An overview of Dryden superaugmented aircraft flying qualities research is presented. This includes F-8 digital fly by wire flight experiments, orbiter flying qualities, shuttle improvements, AFTI/F-16, flying qualities and control system alternatives, Vertical Motion Simulator Shuttle evaluation and Total in Flight Simulator pitch rate criteria

Berry, D. T.

English

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FLYING QUALITIES CRITERIA FOR SUPERAUGMENTED AIRCRAFT 
Donald T. Berry 
NASA Ames Research Center 
Dryden Flight Research Facility 
Edwards, California 
First Annual NASA Aircraft Controls Workshop 
NASA Langley Research Center 
Hampton, Virginia 
October 25-27, 1983 
25 
https://ntrs.nasa.gov/search.jsp?R=19840012501 2020-03-22T08:15:16+00:00Z
SUPERAUGMENTED AIRCRAFT 
Before proceeding with a review of superaugmented aircraft 
activities, it would be prudent to define what we mean by super- 
augmented aircraft. The term is defined below. Early applications 
of feedback control tended to enhance the basic static and dynamic 
stability of aircraft in a way that was equivalent to augmenting the 
basic aerodynamic stability derivatives. The resulting responses 
were improved but conventional. As basic aircraft stability levels 
became weaker and the augmentation became more elaborate, aircraft 
began to depart significantly from classical behavior. 
Certain characteristics are highly typical of superaugmented 
aircraft and are also indicated below. 
Definition 
l Aircraft with flying qualities that are dominated by the 
closed-loop control system rather than 
aerodynamic stability 
Dominant characteristics 
l Large time delays 
l Unconventional longitudinal response 
l Small, effective roll time constants 
26 
AIRCRAFT PITCH RATE POLE/ZERO CONFIGURATIONS 
An' example of a difference between a classical and super- 
augmented aircraft is illustrated below in terms of pitch rate 
transfer functions in the s plane. These diagrams are highly 
idealized but the basic features are quite representative. The 
classical aircraft typically is augmented primarily in damping so 
the closed-loop configuration is similar to an aircraft with good 
aerodynamic damping. Superaugmentation is normally required for 
aircraft with a basic static instability. Proportional plus in- 
tegral compensation is typically used to stabilize the aircraft and 
provide good closed-loop frequency and damping. However, 'the- high 
gains required result in the conventional attitude numerator being 
cancelled by a basic aircraft pole and the effective attitude lead 
being determined by the zero of the proportional plus integral 
compensation. 
Classical Superaugmented 
27 
DRYDEN SUPERAUGMENTED AIRCRAFT FLYING QUALITIES RESEARCH 
Current activities of the Dryden Flight Research Facility that 
pertain to flying qualities of superaugmented aircraft are listed 
here in chronological order of their initiation. It can be seen 
that a variety of programs are underway. The highlights of these 
programs will be covered in the ensuing discussion. However, the 
descriptions will be brief because of the number of activities and 
the space available. This paper, then, will be an overview of Dryden 
superaugmented aircraft flying qualities research. 
Program 
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F-8 DFBW Experiments 
Orbiter flying qualities 
Shuttle FCS improvements 
Nonconventional vehicle 
flying qualities 
AFTI/F-16 
Fiying qualities and control 
system alternatives 
Pilot model measurements 
VMS Shuttle evaluation 
TIFS pitch rate criteria 
Implementation 
In house 
In house, contractor (STI) 
In house, 
contractor (CALSPAN) 
Grant - Purdue 
In house, Air Force 
Contractor study (STI) 
Grant - U. Cal. Davis 
In house, JSC 
Contractor (CALSPAN) 
28 
F-8 DIGITAL FLY-BY-WIRE (DFBW) FLIGHT EXPERIMENTS 
The F-8 DFBW was the world's first fully fly-by-wire airplane. 
Initial program emphasis was on system reliability and redundancy 
management. In recent years, the vehicle has been used to investi- 
gate flying qualities associated with advanced control laws and 
superaugmentation, as listed below. The time delay studies inves- 
tigated the effect of transport delay on flying qualities in land: 
iw3, formation flying, and in-flight refueling. Highly augmented 
aircraft typically have large values of equivalent transport delay. 
