bluuebunny/crossref_metadata_2025 huggingface dataset:
Adaptive Mesh Generation and Visualization
Authors: Remacle Jean‐Francois , Geuzaine C. , Compère Gaëtan , Helenbrook B. T.
Published: December 2010

This chapter discusses some of the main components of mesh adaptation and solution visualization. Theoretical results on the specification of optimal meshes are reviewed and then demonstrated for several 2D and 3D example problems. Some of the more challenging aspects of mesh adaptation are discussed including mesh adaptation for problems with a time evolving solution, for problems where the geometry is specified by an external geometrical model (a CAD model), mesh adaptation for high‐order finite element methods, and anisotropic mesh adaptation. The discussion of solution visualization shows how many of the same techniques used for mesh adaptation can be used for fast and accurate visualizations of high‐order finite element data.
Computational Dynamics
Authors: Bottasso Carlo L.
Published: December 2010

The simulation of aerospace systems leads to multidisciplinary problems dealing with the modeling of complex flexible mechanisms interacting with various other coupled fields. Structural models of the elastic bodies are connected together by mechanical joints and coupled to aerodynamic models, to hydraulic and electromechanical subsystems, engine, sensors, and other elements. Modern multibody dynamics technology, based on a combination of linear and nonlinear finite element methods, techniques for enforcing constraints, coupled simulation methods, and accessory algorithmic tools, is capable of delivering models of high sophistication for a wide range of highly demanding industrial applications in aerospace engineering.
Fundamentals of Fluid–Structure Interaction
Authors: van Brummelen E. Harald , Geuzaine Philippe
Published: December 2010

Fluid–structure interaction is of fundamental importance in many aerospace‐engineering applications on account of its manifestation in aeroelasticity, aerothermoelasticity, and heat transfer.

This chapter is concerned with the fundamentals of fluid–structure interaction and of computational methods for this class of problems. Both kinematic/dynamic and thermal/thermodynamic interactions are considered.

We review the conventional Arbitrary–Lagrangian–Eulerian and three‐field formulations to accommodate the motion of the fluid domain. In addition, we focus on the precise interpretation and proper enforcement of interface conditions. Finally, we examine the strength of the kinematic/dynamic and thermal/thermodynamic coupling in fluid–structure‐interaction problems and its relation to stability and convergence of numerical solution techniques.
Historical Perspective on Experimental Methods
Authors: Ravi‐Chandar Krishnaswamy
Published: December 2010

Aerospace structures are high‐performance structures with stringent requirement on size, weight, load‐carrying capacity, reliability and durability. Over the past century, significant advances have been made in furthering aerospace structures technology. Today's aerospace structures have benefited from significant experimental investigations that have revealed modes of failure – from buckling to fatigue to plastic deformation to fracture that occur in these structures. Experimental characterization, using prototypes and failure investigations, have enabled the generation of a physical understanding of the root causes of degradation of structural performance and the development of procedures for enhancing the reliability and durability. A brief review of some major advances triggered by failures is provided in this chapter to highlight the role of experiments in this process.
Dynamic (Vibration) Testing: Design Certification of Aerospace System
Authors: Aggarwal Pravin K.
Published: December 2010

Certification of the design is part of the overall qualification process for a space system and its components. The purpose of the design certification testing is to ensure that verification/validation demonstrates design compliance with functional and performance requirements. It helps establish the proof that a product will accomplish the intended purposes. Various types of dynamic testing of structures for certification purposes are described in this section, including vibration, shock and acoustic testing. Modal testing is discussed as it frequently complements dynamic testing and is part of the structural verification/validation process leading up to design certification. Examples of dynamic and modal testing are presented as well as the common practices, procedures and standards employed.
Fatigue Properties Characterization of Structural Metals, Composites and Sandwich Structures
Authors: Pelegri Assimina A. , Pan Yi
Published: December 2010

The fatigue properties of materials are necessary for life prediction of material or structure to ensure structural integrity and safety in cases where the structures are subjected to fatigue stress cycles. Several fatigue testing techniques for structural metals, composites, and sandwich structures at coupon level are discussed in this chapter. General considerations such as instrumentation and specimen design are introduced, followed by brief descriptions of the techniques applied to determine stress‐life, strain‐life, and fatigue crack‐growth rate for structural metals and composite materials and the corresponding phenomenological models. Fatigue testing technique applicable to sandwich core materials due to core shear failure is covered too. Procedures for testing the effects of environmental factors such as temperature and moisture on fatigue properties are briefly discussed.
Delamination Toughness Characterization of Laminated Composites
Authors: Davidson Barry D.
Published: December 2010

