Initial Flight Test of the Production Support Flight ... · include production F/A-18 control...

NASA/TM-1999-206581

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

John Carter and Mark StephensonDryden Flight Research CenterEdwards, California

August 1999

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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 StephensonDryden Flight Research CenterEdwards, California

August 1999

National Aeronautics andSpace Administration

Dryden Flight Research CenterEdwards, California 93523-0273

NOTICE

Use of trade names or names of manufacturers in this document does not constitute an official endorsementof such products or manufacturers, either expressed or implied, by the National Aeronautics andSpace Administration.

Available from the following:

NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS)7121 Standard Drive 5285 Port Royal RoadHanover, MD 21076-1320 Springfield, VA 22161-2171(301) 621-0390 (703) 487-4650

INITIAL FLIGHT TEST OF THE PRODUCTIONSUPPORT FLIGHT CONTROL COMPUTERS ATNASA DRYDEN FLIGHT RESEARCH CENTER

John Carter* and Mark Stephenson†

NASA Dryden Flight Research CenterEdwards, California

Abstract

The NASA Dryden Flight Research Center hascompleted the initial flight test of a modified set ofF/A-18 flight control computers that gives the aircraft aresearch control law capability. The production supportflight control computers (PSFCC) provide an increasedcapability for flight research in the control law, handlingqualities, and flight systems areas. The PSFCC feature aresearch flight control processor that is “piggybacked”onto the baseline F/A-18 flight control system. Thisresearch processor allows for pilot selection of researchcontrol law operation in flight. To validate flightoperation, a replication of a standard F/A-18 control lawwas programmed into the research processor and flight-tested over a limited envelope. This paper provides abrief description of the system, summarizes the initialflight test of the PSFCC, and describes futureexperiments for the PSFCC.

Nomenclature

A/D analog to digital

D/A digital to analog

DDI digital display indicator

FCF functional check flight

g gravitational acceleration constant, 32.2 ft/sec2

HARV High Alpha Research Vehicle

KCAS knots calibrated airspeed

NATOPS Naval Air Training and Operating Procedures Standardization

1American Institute of Aero

* Aerospace Engineer. E-mail: [email protected].†Aerospace Engineer. E-mail: mark_stephenson@dfrc. nasa.gov.Copyright 1999 by the American Institute of Aeronautics and

Astronautics, Inc. No copyright is asserted in the United States underTitle 17, U.S. Code. The U.S. Government has a royalty-free license toexercise all rights under the copyright claimed herein for Governmen-tal purposes. All other rights are reserved by the copyright owner.

PSFCC production support flight control computers

RFCS research flight control system

Introduction

Control law software development on aircrafthistorically has been extremely expensive and time-consuming because of the numerous staff hours devotedto design, implementation, and test of flight-criticalsoftware. Large amounts of hours are required becauseof the flight-critical nature of control law function.Extremely thorough testing is required because a controllaw software malfunction could lead to a loss of aircraft,property, or aircrew. Development of an easilymodifiable flight control system capable of reverting to abaseline control system can address these issues.

NASA has developed several aircraft for in-flightcontrol law development. Aircraft such as the NT-33AVariable Stability Aircraft, the F-8 Digital Fly-By-Wireaircraft, and the General Purpose Airborne Simulatorhave been used for in-flight simulation and dynamicsstudies.1, 2 Private organizations that do research havedeveloped aircraft such as the variable stability Learjetand the F-16 Variable Stability In-Flight Simulator TestAircraft (VISTA) that have research flight controlcomputer systems. These systems are designed to allowrelatively fast control law modifications while safety offlight is retained through the primary control system.The systems have also been used to modify dynamiccharacteristics in flight to simulate other airframes.

