Initial Flight Test of the Production Support Flight Control Computers at NASA Dryden Flight Research Center

NASA/TM- 1999-206581

Initial Flight Test of the Production

Support Flight Control Computers at

NASA Dryden Flight Research Center

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NASA/TM- 1999-206581

Initial Flight Test of the Production

Support Flight Control Computers at

NASA Dryden Flight Research Center

John Carter and Mark Stephenson Dryden Flight Research Center Edwards, California National Aeronautics and Space Administration Dryden Flight Research Center Edwards, California 93523-0273 August 1999

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INITIAL FLIGHT TEST OF THE PRODUCTION

SUPPORT FLIGHT CONTROL COMPUTERS AT

NASA DRYDEN FLIGHT RESEARCH CENTER

John Carter* and Mark Stephenson _ NASA Dryden Flight Research Center Edwards, California Abstract PSFCC production support flight control computers The NASA Dryden Flight Research Center has RFCS research flight control system completed the initial flight test of a modified set of F/A-18 flight control computers that gives the aircraft a Introduction research control law capability. The production support flight control computers (PSFCC) provide an increased Control law software development on aircraft capability for flight research in the control law, handling historically has been extremely expensive and time- qualities, and flight systems areas. The PSFCC feature a consuming because of the numerous staff hours devoted research flight control processor that is "piggybacked" to design, implementation, and test of flight-critical onto the baseline F/A-18 flight control system. This software. Large amounts of hours are required because research processor allows for pilot selection of research of the flight-critical nature of control law function.

control law operation in flight. To validate flight Extremely thorough testing is required because a control operation, a replication of a standard F/A- 18 control law law software malfunction could lead to a loss of aircraft, was programmed into the research processor and flight- property, or aircrew. Development of an easily tested over a limited envelope. This paper provides a modifiable flight control system capable of reverting to a brief description of the system, summarizes the initial baseline control system can address these issues.

flight test of the PSFCC, and describes future experiments for the PSFCC.

NASA has developed several aircraft for in-flight control law development. Aircraft such as the NT-33A Nomenclature Variable Stability Aircraft, the F-8 Digital Fly-By-Wire aircraft, and the General Purpose Airborne Simulator A/D analog to digital have been used for in-flight simulation and dynamics studies.I, 2 Private organizations that do research have D/A digital to analog developed aircraft such as the variable stability Learjet DDI digital display indicator and the F-16 Variable Stability In-Flight Simulator Test Aircraft (VISTA) that have research flight control FCF ftmctional check flight computer systems. These systems are designed to allow gravitational acceleration constant, g relatively fast control law modifications while safety of 32.2 ft/sec 2 flight is retained through the primary control system.

The systems have also been used to modify dynamic HARV High Alpha Research Vehicle characteristics in flight to simulate other airframes.

KCAS knots calibrated airspeed Engineers at NASA Dryden Flight Research Center NATOPS Naval Air Training and Operating (Edwards, California) have had recent experience with a Procedures Standardization system designed for rapid control law modification that operates the F/A-18 High Alpha Research Vehicle * Aerospace Engineer. E mall: john cartel@dfl'c.nasa.gov. (HARV) aircraft. 3' 4 The HARV is a modified F/A-18 ?Aerospace Engineer. E mail: markstephenson@dfi'c, nasa.gov.

aircraft with thrust-vectoring paddles that was designed Copyright © 1999 by the American Institute of Aeronautics and for flight test at high angles of attack. Flight control Astronautics, Inc. No copyright is asserted in the United States _mder computers of the HARV were modified to include a Title 17, U.S. Code. The U.S. Govemanent has a royalty fi'ee license to pilot-selectable research control law processor. This exercise all rights under the copyright claimed helein for Govemanen tal proposes. All other rights me _eservedby the copyright owner. system allowed the HARV to operate with conventional American Institute of Aeronautics and Astronautics F/A-18 control lawsfor all phases of flightandhave flight and controllers designed using modern and robust research control lawsavailable atspecified parts of the control theory.

flightenvelope. Reversion to theconventional control

This paper gives a brief description of the function of

laws was accomplished either manually or

the system, presents the results of the initial flight test, automatically withsystem failure orenvelope violation.

