Design Loads for Future Aircraft

301 Pages·2001·4.17 MB·French

RTO-TR-045
AC/323(AVT-024)TP/30
NORTH ATLANTIC TREATY ORGANISATION
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RESEARCH AND TECHNOLOGY ORGANISATION
BP 25, 7 RUE ANCELLE, F-92201 NEUILLY-SUR-SEINE CEDEX, FRANCE
RTO TECHNICAL REPORT 45
Design Loads for Future Aircraft
(Les charges de calcul pour de futurs ae´ronefs)
Work performed by the RTO Applied Vehicle Technology Panel (AVT) TG 024.
Published February 2002
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14.ABSTRACT
ThisRTOTaskGroupreviewedtherequirementswhichregularflightandmanoeuvringwillputasdesignloadsonthestructureoffuture
NATOaircraft,addressingalsosafetyaspects,structuralweight,elasticeffectsandinfluenceofthecontrolsystem.Treatedare:loadcritical
flightmanoeuvresaswellasexternalloadssuchasinducedbyturbulence.Existingspecificationsarereviewedandproceduresforestablishing
designloadsarepresented.Metalandcompositestructuresaretreated,andtheanalysispertainstomainstructuresaswellascritical
subassemblies.Underoperationalaspectsthemonitoringofloadsandofstructuralfatiguearetreatedandsomeactualfailurecasesare
analysed.TherequestforNATOagreementsonrelevantdesigncriteriaismentioned.
15.SUBJECTTERMS
AerodynamicloadsFlightmanoeuversAircraftdesign;GustloadsAirframes;LoadmonitoringsystemsAviationsafety;NATOagreements
Compositestructures;ProceduresDesignloads;RTOTaskGroupDynamicloads;SpecificationsFailureanalysis;StructuralanalysisFatigue
(materials);StructuralweightFlightcontrol;TurbulenceFlightloads
16.SECURITYCLASSIFICATIONOF: 17.LIMITATION 18. 19.NAMEOFRESPONSIBLEPERSON
OFABSTRACT NUMBER Fenster,Lynn
SameasReport [email protected]
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RTO-TR-045
AC/323(AVT-024)TP/30
NORTH ATLANTIC TREATY ORGANISATION
RESEARCH AND TECHNOLOGY ORGANISATION
BP 25, 7 RUE ANCELLE, F-92201 NEUILLY-SUR-SEINE CEDEX, FRANCE
RTO TECHNICAL REPORT 45
Design Loads for Future Aircraft
(Les charges de calcul pour de futurs ae´ronefs)
Work performed by the RTO Applied Vehicle Technology Panel (AVT) TG 024.
The Research and Technology
Organisation (RTO) of NATO
RTO is the single focus in NATO for Defence Research and Technology activities. Its mission is to conduct and promote
cooperative research and information exchange. The objective is to support the development and effective use of national
defence research and technology and to meet the military needs of the Alliance, to maintain a technological lead, and to
provide advice to NATO and national decision makers. The RTO performs its mission with the support of an extensive
network of national experts. It also ensures effective coordination with other NATO bodies involved in R&T activities.
RTO reports both to the Military Committee of NATO and to the Conference of National Armament Directors. It comprises a
Research and Technology Board (RTB) as the highest level of national representation and the Research and Technology
Agency (RTA), a dedicated staff with its headquarters in Neuilly, near Paris, France. In order to facilitate contacts with the
military users and other NATO activities, a small part of the RTA staff is located in NATO Headquarters in Brussels. The
Brussels staff also coordinates RTO’s cooperation with nations in Middle and Eastern Europe, to which RTO attaches
particular importance especially as working together in the field of research is one of the more promising areas of initial
cooperation.