Engineers at NASA Dryden Flight Research Center(Edwards, California) have had recent experience with asystem designed for rapid control law modification thatoperates the F/A-18 High Alpha Research Vehicle(HARV) aircraft.3, 4 The HARV is a modified F/A-18aircraft with thrust-vectoring paddles that was designedfor flight test at high angles of attack. Flight controlcomputers of the HARV were modified to include apilot-selectable research control law processor. Thissystem allowed the HARV to operate with conventional

nautics and Astronautics

F/A-18 control laws for all phases of flight and haveresearch control laws available at specified parts of theflight envelope. Reversion to the conventional controllaws was accomplished either manually orautomatically with system failure or envelope violation.The HARV design provided a flexible platform forcontrol law algorithm research. The ability to restoreaircraft control to a safe, proven system addressed manyof the safety-of-flight issues associated withexperimental control law architectures.

Building on the experience gained from the F/A-18HARV, the United States Navy and NASA Drydenworked in concert with The Boeing Company(St. Louis, Missouri)‡ and Lockheed Martin ControlSystems (Binghamton, New York) to develop a systemthat could operate on any F/A-18 (model A to model D).This system is called the production support flightcontrol computers (PSFCC).5 Several sets of F/A-18computers have been modified into PSFCC. The PSFCCinclude production F/A-18 control processors, researchprocessors, software that controls the transition betweenthe primary and research systems, and cockpit interfacesoftware for research mode selection. For thisdemonstration, the research processors have beenprogrammed with a replication of the standard F/A-18control laws.

To demonstrate the viability of the PSFCC concept,an initial flight test phase has been conducted. Thisphase was performed in March–April 1998. Four flightswere accomplished. A standard U. S. Navy functionalcheck flight (FCF) has been conducted to validate thatnormal F/A-18 operations are not affected, and researchflights have demonstrated PSFCC engage/disengageoperation in a envelope limited for flight safetyconsiderations. Flights to investigate handling qualitieshave been conducted in the F/A-18 replication mode tovalidate the performance of the research processor.

Several new experiments are being prepared for thePSFCC. The first to be flown will be an experimentusing an alternate pilot stick to control the F/A-18aircraft to investigate handling qualities issuesassociated with different pilot stick configurations. Thesecond experiment will involve using the PSFCC toproduce data that will be used to refine the F/A-18aerodynamics database. This database will be used foran F/A-18 flexible wing program. Other proposed flightexperiments include F/A-18 autonomous formation

flight and controllers designed using modern and robustcontrol theory.

This paper gives a brief description of the function ofthe system, presents the results of the initial flight test,and describes the future experiments planned for thePSFCC. Anomalies encountered during ground andflight test are discussed.

Use of trade names or names of manufacturers in thisdocument does not constitute an official endorsement ofsuch products or manufacturers, either expressed orimplied, by the National Aeronautics and SpaceAdministration.

Production Support Flight ControlComputers Functional Description

The PSFCC design uses a research processor inaddition to the baseline F/A-18 flight control computers.A detailed description of the PSFCC implementationhas been published.5 The research flight control systemcan be engaged by the pilot to exercise full-authoritycontrol of the aircraft with research flight control laws.For the initial flight test, only the F/A-18 replicationmode was flight-tested, which duplicated the basicF/A-18 control laws in the research processor.

Figure 1 shows how the PSFCC are integrated into theF/A-18 aircraft flight control system. The F/A-18aircraft is controlled by a quadruply redundant flightcontrol computer system. Figure 2 shows the PSFCCmodification to the basic flight control computer. Theresearch PACE 1750A processor (PerformanceSemiconductor Corporation, Sunnyvale, California) isembedded in the same avionics box as the basic 701Eflight control processors (Lockheed Martin ControlSystems, Binghamton, New York).

The research control laws are programmed in Ada andare completely independent of the basic control laws.This independence allows new research control laws tobe added without affecting the basic flight controlsystem. All information to and from the researchprocessor is handled by the basic flight control systemthrough dual-port random access memory to facilitatecommunication between the research system and thebasic system. This separation also provides good faultisolation of the research processor.

Figure 3 shows all the elements the pilot uses tointerface with the PSFCC. Figure 3(a) shows the F/A-18displays, featuring the digital display indicators (DDIs)

‡Formerly McDonnell Douglas Aerospace, which merged with TheBoeing Company during these tests.

2American Institute of Aeronautics and Astronautics

3

American Institute of Aeronautics and Astronautics

Figure 1. The F/A-18 control system components.

