec for a 45-deg phase tary filtered calibrated airspeed feedback was used for margin. The basic YAV-8B SAS (Configuration I) speeds in excess of 80 knots; longitudinal inertial velocity consisted simply of pitch-rate feedback. was fed back at lower speeds. Gain KVx c set control Roll- and Lateral-Velocity Control- Roll control modes sensitivity, and the feedback gain K205 determined phase are presented in figure A-3; both rate-command/attitude- margin. The forward-loop gain K lgx determined the hold (fig. A-3(a)) and attitude-command/attitude-hold bandwidth and coupled the acceleration command to the (fig. A-3(b)) response types were available. The control nozzle control. stick and trim switch provided the pilot's inputs. Gain For precision hover (fig. A-7(b)), the thumbwheel was K0C established control sensitivity for attitude command switched out and the proportional thumb controller mode; gain K_hol d served the same purpose for the rate provided longitudinal-velocity commands. In this mode, command mode; and gain K_ was used to adjust over- the stick was disconnected from the pitch-attitude com- shoot in roll response. Gains _ and K_ determined mand system. Although most of the hover maneuvering system bandwidth and phase margin, and gain Klg_ was

84 loop gain I PITCH ATTITUDE CONTROLLER

DFD1.3.2.5.5.C

_] Pitch Parallel Servo longitudinal Command trim switch [-0.5585, 1.1170 Note B (fwd, ctr, aft) ( fwd, ctr, all ) +--1.49 TcmdorTRC engaged

Pitch longitudinal Series + + stick Servo (in) 0.05 in 2 in/s +1.5 ° Command (deg)

longitudinal stick trim servo position (in) SeT (0)- 0xfee d (0)

exfeed

Note A - loop is opened and past values o! digital low-pass filter are frozen N F when series servo command exceeds +- 1.49 deg (%)

Note B - corresponding pitch attitude trim range : [ -8 °, 16 ° ]

TRC - Translational Rate Command

GAIN VALUES -- -- LEGEND fl : dynamic pressure gain f2 :FIPM crossfeed f3 : engine nozzle crossfeed K043 = 2.5 K 0 = 4.0 1/S^2 A - denotes integrator balancing K146 = 1.0 _1.5 Ke = 4.0 1Is " - denotes Schmidtt trigger balancing K158 =2.0 "_3.0 K_trim = O. 1396 in/s g (0) - value of g at moment of engagement .0 K175 = 0.5 0.5 K_old = 0.279 rad/in-s [] - multiplier _1 0 •3 o{0.O I 201 ' I ' I I I 1:TS = 0.1 S . i i i i Kec = 0.56 rad-in/s^2 (_- pilot adjustable gain via "gain page" 50 60 70 80 90 100 0 10 20 40 60 80 lOO qbar (p_t) RPM (%) engine nozzle angle (deg) K_ =-1.5 deg/in 1:6 = 1.0 S (_ - signal transfer point

Kbe =-7.5 deg-s^2/rad

Figure A-1. Pitch-attitude command control law. oo L,h 6O

m lo

1D 0

p- 01 Ol =E -3O

-6O I I I I J I f I I I J I I I II

Attitude control "O bandwidth -200 ¢U p. a.

-4OO m_

1.0

.8--

O f- == .6 -- t- O o

• 4 --

.2 I 1 J I I .1 .2 2 4 6 8 10 Frequency, rad/sec

F/gure A-2 Frequency response for baseline attitude command; 120 knots.

86 I ROLL RATE CONTROLLER

DFD 1 3.2.5 5.F

lateral trim switch Off, ctr, rht)

[ I0%, 50% ] Roll Parallel Servo Command ± 1.99 (Ift ctr, rht) loop gain I Roll :_ Series Servo Command (deg)

LEGEND

K147 = 1.0 " - denotes integrator balancing K157 = 0.0 - - denotes Schmidtt trigger balancing K_ = 4.0 1/s K158 = 2.0 g (0) - value of g at moment of engagement Note A - loop is opened and past values of digital low-pass filter are frozen _K6:old= 2.03.73 rad/in-s^3deg,rm K159= 3.0 [] - multiplier when series servo command exceeds +_1.99 deg K_c = 0.6667 rad/in-s^2 "__ = 1.0 s (_ - pilot adjustable gain via "gain page"

Note 13 - corresponding roll attitude trim range + 30 ° 5_b = 0.45 in <_ - signal transfer point

Kig e = 3.75 deg-s^2Jrad

(a) Roll-rate command.

Figure A°3. Roll-axis control laws, 30 ",-4 3_

I I OLL ATTITUDE CONTROLLER i DFD 1,3.2,5.5.G

(rad)

[ 10%, 50% ] Roll lateral _ _ _ _ _ +-'_ 1 Parallel Servo Command (Ift,ctr, rht) t(ir_t?c_rWitrht)_ [ _ _ '_K158_s +,.1l_ -+1.g9 lateral stick _ / _o_0_ I - / trim bias I-'_b _ / Note A I loop gain l (,n) -- 1 I I lateral 6 + " I// _,:,^L_/[ + _ __+ __ - 1 Series ) _- ) Servo

_+2.0o (deg) [_L_--]l -T" _'-_" Command

lateral _pT 1 +(_t_ stick trim ,_- I -'Vl servo position (in) 6QT (0) GAIN VALUES" LEGEND

Note A - loop is opened and past values of digital low-pass filter are frozen KS = 4.0 1/sA2 K147= 1.0 "= - denotes integrator balancing when series servo command exceeds _+1.99 deg K_ =4.0 1/S K157 = 0.0 - - denotes Schmidtt trigger balancing g (0)- value of g at moment of engagement Note B - corresponding roll attitude trim range : _+30° K_trim = 0.2 in K158= 2.0 ¢_hold= 2.0 rad/in-s^3 K176 = 0.5 [] - multiplier K6@ = 3.73 deg_n z$ = 1.0 s Kn(_ _pilot adjustable gain via "gain page" K$c = 0.56 rad/in-s^2 tTS= 0.1 s <_ - signal transfer point 6eb = 0.45 in

Kig¢_ = 3.75 deg-sA2/rad

(b) Roll-attitude command.

