NASA/CP-2001-210389/VOL2 ......................

¢

Pilot-Induced Oscillation Research:

Status at the End of the Century

Compiled by Mary E Shafer and Paul Steinmetz ....

NASA Dryden Flight Research Center ............

Edwards, California ...................

April 2001
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NAS A/CP-2001-210389/VOL2

Pilot-Induced Oscillation Research:

Status at the End of the Century

Compiled by Mary E Shafer and Paul Steinmetz ............

NASA Dryden Flight Research Center =-

Edwards, California _ i

National Aeronautics and

Space Administration

Dryden Flight Research Center

Edwards, California 93523-0273

_L

71! _ii_i

April 2001
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Foreword

"Pilot-Induced Oscillation Research: The._Status at the End of the Century," a workshop

held at NASA Dryden Flight Research Center on 6-8 April 1999, may well be the last

large international workshop of the twentieth century on pilot-induced oscillation (PIO).

With nearly a hundred attendees from ten i_0untdes and thirty presentations (plus two that

were not presented but are included in the proceedings) the workshop did indeed

represent the status of PIO at the end of the:century.

These presentations address the most cu_en___t)nformation available, addressing regulatory

issues, flight test, safety, modeling, prediction, simulation, mitigation or prevention, and

areas that require further research. A!l presentations were approved for publication as

unclassified documents with no limits on their distribution.

This proceedings include the viewgraphs (some with authors' notes) used for the thirty

presentations that were actually given as well as two presentations that were not given

because of time limitations. Four technical paper s on this subject that offer this

information in a more complete form ar(a_Iso included. In addition, copies of the related

announcements and the program are incorporated, to better place the workshop in the

context in which it was presented.

Mary F. Shafer

%

iii
q
CONTENTS

FOREWORD. == iii

VOLUME 1 - SESSIONS I - III

SESSION I - 6 APRIL 1999 ............... _:__. ....................................... 1

1. Modeling the Human Pilot in Single-Axis Linear and Nonlinear Tracking Tasks

Yasser Zeyada and Ronald A. Hess, University of California, Davis ........................... 3

2. Bandwidth Criteria for Category I and I!••PIOs

David G. Mitchell, Hoh Aeronautics, Inc; and David H. Klyde, Systems Technology, Inc .......... 17

3. Criteria for Category I PIOs of Transports Based on Equivalent Systems and Bandwidth

Kenneth F. Rossitto and Edmund J. Field, BoeingPhantom Works ........................... 29

4. Designing to Prevent PIO

John C. Gibson, Consultant, British Aerospace..i_. ...................................... 41

SESSION II - 6 APRIL 1999 .............. ....................................... 53

5. Replicating HAVE PIO on the NASA Ames VMS

Jeffery Schroeder, NASA Ames Research Cente_ _ --i-...................................... 55

6. Replicating HAVE PIO on Air Force Simulators

Ba T. Nguyen, Air Force Research Laboratory 65

7. Prediction of Longitudinal Pilot-lnduced Oscillations Using a Low Order

Equivalent System Approach

John Hodgkinson and Paul T. Glessner, Boeing! and David G. Mitchell, Hoh Aeronautics, Inc ...... 67

8. Recommendations to Improve Future P!O.Simulations

Brian K. Stadler, Air Force Research Laboratory.:2_ ......... , ............................. 81

SESSION III - 7 APRIL 1999 93

9. FAA's History with APC

Guy C. Thiel, FAA ...................... ...................................... 95

10. PIO and the CAA

Graham Weightman, JAA (UK CAA) ...... 107

11. PIO Flight Test Experience at Boeing (Puget Sound) - and the Need for More Research

Brian P. Lee, Boeing Commercial Airplane Group. ...................................... 109

12. The Effects on Flying Qualities and PIO of Non-Linearities in Control Systems

Edmund Field, Boeing Phantom Works ....... .:.... . ..................................... 157

13. Mitigating the APC Threat - a work in progress

Ralph A'Harrah, NASA Headquarters ...... . .................................... 171

V
VOLUME 2 - SESSIONS IV - V

SESSION IV - 7 APRIL1999 ...................................................... 179

14. Flight Testing for APC: Current Practice at Airbus

Pierre Poncelet, Aerospatiale Aeronautique; and Femando Alonso, Airbus Industrie ............. 18 l

15. The Prediction and Suppression of PIO Susceptibility of Large Transport Aircraft

Rogier van der Weerd, Delft University of Technology .................................... 189

16. Flight Testing For PIO

Ralph H. Smith, High Plains Engineering .............................................. 217

17. Use of In-Flight Simulators for PIO Susceptibility Testing and for Flight Test Training

Michael Parrag, Veridian Engineering .................................................. 227

18. A Method for the Flight Test Evaluation of PIO Susceptibility

Thomas R. Twisdale and Michael K. Nelson, USAF Test Pilot School ........................ 259

SESSION V - 8 APRIL 1999 ....................................................... 269

19. Onboard PIO Detection and Prevention

David B. Leggett, Air Force Research Laboratory ........................................ 271

20. Real Time PIO Detection and Compensation

Chadwick J. Cox, Carl Lewis, Robert Pap, and Brian Hall, Accurate Automation Corporation ..... 279

21. PIO Detection with a Real-time Oscillation Verifier (ROVER)

David G. Mitchell, Hob Aeronautics, Inc ............................................... 299

22. Pilot Opinion Ratings and PIO

Michael K. Nelson and Thomas R. Twisdale, USAF Test Pilot School ........................ 305

23. The Need for PIO Demonstration Maneuvers

Vineet Sahasrabudhe and David H. Klyde, Systems Technology, Inc.;

and David G. Mitchell, Hoh Aeronautics, Inc ............................................ 307

VOL_ 3 - SESSION VI AND APPENDICES

SESSION V! - 8 APRIL 1999 ...................................................... 317

24. Boeing T-45 Ground Handling Characteristics

James G. Reinsberg, Boeing St. Louis ................................................. 319

25. Extraction of Pilot-Vehicle Characteristics from Flight Data in the Presence

of Rate Limiting

David H. Klyde, Systems Technology, Inc,; and David G. Mitchell, Hoh Aeronautics, Inc ........ 329

26. Comparison of PIO Severity from Flight and Simulation

Thomas J. Cord, Air Force Research Laboratory ......................................... 343

27. A Summary of the Ground Simulation Comparison Study (GSCS)

for Transport Aircraft

Terry von Klein, Boeing Phantom Works .............................................. 359

28. Real Experiences in the Frequency Domain

Randall E. Bailey and Andrew Markofski, Veridian Engineering ............................ 365

29. Pilot Modeling for Resolving Opinion Rating Discrepancies

David B. Doman, Air Force Research Laboratory ........................................ 391

a$

vi
30. Closing Remarks

Mary F. Shafer, NASA Dryden Flight Research Center ................................... 397

APPENDIX 1: ANNOUNCEMENTS, INFORMATION, AND PROGRAM ................ 399

1. Announcement and call for papers .......... ....................................... 401

2. Information for presenters and attendees (sent by e-mail) ............................. 403

3. Program ......................... _-=_i ...................................... 409

APPENDIX 2: PRESENTATIONS PRINTED BUT NOT GIVEN AT THE WORKSHOP... 411

1. Recent Results of APC Testing with ATTAS

Holger Duda and Gunnar Duus, Deutches Zentrum ftir Luft- und Raumfahrt e.V ............... 413

2. Criteria to Simulation to Flight Testma_ice Versa

David G. Mitchell, Hob Aeronautics, Inc. 439

APPENDIX 3: PAPERS SUPPORTING WORKSHOP PRESENTATIONS ............... 453

1. Designing to Prevent Safety-Related PIO

J.C. Gibson, British Aerospace Warton (retired), Consultant ................................ 455

2. Pilot-Induced Oscillation Prediction with Three Levels

of Simulation Motion Displacement

Jeffery A. Schroeder, William W.Y. Chung, and Duc T. Tran, NASA Ames Research Center;

and Soren Laforce and Norman J. Bengford, SYRE Logicon ................................ 475

3. A Method for the Flight Test Evaluation of PIO Susceptibility

Thomas R. Twisdale and Michael K. Nelson, USAF Test Pilot School ........................ 487

4. Pilot Opinion Ratings and PIO

Michael K. Nelson and Thomas R. Twisdale, USAF Test Pilot School ........................ 493

vii

Ses_n IV

-sin

_179

181
UNEXPERIENCED PILOTS

STRESSFUL ENVIRONMENT: - final apwoach ........

- forma_ flight --

- workload

- heading

_RUNWAY FLY t

attitude and airspeed, and _ aircraft

aligned on the runway centedine

182
183
184
185
186
COMPOS TE FLIGHT

.... - !

FLEXIBLE TOOLS :

_m

_y delay can be adjuste_J

= - " rs-can pmv_posite if,sprays (use of many feedbacks n._ nv, q,... ) ml

187

|NITML L

ii_ml

The Prediction and Suppression of PIO

Susceptibility of Large Transport Aircraft

- An Evaluation of Proposed Methods -

Rogier van der Weerd

DelftUniversity of Technology / Aerospace Engineering

Department of Control and Simulation

6 Apdl 1999

Prepaid and p_sented by

Rogier van der Weerd, M. Sc.

r.vanderweerd@ir.tudelft.nl

Research Associate

Flight Control and Simulation

tel. +31 (0)15 278 9108

fax. +31 (0)15 278 6480

This presentation is based on the results of a study more thoroughly reported in:

Weerd, van der R.; 'PIO Suppression Methods and Their Effects on Large

Transport Aircraft Handling Qualities'; Thesis (M.Sc.), Delft University of

Technology, Delft (The Netherlands), January 1999

The study was carried out under a cooperative agreement between Delft

University of Technology in the Netherlands and The Boeing Company at Long

Beach. A student placement was made possible at the Stability, Control and

Flying Qualities group of Boeing Phantom Works.

The project was carried out under supervision of:

The Boeing Company Delft University of TechnologE

John Hodgkinson Prof.dr.ir. J.A. (Bob) Muider

Dr. Edmund J. Field ir. Samir Bennani

Walter von Klein Jr.

189
|IIIIIN! *

|llltlMI Contents

• Introduction

• Prediction of PIO

- Available Criteria

- Case Study Using Example Aircraft

• Suppression of PIO

- Available Methods

- Case Study Using Example Aircraft

• Conclusions and Recommendations

The study into PIO had two main objectives:

I. Investigate available methods for PIO prediction, including those

recently proposed

2. Investigate possible remedies to PIO

Some of the group's expertise and experience with PIO could be used

to evaluate and validate different criteria and methods using an

example large transport aircraft with different configurations that have

handling qualities that are considered well understood / investigated.

190
cU_ L

iimlJnlll Prediction of PIO

Limitations of Linear Methods (Category I)

Most observed PIOs involved rate saturation of control

surface actuator(s)

• Rate Saturation Result of PIO (poor Cat I properties)

• Or, Rate Saturation Actual Cause of PIO ?