and describes the future experiments planned for the

TheHARVdesign provided a flexibleplatformfor

PSFCC. Anomalies encountered during ground and

control lawalgorithm research. Theabilityto restore

flight test are discussed.

aircraft control toasafe, proven system addressed many

of the safety-of-flight issues associated with

Use of trade names or names of manufacturers in this experimental control lawarchitectures.

document does not constitute an official endorsement of such products or manufacturers, either expressed or

Building ontheexperience gained fromtheF/A-18

implied, by the National Aeronautics and Space

HARV, the UnitedStates NavyandNASADryden

Administration.

workedin concertwith The Boeing Company

(St. Louis,Missouri) + andLockheed MartinControl

Production Support Flight Control

Systems (Binghamton, New York)todevelop a system

that could operate onany F/A-18 (model A tomodel D).

Computers Functional Description

This system is calledthe production support flight

control computers (PSFCC). 5 Several setsof F/A-18 The PSFCC design uses a research processor in addition to the baseline F/A-18 flight control computers.

computers have been modified intoPSFCC. The PSFCC

include production F/A-18 control processors, research A detailed description of the PSFCC implementation has been published. 5 The research flight control system

processors, software that controls the transition between

theprimary and research systems, and cockpit interface can be engaged by the pilot to exercise full-authority

softwarefor research mode selection. For this

control of the aircraft with research flight control laws.

demonstration, the research processors havebeen

For the initial flight test, only the F/A-18 replication

programmed witha replication of thestandard F/A-18

mode was flight-tested, which duplicated the basic control laws.

F/A-18 control laws in the research processor.

Todemonstrate theviabilityof thePSFCC concept, Figure 1 shows how the PSFCC are integrated into the an initial flight test phase has been conducted. This F/A-18 aircraft flight control system. The F/A-18 phase was performed in March-April 1998. Four flights aircraft is controlled by a quadruply redundant flight were accomplished. A standard U. S. Navy functional control computer system. Figure 2 shows the PSFCC check flight (FCF) has been conducted to validate that modification to the basic flight control computer. The normal F/A-18 operations are not affected, and research research PACE 1750A processor (Performance flights have demonstrated PSFCC engage/disengage Semiconductor Corporation, Sunnyvale, California) is operation in a envelope limited for flight safety embedded in the same avionics box as the basic 701E considerations. Flights to investigate handling qualities flight control processors (Lockheed Martin Control have been conducted in the F/A-18 replication mode to Systems, Binghamton, New York).

validate the performance of the research processor.

The research control laws are programmed in Ada and Several new experiments are being prepared for the are completely independent of the basic control laws.

PSFCC. The first to be flown will be an experiment This independence allows new research control laws to using an alternate pilot stick to control the F/A-18 be added without affecting the basic flight control aircraft to investigate handling qualities issues system. All information to and from the research associated with different pilot stick configurations. The processor is handled by the basic flight control system second experiment will involve using the PSFCC to through dual-port random access memory to facilitate produce data that will be used to refine the F/A-18 communication between the research system and the aerodynamics database. This database will be used for basic system. This separation also provides good fault an F/A-18 flexible wing program. Other proposed flight isolation of the research processor.

experiments include F/A-18 autonomous formation Figure 3 shows all the elements the pilot uses to interface with the PSFCC. Figure 3(a) shows the F/A-18 :t:FonneflyMcDonnell Douglas Aerospace, which merged with The displays, featuring the digital display indicators (DDIs) Boeing Company dining these tests.

American Institute of Aeronautics and Astronautics navigation I Inertial i.ir0a,a I [Hea0-up I.' ona,', system computer display U d sp ay

I I

Military specification Analog inputs Mission I 1553 multiplex bus computer Analog outputs

- Rate gyroscopes - Accelerometers _'_II Ill

' ,I N

- Roll stick

_--_111 flight controlcomputers I ', _1 I-Leading-edgeflapsl

- Pitch stick - Rudder pedals

I ' --II-Ailer°ns I

I I L I- Rudders J i - Airdata __ - Ang e of attack UI osew,ee, q steering 970726 Figure 1. The F/A-18 control system components.

