Retrofit Reconfigurable Control of an F/A-18C Tony Page & Dean Meloney Naval Air Systems Command Society of Flight Test Engineers Patuxent River, MD 16

Retrofit Reconfigurable Controlof an F/A-18C

Tony Page&

Dean Meloney

Naval Air Systems Command

Society of Flight Test Engineers

Patuxent River, MD

16 NOV 2005

2Approved for Public Release, 265SPR-140.05

• The Navy has been investing in reconfigurable control technology as part of the Flight Control Predictive Diagnostic project (ONR funded D&I program)

• NAVAIR leveraged several SBIRs to expand research

• One SBIR company developed a novel in-line retrofit reconfig. approach

• Original plan was to flight test the method under the Phase II SBIR with support from NASA

• When NASA support evaporated, decision was made to pursue flight test using D&I funds (Technology Push)

• Limited flight test demonstration (4 flights)

Background


Redistribute control commands to compensate for battle damage or actuator failure

During a pitch maneuver for example, the ailerons and rudders can be deflected to counteract the roll and yaw coupling induced by the damaged/failed stabilator.

Flight Control Reconfiguration


Motivation

Problem: the full capabilities of the aircraft are not realized on production commercial or military vehicles (even those with digital flight control systems), and the pilots are often unable to effectively fly the damaged aircraft

Motivation: many aircraft have intrinsic ability to maintain controlled flight and land despite flight control failures, midair collision damage, or upset conditions …

Automatic reconfiguration to maintain controllability and recover, as closely as possible, the baseline handling qualities of the airplane

Fault Tolerant Control Systems: software and/or hardware to enable fail-safe or fail adaptive operation

Background: numerous documented cases of loss of commercial and military aircraft and life that are attributed to major flight control system failures


Status of Existing ResearchStatus of the Field: variety of techniques and several demonstrations have shown promise of software reconfiguration to handle a large number of otherwise catastrophic upset and damage conditions multiple significant flight demonstrations in the

past 10-15 years, with several involving Boeing (Self-Repairing FCS, PCA, RESTORE)

VISTA F-16 flight tests (Self-Designing Controller, 1996) SDC Milestone:

first time aircraft landed under reconfigurable control

However: significant gap between the research and use of the technology … many methods cannot be applied

to current generation or legacy aircraft

hardware redundancy is common approach to fault tolerant design

V&V steps have received less attention

Federal certification authorities lack the resources to evaluate and certify novel technology

Recent and Ongoing Research …

Address the issues with designs that can be retrofitted into existing aircraft


Retrofit Reconfiguration Architectures

ProductionControl Law

Sensor Data

Pilot Input

u u

PARALLEL ARCHITECTUREmodify outputs of production Controller

Parallel RetrofitControl Module Sensor Data

Examples:

• Direct adaptive control for civil aviation (MIT)

• Control allocation methods (Boeing core effort)

IN-LINE ARCHITECTUREmodify inputs to production Controller

ProductionControl Law

In-line RetrofitControl Module

Sensor Data

Pilot Input

Sensor Data

^ u

Example:

Current work: indirect adaptive model based control (Barron Associates and Boeing)


Comparison of Retrofit Architectures

Both Architectures Designed to be Non-Interfering

• Nonzero inputs only result when performance differs from baseline

Advantages of Parallel Implementation• Control of individual actuators provides more

opportunities to reconfigure the aircraft

Advantages of In-Line Implementation• Command limiting, structural filters, etc.

remain in effect• Safety features of existing CLAW need not

be duplicated or abandoned• Architecture is similar to autopilot

If it isn’t broken, don’t fix it!

More Powerful

Should be easier to certify.Lessened V&V Requirements

(if being added to an existing system)


How Does it Work

Damaged Airplane

Undamaged Airplane

Damaged Airplane

Pilot Inputs

Pilot Inputs

Pilot + RetrofitInputs

Reconfiguration covers up damages to allow pilot to fly airplane with minimal manual corrections to instinctive commands …

• Retrofit control law has model of how aircraft should respond

• Available sensor data is used to identify in real-time a model of how aircraft is responding

• Retrofit control law compares the two models and computes an additive command for pitch stick and roll stick in software


Retrofit Control Law Diagram

Ffq

Ref. Model (Commanded

Response)

Receding Horizon Control

Fcmd

Fpl

f

SystemModel

1/s

1

AW

Model Inputs (states, controls, airdata, etc.)