Cat II Evaluation requires the inclusion of nonlinear behavior

This can be done in

• Time Domain

- Time Domain Neal-Smith - Hess Method for Nonlinear Dynamics

• Frequency Domain Using Describing Function Technique

- DLR's Open Loop Onset Point (OLOP)

191
lit L

im Prediction of PIO

Category I Example - Bandwidth

Two Important Parameters

• Bandwidth Frequency, (OBW

("Speed" of System)

• Phase Roll-Off, zp

("Predictability")

Bode Plot of ___0(j_)

_)s_ck

_andw_lth

re,_ t._ ,,f

The Bandwidth criterion has been shown to be a well performing criterion on

a wide variety of cases.

Extending Bandwidth to systems with nonlinear elements is possible (in fact,

the method of performing a frequency sweep in order to estimate the system

frequency response includes all kinds of nonlinear elements of the real

system). Rate limiting elements in the command path of the EFCS can be

identified easily for a given input amplitude. However, if the rate limiting

element is part of a feedback loop, the identification of the describing

function may fail, as typical nonlinear system behavior gets into play, e.g. the

introduction of multiple equilibria (limit cycles, jump resonance).

REF

Hoh et al 1982.

Mitchell et al 1994

Mitchell et al 1998

192
I!nl! !

IRma Nonlinear Systems (i)

_.imit Cycles - sustained nonlinear oscillations, fixed

amplitude, fixed frequency

Conditions for a Limit Cycle are sought zQ

|

Use neutral stability condition (Popov):

C(jto). N(jto, fi). P(jto) = - 1

1

C(joJ).POo_)=---

N(jto, fi)

NOte,O) is the sinusoidal describing function represenation

• _eo .1_ .11o .1_ .1_ .ao

193
|imllt i

iiIRimm

Nonlinear Systems (ii)

Jump Resonance

No unique relation anymore between

frequency and gain/phase of closedloop response

Phase Jump in Pilot-Vehicle System

.0.

Misadaptation by Pilot

PIO

15

10

S

_o

0 4O

-lS

m.op_

i , a E

-|5_) -1DO *SG

194
ilil!!. ! t

IWILHi Prediction of PIO

Category II Example - OLOP

y U

e Flight ' t

r he I Pilot __.. I I,r-_ ,_.1 Bare,

'_'_9_mi(PureGa{n)l i--_ St'y°tet_ i-" T:FLT___ "_ Airframe F-] I

t / Rate Limit l

0

Rate limiting causes Jump Resonance

OLOP determines "the consequence". ,,

4, Cl Pie

_i7 - ,__ OLOP is Luc0J= "_ TTU(OoosetJ " _ ; .oc,

At the onset frequency

i _.r, ,

• _/_ OLOP

_lo_ It P_ _x) OLOP

REF

Duda 1997

Duda et al 1997

195
Ii! i

illi Case Study Configurations

Of The Example Aircraft

• Receiver Aerial Refueling Task

- Clean Configuration

- High Speed, M = 0.613

- High Altitude, h = 20,000 ft

• Pitch Rate Command System Configurations:

- Old Software Version F

- Updated Software Version H

Added Phase Lags t_=[0.1,0.25]

• Simplifications

- Single Axis

- No Model Uncertainties

- No Structural Dynamics

--> PIO PRONE

--->PIO FREE

The Example Aircraft

High Performance Fly-By-Wire Military Cargo Airplane.

High-wing, four engines, T-tail configuration. Length 175 ft, height 55 ft,

wingspan 170 ft, MTOW 600,000 lbs

'High gain' mission tasks include: Landing/Takeoff Short Austere Airfields and

Aerial Receiver Refueling. PIOs were encountered during developmental flight

testing for both tasks [1],[2]

Configurations

Apart from configurations representing old and updated Electronic Flight Control

System (EFCS) software versions, additional configurations were evaluated that

represent the updated EFCS software with intentionally deteriorated

characteristics.

The latter is accomplished by adding phase lags in the flight control system by

increasing the time constant of a first order filter residing in the command path of

the control laws.

REF

Iloputaife et al 1996

Iloputaife 1997

196
11111111t

|lutlgli Pitch Axis PIO Event

EFCS Software Version F

Pilot initiated emergency

breakaway from tanker

Typical category II PIO:

• "High pilot gain"

• "Pilot is 180 ° out of phase"

with pitch attitude

• Software rate limiting of

elevator command signal

[ Ref. Iloputaife 1997, Iloputaife et a11996 ]

_: Pitch Stick Position I'inJ _ pull

r _. ................. " _ ............ " push

Pitch A_tude [de_]

L1 .......

,tlJElevato_ DeflecSo_ [dog]

AJrlpeed [KIA-S ] ......... "_= .....

REF

Iloputaife et al 1996

Iloputaife 1997

197
llll| I,

irma Example Aircraft

Control Law Changes

2

_t_er

PCIo)| I o

Aillaiml I ._

q_nlo_ I I

Main differences between old and new software

1. Structural filtering optimization --) increase system bandwidth

2. Stick shaping change --) reduce control sensitivity

3. Change rate limits --) fully use actuator capability

[ Ref.lloputaife 1997,11oputaife et a11996 ]

REF

Iloputaife et al 1996

lloputaife 1997

198
OmTm_| L

illtmi Bandwidth Criterion

Validation Using Example Aircraft

_ _ PIO_ SusceptlbTe

PIO Su c pt le if Flight Path Bandwidth Insufficient

I;F,,,o " *

o._ ,.0. I I I ,, o

I No,,o ( | _:" ,) a

Pitch Attitude Bandwidth "_'w [tad/s}

• PlO

_' No PlO

_" Approach Flight TeSt

B-2 ° AO_I

Re fuellrlg FliOhl Test

" Flight Test

0 No PIO X-15 FSght Test

m P_O

r'l No PIg

Exmm_Aln;refl Flight Test

" Source: Klyde, OH 04 a11995

Criterion mapping is not considered to

be successful discrimination since flight

path bandwidth is sufficient for both

configurations

711

| ,

),

_0,

i

o;

t_

i 3 FC_ be l_

os i is 3 2S 1 3S 4 aS

P_ _tu_ _a_,_a_ w_Svv.mata[rl_=]

199
elmlBL &

|u OLOP Criterion

Application to Example Aircraft

ilot

"_ i CUT

Pilot

p,,ch cAi

1. Assume pure gain pilot that exerts sinusoidal stick signal with certain amplitude Irl

2. Determine the onset frequencies of all rate limiting elements using

_ This equaf_on can be soJved

,_._2 t }G' c:" ........ I graphically

3. At the critical rate limiter, cut loop, plot loop transfer function on Nichols Chart

4. OLOP is point on locus for o_= _Oo,,._. Its position can be related to Category II PtO

susceptibility

12

2OO
ira! &

NitKml OLOP Criterion

EFCS Software Version F (old)

Onset Frequencies

Inner-Loop ¢Oor_et=2.05 rad/s

Outer-Loop (donset=3.53 rad/s

__. ,;_i.:_i,: ,!,.

13

201
iIIIIIIIIJlL&

1411uulu OLOP Criterion

Validation Using Example Aircraft

[: ; j: ,-" .--":. ', i .; ' i " " -" • ': : :"

_ ir: '.:- --- NoC_I.q_ryUPlQ',; .."

_1¢ I t i ,

• PIO

_7 No PIO

0 P_O

0 No PIO

• PIO

D No P_O

SDg_O _u_e " F'_ht "re=t

" Fhghl Tel_t

Exiling= _I_FP_ F'_ght Tl_t

• Source: Oucla, H 1_197

2O2
,m,. Res Co hensi ,,...,,,, ults mpre ve °

Criteria Validation

Results Category I Criteria

LOES Bandwidth Gibson Smith- Hess NeaI-Smith

CAP t. Geddes

FC EFCS(F) -/- -/- LI/no -/no -/no Ll/no 4-

FC EFCS(H) LI/- 1.2/- Ll/no -/no -/no Lllno LI/-

Results Category tl Criteria

Hess OLOP Time domain

Nonlinear NeaI-Smith

FC,EFCS(F) yes yes yes

FC. EFCS(H) no no no

L1 ,L2,L3

yes,no

Note: EFCS version F showed PIO tendencies

EFCS version H is the updated, PlO-free configuration

predicted CHR

Predicted PIO

susc ul_t_ility

C rilerion doesn't

include prediction

203
CUMII|&

|N_tmm

Remedy to PIO

"Conventional" Methods

• Change Hardware

- Actuators

- Feel System Characteristics

• Change Control Laws

- Control Allocation / Architecture

- Control Sensitivity"

- Reduce Phase Lags / Filtering"

"Alternative" Methods

• PIO Suppression Filter

- Tail Size

- etc.

- System Bandwidth"

- Loop Gains"

- etc.

- Attenuate Pilot Command At Predefined Pilot Operating Conditions

Software Rate Limiters With Phase Compensation

- Reduce Phase Loss Under Rate Saturation

• Thes e methods wm'e applied during the d_elopn'_nl of th_ example alrcm_ _ F_ _ _

16

On most cases of PIO experienced in the past, the problems were discovered in

a relatively late phase of development, or even, during routine operation. A

solution that allows the established control law structure to remain the same

while eliminating PIO susceptibility surely is preferable.

Goal: Look for methods that solve the PIO problem without having to redesign

control laws.

204
!ml. t

|llll.mll

Position

PIO Suppression Filter

Initial Design

AMPLITUDE ESTIMATION

Ji-.............. t---

i ................................................. •

CONTROL ACTIVITY ESTIMATION

stlCk Shaping Function

A

3

Flight Control Systen_

Input

REF

Powers 1981

205
|llllllnlll PIO Suppression Filter

Functionality

Stick shaping function usually is a

3_ order polynomial:

Y = u ( k_ + k2.Juj + k3-u 2)

Suppression is obtained through:

Y=u(k 1+ k2"lul'K + k3"u2)

In which K is The suppression gain

"Stick desensitizinq"

1B

2O6
|IIITM| L

|tmlLmi PIO Suppression Filter

Response to Example Case

19

......... +:++

• +,l

+ + +

+

[ Source Iloputaife 1997]

PSD of Stick Deflection Signal

5

83

k--

_2

n

0

0 1 2 3 4

F+'equency _rad/s_

Excluding PIO Frame

2O

I1.

0I

0 1 2 3 4

Frequency _radJs_

Including PIO Frame

Sampling Rate

f,=t0 Hz

No. of Samples

N=2,300

Frequency Resolution

A(o=0.14 rad/s

Conclusion:

During 'normal' task execution, pilot inputs contain energy in the frequency region of the

actual PIO (which is about 2.3 rad/s)

REF

Iloputaife 1997

207
eili!l!ll li

liNtlllll Phase Compensated Rate Limiting Schemes 2o

(Rundqwist - Saab Military Aircraft)

ng.e.o..m._

• Under rate saturation, excess

in demand is fed back

• Rate limiter command signal

is attenuated

• Result: Output will change

direCtion when input does

REF.

