Modern Aerospace Research Articles

Advances in Aircraft Flight Control [Book Review

This volume is a recent addition to the Taylor & Francis book series on Systems and Control and represents a review of current practices in the field of flight control design. The book is an outgrowth of a special issue of the International Journal of Control devoted to applications of modern control techniques to aircraft flight control design. Additional contributions were obtained from an AGARD Flight Mechanics Panel Symposium. Considerable effort has been expended in ensuring that this volume is not merely a bound reproduction of previously published papers. A coherent and balanced presentation is evident with admirable production values throughout. The volume includes a foreword by the editor and concludes with an extensive and comprehensive index over ten pages in length. The text has a definite international flavor and contains 15 chapters contributed by 38 authors from six nations, all of whom speak from firsthand experience in the field of flight control design. It should be emphasized at the outset that the treatment of the subject matter in this book is unique in that it is not a tutorial on control system design techniques, per se, but rather a detailed and referenced description of current practice in the aircraft industry. The primary contribution of this volume lies in its ability to capture and describe an important part of the design experience of the aerospace industry, worldwide. The realities of the modern aerospace industry means that, in contrast to his/her senior colleagues, the young engineer now embarking upon a career in aircraft flight control will likely participate in the design of only a few flight control systems. For such young designers, the compilation of experience captured in this book should prove quite valuable. The more experienced engineer or academician also would benefit from its inclusion on their bookshelves.

Renaissance of Aeroelasticity and Its Future

The primary objective of this paper is to demonstrate that the field of aeroelasticity continues to play a critical role in the design of modern aerospace vehicles, and several important problems are still far from being well understood. Furthermore, the emergence of new technologies, such as the use of adaptive materials (sometimes denoted as smart structures technology), providing new actuator and sensor capabilities, has invigorated aeroelasticity, and generated a host of new and challenging research topics that can have a major impact on the design of a new generation of aerospace vehicles.

Life–prediction for constant–stress fatigue in carbon–fibre composites

A detailed analysis has been carried out of the strength and fatigue behaviour under constant–stress cycling of four modern aerospace CFRP laminates, all having the common lay–up [(±45,0 2 ) 2 ] s . Despite some important differences in their basic material characteristics, the fatigue responses of the four materials were similar. This pattern of behaviour has resulted in the development of a descriptive model of constant–life fatigue which has then been used as the basis for a life–prediction procedure. Preliminary attempts at validation of the method have met with a reasonable degree of success and suggest that it could provide designers with a means of selecting newly developed composites for fatigue applications on the basis of far less experimental data than are currently needed for confidence in design.

Reliable Application of Surface Mount Technology in a High-Performance Military Jet Aircraft Environment

Surface mount technology (SMT) has become a dominant force in modern aerospace electronics. Unfortunately, many avionics manufactures have" jumped on the SMT bandwagon" without fully understanding all the complex design and manufacturing issues. This paper attempts to address the most critical issues.

Life prediction for fatigue of T800/5245 carbon-fibre composites: I. Constant-amplitude loading

This paper presents a study of the fatigue behaviour of a [(±45,0 2) 2] s laminate of the T800/5245 composite system. This modern aerospace material consists of high-failure-strain, intermediate-modulus carbon fibres in a toughened bismaleimide resin system. The fatigue response in repeated tension, repeated compression, and mixed tension-compression was determined at constant stress levels over a wide range of R values, and the results are analysed in terms of constant-life diagrams of the kind that can be used to provide design data. The use of such information for life prediction purposes is discussed.

Life prediction for fatigue of T800/5245 carbob-fibre composites: II. Variable-amplitude loading

This is the second of two papers describing the fatigue response of a [(±45,0 2) 2] s laminate of the T800/5245 composite system, a modern aerospace material consisting of high-failure-strain, intermediate-modulus carbon fibres in a toughened bismaleimide resin system. In the first paper, the fatigue response in repeated tension, repeated compression, and mixed tension-compression was determined at constant stress levels over a wide range of R values. The results of those constant-amplitude experiments were then used to define a programme of four- and two-block variable-loading experiments in an attempt to derive predictive methods for such loading conditions. Formulae have been developed to predict life under non-linear cumulative damage conditions and empirical data derived to validate the procedures.

Barons of the Sky: From Early Flight to Strategic Warfare-The Story of the American Aerospace Industry

This panoramic history of the rise of the American aerospace industry traces the careers of the men whose names became synonymous with today's military-industrial complex: Glenn Martin of Martin Marietta, Donald Douglas of McDonnell Douglas, Jack Northrop of Northrop, and Allan and Malcolm Loughead of Lockheed. Weaving together institutional history and individual biography, Wayne Biddle depicts the years of uncertainty after World War I, the bonanza of World War II, and the cut-throat post-war market. Unlike the automobile industry, the aircraft industry could never be sustained by the middle-class consumer economy, and these legendary founders had to depend on the federal government to keep their companies aloft. Biddell tells the thrilling story of obsessed men who, chasing their dreams of flight and success, created the modern aerospace weapons industry.