Figure A-3. Concluded. I LATERAL VELOCITY CONTROLLER

DFD 1.3.2.5 5.H

lateral

( Ift, ctr, rht )

+ trim switch /

Roll Parallel Servo [ 10[_._, 50%_ Command (Ift, ctr, rht) _+1.99 Vy(O)_

loop gain loop gain | Note A I Roll lateral Series proportional ! Servo thumb 8y ° Command controller VI I L':"_I4- -I-dl (%) 5% 50%/s +_100% ± 2.0 ff/SA2 ± 2.0 ° (deg)

lateral _t_T stick trim servo position (in) _T (0) GAIN VALUES LEGEND K147 = 1.0 K_ = 4.0 1/s^2 A - denotes integrator balancing Note A - loop is opened and past values of digital low-pass filter are frozen K157 =0.0 when series servo command exceeds + 1.99 deg K(_ = 4.0 1/s v - denotes Schmidtt trigger balancing K158 = 2.0 KS_) = 3.73 deg/in g (0) - value of g at moment of engagement K177 = 0.5 KVy = 0.5833 1/s [] - multiplier

"Cy =0.8 s KVy c = 22.0 ftJ%-s^2 (_)- pilot adjustable gain via "gain page" Vy =3.0 s Klgy = 0.269 rad/ft <_ - signal transfer point "c_ = 1.0 s Kig(_ = 3.75 deg-s^2/rad

Figure A-4. Lateral-velocity command control law. 40

m 20 "O d "0

-2O I I I I I I I f I I

bandwidth -IO0 Position cont---_ol O_

"lO Velocity control ¢) (U J_ D. -2OO

bandwidth ___._

-30O 1 L L J L [

1.0

0 U e.- 0 .6 e- o o

.2 I I 1 I I I I I I I .1 .2 .4 .6 .8 2 4 Frequency, rad/sec

Figure A-5. Frequency response for baseline lateral translational-rate command in hover.

9O ay _,0.25s+1 (if/s^2) L0.125s+1 I YAW DAMPER

DFD 1.3.2,5.5.1

Series (ra_s)_ _" _ ServoYaw Command -+5.0 ° (deg) lateral LEGEND stick " - denotes integrator balancing (in) " - denotes Schmidtt trigger balancing GAIN VALUES g (0) - value of g at moment of engagement K r = 0.669 s K017 = 1.5 [] - multiplier = 0.83 deg-s^2/ft - pilot adjustable gain via "gain page" KRYy = 3.05 deg/in O - signal transfer point

(a) Yaw damper.

Figure A-6. Yaw-axis control laws. I YAW RATE CONTROLLER i r- -- -loop gain -- -] DFD1.3.25.5.K

I Yaw rudder _ Servo pedal _ Series Command (in) + 5.00 (deg) 0.20in _+1.75 in

GAIN VALUES LEGEND fl : dynamic pressure gain A - denotes integrator balancing K_ = 2.0 1/s K062= 1.0 _" - denotes Schmidtt trigger balancing K_C = 0.2618 rad/in-s K065 = 2.0 g (0)- value of g at moment of engagement Kig _ 10.0 deg-s^2/rad r_ - multiplier

00 i = ' J , i i i i - pilot adjustable gain via "gain page" 0 50 100 ¢[bar (psf) O - signal transfer point

(b) Yaw-rate command.

Figure A-6. Concluded. i LONGITUDINAL ACCELERATION CONTROLLER II | Vcast" -T i OF_,32_sN (kt) / _ ! NoteC _ 1 kt IA [80, 00] iVcas< 80 kt

Nozzle Parallel )- Servo (if/s) Command (deg) Control System Configuration 4 throttle ,,& I - _ .... +,_n_.,'_ I I°°pgain, Nozzle thumbwheel(%)5ttw"_liI _ _ _ I ' _''_''_ - ...... I I _'_'_I + Series ) Servo thumbwheelo tw ! J[_____.J-_l'_/ _ _ __,,_ i V__.._xc -'_ + +4- Command ( Vo ) Note A 5 % 50 %/s _.+100 % nozzle 5- _ I I I + 5.0 ° (deg)

Pearrval/e. ''par -Y" _ II

position 8n(n0_)r' J 1.0 (0_ ;',=LJ. ,I----_ I (deg) Note B I

Note A - In Configuration 4, only the nozzle loop is closed in the propulsion system. 1 Pilot uses throttle to control flight path, and throttle thumbwheel to control acceleration. © Note B - "easy-on" function to blend in the series servo command upon engagement of the control system NSSCA Note D Note C - to minimize transients due to airspeed / groundspeed hysteresis, reset past value of speed-hold integrator to ( V L + V e ) LEGEND Note D - the nozzle series servo command from the longitudinal acceleration controller is stored in GAIN VALUES global memory and used by the longitudinal velocity controller to minimize transients A denotes integrator balancing K_/xc= 10.0 ftJ%-SA2 K071 = 0.7 in the transition between the two controllers KIg x = -1.0 deg-s^2/ft K201 = 1.0 v denotes Schmidtt trigger balancing 1;cf = 4.0 s K202 = 2.0 Airspeed Complementary Filter g (o) value of g at moment of engagement "_b = 1.0 s K205 = 3.0 [] multiplier

Vca^ s = _ 1( Vcas + 1_d" vx-_kt ) pilot adjustable gain via "gain page"

signal transfer point

(a) Acceleration command.