Hanke 1995

Rundqwist et al 1997

2O8
|IIIIIWl L

|ltm_ Phase Compensated Rate Limiting Schemes 2,

Effect on Closed-Loop System Using OLOP

Stability Margin Analysis

Conventional rate limiting:

Phase Jump, undesirable

Alternative rate limiting

Avoids Phase Jump

Retain stability with same rate

limit imposed on system

[ ': "_ ' _ :" U_..arL_pTransn_ls.lo.,

= /' I " ,_X_l.. - Rate Lirn:dit_- ....

:: _cohv_.on@ _Z. _,x " " -

| ...... X : " I -:;:'-::" --')_" "Rate L m ler

_.22r_ -2Cr - tt_ l';w' ::)..' .,_2_3 -l, Ci ._'_ ".,

209
ira| L

|u Conclusions

Category II PIO criteria were successfully validated against a

limited selection of example aircraft configurations

When designed properly, a PIO suppression filter can identify

a developing PIO And take avoidance action.

Phase compensated rate limiters can alleviate the severe

penalty associated with rate saturation in a closed-loop

system.

22

210
eui! l

iRLIH Further Work

23

• Perform similar analysis for other PIO data

• Compare results of this study with recent experimental flight

test data

• Address effect of structural dynamics on handling qualities

and PIO

• Incorporate modern tools for stability analysis (mu, LMIs)

Goal: towards category Ill PIO prediction

211
|_t L

LIEngllm References

Bailey, R.E., Bidlack, TJ.; 'Unified Pilot-Induced Oscillation Theory Volume IV: Time-Domain Neal-Smith Criterion';

Flight Dynamics Directorate, Wright Laboratory Report WL-TR-96-3031, December 1995.

Bailey, R.E., Bidlaek, Tj.; 'A quantitative criterion for Pilot-Induced Oscillations: Time Domain Neal-Smith Criterion';

AIAA-96-3434-CP

Duda, tl.; 'Flying Qualities Criteria Considering Rate Limiting'; DLR-FB 97-15. Braunschweig. 1997 tin German).

Duda, tI., Hovmark, G., Forssell, L.: 'Prediction of Category II Aircraft-Pilot Couplings - New Experimental Results

A1AA-97-3499.

Hanke, D.; 'Handling Qualities Analysis on rate Limiting Elements in Flight Control Systems'; AGARD-AR-333,

February 1995.

Hess, R.A.; 'Model for Human Use of Motion Cues in Vehicular Control'; Journal for Guidance, Control and Dynamics,

VoI.13, No. 3, 1989.

•Hess, R.A.; 'A Unified Theory for Aircraft Handling Qualities and Adverse Aircraft-Pilot Coupling'; AIAA-97-0454.

bHess, R.A.; "Assessing Aircraft Susceptibility to Nonlinear Aircraft-Pilot Coupling, Pilot Induced Oscillations'; AIAA97-3496.

"Hess, R.A.; 'A theory for the Roll-Ratchet Phenomenon in High Performance Aircraft'; A1AA-97-3498.

Hess, RA., Stout, P.W.; "Predicting Handling Qu',dities Levels for Vehicles with Nonlinear Dynamics'; AIAA-98-0494.

Hoh, R.E., Hodgkinson, J.; 'Bandwidth - A Criterion for Highly Augmented Airplanes'; AGARD CP-333. April 1982.

lloputaife, O.I., Svoboda, GJ., Bailey, T.M.;'Handling Qualities Design of the C-17 for receiver-refueling'; AIAA-96-

3746.

lloputaife, O.I.; 'Minimizing Pilot-Induced-Oscillation Susceptibility during C-17 development'; AIAA-97-3497.

Mitchell, D.G., Hob, R.H., Aponso, B.L., Klyde, D.H.; 'The Measurement and Prediction of Pilot-in-the-Loop

Oscillations'; AIAA-q4-3670-CP.

Mitchdl, D.G., Klyde, D.If.; 'A Critical Examination of PIO Prediction Criteria'; AIAA-98-4335.

Powers, B.G.; 'An Adaptive Stick-Gain to Reduce Pilot-lnduced Oscillation tendencies'; Journal of Guidance, Control

and Dynamics, Volume 5, Number 2, 1981.

Rnndqwist, L, Hillgven, It; 'Rate Limiters with Phase Compensation in JAS 39 Gripen'; SAE Aerospace Control and

Guidance Systems Committee, Monterey, CA, March 1997.

212
liM_IL t

|MILmI Backup Slide

Results TDNS Criterion

_,i T_ r'_ P_ • v_ •

Time Domain Neal-Smith Response for

Software Version H. Acquig/rion Time

D= 1.4 seconds.

Response f'or Sofw,'a_ Ve_ion F,

Same Conditions

Discrimination between good and bad configurations lies in

Acquisition Time D for which system grows unstable.

Software Version H allows a smaller acquisition time

Criterion definition doesn't yet provide clear boundaries for D

25

REF

Bailey et al 1995, 1996

213
|II_IMM Backup Slide

Results Hess Nonlinear (i)

Resulting Hess mapping for

• Linear system

• Active rate limiters

(Note: Mapping for Software

version F (old) is not plotted; it

results in an unstable system,

caused by excessive rate

limiting)

Software version H, Added Phase Lags

4

EFCS(H)-L(O 1)

EFCS(H)-L(O 25)

_2

15

O_

0

i

jr •

II _

f

s •

i

05 I t5 2 25 3 35 4 45

Freq_-y In_,'s _.

REF

Hess 1989, 1997 _'b'c, 1998

Hess et al 1998

214
I_t t

Backup Slide

Results Hess Nonlinear (ii)

27

Phase Compensated Rate Limiting Schemes

Effect on Closed-Loop System Using Hess

A,pplication of Hess method

Linear Hess mapping yielded 2,

solid PIO-free prediction

Inclusion of conventional rate

limiter drove pilot-vehicle

system unstable

System with phase

compensated rate limiters is

stable, but not predicted solid

PIO-free (boundary has not

been thoroughly validated)

2

tS

[

O_

O

0

Software Version F (old)

j

j

i

a 2<=PIOR<=4

l

Ip I¢ "" _l

¢ •

05 I 15 2 25 3 35 4 45

Frequency/[mdls:

215

Flight Testing for PIO

Ralph H. Smith

High Plains Engineering

PO Box N

Mojave CA 93502

661-824-1023

www.piofree.com

rsmith @ piofree.com

Introduction

• Theory reduced to practice

• Developed intermittently over 32 years

• Highly nonlinear process

• Theory applied to numerous aircraft cases at

EAFB since 1975

- Several PIO predictions prior to flight test

- Two non-PIO predictions

• Incorporated into TPS curriculum since 95B

217
Priorities

• Solve the airworthiness problem

- Eliminate safety-of-flight issues related to PIO

• PIO sensitivity training

• Proficiency training

• Let the subsystems people deal with CooperHarper ratings and psycho-babble

- Performance definitions are negotiated items

- Workload is indefinable

A Question:

• No self-respecting engineer would design a

servomechanism using criteria that are

routinely accepted for piloted control of

airplanes.

• Why should a FCS be designed to less

stringent criteria than a floppy disk drive

servo?

218
The Process

Predict/Test/Verify

- Characterize the Expectation

- Exercise Experimental Technique

- Understand the Results

Predict

• Theory or Criteria

- Smith-Geddes (implemented in the RSMITH

software)

• Simulation

- Simulate what?

• HQDT

219
Aside: Definition

PIO is pilot-in-the-loop oscillation

PIO generally refers to pilot-in-the-loop

instability

Aside: Characterizing PIO

• PIO due to excessive phase lag in the

airplane

• PIO due to excessive command gain (stick

sensitivity)

Pilot

220
Aside: Phase-Gain Interaction

The RSMITH software was written to

account for the interactions

- Predicts CHR for worst-case tracking

- Predicts max stick sensitivity to avoid PIO

Aside: Slick Sensitivity

The dominant HQ parameter

- Overrides phase-based criteria (including

Smith-Geddes)

Typical airplane:

- Stick sensitivity for no-PIO = insufficient

authority to maneuver

- PIO susceptible

- Non-FBW transports are possible exceptions

221
Testing for PIO

No Phase 3 (Cooper-Harper) testing

HQDT -- the only maneuver that works

- A sufficient criterion for PIO

- Go/No Go engineering criterion

• Closed loop task

• Divergence = PIO susceptibility

• Convergence = Not PIO susceptible

• Task is not a factor

• No Cooper-Harper ratings, no performance standard

Aside: HQDT

• Unnatural act

• The old guys hate it

• The new guys have trouble with it

• Has a theoretical basis: sufficient condition

for PIO

• T-38 experience: proof that susceptibility

does not equal unsuitability

222
Understanding the Results

• Priority: Verify that you tested what you

thought you tested

• Identification of aero parameters

• Model the FCS + airframe

• Freq response analysis of flight data to

confirm model validity

• Write a tech report based on fact, not

expectation

Case History

• Approach & landing task

• Control laws designed to satisfy SmithGeddes criteria using RSMITH program

• Predicted Level 1

• Flight test: Level 2/3

• Initial reaction: failure of criteria

• Fact: Invalid aero model and VSA mech;

criteria worked

223
224
Slope Parameter & Criterion Phase Angle

_, ,.,_ _ w,_ ................... _ ..................... ............................ __ _. i__

lc

©

-1C

,2il

! .31]

I

aid

=o

_la ......... a

, i ! %

_- -- "_' 3 --s - _ i__1711_7 .... ' ............ _ ......

3_

o

3o

,,o

;1o

CHR vs Criterion Phase Angle

225
Case History: HQDT

• HUD tracking task, simulated air-to-air

• PIOR = 5

• Phase 3 tracking: CHR = 8/7/6/5/7

• Phase 3 tracking: PIOR = 5/5/3/3/3

Divergent PIO in HQDT Maneuver (F444_08)

IC7 ........

i 2[ ! f- P : q r2 r,

!....2( _ v v V _, V ti

V lo 'T_ ; .

i7 p

- 7 I : ; I

j _,a _ ':_ id't]

i_

" " " r,f , L I

1

226
Veridian Engineering FlightResearchGroup

Use of In-Flight Simulators

for PIO Susceptibility Testing and for

Flight Test Training

By

Michael Parrag

Veridian Engineering (Calspan)

PIO Workshop

Dryden FRC, Edwards, CA

April 1999

The common denominator for both developmental testing and

flight test training

Realistic task in a realistic environment with uncompromised

visual and motion cues

Rehash Group

227
Before talking about the in-flight simulator "tool" in the PIO context let

me say a few words about PIO phenomenon from a piloting viewpoint

- having endured many as an evaluation pilot on research programs

and having witnessed hundreds as a not so casual observer or safety

pilot in a number of our in-t_ight simulators

Flillhl Rmmch Grip

I would like to briefly review several aspects of the PIO phenomenon:

The variety of pilot input _ aircraft response features that cause

unpredictability, a root causal factor in P]O's

=The pilot's way to characterize a PIO in terms of how it affects this

piloting task

The circumstances that may trigger PIO events.

