s Stability in Aerospace Systems

248 Pages·2002·53.48 MB·English

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ADVISORY GROUP FOR AEROSPACE RESEARCH & DEVELOPMENT
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7 RUE ANCELLE 92200 NEUILLY SUR SEINE FRANCE
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I Stability in Aerospace Systems
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(La Stabilitk dans les Systkmes Mrospatiaux)
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ADVISORY GROUP FOR AEROSPACE RESEARCH & DEVELOPMENT
7 RUE ANCELLE 92200 NEUILLY SUR SEINE FRANCE
AGARD REPORT 789
Stability in Aerospace Systems
(La Stabilitk dans les Systkmes Akrospatiaux)
Papers presented at the Guidance and Control Panel Workshop on Stability in
Aerospace Systems, held at ONERA in Mauzac (Toulouse), France from
23rd-25th June 1992.
Note: Exceptionally, some authors have not submitted texts of their papers,
only copies of the viewgraphs used during their presentations.
AGARD apologisesf or the lack of continuity in these papers, and the
poor quality of some, and hopes that readers will gain some understanding
of the subject matter from them.
- North Atlantic Treaty Organization
Organisation du Traite de I’Atlantique Nord
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The Mission of AGARD
According to its Charter, the mission of AGARD is to bring together the Leading personalities of the NATO nations in the fields
of science and technology relating to aerospace for the following purposes:
- Recommending effective ways for the member nations to use their research and development capabilities for the
common benefit of the NATO community;
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Providing scientific and technical advice and assistance to the Military Committee in the field of aerospace research and
development (with particular regard to its military application);
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Continuously stimulating advances in the aerospace sciences relevant to strengthening the common defence posture;
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Improving the co-operation among member nations in aerospace research and development;
- Exchange of scientific and technical information;
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Providing assistance to member nations for the purpose of increasing their scientific and technical potential;
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Rendering scientific and technical assistance, as requested, to other NATO bodies and to member nations in connection
with research and development problems in the aerospace field.
The highest authority within AGAFCD is the National Delegates Board consisting of officially appointed senior representatives
from each member nation. The mission of AGARD is carried out through the Panels which are composed of experts appointed
by the National Delegates, the Consultant and Exchange Programme and the Aerospace Applications Studies Programme. The
results of AGARD work are reported to the member nations and the NATO Authorities through the AGARD series of
publications of which this is one.
Participation in AGARD activities is by invitation only and is normally limited to citizens of the NATO nations.
The content of this publication has been reproduced
directly from material supplied by AGARD or the authors.
Published February 1993
Copyright 0 AGARD 1993
All Rights Reserved
ISBN 92-835-0702-9
Printed by Specialised Printing Services Limited
40 Chigwell Lane, Loughton, Essex IGlO 3lZ
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Theme
Stability in guidance and control can be illustrated by the following examples:
- Air vehicles subjected to atmospheric instabilities (particularly downbursts and windshears), including flight control in
downbursts, detection of downbursts from the ground or by airborne systems, and aircraft guidance to avoid them.
- Control of fighters at high angles of attack which may become unstable due to a bifurcation point beyond which their
behaviour becomes unpredictable, though belonging to the deterministic domain.
- Control of laminar-turbulent transition for high performance aircraft (subsonic and supersonic), including improvement of
stability by control of transition, and the impact of fully laminar flow on aircraft control.
The concept of stability also needs to be looked at from a theoretical point of view - for example, the impact of uncertainties in
initial conditions on system behaviour. This has links with the concept of model robustness.
The programme was as follows:
1st Session. Fundamental aspects of stability with examples:
The dilemma of stability vs. manoeuvrability and its consequences on military and civilian aircraft; stability and controllability of
non-linear systems; various types of stability of an equilibrium state.
2nd Session. Basic theoretical aspects and chaos:
Newtonian mechanics and thermodynamics; transition from stability to chaos; boundary layer control on a wing or fuselage,
stabilisation of an unstable aircraft (decoupling of the controls of aircraft, helicopters, or convertibles).