The nonlinear control law investigation was a cooperative program 
with the British and studied control laws that varied prefilter time 
constants as a function of feedback error and changed loop structure 
as a function of task. The PI0 suppression filters study (ref. 4) 
was an extension of concepts developed for the Space Shuttle. 
l Time delays 
l Nonlinear control laws (CADRE) 
l PI0 suppression filters 
29 
OEX ORBITER FLYING QUALITIES EXPERIMENT 
This effort is under the sponsorship of the Orbiter Experiments 
Program (OEX). The purpose is to use Shuttle data and flight ex- 
perience to develop flying qualities criteria for next generation 
Shuttlecraft and to improve existing Shuttles where feasible. The 
Shuttle has some unique characteristics and mission tasks; neverthe- 
less, it is a superaugmented vehicle, and there is much technology 
transfer between it and high-performance aircraft. 
l Generate flight data base for criteria for 
current and future Space Shuttlecraft 
l Establish flying qualities data “pipeline” 
l Use flight data to validate analytic/simulator 
studies 
30 
DRYDEN GRANT ACTIVITIES 
Grants under the direction of Dryden that pertain to 
superaugmented aircraft are outlined below. 
The investigator for the Purdue grant is Dr. Dave Schmidt. The 
integrated pilot-optimal control synthesis simultaneously utilizes 
an optimal control pilot model and modern control theory to produce 
control system designs with optimum flying qualities. The optimal 
control approach to the Neal/Smith flying qualities criteria uses an 
optimal control pilot model instead of the classical pilot compensa- 
tion model. The pilot parameter identification techniques study is 
looking at the use of time series analysis to measure pilot dynam- 
ics, strategy, and workload from flight-test time histories. 
Principal investigator for the University of California-Davis 
grant is Dr. Ron Hess. This effort is aimed at using existing pilot 
measurement techniques to obtain data from ongoing flight experi- 
ments and obtain a flight-validated data base of pilot math model 
parameters. Both classical and optimal control models will be used. 
Purdue University: (Schmidt) 
Develop prediction techniques for flying qualities of 
complex, nonconventional vehicles 
l Integrated pilot-optimal control synthesis 
l Optimal control approach to Neal/Smith 
l Pilot parameter identification techniques 
University of California - Davis (Hess) 
Establish flight-validated pilot model data base 
l Analyze F-8 DFBW flight experiments 
31 
AFTI/F-16 FLYING QUALITIES FLIGHT EXPERIENCE 
The AFTI/F-16 is a superaugmented aircraft with direct lift and 
side force control and a task-tailored multimpde flight control sys- 
tem. It is a very ambitious program that is striving to evaluate 
highly advanced control system mechanizations and architectures as 
well as unconventional control laws. Initial program emphasis has 
been on checkout of the digital flight control system and functional 
evaluation of the flight control concepts. Much qualitative flying 
qualities information has been obtained, and the highlights of this 
experience are indicated below. 
l Utility of task-tailored flying qualities demonstrated 
l Technology not available to optimize control modes 
l PI0 and roll ratchet tendencies persist 
32 
AMES VMS SHUTTLE FLIGHT CONTROL IMPROVEMENT STUDY 
The Ames Vertical Motion Simulator (VMS) was used in a recent 
program to study Shuttle flying qualities in approach and landing. 
This program was sponsored by the Johnson Space Center. Dryden parti- 
cipated because of its background in previous Shuttle approach and 
landing studies. The program is outlined below. 
