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Aviation History
1933
1933 - 0870.PDF
SUPPLEMENT TO FLIGHT 76 THE AIRCRAFT ENGINEER OCTOBER 26, 1933 by Professor A. J. S. Pippard and J. F. Baker and described by them in R. <fe M. 948, experiment No. 4. In Part 2 it is assumed that an arbitrary system of loads or displacements (but not a mixture of both) is specified for either terminal bulkhead. The method consists in analysing the given system into a series of com ponent "type systems," in each of which the displacements of the joints throughout the tube have definite values, dependent on the elastic properties of the members. The amplitudes of these component type systems are first evaluated ; the displacements of all the joints in the structure under the given system are then obtained by synthesis. Finally, the stresses in the members are deduced. THE POSSIBLE INCREASE SPEED AIRCRAFT CAUSED BY Garner, M.A., and R. K. the Director R. & M. No IN LEVEL SPEED or HIGH- A DIVING START. By H. M. Cushing. Communicated by of Scientific Research, Air Ministry. 1530. (4 pages and 7 diagrams.) Decem ber 1, 1932. Price 4d. net. The rules for speed records allow the aircraft to dive from a certain height before starting the run along the course. By taking advantage of the dive, the pilot can start the run at a speed much in excess of the true level speed of the aircraft. The drag of modern high-speed aircraft is so low that for these aircraft the excess of speed retained up to the end of the run is appreciable and the average speed over the course is thus considerably greater than the true level speed. The object of the present report is to calculate the maximum increase in speed which can reasonably be obtained by the pilot. A possible gain of speed for the S.6.B. in the dive of 424 ft. per second and of 241 ft. per second along the course may be obtained without excessive accelerations. To obtain these results a very high standard of skill on the part of the pilot is required. On the second speed record on the S.6.B. Flight Lieutenant Stainf orth obtained a gain of speed along the course of an amount which agrees with the theoretical value to the order of accuracy of the measurements. THE VORTEX SYSTEM GENERATED BEHIND A SPHEEE MOVING THROUGH A Viscous FLUID. By H. F. Winny, Ph.D. Communicated by Dr. N. A. V. Piercy. R. & M. No. 1531. (14 pages and 12 diagrams.) September 19, 1932. Price Is. net. The wake of a sphere was investigated in various ways. Visual experi ments preliminary to the present investigation showed the wake to contain a vortex system of spiral arrangement. Hot-wire methods were used to determine the frequency and pitch of the helical disturbance. The average* velocity distribution through the wake indicated a concentration of vorticity at a radius greater than that of the sphere. Eeadings of the average angle of downwash revealed a weak axial vortex, but no circulation round the wake. An electrical condenser in conjunction with an amplifier and oscillo graph was applied to give information as to the fluctuating pressures on the surface of the sphere, and this was supplemented by measurements of average static pressure and total head. The work is incomplete to the extent that the exact form of the spiral system is not determined, but investigation on the present lines of the wake of other solids of revolution would nevertheless be of interest: in particular, the case of the airship. The condenser-oscillograph method of measuring fluctuating pressures on a surface proved satisfactory, and might with advantage be developed for general use. DETERMINATION OF THE BEST BASIS OF AIRCRAFT PER FORMANCE REDUCTION FROM FLIGHT TESTS. PART I. SUPERCHARGED ENGINES. By J. L. Hutchinson, B.A., and E. Finn, B.Sc PART II. TJNSUPERCHABGED EN GINES. By E. Finn, B.Sc. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1532. (16 pages and 27 diagrams.) September 26, 1932. Price 2s. 3d. net. The previous determinations of the power law of supercharged engines indicated a surprising disparity between moderately and fully supercharged types. These results were, however, drawn from the rather slender evidence of a few early flight tests with supercharged engines. A large amount of additional information has now been accumulated from routine performance tests, and it was decided to re-investigate the problem. Tests over a sufficiently wide temperature range were available on 16 air craft when the following conclusions were reached. The original disparity between the results for "moderately and fully supercharged engines is not confirmed. The weighted mean law for both types conforms closely to picrV. Variations of the law from pure pressure to pure density have been found, in particular instances.but as these variations may in some degree be due to errors of measurement, particularly when date is limited, they are not necessarily real. N/~ appears to be a more reliable criterion than Vc /-, possibly because 3X", unlike \c, is unaffected by steady up and down currents. In the second part of the paper, all the available evidence covering a suffi ciently wide temperature range including some of the date used for a previous report on this subject has been analysed and the best basis of reduction deduced for each aircraft separately. "The reliability of the results obtained in each case has been assessed and the weighted mean law extracted from the results. The following conclusions are drawn :— (i) The weighted mean law for unsupercharged engines is very near to pio-i, the best mean law found for supercharged engines in Part I and is the power law indicated by bench tests and used in the correction of bench tests results to standard conditions (Reference 6). This agrees fairly well with the result pSo-s previously found (4 and 7). (ii) The limits of the law in extreme cases are from pure pressure to pure density, but this variation is not necessarily real as explained in Part I. (iii) The work confirms the conclusion of P«rt T that N *Jcr is a better criterion of the basis of reduction than Vc \/ a. THE INFLUENCE OF END FIXING CONDITIONS AND OF BULKHEAD WIRES UPON THE LOADS IN