The state‐of‐the‐art in delamination toughness characterization is reviewed. Widely used methods for determining mode I, II, and mixed‐mode I‐II delamination toughness of laminated composites are first presented. This is followed by a description of the evolving methods for characterizing the mode III and the mixed‐mode toughness under conditions where mode III is present. The effects of mode ratio, temperature, moisture, and interfacial ply orientation on toughness are discussed, as is the representation of static delamination toughness data via failure loci and failure surfaces. Methods are presented to evaluate threshold toughnesses for the onset of fatigue delamination growth and to determine growth rates for stable delamination advance under fatigue loading. The relative advantages of characterizing fatigue delamination growth using energy release rate versus stress intensity factor are also addressed.
Modal Vibration Methods in Structural Health Monitoring
Authors: Worden Keith , Inman Daniel J.
Published: December 2010

This chapter addresses vibration‐based structural health monitoring (SHM) and issues related to using modal data to detect damage in structures using an SHM philosophy. The basic premise is that changes in modal information obtained through providing a known vibration signal in and measuring the vibration response will indicate a change in the structures' mass, damping, or stiffness properties. Furthermore, these changes are thought to correspond to damage in the system. The following text discusses several such methods and examples of SHM through modal methods.
Impedance‐Based Structural Health Monitoring for Aerospace Applications
Authors: Park Gyuhae , Farrar Charles R. , Inman Daniel J.
Published: December 2010

Various experimental studies have demonstrated that an impedance‐based approach to structural health monitoring (SHM) can be an effective means of structural damage detection. Using the self‐sensing and active‐sensing capabilities of piezoelectric materials, the electromechanical impedance response can be monitored to provide a qualitative indication of the local health of a structure. The impedance method also has applications in the field of sensor self‐diagnostics and validation for determining the operational status of piezoelectric active sensors used in SHM. This chapter presents an overview and recent applications of the impedance‐based structural health‐monitoring technique.
Damage Prognosis for Metal and Composite Aerospace Structures
Authors: Adams Douglas E. , Jata Kumar V.
Published: December 2010

It is envisioned that aerospace systems will someday be designed with automated damage prognosis technologies that are used to sense and predict the remaining life of structural components. The goal of implementing damage prognosis in an automated manner is to manage the uncertainties and high costs that are associated with current structural integrity management programs especially as new materials are adopted. This chapter reviews challenges and methods associated with estimating loads, diagnosing the damage state, and predicting the life of structural systems across multiple time and length scales. It is determined that multi‐multi methods that incorporate probabilistic modeling are needed to quantify and manage statistical uncertainties in structural damage prognosis. Applications involving rotary wing and fixed wing aircraft, rocket motors, and wind turbines are highlighted.
Design Principles for Aerospace Structures Utilizing
SHM
Authors: Haugse Eric D. , Young Gerould K. , Derriso Mark M. , Davis Christopher L.
Published: December 2010

Structural health management (SHM) and its related technologies offer the combined benefits of reducing maintenance costs while preserving or improving structural design performance. Advanced SHM technology implementation for in‐service aerospace platforms requires a disciplined approach to quantify how each application can provide benefit in the context of design practices and design and maintenance criteria. The focus of this chapter will be to describe SHM from a broader integrated design perspective and vision for the future. This will be accomplished by first providing a brief historical illustration of how design practices have evolved along with the ability to collect in‐service knowledge. An overview of SHM from a design and integration perspective will then be provided, followed by some examples that demonstrate SHM implementation in the context of a broader design and maintenance perspective.
Structural Materials: Aluminum and its Alloys – Fabrication Technologies
Authors: Schneider Judy A.
Published: December 2010

Aluminum alloys have a wide range of applications in the aerospace industry due in part to a high strength to weight ratio and resistance to corrosion. The relatively low melting temperature of these materials makes them amenable to variety of fabrication methods. Critical to the usage of these materials for aerospace structures is the ability to produce light‐weight structures, complex geometries, and joints of high integrity. The objective of this chapter is to compare the use of different fabrication processes commonly used in the aeronautical industry for aluminum alloys.
Titanium and Its Alloys: Metallurgy, Heat Treatment and Alloy Characteristics
Authors: Boyer Rodney R.
Published: December 2010

Titanium is a very attractive material for aerospace applications due to its high strength:weight ratio, corrosion resistance and temperature capabilities; titanium is used in cryogenic applications as well as for elevated temperature applications up to ∼600°C. Another consideration, becoming more important with increased use of polymer matrix composites usage, is titanium is more compatible with composite materials than the other structural alloys when taking into account both corrosion and coefficient of thermal expansion compatibility with the graphite fibers in the composites. The rationale for using titanium will be discussed in detail and a brief description of the alloy types and their advantages and disadvantages will be presented in (see Titanium and its Alloys: Processing, Fabrication and Mechanical Performance). A wide range of heat treatments can be used for Ti alloys, which can have a significant effect on their properties combinations, which will be explained. A unique aspect of titanium is that even the modulus can be modified by heat treatment and/or processing. Relatively new, emerging alloys are also covered.
Fiber‐Reinforced Polymer Composites: Manufacturing and Certification Issues
Authors: Engelstad Stephen P. , Koon Robert W.
Published: December 2010