Using the understanding of the above factors to structure flight test

methodology oriented at uncovering PIO susceptibility

. Finally, this will lead to how the in-flight simulator is a safe and cost

effective tool to accomplish flight test objectives

flight Research Group Veridtan Engineering

228
FligM Research GmJp

Response Unpredictability

Primary causal factor for PIO

Response Unpredictability

Predominantly a situation where initial response to pilot input

miscues pilot as to where response will end up

or

pilot simply does not get expected response for a given input

Potential Sources of Unpredictability

I I I II I

., Very initial response

- time delay

too high

--onset rate _ too low

,, Mismatch between time to first perceptible

response and response buildup

.: Steady state L,ensitivity

FT_M ReJearch Group Veridian Engln_ring

229
Potential Sources of Unpredictability (Cont.)

• Poor correlation between pilot sensed responses

e.g. pitch rotation vs 'g' buildup (in up and away flight)

or

pitch attitude and flight path angle (in P.A.)

• Dominant cue creating unintended loop closures (synchronous

behavior)

e.g. effects of nzpand ny.

Fli91_ Releich Group Vlrtd/an Er_ineerlng

Potential Sources of Unpredictability (Cont.)

• Non linear effects

large and sharp (sudden) changes in characteristics such as

in command gain scheduling

or

in response characteristics

Mechanical Non-Linearities

- rate limiting in surface actuators or in software along command path

• Control misuse with exotic FCS modes

or

when intuitive pilot behavior can get you in trouble

• Excursion into non-linear aerodynamics

hi altJhi Mach - pilot vehicle motions venture into Mach buffet or stall buffet

Fight Rneas_ Group _/e,ddlan Engine_r/ng

230
Potential Sources of Unpredictability (Cont.)

• A major design culprit

• Overaugmenta_on

• excessive FCS gains in name of"robustness" or

"agility"

Flighi Rl_.eich Group

Potential Sources of Unpredictability (Cont.)

, Some outcomes:

overly abrupt dynamics in pitch/roll

causes staircase inpuUresponsein grossacquisition and causes hi freq/Iow

amplitudePIO in finetracking(bobbles)

- requires use of more sensorfi!tering -----> time delay

-drives rigid body dynamics closer to aeroelastic modes structuring

filtering _ time delay

-hi fb + hi command gains _ rate saturation more likely

-often worse in turbulence

- unnecessary wear/fatigue on actuators, surfaces and associated

structures

FItoht Rel_ur.h Grip Vlrldtan Englnmb'tng

231
Potential Sources of Unpredictability (Cont.)

• Another major design culprit ---_ FCS complexity

- designer cannot anticipate all possible interaction

between FCS and pilot

.-. cannot guarantee =PIO free"

ii

F_ild I_te_amh Gr_

Types of PIO

Pilot's Interpretation

based on how PIO

interacts with task

232
Types of PIO

(Pilot's Interpretation)

• PlO's have two distinguishing features namely, frequency and

amplitude, that determine how the pilot can deal with PIO in context of

a task

Examples

• Hi freq, low amplitude such as in roll with very short -cR

roll ratcheting

- excessive p causes significant n. which cause rapid reversals by pilot -

Y=

settles into "dominant cue/synchronous behavior"

- viewed by pilot as very annoying but task remains controllable; pilot can

easily judge average of PlO's

Riglt Re=each Group Verldian Engineering

Types of PIO

(Pilot's Interpretation) (Cont.)

, Low freq., larger amplitude -----_oRen seen with rate limiting

pilot is unable to judge average of oscillations

generally not controllable if task constraints do not permit pilot to back out

• Medium frequency------)- gray area; degree of problem caused in task

depends on:

amplitude of PIO

how much he is "driven" by a dominant cue

whether pilot can manipulate "average" to continue task

personal piloting technique - can pilot tone down his inputs?

RiIIM Research Group

233
Fllghl Research Greup

III

Circumstances which

may "trigger" PlOs

Circumstances which may "trigger" PlO's

.- Found accidentally in an aggressive or high precision task scenario

when undesireable aspects of the Pilot-Vehicle System and/or

environment come in coincidence or change unexpectedly

major objective during development should be to minimize, risk of this

,, Uncovered duringftight test by a determined and disciplined process of

exploration and discovery

utilizing high gain tasks under demanding environmental conditions

• process intended specifically to prevent "accidental" discovery of PIO where

consequences are generally more serious

. In both cases, pilot demands rapid response and precise performance

F_ht Rel.urch Gto_fl_

234
Circumstances which may "trigger" PlO's

• In the course of a high gain task scena_rio, when one or more

undesirable elements influencing the Pilot-Vehicle System closed loop

performance surface unexpectedly

- In general, when sudden or anomalous changes occur in pilot behavior,

effective vehicle dynamics or in fee_lback to the pilot

-Atmospheric upsets such as:

turbulence

crosswind

wake turbulence

windshear

Fligtt Rel_ea'ch Gfmp Veridian Enginesrfng

Circumstances which may "trigger" PlO's

(Cont.)

,,FCS mode change during a high gain task

esp. with significant change in [NC + FCS] dynamics, trim change

or FCS dead time

,, Mode change with gear/flaps or air/ground switch or

unexpected FCS mode due to erroneous input from aircraft

sensors

e.g. FCS gains for wrong flap deflection

,, Mixed manual and auto FCS modes when intuitive

behavior mixes with auto control law to give unpredictable

response

e.g. auto compensation for engine out - - - creating control problem

when pilot does get in loop

Flight Research Group Verfdian £nglneerlng

235
Circumstances which may "trigger" PlO's

(Cont.)

• In course of low gain monitoring tasks (pilot out of

loop), sudden change:

- Surprise (shock) - startle effect

"hours of boredom punctuated by seconds of sheer panic"

sudden entry into control loop due to upset or change in

pilot's perception _ often results in much bigger

correction than needed

e.g. akin to sudden awareness after dozing off at the

wheel of a car

- unexpected actuation of some a/c configuration device such as auto

speed brakes, L.E. slats

-system failure ---_),-e.g. runaway trim, sensor or display failure

_gN It_ie, h Grip _Hd_an Er_t_ng

Circumstances which may "trigger" PlO's

(Cont.)

Upset after "hidden onset" e.g. autopilot becomes saturated by turbulence

upset, hinge moments due to ice - - - then "lets go";

pilot is faced with out of trim upset

above scenario but under conditions where handling qualities are marginal +

close to aircraft limits

lack of "situational awareness" leading to inappropriate interaction between

pilot and automatic systems

"pilot and copilot fighting each other" - - - on the controls

R_l_rch Gm,ull

236
Circumstances which may "trigger" PlO's

(Cont.)

In Summary

PIO is outcome of the latter only or both

Flight Rel, eich Group

_o wo,*,,*,o_L _,,_.o=,,11mu

VeHdian Englnaerlng

The Determined "PIO Search" Flight Test

Process

Illl

Objective is to minimize risk of PIO

occurrence in operational use

•_Need to find the "black holes" in flight test -

military testing - civil certification

R_ht Retch'oh Group Veridian EnglnNHng

237
To ensure coverage of vast set of

circumstances in which PlO's can occur

Need to test in combination:

• All potential [aircraft + FCS] modes/configurations

-low probability of occurrence is not excuse not to test

• Relatively extreme environment conditions - progressively but

sufficiently early

• Aggressive yet high precision tasks

• Clever introduction of "b'igger events" described previously - to

reproduce surprise and stress to force "unusual control inputs"

FI_gN P,esemch Gfuap

This is difficult to implement!

Elements of rigorous/determined PIO search

process

• High gain tasks

need to work high frequency portion of PVS to experience

phase lags associated with many initial response problems

t = 0÷ _ high freq

= Unfavorable atmospheric conditions

• Secondary task loading

• Piloting technique

• Urgency of control action

- maybe combined with triggers?

, State of pilot's situational awareness

238
Must pay careful attention to these process elements because dealing with

flying quality CLIFF

handling _ !

quality _

pilot closed loop gain

GOING OVER IS SENSITIVE TO PROCESS ELEMENTS

F|ighl Rmz_ Grip VeHd_an E_tneerlng

TASK

3,PA---_ Approach

vs

Flare and Touchdown

Lake Bed vs RunwayY

vs Carrier

. UP AND AWAY---'_ Formation

vs

A/A Tracking

vs

AJA Refueling

Need Tight (Demanding) Task for Proper Discriminationt

FliIIM ReM,trch Group V_idkmn Engineering

239
Closed-Loop Standards of Performance

• Well Defined Predetermined Standards for

Desired Performance

Adequate Performance

e.g. in terms of mil errors for _'acking or

touchdown box on runway

• Ensure that pilots are proficient in mechanics of task

Fl_gt/R_ear©h Gr_Jp

F_ _h Group

Environmental Factors

, Turbulence including gust upsets

Cross-winds

. Day-Night; - VFR - IFR

i.e. Visual Cues

Secondary Task Load

240
Pilot Closed-Loop Gain

• Aggressiveness in Task

-Operationally Realistic

- Pilot Chooses ! can back out!

• "Pucker Factor" - - - Forced On Pilot by Environment/task

constraints

-PIO's ARE NOT Optional

Fligld Releach Gr=up

III

Representative Piloting Technique

, ; ........ ,,,,

. Aircraft needs to be PIO safe for entire piloting population

i ' "/

• Piloting population is not uniform

There are low gain predictive types

There are high gain "ham fisted" types

• Both types need to be covered in PIO search, but especially latter

. Should also include:

Pilot unfamiliar with particular aircraft being tested, unbiased first opinions can

be very telling

Test pilots who have experienced PlOs in past and who can effectively

communicate their evaluations

Flight RRe_u,ch Group VertdJan Englne.odng

241
Urgency of Control Action

• Need to brief pilots:

-to initiate aggressive gross acquisition

- about compelling and immediacy to recovery from upset

-"time to acquire" is the cdtical element

Frligld Rnearch Gtcup

State of Pilot's Situational Awareness

] .....

Situational Awareness (S.A.) _ Pilot being fully cognizant of current

aircraft state (configuration, FCS mode, autopilot mode etc.), of

appropriate control strategy, or of his environment (weather, other

aircraft)

Lack thereof or sudden change in S.A. may generate trigger or

otherwise cause an "inappropriate" control input

may be related to workload, understanding of FCS modes, piloting

technique etc.

consideration of the above possibilities needs to somehow be worked into

the test plan

e.g. doing "blind" tests when safely feasible

Fight ReMqwch Group

242
Fllgl/Rmi¢h Group

Tools of Pilot-in-the-loop

Tests

With Current New Technology

ii iiiilill II I

- - FBW Aircraft

I

_ Reliance on predictive ,analytic metrics

Inadequate for handling qualities

, Pilot-in-the-loop evaluations essential

FlightRnutch Gfoup VeHdfan Engineering

243
Pilot-in-the-Loop Evaluations

• Only means of integrating all dynamic elements in closed loop

Pilot

Controllers/Feel System

A/C + FCS

Displays

Weapon Systems

In context of mission-oriented tasks

• Only credible means of assessing handling quality goodness and

minimizing risks of hidden "cliffs"

Fltllhl Rmuch Grm_p VeHdian Engineering

Tools of Pilot-in-the-Loop Evaluations

Ground-Based Simulators

In-Flight Simulators

Prototypes

Operational Vehicles

FIk_ P,_.h_J_ eto_ VeHdian Engineerfng

244
Tools of Pilot-in-the-Loop Evaluations

• Considerations:

Ground Based Simulators

-Readily available at design site

-Serves key role in developmental evolution of dynamic elements

- Limitations:

Fidelity of synthetic visual and motion cues

worst in conditions where many current FCS problems erupt

Task environment_>- control strategy (can be quite different from

flight)

Lack of real flight stress

Fltghl Rmi©h Greup VerldMn Engineer_ng

Tools of Pilot-in-the,Loop Evaluations (Cont.)