The total spectrum of R&T activities is covered by the following 7 bodies:
• AVT Applied Vehicle Technology Panel
• HFM Human Factors and Medicine Panel
• IST Information Systems Technology Panel
• NMSG NATO Modelling and Simulation Group
• SAS Studies, Analysis and Simulation Panel
• SCI Systems Concepts and Integration Panel
• SET Sensors and Electronics Technology Panel
These bodies are made up of national representatives as well as generally recognised ‘world class’ scientists. They also
provide a communication link to military users and other NATO bodies. RTO’s scientific and technological work is carried
out by Technical Teams, created for specific activities and with a specific duration. Such Technical Teams can organise
workshops, symposia, field trials, lecture series and training courses. An important function of these Technical Teams is to
ensure the continuity of the expert networks.
RTO builds upon earlier cooperation in defence research and technology as set-up under the Advisory Group for Aerospace
Research and Development (AGARD) and the Defence Research Group (DRG). AGARD and the DRG share common roots
in that they were both established at the initiative of Dr Theodore von Ka´rma´n, a leading aerospace scientist, who early on
recognised the importance of scientific support for the Allied Armed Forces. RTO is capitalising on these common roots in
order to provide the Alliance and the NATO nations with a strong scientific and technological basis that will guarantee a
solid base for the future.
The content of this publication has been reproduced
directly from material supplied by RTO or the authors.
Published February 2002
Copyright  RTO/NATO 2002
All Rights Reserved
ISBN 92-837-1077-0
Printed by St. Joseph Ottawa/Hull
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ii
Design Loads for Future Aircraft
(RTO TR-045 / AVT-024)
Executive Summary
The selection of design loads and requirements is defining the structural weight of airplanes and their
safety. Therefore the definition of requirements should be performed very critically by the customer
and structural weight should be assessed based on sensitivity analysis of the total aircraft which
includes flight manoeuvre simulation, flight control system, aerodynamics and elastic effects
introduced by finite elements. To produce these analyses is the job of the aircraft companies.
After selection of most load critical flight manoeuvres (pull up manoeuvres, initiation of roll
manoeuvres etc.) the calculation of airloads and inertia loads must include the flight control system and
its failure cases because it affects the motion of the control surfaces and therefore the aircraft.
With the advent of carbon fibre composite structures discrete loads are the predominant limiting design
conditions but it should be emphasised that most structures are of a hybrid nature with metal frame
which are still susceptible to fatigue loads. For airplanes designed to civil requirements such as
transport airplanes, tankers etc. the definition of continuous turbulence and inclusion of FCS failure
cases and nonlinearities such as control surface angles is extremely important.
There was a long way from load assumptions used by the Wright Brothers who designed their Flyer to
a 5g limit to the load limiting capabilities of the care free handling flight control system of the
Eurofighter. Also the US-Airforce Mil-Specifications which were used to design NATO airplanes such
as Tornado, F16 and F18 in the 1970’s are obsolete today and the MIL-A-87221 (USAF) is only a
frame without the essential quantitative material. All these issues are addressed in this manual
including comparisons of regulations and descriptions of new specifications. Complete procedures how
to establish design loads are presented which should help for the design of new airplanes.
The importance of dynamic phenomena which produce design loads for various aircraft parts such as
intakes, leading edges etc. is also highlighted. Loads monitoring systems are necessary to prove
calculated loads and monitor fatigue loads to establish the remaining structural life. There is a
description of a modern system.
For transport type aircraft gust load cases are the most critical for strength design and they are also the
main fatigue loading source for the major part of the structure. Methods for discrete and continuous
gust loading cases are presented together with nonlinear example calculations.
