Showing papers in "The Aeronautical Quarterly in 1959"

Flow in a Viscous Trailing Vortex

Abstract: The equations of motion for an isolated laminar viscous vortex at moderate to large Reynolds numbers are linearised, by assuming that both the rotational velocity and the deficit of longitudinal velocity are small compared with that in the free stream. The rotational motion and the longitudinal motion may then be superimposed and solutions are readily obtained for each. If the vortex is generated by a body with profile drag it is predicted that the deficit of longitudinal velocity will be positive, which is in agreement with experimental observation. Further details of the solution and its relation to the flow in real vortices are discussed; and the theory is compared with some measurements in a turbulent vortex.

The Vibrations of a Thin-Walled Stiffened Cylinder in an Acoustic Field

Abstract: When a vibrating structure encloses a volume of fluid, the acoustic effects within this volume modify considerably the response characteristics of the structure, provided that the cylinder is vibrating in radial modes only. Measurements made of the displacement caused by a particular sound wave are of the same order as the values predicted. The calculation of the response of the cylinder to an acoustic wave also yields the sound field inside the cylinder and, again, the results are in general agreement with practical experience.

Combustion in Liquid-Fuel Rocket Motors †

Abstract: The paper provides a simplified picture of the processes occurring in liquid bi-propellant rocket motors. Droplet vaporisation, chemical reaction, and drag between gas and droplet are considered for a one-dimensional model. Quantitative theoretical results are presented for the variation of droplet size, droplet velocity, gas temperature and gas velocity within the chamber, particular attention being paid to the calculation of L*. The theory is applied to the German V2 rocket motor. Practical conclusions from, and extensions to, the theory are discussed.

The Stress Concentration Factors in Cylindrical Tubes with Transverse Circular Holes

Abstract: The “frozen stress” techniques of photoelasticity can give a complete knowledge of the stress, system in a solid body, but the examination of the stresses requires more time and care than in corresponding flat plate tests. In tests on tubes with transverse circular holes, sponsored by The Royal Aeronautical Society, all practicable geometrical shapes are examined and the maximum stress is measured in tension, bending and torsion. The results are comprehensive and show the inadequacy of previous results. In all cases the maximum stress occurs inside the bore of the hole. The accuracy of all the graphs of stress concentration factors is better than five per cent.

Thermal Stresses in Rectangular Plates

Abstract: The characteristic functions for beam vibration modes are used to derive an approximate solution for the calculation of thermal stresses in rectangular isotropic flat plates subjected to arbitrary temperature distributions in the plane of the plate and constant temperatures through the plate thickness. The thermal stresses are obtained in the form of generalised Fourier expansions in terms of the characteristic functions, and their derivatives, representing normal modes of vibration of a clamped-clamped beam. Since these functions have recently been tabulated, the practical application of this new method to the thermoelastic stress analysis of plates presents no difficulty.

Stresses Around Reinforced Elliptical Holes, with Applications to Pressure Cabin Windows

Abstract: An analytical solution, using complex variable methods, is given for the problem of the stress distribution due to an elliptical hole, reinforced around its boundary, in a plane sheet subjected at infinity either to an arbitrary constant stress system or to a bending type stress system. Numerical results were obtained for a wide range of parameters, including three different shapes of ellipse, and ten different amounts of reinforcement. Poisson's ratio was assumed to be 1/3.

Supersonic Flow Past Slender Pointed Wings with “Similar” Cross Sections at Zero Lift

Abstract: Some recent theoretical work on slender pointed wings at zero lift is co-ordinated and extended. The wings considered may have any pointed plan form shape, provided that the trailing edge is straight and unswept. The root section profile and cross-section shapes are arbitrary, provided that, on any one wing, the latter are “descriptively similar” (diamond or parabolic biconvex for instance), though not necessarily geometrically similar. The chief aim of the work is to find wings with simple geometry, low wave drag and pressure distributions which are unlikely to be seriously affected by viscous effects. Wave drag and pressure distributions are calculated by slender-wing theory. General formulae, which are both simple and instructive, are given for the wave drag and the overall pressure distribution, with particular emphasis on the root pressure distribution. Results for a number of wings of special interest are presented and discussed.

Plasto-Elastic Stress Distributions in Lugs

Abstract: A photoelastic layer was bonded to the face of aluminium alloy lugs and the strain distribution in the lugs was determined from the photoelastic fringe patterns which were recorded in a reflection-type polariscope. The semicircularly- ended lugs were loaded through neat fitting hardened steel pins. Assuming the maximum shear stress criterion of yield, the region of yielding under different loads was determined from the fringe patterns. Yield contours are shown for each of the four ratios of (hole diameter)/(lug width) tested. The greatest shear strains in the lugs were related to the applied loads. The extent of yield across the section normal to the direction of loading was measured for different loads and it was found that the progress of yield across this section is independent of the (hole diameter)/(lug width) ratio. The residual stresses on this section were also estimated. Complete yielding across the lug was related to the properties of the material and to the fracture strength of the lugs. Local yielding due to surface irregularities remained local, showing that “bedding in” does not weaken the component under static loading conditions.

Trends in the Development of Liquid Propellant Rocket Engines

Abstract: The authors predict that rocket engines will fall into two categories. In both, combustion pressures will approach 200 atmospheres to attain optimum vehicle performance, balancing increased pumping losses and engine mass against increased expansion efficiency and reduced dissociation. For general purposes, engines will be intrinsically convenient: storable propellants will give specific impulses around 270 lb. sec./lb., and engine specific weights will be between 0·02 and 0·03. For exacting applications, the greatest overall convenience may necessitate using unpleasant propellants so as to obtain the highest performance. Immediate research into the use and handling of these is essential if future engine development is not to be hampered.

The Eftect of Jet Noise on Aircraft Structures

Abstract: The present state of knowledge on the problem of fatigue failure due to vibrations excited by jet noise is reviewed. It is concluded that it should currently be possible to make reasonable estimates of the stress levels set up in a structure by jet noise but, in general, the resultant fatigue life of the components cannot be estimated with any confidence.

Symmetrically Loaded Circular Plates under the Combined Action of Lateral and End Loading

Abstract: Expressions are obtained for the radial and tangential bending moments in a circular plate under the combined action of (a) a lateral load concentrated on the circumference of a circle and an end tension or compression, and (b) a uniformly distributed lateral load, having a diameter less than the diameter of the plate, and an end tension or compression. For both types of loading, solutions are obtained for plates which are simply-supported and for plates with an arbitrary end rotation. In addition, the following limiting cases are considered: (i) concentrated lateral load with end tension or compression, and (ii) an infinite plate under the simultaneous action of an end tension and a lateral load concentrated on the circumference of a circle of finite diameter.

Note on the Forces that Act near the Centre and the Tips of a Swept-Back Wing

Abstract: The momentum equation is used to calculate the drag that acts near the tip of a semi-infinite swept-forward wing of constant chord that is at zero incidence to a uniform stream of incompressible, inviscid fluid. The drag is given as a function of wing section and angle of sweep and is shown to be unaffected by shaping the tip. The results may be used to calculate the drag that acts near die centre and the thrusts that act near the tips of a swept-back wing, provided that its aspect ratio is sufficiently great for the regions where the different forces act to be separated. Some results due to Neumark and to Kuchemann and Weber suggest that this will be so provided that the aspect ratio is greater than about two. The results are combined with some due to these authors to estimate the spanwise extent of the forces. It is found that this extent decreases as the angle of sweep is increased and that it depends quite markedly on the wing section.