Future Aircraft Design Research Articles

Response of segmented-stiffness composite cylinders to axial end shortening

Composite fuselage structures that utilize different laminates in the crown, sides and keel may be part of future aircraft designs. Here exact, approximate and finite element solutions for the geometrically linear response to axial end shortening of cylinders constructed in this segmented fashion are investigated. It is concluded that circumferential displacements are the feature that distinguishes these designs from more conventional single-laminate designs. Additionally, it is the difference in effective laminate Poisson's ratios from one segment to the next, as opposed to the difference in effective laminate extensional or shear moduli, that is responsible for the circumferential displacement. However, for short cylinders ( L R = 2) with clamped boundaries, the circumferential displacement is greatly suppressed relative to the case of longer cylinders ( L R = 20) , while the radial displacement is not as dramatically influenced by length. This trait can be traced to the wavelengths that govern circumferential and radial responses, and can be interpreted as the Saint-Venant effect for circumferential displacement having a different characteristic length than the Saint-Venant effect for radial displacement.

Future large aircraft design — the delta with suction

AbstractSince the 1970s, large passenger aircraft design has evolved by modest, but commercially significant, incremental change following the underwing pod concept pioneered by the Boeing 707. In the 21st century, the market is likely to require greater passenger capacity to deal with air-side congestion and higher performance and operational efficiency to justify investment and conserve finite fossil fuel resources. Public opinion will require far greater emphasis on control of noise and engine exhaust pollution. There is likely to be much increased emphasis on pollution in the upper-atmosphere and its environmental impact. In such a situation, it is questionable whether the evolutionary design route can produce the necessary advances and this must stimulate the search for radical design alternatives.A revolutionary approach, involving the delta planform combined with wing laminar flow control and its impact on overall design, is given a preliminary study in this paper. This has been carried out by assuming that major improvements in drag can be obtained by extensive laminarisation. Using non-dimensional methods, the resulting broad interactive impacts on airframe and engine design and performance are derived. The effect of assuming varying quantities of low-energy air sucked from the foot of the boundary layer is studied and suction-system performance examined.In addition to the large potential improvements in range, a strong relationship between lower drag, lower cruising altitude and lower cruise engine size is identified. In the study, several factors emerge which may combine to drive large aircraft design towards low aspect ratio and the integrated delta wing planform. This paper is intended as a stimulus and a basis for further study and research.

Modern experimental techniques for high-speed flow measurements

ITHIN the last few years there has been a marked increase in interest in supersonic and hypersonic flow regimes. This has been partly as a result of the establishment of a transatmpspheric vehicle and the National Aerospace Plane (NASP) program. Addressing the technology problems for these future systems will provide a significant challenge for the aerospace community. Supersonic and hypersonic airbreathing vehicles are highly integrated systems involving strongly coupled technologies. The conceptual design process for various components requires analytical and experimental tools. The flowfield regimes include the internal combustion of propulsion systems, the external flow of the vehicle, and the overall performance of the system. The rebirth of interest in high-speed flows follows a period of inactivity. During the 1960's, considerable research was conducted on supersonic and hypersonic flows. Much of the research was directed at understanding the problem of re-entry. Test facilities such as supersonic/hypersonic wind tunnels, shock tunnels, and shock tubes were established. The diagnostic instrumentation in these facilities provided limited data. The instrumentation included pressure transducers, heattransfer gages, schlieren and inter ferometry, and gas-sampling probes. The data were sufficient to help understand the flow phenomena. With the advent of computer and laser technologies, the activities in the area of computational fluid dynamics (CFD) and sophisticated instrumentation were accelerated. The design and analysis of re-entry-type vehicles have become increasingly dependent upon numerical schemes for predicting the flowfield.1 The adequacy of CFD as the sole design tool for aerodynamic vehicles in the foreseeable future is doubtful. 2 CFD produces more detailed aerodynamic information faster than previously possible, particularly on simple configurations such as an airfoil section, a fuselage, or even a complete wing. However, reliable modeling of complex complete configurations including vortex interactions, boundary-layer transition, and chemistry are not yet available. Even the detailed physics of the flow near the leading or trailing edge of a wing is very difficult, if not impossible,, to compute within the required accuracy. Experimental aerodynamics, therefore, remain an important component in the design of future transport aircraft. This is even more true in terms of development of the propulsion system. To examine the applicability of various diagnostic techniques, it is necessary to establish the measurement requirements in terms of the parameters and the measurement environments. This in turn requires the examination of the available or proposed design facilities. Figure 1 shows the performance envelope of some existing ground test facilities.3 Also shown is the performance profile for a proposed entry research vehicle (ERV). The research vehicle is proposed for investigation of basic flowfield phenomena for high-altitude/ hypervelocity flights. Nonintrusive measurement techniques are also needed in support of candidate flight experiments. Examination of the performance envelope of existing flow facilities (e.g., Fig. 1) will help determine the required dynamic range of the instrumentation employed in these facilities.4 It is also generally agreed that the environments associated with supersonic and hypersonic test facilities are harsh both inside and outside the test facility. Inside, the measurement environment is characterized by high temperatures, high velocities, and high noise levels. Outside, it is characterized by high noise and vibration levels and by varying temperature and pressure fields, which can adversely affect the alignment and overall performance. For application of optical techniques, this requires that all optical components be mounted independent of