Commands

States

Co

ntr

ol

Fi

2

1

3

Design Concept: Adaptively computed gains are applied to feedforward, feedback, and integral error states to yield control variables (which are increments to pilot commands that recover, to the extent possible, nominal flying qualities)


Major ComponentsReference Model (Prescribed Offline)

• Low order equivalent system transfer functions from pilot stick to aircraft responses (i.e. pitch stick to pitch rate, roll stick to roll rate, etc.)

Parameter ID System Model (Adapted Online) • State Space model with time varying parameters• Modified Sequential Least Squares algorithm – a regularized

parameter estimation method to determine system model terms

Model-Based Adaptive Control (Solved Online) • Online control design procedure that operates on

the system and reference models to generate controlcommands that cause aircraft dynamics to trackreference models.

• Continuous-time formulation of receding horizoncontrol for a state-space system model

1

2

3

How you want theA/C to respond

How the A/C isactually responding

How to make theA/C respond morelike what you want


Retrofit Control Law Testing

Batch simulation

Tens of thousands of NRTCASTLE simulation cases

Pilot-in-the-loop

Successful software only pilot-in-the-loop simulationtesting with Boeing andNavy Pilots

Hardware-in-the-loop

Extensive pilot-in-the-loop verificationof retrofit control running real-timein the FSFCC

Flight Testing

Two flights completed

Mach Number

0 0.1 0.90.80.70.60.50.40.30.20

5

10

15

20

25

30

35

40

Class BEnvelope 400

300

200100

250 KCASProcedural Limit

Altitude(kft)

DynamicPressure (psf)

NRT Test PointPiloted Soft. Only Sim. Test Point

HILS & Flight Test Points


Batch Simulation Results

• Completed extensive simulation testing using the Navy’s high-fidelity simulation environment (CASTLE)– Wide range of failures and damage– Turbulence– Sensor Noise– Different Aircraft Configurations

• 75% of cases rated as good or excellent with regards to ability to restore nominal flying qualities

• 85% of cases rated as fair or better

• Majority of remaining cases did not have sufficient control power to achieve fair or better due to physical limitations


Piloted Simulation Results

1 2 3 4 5 6 7 8 9 10

Excellent Fair: Some Mildly Unpleasant Deficiencies

Moderately Objectionable Deficiencies

MajorDeficiencies

Loss of Control During Some Operations

Cooper-Harper Handling Qualities Ratings

Nominal F/A-18

Pilot A Pilot B

F/A-18 with Retrofit (for failure cases)

Pilot A Pilot B

F/A-18 with Production CAS (for failure cases)

Pilot A Pilot B

Piloted Simulation Scope• Navy and Boeing pilots

• Three flight conditions1: (0.7M, 20kft) 2: (0.9M, 30kft) 3: (0.6M, 30 kft)

• Failures to primary aerodynamic control surfaces(stab., aileron, rudder)

Bars comprise 12 to 15 HQR assessments of refueling, target tracking, bank / heading / pitch capture, etc.


Pilot Comments and Observations

• Pilot Tracking Task (Mach 0.60, 30 kft), Left Stabilator 6 deg. Down

• Close agreement between commanded & achieved pitch and roll

• Data confirms pilot’s observation that

“Improvement was eliminating the strong right roll-off and the roll coupling with pitch. A yaw left with pitch up, yaw right with pitch down was introduced.”

• Inflight Refueling Task (Mach 0.70, 20 kft), Left Aileron 20 deg. Down

• Close agreement between commanded & achieved pitch and roll

• Uncommanded yaw significantly less for this flight condition and task

• Data supports pilot assessment of system for this case

“The elimination of the constant left stick input and the roll coupling were a sure improvement. It was hard to see a degradation in tanking resulting from any yaw coupling that may have been present. Difficult, but roughly equivalent to the baseline airplane.”


