The high values of specific strength and stiffness of carbon fibre composite materials have already been discussed by Mr. T. Sharpies in his paper and require no further comment. Therefore, I would like to consider the benefits to direct operating costs (DOC) which can be obtained by the application of Carbon Fibre Composites (CFC) to a civil transport aircraft.

Figure 1 is taken from a paper presented by Stewart and Campion at the Atlantic Aeronautical Conference last year. In this figure are shown the benefits in DOC which arise due to the application of the following advanced technologies:

The integration of a system—or a group of systems — into a modern fixed-wing aircraft can only be satisfactorily achieved if the fuel penalty incurred by the aircraft is minimised, i.e. if the amount of fuel needed to restore the initial aircraft performance is kept to a minimum.

Over the years, aircraft systems have had to meet more and more stringent requirements which reflect not only on the increasing performance of aircraft, but also on the greater demands made by systems on the aircraft, a somewhat extreme example being that of the Mach 2 + Rockwell International B-l bomber on which the cooling requirements for the avionic equipment were to exceed several hundred kilowatts.

As such trends are likely to continue in the foreseeable future, the current deteriorating situation regarding fuel supplies and the ever rising costs involved, stresses the need for ensuring that systems on the next generation aircraft are designed for the least penalty and most efficient use of the available fuel.

The log-law for the turbulent flow in a smooth pipe is written as:

With uT determined from the pressure drop along the pipe, the measured velocity distribution can readily be used to determine values of K and B. Alternatively, the power-law variation is written as:

involving again two constants, to be similarly determined.

The behaviour of a thin tensioned sheet with an opening has been the subject of a number of recent investigations. In this type of problem, as in an aircraft structure, a skin carries all or some of the in-plane load as well as a lateral pressure load. Failure often results from the development of fatigue cracks which propagate from a stress concentration at the cut-out being subjected to structural vibration excited by acoustic pressure fluctuations. The Comet disaster in 1954 was due to the structural failure of the pressure cabin, brought about by the development of fatigue cracks from high stress concentration regions around the corners of the windows. The cases of statically tensioned, uniaxially and biaxi-ally loaded plates having a central crack subjected to acoustic excitation have been studied. These investigations were concerned with the basic features of plate vibration; i.e., mode shapes at a resonance frequency, the resonance frequency versus load behaviour and the crack propagation rates.

The intersection of two oblique shock waves of opposite families is a common occurrence in supersonic flows. It can result either in a regular intersection, where the downstream waves are weak shocks and a single slip line emanates from the intersection, or in a form of Mach reflection where a strong shock bridges the gap between two three-shock confluences each of which generates a slip line. The transition between regular and Mach reflection has been discussed for the symmetrical case by Henderson and Lozzi and by Horning et al. The conditions at a three-shock confluence point have been analysed for two-dimensional flow by Henderson and for three-dimensional flow by Hunt and Lamont and by Rudman.

The flight test engineer constantly strives to provide solutions to the problems of testing, developing and proving the progressively more complex and accurate navigation and attack systems of modern military aircraft. The biggest such challenge in Europe for some time was probably the flight trials programme on the swing-wing Tornado aircraft which has a digitally based, self contained, al-lweather NAV/ATTACK avionics system. This paper covers the philosophy and techniques adopted for the flight testing and subsequent analysis of major elements of this system.

Is flight simulation of academic interest? As we have a fairly substantial involvement at Cranfield, the answer must be ‘Yes'—although the amount of student involvement is small and our main activity is in contract work. This is explained later in the paper.

Most of the flight simulation work takes place in the Aeronautical Instrumentation and Data Processing Laboratories of the College of Aeronautics. Some takes place in the School of Electronic Systems Design.

Design studies have shown that the successful application of carbon fibre composites to suitable components in the RB 211 engine nacelle could achieve initially a weight saving of 200 to 250 kg per power plant.

In the future the employment of the long mixed flow nacelle, and possibly higher by-pass ratio cycles, aimed at optimising engine design for maximum fuel and operating economy, will emphasise even further the need for lightweight nacelle structures.

Boeing has recently completed a structural integrity reassessment of 707 aircraft models, and released a Supplemental Inspection Document (SID). Similar activities are now progressing for model 727. Structural reassessments are continuous over the operational life of all Boeing aircraft models and used for developing inspection information directed toward detecting structural damage before it becomes a serious problem in the fleet.

The fail-safe design concept requires interaction between the designer /manufacturer and the airline operators. Within this concept, maintenance and inspection are equally important as the basic design. It is important for operators to provide continuous vigilance of aircraft structure to detect damage and perform timely maintenance. Knowledge of damage that is occurring in the fleet is essential to the manufacturer to provide timely advice through service bulletins or other publications. This interchange is depicted in Fig. 1, and is the foundation of the fail-safe design concept.