__Base_ine F/A-18 central processing unit (701 E) )__ Surface Military actuator specification analog 1553 nputs interface ::::::::::::::::::: :::::::::::::::::::::::: :::::::::::::::::::::::: :_:::::::::::::::::::::::: ::::::::::::::::::: :::::::::::::::::::::::: :::::::::::::::::::::::: :::::::::::::::::::::::::: i_i_i_i_i_i_i _ _ Output iiiiiiiiiiiiiiiiiiiiiiiiii iiiiiiiii_:'-ii Input signal iiiiiiiiiiiiiiiiiiiiiiii Control iiiiiiiiiiiiiiiiiiiiiiii signal iiiiiiiiiiiiiiiiiiiiiiiiii Actuator iiiiiiiiiiiiiiiiiii _ _ _ signal iiiiiiiiiiiiiiiiiii management iiiiiiiiiiiiiiiiiiiiiiii laws iiiiiiiiiiiiiiiiiiiiiiii select and iiiiiiiiiiiiiiiiiiiiiiiiii management iiiiiiiii_ii iiiiiiiiiiiiiiiiiiiiiiii iiiiiiiiiiiiiiiiiiiiiiii faderlogic iiiiiiiiiiiiiiiiiiiiiiiiii ::::::::::::::::::: :::::::::::::::::::::::: :::::::::::::::::::::::: :::::::::::::::::::::::::: ::::::::::::::::::: :::::::::::::::::::::::: :::::::::::::::::::::::: :::::::::::::::::::::::::: ::::::::::::::::::: :::::::::::::::::::::::: :::::::::::::::::::::::: :::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

// //

990091 Figure 2. Integration of research processor and baseline F/A-18 systems. 3 American Institute of Aeronautics and Astronautics

andthe up-frontcontroller thatis usedto program

buttons fortheDDI.Figure 3(b)shows theDDIdisplay

with the programmable buttons and"arm" discrete

displayed. Figure 3(c)shows thepilotstickwiththe

nosewheel steering button and the paddle switch.

(c)Pilotstick withnosewheel steering button and paddle

switch.

Figure 3.Concluded.

The research software has been preprogrammed with two sets of requirements: arm requirements and engage/disengage requirements. When the research (a)Digitaldisplay indicators and up-front controller.

mode is requested by selecting a DDI button, all of the arming requirements are checked. The aircraft parameters currently checked for arm/disengage are differential stabilator, normal acceleration, yaw rate, bank angle, altitude, and Mach number. The parameters Arm cue --_ _IGHT/,,_ AUTO_ must meet the requirements to allow the system to be Table number---_ i ( OFF _ DAY N armed (enabled) and then engaged (activated). If the arming requirements are met, the PSFCC will give an Prog _::::b:: er --_ _'_ _ [_ _ _ "armed" indication on the DDI. The pilot can attempt to engage the mode by pressing the nosewheel steering button at the bottom of the control stick. If all engagement requirements are satisfied, the PSFCC will buttons --_ \_-c"_'- B -_-; "-_'-_'-_ engage. The pilot may disengage the system by deploying the flaps, activating the spin-recovery mode,

\C3-c -0

or depressing the autopilot disengage switch (paddle

\E3- -0

switch) at the bottom of the control stick. Automatic disengagements will occur if engage limits are violated

o ©Od]©© o

or a system failure is detected. Reference 5 provides BRT CONT more detail on PSFCC operation.

Source: McDonnell Douglas Aerospace, St, Louis, Missouri 970728 "Class B" Envelope (b) Digital display indicator with program buttons.

The baseline processor and all interface software to Figure 3. The F/A-18 cockpit displays and pilot stick. the research processor had extensive testing to a "class Amelican/nsfimte of Aeronautics and Astronautics A," or flight-critical, level. The initial software version with the PSFCC. Currently, four strip charts show in the research processor did not have the testing standard parameters for flight control system necessary to be used for class A aircraft control. monitoring. These parameters include aircraft angles, Because the research Ada control law software had not rates, accelerations, airdata, surface deflections, and been tested to NASA flight-critical standards, the pilot commands.