Figure 2. Integration of research processor and baseline F/A-18 systems.

3

Inertial navigation

system

Mission computer

Military specification1553 multiplex bus

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– Rate gyroscopes – Accelerometers

– Pitch stick – Roll stick – Rudder pedals

– Airdata– Angle of attack

Multifunctional display

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– Stabilators – Trailing-edge flaps

– Leading-edge flaps– Ailerons– Rudders

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Baseline F/A-18 central processing unit (701E)

PACE 1750A research processor

and the up-front controller that is used to programbuttons for the DDI. Figure 3(b) shows the DDI displaywith the programmable buttons and “arm” discretedisplayed. Figure 3(c) shows the pilot stick with thenosewheel steering button and the paddle switch.

(a) Digital display indicators and up-front controller.

(b) Digital display indicator with program buttons.

Figure 3. The F/A-18 cockpit displays and pilot stick.

(c) Pilot stick with nosewheel steering button and paddleswitch.

Figure 3. Concluded.

The research software has been preprogrammed withtwo sets of requirements: arm requirements andengage/disengage requirements. When the researchmode is requested by selecting a DDI button, all of thearming requirements are checked. The aircraftparameters currently checked for arm/disengage aredifferential stabilator, normal acceleration, yaw rate,bank angle, altitude, and Mach number. The parametersmust meet the requirements to allow the system to bearmed (enabled) and then engaged (activated). If thearming requirements are met, the PSFCC will give an“armed” indication on the DDI. The pilot can attemptto engage the mode by pressing the nosewheel steeringbutton at the bottom of the control stick. If allengagement requirements are satisfied, the PSFCC willengage. The pilot may disengage the system bydeploying the flaps, activating the spin-recovery mode,or depressing the autopilot disengage switch (paddleswitch) at the bottom of the control stick. Automaticdisengagements will occur if engage limits are violatedor a system failure is detected. Reference 5 providesmore detail on PSFCC operation.

“Class B” Envelope

The baseline processor and all interface software tothe research processor had extensive testing to a “class

NIGHTOFF

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Source: McDonnell Douglas Aerospace, St. Louis, Missouri

Table number

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A,” or flight-critical, level. The initial software versionin the research processor did not have the testingnecessary to be used for class A aircraft control.Because the research Ada control law software had notbeen tested to NASA flight-critical standards, thePSFCC could be demonstrated only in a limited, or“class B,” envelope. The class B envelope boundary wasdefined using the assumption that given a software faultduring which all surfaces are commanded to worst-casefull deflections at their respective rate limits, the aircraftremains within known structural limitations. For theinitial PSFCC flight test, body-axis acceleration limits(because of wing modifications) were ±1 g lateral and+6/–3.5 g normal acceleration.

Figure 4 shows the class B envelope. The envelopewas divided into five regions where handling qualitiesmaneuvers were flown. A 4-g normal disengageacceleration limit was necessary to ensure that theaircraft would stay within the 6-g normal accelerationstructural limit in the event of a software fault duringhigh g loading. A procedural limit of 250 knotscalibrated airspeed (KCAS) and a maximum altitudelimit of 32,500 ft were enforced.

Figure 4. Class B envelope with five handling qualitiesregions.

Control Room Displays

Several strip-chart configurations and control roomdisplays that were used to monitor system operation andverify safe flight operations have been designed for use

with the PSFCC. Currently, four strip charts showstandard parameters for flight control systemmonitoring. These parameters include aircraft angles,rates, accelerations, airdata, surface deflections, andpilot commands.

In addition, computer monitor displays providecontrol room personnel with PSFCC status information.The display shown in figure 5 provides current status ofthe PSFCC hardware. This display shows the 701E and1750A processor fault information such as sensorfailures, processor timeouts, and validity bits. Thedisplay shown in figure 6 provides 1750A processorresearch software information such as armed/engagedstatus, operating research mode, and reasons fordisengagement. This information is used to augment thedisplays available to the pilot that give limited insightinto system operation and failure messages. In additionto these two displays, other displays can be used thatshow current actuator commands and research softwarelimits as well as baseline F/A-18 and research softwaresymmetric stabilator commands.