3rd Session. Applications of aerospace techniques:
a) External parameters: the atmosphere, turbulence, windshears and downbursts; their detection and modelling (methods of
detection - whether ground or air based - the information processing of the data collected); control laws when flying
through atmospheric disturbances; criteria.
b) Control of the flow around wings and fuselage. C, and C, variations with boundary layer effects. Stability of a spin.
Prediction of the instability and consequences for vehicle guidance.
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Thkme
Les problkmes de stabiliti dans l’optique du guidage et du pilotage peuvent &trei Llustris par les exemples suivants:
- Vihicules airiens soumis aux instabilitis atmosphiriques (particulierement les cisaillements de vents) incluant le contrBle du
vol dans un “downburst”a insi que la detection de ceux-ci, soit du sol, soit bord de l‘avion, et le guidage de l‘avion pour kiter
ces phinomknes.
- ContrBle des chasseurs a des trks grandes incidences qui peuvent devenir instables a cause de “bifurcations” demkre
lesquelles le comportement des vehicules devient imprivisible, bien qu’appartenant au domaine “determint”.
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Contrble de la transition laminaire-turbulent pour les avions a hautes performances (subsoniques ou supersoniques),
incluant l’amtlioration de la stabiliti grlce au contrBle de la transition et l’impact d‘un icoulement totalement laminaire sur le
comportement de l’avion.
Le concept de stabiliti doit &re tgalement considiri d’un point de vue thiorique, par exemple, en examinant les constquences
des incertitudes sur les conditions initiales sur le comportement du systeme. Ce problkme est lie, d‘ailleurs, au concept plus
giniral de la “robustesse” d’un modkle.
Le programme de l’atelier a 6t6 le suivant:
Itre Session. ‘Aspects fondamentaux de la stabiliti et exemples”
Le dilemme stabilitUmanoeuvrabilit6 et ses consiquences sur la stabiliti des aironefs civils et militaires; la stabiliti et la
pilotabiliti des systkmes non-lintaires; diffirents types de stabiliti d’un “point”d ‘iquilibre (Ctat).
22me Session. “Aspects thionques fondamentaux et chaos”
Micanique newtonienne et thermodynamique; transition stabilitUchaos; contrble de la couche limite sur une aile ou un
fuselage, stabilisation d’un avion instable (dicouplage des commandes dans un avion, un hklicoptkre ou un convertible).
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32me Session. ‘Applications aux techniques airospatiales”
a) Les paramktres extemes: l‘atmosphkre, la turbulence, les cisaillements de vents et les “downbursts”;l eurs dttecteurs et leur i
modilisation (mithode de detection - sol ou airoportie - et traitement de l’information collectie); lois de contrBle en vol
en atmosphkres trks turbulentes; critkres.
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b) ContrBle de l’icoulement autour des ailes et du fuselage; C, et Cx lorsqu’on prend en compte la couche limite; stabiliti d’un
avion en vrille; prkdiction de l’instabilitt et constquences pour le guidage du vihicule.
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Guidance and Control Panel
Chairman: Mr S. Leek Deputy Chairman: Mr J.K. Ramage
British Aerospace Chief, Flight Control
Defence Dynamics Ltd Advanced Development Branch
PO Box 19 Wright Laboratory (WL/FIGX)
Six Hills Way, Stevenage Wright-Patterson AFB,
Herts SG12DA OH 45433
United Kingdom United States
TECHNICAL PROGRAMME COMMITTEE
Chairman: Dr M.J. Pelegrin P)
Members: Dr A. Benoit (BE)
Prof. R.C. Onken FE)
Mr J. Bardal (NO)
Mr J.K. Ramage (US)
HOST NATION COORDINATOR
Dr M.J. Pelegrin
Haut Conseiller a I'ONERA
ONEWC E R T
BP 4025
2 avenue Edouard Belin
F-31055 Toulouse Cedex
France
PANEL EXECUTIVE
Commandant M. Mouhamad, FAF
Mail from Europe: Mail from US and Canada:
AGARD-OTAN AGARD-NATO
Attn: GCP Executive Attn: GCP Executive
7, rue Ancelle Unit 21551
F-92200 Neuilly-sur-Seine APO AE 09777
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Tel: [phone]
Telex: 610176 (France)
Telefax: 33 (1) 47 38 57 99
ACKNOWLEDGEMENTS/REMERCIEMENTS
The Panel wishes to express its thanks to the French National Delegates to AGARD for the invitation to hold this meeting in