Figure A- 7. Longitudinal-axis control laws. 4_

J LONGITUDINAL VELOCITY CONTROLLER i

DFD 1.3.2.5.5.0

[40%,80% ] [2 °, 90 °] Nozzle (R/s) > Servo Vx _._ CommandParallel v#0)_ (deg)

loop gain longitudinal I _ I / Nozzle proportional ______'+ _ I _ i + +_ Series l • Servo controller -- Ill _ _ _ _ + I_C_L_J L _ I I_ I_ Command ( % ) 5 % 200 %/s _+100 % +16.89 *K202 ft/s I I (deg) nozzle 6n _ I I parallel par-'<(_ I thumb 6x---_1_-"_"_-11-'_7"_ -I-t _RA,_-_'-7_I_Vx,-.I'_'_I servo-----)_ 0_ >i i /r" _K'gxl-'_'_'_" _ i_ position 8n( ) J 1.0 (0) ----_1_ 1 J I par Note A ICNOZCMD NSSCA = 0.0 Note C Note A - "easy-on" function to blend in the series sel'vO command upon engagement of the control system (deg) _+._ Note B - the nozzle series servo command from the longitudinal acceleration controller is stored in global memory and used by the longitudinal velocity controller to minimize transients NSSCA in the transition between the two controllers Note B Note C - one-shot switch ICNOZCMD is momentarily closed at instant the longitudinal velocity controller is engaged; also, the nozzle sedes servo command from the longitudinal GAIN VALUES LEGEND acceleration controller, NSSCA, is set to 0.0 to allow re-engagements of the longitudinal K082 = 0.75 A - denotes integrator balancing velocity controller KVXc = - 22.0 ft/%-s^2 KIg x = - 1.0 deg-s^2/ft K202 = 2.0 _" - denotes Schmidtt trigger balancing 1: =0.8s K205 = 3.0 x g (0) - value of g at moment of engagement _Vx = 3.0 s [] - multiplier

"Eb = 1.0 s Q- pilot adjustable gain via "gain page" 1: =2.0s wo _> - signal transfer point T.vxc=0.5714s

(b) Longitudinal-velocity command.

Figure A- 7. Concluded. was performed at a constant pitch attitude, attitude control showed a bandwidth for a 45-deg phase margin of changes could be made by using the trim switch. The 0.64 rad/sec. The bandwidth for vertical-velocity control functions of the control gains were similar to those for the was 3.6 rad/sec. acceleration command. As shown in the longitudinal- A height-rate damper, shown in figure A- 13, was velocity frequency response to the longitudinal propor- implemented as an alternative to the vertical-velocity tional thumb controller in figure A-8, the bandwidth for a command system and was the basis of Configuration 4. 45-deg phase margin ['or longitudinal-position control in This control law consisted simply of a command input hover was 0.36 rad/sec; for longitudinal-velocity control through the throttle handle along with vertical-velocity the bandwidth for a 45-deg phase margin was 1.1 rad/sec. feedback. It was designed to produce a bandwidth simihtr Flightpath and Vertical-Velocity Control - The to that of the vertical-velocity command. flightpath angle or vertical-velocity command originated with the throttle thumbwheel. This command input, in Head-Up Display Laws combination with the normal acceleration and vertical- velocity feedbacks, was the essence of the flightpath Drive laws for the flightpath symbol, horizontal-velocity control law for transition (fig. A-9). The velocity V x was predictor ball, and vertical-velocity diamond are described ground speed along track and was used to convert the in general in references 9-12+ Specific characteristics for pilot's flightpath-angle command to an equivalent these laws as currently used on the VSRA arc noted in the vertical-velocity command. For ground speeds below discussion that follows. 100 ft/sec, this velocity was frozen at the 100-ft/sec value As indicated in reference 9, the flightpath symbol was to convert the pilot's command from flightpath angle to quickened to compensate for lags in the airframe and vertical velocity as appropriate for hover and low-speed propulsion-system response. For Configurations 1,2, flight. The gain Ky determined control sensitivity, gain and 4, where thrust was controlled manually using the KVz, the phase margin, and gain Klg z, the system throttle, the flightpath compensation included lagged pitch bandwidth. Positive feedback of the lagged servo com- rate and washed-out throttle commands in combination mand provided proportional-plus-integral compensation with the true flightpath in accordance with the equation in the forward loop. The time constant x z was scheduled with engine rpm to provide first-order compensation for nqO the engine thrust lag. The flightpath frequency response t'q- S+(_ w to frequency sweeps with the throttle thumbwheel is presented in figure A- 10(a) tor the flight condition of a 3-deg descent at 80 knots. These data show a bandwidth for altitude control of 0.38 rad/sec for a 45-deg phase margin. L k Vtl )_,s+crw) I_VtlJ.J The bandwidth of flightpath control was obtained from a where frequency response plot of the integral of normal acceleration, shown in figure A-10(b). The integral of normal o w = Zwhove r + Vaf Z' w + Zwdamper acceleration was used instead of flightpath response since Zwhover = 0.02 sec -1 it showed higher coherence with respect to the control input at frequencies defining flightpath bandwidth. From Z'w = 0.00164 rad/ft this figure, the flightpath bandwidth is 1.6 tad/see. Zwdamper = 0.77 sec -1 The hover vertical-velocity control law, shown in figure A- 11, had a similar form to that for flightpath Kq = 0.25 ft/sec/deg control, with the addition of altitude feedback to provide a K8 T = ASTsin 0j/Ow height-hold function in hover. The reference altitude h H AST = 1.09 ft/sec2/deg was synchronized with the measured radar altitude until the pilot's vertical-velocity command was centered and the vertical velocity was less than I ft/sec, at which time The pitch-rate term was blended out tbr speeds below the reference altitude was held at its past value. Also, for 55 knots and the ground speed was frozen at 100 ft/scc this condition, the vertical-velocity feedback and com- for speeds less than 100 ft/sec. For Configuration 3, the mand gains were doubled to increase bandwidth ['or the flightpath was complemented with its commanded value attitude-hold loop. Control sensitivity was established by in the short term according to the gain KVzc- The vertical-velocity frequency response t'or frequency sweeps with the thumbwheel controller in hover is presented in figure A-12. Vertical-position