This chapter is targeted as a high‐level primer for the basic requirements and issues regarding the certification and manufacturing of composite aircraft structure. It begins with a review of the general certification requirements. This includes discussion on material and process development, manufacturing and quality assessment, building block testing, analysis, structural testing, and supportability. Different manufacturing options are then reviewed, which cover material selections, material placement, resin infusion, curing, and joining options. A final discussion provides guidance on key issues in bonded versus mechanically fastened joints.
Load‐Bearing Laminated Composite Structures
Authors: Chan Wen S.
Published: December 2010

This chapter covers the description of the basic terminologies and load‐deformation relationships of fiber reinforced laminated composites. The terminologies include laminate coding, lamina and laminate coordinate systems, symmetric and unsymmetrical laminates, balanced and unbalanced laminates, antisymmetric laminate‐and quasi‐isotropic laminate. The elastic stress/strain relationship of lamina and the laminate constitutive relationship (classical laminated plate theory) are described. Illustrations of computational procedures of lamina stresses and lamina failure prediction in laminated structures are also included. The out‐of‐plane laminate failure criterion is briefly depicted. The extensional [

A

], coupling [

B

] and bending [

D

] stiffness matrices of laminate are explicitly expressed. The structural response of a laminate due to the components of the

A

,

B

and

D

matrices is also depicted in this article. The characteristics of laminates used in the primary structures for aerospace applications are described. Edge delamination, a unique behavior of load‐bearing laminate structures is also explained. Design approaches for laminate strength improvement are also addressed.
Fiber‐Reinforced Polymer Matrix Composites: Pressure Vessels for Aerospace Applications
Authors: Chang James , Newhouse Norman
Published: December 2010

A composite overwrapped pressure vessel (COPV) is a thin liner overwrapped by fiber reinforced polymer matrix composite material (FRPMC) through either wet filament winding process or layup with prepegs. Because of the weight benefit, space shuttle and International Space Station used COPVs for the storage of various fluids including gaseous oxygen, gaseous nitrogen, and gaseous helium. Other space systems such as launch vehicles and satellites also use COPVs in their propulsion or control subsystems. This chapter describes briefly the manufacturing process for producing a COPV and some key design and test requirements that are being imposed on space flight COPVs.
Lightweight Sandwich Structures
Authors: Vizzini Anthony J.
Published: December 2010

Ligh‐weight sandwich structures are utilized for their relatively high specific bending rigidity and strength. In addition, the core material can be selected to optimize the performance of the structure with respect to various transport phenomena such as fire retardation, thermal conduction, and sound transmission/absorption. Although sandwich structures can be seen as simple structural elements, their manufacture requires a series of steps necessitating the design of the manufacturing process often in tandem with the mechanical design.
Metal‐to‐Metal and Metal‐to‐Composite Bonded and Bolted Structural Joints
Authors: Ahn Junghyun , Duffala Nicole
Published: December 2010

To provide basic understanding of joints in aerospace composite structures, engineering approaches in designing composite bonded and mechanically fastened joints are described in this chapter. For each joint configurations, design and application aspect in aerospace structures were explained. Fundamental methods behind theoretical derivation of each joint configuration are explained. As an example for a real‐life design implementation of hybrid joints, integrated analysis approach using finite element analysis is presented at the end of chapter.
Mechanical Behavior of Nanomaterials
Authors: Chasiotis Ioannis
Published: December 2010

Nanomaterials for aerospace applications are dominated by nanostructured polymer matrix composites that are designed to improve on the mechanical, electrical, and thermal properties of polymers and polymeric matrices in laminate and woven composites. The design, manufacturing, and evaluation of nanocomposites are currently in progress, and this chapter provides a discussion on the state‐of‐the‐art mechanical improvements provided by this class of nanostructured materials. The effects of nanoparticle aspect ratio, size, and weight fraction on the elastic stiffness, mechanical strength, and fracture toughness are discussed in the perspective of existing knowledge on the mechanics of microscale particle reinforced polymers.
TiAl Intermetallics
Authors: Appel Fritz
Published: December 2010