1 Mauzac and for the facilities and personnel which made the meeting possible.
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Le Panel tient a remercier les Dtlkgues Nationaux de la France prks I'AGARD de leur invitation a tenir cette rtunion a Mauzac
I et de la mise a disposition de personnel et des installations ntcessaires.
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Contents
Page
Theme iii
Theme iv
Guidance and Control Panel V
Introduction viii
by M.J. Pelegrin
Reference
Expos6 d’ouverture (Opening Address) OA
par M. Btnichou
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SESSION I FUNDAMENTAL ASPECTS OF STABILITY WITH EXAMPLES
Chairman: Dr A. Benoit (BE)
StabilitC Hydrodynamique des Ecoulements CisaillCs 1
(Hydrodynamic Stability of Free Shear Flows)
par P. Huerre et L.G. Redekopp
Chaotic Time Series Analysis 2
by J. Stark
Exploring Chaos: A Toolkit and Some Ways to Use It 3
by M. Samuelides
Stability Analysis and Aerospace Vehicle Dynamics 4
by P.Y. Willems
Chaos Mechanisms in Some Turbulent Shear Flows* 5t
by B. Nicolaenko
On Non-Linear Longitudinal Stability of an Aircraft in a Dive in the 6
Presence of Atmospheric Disturbances**
by L.M.B.C. Campos and A.A. Fonseca
Discussion: Questions and Answers (Papers 1,2,6) D1
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SESSION I1 BASIC THEORETICAL ASPECTS AND CHAOS
Chairman: Mr S. Leek (UK)
Stability of Viscoelastic Flow: Physical and Numerical Considerations 7
by M.J. Crochet and C. Bodart
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Dynamics and Control of Coherent Structures in the Turbulent Wall Layer An Overview* 8
by G. Berkooz, P. Holmes and J. Lumley
Chaos, Entropy and Reversibility: A Simple Example 9
by C. Marchal
Analyse Non LinCaire et Dynamique du Vol 10
par P. Guicheteau
* FDP contribution.
** FMP contribution.
t Not available at time of printing.
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Reference
Decoupling of Aircraft Responses 11
by D.J. Moorhouse
Discussion: Questions and Answers (Papers 8,10,11) D2
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SESSION 111 APPLICATIONS TO AEROSPACE TECHNIQUES
Chairman: Dr C.H. Houpis (US)
Boundary Layer Transition: Prediction and Wind Tunnel Simulation' 12
by D. Arnal
Modeling Nonlinear Aerodynamic Loads for Aircraft Stability and Control Analysis* 13
by J.E. Jenkins and J.H. Myatt
Stability Model of the Atmosphere** 14
by A. Knuppel, D. Martens and A.H. Siemer
Utilizing Quantitative Feedback Theory Design Technique for Flight Control System 15
by C.H. Houpis
Adaptive Reconfigurable Flight Controls for High Angle of Attack Aircraft Agility 16
by T. Sadeghi, M. Tascillo, A. Simons and K. Lai
Toward Intelligent Flight Control 17
by R.F.S tengel
X-29: Longitudinal Instability at High Angle-of-Attack 18
by L.A. Walchli
Discussion: Questions and Answers (Papers 13,15,16,17,18) D3
* FDP contribution.