95 4O

m 20 'ID

'10

m _ 0

-2O

Position control bandwidth Velocity control -1 O0 bandwidth

"0 =; U) -200 a.

-3OO I I I I Ilif I J J I J ill

1.0

8 --

¢t

=e 6-- t- o ¢J

•4 --

.2 I I I I ItJl J I I I I III I I I .01 .02 04 06 08 1 .2 .4 .6 .8 2 4 5 Frequency, rad/sec

Figure A-8. Frequency response for baseline longitudinal translational-rate command in hover.

96 r loop gain ------I LIGHT PATH CONTROLLER i

DFD 1 3.2.5 5.Q

(ft/s^2) IIii (NF _, Vz " __, [ 40%, 80% ] [ 20 °, 75 ° ] Throttle Parallel • Servo Command (deg) (fVs) I_:LI ++_KZOO;z[ ...... s+_ < | i i i _e_____ 74.9______...... (ft/s) _ _ ] _ Note All + 4.99 ° Throttle Series • Servo throttle 6ttw -_'--7_H- RA.TE-_--"__ K Vz _" Command thumbwheel throttle (deg) (%) 5% 50%/s ±100% Note C parallel servo 6tpat position Note A - loop is opened and past values of digital low-pass filter are frozen (deg) 1.0 (0) when series servo command exceeds ± 4.99 deg or parallel servo Note B command exceeds 74.9 deg Note B - "easy-on" function to blend in the series servo command upon engagement of the control system > Note C - use the throttle clutch position as measure of the throttle parallel servo position TSSCA Note D - the throttle series servo command from the flight path controller is stored in global Note D memory and used by the vertical velocity controller to minimize transients in the transition between the two controllers GAIN VALUES LEGEND fl : engine time constant f2 : throttle gearing K091 = 0.1 Kvz = 0.88 1/s A - denotes integrator balancing Ky = 0.11 rad/% K136 = 1.0 "," - denotes Schmidtt trigger balancing ¢ 60 10 K206 = 1.0 Ktg z = - 30 %-s^2/ft g (0) - value of g at moment of engagement 05 eo 40 l_vz = 0.0796 s K207 = 1.0 [] - multiplier "5 0.0 ' ' ' i_ ' ' ' I ' ' _ I _- 20, , , ' I 1:b = 1.0 s Q- pilot adjustable gain via "gain page" 0 40 80 120 0 40 80 120 RPM (%) RPM(%) "r,NF = 5.0 s <_ - signal transfer point

Figure A-9. Flightpath command control law.

..4 2O

"0 =1

C 0"} ¢U

-10

-20 [ 1 ] 1 J I I

Altitude control bandwidth -5O

4) '10 -100 (n J= a.

-150

-2O0

1.0

tO e- ¢1)

t- O o

.2 I I i I I I I J .1 .2 .4 .6 .8 1 2 Frequency, rad/sec

(a) Flightpath response.

Figure A- 10. Frequency response basefine flightpath command system; 80 knots.

98 4O

m 20 "0

=_ 0

I I I I [ I I I I l -20

-5O

"tO -1 O0 Flightpath control t- bandwidth O.

-150

] L J _.t__.L___L_J.__L -200

1.0

¢J e--

t- 0 0

I I I I I I t I I I .2 .1 .2 .4 .6 .8 2 4 Frequency, rad/sec

(b) Integral of normal acceleration response.

Figure A- 10. Concluded.

99 loop gain ------VERTICAL VELOCITY CONTROLLER j

DFD 1.3.2.5.5.R (ftJs^2)

[40%,80%] [ 20 °, 75 ° ] Throttle Parallel Servo Command (deg)

74.9 °

± 4.99 ° Note A Throttle Series Servo throttle 5ttw 4- Command thumbwheel throttle ± 5.0 ° (deg) (%) 5% 50 °/Js ±100% Note C parallel servo 6tpar ^ position 5ttw (deg) 1.0, Note B Note A - loop is opened and past values of digital Iow-pes_ filler are frozen when series servo command exceeds + 4.99 deg or parallel servo command exceeds 74.9 deg ICTHRCMD Note B - "easy-on"function to blend inthe series senre command upon engagement TSSCA = 0.0 of the control system Note C - use the throttle dutch Apo_lJonas measure of the throttle parallel servo position Note F Note O- a_itu(_ hotd _c: if( E,ttw-- O.O .AND. tVzl < 1.0"K238 ) then antivate switch Note E- the throttle sedes sei'vo command from the flight pllth controlef is stored in global memory and used by the vertical velocity controller to minimize transients in the transition between the two controllers TSSCA Note F - one-shot switch ICTHRCMD is momentarily closed at instant the vertical velocity Note E controller is engaged; also, the throttle series servo command from the flight Path controller. TSSCA, is set to 0.0 to allow re-engagements of the velltcal w,doctty ¢or_ro_ler GAIN VALUES LEGEND

A - denotes integrator balancing ft :engine time constant f2 : throttle _leadng v - denotes Schmidtt trigger balancing KVZc= 10.0 fl-%/s K091 = 0.1 Kig z = - 30 %-s^2/ff K136 = 1.0 g (0) - value of g at moment of engagement 1;_,z = 0.0796 s K206 = 1.0 [] - multiplier 4O "_b = 1.0 s K207 = 1.0 05 (_- pilot adjustable gain via 'gain page" 20 ', _NF = 5.0 S K23_ = 1.0 <_ - signal transfer paint 0 40 80 120 0 40 80 120 RPM (%) RPM (%) "['wo = 2.0 s

Figure A-11, Vertical-velocity command control law. 20

& = 0 C ---..,.