Verification and Validation Testing

Extensive verification and validation ground testingwas performed on the PSFCC before aircraftinstallation. Details on the verification and validation ofthe PSFCC previously have been published.5

During verification and validation, two anomalieswere uncovered that affected flight operations. Becausethe F/A-18 aircraft has a forward-loop integrator in thepitch axis, aligning the pitch integrator states of both thebaseline and research control laws is necessary toprevent undesirable stabilator transients during modetransition. These stabilator transients can result inunwanted aircraft motion during the engage ordisengage of the system. Verification and validationtesting uncovered an oversight in the original softwareload that caused “drift” of the integrator alignment whenthe system is armed. The “drift” producedapproximately 1.5 deg/min divergence between theresearch stabilator pitch command and the baselinecomputed command. Research software engagementswith more than 2° of drift produced noticeable, andsometimes objectionable, normal accelerationtransients.

The second anomaly uncovered during verificationand validation testing was traced to the initialization of ayaw-rate cancellation filter in the lateral-directionalaxis. In the initial PSFCC software load, this filter wasnot initialized prior to research control law engagement.The filter therefore required a time interval to achieve

.4 .5 .6 .7 .8 .9.3.2.10

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Figure 5. PSFCC hardware failure page.

steady-state values after the engagement of the researchsoftware, which resulted in a transient in directionalcommand for a maximum of 5 sec after engagement.

Safety issues related to these anomalies weremitigated through mission rules that specified controlroom concurrence between arming, engaging, andmaneuvering. The two anomalies have been addressedand fixed for future PSFCC flight tests.

On-Aircraft Tests

Aircraft ground tests are performed on most flight testprograms to verify proper operation of aircraft systems.Checkout of these systems includes PSFCC operation,instrumentation systems, and control room displays. Forthe PSFCC program, a combined systems test andpreflight test were performed prior to first flight.

A combined systems test is a routine ground testin which the experiment radiates telemetered

instrumentation to the control room for the first time.The test is used to uncover and correct deficiencies inaircraft operation, data acquisition systems, and controlroom displays. The preflight test is used as a final testand checkout of aircraft systems under their own power.U. S. Navy ground testing procedures were referenced,used, and integrated into standard NASA procedures forthe preflight test. The Naval Air Training and OperatingProcedures Standardization (NATOPS) was used toensure test coverage of all potentially affected aircraftsystems after the installation of the PSFCC.The NATOPS-recommended tests included engine-crossbleed checks and built-in tests.

During ground engine-crossbleed checks, error codesconsidered unacceptable were encountered for two offour stabilator channels. The aircrew performed allstandard NATOPS troubleshooting procedures with theexception of replacing flight control computers. Findingnothing objectionable, the crew recommended repeating


990094

Figure 6. PSFCC 1750A research software page.

the ground test. The ground test successfully passed onthe second attempt, clearing the way for first flight.

Flight Test

The PSFCC were flight-tested from March 11 toApril 7, 1998. Four flights were conducted thatdemonstrated the basic functionality of the PSFCCwithin a limited flight envelope. The program consistedof three phases: FCF, PSFCC functional testing, andhandling qualities testing.

Functional Check Flight

In accordance with NATOPS procedures, the aircraftperformed a “profile C” FCF. The profile C FCF is usedfor any F/A-18 production aircraft that has had extendeddowntime or flight control computers replaced. The FCFconsists of the following:

• Flight Control System Rig Check. Releasecontrols and time how long rolling to a 30° bankangle takes at various airspeeds. The time to roll30° was in all cases more than 8 sec (maximumspeed of 550 KCAS), which passed the NATOPScriterion (5 sec at 550 KCAS).

• Flight Controls Check. Check aircraft dampingwith small amplitude inputs in all three axes from300 to 350 KCAS.

• Autopilot Mode Check. Use heading hold, altitudehold, heading select, and barometric altitude hold.