I

History indicates that for demanding highgain tasks, ground based simulation has

often been misleading - failed to expose

dangerous problems

Flight Research Group

245
Tools of Pilot-in-the-Loop Evaluations (Cont.)

• In-Flight Simulators (IFS)

-Visual and motion cue environment correct/real, not

synthetic

- Real flight stress

-Real piloting tasks

FIIUN Relezch Grip

Tools of Pilot-in-the Loop Evaluations (Cont.)

,- In-Flight Simulator (Cont.)

- Limitations

- If IFS Not 6 DOF _ some cues may not be fully representative

- A number of scenarios outside capabilities of currently operational

IFS's.

e.g. in high o_etc.

- Only as good as model

- However, for a given "model"-_->gives most credible handling quality

answers

-Generally much more credible effects of turbulence than in ground sim

R_earch Group Veridlan Engineering

246
Objectives of IFS

• Verify/check ground sim results in real flight environment

• "Calibrate" ground simulator

-Test pilots become tuned how to better use it for credible results given its

particular cueing limitations ..........

• Historically has brought small dedicated problem-solving oriented flight

test team together

- Fostered communication

Pilots _ Engineers _ Managers

Flig_/Research Group

Tools of Pilot-in-the'LOop Evaluations (Cont.)

Prototype Vehicle

_.Very Costly Tool

economically and from schedule viewpoint

High risk environment in which to test potentially

questionable or unknown characteristics

_High Cost and Risk Tool in which to test modifications/fixes

Operational Vehicle

_=Once a vehicle is operational problem, fixing is a major

fiasco

Right Research Group

247
Test Pilot Evaluation Tools

• Flight Test Tasks/Techniques

• Communication Tools

Ftlgkl Rf_irr,,h Group VerldJon Er_ineetfng

Flight Test Tasks

, , i

"Real" Tasks

Using no special displays

Single element or combination of elements from an operational

scenario

pitch or roll attitude captures

- 45° bank level (const. altitude) turns with aggressive reversal

- Close formation flight

• Air to Air Tracking

-Probe and Drogue refueling task

Offset landing approaches

aggressive alternate tracking of runway edge @ 100 ft AGL (or

altitude safely appropriate for particular aircraft size)

FNh_ Rem,r.h _,,).p Veridbn Englneerfng

248
Flight Test Tasks (Cont.)

Synthetic Tasks

-Tracking task presented on a convenient pilot display such as:

HUD (Head Up Display)

MFD (Multi Function Display)

Attitude Director Bars

-or presented on a removable LCD display with tasks preprogrammed on a

P.C. computer (demonstrated in Learjet)

• Tasks must include single axis and combined axes elements with

sufficient frequency and amplitude content on the tracking bar to test for

PIO susceptibility with both single axis and coupled inputs

-Need to brief pilot to aggressively work to keep errors zero

-high gain - aggressive closed loop behavior _ works on high frequency

portion of pilot - vehicle transfer characteristics

-High freq -- quick or sharp initial response

FllgM Rtsexch Gteup Ver_dlan Er_ineertng

Flight Test Tasks (Cont.)

Synthetic Tasks (Cont.)

....this is region where problematic (cliffy) phase lags, phase rates and rate

saturation effects occur

-Tasks should be programmed to occasionally require inputs from pilot that

may seem operationally unrealistic

e.g. rapid, full throw inputs

, Primary objective of tasks is to expose PIO/dangerous overcontrol

potential

-_minimize risks of occurrence once aircraft is "certified"

• Hence, need to force test input se(:luences that stress the pilot-vehicle

system to extremes even if unrealistic from an ops standpoint e.g.

"klunk" inputs used by Saab - _-

- Flight test needs to establish _ around the operational envelope

Right Rexarch Group Vedd_n Englneertt_

249
Flight Test Tasks (Cont.)

Synthetic Tasks (Cont.)

• Tracking bar programmable in both pitch and roll which the pilot chases

with body axis fixed symbol such as a waterline pitch marker

-This implementation has been successfully utilized on military aircraft by

projecting this task on a HUD

-demonstrated in Learjet projected on a head down LCD display

- In either head up or head down Implementation, can record tracking error in

both pitch and roll and correlate with pilot input activity

FligN RI_Iiwch Greup Vertd_an Engineering

airspeed

F§ght Resea_.h Group

Flight Test Tasks (Cont.)

Synthetic Tasks (Cont.)

command bar

_e rline marker _to be _ altitude

matched with command bar

Learjet LCD Display of Tracking Tasks

250
Flight Test Tasks (Cont.)

Synthetic Tasks (Cont.)

• Two types of tasks

1. Discrete Tracking Task (DTT)

-combination of steps, ramps in both pitch and roll but "coordinated"

-can separately control amplitude of pitch and roll separately to match

task to nature of aircraft being tested

-objective is to elicit both gross acquisition and fine tracking activity

2. Sum of Sines

-combination of sine waves of different frequencies

-1st or 2nd order frequency roll off (filter)

-pitch and roll amplitudes separately controllable again to match task

to aircraft being tested

-objective is to elicit aggressive line tracking activity

Flight RNelch Group Veridlan Engineering

Flight Test Tasks (Cont.)

_ i' i _i _iii_ilri_i

: : . : :

!

Flight Research Group

Discrete Tracking Task

Vel_di_ln Eng/nHrlng

251
FHgM Rmir_h Group

Flight Test Tasks (Cont.)

, ._:-.::....... :....... ::---._-i ...... " ...... i....... i---:., i......

., 20 . 40 _., 63 I10 100 _20 ?40 160 1110

Sum of SinesTracking Task

(similar in roll)

Flight Test Tasks (Cont.)

Other Considerations

• "Triggers" of PIO should be inherent in developed tasks whenever

feasible

• Need to consider task environment issues

effects of turbulence

conditions of visual cues

• FiT's must be tested against known problem configurations and

consistently expose potential or latent "black holes"

. FTT's must generally indicate "good" aircraft to indeed be good

Flighl R._r_h Group

252
Special Issues Pertaining to Civil Certification

- A major hurdle is to get past barrier from pilots or managers on

test techniques that "transports are not flown this way" or that

certain pilot inputs are unrealistic.

-there needs to be recognition that night test]certification test should

establish adequate "margins"

-ensure no "cliffs" on the edge of envelope

-account for unusual inputs from "startle" factor

F_gl_ Rmach Group Verldian Engineering

Test Pilot Communication Tools

I i i

-. Need proper tools to ensure orderly process for test pilots to solidify and

effectively communication their evaluation or assessment to engineers,

managers, and other pilots

Comment Cards

- checklist for comments

- comments are meat of evaluation data

,, Cooper-Harper Rating Scale

- consideration of "average pilot"

- cutoff for "exceptional attention, skill or strength" in civil certification?

Flight Rlse_n:h Grip

253
Test Pilot Communication Tools (Cont.)

• PIO Rating Scale

- current scale

-suggested modification

-too much arguing about PIO rating scale when most important

pilot evaluation issue is task/F]-I-'s that expose problems - rest

is merely organizing how pilot reports what he has seen

Flilllt Rmxdt Ormtp

254
NO

• u_rm_a nd_ m_ _"s do occur _t _|1 pe _,_

_ue YES

• NO YES

Osol a_o_ do oc<ur bd ta_ can be oom pl_lBd

I_k; t=_ may P.I_. _o be a_r<_ed to ml_ta_ D

I Enter Plot Co_rol Alem pt_LOQp to I

Flight Rtuarch Group

_1_! D_t ud01.x_ Or _oi_a Tplol _o'_ may

m

c=_e d_ge_ _1=_=o_ FIo_ mu_t open

t o=r_r_ b_O by _u=n9 ¢x f_.. Z_g _e sti

PIO Tendency Classification

Suggested Modified Scale

VartdJan Engineering

Unique Instrumentation Requirements for PIO

Related Flight Tests

, During Flight Test

- Data sampling rates 30 hz or higher for rigid body PVS dynamics

i.e. fast variables

- Lower data rates for slow variables such as altitude airspeed

- should get derivative of aircraft rotational rates and perhaps even 2nd

derivative - - - "jerk" motions

-- instrument for nzp, nyp

- should instrument for actuator rates and control margins

Right Retearch Group Vettdlan Engineering

255
Unique Instrumentation Requirements for PIO

• In Operational Use

-Flight Data Recorder

-Sufficient data channels to record critical variable

-Sampling rates for critical parameters need to be at least 15-20 hz

FUIIhI R_a.r.h G_eup

I i,

Management Issues

Pertaining to PIO Problem

256
Management Issues

• Industry awareness of PIO is poor

• Lack of understanding of phenomenon and implications to

design process

flight test process

• Flight test teams need specialized training to improve ability to test FBW

in general and for PIO in particular

-exposure of test pilots and FTE's to a variety of PlO's in in-flight simulator

aircraft is excellent conditioner for test teams

"A good scare is worth more than good advise"

-makes them "true believers" in PIO search process

F_gtlt Relearc_ Group VeHdlan Engtnee/tng

Management Issues (Cont.)

• ] ]1 I I]

• Managers need to support a structured approach to test process from

early in design to service entry

use all the tools at their disposal, integrated recognizing each tool

strengths and limitations

• Managers need to treat flight test as a process of discovery rather

than as mundane validation of predictions

• What information from flight test needs to be communicated to the

operational pilot

overcome the "marketing hurdle"

F_4tM Research Group Ve,'tdMn EnglnNHng

257
Flight Test Training

I

• Exposure of test pilots and flight test engineers to real PlO's in the

variety of tasks presented earlier becomes an invaluable career

experience to:

-Appreciate the significance of the phenomenon

-Appreciate the criticality of various tasks and of task environment towards

the propensity to PIO

- Ensure that these flight test crews will appropriately adjudicate any test

planning process with regards to PIO in which they will participate in the

course of their career

Flighl Relli,;h Grcclp

Flight Test Training (Cont.)

to reiterate

"A good scare is worth more than good advice"

Flight Rese=rch G_ap

258
A Method for the Flight Test

Evaluation of PIO Susceptibility

Thomas R. Twisdale & Michael K. Nelson

412thTW/TSFT/USAF Test Pilot School

259
Handling qualities testing is the most important of

all flying qualities testing

Handling qualities are the dynamics, or

characteristics, of the pilot plus the airplane.