Intermetallic titanium aluminides offer an attractive combination of low density and good oxidation and ignition resistance with unique mechanical properties. Thus, they are one of the few classes of emerging materials that have the potential to be used in demanding high‐temperature structural applications whenever specific strength and stiffness are of major concern. Advanced TiAl alloys have very complex microstructures with important features at the nanometer scale. There is an intimate correlation between the alloy chemistry, constitution, microstructure, and mechanical properties, which has to be considered in order to meet the desired properties. These concerns are addressed in this chapter through a global commentary on the physical metallurgy of TiAl‐based alloys. Particular emphasis is paid on recent developments of TiAl alloys with enhanced high‐temperature capability for application in aeroengines. Since TiAl alloys are now at the point of application, this chapter serves the materials' engineers as guidance in the huge body of literature concerning gamma titanium aluminide alloys going back nearly 20 years.
Metal‐Based Composite Materials for High‐Temperature Application
Authors: Withers Philip J.
Published: December 2010

Metal matrix composites offer the potential for improved specific properties as well as increased elevated temperature performance relative to their unreinforced alloys. These are critical attributes for many aeroengine applications, making composites attractive despite their higher cost. For brittle matrix systems such as intermetallics, reinforcement can also be used as a means of improving toughness. In this chapter, a wide range of long fiber and discontinuously reinforced composite systems are considered from an aeroengine perspective based on aluminum, titanium, and intermetallic matrices moving from moderate‐temperature systems towards hot ones. Processing methods appropriate to each type are described. Properties such as specific stiffness, strength, creep, and fatigue performance are considered. Another important aspect is the propensity to generate residual stresses as a function of the mismatch in thermal expansion between the phases. In the final section a range of potential aeroengine applications is examined.
Polycrystalline Nickel‐Based Superalloys: Processing, Performance, and Application
Authors: Mitchell Robert J.
Published: December 2010

This chapter provides an introduction to polycrystalline nickel‐based superalloys and their application in aero gas turbines as critical rotating components. The chapter outlines the severe operating conditions in which these alloys operate and how they and the environment have evolved over time. The basics of superalloy metallurgy are presented with reference to the role of solid solution strengthening, precipitation hardening, minor phases, and trace elements. The role of microstructure on mechanical properties is discussed with specific reference to grain size, precipitate size, morphology and distribution, and grain boundary character. Heat treatment technology and the role of heat treatments in determining both microstructure and mechanical properties are also discussed. Processing routes are presented, outlining the multiple complex steps that are used in production of these components. The chapter concludes by presenting a brief synopsis of some of the latest advances in the field of polycrystalline nickel‐based superalloys. The chapter contains useful figures and tables and a detailed reference list, proving an excellent starting point for further study in this field.
Beyond Nickel Based Superalloys
Authors: Tsakiropoulos Panos
Published: December 2010

In the most advanced gas turbine engines, the gas temperature exceeds the melting temperature of Ni based superalloys. Further improvements in the performance of gas turbines require operation of metallic materials at higher temperatures. Research programs on Nb and Mo silicide based alloys have demonstrated that these materials can offer attractive mechanical properties that justify their consideration as suitable candidate materials to replace Ni based superalloys in specific structural applications in gas turbine engines. The research has also demonstrated that oxidation behavior of developmental alloys can be significantly improved via selection of specific alloy elements. The ongoing research to develop new alloys is outlined with the emphasis on new metallic materials based on the refractory metals Nb and Mo. For the Nb based alloys, alloy development research based on the Nb–Si–Ti system with transition/refractory and free electron metal additions is reviewed. For the Mo based alloys, the review concentrates on alloys based on the Mo–Si–B and Mo–Si–Al systems.
Solid State Welding of Aeroengine Materials
Authors: Preuss Michael , Threadgill Philip
Published: December 2010

The development of advanced aeroengine materials with improved high temperature capability has led to the requirement of solid state welding, with friction welding being the most viable technique. Particularly common in the aeroengine industry are inertia and linear friction welding, which will be considered in this chapter. First, a brief historical overview of the development of these solid state joining techniques will be provided. This is followed by a description of the basics of the process and the fundamental aspects of inertia and linear friction welding. Central to friction welding is the heating of two metal interfaces by friction resulting in severe deformation and often very steep temperature gradients across the weld line. Consequently, a central aspect to understanding inertia and linear friction welding is the detailed description of microstructural changes within the thermomechanically and heat affected zone, which ultimately impact on the mechanical properties of the weld and the residual stress development. Critical in the development of appropriate post weld heat treatments is to mitigate residual stresses without compromising the microstructure and mechanical properties. This is particularly difficult when working with dissimilar welds.
Superplastic Forming and Diffusion Bonding of Titanium Alloys
Authors: Ridley Norman
Published: December 2010

