Showing papers in "Aeronautical Journal in 1965"

A Simple Correlation of Turbine Efficiency

Abstract: For a number of years it has been the practice at Rolls-Royce to determine the basic aerodynamic characteristics of the turbines of our engines by tests of model turbines. The first model of the single-stage Derwent I turbine was tested In 1945 and a design point efficiency of 75 per cent was measured. Since then over 600 different turbine configurations have been tested and many of the more recent turbines have achieved efficiencies appreciably better than 90 per cent. Typical of modern turbines is the Spey two-shaft turbine in which the four stages reach a design point efficiency of a little over 92 per cent. This paper presents a description of the test techniques which are used in this work and also a simple method of correlation which relates the efficiency of some 70 turbine stages to the velocity triangles and enables the efficiency of those turbines, which fall within the scope of the correlation, to be predicted with an accuracy better than ± 2 per cent. The measured value of turbine efficiency can be markedly influenced by the measurement technique, so the way in which the turbines are manufactured and tested is described in some detail.

On the Closed Motion of a Fluid in a Square Cavity

Abstract: This paper is concerned with two-dimensional, incompressible fluid motion generated within a square cavity (a) by an outer stream and (b) by the action of a flat surface passing over one of its sides. This type of motion (“cavity flow”) is considered to consist of a boundary layer surrounding an inviscid “core.” A solution of a linearised form of von Mises’ equation is obtained for steady flow in the boundary layer for constant pressure and that of a small periodic variation around the walls of the cavity. From this analysis the vorticity imparted to the core is obtained. The motion in the core is then determined on the basis of the persistence of this value of the vorticity. Experimental results are given for (a) and (b) and compared with the theory. A method of solution of the non-linear boundary layer problem is indicated.

A Simple Device for Preventing Turbulent Contamination on Swept Leading Edges

Abstract: On unswept wings, or wings with small amounts of sweep, the favourable pressure gradient round the leading edge, where the flow is rapidly accelerated away from the stagnation line, ensures a certain amount of laminar flow, provided the wing surface is sufficiently smooth. On highly swept wings, however, it has been found that turbulent flow can exist on the attachment line itself and there are therefore no naturally occurring regions of laminar flow. This trouble arises from the turbulence at the root of the wing, which sweeps along the attachment line. If the Reynolds number of this turbulent attachment line boundary layer is greater than some critical value, the whole attachment line boundary layer remains turbulent and the complete wing is contaminated. But if the Reynolds number is below the critical value, the turbulence decays along the leading edge and the boundary layer on the attachment line reverts back to the laminar state. This situation arises when the leading edge radius is small and the wing is only slightly swept. The attachment line boundary layer Reynolds number, Rθ, is given by the following equation:

Atmospheric Gusts: Present State of the Art and Further Research

Abstract: Starting with atmospheric motions on a global scale, different categories of atmospheric turbulence are discussed. It is pointed out that the turbulence within the earth’s boundary layer is comparatively better understood than any other type of turbulence, due to a concerted effort by meteorologists and by aircraft engineers. Clear air turbulence, turbulence in clouds and storms are subjects of active research, but we are still at the beginning of the understanding of these phenomena.The influence of atmospheric turbulence on some aspects of aircraft engineering is mentioned and the problem of the calculation or turbulence-induced loads is discussed in some detail. It is pointed out that the estimation of turbulence loads is a transposition of experience gained on one aircraft to another. The most simple technique of doing so is to assume that the atmospheric turbulence can be represented by a collection of single, isolated gusts and by making very simplifying assumptions about the dynamics of aircraft response. This technique, the discrete gust approach, in spite of serious theoretical reservations, has worked admirably well, but it appears that in many applications the limits of usefulness of the discrete gust approach have been reached. The alternative way of dealing with gusts is to treat them as a basically continuous phenomenon using the comparatively recently developed spectral technique. This technique not only permits the aircraft dynamics to be properly accounted for, but also describes the atmospheric turbulence in more realistic fashion, understandable not only to aircraft engineers but also to meteorologists and students of fluid dynamics.