Retrofit Algorithm Selection

• meaningful demonstration possible without pedal-augmented retrofit architecture

• stick-only architecture representsappropriate tradeoff of performanceand hardware implementation feasibilityin the 1750A

Reconfiguration improvementsof the stick and pedal retrofitcontrol law are lessened slightlybecause of slower update ratesin the 1750A hardware…

Substantial reconfiguration benefits shown in piloted simulations with rudder pedal omitted from retrofit algorithm

Conclusion: use stick-only retrofit architecturefor HILS and flight testing


Flight Hardware

FSFCC

• Fleet Support Flight Control Computer (FSFCC)(formerly the Production Support FCC (PSFCC))

• Standard F/A-18A-D FCC but with an additional processor card in each channel

• During flight, control of the aircraft can be passed from the baseline (701E) processors to the research (1750A) processors in order to perform an experiment

• Control is passed back to the standard flight control system in the event that any of the multiple safety monitors are tripped (or manually via paddle switch)


Implementation of Retrofit ControllerF/A-18 Fleet Support Flight Control Computer

ControlLaws

(V10.1)

InputSignalMgmt

Output Signal Select & Fader Logic

ActuatorSignal Mgmt

Baseline F/A-18 Central Processing Unit (701E)

Surface Actuator Analog Interface

Built-In Test, Executive, and Data Management

Military Spec1553 Inputs

AnalogInputs

Executive

PACE 1750A Research Processor

Dual-Port Random Access Memory (DPRAM)

RetrofitCLAW

FailureSim

pilot actpilot Streamlined

Copy ofF/A-18 CAS


701E Safety Monitoring

Criteria Name Description

AOA/Air Data Fail Air Data Fail or AOA Fail w/ NO WOW

Disengage Request Selected ADS Switch

RFCS Data Not Ready Set when RFCS Data Ready Test Fails

RFCS Command not Valid Set when RFCS Command Min/Max Level Exceeded

RFCS NoGo Indication Signal read from local dual port and set by 1750A. 1750A-defined logic sets no go status

Actuator Failure Any 1 of 36 Failures

Dual Discrete Any 1 of the 15 Dual Discrete Failures

Quad Discrete Failure Any 1 of the 28 Quad Discrete Failures

Quad Sensor Failure Any 2 for DISENGAGE Failures

1750A Processor Failures 1750A Watch Dog Monitor, 1750A Watch Dog Monitor Fail on Power Up,1750A CPU Fail, 1750A PBIT PROM pair Checksum Fail, 1750A PBIT Register Fail Flag, Cross Channel Data Test Fail

Dual Port Ram Invalid Dual Port RAM Ready Fail Flag, Dual Port RAM Fail Flag, or Integrator Seed Out of Limits

MUX Bus Invalid MUX Bus Valid Flag Word

DEL/AUTOPILOT/MECH Modes in which you cannot stay Engaged: Pitch DEL, Roll DEL, Yaw DEL, Mechanical Backup - BIT, IBIT

Master Caution LEF Hydraulic Motor Fail, Flaps OFF Caution, Rudder OFF Caution, Aileron OFF Caution, Stabilator OFF Caution, DEL ON Caution

Channel OFF Local X, Y, or Z OFF

Automatic Disengage Criteria


1750A Safety Monitoring

• Checks health and status of miscellaneous parameters

– For example: Spin, Spin switch, heading hold

• Envelope limits

– Monitors p, q, r, Nz, Altitude, Airspeed, etc.