Following a brief history of superplasticity leading to work that demonstrated the feasibility of combining superplastic forming (SPF) and diffusion bonding (DB) of α/β Ti alloys, the characteristics and the requirements for SP behavior are outlined. The importance of a high‐strain‐rate sensitivity, ormvalue, in inhibiting neck propagation in SP‐tensile specimens and differential thinning during SPF is explained. Factors affecting superplasticity in α/β Ti alloys are identified, important α/β alloys are listed, and the processing of material for SPF is described. The principles and practice of SPF and DB are explained, problems associated with the high temperatures involved are discussed, and procedures for testing the quality of diffusion bonds are considered. Typical aerospace applications of the products of DB and/or SPF are given.
Shape Memory Alloys
Authors: Shaw John A. , Churchill Christopher B. , Lagoudas Dimitris C. , Kumar Parikshith
Published: December 2010

An overview of shape memory alloys (SMAs) is presented, identifying some of the known alloy systems, their distinctive thermo‐mechanical properties, and the atomic‐level and microstructural mechanisms responsible for their remarkable behaviors. Some less known and unusual phenomena in their thermo‐mechanical response are highlighted that have created pitfalls for the casual user. A few interesting applications of SMAs, especially in the aerospace field, are briefly described that have enabled novel manufacturing techniques, deployable mechanisms, and adaptive structures.
Electroactive Polymers (EAP) as Actuators for Aerospace Engineering
Authors: Bar‐Cohen Yoseph
Published: December 2010

Most biological systems that are larger than a bacteria use muscles as their actuators. Muscles are capable of lifting large loads with short time response in the range of milliseconds but they are driven by a complex mechanism that is very difficult to mimic. Electroactive polymers (EAP) are human made actuators that most closely emulate biological muscles earning them the moniker “artificial muscles”. Initially, EAP received relatively little attention due to their limited actuation capability. In the last twenty years a series of EAP materials have emerged that respond to electrical stimulation with a significant shape change. Using these materials as actuators, various novel mechanisms and devices were already demonstrated including robot fish, miniature gripper, loudspeaker, active diaphragm, catheter steering element,, and dust‐wiper. The impressive advances in improving their actuation strain capability are attracting the attention of engineers and scientists from many different disciplines. These materials are particularly attractive to biomimetic applications allowing for producing biologically inspired intelligent inventions. Increasingly, engineers are able to develop EAP actuated mechanisms that were previously considered science fiction. This chapter reviews the state of the art, challenges, and potential applications of EAP materials to aerospace engineering.
Materials in Space: An Introduction and Overview
Authors: Chambers Alan R.
Published: December 2010

The components of the space environment which affect the performance of materials in space are described. These include the gaseous atmosphere of low Earth orbit (LEO), atomic oxygen, radiation including vacuum ultraviolet, soft X‐rays and cosmic rays and debris both natural and man‐made. The effect of the environment on the performance of common spacecraft materials and components are identified and the developments in materials and design to combat degradation are considered. The paper serves as introduction to the more detailed contributions in this chapter.
Surface Modification of Space Materials
Authors: Kleiman Jacob I.
Published: December 2010

Surface engineering techniques are being used extensively in the aerospace and space industries as well as a variety of other industries to develop, maintain, or change a wide range of functional properties, including physical, chemical, electrical, electronic, magnetic, mechanical, wear‐resistant and corrosion‐resistant properties. An overview of the present, state‐of‐the‐art, situation in the field of surface modification of space materials is presented. A number of surface modification technological solutions that differ from the traditional protective coating approaches are discussed that change the surface properties of treated materials thus protecting them from the hazards of low earth orbit (LEO) and geostationary orbit (GEO) environments or impairing new functional properties to space materials used in LEO/GEO, with examples of their testing, characterization and applications provided.
Space Environment Simulation and Materials Testing
Authors: Tighe Adrian P.
Published: December 2010

This chapter describes the design and types of ground‐based test facilities used to simulate the effects of the space environment on materials. The ability of the facilities to replicate the environment is discussed. First, an overview is given of the design and operational requirements common to most types of facility, including the design of the vacuum facility, the requirements for the test environment, sampling handling and storage requirements, as well as cleanliness and contamination control requirements. Various measurement philosophies are also discussed. The different test facilities most commonly used are described, covering vacuum outgassing, atomic oxygen simulation, thermal testing, electromagnetic radiation and charged particle testing, micrometeoroid and orbital debris simulation, and testing in a pressurized environment. In each case, the facility design, test standards, and data analysis methodology are discussed. Other environments that are also mentioned briefly are planetary environments, spacecraft launch and re‐entry environments, synergistic test environments, and on‐ground environments.
Cruise Performance of Fixed‐wing Aircraft
Authors: Young Trevor M.
Published: December 2010