Technical notes: Triangular Elements with Linearly Varying Strain for the Matrix Displacement Method

Abstract: A decade has elapsed since triangular elements under constant strain and stress were independently introduced within the matrix Displacement Method by the Turner group at Boeing and the Aeronautical Structures Department at Imperial College. They proved a considerable success in the practical analysis of complex membrane shapes as occur in modern aircraft wings. However, the original formulation based on a local cartesian system of axes and the classical concept of stress and strain inevitably leads to an unsymmetrical and aesthetically (as well as computationally) unfavourable expression for the stiffness matrix k. Moreover, the method was restricted to isotropic media. The necessity of extending the theory to finite displacements ultimately showed the inadequacy of the past approach and guided the writer to the creation of new concepts, e.g. the natural stiffness of an element. This natural stiffness, which ignores the rigid body motions and is hence of dimensions (3 X 3) for a triangle with three nodal points, relates in a concise manner the nodal force components parallel to the sides and the elongations of the sides themselves. A powerful tool in its derivation and further development was a new definition of stress and strain vectors which excludes shearing contributions and only works with direct components parallel to the sides. The idea has also been extended to tetrahedra and many standard elements which are incorporated as a basic feature in the structural language ASKA (Automatic System for Kinematic Analysis) developed at ISD by the Applied Programming Group under Dr. H. Kamel. These fundamental ideas were emphasised in the author's recent lecture to the Society.

The Dependence of Diffuser Performance upon Inlet Flow Conditions

Abstract: It was recently stated by Cockrell, Diamond and Jones(1) that attempts to correlate diffuser loss coefficients with the inlet boundary layer momentum thickness were generally unsatisfactory. In particular, it had proved impossible to align various results from diffuser tests which had been made with differing inlet flow conditions. The two methods of thickening the diffuser inlet boundary layer, using either(a) a length of parallel pipe, or(b) screen rings at inlet to the diffuserled to a corresponding variation in diffuser performance.The conclusion was drawn that “the manner by which an inlet boundary layer has been thickened is as significant in determining diffuser performance as is the thickness of the layer. No satisfactory inlet flow parameter is at present known”.

Lift Turbo-fans

Abstract: In the past decade many powerplant systems have been proposed for VTOL aircraft. Of these, flight tests have shown the lift jet and vectored thrust engine to be practical and suitable for forming the basis of operational VTOL military strike aircraft. High on the list of proposed VTOL powerplant systems is the lift turbo-fan which has the inherent advantages of better hover fuel consumption, lower efflux velocity and lower jet noise. So far there has been no practical demonstration of this type of powerplant in Europe, and it is useful to look at some of the studies that have been made to compare the characteristics of the lift fan and the lift jet.The paper compares the Rolls-Royce RB 162 16:1 thrust/weight ratio lift jet and its installation with a range of Rolls-Royce lift fans derived from the RB 162 using the latter as the gas generator.The comparisons between the basic engines reveal the fan to have worse thrust/volume, thrust/weight and response rates. The installation of these engines in a lift pod is fully described showing the equipment required for complete VTOL powerplant. A comparison of the Installed weight breakdown for the two types of pod is made. Some of the advantage of the fans’ inherently lower fuel consumption is lost in the longer take-off transition time which accrues from the higher momentum drag of the lift fans and higher pod drag.Looking to the future, the authors suggest fan engines based on more advanced gas generators and having a greater degree of ingenuity to minimise the weight and volume penalties.

Operational Research and Aviation Management: Part II Procurement and Capital Investment Programmes

Abstract: The previous paper in this series described what operational research is and illustrated some of its methods. The succeeding articles are concerned with considering some of the problems in the different branches of the aviation industry and showing how OR may be profitably applied to them.This paper and the next form a continuous narrative. They differ in that the first concentrates on capital investment programmes and the procurement of aircraft, while the programmes and the procurement of running an airline. In the first, a discussion of cost structure leads on to some detailed models. A further series of models forms the basis of the second.

Microbiological Attack in Aircraft Fuel Systems

Abstract: — A great deal of publicity has been given in recent years to the problems caused by microbiological attack on aviation fuels, although there had been considerable experience of the subject before the first serious problems arose in aviation. Intensive studies of the nature of the attack have shown that although limited use of biocides has been successful, the best control is by the elimination of stagnant water from the fuel supply system and the aircraft fuel system.

Cowl Shapes of Minimum Drag in Supersonic Flow: Part 1. Comparison of the Guderley and Newtonian Optima

Abstract: Guderley, Armitage and Valentine have computed the inlet and closed body contours which form the forepart of an axially symmetric body, of given length and fineness ratio, having minimum pressure drag. The solution is not based on a simplified pressure law, such as the Newtonian impact law, because by a suitable choice of control surface for mass flow and momentum they are able to employ the general flow equations. It is clear, however, from an analysis of their tabulated results that their cowl shapes fall on a single curve for a given value of Δ= d i d t , the ratio of the initial to the final diameter of the cowl, when plotted in terms of a dimensionless length ξ= x/l and thickness η= y/d t , as in Fig. 1. Furthermore Fig. 1 shows that, except for small values of Δ, the Guderley shapes are indistinguishable from the optimum shapes calculated from Newtonian impact theory. The shape and characteristics of the Newtonian duct of given length and thickness, offering minimum drag to the external stream, are derived using the slender-body approximation. Ducts for which Δ > 0.04 are shown to be sufficiently slender. The slopes of those with 0 ≤ Δ