– Parameters must be within predefined limits in order to engage the research processor

– Research processor will automatically disengage if necessary

– Limits are contained in a lookup table

– Pilot selects table entry through DDI inputs


HILS and Flight Test Plan

• Conduct flight test maneuvers and evaluate handling qualities for the following scenarios:

– Retrofit control inactive, no failures(provides nominal performance baseline)

– Retrofit control active, no failures(demonstrates non-interference)

– Retrofit control inactive, with failures(provides degraded performance baseline)

– Retrofit control active, with failures(demonstrates benefit of reconfiguration)

• Failures under consideration

– Right aileron stuck at given position (± 30° offset)

– Right stabilator stuck at given position (± 6° offset)


HILS and Flight Test Plan (cont’d)

• Flight test maneuvers

– Stick doublets

– Pitch and bank angle captures

– “Guns” tracking (with chase as target)

• Aircraft configuration

– F/A-18C

– Clean with exceptionof center-line tank

– CR and PA

0 2 4 6 8 10-1.5

-1

-0.5

0

0.5

1

1.5

Time (sec)

stick / max(stick)

q / max (q)


1 2 3 4 5 6 7 8 9 10



MajorDeficiencies



Pitch Attitude Capture

Bank-to-Bank Rolls

Retrofit – Smooth Mnvr. / Coarse Tracking

Retrofit – Aggressive Mnvr. / Fine Tracking

V10.1 CAS – Smooth Mnvr. / Coarse Tracking

V10.1 CAS – Aggressive Mnvr. / Fine TrackingLegend

Guns Tracking

Pilot: “TOD” (Maj. Matt Doyle)

HILS Results: 30° Aileron Failure (UA)

HQR = 2.0

HQR = 1.0

HQR = 1.5

Average HQR = 1.5


Flight Test: 30° Aileron Failure (v10.1)


Flight Test: 30° Aileron Failure (Retrofit)


1 2 3 4 5 6 7 8 9 10



MajorDeficiencies



Pitch AttitudeCapture

Bank-to-BankRolls

Retrofit – Smooth Mnvr. / Coarse Tracking

Retrofit – Aggressive Mnvr. / Fine Tracking

V10.1 CAS – Smooth Mnvr. / Coarse Tracking

V10.1 CAS – Aggressive Mnvr. / Fine TrackingLegend

Guns Tracking*(Level Turn)

Pilot: “TOD” (Maj. Matt Doyle)

Flight Results: 30° Aileron Failure (UA)

Guns Tracking*(Maneuvering)

HQR = 2.0

HQR = 1.0

HQR = 1.0

HQR = 2.5

Average HQR = 1.6


R&D Summary

1 2 3 4 5 6 7 8 9 101 2 3 4 5 6 7 8 9 10



MajorDeficiencies



Nominal F/A-18

F/A-18 with Retrofit (for failure cases) F/A-18 with Production CAS

(for failure cases)

Pilot A

Pilot APilot A Pilot B

Pilot B

Pilot B

• Tens of thousands of NRT CASTLE simulation cases

• Successful piloted simulations with Boeing & Navy pilots

• Implementation in US Navy F/A-18 FSFCC

• Successful HILS piloted testing

• Half way through flight test program

F/A-18 flight testing at Patuxent River NAS …

NO

NE

LEF

har

dove

r (-

)

LEF

lock

ed @

eng

age

LEF

har

dove

r (+

)

LEF

dam

ped

trai

l

AIL

har

dove

r (-

)

AIL

lock

ed @

eng

age

AIL

har

dove

r (+

)

AIL

dam

ped

trai

l

TE

F h

ardo

ver

(-)

TE

F lo

cked

@ e

ngag

e

TE

F h

ardo

ver

(+)

TE

F m

issi

ng

TE

F h

ydra

ulic

fai

lure

TE

F d

ampe

d tr

ail

ST

AB

har

dove

r (-

)

ST

AB

lock

ed @

eng

age

ST

AB

har

dove

r (+

)

ST

AB

hyd

raul

ic f

ailu

re

ST

AB

dam

ped

trai

l

RU

D h

ardo

ver

(-)

RU

D lo

cked

@ e

ngag

e

RU

D h

ardo

ver

(+)

RU

D d

ampe

d tr

ail

trim n/athrottle step n/asmall amplitude pitch doublet n/asmall amplitude roll doublet n/asmall amplitude yaw doublet n/amoderate amplitude pitch doublet n/amoderate amplitude roll doublet n/amoderate amplitude yaw doublet n/alarge amplitude pitch doublet n/alarge amplitude roll doublet n/alarge amplitude yaw doublet n/across control n/aloaded roll n/a

