bluuebunny/crossref_metadata_2025_split huggingface dataset:
The properties of crossed flexure pivots, and the influence of the point at which the strips cross
Authors: Wittrick W. H. 
Published: July 2016

SummmaryIt is shown that the rotational stiffness of a crossed flexure pivot varies considerably when subjected to an applied force. The type of variation can be radically changed simply by moving the point at which the strips cross. The relation between torque and rotation for a given applied force is not exactly linear and the extent of the non-linearity is determined by taking into account the small movements of the centre of rotation of the pivot. Finally, for design purposes, an analysis of the maximum stresses in the strips is given.Crossed flexure pivots, of the type shown in Fig. 1, are extensively used in aeronautical research equipment to replace knife edges or ball bearings. Perhaps the most frequent use is for the fulcrum of the balance arm in a wind tunnel balance. Here, a null-point method of reading is almost invariably used, so that the prime considerations influencing the design of a flexure pivot for such a purpose are (a) that the applied loads should not cause instability of the pivot, and (b) that the rotational stiffness should be small enough to give adequate sensitivity.
The Anti-Symmetric Vibrations of Aircraft
Authors: Traill-Nash R. W. 
Published: July 2016

SummaryIt is assumed that pure anti-symmetric vibrations of an aircraft can exist, involving fuselage torsion but excluding fuselage bending. With this assumption, which in most cases is a reasonable approximation, the eigenvalue equations for anti-symmetric vibrations of a complete aircraft are derived in a very general form. The “lumped mass” approximation to the continuous mass distribution is used and sub-matrices are associated with properties of relatively simple branches of the system. The final eigenvalue equations are expressed in terms of these sub-matrices so that in a numerical application the physical system as such is considered only in relation to properties of the simple branches. It is assumed initially that the aircraft wing and tail have flexural axes of the conventional type, but the treatment is generalised to cover swept and cranked wing aircraft.
Beams on Cross-Girders with Clamped Ends
Authors: Klitchieff J.M. 
Published: July 2016

In a previous paper it was assumed that the cross-girders are freely supported at their ends. In practice these ends can often be considered as clamped (“ built-in ”), for example, a span of continuous bottom-girders of a ship between two transverse bulkheads.In the following discussion it is assumed that the ends of the cross-girders are clamped, conditions at the ends of the main beams remaining arbitrary, as in Ref. 1.
The Theory of Aerofoils in Unsteady Motion
Authors: Radok J. R. M. 
Published: July 2016

SummaryThe theory of aerofoils in unsteady flow, which has made substantial progress in the last decade due largely to the ground work of Küssner and his co-workers, is presented here in a form suitable for application in aeroelastic problems, particularly those concerned with the dynamic loads on aircraft arising from gusts.Exact expressions are given for the aerodynamic lift and moment for an oscillating aerofoil as well as for the case of arbitrary motion through disturbed air. The expressions for the latter case involve two special functions, generally referred to as Wagner and Küssner functions. Exact values of these functions are tabulated together with useful approximations. The problem of a wing-tail combination is discussed and a method of solution indicated. The bibliography at the end of the paper lists the most important publications in this field.
The Dust Problem in Hot-Wire Anemometry
Authors: Collis D. C. 
Published: July 2016

SummaryExperimental work is described showing that a major cause of changes in the calibrations of hot-wire anemometers consists in the precipitation of dust on the upstream surface of the wire during use. A simple means of cleaning the air in closed-circuit wind tunnels is described. The rate of change of calibration due to dust was reduced in the Manchester University Fluid Motion Laboratory by at least a factor of 15, by adequate cleaning of the air and by minimising the amount of interchange between the tunnel air and the atmosphere. It is concluded that where accurate results are required from hot wires used in a wind tunnel, the tunnel should be designed to be dust-free.
Buckling of Oblique Plates with Clamped Edges under Uniform Compression
Authors: Wittrick W. H. 
Published: July 2016

SummaryThe problem of the buckling of flat oblique plates (i.e.in the shape of parallelograms) with all edges clamped under a uniform system of stress is considered. An energy method of calculating the critical stresses is developed and applied to the particular case of a clamped oblique plate under uniform compression parallel to two of the sides. Numerical values for the buckling stress coefficient are obtained for plates having acute angles of 60° and 45°, and side ratios varying between 3/5 and 5/3.
Flow Changes in Gases in which Mass and Impulse are Conserved
Authors: Dawson L. G. 
Published: July 2016