F-16XL demonstrates new capabilities in flight test at Edwards Air Force Base

The F-16XL was an evolutionary aircraft developed by building on the proved capabilities of the F-16's fly-bywire flight control system, relaxed static stability, and vortex flow control. Two F-16 fuselages were stretched and modified with a new cranked arrow wing that included a low-drag conformal weapon carriage. The goal was to provide improved operational effectiveness of the F-16 in the air-to-ground role without degrading the F-16's air-to-air capabilities. Design goals also included survivability enhancement through increased speed, maneuverability, and reduced radar signature along with retention of the F-16's reliability and maintainability through 80% commonality with the F-16. The F-16XL successfully met most of these goals. Improvements in air-to-ground effectiveness were a 35-65% increase in mission radius, an increased external weapons payload capability of 15,000 Ib, increased speed, and outstanding high-angle-of-attack flying qualities with air-to-ground weapons. Areas identified for improvement were primarily related to the low thrust-to-weight ratio of the XL during heavyweight takeoff and sustained maneuvering. The concepts demonstrated by the F-16XL will impact all future fighter aircraft design programs.

Blended blown flaps and vectored thrust for low-speed flight

Short take-off and landing (STOL) capability is a recurring design goal for current and future aircraft design studies to meet reduced field length requirements, provide increased stores bring back capability, enhance carrier aircraft payload launch and recovery envelopes, and improve in-flight maneuvering. The Grumman Corporation has conducted a study to design and build an A-6 STOL demonstrator aircraft for the Navy that employes two-dimensional vectored nozzles and chordwise blowing for low-speed flight. If completed, this program would demonstrate operationally acceptable STOL performance with minimum loss in cruise performance. The results of a two-dimensional airfoil test determined that a plain blown flap with a large-radius, upper leading-edge blowing segment and a conventional-shaped trailing-edge section had better high-lift capability for the available blowing momentum of the design. Extensive three-dimensional wind tunnel testing verified predicted longitudinal characteristics, showed acceptable longitudinal and lateral-directional control, and defined design limitations associated with the high-lift system.

Advanced Materials in Future Aircraft Design

As Professor Joad used to say — “It all depends what you mean by…” In this instance it all depends what you mean by future aircraft designs. There are many parameters which must be examined when choosing materials for any specific project, these involve material and manufacturing costs, aircraft performance, material performance and costs to the user such as damage tolerance, maintenance costs etc. The way in which these parameters are interwoven will depend considerably on the type of project being undertaken. A light aircraft for the Tiger Club would require a different mix of criteria to an advanced combat aircraft for the RAF. These in turn would be different from the selection that would be made for a one‐shot vehicle such as a booster rocket. In order to narrow this field we will concentrate on the type of aircraft which is typical of Kingston designs, the small high performance aircraft for use by the Air Forces of the world.