Methods are presented for the determination of the range and endurance of fixed‐wing airplanes with thrust‐rated powerplants (e.g. turbo‐jets and turbofans) and power‐rated powerplants (e.g. piston‐propeller and turbo‐propeller). Range and endurance integral expressions are derived, and numerical techniques for their evaluation outlined. Analytical solutions for the integral expressions are presented based on the following sets of assumptions: (i) cruise at constant height and constant lift coefficient, (ii) cruise at constant airspeed and constant lift coefficient (i.e. the Breguet solution), and (iii) cruise at constant height and constant airspeed. There are two conventions for the definition of the specific fuel consumption (SFC): it can be defined either in terms of the mass flow rate or the weight flow rate of the fuel. This leads to two sets of expressions for range and endurance; both conventions are covered in this chapter. The determination of the fuel required for an airplane to fly a complete mission – which includes the takeoff, climb, cruise, descent, approach and land – is a relatively complex calculation; however, considerable insight into an airplane's range is achieved by studying the cruise segment in isolation – this approach is outlined.
Static Lateral Stability
Authors: Filippone Antonio
Published: December 2010

This chapter deals with the static lateral stability and trim conditions for a fixed‐wing aircraft having a conventional geometry (wing, horizontal, and vertical tail plane). The aircraft is considered as a rigid body. The basic control systems are shown for a conventional vehicle consisting of a wing with aileron, a horizontal tail with elevator, and a vertical tail with rudder. The simple case of a banked turn is presented.Then the pitching moment equations are derived for the wing alone and the full aircraft. Two particular cases are considered: (i) minimum control speed in air for a flight with asymmetric thrust; (ii) aircraft in straight rolling motion without inertia coupling.The lateral stability conditions in roll are derived and the main parametric effects are discussed.
Longitudinal Dynamic Stability
Authors: Yechout Thomas R.
Published: December 2010

Longitudinal dynamic stability addresses the time history of motion following a disturbance in pitch. This chapter summarizes the most commonly used approach to analyze the two predominant longitudinal dynamic stability modes, usually referred to as the short period and phugoid. A review of the development of the six non‐linear aircraft equations of motion, along with a review of the three linearized longitudinal equations is a realistic prerequisite for the reader. A significant degree of importance is placed on obtaining excellent longitudinal dynamic stability characteristics in an aircraft design, with special emphasis on the short period mode, since the pilot's ability to accomplish tracking and maneuvering tasks is directly affected by these characteristics. In recent decades, baseline aircraft dynamic stability characteristics have been typically compromised in aircraft designs. This design compromise has been chosen in favor of decreased drag to obtain performance improvements such as increased range, endurance, and turning performance, with the knowledge that feedback control systems will be added to the design to “modify” the baseline dynamic stability and obtain excellent dynamic stability or handling quality characteristics.
Rotary‐Wing Dynamic Stability
Authors: Lee David A.
Published: December 2010

The dynamic stability of a rotary‐wing aircraft is assessed by predicting and observing the aircraft motion following a disturbance from trimmed flight. Varying time scales for the dynamic stability assessment separate the stability modes. A short time scale of 2–3 s highlights the control response. A longer time scale up to a maximum of typically 60 s describes the “classical” dynamic stability. For a conventional helicopter, the effects of the main rotor dominate the control response and dynamic stability characteristics, although other key contributions must be considered. These contributions can be quantified via stability and control derivative sets enabling estimates of engineering parameters. Comparisons can be made of these parameters against handling quality metrics to predict handling quality rating (HQR) levels. Flight testing involving longitudinal and lateral‐directional control response tests and dynamic stability tests are relatively straightforward but will always be supported by mission‐related handling tasks, where HQR values are assigned by qualified test pilots. Cross‐coupling assessments are a significant feature of control response and dynamic stability testing. The principles and practices of dynamic stability modeling and flight testing have applications to unconventional rotary‐wing configurations but only after cautious appraisal of the likely outcomes.
Fixed‐Wing Control and Handling Qualities
Authors: Hess Ronald A.
Published: December 2010

An introduction into the control and handling qualities of fixed‐wing aircraft is presented. Military handling qualities specifications are discussed followed by examples of specification requirements for aircraft longitudinal and lateral/directional modes of motion. Lower‐order equivalent systems are introduced as a means for accommodating the higher‐order, nonclassical dynamics that accompany the introduction of stability and command augmentation systems. Other frequency domain handling qualities criteria such as bandwidth/phase delay are introduced. Techniques that have their basis in control theoretic models of the human pilot complete the chapter.
Rotary‐Wing Control and Handling Qualities
Authors: Cooke Alastair K.
Published: December 2010

The conventional helicopter is controlled by altering the pitch of the rotor blades (feather angle) in a suitable manner to change the magnitude and, in the case of the main rotor, alter the orientation of the thrust vector. The orientation of the main rotor should ideally mirror the position of the cyclic stick in the cockpit and this is usually achieved by providing a suitable mix of longitudinal and lateral feather commands. A study of the flapping dynamics provides insight into how this mixing is accomplished for rotors with different amounts of flapping stiffness and hinge offset.