SummaryThis note discusses changes in the state of a gas flowing in a duct of constant area. In the past, changes, such as normal shock waves, combustion and other phenomena, which are defined by the equations of energy, conservation of momentum and mass flow, have each been treated on their merits. In this note a method is developed whereby all phenomena governed by these three equations can be solved by a single general method. The method rests on the derivation of a parameter which is unaltered in value by the change, in all cases where the total temperature is constant. A shock wave is an example of such a discontinuity. In problems of heat addition or extraction, the parameter changes its value only because of the change in total temperature. The change in total temperature may be calculated from the known quantity of heat added or extracted.The parameters derived are useful in showing how problems of this type should be attacked analytically. With oblique waves it is easy to derive a relation between the normal velocities before and after the wave, and it is probable that this relationship has not been published before.
Compressor-Turbine Matching of Two-Spool Turbo-props
Authors: Morley A. W. 
Published: July 2016

SummaryThe problem of the best division of pressure ratio between the two spools is investigated by means of simplified expressions for component characteristics. It is found that a unique position of the L.P. compressor operating line (i.e. maximum L.P. flexibility) is obtained when the H.P. compressor operating line is vertical. This arrangement requires a low pressure ratio on the H.P. spool and gives an engine whose power is sensitive to air intake temperature changes, so that the H.P. rotor tends to overspeed at sea level and surge at high altitude. Checks by standard methods show that the algebraic approach is useful for understanding the two-spool matching problem.
Oil Damped Free Vibration with Particular Reference to Systems having Nearly-Equal Natural Frequencies
Authors: Bishop R. E. D. , Johnson D. C. 
Published: July 2016

SummaryThis paper concerns the free vibration of linear systems which are subject to damping. The general theory for a system having n degrees of freedom is recalled and illustrated by means of a simple example. Using an analytical method, the approximate theory for small damping is derived, showing the nature of the entrainment of the principal modes; the results are found to confirm those of Southwell (who uses a physical argument) and they are illustrated by an example. The approximate theory is shown to need modification when there are two nearly-equal natural frequencies and the appropriate corrections are found. The analysis is made somewhat complicated by the existence of two criteria of “ smallness ” instead of one; these are the difference between the close natural frequencies and the amount of the damping.
The Shock Pattern of a Wing-Body Combination, Far from the Flight Path
Authors: Walkden F. 
Published: July 2016

SummaryThe position and strength of the front shock wave at large distances from a wing-body combination, are deduced from the linear theory for the combination, using a method developed by Whitham. The combination consists of a body of revolution and a wing which has thickness and is lifting. The effects of interference between the flow over the body and the flow over the wing are included. In any direction the flow far from the wing-body combination is equivalent to the flow past a body of revolution determined from the configuration of the combination. The modified formulae for unsteady flow are given and some results are evaluated for the combination of a body of revolution and a delta wing with subsonic leading edges.
The Vibrations of a Thin-Walled Stiffened Cylinder in an Acoustic Field
Authors: Foxwell J. H. , Franklin R. E. 
Published: July 2016

SummaryWhen 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.
Note on the Forces that Act near the Centre and the Tips of a Swept-Back Wing
Authors: Hurley D. G. 
Published: July 2016

SummaryThe 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 Küchemann 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.
On the Buckling of Certain Optimum Plate Structures with Linearly Varying Thickness
Authors: Mansfield E. H. 
Published: July 2016

SummaryThis paper is concerned with the buckling under uniform longitudinal compression of a variety of structures composed of plates whose thickness tapers linearly to zero across the section. Such structures include the angle of Fig. 1, the strut of cruciform section of Fig. 2 and the simply-supported strip of Fig. 3. For given cross-sectional area and overall dimensions (e.g. length of arm) the sections with linearly varying thickness achieve a greater buckling load (assuming that local buckling, rather than Euler buckling, is the criterion) than sections with any other smooth variation of thickness. These particular sections are therefore optimum sections and, even if they may not be used in practice, provide a convenient yardstick for purposes of comparison. The buckling loads are considerably greater than those for the corresponding “constant thickness” sections.
Struts with Linearly Varying Axial Loading
Authors: Przemieniecki J. S. 
Published: July 2016

SummaryAnalytical solutions for the deflections and bending moments are derived for elastic struts with linearly varying axial loading applied either (a) along the undeformed straight strut axis or (b) at the strut axis in the deflected position. The instability of struts with various end conditions is discussed and the stability criteria are given as a series of curves relating the maximum compressive axial load with the maximum distributed loading. Furthermore, explicit formulae for the deflections and bending moment distributions have been compiled for several typical cases of lateral loading combined with the axial loading of the type (a), which is of some practical importance in aircraft structures. A numerical example is included to show the practical application of the general analysis to a typical strut problem.
Reattachment of a Two-Dimensional, Incompressible Jet to an Adjacent Flat Plate
Authors: Bourque C. , Newman B. G. 
Published: July 2016