PSFCC could be demonstrated only in a limited, or In addition, computer monitor displays provide "class B," envelope. The class B envelope boundary was control room personnel with PSFCC status information.

defined using the assumption that given a software fault The display shown in figure 5 provides current status of during which all surfaces are commanded to worst-case the PSFCC hardware. This display shows the 701E and full deflections at their respective rate limits, the aircraft 1750A processor fault information such as sensor remains within known structural limitations. For the failures, processor timeouts, and validity bits. The initial PSFCC flight test, body-axis acceleration limits display shown in figure 6 provides 1750A processor (because of wing modifications) were _+1 g lateral and research software information such as armed/engaged +6/-3.5 g normal acceleration.

status, operating research mode, and reasons for Figure 4 shows the class B envelope. The envelope disengagement. This information is used to augment the was divided into five regions where handling qualities displays available to the pilot that give limited insight maneuvers were flown. A 4-g normal disengage into system operation and failure messages. In addition acceleration limit was necessary to ensure that the to these two displays, other displays can be used that show current actuator commands and research software aircraft would stay within the 6-g normal acceleration limits as well as baseline F/A-18 and research software structural limit in the event of a software fault during high g loading. A procedural limit of 250knots symmetric stabilator commands.

calibrated airspeed (KCAS) and a maximum altitude Verification and Validation Testing limit of 32,500 ft were enforced.

Extensive verification and validation ground testing was performed on the PSFCC before aircraft Dynamic installation. Details on the verification and validation of pressure, the PSFCC previously have been published. 5 40 x 10 3 Ibf/in2 _ N During verification and validation, two anomalies were uncovered that affected flight operations. Because the F/A-18 aircraft has a forward-loop integrator in the 30 ........... ............. ......... __30¢ pitch axis, aligning the pitch integrator states of both the baseline and research control laws is necessary to prevent undesirable stabilator transients during mode transition. These stabilator transients can result in Altitude, t J/_ /_4_0 KC_ It 20 ....................... V I " S.............

unwanted aircraft motion during the engage or 15 ........... i--__ocedura / disengage of the system. Verification and validation __ ,/rlmit testing uncovered an oversight in the original software

10 i :: i/Y i i

load that caused "drift" of the integrator alignment when the system is armed. The "drift" produced approximately 1.5 deg/min divergence between the 0 .1 .2 .3 .4 .5 .6 .7 .8 .9 research stabilator pitch command and the baseline Mach number computed command. Research software engagements 990092 with more than 2 ° of drift produced noticeable, and Figure 4. Class B envelope with five handling qualities sometimes objectionable, normal acceleration regions.

transients.

The second anomaly uncovered during verification and validation testing was traced to the initialization of a Control Room Displays yaw-rate cancellation filter in the lateral-directional Several strip-chart configurations and control room axis. In the initial PSFCC software load, this filter was displays that were used to monitor system operation and not initialized prior to research control law engagement.

verify safe flight operations have been designed for use The filter therefore required a time interval to achieve American Institute of Aeronautics and Astronautics _:_ii_i_iiii_i_!i!_i!!!i_i_!i!ii_!i!!_!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!i_!i!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!_!!!!!!i ............. _i........................ i!i!i!i!'i __!_____!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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instrumentation to the control room for the first time.

steady-state values after the engagement of the research The test is used to uncover and correct deficiencies in software, which resulted in a transient in directional command for a maximum of 5 sec after engagement. aircraft operation, data acquisition systems, and control room displays. The preflight test is used as a final test Safety issues related to these anomalies were and checkout of aircraft systems under their own power.

mitigated through mission rules that specified control U. S. Navy ground testing procedures were referenced, room concurrence between arming, engaging, and used, and integrated into standard NASA procedures for maneuvering. The two anomalies have been addressed the preflight test. The Naval Air Training and Operating and fixed for future PSFCC flight tests.

Procedures Standardization (NATOPS) was used to ensure test coverage of all potentially affected aircraft On-Aircraft Tests systems after the installation of the PSFCC.

The NATOPS-recommended tests included engine- Aircraft ground tests are performed on most flight test crossbleed checks and built-in tests.

programs to verify proper operation of aircraft systems.