As the handling qualities of the typical helicopter are less than ideal most are fitted with a command and stability augmentation system which permits some tailoring of the response characteristics. The determination of the best mix of handling qualities was the subject of much international research in the late twentieth century; resulting in the publication of the USAMC's Technical Report ADS‐33E‐PRF, “Handling Qualities Requirements for Military Rotorcraft,” which is considered to be a seminal document by many within the rotorcraft community.
Special Features of Guided Weapon Stability and Control
Authors: Bray Derek
Published: December 2010

The fundamental principles of aerodynamic stability and control are just as applicable to guided weapons (GWs) as to the more commonly understood fixed‐wing aircraft. The different operational characteristics, however, result in distinct nuances between the two classes. For instance, many GWs, especially those designed for fighter aircraft attack, have relatively high lateral acceleration requirements. The majority of GWs also operate in the supersonic regime, often well above the speeds typically encountered by even the fastest aircraft. Additionally, most GWs are of axisymmetric designs. All of this, and more besides, means that GW stability and control merits specialized treatment.

This chapter provides a detailed overview and analysis of aerodynamic stability and control, as applied specifically to the case of GWs (missiles). The principal subjects covered in this chapter include trim, static and dynamic stability considerations, stability derivatives, airframe configurations, and aerodynamic control methods.
Nonlinear Flight Control Systems
Authors: Kim Seungkeun , Tsourdos Antonios , White Brian A.
Published: December 2010

This chapter aims to provide the reader with a basic understanding of nonlinear control theory and its applicability to flight control system design. To begin with the limitation of the gain‐scheduling technique widely used for flight control is discussed, and subsequently the taxonomy of the system dynamics is touched in order to help understand how the model characteristics affects the nonlinear controller design. Then nonlinear control theories attractive to flight control system are briefly introduced with tutorials and control law derivations based on aircraft dynamics, which includes feedback linearization, sliding mode control, backstepping control, receding horizon control and other approaches. This chapter finishes with giving conclusions and perspectives of the nonlinear flight control systems.
Flight Formation Control
Authors: Innocenti Mario , Pollini Lorenzo
Published: December 2010

This chapter presents an overview of the main issues relating to guidance and control of aircraft flying in a formation. Formation flight is a demanding task when performed manually, and it is a challenge for the flight control engineer, when performed in an automated fashion or by autonomous unmanned vehicles. The chapter focuses primarily on the investigation of possible formation structures to be used in an operational environment, with emphasis on optimization with respect to data information transfer among the elements (nodes) of the formation itself. The final objective is the capability of maintaining a formation in the presence of a failure of one of the vehicles/components, such as the loss of an aircraft, with a high degree of autonomy and possibly without intervention from ground and/or command operators. Although the emphasis is on unmanned aircraft, the principles could be extended to automated manned formation flight as well.
Antennas and Electromagnetic Wave Propagation: Radar, Seekers and Sensors, Tracking, and Target Recognition
Authors: Hall Peter S.
Published: December 2010

Radars use controlled beams of electromagnetic energy to detect or track targets. The antenna is the device that controls the energy projection. It is necessary to study antenna types and designs to understand the limitations on this control and, in particular, how narrow a beam can be at the operating frequency. In general, the higher the frequency, the narrower the beamwidth. In addition, the properties of the atmosphere can affect the propagation of the energy, and in general the energy is more heavily attenuated at higher frequencies. It is clear that one cannot easily have long range and narrow beamwidths from the same equipment, and thus the design of the antenna and an appreciation of radio wave propagation become central to the operation of radar systems. This chapter gives an overview of how antennas operate, the various types of antennas that have been developed and describes the principles of radio wave propagation.
Radar Basics and Applications
Authors: Stove Andrew G.
Published: December 2010

The chapter provides a brief outline of the theory of radar and illustrations of the range of applications of radar in aerospace systems. An outline of the derivation and application of the radar range equation is provided, together with basic detection curves and rules of thumb to use these in simple performance calculations. The effects of clutter and multipath are also briefly discussed. Besides the discussion of conventional radar designs, synthetic aperture radars and electronically scanned arrays are briefly introduced. Applications of ground‐based radars to observe aircraft and of airborne radars are briefly described. A very brief introduction to countermeasures to radar is also included. It is intended that this introduction will be supplemented by the more detailed discussion of many of these topics in other chapters of the encyclopedia.
Backscatter from Land and Sea
Authors: Watts Simon , Ward Keith D.
Published: December 2010