Handling qualities testing is based on three

principles

model validation test method

build-up approach

completeness

260
Model validation test method

1. Predict the airplane response, based on a

model.

2. Test the prediction.

0 Validate or correct the model, based on the

test results.

Build-up approach

Testing progresses from the lowest to the

highest level of risk.

Completeness

Evaluate the FULL spectrum of handling

qualities.

261
Three phases of handling qualities testing

Phase 1: Low bandwidth testing

Phase 2: High bandwidth testing

Phase 3: Operational testing

262
Phase 1: Low bandwidth testing

Purpose:

evaluate low bandwidth hq (smooth, low

frequency, non-aggressive control)

familiarization

warm-up

"get acquainted"

Test Maneuvers

open-loop (NOT handling qualities)

semi-closed-loop

low bandwidth maneuvering

low bandwidth tracking

Test data

pilot comments

time histories

263
Phase 2: High bandwidth testing

Purpose

evaluate high bandwidth hq (abrupt, high

frequency, aggressive, small and large

amplitude control)

"stress testing"

"safety gate"

Test maneuvers

HQDT (principally)

simulated carrier approaches

Test data: pilot comments and ratings (PIO

and analog scale)

264
Phase 3: Operational evaluation

Purpose: evaluate whether handling qualities

are adequate to perform the design mission

Test maneuvers: depends on airplane and

mission

Task performance standards: traceable to

mission

Test data

pilot comments and ratings (CooperHarper, PIO, analog scale)

measured task performance

265
Phase 2: High bandwidth testing

Purpose

evaluate high bandwidth hq (abrupt, high

frequency, aggressive, small and large

amplitude control)

"stress testing"

"safety gate"

Test maneuvers

HQDT (principally)

simulated carrier approaches

Test data: pilot comments and ratings (PIO

and analog scale)

266
HQDT

special piloting technique:

track a precision aim point as aggressively

and as assiduously as possible, always

striving to correct even the smallest of

tracking errors

267
Objections to HQDT

pilots don't fly that way

OK for fighters, but not for large airplanes

causes degraded task performance

HQDT makes any airplane look bad

done for engineers, not pilots

268
Session V

269

)

David B. Leggett

AFRL/VAAD

Wright-Patterson AFB_ Q_3

Phone: (937) 255-1_498

FAX: (937) 656-4000

.._.,,_,il- ,hv;,_ _e_ett@va.wpafb.af.mfl

BACKGROUND

THE BEST WAY TO AVOID PIO PROBLEMS IS TO

DESIGN THE FLIGHT CONTROL SYSTEM SO

THAT THE AIRCRAFT DOES NOT HAVE ANY PIO

TENDENCIES

But...

- Aerodyamic prediction methods (CFD, wind tunnel) are not

perfect

- Design criteria and analysis methods are not perfect, particularly

with regard to the effects o_fsignificant nonlinearites

- Flight control changes to fix PIO problems detected late in the

development cycle can be "expensive" to fix

271
THEORETICAL

BENEFITS

• Quick, cheap fix

• Valuable safety net in flight test, even if

not intended for operational use

• Detection algorithms can provide

valuable data during development and

flight test

• May only mitigate PIO tendency, not solve

it

• Always impacts general handling qualities

272
VARIOUS APPROACHES

• Suppression filters

• Rate limiting algorithms

• PIO detectors

• PIO preventers

- Passive

- Active

• Force cueing

SUPPRESSION FILTERS

Low-pass filter in the forward path to

prevent pilot inputs from exciting PIO

tendency

Attenuates command and adds phase lag to

the aircraft response, degrading general

handling qualities, especially for high

bandwidth tasks

273
SPACE SHUTTLE

ADAPTIVE PIO SUPPRESSOR

4

Q

 'inAn/

If4¢

Output from sine wave input,

A -- 10 deg, co -- 2.5 ra_sec

_| O I m

D i

*' Sl I _o',,o00Z

4 $ I? 16 _0

Frequency-dependent attenuation

M _ elo Lelore_m

Pitch rate response to 15-deg 8p step inpt_t

RATE LIMITING ALGORITHMS

• Eliminates or reduces the phase lag due to

rate limiting

• Introduces a bias between commanded

output and actual output, attenuates

command and reduces control power

• Removing bias causes "uncommanded

motions"

• Only good for PIO tendencies caused by

rate limiting

274
] Basic Concept

i_1 -.

i I

Bias generated

by asymmetric

input

"Uneommanded"

Response Generated

by Bias Removal

i a ) . s • I | i

J

i

Pilot Task RLC

A BAT Off

On

PA Off

On

B PA Off

On

C PA Off

On

CHR PIOR

$ 4

_ 3

lO 5

4 2-3

10 5

4, 5 2,2

I0 6

Comments

I noniinear, lumpy, seems like a delay but not time delay

undesireable motions

abrupt maneuvers get divergent behavior, large bul slow

amplitude divergence, no evidence during approach

some lack of precision, 5 deg overshoots, sense thai I'm

in control, no tendency to get into divergence, precision

not qu]le what I'd like, small wallowing, tendency to

overcontrol, task compromised slightly

PIO prone, abrupt inputs do cause oscillations which may

be divergent

no difficulties with PlO, small tendency to be imprecise,

little more tendency to w_allow when you try to be

precise, trying to be more precise brought out tendency

to ovcreontrol

no way to stay in the loop on that, holy s--t!, PIO nuuc

on the scale, stick all the way over and aircraft still going

the other way

still goes slow, could definitely feel rate limiting but i!

was not PIO prone like the last one, big difference

275
• Warning activated by detection of PIO, rate

limiting, or other related phenomena

• Warning can be:

- Light

- Audio warning

- Warning on HUD

- Force feedback through stick

• Pilot must recognize and adapt

ACTIVE PIO SUPPRESSION

• Changes to control system activated by

detection of PIO, rate limiting, or other

related phenomena

- Reduce forward path gain

- Pass pilot input through low-pass filter

- Force feedback through control stick

• May have more adverse effects than the PIO

276
PIO DETECTION AND

ACTIVE SUPPRESSION

...... Pitch.Angle

"=_-_O°o_7__:_ _ _ 3 ................. _ _56--

NetworkIndicationofPIO

°;t I '_ ..... _j

O_ r-" I 2 3 4 S 6

Pilot Gain Multiplier

0.5 !

0 I 2 3 4 5 6

• Pilot Input

_q

....

Time in Seconds

CONCLUSIONS

• These techniques can work

• Although not the first choice, they may

present a program with an alternative to

"complete redesign" or "tell pilot not to

do that"

• Detection algorithms provide handy

data analysis capability

• There are serious drawbacks, design of

these algorithms should not be taken

lightly

277

Accurate Automation Corporation

Real Time PIO Detection and

Compensation

Chadwick Cox, Carl Lewis,

Robert Pap, Brian Hall

Accurate Automation Corporation

7001 Shallowford Road

Chattanooga, TN 37421

ccox@accurate-automation.com

423-894-4646

Accurate Automatiot_ Corporafon

Accurate Automation Corporation

Thanks

• Charles Suchomel - AFRL, COTR

• Brian Stadler - AFRL

• David Legget - AFRL

• Thomas Cord -AFRL

• Ba Nguyen - AFRL

Accurate Automation Corporafon

279
Accurate Automation Corporation

Neural Network Compensation Strategy for

Preventing Pilot-Induced Oscillations

Air Force Phase II SBIR F33615-96-C-3608

COTR: Chuck Suchomel AFRLNACD

Objective: Develop a Smart Neural Network-Based Controller to Prevent

Pilot-Induced Oscillations.

YF-22A CRASH

,

In Data From Events Where PIO

Have Played a Major Pa rt

2. Designed a Neural Network To

Recognize the PIO and Help The

Pilot to Fly Out of the Problem

3. Designed an Advanced Hardware

Controller to Validate th e Concept

4. Patent Pending

Recognize Pilot-Induced Oscillations' _° _ ............. ....... ;:_;_

• .*c'_- = a_"

%

, • %.°-°%

Accurate Automation Corporaton

Av_

Accurate Automation Corporation

Results to Date

Patent will be issued soon

Detector/Compensator tested in closed loop with

simulated configurations on AFRL 6-DOF piloted

simulator

Detector tested with F-16 PIO data, HARV PIO data,

and simulated NT-33 data (MS-l)

Detector/Compensator tested in open and closed

loop with simulated F-16

Accurate Automation Corporafon

280
Accurate Automation Corporation

Results to Date

Designed hardware

VME

DSP

NNP ® interface

VME to 1553 interface

A/D, D/A, digital interfaces

Accurate Automation Corporaforl

Accurate Automation Corporation

Presentation Topics

• PIO Detection and Compensation

• Simulation Testing

• PIO Hardware

Accurate AutomaEon Corporafon

281
Accurate Automation Corporation

Concept

• While a PIO occurs, a detector flags

the PIO.

• If no PIO is occurring, the detector

outputs a zero.

• When the detector flags a PIO, a

compensator is engaged.

Accurate Automation Corporafon " Av,c

Accurate Automation Corporation

PIO Detector Goals

• Real time operation

• Accurate

• Robust

- configurations

- pilots

- noise

• Simple

Accurate Automatiott Corporalon

282
Accurate Automation Corporation

PIO Compensator Goals

• Activated when PIO occur

• Never active when PIO not occurring

• Stops PIO

• Acceptable to Pilots

Accurate A{_tomation CorporaJon

• ,v,

Accurate Automation Corporation

PIO Detection

• PIO detection is simple and clean

- simple algorithm _

- runs in real time

-only straightforward preprocessing

required

-works in longitudinal and lateral axes

-works for many configu rations

- accurate

Accurate Automation Corf'_rafon

is

283
Accurate Automation Corporation

PIO Compensation

• How to compensate for PIO is still

unresolved.

-We have tested simple authority

reduction and a PIO filter

- Pilot's do not like to have their authority

reduced

-Sometimes different situations call for

different types of compensation

- More testing is necessary.

Accurate Automation CorporaIon

Accurate Automation Corporabon

Algorithm Development

• We used MS-1 simulation data, HARV

data, and F-16 simulation data to

develop the detector.

• An iterative process was used to train

the detector.

• The compensator was developed with

simulated HAVE PIO configurations.

Accurate Automation Corparaion

284
Accurate Automation Corporation

Simulation Testing

• Tested detector with MS-1 PIO data

• Tested detector/compensator with

simulated HAVE PIO configurations

and simple pilot model

• Tested detector, advisory, and

compensator in LAMARS simulator

Accurate A{ztomation Corporafon

• A&

Accurate Automation Corporation

Detection of MS-1 Simulated PIO

1 _00 --

0.50 -- /

0.00 _ --_

_o_o _/_

-1.00 -- _

-150 --

0.00

k

4.50 9.00 13.50 ! 8.00 22 -'_0

Accurate Automation Corporafon

285
Accurate Automafion Corporation

Piloted Simulation Testing

• Performed in AFRL LAMARS

fidelity motion base simulator

high-

• Tested a PIO

compensators

detector and two

• Gathered data to improve detection

and compensation methods

Accurate Automation Corporafon

Accurate Automatiot7 Corporation

Piloted Simulation Testing Rational

• Only human in the loop testing can

tell you how a compensator or

advisory will effect the performance

of a pilot.