Checkout of these systems includes PSFCC operation, During ground engine-crossbleed checks, error codes instrumentation systems, and control room displays. For considered unacceptable were encountered for two of the PSFCC program, a combined systems test and four stabilator channels. The aircrew performed all preflight test were performed prior to first flight.

standard NATOPS troubleshooting procedures with the exception of replacing flight control computers. Finding A combined systems test is a routine ground test nothing objectionable, the crew recommended repeating in which the experiment radiates telemetered American Institute of Aeronautics and Astronautics !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!::___________::_:!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

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iiiililililililililiiii ::" "'ii :! ....................... i!iil:!iii::'_i:: ":ii" :!ii i_!iiiilililililililililililililililililililililililililililililililili_i _iir ":' i:" _iii:-i .......... iiiii:: _ii:: i_ "!i! !'- r -!iiilr _::'ii_i ! "iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiill .............. _ r-!-_!- _iii:' r ::" iiiii:: iii: i_ "!i! !'- r _iiiilr _i_:: _iii ! "!iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii iiiil iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii i!iiiiiiiiiiiiiiiiiiiiiiiiiiiiiii! !iiiiiiiiiiiiiiiiiii iiiiii i ii iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii i ii iiiiiiiiiiiiiii iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii 990094 Figure 6. PSFCC 1750A research software page.

the ground test. The ground test successfully passed on • Flight Control System Rig Check. Release the second attempt, clearing the way for first flight. controls and time how long rolling to a 30 ° bank angle takes at various airspeeds. The time to roll Flight Test 30 ° was in all cases more than 8 sec (maximum speed of 550 KCAS), which passed the NATOPS The PSFCC were flight-tested from March 11 to criterion (5 sec at 550 KCAS).

April7, 1998. Four flights were conducted that • Flight Controls Check. Check aircraft damping demonstrated the basic functionality of the PSFCC with small amplitude inputs in all three axes from within a limited flight envelope. The program consisted 300 to 350 KCAS.

of three phases: FCF, PSFCC functional testing, and • Autopilot Mode Check. Use heading hold, altitude handling qualities testing.

hold, heading select, and barometric altitude hold.

Functional Check Flight • Leading-Edge Flap System Check. Windup turn to 35 ° angle of attack to examine any difference in In accordance with NATOPS procedures, the aircraft leading-edge flap position (criterion is 5°).

performed a "profile C" FCE The profile C FCF is used for any F/A- 18 production aircraft that has had extended • Spin-Recovery Mode Check. Enable the spin- downtime or flight control computers replaced. The FCF recovery mode switch to ensure proper operation consists of the following: and displays.

American Institute of Aeronautics and Astronautics

• Crossbleed Airstart. Crossbleed airstartboth

disengagement tests. The initial tests were performed in

engines. the middle of the class B envelope, 184 KCAS

(Mach 0.45) at an altitude of 25,000 ft. Arming tests

• Trailing-Edge Flap Test. Move the flap switch to

were performed before the engagement tests. The one-half and note any difference in left and right system was armed for 55 sec to measure the stabilator trailing-edge flap position.

drift, and the system was disarmed using the paddle switch.

• g Loading Check. Pull to +5 g and push to -1 g.

• Emergency Landing Gear Check. Check Figure 7 shows a time history of the aircraft stabilator emergency landing gear operation.

command and the research stabilator command during the stabilator drift test. The drift measured in flight was Two attempts were made at the functional check slightly larger than was seen in the hardware-in-the-loop flight. On the first attempt, the aircraft passed all the simulation (approximately 1.8 ° of drift after 55 sec of tests up to the crossbleed airstart. During the crossbleed arming), and the pilot disarm was successful. This larger airstart, the same stabilator error codes were drift rate was not surprising because atmospheric effects encountered that were seen during the preflight engine- and system noise existed in flight.

crossbleed check. The aircraft returned to base, and one of the PSFCC was replaced. A second attempt at a In the next test, the cockpit spin-recovery mode functional check flight was made, this time successfully.

switch was used to disarm the system successfully.

The error codes were traced to an analog card that is part Aircraft maneuvering was used to test the normal of the baseline control system. acceleration, Mach, and altitude disarm limits. The armed system was flown in a windup turn to 4.2 g, with Research Flight Control System disarming occurring at 4.0 g. The lower disarm limits for Mach and altitude were checked by descending Engage/Disengage Tests slowly through an altitude of 19,000 ft, returning to the The next flight was the first evaluation of the research arming envelope, and then decelerating through Mach 0.4 with successful disarms.

system and primarily consisted of arm, engagement, and 2 m 1 m Arm, 17 sec Disarm, 72 sec 7 1 _- 701E stabilator /

: \ comman° /_

-1 Symmetric stabilator -2 position, deg -- command -3 -4 -- --5 --

I I I I I I I

-6 10 20 30 40 50 60 70 80 Time, sec 990095 Figure 7. Integrator drift test: research flight control system and 701E stabilator commands were monitored during armed flight.