• Leading-Edge Flap System Check. Windup turnto 35° angle of attack to examine any difference inleading-edge flap position (criterion is 5°).

• Spin-Recovery Mode Check. Enable the spin-recovery mode switch to ensure proper operationand displays.


• Crossbleed Airstart. Crossbleed airstart bothengines.

• Trailing-Edge Flap Test. Move the flap switch toone-half and note any difference in left and righttrailing-edge flap position.

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

• Emergency Landing Gear Check. Checkemergency landing gear operation.

Two attempts were made at the functional checkflight. On the first attempt, the aircraft passed all thetests up to the crossbleed airstart. During the crossbleedairstart, the same stabilator error codes wereencountered that were seen during the preflight engine-crossbleed check. The aircraft returned to base, and oneof the PSFCC was replaced. A second attempt at afunctional check flight was made, this time successfully.The error codes were traced to an analog card that is partof the baseline control system.

Research Flight Control SystemEngage/Disengage Tests

The next flight was the first evaluation of the researchsystem and primarily consisted of arm, engagement, and

disengagement tests. The initial tests were performed inthe middle of the class B envelope, 184 KCAS(Mach 0.45) at an altitude of 25,000 ft. Arming testswere performed before the engagement tests. Thesystem was armed for 55 sec to measure the stabilatordrift, and the system was disarmed using the paddleswitch.

Figure 7 shows a time history of the aircraft stabilatorcommand and the research stabilator command duringthe stabilator drift test. The drift measured in flight wasslightly larger than was seen in the hardware-in-the-loopsimulation (approximately 1.8° of drift after 55 sec ofarming), and the pilot disarm was successful. This largerdrift rate was not surprising because atmospheric effectsand system noise existed in flight.

In the next test, the cockpit spin-recovery modeswitch was used to disarm the system successfully.Aircraft maneuvering was used to test the normalacceleration, Mach, and altitude disarm limits. Thearmed system was flown in a windup turn to 4.2 g, withdisarming occurring at 4.0 g. The lower disarm limitsfor Mach and altitude were checked by descendingslowly through an altitude of 19,000 ft, returning to thearming envelope, and then decelerating throughMach 0.4 with successful disarms.


Figure 7. Integrator drift test: research flight control system and 701E stabilator commands were monitored duringarmed flight.

403020

Arm, 17 sec Disarm, 72 sec

{

Difference = 0.2° Difference = 1.8°

RFCS stabilator command

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The engagement/disengagement tests were performedin the same manner, with a disengagement altitude of15,000 ft. The lower Mach limit of 0.2 was not testedbecause it would require high-angle-of-attack flight. Allof the disarm/disengagement tests were performedsuccessfully. Figure 8 shows a disengagement atapproximately 4 g normal acceleration. Note that nonoticeable transients exist in either aircraft surfaces orstates. The mission rules requiring control roomconcurrence between arming, engaging, andmaneuvering proved to be satisfactory.

Handling Qualities Flights

The remaining two flights were devoted to gatheringhandling qualities data. The handling qualities testswere performed at five flight conditions correspondingto the center of the five regions shown in figure 4:

• Mach 0.45 at an altitude of 25,000 ft.





For all of these flight conditions, a test maneuverblock was accomplished with the baseline controlsoftware and the research control software thatconsisted of the following maneuvers:

• doublets in each axis.

• 0°-60°-60°-0° bank angle captures.

• 360° rolls.

• 20° pitch angle captures.

• full-pedal steady-heading sideslips.

• lateral frequency sweeps.

At Mach 0.35 and an altitude of 20,000 ft, no 360°rolls were performed. For handling qualitiesevaluations, a qualitative comparison was made between


Figure 8. Windup turn, 4-g disengage: no significant transients caused by research flight control system disengage.

80 80.5 81 81.5

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the standard F/A-18 and the research F/A-18 replicationmode. All of the test blocks were flown back-to-back,disengaged and then engaged. The pilot was asked todescribe any differences between the two flight controlsystems. The pilots reported no differences between theF/A-18 replication mode and the standard F/A-18 flightcontrol system operation.