In the appendix there is a description of failure cases and their effect on loads for transport aircraft and
a specification of a landing gear which could be used as an example how to specify the whole structure
as a system. The military use of this manual is to establish procedures to build the lightest structure for
the military requirements. Agreement on requirements and design loads within the NATO countries
could standardise pilot training, aircraft usage, increase aircraft life and reduce maintenance. Since the
search of the best usage of the aircraft for its military purpose will continue to integrate structure and
avionics such as fire and flight control systems as an example there will be a continuous need for
future work.
iii
Les charges de calcul pour de futurs ae´ronefs
(RTO TR-045 / AVT-024)
Synthe`se
Le choix des charges the´oriques et des spe´cifications de´termine la masse structurale des ae´ronefs et leur
se´curite´. C’est pourquoi la de´finition des spe´cifications doit eˆtre re´alise´e de fac¸on tre`s rigoureuse par le
client, la masse structurale e´tant, dans ce cas, e´value´e a` partir d’une e´tude de sensibilite´ de l’ae´ronef dans
son ensemble, couvrant une simulation d’e´volution en vol, un syste`me de commandes de vol, des
conside´rations ae´rodynamiques et d’e´ventuels effets e´lastiques introduits par des e´le´ments finis. Il incombe
aux avionneurs d’effectuer ces e´tudes.
Apre`s avoir de´fini les e´volutions en vol les plus critiques en termes de charges (ressource, tonneau, etc.), le
calcul des charges ae´rodynamiques et des charges d’inertie doit e´galement inclure le syste`me de commande
de vol et ses de´faillances potentielles car il a une incidence sur le mouvement des gouvernes et par
conse´quent sur l’ae´ronef.
Avec l’ave`nement des structures composites en fibre de carbone, les charges discre`tes sont devenues les
principales conditions restrictives pour la conception, mais il est a` noter que la plupart des structures sont
hybrides avec une cellule me´tallique et restent vulne´rables aux charges de fatigue. En ce qui concerne les
ae´ronefs conc¸us selon des spe´cifications civiles, tels que les avions de transport, les avions ravitailleurs,
etc., la de´finition de la turbulence continue et l’inclusion des cas de pannes du syste`me de commandes de
vol (FCS) et des non-line´arite´s, tels que les angles de gouverne, sont extreˆmement importantes.
Un long chemin se´pare les hypothe`ses de charge retenues par les fre`res Wright, qui ont conc¸u leur “Flyer”
pour un facteur de charge limite de 5g, et les caracte´ristiques de limite de charge du syste`me de commandes
de vol a` pilotage se´curise´ de l’Eurofighter. De meˆme, les spe´cifications MIL de l’US-Airforce, utilise´es
dans les anne´es 70 pour la conception des avions de combat de l’OTAN, tels que le Tornado, le F16 et le
F18, sont aujourd’hui obsole`tes et la spe´cification MIL-A-87221 (USAF) ne repre´sente qu’un cadre, de´nue´
du mate´riau quantitatif essentiel. L’ensemble de ces questions est aborde´ dans le pre´sent manuel avec la
comparaison des re`glements et des descriptions de nouvelles spe´cifications. Des proce´dures comple`tes
permettant de de´finir des charges de calcul sont pre´sente´es, ce qui devrait faciliter la conception des
nouveaux ae´ronefs.
L’importance des phe´nome`nes dynamiques, qui ge´ne`rent des charges de calcul s’appliquant a` diffe´rents
e´le´ments de l’ae´ronef, tels que les entre´es d’air, les bords d’attaque etc. est e´galement souligne´e. Des
syste`mes de surveillance des charges sont ne´cessaires pour justifier les charges calcule´es et surveiller les
charges de fatigue en vue d’e´tablir la dure´e de vie structurale restante. La description d’un syste`me moderne
est donne´e.
Pour les ae´ronefs de transport, les charges de rafale sont l’e´le´ment le plus critique en ce qui concerne les
calculs de re´sistance, et elles sont e´galement la principale source de charges de fatigue pour la majeure
partie de la structure. Les me´thodes relatives aux cas de charges de rafale continues et discontinues sont
pre´sente´es avec des calculs d’exemple non line´aires.