American Institute of Aeronautics and Astronautics The engagement/disengagement tests were performed • Mach 0.45 at an altitude of 20,000 ft.

in thesame manner, witha disengagement altitude of

• Mach 0.40 at an altitude of 28,000 ft.

15,000 ft. Thelower Mach limit of 0.2wasnottested

• Mach 0.35 at an altitude of 20,000 ft.

because it would require high-angle-of-attack flight. All

of the disarm/disengagement testswereperformed

For all of these flight conditions, a test maneuver

successfully. Figure8 showsa disengagement at

block was accomplished with the baseline control

approximately 4 g normal acceleration. Note that no

software and the research control software that noticeable transients exist in either aircraft surfaces or consisted of the following maneuvers: states. The mission rules requiring control room concurrence between arming, engaging, and • doublets in each axis.

maneuvering proved to be satisfactory.

• 00-600-600-0 ° bank angle captures.

Handling Qualities Flights • 360 ° rolls.

• 20 ° pitch angle captures.

The remaining two flights were devoted to gathering handling qualities data. The handling qualities tests • full-pedal steady-heading sideslips.

were performed at five flight conditions corresponding • lateral frequency sweeps.

to the center of the five regions shown in figure 4: At Mach 0.35 and an altitude of 20,000 ft, no 360 ° • Mach 0.45 at an altitude of 25,000 ft.

rolls were performed. For handling qualities • Mach 0.55 at an altitude of 28,000 ft.

evaluations, a qualitative comparison was made between Symmetric _ 10 stabilator, dig

I I I I

- 2O Normal acceleration, 2 g

o I I I I I I I

Pitch rate, dig/sic 20 fl _._

i i i

o I I I I

f RFCS disengage RFCS engage

I I I I I I I I I

-1 80 80.5 81 81.5 82 82.5 83 83.5 84 84.5 85 Time, sic 990096 Figure 8. Windup turn, 4-g disengage: no significant transients caused by research flight control system disengage.

Amelican Institute of Aeronautics and Astronautics thestandard F/A- 18and theresearch F/A- 18replication data from the PSFCC flights were used as an input to the mode. All of thetestblocks were flownback-to-back, NASA Dryden F/A-18 nonlinear six-degree-of-freedom

disengaged andthenengaged. Thepilotwasasked to

simulation. Both the baseline system and the research

describe anydifferences between thetwoflightcontrol

F/A-18 replication software flight data were processed

systems. Thepilots reported nodifferences between the

at the five handling qualities flight conditions. Using

F/A-18 replication mode and thestandard F/A-18 flight

recorded pilot inputs, simulated time histories were control system operation.

calculated for comparison with flight data for rates, accelerations, and surface positions throughout the class

Duringthe flight test, a numberof nuisance

B envelope. When plotting these data, the symmetric

disengagements occurred. The research processor

stabilator and angle-of-attack traces were biased to disengaged withnobaseline system errorindications.

account for small differences in the longitudinal trim

The research software gave anerrorindication thatone

conditions between the flight data and the simulation.

ofthebaseline computer channels hadfailed, although

no indication wasgivenfrom the baseline F/A-18

Figures 9 to 11 show typical comparisons of the

system. Furtherinvestigation is pending on these

F/A-18 research replication software flight data to the disengagements.

simulation. Pilot pitch, roll, and yaw input doublets were performed in region I of the class B envelope, at Flight Test Data Comparisons Mach 0.45 and an altitude of 25,000 ft. The time In order to further verify that the F/A-18 replication histories compare symmetric and differential surface mode is functioning like a standard F/A-18 mode, flight positions, pitch rate, roll rate, yaw rate, angle of attack, -- Simulation ..... Flight Pitch stick, in.

I I I I I

-2 Symmetric stabilator, deg

I i

I I I I I

-10 Angle of attack,

,° t

deg Pitch rate, deg/sec B m

I I I I I I I I I

-10 .5 Normal acceleration, g

I I I I I I I I I

--.5 0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Time, sec 990097 Figure 9. Simulation-to-flight comparison of a pitch doublet in research mode.