-10

I I I L. I I I I I L -2O

-50of____/__ bandwidth Position control "0 -100

t-- n °I Velocity control bandwidth -150

I L 1111 I I -200 ...... L...... _ ..... [

1.0

¢- 0

.4--

I .2 I I I I I I I I I .1 .2 .4 .6 .8 Frequency, rad/sec

Figure A- 12. Frequency response for baseline vertical-velocity command in hover.

101 VERTICAL DAMPER (f_s) Vz DFD 13255 P

Throttle

+ _-I Servo _] Series (deg) + Command •ro, ,e t + 5.0 ° (deg) st(o)

1.0 (0) Note A

Note A - "easy-on" function to blend in the throttle series servo GAIN VALUES LEGEND command upon engagement of the control system KVz = 10 deg-s/ft K170 = 10 A - denotes integrator balancing

Kst = 10 deg/deg K178 = 1.85 _" - denotes Schmidtt trigger balancing

g (0) - value of g at moment of engagement [] - multiplier (_- pilot adjustable gain via "gain page"

<_ * signal transfer point

Figure A- 13 Height-rate damper control law T 6 = 10see

K0c = 0.247 Yq :573I,an'IKhcVtl _s+my )) '/--h_ Vtl )J K_c = 1.287 where the gain Khc = 1.1 and the washout frequency D. o = 1.75 tad/see my =0.44 sec -1. " D x = 1.38 rad/sec During the latter stages of the deceleration as the aircraft approached the intended point of hover, selective changes Dy = 4.23 rad/sec were made to the approach display to provide guidance for the hover-point capture. Specifically, the longitudinal- For Configurations 3 and 4, the commanded horizontal velocity vector, predicted longitudinal velocity, and velocities from the proportional thumb controller were station-keeping cross appeared referenced to the vertical- displayed directly. velocity diamond symbol, as shown in figure 4(a). The drive law [or predicted longitudinal velocity is shown in The vertical-velocity diamond's displacement, two, was the following discussion of the hover display. proportional to complemented vertical speed. For Con- figurations 1 and 2, vertical velocity is complemented For the vertical landing, drive laws for the horizontal- with vertical acceleration so that velocity predictor ball and vertical-velocity diamond included compensation for aircraft and propulsion-system lags. In this case, for Configurations I and 2, true hori- twc =Kw h + KST_STT6 '------2_ T6s+I s+C_ w zontal velocities were complemented with translational accelerations and washed-out control commands where according to the relationships: Kw = 0.2 deg/ft/sec

s+l/T6 '0x- g(0+ 0J T 6 = 10 sec

KST = 1.45 ft/sec2/deg

_w = 0.02 sec -I -K0c (S+_ul(S+Dx)

When translational-rate command or the height damper were engaged, vertical velocity was complemented with T_, washed-out vertical-velocity command from the thumb- Vy c = Vy + s+l/T 6 wheel or throttle, so that

tWo = K w li + c +KOc I (S+Ov)(S+s(s + 4..Qo)Dy ) l_la t where and my = 0.44 sec -I . A horizontal bar indicated the altitude remaining to touchdown. Attitude, air velocity. _u = 0.05 sec -1 engine rpm, thrust vector angle, heading, vertical-velocity _v = 0.05 sec -1 limits, and wind direction were provided as situation information. T o = 2

103 Table2.Handlingquality,ratingsandcomments

Config Pilot Dates/Runs Segment HQR Comments

1 PilotA 2/2/95 Approach 4 Pitch control is highest workload. Hobaugh 50602,05.10 50702 Hover acquisition 4 Pitch reference is lacking. 213195 50902 Vertical landing 3 Can maintain position and descent rate. 51104 PilotC 5/3/95 Hover acquisition Would expect high workload to acquire and hold hoxer point. O'Donoghue55302,04 5/4/95 Vertical landing -5-6 Due to high workload for height control. 55509 55602 PilotD 6/21/95 Approach 4 Control of attitude is smooth, but requires effort to stabilize. Heave response at nozzle drop is significant Stortz 56209 and requires attention and effort to compensate. Abrupt lift loss at lower speeds requires significant 56401 compensatory input with the throttle. None of these characteristics is conducive to a decelerating 6129195 approach in IMC. Yaw is easily excited during approach, especially in turbulence. 55701-05 9/5/95 Hover acquisition 5 High workload associated v, ith large attitude change for hover acquisition in combination with height 58202,03 control. More comfortable to do it with visual references than HUD guidance.

Vertical landing 5 Height control difficult. Vertical velocity wanders following initial input. Get better height control with visual cues. Heading wanders. PilotE 9115195 Approach 4 Deceleration is comlortable--profile not too aggressive. Pitch control is principal contributor to Hardy 58603.04 workload--large trim changes and pitch control of deceleration. 9119195 59201-04 Hover acquisition 4.5 Final deceleration guidance fairly easy to use. but close attention required to avoid under- or 59303 overshooting station-keeping point.

