Criteria for Low-Speed Longitudinal Handling Qualities: of Transport Aircraft with Closed-Loop Flight Control Systems

151 Pages·1985·3.62 MB·English

by  H. A. Mooij (auth.)

CRITERIA FOR LOW-SPEED LONGITUDINAL HANDLING QUALITIES
CRITERIA FOR LOW-SPEED
LONGITUDINAL HANDLING
QUALITIES
of Transport Aircraft with Closed-Loop Flight Control Systems
by
H.A. MOOIJ
Nationaal Lucht- en Ruimtevaartlaboratorium
National Aerospace Laboratory NLR
The Netherlands
Springer-Science+Business Media, B.V. 1985
ISBN 978-90-481-8285-5 ISBN 978-94-017-1193-7 (e Book)
DOI 10.1007/978-94-017-1193-7
Copyright/legal notice
© 1985 by Springer Science+Business Media Dordrecht
Originally published by Martinus Nijhoff Publishers in 1985
Ali rights reserved. No part of this publication may be reproduced, stored in a
retrieval system, or transmitted in any form or by any means, mechanical,
photocopying, recording, or otherwise, without prior written permission of the
publishers,
Springer-Science+Business Media, B.V.
v
PREFACE
In-fl ight simulation experiments performed in 1967 with a variable-stabil ity aircraft during the
author's stay at Princeton University, motivated the study of handl ing characteristics of future
transport aircraft with closed-loop fl ight control systems. In 1972, the first experiment took place
at the National Aerospace Laboratory NLR, using one of its research aircraft. In anticipation of
expected developments in (digital) fl ight control technology, the research programme following the
first experiments was aimed at the establ ishment of quantitative handl ing qual ities criteria.
An appreciable part of that programme has been sponsored by the Netherlands Agency for Aerospace
Programs (Nederlands Instituut voor VI iegtuigontwikkel ing en Ruimtevaart) and the Department of Civil
Aviation of the Netherlands (Rijksluchtvaartdienst).
In 1981, a thorough review of the extensive and valuable data gathered was started. The result,
presented in this book, was also included in the author's thesis for a Ph.D. degree of the Delft
University of Technology.
To introduce the reader to the multi-discipl inary field of handl ing qual ities research,
introductory chapters are presented on longitudinal aircraft dynamics, closed-loop fl ight
control systems using non-mechanical signal transmission, human pilot dynamics, hand I ing
qual ities assessment techniques, and the present status of handl ing qual ity criteria.
A treatise on quantitative criteria for future aircraft is given, based on the results
of manned simulation experiments using a ground-based and an in-fl ight simulator. A number
of combinations of aircraft and rate-command/attitude-hold fl ight control systems was
evaluated. Manoeuvre-enhancement systems were incorporated in some of the combinations.
Two groups of criteria are distinguished in the analysis of the results: criteria based
on the dynamic characteristics of only the aircraft and criteria based on the dynamic
characteristics of the pilot/aircraft closed-loop system.
Only a I imited number of the existing criteria showed merit with respect to the evaluated
transport aircraft configurations. The fol lowing (new) criteria are proposed: the NLR Rise-Time
and Settl ing-Time Criterion, the Modified Neal-Smith Criterion for Transport Aircraft, and the
NLR Criterion on Precision FI ight-Path Control.
Many NLR colleagues have contributed significantly to the preparation of this book by
providing inspiration, by performing calculations, by participating in stimulating discussions, or
by vetting the manuscript. Often the discussions have led to moderating, tuning, or even sharpening
the author's conclusions. He is very grateful for this invaluable assistance.
A special word of appreciation goes to John Buhrman, the author's early mentor at NLR and
for fifteen years his tutor during the transformation of scribbl ings into publ ications. As a
friend he gave his accurate advice concerning the various drafts of this book which led to distinct
improvements throughout.
The author is much obi iged for the close attention with which the manuscript was moulded into its
final form. He owes his col leagues: the typists, the draughtsmen, and the technical editor, many
thanks. Any blame for remaining errors or omissions rests solely with the author.