L’annexe pre´sente une description des cas de panne et de leurs effets sur les charges pour les avions de
transport, ainsi que la spe´cification d’un train d’atterrissage qui pourrait eˆtre utilise´e comme exemple pour
e´tablir la spe´cification de l’ensemble de la structure en tant que syste`me. Ce manuel permet de mettre au
point des proce´dures pour la fabrication de structures les plus le´ge`res re´pondant aux spe´cifications
militaires. Un accord portant sur les spe´cifications et les charges de calcul en vigueur dans les pays de
l’OTAN pourrait conduire a` la standardisation de la formation des pilotes et de l’exploitation des ae´ronefs,
associe´e a` l’accroissement de la dure´e de vie des ae´ronefs et a` l’alle`gement de la maintenance. En
conclusion, e´tant donne´ que la recherche de l’exploitation optimale d’un ae´ronef a` des fins militaires
continuera d’inte´grer la structure et l’avionique, tel que par exemple les syste`mes de commandes de vol et
de tir, la demande de travaux de recherche sera maintenue.
iv
Contents
Page
Executive Summary iii
Synthe`se iv
Publications of the RTO Applied Vehicle Technology Panel ix
Task Group Members xi
1 Introduction 1
2 Loads Requirements Review 1
2.1 The development of maneuver load criteria for agile aircraft 1
2.1.1 Introduction 1
2.1.2 Status of present Criteria 1
2.1.3 The influence of piloting technique 6
2.1.4 The influence of advanced control systems 7
2.1.5 Conclusion 8
2.1.6 References 9
2.2 Changes in USAF Structural Loads Requirements 9
2.2.1 Introduction 9
2.2.2 Structural Loading Condition 9
2.2.3 Flight Loading Conditions 10
2.2.4 Ground Loading Conditions 10
3 Maneuver Loads 18
3.1 Classical Approach 18
3.1.1 Definitions 18
3.1.2 Limit Load Concept 19
3.1.3 Safety Factors Review 20
3.2 Non Classical Approach 21
3.2.1 Maximum Load Concept 21
3.2.2 Operational Flight Parameter Approach 26
3.2.3 Determination and Verification of Operational Maneuver Parameters and Time 27
Histories
3.2.4 Flight Loads derived from Operational Maneuvers 36
3.2.5 Flight Parameter Envelopes Approach 40
3.3 Dynamic Loads 52
3.3.1 Introduction 52
3.3.2 Types of Dynamically Acting Loads 52
3.3.3 Prediction Process & Methods 56
3.3.4 Design Assumptions, Criteria and Certification 59
3.3.5 Developments 59
3.3.6 Summary 60
3.3.7 Acknowledgements 61
3.3.8 References 61
3.4 Managing the Technical Risk - Dynamic Loads in-flight Monitoring 62
3.4.1 Dynamic Loads Monitoring System 62
3.4.2 Dynamic Loading Phenomena Monitored 63
3.4.3 Dynamic Loads Monitoring System Implementation 63
3.5 Airframe Certification Against Birdstrike Threats 68
3.5.1 Certification via Empirical Testing 68
3.5.2 References 69
v
4 Gust loads 70
4.1 Introduction 70
4.1.1 Discrete Gusts 70
4.1.2 Continuous Gusts 71
4.1.3 Gust Load Requirements 71
4.2 Overview of Gust Requirements 72
4.2.1 Draft NPRM on Continuous Turbulence 72
4.3 Comparison of Methods to calculated Continuous Turbulence Design Loads for 72
Non-Linear Aircraft
4.3.1 Analyses made by NLR 73
4.3.2 Analyses made by the University of Manchester 74
4.4 Conclusions & Recommendations 76
4.5 References 76
4.6 Appendix A4.1 85
4.6.1 Stochastic Methods 85