During the flight test, a number of nuisancedisengagements occurred. The research processordisengaged with no baseline system error indications.The research software gave an error indication that oneof the baseline computer channels had failed, althoughno indication was given from the baseline F/A-18system. Further investigation is pending on thesedisengagements.

Flight Test Data Comparisons

In order to further verify that the F/A-18 replicationmode is functioning like a standard F/A-18 mode, flight

data from the PSFCC flights were used as an input to theNASA Dryden F/A-18 nonlinear six-degree-of-freedomsimulation. Both the baseline system and the researchF/A-18 replication software flight data were processedat the five handling qualities flight conditions. Usingrecorded pilot inputs, simulated time histories werecalculated for comparison with flight data for rates,accelerations, and surface positions throughout the classB envelope. When plotting these data, the symmetricstabilator and angle-of-attack traces were biased toaccount for small differences in the longitudinal trimconditions between the flight data and the simulation.

Figures 9 to 11 show typical comparisons of theF/A-18 research replication software flight data to thesimulation. Pilot pitch, roll, and yaw input doubletswere performed in region I of the class B envelope, atMach 0.45 and an altitude of 25,000 ft. The timehistories compare symmetric and differential surfacepositions, pitch rate, roll rate, yaw rate, angle of attack,


Figure 9. Simulation-to-flight comparison of a pitch doublet in research mode.

2.50 .5 1.0 1.5 2.0 3.0 3.5 4.0 4.5 5.0

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SimulationFlight

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American Institute of Aeronautics and Astronautics

Figure 10. Simulation-to-flight comparison of a roll doublet in research mode.

2.52.01.51.0.50 3.53.0 4.5 5.04.0

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Figure 11. Simulation-to-flight comparison of yaw doublet in research mode.

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and normal acceleration. These comparisons showdifferences between the simulated data and the flightdata. The magnitude of the differences was comparedfor both the baseline and research software and found tobe the same. Because the baseline control software andthe research control software flight data show the samedifferences to the simulation data, the research F/A-18control law replication mode is concluded to performlike the baseline F/A-18 control laws.

The lateral frequency sweep data were reduced andfrequency responses of standard F/A-18 and researchmode flight were calculated. Figure 12 shows acomparison of a frequency response of roll rate to lateralstick for both the standard F/A-18 control system andthe research control law. These frequency responsesshowed good agreement. Because very little differenceexisted in the phase response, the conclusion can bemade that the research software mode does notintroduce any significant phase lag into the controlsystem operation.

Planned Activities for the ProductionSupport Flight Control Computers

Many different experiments are planned for thePSFCC in the coming years. The most immediateactivity involves using the PSFCC research processor asa precision airframe surface excitation tool foraerodynamic parameter identification. Inputs can beapplied to individual surfaces in a timed way to producehigh-quality parameter identification data. These datawill be used to refine F/A-18 aircraft aerodynamicdatabases for use on NASA Dryden research programs,in particular the Active Aeroelastic Wing program.

The PSFCC will also be used as a generic interface forunique flight control hardware. Analog inputs areavailable for interface between the research processorand external devices. Software that can interfacealternate aircraft control sticks with the researchprocessor has been written and bench-tested. NASADryden currently is scheduling an experiment to use a


Figure 12. Frequency response of roll rate to lateral stick for standard F/A-18 and research mode flight data.

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pedestal-mounted center aircraft control stick from theback seat of an F/A-18 aircraft to determine if this uniquestick produces any handling qualities differences. Thisinterface also will be used for F/A-18 autonomousformation flight experiments. Stick commands will beinput through the analog inputs from a guidancecomputer to perform initial formation flight experiments.

An ongoing use for the PSFCC will be to flight-testexperimental control law methodologies. Currentproposed designs include H infinity and nonlineardynamic inversion controllers. Because the F/A-18aircraft has many surfaces that produce rolling andyawing moments, it is a very good platform for surfaceallocation experiments. Several surface allocationalgorithms are being investigated for in-flightexperiments.