** FMP contribution.
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INTRODUCTION
by Dr M.J. PELEGRIN, Programme Committee Chairman
Is stability a measurable quantity - like mass or an Recently. new vocabulary has been introduced: strange
identifiable quantity - like temperature? There are many attractor instead of equilibrium point or limit cycle.
definitions of stability, sometimes contradictory: in fact,
it is a subjective quantity which should be defined in the All chapters of physics are affected by the concepts of
context of the theme considered The reference system in stability. Mechanical systems were the first to be affected
which the system evolves should be defined stability by Poincark's approach. Theories and studies concern
may exist in a given reference system, but no longer non linear systems. All that can be said about linear
exists in other reference systems. Stability seems to be a systems has been said at the present time. No global
dominant factor for aircraft or missile control - or any solution is expected The robustness concept of a control
type of vehicle. However, stability and manoeuvrability system is an extension of linear systems studies. This
are two opposing factors which intervene in aircraft concept is important for applications in industry or
control: for civilian aircraft stability is the dominant vehicle control. Robustness can be defined as the
factor; for military aircraft or missiles manoeuvrability is capacity (capability) of coping with the specified
the dominant factor. The above are some of the reasons performances in spite of some unknown concerning the
which led to the organization of a Workshop on parameters which define the system to be controlled - or
"Stability" for the AGARD community. sometimes, the controller parameters themselves.
Obviously, a linear differential equation with such
Basically, stability is related to irreversibility which uncertainties on coefficients is no longer a linear
means energy dissipation for linear systems, but linear equation. In fact, even in the beginning of linear system
systems are very rare though they also often represent a studies "phase margin" and "gain margin" were used to
suitable approximation of non linear systems. Stability is compensate for some errors in the system description.
also a matter of accuracy. Let's take the earth's rotation: Nowadays more elaborate techniques such as H,
is it stable or unstable? This question has no meaning optimization enables us to deal with multi-input, multi-
until the range of accuracy we are looking for, and in output systems.
fact, the whole context is specified. Due to the accuracy
of existing atomic clocks, it is demonstrated that daily The stability concept is widely used in theimodynamics,
variations are of the order of lms yearly or pluri-annual at least before statistical thermodynamics came into
variations of the order of tens of ms, occur in a pseudo being. Irreversibility - at least from a practical point of
periodic manner. However, the angular velocity is view - leads to the entropy concept, which simply says
necessarily decreasing on a long-range basis: this is that "in an autonomous system entropy can only
mainly due to the water/earth friction of tides. In the pre- increase". Irreversibility is no longer accepted as a
Cambrian period (400 M years) the day was 15 hours! universal law in statistical thermodynamics, namely those
What has been said about the angular velocity of the who study "chaos". Maxwell's devil could operate ... if
earth could also be said about the direction of the earth's we wait an appropriate very long time.
momentum. At the pole the Face of the rotational vector
moves continuously in a circle of about 2m in diameter. We can probably say that the dilemma !'stability-
However, for all human activities the earth's rotation is instability" has mainly progressed in fluid mechanics,
considered (except by some astronomers) as stable. aero and hydro dynamics and spectacular (in both
meanings of the word) results arose from the Bemard's
Poincark in the 1870s studied stability for non- curls; they directly derive from a non-organized
autonomous and autonomous problems. Ljapounov in the structure; order came up from disorder! If the heating of
1900s introduced a way of proving whether or not the fluid is adjusted, it can be stable as long as we do
stability was sufficient, but not the necessary conditions. not modify the heat transfer (it is a non-autonomous
Thereafter the behaviour of a system in the vicinity of an system).
"equilibrium point" was studied in detail (Poincark) and
equilibrium points or "singularities" were classified as Nonetheless. in this domain, the aerodynamic flow
nodes-summits-focus-saddle. around a wing can be stable though instability may
locally appear in the boundary layer: during a "normal
A variety of possible behaviour in the vicinity of a point, flight" the boundary layer becomes turbulent (i.e., locally
the limit cycles. which can be stable or unstable. were unstable) somewhere between one-half or two-thirds of
introduced; they generalized the stability point by letting the wing chord. Buffet phenomena is due to the escape
a periodic motion, noimally of a small amplitude. around of curls from the boundary layer, a phenomena which
the stability point (in the phase plane or space). should be avoided for aircraft performance and passenger
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