• Pilot models are not adequate.

-They are good on ly for initial testing.

-Not all problems can be uncovered with

pilot models.

Accurate Automation Corporafon

286
Accurate Automation Corporation

Major Questions

• Does the detector perform

adequately?

- Must not trigger when it shouldn't

• Does the compensator perform

adequately?

- Must not cause a bigger problem when

it is on.

- Preferably must allow the pilot to

perform his task.

Accurate Automatio_ Corporaion

Accurale Automation Corporation

Detection Issues

• Does the detector perform

adequately?

- Does is stay off when there is no PIO?

- Does it come on when there is a PIO?

- Does it work across a wid e range of

configurations?

- Does it work across a wid e range of

pilots?

- Is it robust to noise?

Accurate Automatio_] Corporafon

287
Accurate Automation Corporatiorl

Compensation Issues

• Does the compensator perform

adequately?

- Does it stop PIO?

- Can the task still be performed?

- Do pilots mind having their authority

reduced?

- Does filter induced delay cause other

problems?

Accurate Atdomation Corporafon

Accurate Autotr_ation Corporation

Compensation Issues

• Do different PIO call for different

compensation?

-Use gain compensation with explosive

PIO?

-Use filter compensation with mild to

medium PIO?

- Use other methods?

Accurate Automatio/_ CorporaSon

288
Accurate Automation Corporation

Compensator Types

• Gain Compensator

- Ramp in

- Ramp out

- Minimum authority

• Filter Compensator

- Ramp in

- Ramp out

- Minimum authority

Accurate Automation Corporalon

Accurate A_domation Corporahon

Simulation Testing Methodology

• Succinct matrix

-HAVE PIO and landing task

-HAVE LIMTS like configurations with

tracking task

• Short look instead of long look

• Random presentation

• Repeats allowed

-this allowed us to use short look

without confidence levels

Accurate Automation Corporafon

289
Accurate Automation Corporation

Simulation Testing Matrix

Advisory/Compensation Options

• Four Cases

- PIO detection but n o advisory, no

compensation

- Detection and advisory, no

compensation

- Detection and no advisory,

compensation

-Detection and advisory, compensation

Accurate Automation Corporafon

J_'L

• Av&

Accurate Automa#on Corporation

Simulation Testing MethodologyPilots

one Navy test pilot, one civilian

acrobatic pilot, and five Air Force

test pilots

• prebriefed pilots

• did not lead the pilots

• tried not to let pilots

configurations

compare

• performance feedback provided at

end of run

Accurate Automation Corporafon

29O
Accurate Automation Corporation

Simulation Testing MethodologyPilots

• made pilots go through the

scales when giving ratings

• rating/Questionnaire cards

with pilot in cockpit

• debriefed the pilots

• frequent breaks

Accurate Automation Corpora|or7

Accurate Automation Corporation

Simulation TestingPilot Subjective Data

• Pilot briefings

-configurations, tasks, motion, ratings,

adequate and desired

• Pilot comment card

-PIO scale (Mike Parrag - Veridian) and

Cooper-Harper scale

- Questions

• Pilot's asked to give

assessment of algorithms

Accurate Automation CorporaSon

frank

291
Accurate Automation Corporation

Simulation Testing - Configurations

• HAVE PIO - Category I

-Baseline Longitudinal 2-1,3-1,5-1

-Primary Longitudinal 2-5, 5-9, 5-10

-Secondary Longitudinal 2-8, 3-12, 3-13

• HAVE LIMITS - Category II

-2P, 2DU, 2D, 2DV

- Rate limit adapted to pilot to force PIO

Accurate Automation Corporaforl

Accurate Automation Corporation

Simulation Testing - Pilots' Tasks

• Offset landing

- pilot must land aircraft within target zone

starting from an offset approach

- HAVE PIO configurations

Discrete tracking

- pilot tracks steps and ramps

- HAVE LIMITS

Accurate Automation Corporafon

292
Accurate A utomation Corporation

Simulation Testing - Time Series Data

• All detector and compensator inputs,

internal variables, and outputs

• aircraft state variables

• pilot outputs

• task and performance data

• pilot PIO indicators (trigger pulls at

about where a PIO occurs)

Accurate Automa/io_] Corporafon Av&

Accurate Automation Corporation

Simulation Testing Results

• Detector works very well in pitch and

roll

• Gain compensator stops PIO but

pilots don't like it

• Filter compensator had problems

• Much analysis still to be done

Accurate Automation Corporafon

293
Report number 20 is missing slides 31 to 34; they were unavailable at the time of publication.

Accurate Au(omation Corporation

Simulation Testing ResultDivergent PIO

Accurate Automation Corporaiorl

,dll'_, kl& I

Ace(irate Automabon Corporation

Simulation Testing ResultNO PIO

Accurate Automation Corporaion

,B_k'lk I

294
Accurate Autorrlation Corporation

Simulation Testing ResultNO PIO

Accurate Automation Corporafon

Av&

Accurate Automation Corporation

Simulation Testing ResultNO PIO

Accurate Automation Corporafon

295
Accurate Automation Corporation

Simulation Testing Results -

Pilot Comments

• Advisory well correlated to pilot

assessment of PIO

• Some pilots found advisory

helpful

• Some pilots said advisory didn't

give them additional information

• Some pilots commented on

timeliness of detection

Accurate Automation Corpora|on

Accurate Automatiotl Corporation

Simulation Testing Results -

Pilot Comments

• Pilots said gain compensation

stopped PIO, but interfered with

task

• Delay induced by filter

compensator caused problems

• Pilots felt

them with

landing

that motion helped

tasks, especially

Accurate Automahon Corporaion

296
Accurate Automation Corporation

Simulation Testing Results -

Observations

• Pilots improved

performance over time

their

• One "golden arm" pilot could fly

almost anything

• Pilots sometime adapted to gain

reduction

Accurate Automation CofporaJotJ

/I_ _

Accurate Automation CorporatJ_)n

PIO Compensation Hardware

• board hosts PIO detection and

compensation algorithms

• DSP

• includes interface to multiple AAC

NNPs.

• VME bus with 1553 interface

• A/D, D/A, and digital interfaces

Accurate Automation Corporafon

297
• Developed

detector

Accurate Automation Corporation

Conclusions

a real-time PIO

• Developed a real-time PIO

compensator

• Tested

compensator

piloted simulators

• Continuing simulation testing

• Developing hardware

Accurate Automation Corporafon

detector and

in a high fidelity

Av_

Accurate Automation Corporation

Next Steps

• Analyze data

• More simulation testing

- larger matrix, operational pilots, new

advisories, force feedback

• Flight Testing

• Develop PIO Classifier

• Develop a good compensation

method

Accurate Automation Corporafon

298
PIO Detection with a Real-time

Oscillation Verifier (ROVER)

David G. Mitchell

Technical Director

Hoh Aeronautics, Inc.

Pilot Induced Oscillation Research Workshop

NASA Dryden Flight Research Center

8 April 1999

•Prevention of PIOs in Flight

• Fundamental goal is to prevent PIOs by design

- On-board detector could be a valuable flight test tool

- Application for failures, unusual Ioadings and flight conditions

• Monitor airplane responses and pilot inputs to look for:

- Oscillations of proper frequency range

- Airplane out of phase with pilot

- Amplitudes of input and output large

• Concept developed under current contract

- Has not actually been applied real-time

- Applying for patent

- Looking for follow-on funding for further development

299
Real-Time Detection of PIOs

Time histories of dozens of PIOs have been examined

in detail

Underlying conclusions:

- There is no cleady identifiable "pre-Pl(7' condition

- Many of the precursors to PIO occur in normal operation

- It will not be possible to detect and stop a PIO before it starts

- The best we will be able to do is detect one in the first halfcycle (or so)

Real-time Oscillation VERifier

(ROVER)

• Assumptions:

- Pilot operates more or less sinusoidally

- Pilot adopts synchronous behavi_orin PIO

- Airplane is 180" out of phase with pilot in a PIO

• Apply a moderate amount of filtering

- Bandpass to emphasize range of expected PIO frequencies

- Both input and output filtered to minimize impact

° Test for:

- Oscillation frequency within range for PIO

- 90" phase lag between control input and pitch rate

- Proper amplitude of input and output

300
YF-22A Mishap

"_ 20 -

0 •

.c -2Q -

t.,0 _ V V v

_20 -

10 -

"_. 0 --

-I@3 5

-20 -

4°

z° -

o

30 35 40 45

t;;: ^ -

w._ 10 _ . . .

-20 - _ |see) - v - V v

-34 -

up =rod impactw_

Output for YF-22A Mishap

2_I_ ............... _oo ...... b ..................

,0qu=,., .......o..... _o __Ooo---+--_--_--?o__

: O[ O :

_as¢

(dcg)

30 35 4n 45

Time I sc.c)

2130

is0 .................. _.... o o o _ ,o o ?

l ! oo ! !

!o o _ o o '

50 o ............ _ ............. ._..............

o o ! i

0

30 35 40 45

Time (_.ec)

i o o o i

4 ,..........__._.+...........£...... ? o-_ .-,.-o ...... "

o

Peak ,'ak_es _ O + 0 ' '

I ': o,_ !' + !

Time (_¢¢)

301
Output for YF-22A Mishap

Pit) Flags

4 .............. _ - - .

3 ............... _ .............

P10_c_'cTi"_' 2 ..........................

l: ...............

0:

30 35 4(} 45

Time (sec)

q. r "> "? ¢, ,% --:'I'." C % :7" ':'_ ":"

P|O Fbgs ph&se .............. _ ........

o,nle_: ............ _ -- . - - - - +

30 35 40 45

T_q',c (sec)

Application as a Flight Test Tool

Time-domain verifier for frequency sweeps

U_ .... h_I._O i_/_J'___-':';'- -i'i ..... '---- '_! , i ! ',!i ! i'!iii]'., ih.t

-[ .....!......i ....-........ _ " tilll_'l"ll

O I (} 20 30 40 _O 60 7N 80

Time (sec)

/ ; : i st_ckforce (]_C'¢D _ i

0 10 20 30 40 ._0 60 "tO 80

The (see)

302
Application as a Flight Test Tool

Time-domain verifier for frequency sweeps

Frequency

(rad. sec)

Ph_

(deg)

Identified Frequency and Phase

o

0o

c,

o- 0 0 O 0 -- __

o I0 20 3a 40 50 e_ -70- _o

Tim_ (st'c)

^

I00 ............. ::S : 7 0 cO0

0_000 0

0 0

% C 0 2_' vlo o. 3T 4_'_ 50 _ 7, ,n

Tim° (see)

Continuing Development

• Extend to roll

• Extend to normal acceleration

• Select best filters for bandpass, removing noisy data

• Requires tailoring

- Different flight conditions (higher thresholds up-and-away)

- Different cockpit effectors (force vs. displacement)

- Adapt to failures (reduce thresholds if sensors lost)

• Active intervention vs. alerting

- Should depend upon complexity of flight control system.

degree of instability, mission roles

- Form of active intervention will depend upon flight condition

3O3

Pilot Opinion Ratings and PIO

Thomas R. Twisdale & Michael K. Nelson

412thTW/TSFT/USAF Test Pilot School

See Paper no. 4 in Appendix 3

305

THE NEED FOR PIO

DEMONSTRATION MANEUVERS

Vineet Sahasrabudhe

David H. Ktydc

Systems Technology, Inc.