AmeJican Institute of Aeronautics and Astronautics -- Simulation .... Flight Roll stick, in.

I I I I I I I I I

Differential stabilator, deg

I I I I I I I I I

Differential aileron, deg

t

I I I I I I I I I

m 50 100 .

Roll rate, deg/sec

_iot

I I I I I I I I I

Lateral acceleration, m g

I I I I I I I I I

0 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Time, sec 990099 Figure 10. Simulation-to-flight comparison of a roll doublet in research mode.

Atne_ican Institute of Aeronautics and Astronautics -- Simulation ..... Flight Yaw pedal, Ibf

1°!1

I I I I I I I

ml Rudder position, -- _ m -- deg

:1

I I I I I I I I I

Yaw rate, deg/sec

I I I I I I I I I

Roll rate, deg/sec

I I I I I I I I I

.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Time, sec 990100 Figure 11. Simulation-to-flight comparison of yaw doublet in research mode.

Planned Activities for the Production and normal acceleration. These comparisons show differences between the simulated data and the flight Support Flight Control Computers data. The magnitude of the differences was compared for both the baseline and research software and found to Many different experiments are planned for the be the same. Because the baseline control software and PSFCC in the coming years. The most immediate the research control software flight data show the same activity involves using the PSFCC research processor as differences to the simulation data, the research F/A-18 a precision airframe surface excitation tool for control law replication mode is concluded to perform aerodynamic parameter identification. Inputs can be like the baseline F/A-18 control laws. applied to individual surfaces in a timed way to produce high-quality parameter identification data. These data The lateral frequency sweep data were reduced and will be used to refine F/A-18 aircraft aerodynamic frequency responses of standard F/A-18 and research databases for use on NASA Dryden research programs, mode flight were calculated. Figure 12 shows a in particular the Active Aeroelastic Wing program.

comparison of a frequency response of roll rate to lateral The PSFCC will also be used as a generic interface for stick for both the standard F/A-18 control system and unique flight control hardware. Analog inputs are the research control law. These frequency responses available for interface between the research processor showed good agreement. Because very little difference and external devices. Software that can interface existed in the phase response, the conclusion can be alternate aircraft control sticks with the research made that the research software mode does not processor has been written and bench-tested. NASA introduce any significant phase lag into the control Dryden currently is scheduling an experiment to use a system operation.

American Institute of Aeronautics and Astronautics -- Standard F/A-18 aircraft .... RFCS mode 30 -- 20 -- Magnitude, dB 10 -- 0 -- /

I I III I I I I I I III

--10 0 m Phase,

-- 50 'I

deg -- 100 m -- 150

1 J L

-- 200 10 0 101 Frequency, rad/sec 990101 Figure 12. Frequency response of roll rate to lateral stick for standard F/A-18 and research mode flight data.

pedestal-mounted center aircraft control stick from the NASA Dryden Flight Research Center. The evaluation back seat of an F/A- 18 aircraft to determine if this unique was done over four flights within a limited "class B" stick produces any handling qualities differences. This envelope. Three segments of the flight test have been interface also will be used for F/A-18 autonomous performed: functional checks, PSFCC research software formation flight experiments. Stick commands will be engagement/disengagement checks, and handling input through the analog inputs from a guidance qualities assessments. The PSFCC have successfully computer to perform initial formation flight experiments.

performed a Naval Air Training and Operating Procedures Standardization "profile C" functional check An ongoing use for the PSFCC will be to flight-test flight. The engagement/disengagement logic of the experimental control law methodologies. Current PSFCC has been successfully demonstrated. Pilot proposed designs include H infinity and nonlinear comments and comparisons between flight data and dynamic inversion controllers. Because the F/A-18 NASA Dryden six-degree-of-freedom simulation time aircraft has many surfaces that produce rolling and histories and lateral frequency response data indicate yawing moments, it is a very good platform for surface that the research F/A-18 replication software operates allocation experiments. Several surface allocation the same way as the F/A-18 standard flight control algorithms are being investigated for in-flight system for the envelope tested.

experiments.

Two software anomalies (the integrator drift and yaw- Conclusion axis filter initialization) were encountered during the ground testing but were remedied through procedure.