Conclusion

Initial flight testing of the production support flightcontrol computers (PSFCC) has been completed at

NASA Dryden Flight Research Center. The evaluationwas done over four flights within a limited “class B”envelope. Three segments of the flight test have beenperformed: functional checks, PSFCC research softwareengagement/disengagement checks, and handlingqualities assessments. The PSFCC have successfullyperformed a Naval Air Training and OperatingProcedures Standardization “profile C” functional checkflight. The engagement/disengagement logic of thePSFCC has been successfully demonstrated. Pilotcomments and comparisons between flight data andNASA Dryden six-degree-of-freedom simulation timehistories and lateral frequency response data indicatethat the research F/A-18 replication software operatesthe same way as the F/A-18 standard flight controlsystem for the envelope tested.

Two software anomalies (the integrator drift and yaw-axis filter initialization) were encountered during theground testing but were remedied through procedure.The flight integrator drift was greater than the drift


found during bench testing, but presented nooperational problems during flight test. No undesirablelateral-directional transients caused by the yaw filterinitialization occurred during flight test. Both of theseanomalies will be fixed in the next research softwareversion. Nuisance disengages were encountered duringthe flight test; they are currently being investigated.

A variety of experiments are planned for the PSFCC.The PSFCC will be used to refine the F/A-18aerodynamic database by providing in-flight surfaceinputs for aerodynamic parameter identification.Alternate pilot control sticks will be used with thePSFCC to investigate their effects on F/A-18 handlingqualities. Some F/A-18 autonomous formation flightexperiments will be performed using PSFCC tointerface between the formation flight guidancealgorithms and the baseline aircraft system.Experimental control law architectures and surfaceallocation algorithms will be flight-tested using thisresearch flight control computer system. This initialflight test proved the viability of the PSFCC for genericflight controls and flight systems research and was thefirst step for many future flight research programs.

References

1Shafer, Mary F., In-Flight Simulation Studies at theNASA Dryden Flight Research Facility, NASATM-4396, 1992.

2Markman, Steve and Bill Holder, One-of-a-KindResearch Aircraft: A History of In-Flight Simulators,Testbeds, and Prototypes, Schiffer Publishing Ltd.,Atglen, PA, 1995.

3Pahle, Joseph W., Bruce Powers, Victoria Regenie,Vince Chacon, Steve Degroote, and Steven Murnyak,Research Flight-Control System Development for theF-18 High Alpha Research Vehicle, NASA TM-104232,1991.

4Regenie, Victoria A., Michael Earls, Jeanette Le, andMichael Thomson, Experience With Ada on the F-18High Alpha Research Vehicle Flight Test Program,NASA TM-104259, 1992.

5Carter, John F., Production Support Flight ControlComputers: Research Capability for F/A-18 Aircraft atDryden Flight Research Center, NASA TM-97-206233,1997.


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

Prescribed by ANSI Std. Z39-18298-102

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

WU 529-30-24-00-36-00-SRA

John Carter and Mark Stephenson

NASA Dryden Flight Research CenterP.O. Box 273Edwards, California 93523-0273

H-2343

National Aeronautics and Space AdministrationWashington, DC 20546-0001 NASA/TM-1999-206581

The NASA Dryden Flight Research Center has completed the initial flight test of a modified set of F/A-18flight control computers that gives the aircraft a research control law capability. The production support flightcontrol computers (PSFCC) provide an increased capability for flight research in the control law, handlingqualities, 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 researchcontrol law operation in flight. To validate flight operation, a replication of a standard F/A-18 control law wasprogrammed into the research processor and flight-tested over a limited envelope. This paper provides a briefdescription of the system, summarizes the initial flight test of the PSFCC, and describes future experiments forthe PSFCC.

Aircraft testing, Control law research, F/A-18, Flight control, Production supportflight control computers A03

20

Unclassified Unclassified Unclassified Unlimited

August 1999 Technical Memorandum

Presented as AIAA 99-4203 at the AIAA Guidance, Navigation, and Control Conference, Portland, Oregon,August 9–11, 1999.

Unclassified—UnlimitedSubject Category 08

Initial Flight Test of the Production Support Flight ... · include production F/A-18 control...

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