Vertical landing 4 Workload maintaining altitude during translation to landing pad and maintaining control of sink rate during descent is fairly high. Vertical-velocity caret gets lost in hover display. Attitude control smooth. A 2/1/95 Approach 3 Easy to stabilize speed. Difficult to make small pitch changes in presence of trim followup. 50503.04,09 2/2/95 Hover acquisition 3 Used nozzle for large adjustments, pitch attitude for small corrections to longitudinal speed and position. 50603,06,08,11 50703,07,08 Vertical landing 4 Stick trim followup annoying--fights pilot's inputs. Roll axis too sensitive. 50802,03 2/3195 Slow landing Improvement over AV-8B due to pitch decoupling from thrust control. 50904,06,07 51004 51105,08 Table2.Continued

Config Pilot Dates/Runs Segment HQR Comments PilotB 2/9/95 Approach 3 Like perspective on ghost, flashing cues. Clear improvement in stablity from Configuration I. Mlnarik 51401-03 51501,06 Hover acquisition 4 Moderate compensation for desired performance. Directional stability goes away at abot, l 30 kts. Nose 51601,03 wanders. Difficult to control ho'_ er symbology to station-keeping point. Clutter objectionable.

Vertical landing 5 Drifted off touchdown point outside 5-fl circle. Looking outside for cues. Still on learning curve. Liked allowable-sink-rate bar. Easy to switch from approach to hover.

Slow landing Easy to control to ghost aircraft. More stable than AV-SB. Stick forces high. C 5/4195 Approach Definite improvement over basic YAV-SB SAS. Easy to fly approach. Almost an open-loop task. Nozzle 55402-07 drop cues were clear and unambiguous. Control of deceleration straightforward and predictable. Some 55502-06,08 annoying pitch trim offloads. Roll response nice. Consistently achieved desired performance. Liked 5/9/95 throttle for flightpath control. 55901-04 Hover acquisition 4 Achieved desired performance for position and altitude control. Workload higher for height control. Height control with throttle is biggest difficulty. Tight throttle control required with frequent inputs IO control height. Pitch-attitude changes led to throttle adjustments to hold height. Control to initial hover easy. Control of deceleration not difficult, although frequent stick inputs required. Liked having velocity vector and predictor ball come on at 25 knots instead of 20.

Vertical landing 5 Desired to adequate perlbrmance with medium to high workload. Height excursions during translation to landing point with frequent throttle inputs required to hold target height. Height control difficulty like that with AV-SA. Control of horizontal position required small stick inputs to maintain desired precision. Controlled velocity vector directly instead of using predictor ball. Coordination of control inputs drove workload up. D 6/27195 Approach 4 Similar difficulties to basic YAV-8B for flightpath control. Pitch-control forces feel nonlinear because of 56901-05 way trim comes in to offload the series servo. Objectionable yaw excursions. 57001-04 6/28/95 Hover acquisition 5 Fighting pitch trim to control to hover point. 57201-06 57301-04 Vertical landing 5 Height control difficult as for basic YAV-8B. Roll response seems poorly damped. When series servo 6/29/95 limits, roll response more abrupt--acceleration type. 57502 Table2.Continued

Config Pilot Dates/Runs Segment HQR Comments

2 E 9/19/95 Approach 4 Pitch-attitude hold helps attitude control during deceleration. 59301,02 9/20/95 Hover acquisition 4.5 Final deceleration guidance fairly easy to use but close attention required to avoid under- or overshoot- 59601-05 ing station-keeping point. Like the attitude command force gradient to help gage the final deceleration. 59701,02 Vertical landing Workload maintaining altitude during translation to landing pad and maintaining control of sink rate during descent is fairly high. Vertical-velocity caret gets lost in hover display,. Attitude control smooth. Attitude hold helps, but roll response is nonlinearivery solid at first, then takes off. A 2/1/95 Approach 3/2 Rating depends on tight vs. loose control of ghost. Might like actual flightpath shown along with 50505-08 quickened flightpath. Quickening not perfect. Easy to track ghost. Hands off much of the time. 2/2/95 Sometimes requires many small inputs. 50604,07,09,12 50704,05,06,Hover acquisition Only a few thumbwheel inputs required to capture hover point and altitude. 09,10 50804,05 Vertical landing Jerky longitudinal response. Smooth lateral response. Some lag apparent during tight longitudinal- 2/3/95 position control. Love translational-rate command. Sink-rate response lags thumbwheel. Significant 50905.08,09 workload reduction. 51002,03 51106,10 Slow landing Flightpath lag noticeable. Easy to set speed and flightpath, a task that is difficult in AV-8B. Good system for austere site operationsinarrow roads. 2/9/95 Approach 4 Oscillatory tracking of ghost early in approach--fed by nozzle hysteresis. Can get performance with 51404.06,07 thumbwheel, but would prefer to use throttle. Would like to see actual flightpath along with quickened 51502-05 flightpath. 51602.04 Hover acquisition 3 Easy to perform task.

Vertical landing 3 Easy to perform task.