An important factor influencing the performance of radar systems is the nature of the signal scattered back from the land and sea. Much research has been undertaken on this topic of radar clutter since the invention of radar, and there remains much to be done to understand clutter and its effect on radar behavior. This chapter presents an overview of the current state of knowledge and gives detailed examples of some aspects. First, the calculation of radar backscatter is considered using a description of the scattering surface (the land or sea) and the equations governing electromagnetic fields. It is shown that in order to obtain useful quantitative results it is necessary to apply approximations to the surface description and the scattering calculations, and this limits the progress that can be made. For this reason many of the advances to date have been made through analysis of radar data. Radar clutter characteristics derived from this analysis are shown here, such as normalized radar cross section (

), amplitude statistics, temporal fluctuations, the Doppler spectrum, and spatial correlation. This is followed by a description of these characteristics for land and sea clutter, and how they change with radar parameters, geometry, and environmental conditions.
Synthetic Aperture Radar
Authors: Moccia Antonio
Published: December 2010

Since its appearance in the 1950s, synthetic aperture radar (SAR) has been experiencing a continuous growth in systems, performance, and applications. Thanks to its possibility of any‐weather and any‐time operation, SAR became rapidly a primary remote sensing system for Earth and planetary observation, and, today, a widening of its application in more demanding fields, such as natural hazards or surveillance, is noticeable: as an example, by using airborne SAR, it is possible to obtain 3‐D images of a surface with centimeter resolution, detect surface variation, and indicate moving targets. This chapter intends to give an overview of SAR operation and performance, with special emphasis on aspects related to aerospace engineering. Basic geometry to define SAR observation is introduced, illustrating how dynamics of the aerospace platform embarking SAR is fundamental to image formation. It is explained how SAR operates by exploiting the range‐Doppler approach and how a noteworthy increase of azimuth resolution is achievable. Multistatic configurations are then presented with special emphasis on cross‐track and along‐track SAR interferometry, showing how digital elevation model and moving target identification can be obtained. The principles of SAR processing are outlined, and the orders of magnitude of overall configurations and achievable performance are given. Finally, a brief introduction to future SAR systems is given, discussing potentialities of multiple antennas distributed on aerospace platforms flying in formations.
Radar Missile Seekers
Authors: Baker Chris J. , Zyweck Anthony
Published: December 2010

Modern missiles represent an example of a highly integrated set of subsystems that all interact cooperatively to guide the missile to its target. The key to intercepting moving targets is the missile seeker, and for all weather, day/night, and long‐range performance, the RF seeker is the preferred option. RF seekers are often viewed as “little” airborne intercept (AI) radars. There are considerable functional differences between RF seekers and their larger cousins because of the different requirements for missile guidance when compared to airborne surveillance. This chapter begins by reviewing the characteristics of a modern RF missile, which impact the RF seeker requirements. The role of the RF seeker is then explored and differences between RF seekers and AI radars are highlighted. The key figures of merit for RF seeker performance are reviewed and their effects on modern RF seeker design are explained. There have been many different RF seeker designs over the years but the modern active coherent seeker is currently prevalent. The key aspects of a generic active RF seeker configuration are discussed. Finally, some advanced RF seeker trends are discussed. The benefits of increased operating frequency and instantaneous bandwidth are covered as well as the emerging requirement to reduce seeker signatures for improved effective engagement range and compatibility with low observable launch platforms. Several aspects of seeker design that improve electronic protection are also discussed.
Global Navigation Satellite Systems
Authors: Axelrad Penina
Published: December 2010

A Global Navigation Satellite System (GNSS) enables continuous positioning anywhere on or near the Earth surface by means of radio signals transmitted from orbiting satellites. The system comprises a constellation of about 20 or more satellites, a network of ground stations for monitoring and control of the satellites, and an unlimited number of users who passively receive the signals and employ them for positioning and other applications. GNSS satellites transmit carrier signals in the range of 1.1–1.8 GHz, which are modulated by digital codes, termed pseudo‐random noise (PRN) codes. The codes are selected so as to enable all satellites in the constellation to transmit at the same frequency with minimal interference, and to permit range measurements to be made. Given information on the satellite locations and measurements of range to at least four satellites, a receiver on or near the surface of the Earth can solve for its three dimensional position and time. GNSS is widely used for navigation and positioning of aircraft and satellites. Aviation users in particular, have very stringent requirements that are driving current augmentation and modernization efforts.
High‐Precision Three‐Axis Pointing and Control
Authors: Bayard David S.
Published: December 2010

This chapter discusses spacecraft precision three‐axis attitude control based on reaction wheel actuation and star tracker and gyro sensing. The nonlinear dynamics and kinematics associated with a rigid body withnreaction wheels are presented. A linearized controller usingnreaction wheels is designed that stabilizes the three‐axis attitude dynamics, while commanding desired spacecraft attitude, rate, and acceleration. Properties of the attitude controller are discussed including its stability, command tracking, and disturbance rejection properties. Sensor errors and reaction wheel disturbances are discussed as the two main sources of pointing error. Methods are presented to model these errors and to deal with their effects.