Aircraft Characteristics and Air Traffic Systems

It is likely that in the future aircraft designs will be increasingly tailored to optimize the traffic system rather than the economics of the aircraft considered in isolation. In this paper Mr. Attwooll, of the Mathematics Department at the Royal Aircraft Establishment, discusses the effect on the properties of air traffic systems of the individual characteristics of aircraft. This paper (published by permission of the Ministry of Defence), which reflects Mr. Attwooll's personal views rather than any official policy, was read at a meeting of the Institute in London on 28 November 1973 with the President in the Chair.

Technology for Low Noise Aircraft -- The NASA Quiet Engines

Review of the major goals, procedures, and results of the Quiet Engine Program that was initiated four years ago and is now nearing completion. This program has developed and demonstrated, in full-scale, experimental engine tests, technology advances which, if applied to the design of future aircraft, will help produce equipment with noise levels considerably lower than the older narrow-body aircraft and significantly lower than the new wide-body aircraft flying at present. However, the application of this noise reduction technology will result in increases in aircraft operating costs. Future aircraft noise reduction research should, therefore, consider improvements in the economics associated with noise reduction technology.

Aerodynamic Research for Future Civil Aircraft

In this lecture I have tried to make a judicious selection of the aerodynamic problems involved in the design of future civil aircraft. The choice is necessarily restrictive because of the time limitations of the lecture, so it must be emphasised that the list of problem areas considered is by no means complete. Also, the choice is flavoured by my present field of activity in low-speed wind tunnel work, so some important areas will be excluded on this account.

Research Relating to Long-Range Supersonic Cruising Aircraft

The NASA Langley Research Center has conducted an intensive and broad research programme on supersonic cruising aircraft for some 10 to 12 years. During the course of this effort to advance the state of technology of supersonic flight, a number of interesting research or design techniques and approaches have evolved. Several of these which have application to present and future aircraft design are discussed. The use of highspeed computing equipment in the application of linear theory to the problems of optimising supersonic cruising efficiency is treated. Experimental techniques employed in the study of drag at transonic speeds in wind tunnels are described. In the area of aircraft operations, attention is directed toward unique simulation methods employed in studying the relationship between air traffic control systems and supersonic aircraft.

The Human Computer in Flight Control

It is the unique decision-making ability which makes the human operator particularly suited to accomplish flight control computation. His decisions range from the simplest repetitive determination of control actions, each intended to minimize the error, to complex problems of the sequential reprogramming of all the lower levels of decision which, in totality, comprise his information transduction process. The human sensory-input and motor-output channels must be properly used in order to insure maximum efficiency of the over-all human computer. The perceived noise can only be separated from the signal after the decision-making operation to be performed has been clearly identified. Human noise filter and information handling rate characteristics may be enhanced through the utilization of inherent qualities of the various input and output channels. A brief summary is made of the considerable effort which has been devoted toward the development of mathematical models for human tracking. It is emphasized that the human decision-making ability must be incorporated into the model before a realistic representation can be attained. A stochastic model is considered which is constructed in a heuristic manner, incorporating the decision-making ability. Specific direction is indicated which may yield the most fruitful approach to the mathematical analysis of human flight control computation. This future model would be of great value as a link between the related work in the fields of neurophysiology, biophysics, and psychology. Most important, it should provide a cockpit synthesis technique which will aid the design of future manned aircraft.

Alternating versus direct current for aircraft-radio power supply

Recent designs of aircraft-radio equipment have provided for operation from existing aircraft electric systems, and little attention has been given to providing the electric system that is best suited for radio equipment use. This has been a natural and proper approach, because of the relatively small load requirements of aircraft radio. Accordingly, comparatively little attention has been given to the effects of the type of power supply on the characteristics of aircraft radio equipment. It is the authors' belief that a review of the subject is desirable at this time to assist aircraft designers in making a proper choice of the electric system to be provided on future aircraft designs, as well as possible modifications to the electric systems on aircraft now in use. This paper considers the effects of the various types of aircraft electric systems on the characteristics of the radio equipment, from the standpoints of weight, efficiency, reliability, simplicity, flexibility, and emergency operation. The various types of a-c and d-c power supplies are discussed, and consideration is given to the effects of frequency and number of phases on a-c power supplies.