THE MEMBERS OF AN AEROPLANE FUSELAGE UNDER COMBINED BENDING AND TORSION. By G. W. Mullett, D.I.C., Whitworth Scholar. Communicated by Prof. L. Bairstow. R. & M. No. 1533. (30 pages and 10 diagrams.) April 28, 1933. Price Is. 6d. net. A particular fuselage is stressed for three conditions of support at the for ward bulkhead and the loads so obtained compared. Since it was also desired to determine the effect upon the internal load distribution of ignoring inter mediate bulkhead wires, each of the three Bets of stressing calculations, for the particular fuselage above, was based first on the assumption that all bulkhead wires were operative and then on the assumption that the inter mediate bulkhead wires could be ignored. It then became necessary to consider the supporting forces which were assumed to act at the forward bulkhead of the fuselage for the purposes of these stressing calculations. It was found that the internal loads in the particular fuselage structure considered are sensitive to end fixing conditions but are comparatively little affected by the omission of intermediate bulkhead wires. The effect of any axial constraint at the forward bulkhead is relatively small, when support is assumed at all four corner joints of the bulkhead, but is much larger when support is assumed at only two corner joints, so that, in this latter case, any warping which may occur in the forward bulkhead may seriously affect the loads in the members near the front of the fuselage. Finally, the effect of any constraint in the plane of the forward bulkhead is, in general, confined to the members composing the bulkhead. EFFECT OF STIFF RIBS ON THE TORSIONAL OF AEROPLANE WINGS. By H. Roxbee Cox, ON THE STIFFNESS Ph.D., D.I.C., B.Sc., and D. Williams, B.Sc A.M.I.Mech.E. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1536. (18 pages and 3 diagrams.) January 5, 1933. Price Is. net. The torsional stiffness of an aeroplane wing with two or more spars is very considerably under-estimated if, in its computation, the influence of the ribs is ignored. If the spars have any appreciable inherent torsional stiffness and are well connected by ribs stiff in their own planes, any differential movement of the spars is accompanied by twisting of the spars, thus bringing into play their torsional stiffnesses. If the ribs are capable of resisting torsion a further restriction is imposed on the distortion of the spars. If actual ribs combine both flexural and torsional stiffness, then the effects described will be simultaneous. These questions are treated from a theoretical standpoint and illustrated by numerical cases. The general inferences of the work are :— To obtain maximum wing torsional stiffness— (a) the torsional stiffness of the spars should be as great as possible, com patible with their flexural moduli; (b) the spars should be joined together near the wing-tip by a rib very stiff in its own plane ; (c) if the spars are tapered appreciably, this should be augmented by adding one or two more ribs stiff in their own planes in the taper region ; (rf) as many ribs as possible should be designed to have high torsional stiffness, especially in the tip region ; (e) all ribs should be firmly attached to the spars. These conclusions have been arrived at by consideration of a two-spar wing. They are, of course, valid for a multi-spar wing. They indicate, among other things, that ihe low degree of torsional stiffness frequently associated with large two-spar, fabric-covered monoplane wings is a disability which might be satisfactorily overcome without recourse to a less orthodox type of construction. THE EFFECT OF THE RIBS ON THE STRESSES IN THE SPARS OF A TWO-SPAR WING SUBJECTED TO THE MOST GENERAL TYPE OF LOADING. By D. Williams, B.Sc., A.M.I.Mech.E., and H. Roxbee Cox, Ph.D., D.I.C., B.Sc. Communicated by the Director of Scientific Research, Air Ministry. R. & M. No. 1538. (12 pages and 6 diagrams.) January 17, 1933. Price Is. net. It has been shown in Refs. 1, 2, 3 and 4* that in a wing in which the spars, by virtue of the shape of their cross-sections (e.g., " box " section spars), are efficient individually in resisting torsion, the stiffness of the wing as a wri01e against torsion depends to a great extent on the stiffness of the ribs. w°™ the ribs are stiff in their own planes and firmly connected to the spars, trie wing torsional stiffness added by means of the ribs to that inherent in tne bending stiffnesses of the spars is considerable. Further wing torsional stiffness is added if the ribs are torsionally stiff. A large number of aeroplane wings have spars of the kind just referred i >. and it is found that many embody ribs sufficiently stiff in their planes ana sufficiently well connected to the spars for neglect of the rib effect to give a serious underestimate of torsional stiffness. The torsional stiffness ol no. are not however at present usually such as to hava an appreciable effect torsional stiffness calculations. Hnn» In the present report the general case is considered in which the spai .sec«""', and the aerodynamic loading vary along the span. The rib-effect is <M_ u> • nature of a " relief" the magnitude of which is illustrated by a «™e""*j example on a typical single-bay biplane top wing subjected to convention C.P. forward, C.P. back and nose-diving loadings. , An example indicates that in designs incorporating stiff ribs rigidly <-nected to the spars, this relief is appreciable. Its magnitude increases wiu the ratio of torsional to flexural loading on a wing. * Bef. 1. " Cases of purelv torsional loading on stripped aeroplane wings, by H. Roxbee Cox. R. & M. 1436. , . ,„.rtinc ~ Ref. 2. "Distortions of stripped aeroplane wings under torsional loauiub by D. Williams. R. & M. 1507. , „m . Q„rnniane Ref. 3. "On the effect of stiff ribs on the torsional stiffness of aeropi*' wings." by H. Roxbee Cox and D. Williams. R. & M. 1536. ,mder Ref. 4. " Experiments on the distortion of a stripped **^JJ^|fl torsional loading," by D. Williams and H. F. Vessey. 1603/2F (Unpublished). ippea meuti wins ~--R.A.B. Report No.A.U- 1072/*
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