Initial flight testing of the production support flight control computers (PSFCC) has been completed at The flight integrator drift was greater than the drift American Institute of Aeronautics and Astronautics found during bench testing, but presented no References operational problems during flight test. No undesirable 1Shafer, Mary E, In-Flight Simulation Studies at the lateral-directional transients caused by the yaw filter NASA Dryden Flight Research Facility, NASA initialization occurred during flight test. Both of these TM-4396, 1992.

anomalies will be fixed in the next research software version. Nuisance disengages were encountered during 2Markman, Steve and Bill Holder, One-of-a-Kind the flight test; they are currently being investigated.

Research Aircraft." A History of In-Flight Simulators, Testbeds, and Prototypes, Schiffer Publishing Ltd., A variety of experiments are planned for the PSFCC.

Atglen, PA, 1995.

The PSFCC will be used to refine the F/A-18 aerodynamic database by providing in-flight surface 3pahle, Joseph W., Bruce Powers, Victoria Regenie, inputs for aerodynamic parameter identification.

Vince Chacon, Steve Degroote, and Steven Muruyak, Alternate pilot control sticks will be used with the Research Flight-Control System Development for the PSFCC to investigate their effects on F/A-18 handling F-18 High Alpha Research Vehicle, NASA TM-104232, 1991.

qualities. Some F/A-18 autonomous formation flight experiments will be performed using PSFCC to 4Regenie, Victoria A., Michael Earls, Jeanette Le, and interface between the formation flight guidance Michael Thomson, Experience With Ada on the F-18 algorithms and the baseline aircraft system.

High Alpha Research Vehicle Flight Test Program, Experimental control law architectures and surface NASA TM-104259, 1992.

allocation algorithms will be flight-tested using this research flight control computer system. This initial 5Carter, John F., Production Support Flight Control flight test proved the viability of the PSFCC for generic Computers: Research Capability for F/A-18 Aircraft at flight controls and flight systems research and was the Dryden Flight Research Center, NASA TM-97-206233, first step for many future flight research programs.

1997.

Ainelican lnsfitme of Aeronautics and Astronautics

REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188 Public reporting burden for this collection of information is estimated 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 other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Re )orts, 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. REPORTTYPE AND DATES COVERED August 1999 Technical Memorandum 4.TITLE AND SUBTITLE 5. FUNDING NUMBERS Initial Flight Test of the Production Support Flight Control Computers at NASA Dryden Flight Research Center WU 529-30-24-00-36-00-SRA 6. AUTHOR(S) John Carter and Mark Stephenson 8. PERFORMING ORGANIZATION 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) REPORT NUMBER NASA Dryden Flight Research Center RO. Box 273 H-2343 Edwards, California 93523-0273 10. SPONSORING/MONITORING 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) AGENCY REPORT NUMBER National Aeronautics and Space Administration NASA/TM-1999-206581 Washington, DC 20546-0001 11. SUPPLEMENTARY NOTES Presented as AIAA 99-4203 at the AIAA Guidance, Navigation, and Control Conference, Portland, Oregon, August 9-11, 1999.

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE Unclassified--Unlimited Subject Category 08 13. ABSTRACT (Maximum 200 words) The NASA Dryden Flight Research Center has completed the initial flight test of a modified set of F/A-18 flight control computers that gives the aircraft a research control law capability. The production support flight control computers (PSFCC) provide an increased capability for flight research in the control law, handling qualities, and flight systems areas. The PSFCC feature a research flight control processor that is "piggybacked" onto the baseline F/A-18 flight control system. This research processor allows for pilot selection of research control law operation in flight. To validate flight operation, a replication of a standard F/A-18 control law was programmed into the research processor and flight-tested over a limited envelope. This paper provides a brief description of the system, summarizes the initial flight test of the PSFCC, and describes future experiments for the PSFCC.

14. SUBJECTTERMS 15. NUMBER OF PAGES Aircraft testing, Control law research, F/A-18, Flight control, Production support 16. PRICE CODE flight control computers A03 17. SECURITY CLASSIFICATION 18. SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20. LIMITATION OF ABSTRACT OF REPORT OFTHIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified Unlimited NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) Prescribed by ANSI Std. Z39-18 298-102