David G. Mitchell

Hob Aeronautics, Inc.

Pilot-Induced Oscillation Research:

Thc Status at the End of the Century

NASA Dryden Flight Research Center

6-8 April 1999

OVERVIEW

• Identify relevance of demonstration maneuvers for PIO

• Review USAF Handling Qualities Demonstration

Maneuvers program

• Exposing PIO

- Probe-and-drogue refueling example

HUD tracking example -

• The need for PIO specific maneuvers

• Additional candidate PIO demonstration maneuvers

6-8 April 1999 PIO Research Status Workshop

307
RELEVANCE TO PIO

• Objective of the USAF program was to develop a catalog

of repeatable maneuvers to evaluate closed-loop handling

qualities

• Some of the maneuvers included in the final catalog also

exposed P]O and/or PIO tendenci es

• The continued occurrence of PIO in operational aircraft

(mi litary and commercial) indi cares a strong need to

develop a similar catalog for PIO

6-8 April 1999 PIO Research Status Workshop

DEMONSTRATION MANEUVERS

PROGRAM BACKGROUND

• Phase II SBIR for the USAF Flight Dynamics Directorate

- Air Force Technical Contact: Thomas L Cord

• Phase I results published as STI TR-1298-1 and as Appendix C of WLTR-94-3 t 62

• Proposed Maneuver Catalog published as STI ITR-1310-1

Distributed to USAF F1GC mailing list for review

• STEMS Flight Test Evaluation with the NASA F/A-18 HARV

published as STI ITR-1310-2 and as WL-TR-97-3002

• Phase II Results published as WL-TR-97-3099 & WL-TR-97-3100

- Volume I: Maneuver Development Process (-3099)

- Volume It: Maneuver Catalog (-3100)

6-8 April 1999 PIO Research Status Workshop

308
MISSION-ORIENTED

REQUIREMENTS

• Requirements are based on Mission Task Elements

(MTEs) that relate to actual operations

• References to aircraft size are removed

• Allow for multiple response-types

• Provide predicted handling qualities

• Demonstration maneuvers are designed to

complement the mission- oriented approach

6-8 April 1999 PIO Research Status Workshop

HANDLING QUALITIES

DEMONSTRATION MANEUVERS

• Evaluate all aircraft types (military and civil) and

mission tasks

• Provide consistent maneuver definitions including

desired/adequate performance requirements

• Evaluate total system: flight controls, pilot-vehicle

interface, advanced displays and vision aids, etc.

• Provide ultimate check of handling qualities

through piloted evaluation

6-8 April 1999 PIO Research Status Workshop

309
MANEUVER CATEGORIES

I nl

• Non-Precision, Non-Aggressive

Takeoff, Landing, WaveoflTGo-Around

Heading and Altitude Changcs

• Non-Precision, Aggressive

Air-to-Air Gross Acquisition

• Precision, Non-Aggressive

Precision Offset Landing

- Attitude Capture and Hold

• Precision, Aggressive

- Air-to-Air Fine Tracking

6-8 April 1999 PIO Research Status Workshop

MANEUVER EVALUATIONS

• Flight Test Evaluations

- NASA Dryden F/A-18 HARV: STEMS

- USAF TPS HAVE GAS II: Probe-and-Drogue Refueling

- USAF TPS HAVE LIMITS: HUD Tracking

- General aviation aircraft: numerous maneuvers

• Flight Test Reviews

- Large aircraft flying qualities (TIFS): Precision Offset Landing

- USAF TPS HAVE CAP: Precision Offset Lauding

- USAF TPS HAVE TRACK: Simulated Aerial Refueling

• Pilot-in-the-Loop Simulation

- NASA Dryden SR-71 Simulator: Supersonic Maneuver Set

McDonnell Douglas: PIO maneuver development

6-8 April 1999 PIO Research Status Workshop @

310
MANEUVER CATALOG

• Final catalog contains 36 maneuvers

- Flight test evaluations: 18 Maneuvers

- Simulator evaluations: 16 Maneuvers

- 5 maneuvers need refinement

• Catalog spans the range of piloted control

• Flight conditions range from post-stall to supersonic, and

from takeoff to landing

• Catalog is a living document

- Revisions and additions are expected as new research is conducted

6-8 April 1999 PIO Research Status Workshop

EXPOSING PIO

• Demonstration Maneuvers that have produced flight test

PIOs

- Aerial refueling, particular!yprobe-and-drogue

- HUD tracking

- Precision offset landing

• Demonstration Maneuvers that have exposed PIO

tendencies

- Air-to air and air-to-ground fine tracking

- Attitude captures

- Gross acquisitions (often expose Category II tendencies)

6-8 April 1999 PIO Research Status Workshop

311
RECENT EVOLUTION OF

PROBE-AND-DROGUE REFUELING

• USN F-14 Dual Hydraulic Failure Study (1991)

Revealed potential explosive nature of probe-and-drogue refueling task for severely

rate limited configurations

Formation flying (prior to hook-up) did not expose poor handling qualitics

Tracking drill devised to "shake out" configurations prior to hook-up

• USAF TPS HAVE GAS (1993)

Evaluation of different response-types using probe-and-drogue hook-up task

Handling qualities performance requircmcnts (based on number of attempts to

achieve three successful hook-ups) were not sufficiently discriminating

• Notice of Change to MIL-STD-1797A (1995)

- HAVE GAS task with additional requirement to avoid contact with basket webbing

for desired performance

USAF TPS HAVE GAS II (1997)

PIO Research Status Workshop

HAVE GAS II

PROGRAM SUMMARY

• USAF TPS Class 96B Test Management Project conducted in spring

1997

• Objective: Identify the task that best reveals aircraft closed-loop probeand-drogue refueling handling qualities

• Seven flight test sorties: NASA F/A-18 (4 Sorties) and USAF variable

stability NT-33A, operated by Calspan, (3 sorties)

• Candidate evaluation tasks: Hook-Up, Tracking, and Aiming Tasks

• Both qualitative and quantitative results clearly indicated that the

tracking task best exposed closed-loop handling qualities

• To capture potential problems close-in to the basket, the hook-up task

should be performed in concert with the tracking task

6-8 Apd11999 PIO Research Status Workshop

312
6-8 April 1999

DROGUE TRACKING

CONFIGURATION

Side Vi ew

',. ...... !

View From Cockpit

PIO Research Status Workshop

6-8 April 1999

DROGUE TRACKING TASK

FOR PIO

HAVE GAS II

Video Example

PIO Research Status Workshop @

313
PROBE-AND-DROGUE TASK

FOR PIO: CONCLUSIONS

• Probe-and-drogue refueling has exposed all three PIO

Categories in flight test

• HAVE GAS II program defined repeatable evaluation tasks

based on drogue tracking and hook-ups

• Turbulence can have a significant impact on task

performance and should therefore be accounted for in the

evaluation process

• A method should be employed to verify drogue tracking

distance (chase plane, differential GPS, etc.)

6-8 April 1999 PIO Research Status Workshop

HUD TRACKING TASKS FOR PIO

• Recent Experience

- USAF TPS HAVE LIMITS

- McDonnell Douglas ground simulation comparison study

- STI development of pilot evaluation tool (PASS) using sum-ofsines tracking tasks

-HAI PIO simulations on LAMARS using discrete ( "step-andramp," "Calspan" or "SAAB") tracking tasks

• Sum-of-Sines effective for identifying pilot dynamics and

PIO tendencies, especially Category I

• Discrete Tracking effective for identifying PIO tendencies,

especially Category II

6-8 April 1999 PIO Research Status Workshop

314
HUD TRACKING TASKS FOR PIO

HAVE LIMITS

Video Example

6-8 April 1999 PIO Research Status Workshop

HUD TRACKING TASKS FOR PIO:

CONCLUSIONS

6-8 April 1999

There may be initial pilot reluctance to sum-of-sines task

Discrete tracking is most effective as a two-axis task

- Reduces pilot "learning"

- Exposes both pitch and roll problems

Verbal readouts not effective

- Introduces undesired variability with commands

- Must be single-axis only

- Potential for pilot confusion over command values

- No way to monitor tracking performance

- Must be steps only, since "ramps" cannot be introduced verbally

PlO Research Status Workshop

315
DEMONSTRATION MANEUVERS

FOR PIO

• Need for dedicated PIO Demonstration Maneuvers

- PIO is not an operational event

- PIO testing should be distinct from handling qualities

- Some testing will be inconsistent with operational testing (e.g.,

HUD tracking or close formation with a transport)

• Additional candidate PIO Demonstration Maneuvers

- SAAB Klonk method

- HQDT

- Rapid attitude captures

- Others?

6-8 April 1999 PIO Research Status Workshop

316

REPORT DOCUMENTATION PAGE ! Form OMB Approved No. 0704-0188

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

April 2001

4. TITLE AND' SUBTITLE

Pilot-Induced Oscillation Research:

Status at the End of the Century

i

6. AUTHOR(S)

Compiled by Mary F. Shafer and Paul Steinmetz

7. PEI_FORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Dryden Flight Research Center

P.O. Box 273

Edwards, California 93523-0273

] 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

11.SUPPLEMENTARY NOTES

3. REPORTTYPEANDDATESCOVERED

Conference Publication

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5. FUNDING NUMBERS

8. PERFORMING ORGANIZATION

REPORT NUMBER

H-2407

10. SPONSORING/MONITORING

AGENCY REPORTNUMBER

HASA/CP-2001-210389/

VOL2

WU 529-55-24-E8-RR-00-000

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Unclassified--Unlimited

Subject Category 08

This report is available at http://www.dfrc.nasa.gov/DTRS/

i2b, DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

The workshop "Pilot-Induced Oscillation Research: The Status at the End of the Century," was held at NASA

Dryden Flight Research Center on 6-8 April 1999. The presentations at this conference addressed the most

current information available, addressing regulatory issues, flight test, safety, modeling, prediction, simulation,

mitigation or prevention, and areas that require further research. All presentations were approved for publication

as unclassified documents with no limits on their distribution. This proceedings includes the viewgraphs (some

with author's notes) used for thirty presentations that were actually given and two presentations that were not

given because of time limitations. Four technical papers on this subject are also included.

14.SUBJECTTERMS

Flight control, Flight safety, Pilot-induced oscillation, Simulation of flight test

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