4.6.2 Deterministic Methods 87
4.7 Appendix A4.2 Description of Aircraft Models 91
5 A More Global Approach 96
5.1 Why a more global approach 96
5.2 Limit Loads 96
5.2.1 Basic principles of the “more global approach” for limit loads 96
5.2.2 “Maximum Loads” through “Load Severity Indicators” 96
5.2.3 “Maximum Loads Expected in Service” 97
5.2.4 Application to design of “fly by wire” aircraft 97
5.3 Ultimate load definition and Safety Factors for multiphysical effects 97
5.4 Safety factors evolution with innovations 98
5.4.1 The particular case of fly by wire aircraft 98
5.4.2 Towards probabilistic approaches 98
Appendix A The Impact of Electronic Flight Control System (EFCS) Failure Cases on
Structural Design Loads 99
A.1 Introduction 101
A.2 Certification Requirements 102
A.3 EFCS Failures 103
A.4 Procedure to Handle Failure Cases in Loads 104
A.5 Consequences on Design 105
A.6 OFIS, Approaches to OFC Detection 107
A.7 Conclusion 108
A.8 References 108
Appendix B The NATO Aircraft Landing Gear Design Specification 111
B.1 Introduction 113
B.2 Scope 113
B.3 Application 113
B.3.1 Program 113
B.3.2 Aircraft 113
B.3.3 Landing Gear Structure 114
B.3.4 Use 114
B.3.5 Structure 114
B.3.6 Instructional Handbook 114
B.3.7 Deviations 114
B.4 Applicable Documents 114
vi
B.5 Requirements 114
B.5.1 Detailed Structural Design Requirements 114
B.5.2 General Parameters 117
B.5.3 Specific Design and Construction Parameters 160
B.5.4 Structural Loading Conditions 177
B.5.5 Vibration 188
B.5.6 Strength 189
B.5.7 Durability 194
B.5.8 Damage Tolerance 200
B.5.9 Durability and Damage Tolerance Control 206
B.5.10 Sensitivity Analysis 208
B.5.11 Force Management 208
B.5.12 Production Facilities, Capabilities, and Processes 211
B.5.13 Engineering Data Requirements 211
B.6 Verification 212
B.6.1 Detailed Structural Design Requirements 212
B.6.2 General Parameters 214
B.6.3 Specific Design and Construction Parameters 224
B.6.4 Structural Loading Conditions 226
B.6.5 Vibration 232
B.6.6 Strength 236
B.7 Definitions 265
B.7.1 Acoustic Environment 265
B.7.2 Aerial Delivery 265
B.7.3 Aeroacoustic Fatigue 265
B.7.4 Aeroacoustic Load 265
B.7.5 Aircraft 265
B.7.6 Airframe 265
B.7.7 Air Transport 265
B.7.8 Air Vehicle 265
B.7.9 Auxiliary Systems 265
B.7.10 Container Delivery System (CDS) 265
B.7.11 Damage Tolerance 265
B.7.12 Damping Coefficient (G) 265
B.7.13 Degree of Inspectability 265
B.7.14 Discipline 266
B.7.15 Divergence 266
B.7.16 Durability 266
B.7.17 Durability Service Life 266
B.7.18 Factor Of Uncertainty 266
B.7.19 Fail-Safe Crack Arrest Structure 266
B.7.20 Critical Parts 266
B.7.21 Frequency of Inspection 267
B.7.22 Hardness 267
B.7.23 Initial Quality 267
B.7.24 Load Factor 267
B.7.25 Margin of Safety 267
B.7.26 Minimum Assumed Initial Damage Size 267
B.7.27 Minimum Assumed In-Service Damage Size 267
B.7.28 Minimum Period of Unrepaired Service Usage 267
B.7.29 Multiple Load Path — Fail-Safe Structure 267
B.7.30 Operational Needs 267
B.7.31 Pallet 267
B.7.32 Personnel Ear Protection 267
B.7.33 Pure Tone or Narrow Band 267
B.7.34 Reported Sound Pressure Level 267
B.7.35 Safety of Flight Structure 268
B.7.36 Slow Crack Growth Structure 268
vii