Erect and Inverted Spinning with Particular Reference to the Hunter

Abstract: With the introduction of each new generation of combat aircraft it has become popular to assume that they will be operated in a more conservative manner than previously and that less attention, therefore, need be paid to their spinning characteristics. Current experience, however, shows that inadvertent spins will continue to occur, and must be allowed for, if these aircraft are to be operated effectively and to the limit of their capability.In this connection the Hunter provides an interesting case history, since it has been put to widescale use in a variety of roles and its erect and inverted spinning characteristics have been thoroughly investigated. These characteristics will be described both for their own sake and because of the applicability which they have to current high performance aircraft.

Aeronautical Research at the University of Southampton

Abstract: F. W. Lanchester obtained his first technical education at the Hartley Institute in Southampton, later to become the University of Southampton, during the years 1886–89. His autobiography describes in vivid terms the primitive nature of the workshop and apparatus available. He would indeed be shocked at the wealth of modern equipment now encountered in engineering departments of a University. At the same time, no one can possibly say that this lack of equipment influenced his pioneer spirit or his extraordinary clarity of thought, not only in the fields of aeronautical and automobile engineering, but also in subjects as diverse as the musical scale, poetry and even relativity.

Design and Development of Small Aircraft Gas Turbines in France

Abstract: To Describe the development in France of small gas turbines of necessity confines one to the products of the Turbomeca Company. It is therefore not through lack of modesty that I speak of those engines which have been designed and built under my direction. After the Second World War our aims were quite ambitious. We envisaged the creation of jet engines up to 6000 kg (13200 lb) thrust, as well as the aircraft to suit. We soon realised that such ideas were far beyond the industrial and financial possibilities of the time.

RAE Guided Weapon Test Vehicles in the 1950s

Abstract: A test vehicle, in the G.W. sense is a body used in free flight to test components, structures, aerodynamics, servo controls, guidance systems and propulsion. The body may have weapon-like characteristics or may be designed purely to investigate a particular phenomenon or theory which has a bearing on the design of weapons. From the inception of the G.W. Department this work was given an important place in the programme and played a major part in laying the foundation of knowledge and experience on which the G.W. work in this country was built. Two early test vehicles were CTV.1 and KTV.1. CTV.1 was used for a good deal of aerodynamic investigation, together with the development of free flight instrumentation and measurement techniques, it was our first “beam rider”, and was also used in a command guided role. The beam riding work was done in co-operation with TRE who were responsible for the guidance aspects of CTV.1. RTV.1 was a larger vehicle used mainly on beam riding guidance research. A later version was used in a vertically launched role to study launching and stability problems preparatory to the Black Knight work. The CTV series culminated in CTV.S which itself took various forms. The CTV.S Series I was designed for aerodynamic measurements on a coasting dart at high incidences and therefore high altitude. CTV.S Series 2 was designed for kinetic heating investigations while CTV.5 Series 3 was an upper atmosphere sounding rocket, later known as Skylark and still providing a valuable service. RTV.2 was designed for further work on liquid fuel propulsion and semi-active radar guidance research and was developed further to become the better known GPV. An interesting method of recovery from the sea was developed for this vehicle. With the requirement for ballistic missiles and satellite launchers a whole new field of work on missile structures, stability, control and guidance was opened up. This called for the development of the latest and very successful test vehicle, Black Knight.

Use of Longeron Anchored Cables in Multilobed Liquid Booster Tanks

Abstract: The use of multilobed pressure vessels is not new. Such structures have been used in civil engineering applications for many years. It has been recognised that substantial weight savings are possible by reducing the radius of curvature by lobing. Usually the resulting discontinuity stresses at the junctions of the lobes have been balanced by attaching flat plates.

A Review of Panel Flutter at Low Supersonic Speeds

Abstract: It has been shown both experimentally and theoretically that the Mach number range from 1·0 to 1·5 is very critical for panel flutter. Also, the correlation between experiment and theory in the above range has generally been poor.Sufficient papers have now been written which are relevant to the title subject that it is possible to make a review of the subject and to make recommendations for further work. These papers are reviewed in approximate chronological order. In all cases the panels referred to are rectangular and unswept with the air flow on one side only, unless otherwise stated.