September 1984 H.A. Mooij
VII
CONTENTS
Page
BACKGROUND AND OUTLINE OF THE BOOK
1.1 Background
1.1.1 Aircraft control and handling qualities
1.1.t Aircraft efficiency and the future piloting task
1.1.3 The final approach and landing 2
1.1.4 Manoeuvring 3
1.1.5 The pilot/aircraft system 3
1.2 Outl ine of the book 4
PART I: I NTRODUCTORY CHAPTERS 5
2 LONGITUDINAL DYNAMICS 7
2.1 General
7
2.2 Equations of motion 7
2.3 Transfer functions 11
2.4 References 13
3 PRIMARY CLOSED-LOOP FLIGHT CONTROL SYSTEMS 15
3.1 Historical development 15
3.1.1 The early days 15
3.1.2 Pitch- and roll-angle stabi 1 izers 15
3.1.3 Autopilot with manoeuvring capabil ity 16
3.1.4 Stabil ity augmentation for turbojet aircraft 17
3.1.5 Full-time stabil ization 18
3.2 Functions of closed-loop fl ight control systems 18
3.2.1 General 18
3.2.2 Stabi 1 ization 19
3.2.3 Manoeuvring 21
3.2.4 Concluding observations 22
3.3 Interfaces between pilot and aircraft 23
3.3.1 Flight instruments 23
3.3.2 Manipulators 23
3.4 References 24
4 MATHEMATICAL MODELS OF THE CONTROL BEHAVIOUR OF THE HUMAN PILOT 27
4.1 General 27
4.2 Human pilot dynamics in closed-loop control tasks 28
4.3 An example of verification of the Crossover Model 31
4.4 Re fe rences 34
VIII
5 TECHNIQUES FOR THE ASSESSMENT OF HANDLING QUALITIES 37
5.1 General 37
5.2 Evaluation pilots and assessment techniques 38
5.2.1 Introduction 38
5.2.2 Qual ifications of evaluation pilots 38
5.2.3 Number of evaluation pi lots 38
5.2.4 Task selection 39
5.2.5 Rating scales 40
5.2.6 Questionnaires and comment cards 42
5.2.7 Briefing of evaluation pilots prior to experiments 43
5.3 Tools for simulation 43
5.3.1 Introduction 43
5.3.2 The ground-based simulator 43
5.3.3 The in-fl ight simulator 44
5.4 References
45
6 STATUS OF HANDLING QUALITY CRITERIA 47
6.1 Historical development 47
6.2 The structure of the US mil itary specifications 48
6.3 Criteria with respect to the longitudinal motion 50
6.3.1 Introduction 50
6.3.2 Criteria for manoeuvring in MIL-Spec and Calspan-SCR 52
6.3.3 Additional publ ished criteria for manoeuvring 58
6.3.4 Summary 61
6.4 Re fe rences 62
PART I I: EXPERIMENTS AND RESULTS 65
7 DESIGN OF THE EXPERIMENTS 67
7.1 General 67
7.2 Simulated aircraft and fl ight control system 68
7.2.1 Models of aircraft and fl ight control system 68
7.2.2 Configurations; pitch-angle response variations 71
7.2.3 Configurations; flight-path-angle response variations 76
7.3 Simulation facilities 78
7.3.1 Ground-based simulation facil ity 78
7.3.2 In-flight simulation facility 81
7.4 Task and environmental conditions 82
7.4.1 Evaluation task 82
7.4.2 Environmental conditions 83
7.5 Pilots and their instruction 84
7.5.1 Evaluation pilots 84
7.5.2 Briefing guide, rating information and comment card 85
7.6 References 85
IX
8 RESULTS OF THE EXPERIMENTS 89
8.1 General 89
8.2 Simulation verification 89
8.3 Pi lot ratings and comments 92
8.3.1 General 92
8.3.2 Pilot ratings 92
8.3.3 Pi lot comments 94
8.4 Pilot/aircraft system performance 97
8.5 Concluding observations 98
8.6 References 99
9 CRITERIA BASED ON THE RESULTS OF THE EXPERIMENTS 101
9.1 General 101
9.2 Mathematical representations of the aircraft 103
9.3 Criteria based on the aircraft only 104
9.3.1 Introduction 104
9.3.2 Cr ite ria 104
9.4 Criteria based on the pilot/aircraft system 114
9.4.1 Introduction 114
9.4.2 Pitch-angle control criteria liS
9.4.3 Fl ight-path control criterion 122
9.5 Summary 126
9.6 References 127
10 CONCLUSIONS 129
APPENDIX A SYMBOLS, ACRONYMS, AND REFERENCE FRAMES 133
APPENDIX B BRIEFING GUIDE, RATING INFORMATION, AND COMMENT CARD 137
APPENDIX C PILOT COMMENTS (FLIGHT) 143
BACKGROUNO AND OUTLINE OF THE BOOK
1.1 Background The suitabil ity of an aircraft with respect
to human pi lot control is determined by its so
1.1.1 Aircraft control and handling qualities called handling qualities, which refer to those
qual ities or characteristics of the aircraft that
Unl ike most forms of transport (by sea, govern the ease and precision with which a pilot
road, railroad), transport through the air can in is able to perform his control task.
principle take place in the full three-dimensional The handl ing qual ities of an aircraft can be
space. As a consequence, controll ing the fl ight evaluated by pilots who have the proper background
path of an aircraft is essentially far more compl i and who have been thoroughly instructed in the
cated than that of a surface-bound (or line-bound) techniques related to this type of work. Their
vehicle. opinions are reasonably reproducible and therefore
The problems associated with control of an of value in experimental research. One of the main
aircraft precluded the development of a successful elements in their judgement is their own measure
aircraft in the early stage of aviation for quite ment of the required "mental workload" while per
some time. It is generally agreed that one of the forming certain tasks with an aircraft presented
principal contributions of Wi lbur and Orvi lie to them.