SummaryAs part of a general investigation into Coanda effect, a study has been made of the reattachment of a two-dimensional, incompressible, turbulent jet to an adjacent, inclined, flat plate. The jet separates from the boundaries at the slot lips and reattaches to the plate downstream, a phenomenon which is associated with the lowering of the pressure between the jet and the plate accompanying the entrainment of fluid there. It is found that the flow becomes independent of both the length of the plate and the Reynolds number when these parameters are sufficiently large: the flow, scaled with respect to the width of the slot, is then uniquely determined by the plate inclination. Two approximate theories are developed for the mean pressure within the separation bubble, the position of reattachment and the increase in volume flow from the slot: the agreement with experiment is fairly satisfactory. These theories are a development of Dodds's analysis for the reattachment of a jet to a plate offset from, and parallel to, the axis of the slot and, for the purpose of comparison, a limited study is also made of this flow.
The Stability of the Short-Period Motion of an Airframe Having Non-Linear Normal Force and Pitching Moment Curves
Authors: Christopher P. A. T. 
Published: July 2016

SummaryThe analysis of the stability of second-order non-linear systems by Poincare's method of singular points in the phase plane is briefly presented and used to determine stability criteria for the short-period motion of an airframe having non-linear normal force and pitching moment curves. These results are then compared with those obtained by the application of quasilinear stability theory.
The Design of Wing Plan Forms for Transonic Speeds
Authors: Lock R. C. 
Published: July 2016

SummaryA method is suggested for designing the shape of the plan form of an unwarped swept-back wing so as to control the magnitude of the singularity that occurs in the chordwise loading distribution at the leading edge. At a Mach number of unity it is possible to do this simply and directly by an approximate application of linearised lifting-surface theory. Details are given of three families of wing plan forms, of varying sweep and aspect ratio, in all of which the strength of the leading-edge singularity is held constant near the wing tips, behind the Mach line from the root trailing edge. The local chordwise load distributions have been calculated in detail for several of these wings and it is found that in all cases the loading curves become effectively independent of spanwise position over that part of the span for which the singularity is constant.
Theoretical Pressure Distribution at Zero Lift at Supersonic Speeds for Slender Delta Wings having Fuselages of Circular Cross Section
Authors: Lock R. C. 
Published: July 2016

SummaryA method is developed for calculating the pressure distribution at zero lift for a class of slender configurations consisting of a wing of delta type plan form combined with a body of revolution of the same overall length. Slender-body and slender-wing theory are combined to take into account the interference between the wing and the fuselage. An expression is found for the pressure at a general point on the wing or fuselage, although some numerical integration is still needed. This expression is simplified to obtain algebraic formulae for the pressure at the wing-fuselage junction and along the top of the fuselage. A further simplification is possible when the fuselage radius is small compared with the local wing semi-span. A particular example is considered consisting of a “Newby” wing with a parabolic fuselage; pressure distributions and drag curves are calculated.
The Elastic Stress Concentration Factors in Shouldered Shafts
Authors: Allison I. M. 
Published: July 2016

SummaryThe photoelastic “stress freezing” technique has been employed to evaluate the elastic stress concentration factors associated with the fillet blend radius in a number of shouldered shafts. The full range of practical sizes of blend radius and depth of shoulder has been examined. Comprehensive results for the shaft subjected to torsion, pure bending and axial load are given in this (Part I) and in two subsequent papers (Parts II and III).The accuracy of the graphs of stress concentration factors is better than six per cent. Comparison has been made with the existing theoretical and experimental results for each mode of loading. The results of an investigation into die limiting value of the stress concentration factor (for a particular shoulder radius) as the depth of the shoulder is increased to infinity are included in Part III.
The Static Aeroelastic Deformation of Slender Configurations
Authors: Hancock G. J. 
Published: July 2016

SummaryBy consideration of a series of simple models the static aeroelasticity of conventional aircraft is first discussed and then extended to the integrated configuration combining fuselage, wing and tail. It is shown that, on the basis of linear aerodynamics, a maximum speed exists at which control is possible. Overall deformations and control forces become large at speeds approaching this critical condition. Part II, to be published, contains calculations on slender plate aircraft including non-linear aerodynamics.
The Buckling of a Reinforced Circular Plate under Uniform Radial Thrust
Authors: Cook I. T. , Parsons H. W. 
Published: July 2016

SummaryAn exact solution for the symmetrical buckling under uniform radial thrust is obtained for a thin circular plate having a particular type of thickness function for the cases in which the edge of the plate is either clamped or simply-supported. In both cases it is found that the critical thrust necessary to produce buckling can be increased from its value for the uniform circular plate of the same material and volume by concentrating material in the central region of the plate. For the clamped plate the increase is about 18 per cent and for the simply-supported plate about 29 per cent.
The Non-steady Irrotational Flow of an Inviscid, Incompressible Fluid, with Special Reference to Changes in Total Pressure through Flow Machines
Authors: Preston J. H. 
Published: July 2016