The honeycomb sandwich type of construction in plate and shell shapes is playing an increasing role in aerospace structures where structural efficiency is important. In some applications, such as wing or control surface trailing edges, the core is of non-constant thickness, and in others, such as engine thrust reverser buckets, the shell shape is doubly curved. Faceplates are commonly manufactured from aluminium, stainless steel or other metals, but the use of anisotropic materials, such as carbon fibre reinforced plastics (CFRP) can be expected to increase in the future.

In finite element analysis, as in analytical work, sandwich plates and shells have received far less attention than thin plates and shells. However, elements have been developed specifically for sandwich plates by Barnard, Cook and Bartelds and Ottens. Of these, only the latter allows a non-constant core thickness. Evidently, such elements could be used in a facet shell representation. Only two general (as opposed to axisymmetric) curved elements specifically formulated to deal with sandwich shells seem to have appeared in the literature. Both are subject to deficiencies as noted for thin shells by Morris, and Webber discusses certain geometrical errors in the doubly curved element of Reference 5. Furthermore, both are of limited practical application. It may be concluded, therefore, that there is a need for a honeycomb sandwich shell element which is easy to use and accurate while being capable of modelling the full range of materials and shapes found in practical structures. To this end, a family of elements for use in the linear elastic finite element method is formulated. They are of general doubly curved shape and can be used to approximate thick and thin shells of positive, zero and negative Gaussian curvature in a simple and straightforward manner. They also include anisotropic faces and non-constant core thickness. Degrees of freedom are limited to three displacements at each node, and this allows mixing with other element types.

The phenomenon of aerodynamic coupling between the longitudinal and lateral motion at high incidence is well known. In recent years, there have been a number of attempts to analyse the behaviour of aircraft allowing for this coupling. One of the more practical methods of approach is that of Kalviste, in which the aircraft rotary motion alone is considered, the aircraft having a certain angle of sideslip in the steady state. However, that method is essentially based on linearised equations. In this note, we show how Kalviste's analysis can be modified to include certain non-linear aerodynamic effects. In particular, some unstable modes only become apparent on introducing the non-linear terms.

Little information is available on the behaviour of the base pressure on a body of revolution having a following body in its wake. A preliminary investigation for the case of axisymmetric rear body has been reported by Mishra and Chatterjee. Their experiments were conducted on a 20° included-angle blunt cone. Mishra and Das reported an investigation for the case of asymmetric rear bodies having the same diameter. These investigations indicate significant rear body effects on the base pressure.

In multistage rockets, the flow characteristics of upper stages could be seriously affected by the proximity of a lower stage after they separate from one another.

Recent research into the fluid mechanics of hitting objects with air jets to eject unacceptable ones from a line of such particles in flight has shown the need for a better method of predicting the drag force involved since this is also the deflecting force in such an application. In most cases, the transverse dimensions of the jet are similar to, or smaller than, those of the target body so a drag force estimate based on infinite flow is likely to be seriously in error. Corrections are therefore needed to allow for jet diameters ranging from a fraction of the object’s size to many times that size. Achenbach investigated the blockage corrections for spheres in a closed circular wind tunnel but to the best of the authors’ knowledge no such results have been available for spheres in open jets, where the correction will in any case be of opposite sign.

Screens and contraction are used to achieve a low level of free-stream turbulence in the test-section of a wind tunnel. The effect of contraction on turbulence was initially studied, theoretically, by Prandtl, Taylor, Ribner and Tucker and Batchelor and Proudman. The last two theories, called rapid distortion theory, take into account the random nature of turbulence, but assume that the turbulence is initially isotropic, the effect of viscosity is small and the distortion is rapid.

Of all the branches of engineering, we regard aeronautical engineering as that which most needs simulation as an essential element of its constitution. Not even by choice may an aeronautical engineer be unfamiliar with simulation, for its advantages in the phases of design, production, and operation of aircraft are recognised by every aeronautical organisation, and its effectiveness, either in producing acceptable answers to flight problems, or in demonstrating flight characteristics, is the authority by which academics can insist upon the inclusion of the elements of simulation in their syllabuses. It is our belief that simulation has come to occupy this central position mainly as a result of the fundamental problems of safe flight.

As we are all aware, an aircraft in flight has six degrees of freedom. Three translational, that is, lateral, longitudinal and vertical and three rotational that is, rotation about the roll pitch and yaw axes. It is the actuation and control of the surfaces which cause rotation that will be discussed.

For the vast majority of aircraft, control in the three axes of rotation is achieved by three distinct movable surfaces which are elevators for pitch control, ailerons for roll control and rudder for yaw control. The effects of these controls are as follows—Fig. 1 the elevators will alter the angle of attack of the aircraft to the air and unless power is increased will result in a reduction in airspeed. If the airspeed is allowed to drop too much there will be a loss of lift on the wing and eventually a stall will occur. The ailerons will cause the aircraft to roll and alter the angle of bank. In so doing however the aircraft will begin to side slip, thus as there is more surface area aft of the cg than before it, the aircraft will turn.