Wright around the turn of the century is their ob The present knowledge concerning handl ing
servation that a large amount of inherent stabil qual ity criteria is, however, not fully adequate
ity of the fl ight condition, which in the early for the next generation of transport aircraft, in
days was cons i de red mandatory, is not abso I ute I y which new types of flight control systems are ex
necessary if only the operator could be provided pected.
with sufficient powerful controls with which "to
balance and to steer". This impl ied that the
human pi lot, operating on feedback signals, could 1.1.2 Aircraft efficiency and the future piloting
use the controls to stabil ize the aircraft. task
Aircraft of the present time can be con
trol led either by means of automatic equipment or For reasons of improved aircraft efficiency,
by the human pi lot. The control functions which future appl ication of the so-cal led relaxed static
have to be performed are the deflecting of aero stabil ity concept is expected. This concept means
dynamic control surfaces and the changing of operation in a centre-of-gravity range of the
engine thrust levels in order to: aircraft which is more aft than used in existing
- establ ish an equil ibrium state of the designs, implying operation of a basic airframe
aircraft motion, which under certain loading conditions can be stat
- stabi I ize the aircraft motion after a ically unstable. Operation at more aft centre-of
disturbance, gravity locations al lows reduction of the area of
- manoeuvre the aircraft from one equil ibri the horizontal tail surface. The gains in effi
um state to another. ciency are primari ly due to reduced weight (reduced
Because of the transport role of aircraft in horizontal tail size) and due to reduced trim drag
an earth-related reference system, guidance is (improvement of the ratio between the airloads on
essential during fl ight. The term guidance is here wing and horizontal tail). This development wil I
understood to comprise al I types of information to be one of the major reasons for the emergence of
which the pilot has to, or at least can, respond full-time artificial stabil ization systems in
in performing his task of controll ing the fl ight transport aircraft. A dominant feature of these
path of his aircraft. systems may be in particular the three-axes atti-
2
tude stabil ization. One of the possible mechaniza ILS LOCALIZER
"GLIDE PATH PLANE"
tions of a fl ight control system with this feature
is a system accepting commands of "attitude rate"
given by the pilot and attitude stabil ization
("attitude hold") when no commands are given.
Such a system is often indicated as "rate-command/
attitude-hold". These characteristics, coupled
ILS GLIOE·SLOPE "LOCALIZER PLANE"
with the most likely simultaneous automatic sta TRANSMITIER ,
\
bil ization of the airspeed, lead in principle to \
the el imination of the stabi 1 ization function men Fig. 1.1 Final approach and landing path.
tioned earl ier as part of the task of the pilot. In the presently most usual approach proce
The consequences of the el imination of the dure, the first step is to manoeuvre the aircraft
stabil ization function from the task of the pilot into a certain ground-fixed vertical plane, the
are to be establ ished. New insight is to be gained "local izer", indicated in figure 1.1. This plane
into the matter of numerical criteria for adequate is electronically generated by the so-cal led
handl ing qual ities related to the response of the Instrument Landing System (ILS) and contains the
aircraft to manipulator inputs. No val idated in centrel ine of the runway to be used for landing.
formation in this field is presently avai lable for After the interception, while in level fl ight, the
transport aircraft with the above-mentioned fl ight nominal path intersects with a second ILS-plane,
control systems. the "gl ide path". As indicated in figure 1.1, this
Especially those phases of fl ight which take plane intersects the groundplane at aline perpen
place at airspeeds close to allowable minima and dicular to the runway centrel ine and slopes upward.
at low height above the ground demand attention, The intersection 1 ine of the two ILS-planes is
due to their critical nature from the point of usually indicated as the "gl ide path or gl ide
view of safety. From the two phases in this slope", which ends at the ground at some distance
category, take-off fol lowed by initial cl imb and beyond the runway threshold.
final approach followed by landing, the latter During the interception and tracking of the
presents possibly the most demanding task for the local izer and the gl ide path, the pilot concen
pi lot. trates his attention on the primary fl ight instru
Through the study described in this book, ments and the ILS deviation indicator. Whi Ie the
more insight has been gained into the required aircraft is on the ILS, the pilot decelerates the
handl ing qual ities expressed in criteria for a aircraft and reconfigures it into the landing con
generation of transport aircraft expected in the figuration by deflecting the wing leading-edge and
near future. I t has been attempted to present the trail ing-edge flaps and lowering the undercarriage.
results in a form which is practicable for both Mi ld manoeuvres are necessary to counteract the
the fl ight control system designers and the certi deviations from localizer and glide slope due to
fying authorities. atmospheric disturbances and possible irregulari
ties in the guidance signals. At several hundred
feet above the ground, the pilot switches his at
1.1.3 The final approach and landing tention from the instrument information to the
outside visual scene, which may again lead to some
To famil iarize the reader with the meaning minor approach path corrections. The landing is
of the control functions performed by the pi lot as initiated by gradually rotating the aircraft. This
well as with some associated guidance aspects, a results in a change of the velocity vector to a
description of the piloting task during the final virtually horizontal direction. The aircraft is
approach and landing is in order. First the path then flown with the main wheels against the runway
to be flown wi 11 be described. surface in such a way that a soft but positive