SummaryIn this paper the way in which an inviscid incompressible fluid changes its total pressure is discussed. The basic equations are set out and it is shown that changes in total pressure are essentially associated with time variable flows. Simple examples are worked to illustrate this and finally application is made to single-stage flow machines, using a simple vortex representation.
Boundary-Layer Flow Between the Attachment Lines on a Flat Plate Delta Wing at Incidence
Authors: Cooke J. C. 
Published: July 2016

SummaryA three-dimensional laminar-boundary-layer calculation is carried out over the area concerned. The external flow is simplified, being calculated by slender-body theory assuming conical flow, with two point vortices above the wing, their positions and strength being determined by experiment. Attempts are made to draw transition fronts both for two-dimensional and sweep instability from this calculation. The combination of these gives fronts similar to those observed in some experiments. Because there is little or no pressure gradient over the area in question it is suggested that it is a region where distributed suction might usefully be applied in order to maintain laminar flow and reduce drag.
On the Use of Linearised Unsteady Aerofoil Theory in Arbitrarily Moving Axis Systems
Authors: Milne R. D. 
Published: July 2016

SummaryA linearised, unsteady aerofoil theory is constructed which refers to an axis system which remains in the near vicinity of an aerofoil moving along an arbitrary flight path through a fluid at rest. The potential equation, the pressure equation and the boundary conditions at the aerofoil and in the wake are shown to be formally identical to those usually derived on the basis of an axis system translating uniformly through the fluid.
Shear Buckling of Clamped and Simply–Supported Infinitely Long Plates Reinforced by Transverse Stiffeners
Authors: Cook I. T. , Rockey K. C. 
Published: July 2016

SummaryThe paper presents a solution to the buckling of infinitely long plates clamped along the edges, together with an extension of the solution obtained by Stein and Fralich for the case when the edges are simply-supported. It is shown that, as a consequence of increasing the edge support from that of a simple support to one in which both deflection and rotation are prevented, the rigidity which an intermediate transverse stiffener must possess in order to support the plate effectively is much reduced. Agreement between the theoretical relationships and existing experimental data is good.
The Flow Close to the Surface of a Circular Cone at Incidence to a Supersonic Stream
Authors: Woods B. A. 
Published: July 2016

SummaryA theory is presented describing the flow close to the surface of a circular cone at incidence to a supersonic stream, which reconciles the first order theory of Stone (on which the widely used M.I.T. Cone Tables are based) with the physically necessary condition that the entropy on the cone surface be constant.However, the results of this “vortical layer” solution appear to invalidate the method used in Ref. 1 to apply a boundary condition at the cone surface, and so to cast doubt on the results obtained by this theory.
Shear Buckling of Clamped and Simply-Supported Infinitely Long Plates Reinforced by Closed-Section Transverse Stiffeners
Authors: Cook I. T. , Rockey K. C. 
Published: July 2016

SummaryThe paper presents a solution to the buckling of infinitely long plates when they are reinforced by transverse stiffeners possessing both torsional and flexural rigidity. The cases of both edges being clamped and simply-supported are dealt with. Numerical results are presented for the ratio of torsional rigidity to flexural rigidity as obtained with a thin-walled circular tube. When the stiffeners are completely rigid, in which case the individual panels are clamped along the transverse edges, the results obtained are in agreement with existing solutions for isolated rectangular plates.
The Use of an Interference-Fit Bush to Improve the Fatigue Life of a Pin-Jointed Connection
Authors: Lambert T. H. , Brailey R. J. 
Published: July 2016

SummaryThe fatigue life of a pin-jointed connection can be optimised by using a moderately high degree of interference between the loading pin and plate. Where a joint has to be assembled in confined conditions, difficulty may be experienced in inserting the interference-fit pin and one possible solution is to use a pre-assembled interference-fit bush in the plate, leaving only a light interference-fit pin to be pressed in on assembly of the joint. It is shown that a relatively thick bush of diametral ratio 4/3 will give a reduction in shear stress concentration factor for the plate comparable with that obtained with a solid pin, but that maximum benefit is not obtained with a thinner bush of diametral ratio 8/7. Where thin bushes are essential in order to maintain the ultimate tensile and fatigue strengths of the plate and /or the ultimate and fatigue strengths of the pin, the shear stress concentration factor for the plate is reduced as the modular ratio of bush to plate is increased and as the interference fit of the loading pin in the bush is increased.