Effect of post-weld heat treatment on mechanical properties of gas-tungsten arc welds of Al-Li alloy 8090

The modern aerospace industry needs advanced structural materials to meet stringent design requirements. This has added considerable impetus to the development of a gamut of new lightweight materials, to derive specific advantages over conventional alloys. Of these materials, Al-Li alloys offer several unique properties such as high stiffness, low density and excellent formability. These inherent properties combined with simultaneous improvements in manufacturing and/or fabrication techniques [1] have focused considerable interest on Al-Li alloys.

Vibrational analyses of glass-reinforced polyester composite plates reinforced by a minimum mass central stiffener

Thin plates are extensively used in many fields of engineering, from ship superstructures, to the high technology of the modern aerospace industries. Flat plates which are incorporated into certain types of these structures have to be stiffened when the breadth/thickness ratio of the plate exceeds certain limits. In some structures, the addition of stiffeners to the plate would introduce a weight penalty. Consequently, it would be advantageous to keep the total mass of the plate constant by taking a thin uniform layer of constant thickness from the plate and forming it into one or several stiffeners. This would result in a considerable increase in the natural frequencies of the plate structure and a reduction of its vibration amplitudes whilst retaining the same mass of the plate system. Top-hat and rectangular stiffeners with different cross-sectional configurations have been investigated in order to increase the structural dynamic efficiency of these plates. The variables of the cross-section of the stiffeners were width and thickness but the mass of these stiffeners was kept constant.

Metal flow of hot form-rolled helical gears and their fatigue strength after carbonizing: Tanaka, T., Matsui, M., Sawamura, M. and Danno, A. J. Jpn. Soc. Technol. Plast.30 (7), 1038–1043, July 1989 (in Japanese)

This paper presents a study of the fatigue behaviour of a [(±45,02)2]s laminate of the T800/5245 composite system. This modern aerospace material consists of high-failure-strain, intermediate-modulus carbon fibres in a toughened bismaleimide resin system. The fatigue response in repeated tension, repeated compression, and mixed tension-compression was determined at constant stress levels over a wide range of R values, and the results are analysed in terms of constant-life diagrams of the kind that can be used to provide design data. The use of such information for life prediction purposes is discussed.

Autoclave age forming large aluminum aircraft panels

The forming of large aluminum panels to attain airfoil sections and complex curvatures for use in modern metal aircraft and aerospace structures poses many problems that are not easily resolved by conventional mechanical forming methods. Textron Aerostructures has developed a forming method that has proven to be highly viable for forming large aluminum panels. This method is called autoclave age forming. The method uses the heat and pressure capabilities of an autoclave along with special tooling and techniques to enhance and exploit the basic stress relaxation phenomenon that occurs during the artificial aging of metal. This paper begins by describing the concept behind the autoclave age forming method. It continues by comparing the forming mechanisms used and the residual stress levels imparted by age forming and cold mechanical forming methods. Then, it will review the enhancements made to age forming by the use of an autoclave and special tooling. Finally, the paper will conclude by presenting production applications of the autoclave age forming method.

Aging and performance of structural film adhesives. III. Effect of humidity on a modern aerospace adhesive

AbstractThe aging of an uncured, DGEBA‐based commercial film adhesive exposed to high humidity at 40°C was monitored by high performance liquid chromatography (HPLC), thermal analysis, solubility, flow, and mechanical testing of joints. DGEBA and brominated DGEBA resins, and representative mixes of these were hydrolyzed in vitro. It is suggested that the major reaction at 40°C is polymerization, which is accelerated by moisture and leads to a crosslinked structure different to that resulting from normal cure. The poorer adhesive performance after aging is mainly the result of reduced resin flow during joint formation, although there is some contribution from the hydrolysis of epoxide groups which leads to lower crosslink density in the cured adhesive. The softening point of the uncured material and Tg of the cured material are useful indicators of the quality of this adhesive which, compared to some earlier formulations, has improved resistance to these conditions.

A Formal Computer Based Design Environment for Aircraft Engine Control Systems

Manufacturers of modern aerospace systems often use formalistic design methods, frequently of a modular and hierarchical nature to specify the model of the system in question. This often takes the form of a graphical representation, and hence the development of a graphical interface to the variety of software tools used would enhance the productivity and consistency of such work. In this paper a graphical operating system (ARGOS) is used as an interface for the time response package TSIM in the investigation of jet engine control system performance.

Development and applications of multirate digital control

Multiple sample rate digital control systems are of prominent interest in current control research, development, and applications. Modern aerospace vehicles and systems are described by high-order dynamic models which typically include phenomena covering a wide range of characteristic frequencies and instrumentation measurements available at multiple rates. A multirate control structure allows the designer to accommodate multiple information rates and implement required control computations within the finite computational capabilities of an on-board computer. In this paper the historical development, representative design approaches, and example applications of multirate digital control are outlined. A brief survey of traditional design approaches and techniques currently in development is presented. Potential future areas of research and application of multirate control are suggested and discussed.