NO

NE

LEF

har

dove

r (-

)

LEF

lock

ed @

eng

age

LEF

har

dove

r (+

)

LEF

dam

ped

trai

l

AIL

har

dove

r (-

)

AIL

lock

ed @

eng

age

AIL

har

dove

r (+

)

AIL

dam

ped

trai

l

TE

F h

ardo

ver

(-)

TE

F lo

cked

@ e

ngag

e

TE

F h

ardo

ver

(+)

TE

F m

issi

ng

TE

F h

ydra

ulic

fai

lure

TE

F d

ampe

d tr

ail

ST

AB

har

dove

r (-

)

ST

AB

lock

ed @

eng

age

ST

AB

har

dove

r (+

)

ST

AB

hyd

raul

ic f

ailu

re

ST

AB

dam

ped

trai

l

RU

D h

ardo

ver

(-)

RU

D lo

cked

@ e

ngag

e

RU

D h

ardo

ver

(+)

RU

D d

ampe

d tr

ail

trimthrottle stepsmall amplitude pitch doubletsmall amplitude roll doubletsmall amplitude yaw doubletmoderate amplitude pitch doubletmoderate amplitude roll doubletmoderate amplitude yaw doubletlarge amplitude pitch doubletlarge amplitude roll doubletlarge amplitude yaw doubletcross controlloaded roll

NO

NE

LEF

har

dove

r (-

)

LEF

lock

ed @

eng

age

LEF

har

dove

r (+

)

LEF

dam

ped

trai

l

AIL

har

dove

r (-

)

AIL

lock

ed @

eng

age

AIL

har

dove

r (+

)

AIL

dam

ped

trai

l

TE

F h

ardo

ver

(-)

TE

F lo

cked

@ e

ngag

e

TE

F h

ardo

ver

(+)

TE

F m

issi

ng

TE

F h

ydra

ulic

fai

lure

TE

F d

ampe

d tr

ail

ST

AB

har

dove

r (-

)

ST

AB

lock

ed @

eng

age

ST

AB

har

dove

r (+

)

ST

AB

hyd

raul

ic f

ailu

re

ST

AB

dam

ped

trai

l

RU

D h

ardo

ver

(-)

RU

D lo

cked

@ e

ngag

e

RU

D h

ardo

ver

(+)

RU

D d

ampe

d tr

ail


NO

NE

LEF

har

dove

r (-

)

LEF

lock

ed @

eng

age

LEF

har

dove

r (+

)

LEF

dam

ped

trai

l

AIL

har

dove

r (-

)

AIL

lock

ed @

eng

age

AIL

har

dove

r (+

)

AIL

dam

ped

trai

l

TE

F h

ardo

ver

(-)

TE

F lo

cked

@ e

ngag

e

TE

F h

ardo

ver

(+)

TE

F m

issi

ng

TE

F h

ydra

ulic

fai

lure

TE

F d

ampe

d tr

ail

ST

AB

har

dove

r (-

)

ST

AB

lock

ed @

eng

age

ST

AB

har

dove

r (+

)

ST

AB

hyd

raul

ic f

ailu

re

ST

AB

dam

ped

trai

l

RU

D h

ardo

ver

(-)

RU

D lo

cked

@ e

ngag

e

RU

D h

ardo

ver

(+)

RU

D d

ampe

d tr

ail


NO

NE

LEF

har

dove

r (-

)

LEF

lock

ed @

eng

age

LEF

har

dove

r (+

)

LEF

dam

ped

trai

l

AIL

har

dove

r (-

)

AIL

lock

ed @

eng

age

AIL

har

dove

r (+

)

AIL

dam

ped

trai

l

TE

F h

ardo

ver

(-)

TE

F lo

cked

@ e

ngag

e

TE

F h

ardo

ver

(+)