Objectives 
Evaluate proposed changes to Shuttle FCS to improve 
flying qualities in approach and landing 
Configurations 
l Baseline Shuttle 
l Shaped pitch rate 
l Lead/lag prefilter 
l Slapdown system 
l Rate command/att hold 
l Sink rate command 
. c* 
Results 
l Shaped pitch rate, slapdown, and C* best of mods 
l Slapdown and C* eliminated after aggravated maneuvers 
due to rate limiting 
l Pilots with extensive Shuttle training preferred baseline 
system 
l Test pilots without Shuttle training preferred shaped pitch 
rate 
33 
TIFS PITCH RATE CRITERIA FLIGHT RESEARCH PROGRAM 
The Air Force/Calspan Total In-Flight Simulator (TIFS) very re- 
cently completed a program under joint Dryden/Langley sponsorship to 
investigate flying qualities criteria for pitch rate command systems. 
The objectives of the program and configurations tested are outlined 
below. Preliminary results indicate that superaugmented configura- 
tions were rated level two or three. Prefilters that tended to re- 
store more classical aircraft response improved the ratings. 
Objectives 
l Generate flight data base for improved pitch rate 
command systems 
l Emphasis on superaugmented aircraft 
Configurations 
200,000 lb class advanced aircraft 
Negative static stability 
Neutral static stability 
Proportional + integral augmentation 
With/without prefilters 
Pitch rate augmentation 
34 
SUMMARY 
This review can be summarized as follows. 
l Additional data needed to develop superaugmented aircraft 
flying qualities criteria 
l Dryden activities aimed at increased understanding of 
superaugmentation and providing flight-validated data base 
l Current effort involves F-8 DFBW, Space Shuttle, 
AFTVF-I6 and X=29 
35 
BIBLIOGRAPHY 
1. Radford;R. C., Smith, R. E., and Bailey, R. E., "Landing Flying 
Qualities Evaluation for Augmented Aircraft,' NASA CR-163097, 
Aug. '80. 
2. Schmidt, D. K., and Innocenti, M., "Pilot Optimal Multivariable 
Control Synthesis by Output Feedback," NASA CR-163112, Jul. ‘81. 
3. Teper, G. L. et al., "Analysis of Shuttle Orbiter Approach and 
Landing Conditions," NASA CR-163108, Jul. '81. 
4. Powers, B. G., "An Adaptive Stick-Gain to Reduce Pilot-Induced 
Oscillation Tendencies,' Journ. of Guid., Contr., and Dynam., 
Mar .-Apr. ‘82, pp. 138-142. 
5. Weingarten, N. C., and Chalk, C. R., "In-Flight Investigation of 
the Effects of Pilot Location and Control System Design on Airplane 
Flying Qualities for Approach and Landing," NASA CR-163115, 
Jan. ‘82. 
6. Bacon, B. J., and Schmidt, D. K., 'A Modern Approach to Pilot/ 
Vehicle Analysis and the Neal Smith Criteria,' AIAA Paper 
No. 82-1357, Aug. ‘82. 
7. Berry, D. T., "Flying Qualities: A Costly Lapse in Flight Control 
Design?," Astronautics and Aeronautics, vol. 20, no. 4, Apr. ‘82, 
PP. 35,54-57. 
8. Berry, D. T. et al., 'In-Flight Evaluation of Control System Pure 
Time Delays,' Journ. of Aircraft, vol. 19, no. 4, Apr. ‘82, 
PP. 318-323. 
9. Meyers, T. T., Johnston, D. E., and McRuer, D., 'Space Shuttle 
Flying Qualities and Flight Control Assessment Study,' Phase 1, 
NASA CR-170391, Jun. ‘82; Phase 2, NASA CR-170406; Phase 3, 
NASA CR-17040 
10. Shafer, M. F., Smith, R. E., and Stewart, J. F., "Flight Test 
Experience with Pilot-Induced Oscillation Suppression Filters," 
AIAA Paper No. 83-2107, Aug. '83. 
11. Larson, R. R., Smith, R. E., and Krambeer, K. D., "Flight Test 
Results Using Non-Linear Control With the F-8 Digital Fly-By-Wire 
Aircraft," AIAA Paper No. 2174, Aug. '83. 
12. Weingarten, N. C., and Chalk, C. R., "Application of Calspan Pitch 
Rate Control System to the Space Shuttle for Approach and Landing,' 
NASA CR-170402, May '83. 
36 


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