AIRMEC '83

The 3rd international Aircraft Maintenance Engineering Exhibition and Congress, AIRMEC 83, was staged in Düsseldorf for the first time. The space‐city style raised walkways, with their oval glass roofing, which link the halls and buildings of the Düsseldorf Exhibition Centre, made an appropriate setting for an Exhibition of modern Aerospace technology. The Exhibition occupied a stand space of approximately 3,000 sq. metres. The displays offered a comprehensive picture of current developments in the servicing and overhauling of aircraft of all kinds. AIRMEC 83 attracted exhibitors from 15 countries. Of the 110 companies taking part, 45 were from West Germany. Britain had the second largest group, with 18 stands covering a floor space of 352 m2. Thirteen of the British contingent were grouped together in a British Joint Venture organised by the British Overseas Trade Board. Visiting the various stands, I found that most of the exhibitors were pleased not only with the attendance figures (2,500), but also with the quality of the visitors. Those attending the show came from 34 countries, and were, almost without exception, members of the technical management of their company or were sales executives. More than half were from establishments with more than a thousand employees. However, on the Friday, which was the last day, a number of exhibitors were complaining about the timing of the Conference in relation to the exhibition. The Conference ended on the Thursday lunch‐time, as a result, attendance at the Exhibition was somewhat sparse on the Friday morning and virtually non‐existent in the afternoon. Many exhibitors felt that the Conference should have been spread over the full period of the Exhibition. During the Conference, experts from 10 countries delivered a total of 32 lectures on aircraft maintenance and overhauling. These ranged from a series of lectures on hangars to training of personnel, design of engine maintenance and computer‐aided maintenance and spares management. The knowledge gained was not only of significance for airlines of developing and emerging industrial countries that have no sophisticated maintenance facilities of their own, but also to long‐established airlines. In times of dwindling profits, every airline has to keep a careful eye on possibilities for cutting operating expenditure, whilst at the same time ensuring optimum safety of the aircraft. Through the international exchange of experience and the presentation of new maintenance techniques, AIRMEC greatly contributed to the achievement of this objective.

Paper 25S: Sliding Noble Metal Electric Contacts

Sliding electric contacts have the unique requirement of low and stable resistance without high friction and wear. Electrical breakdown of surface films, which can establish metallic contact between touching members, occurs only with appreciable circuit voltages. Consequently, noble metals alone are suitable for contacts that serve the low energy circuits of modern computer, communications and aerospace equipment. Approaches used by the engineer to reduce the friction and wear of noble contact metals include: design with low normal loads, careful selection of contact materials and lubrication. Gold coatings, generally as thin electrodeposits, have become the most widely used contact material for separable connector contacts, instrument slip rings and similar devices.The ‘prow formation’ wear mechanism dominates the dry sliding of most noble contact metals, particularly during the early stages of sliding where break-in phenomena occur. Recent work shows that there is a critical load-dependent roughness for prow formation. The wear mechanisms of gold electrodeposits may differ from those of the wrought metal because of their characteristic topographic and crystallographic orientations.Lubricants are often used for sliding noble metal contacts. Solid lubricants are effective only on rough surfaces. When contacts become burnished through use the lubricant reservoirs disappear and high wear commences. Thin films of lubricants having a fluid component, however, do not have this limitation, for they demonstrate hydrodynamic lift and self-healing qualities. Above a certain velocity, characteristic of the system, wear may be negligible with fluid-containing lubricants. Their ability to function on smooth surfaces is important, for the as-plated porosity of electrodeposited metals (which leads to deleterious contact corrosion) is directly related to roughness. Finally, coatings for thin gold-plated contacts have been developed which combine corrosion inhibitors and lubricants.

Variable point guidance for space missions.

An explicit space guidance scheme, which combines the phasing and propellant advantages of parking orbits with the rapid response time of direct ascent, is described. Resulting flight plans yield multiburn trajectories spanning the continuum from direct ascent (2-burns) to parking orbit approaches (4 or more burns). The onboard computer selects automatically and continuously the flight plan depending on instantaneous geometry. The system reaction time to an arbitrary mission situation is measured in seconds. Results of a computer sizing study are presented, showing that the scheme can be implemented in a modern aerospace computer.

Representing Great Britain's Aerospace Industry

IN less than two years‘ time—on March 29, 1966—the Society of British Aerospace Companies will celebrate the completion of fifty years’ activity. It was on March 29, 1916, that the Society of British Aircraft Constructors was incorporated, thus being younger than the Royal Aeronautical Society and Royal Aero Club but two years older than the Royal Air Force. The Society continued under that title until February 26 this year, when by special resolution at an extraordinary general meeting its name was changed to the ‘Society of British Aerospace Companies’. The new title thus retains the well‐known initials S.B.A.C. but embraces more appropriately the wide range of activities of the Society's Members— not only the manufacture of aircraft, but of engines, missiles, electronics, hydraulics, electrical equipment, and all other components and materials essential to a modern aerospace industry. The new title also brings the Society into line with comparable engineering associations in the United States, France, Germany and Italy.