TE

F m

issi

ng

TE

F h

ydra

ulic

fai

lure

TE

F d

ampe

d tr

ail

ST

AB

har

dove

r (-

)

ST

AB

lock

ed @

eng

age

ST

AB

har

dove

r (+

)

ST

AB

hyd

raul

ic f

ailu

re

ST

AB

dam

ped

trai

l

RU

D h

ardo

ver

(-)

RU

D lo

cked

@ e

ngag

e

RU

D h

ardo

ver

(+)

RU

D d

ampe

d tr

ail


NO

NE

LEF

har

dove

r (-

)

LEF

lock

ed @

eng

age

LEF

har

dove

r (+

)

LEF

dam

ped

trai

l

AIL

har

dove

r (-

)

AIL

lock

ed @

eng

age

AIL

har

dove

r (+

)

AIL

dam

ped

trai

l

TE

F h

ardo

ver

(-)

TE

F lo

cked

@ e

ngag

e

TE

F h

ardo

ver

(+)

TE

F m

issi

ng

TE

F h

ydra

ulic

fai

lure

TE

F d

ampe

d tr

ail

ST

AB

har

dove

r (-

)

ST

AB

lock

ed @

eng

age

ST

AB

har

dove

r (+

)

ST

AB

hyd

raul

ic f

ailu

re

ST

AB

dam

ped

trai

l

RU

D h

ardo

ver

(-)

RU

D lo

cked

@ e

ngag

e

RU

D h

ardo

ver

(+)

RU

D d

ampe

d tr

ail


Mach Number

0 0.1 0.90.80.70.60.50.40.30.20

5

10

15

20

25

30

35

40

Class BEnvelope 400

300

200100

250 KCASProcedural Limit

Altitude(kft)

DynamicPressure (psf)

NRT Piloted Soft. Only Sim. HILS & Flight Test


Back-up Slides


Open Literature Publications

Barron Associates, Inc.

Ward, D. and Monaco, J., "System Identification for Retrofit Reconfigurable Control of an F/A-18," AIAA Journal of Aircraft (to be published).

Monaco, J., Ward, D., and Bateman, A., "A Retrofit Architecture for Model-Based Adaptive Flight Control," AIAA Paper No. 2004-6281, in Proc.of AIAA Intelligent Systems Conference, Sep. 2004.

Boeing and NAVAIR

Black, S., et. al., "Reconfigurable Control and Fault Identification System," 2004 IEEE Aerospace Conference. March 6-13, 2004, Big Sky, MT.


NAVAIR Program Background• The Navy has been investing in reconfigurable control technology as part

of the Flight Control Predictive Diagnostic (FCPD) project

• FCPD Objective: To develop & demonstrate damage & failure diagnostics/prognostics approaches for reconfigurable control, condition-based maintenance, and improved situational awareness

Flight ControlReconfiguration

Faults, Health Observable at A/C System Level

Pilot or Autonomous System Action:• Reconfiguration Compensates for Damage and Failures

Health, Faults,Anomaly

Aircraft LevelDamage ID

Health StatusFusion

ComponentStatus

Maintenance Support: • Prognostics

System andComponent Health

Component Health

Inform of remaining capabilityFaults, Health Observable at Component Level

Ability to perform in-flight tests without disrupting flight


FSFCC Hardware is Flight Proven

• Developed jointly by NAVAIR and NASA

• Derivative of NASA HARV configuration

• Compatible with any F/A-18A-D– Requires flight test jumpers installed on MCs

– Requires DAF

• Originally Flight tested at NASA Dryden and at Patuxent River in 1998 (FSFCC V1.1 Software)– 3 flights at NASA Dryden