Slow landing Holds speed well. Easy to set flightpath. Would like to select speed as a function of ,xeight. Table2.Continued

Comments Config Pilot Dates/Runs Segment HQR 3 C 5/3/95 Approach 3 Stick thumbwheel too sensiuve for accelerauon control in speed range of 110-120 knots and breakout 55002-06 forces high: not sensitive enough at lower speeds. Throttle thumbwheel too sensitive fl_r flightpath 55101-08 control semi-jet-borne ( 110-120 knots). Sensitivity OK during latter stages of approach. Difficulty 55201-07 with flightpath control during initial approach--nozzle hysteresis excites flightpath excursions. Below 5/9/95 100 knots, flightpath and deceleration control have low workload with desired performance, 55702-09 55801-03 Hover acquisition 2 Establishment of initial hover easy to accomplish. Stick thumbwheel adequate for precise control of longitudinal position. Lateral positioning easily accomplished. Height control good--basically open loop, Vertical-velocity control precise with thumbwheel; height hold good with thumbwheel in detent. Height control is nearly open loop because of height hold. Desired performance achieved with minimal compensation. Too much mode switching required to get into hover mode. Switch control and display together. Prefer manual discrete switch to TRC, Can confuse use of two thumbwheels. Prefer to have thumbwheel on stick for longitudinal-acceleration control, with throttle controlling flightpath and vertical velocity.

Vertical landing 4 Proportional thumb controller too sensitive ( nitial sensitivity) and breakout was high. Prefer to use stick instead of proportional thumb controller for TRC. Lurching motion made precise horizontal positioning difficult. Residual longitudinal drift required compensatory inputs that increased workload. Moderate pilot compensation. Controlled velocity vector instead of predictor ball with proportional thumb controller. Still. TRC mode reduces workload and would be essentially open-loop control if drift were not present and sensitivities were more agreeable. Vertical-velocity control easily achieved and essentially open-loop control. Greatest contribution to workload reduction. Desired performance achieved, but continually controlling proportional thumb controller to hold hover position longitudinally and laterally during descent to touchdown--annoying deficiency,

Slow landing 2 Approach easy' to fly, Flightpath and speed control easy. 4 Control of landing requires pitch compensation to hold landing attitude in ground effect. Pitch series ser_o saturates and does not hold attitude for nose-down ground effect. Sink-rate control good.

.,,.-..1 o Oc:

Table ,.."_Continued

Config Pilot Dates/Runs Segment HQR Comments 3 D 6121195 Approach 4 Would like to initially engage system at normal pattern speed of 130 knots, 40 nozzles. Oscillatory 56201-08 flightpath and speed response when tracking path prior to deceleration is objectionable. Cannot get 56301-03,06- desired performance. Pitch-trim cycles chasing throttle and nozzle excursions. Difficult to use throttle 08 thumbwheel because not raised enough above throttle body and not enough friction. Thumbwheel also 6/22/95 too sensitive. Would like to control flightpath with attitude early in approach while wing lift is 56501-03 sufficient. Flightpath control during final stage of approach is good. Directional control weak. 56601,02 6127195 Hover acquisition 3 Easy to come to precise hover. Only objection is switching guidance and display from approach to hover. 56801-06 6129195 Vertical landing 3 Height control is easy and precise. Eliminates workload of throttle control. Aggressive longitudinal 57504,05 maneuvers with TRC causes disparity between predictor ball and velocity vector. Hover position 9/1/95 control precise---easy to stabilize over pad. TRC response is tight and crisp. Bank-angle excursions 58101-04 are reasonable and comfortable. Heading wanders. Rearward drift noticeable in ground effect (IGE). 9/11/95 58301-03 Slow landing 5 Did not have enough downward correction authority lk)r flightpath control. Flightpath response sluggish 58401,02 in flare. Lag of actual flightpath is noticeable. 9/18/95 59002-04 Vertical landing 5 Longitudinal TRC bandwidth = 0.18 rad/sec. Very sluggish, hard to predict where it will stop when 9/22/95 with proportional thumb controller is centered. 59801-03 bandwidth 4 Long TRC bandwidth (BW) = 0.3 tad/see. Noticeably sluggish, but desired performance achieved. 59901,02 variations 5 Lateral TRC BW = 0.18 rad/sec. Sluggish. Steady velocity and bank angle OK. Poor predictability for 510001-03 closure on hover point. 9125195 5 Lateral TRC BW = 0.24 rad/sec. Initial response OK, but still too sluggish. 510101-04 5 Vertical-velocity command BW = 0.44 rad/sec. Noticeably sluggish. Marginal for height control. 510201-04 Borderline desircd performance lk)r shorebased landing; not desired performance for shipboard 510301-04 recovery. 4 Vertical-velocity command BW = 0.54 rad/sec. Still too sluggish. Table2.Continued

Config Pilot Dates/Runs Segment HQR Comments 3 E 3124195 Approach 4 Throttle/nozzle oscillations noted during initial stages of the approach near 120 knots. Once decelerauon 52901-08 begins, these oscillations go away. Did not factor them into rating. Pitch and yaw can be active in 9115195 turbulence. Hard to make small inputs with either thumbwheel, leading to overcontrol. Deceleration 58602,05 profile nice. Would be satisfactory with better inceptors. 58701-04 58805 Hover acquisition 3 Use acceleration command tape for final deceleration to determine when to center the thumbwheel for 9119195 hover. Leveling out before the hover helps separate the deceleration and height control. 59104-06 9/20/95 Vertical landing 3 Control of translation pretty nice, except response to the proportional thumb controller seems jerky 59502-07 unless the inputs are smooth. Station keeping is excellent, holding position and altitude hands off for 9/28/95 extended times. Height control very easy: just set a sink rate and forget it. The landing task alone 510901,02 would be HQR 2. 511001-04 511301-05 Vertical landing 3 Longitudinal TRC bandwidth = 0.3 radlsec. Smoother than baseline configuration with just a little looser 511401-03 with control. 511501-03 bandwidth 4 Longitudinal TRC BW = 0,18 rad/sec. Control of longitudinal position definitely too loose. variations 3 Lateral TRC BW = 0.18 rad/sec. Noticeably looser than baseline, but still satisfactory. 4 Lateral TRC BW = 0.12 rad/sec. Quite loose for lateral positioning. 3 Vertical-velocity command BW = 0.44 rad/sec. Similar response fl_r height control, Did not evaluate for touchdown. 5 Vertical-velocity command BW = 0.3 rad/sec. Control of altitude changes loose. Held altitude well during translations. During landing it acted like it could not get through ground effect. C 9127195 Approach 3 Tracking ghost on approach easy and predictable. Below 80 knots, large nozzle movements during 510601-04 deceleration require compensation with thrust to track the ghost. Corrections with acceleration 510701-04 command thumbwheel in close also require corrections with the throttle to hold height at the station- 510801-05 keeping point.