– 11 flights at Patuxent River

– All test objectives met


Pilot Interface

LEF

TEF

AIL

RUDSTAB

NIGHT

OFF

AUTO

DAY

SV1SV2

SV1SV2

SV1SV2

SV1SV2

BRT CONT

MENU MNVRFCS

G

BLIN

MODE

OAV

1

2

3

4

5

PRY

STICKPEDAL

AOABADSA

PROCDEGD

1 2 3 4

CAS

LEF

TEF

AIL

RUDSTAB

NIGHT

OFF

AUTO

DAY

SV1SV2

SV1SV2

SV1SV2

SV1SV2

BRT CONT

MENU MNVRFCS

G

BLIN

MODE

OAV

1

2

3

4

5

PRY

STICKPEDAL

AOABADSA

PROCDEGD

1 2 3 4

CAS

LEF

TEF

AIL

RUDSTAB

NIGHT

OFF

AUTO

DAY

SV1SV2

SV1SV2

SV1SV2

SV1SV2

BRT CONT

MENU MNVRFCS

G

BLIN

MODE

OAV

1

2

3

4

5

PRY

STICKPEDAL

AOABADSA

PROCDEGD

1 2 3 4

CAS

LEF

TEF

AIL

RUDSTAB

NIGHT

OFF

AUTO

DAY

SV1SV2

SV1SV2

SV1SV2

SV1SV2

BRT CONT

MENU MNVRFCS

G

BLIN

MODE

OAV

1

2

3

4

5

PRY

STICKPEDAL

AOABADSA

PROCDEGD

1 2 3 4

CAS

DDI [A] to completesequence and arm FSFCC

DDI [B], [C], [D] combinations to define test

NWS button to engage FSFCC

ADS paddle to disengage FSFCC

1 2

3 4For Example

DCCBBB = Table 22 Row 0(Fail R Stab to 0)

CCBCB = Table 4 Row 3(Nz Upper Limit Table Entry 1)


Major ComponentsReference Model (Prescribed Offline)

A model that encodes the desired aircraft responsesto pilot inputs as a function of operating condition, etc.

• Low order equivalent system transfer functions from pilot stick to aircraft responses (i.e. pitch stick to pitch rate, roll stick to roll rate, etc.)

• Model parameters computed from high-fidelity simulation data of nominal (unimpaired) aircraft

• Model parameters at a given operating condition are functions of input magnitude (see figure)

• Reference model integrated online (80 Hz update in the 1750A FSFCC)

Parameter ID System Model (Adapted Online) A model that encodes the dynamical responses of the aircraft as it maneuvers through the flight envelope.

• State Space model with time varying parameters

• Modified Sequential Least Squares algorithm – a regularized parameter estimation method to determine system model terms

• MSLS update of system model done online (5 Hz update in the 1750A FSFCC)

1

2

-3 -2 -1 0 1 2 3

Roll Stick (in)

K (

1/in

-se

c)

Powered Approach

Transonic Cruise

Supercruise

-3 -2 -1 0 1 2 3

Roll Stick (in)

K (

1/in

-se

c)

Powered Approach

Transonic Cruise

Supercruise

Example: Transfer Function Gain, Roll Axis Ref. Model


Major Components (cont’d)

Model-Based Adaptive Control (Solved Online) Online control design procedure that operates on the system and reference models to generate control commands that cause aircraft dynamics to track reference models.

• Continuous-time formulation of receding horizon control for a state-space system model

• “Optimal” solution via differential Riccati equations replaced with approximate solution to integrate control law gains directly

– 30 percent less memory, 25 percent faster computation

– Closed loop simulation performance comparable for set of test cases considered

• Control gain differential equations solved online (10 Hz update in 1750A FSFCC)

• Most recent control gains applied at basic frame rate (80 Hz in 1750A FSFCC)

3


Control Law Cost Function

RHO is a solution to the finite horizon optimization problem that minimizes

dtuQuxQxyyQyyFdtJff t

tt

uT

IITIrT

Tr

t

tt

00

21

21

21 )()(

nnTQ

nniQ

mmuQ

symmetric positive semidefinite weighting matrix that assigns importance to predicted tracking error

symmetric positive semidefinite weighting matrix that assigns importance to integrated tracking error

symmetric positive definite weighting matrix that penalizes control effort

Documents

Retrofit Reconfigurable Control of an F/A-18C Tony Page & Dean Meloney Naval Air Systems Command Society of Flight Test Engineers Patuxent River, MD 16