Hover acquisition 3 A little compensation required if the station-keeping point capture is aggressive. Transition from approach mode to hover mode very smooth and easy. Thumbwheel sensitivity OK. Need more deceleration authority on the thumbwheel. Consider a blend of the deceleration from 0.1 to 0.05g instead of the step change.

Vertical landing 2 Hover control almost open loop. Height control like vertical-velocity command. Proportional thumb controller mechanical characteristics seemed good. If very aggressive with proportional thumb controller during translation to the landing pad, some compensation required with the throttle. Difficult to command so much vertical velocity that throttle series servo would saturate, Table2.Concluded Config Pilot Dates/Runs Segment HQR Comments 4 D 9/26/95 Approach 3 Naturaltousethrottleforflightpathcontrol.Stick,throttle,thumbwheel,andappropriatecombinationof 510401-03 inceptors.Mechanicalcharacteristicsofthumbwheelneedwork--tooshroudedwithoutenoughof 510501-04 wheelexposedtothumb,breakout;sensitivitytoolow. Hoveracquisition4 Guidanceneedstobefixedforclosuretothestation-keepingpoint.Onelevelofdecelerationwould sufficetocarryintoinitialhoveratstation-keepingpoint.

Verticallanding 3 Translational-ratecommand is straightforward. Natural to do height control with throttle. Good height control.

9/28/95 Approach 5 Difficult to use thumbwheel for deceleration while using throttle for flightpath control. Likely a problem 511101-04 of ergonomics of the controller rather than doing two things with one hand. Tended to chase flightpath 511201-04 control at 120 knots. Quickening of flightpath symbol in response to throttle may be off for this configuration. Could improve to HQR 4 with improved quickening.

Hoveracquisition4 Difficult to hold the throttle while reaching the thumbwheel.

Verticallanding 3 Height control required a little eflort without altitude-hold feature, but still a big improvement on unaugmented height control. Vertical landing very easy and would warrant an HQR 2 by itself.

Form Approved REPORT DOCUMENTATION PAGE OUBNoo7o+o188

Public reporting burden for this collection of inlormation is eslimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any olher aspect of Ihis collection of information, including suggestions for reducing Ibis burden, to Washinglon Headquarters Services, Directorate for information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503. 1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE |3. REPORT TYPE AND DATES COVERED April 1996 I Technical Paper I 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS Flight Evaluation of Advanced Controls and Displays for Transition and Landing on the NASA V/STOL Systems Research Aircraft 505-68-33 6. AUTHOR(S) James A. Franklin, Michael W. Stortz, Paul F. Borchers, and Ernesto Moralez III

7. PERFORMINGORGANIZATIONNAME(S)AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER Ames Research Center Moffett Field, CA 94035- 1000 A-961333

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITORING AGENCY REPORT NUMBER

National Aeronautics and Space Administration Washington, DC 20546-0001 NASA TP-3607

11. SUPPLEMENTARY NOTES Point of Contact: James A. Franklin, Ames Research Center, MS 21 i-2, Moffett Field, CA 94035-1000 (415) 604-6004

,12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b, DISTRIBUTION CODE

Unclassified -- Unlimited Subject Category 02

13. ABSTRACT (Maximum 200 words) Flight experiments were conducted on Ames Research Center's V/STOL Systems Research Aircraft (VSRA) to assess the influence of advanced control modes and head-up displays (HUDs) on flying qualities for precision approach and landing operations. Evaluations were made for decelerating approaches to hover followed by a vertical landing and for slow landings for four control/ display mode combinations: the basic YAV-8B stability augmentation system; attitude command for pitch, roll, and yaw; flightpath/ acceleration command with translational rate command in the hover; and height-rate damping with translational-rate command. Head-up displays used in conjunction with these control modes provided flightpath tracking/pursuit guidance and deceleration commands for the decelerating approach and a mixed horizontal and vertical presentation for precision hover and landing. Flying qualities were established and control usage and bandwidth were documented for candidate control modes and displays for the approach and vertical landing. Minimally satisfactory bandwidths were determined for the translational-rate command system. Test pilot and engineer teams froln the Naval Air Warfare Center, the Boeing Military Airplane Group, Lockheed Martin, McDonnell Douglas Aerospace, Northrop Grumman, Rolls-Royce, and the British Defence Research Agency participated in the program along with NASA research pilots from the Ames and Lewis Research Centers. The results, in conjunction with related ground-based simulation data, indicate that the flightpath/longitudinal-acceleration command response type in conjunction with pursuit tracking and deceleration guidance on the HUD would be essential for operation to instrument minimums significantly lower than the minimums for the AV-8B. It would also be a superior mode for performing slow landings where precise control to an austere landing area such as a narrow road is demanded. The translational-rate command system would reduce pilot workload for demanding vertical landing tasks aboard ship and in confined land-based sites.

14. SUBJECT TERMS 15. NUMBER OF PAGES STOVE V/STOL, Flight/Propulsion control, Flying qualities, 114 16. PRICE CODE Approach and landing, Flight research A06

17, SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT Unclassified Unclassified

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Sld zag*le