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Aviation History
1926
1926 - 0209.PDF
MARCH 25, 1?26 THE AIRCRAFT ENGINEER SUPPLEMENT TOFLIGHT stagger, are such as to lead to high speed of auto-rotation at a large angle of incidence. Further, it is pointed out that such characteristics render a biplane less statically stable in pitch than one with larger gap and stagger, and therefore it has less tendency to " unstall " than is usual ; it is shown that these characteristics are likely to lead to danger in recovery from a spin, unless the centre of gravity is well forward and or there is a very good margin of control. A considerable amount of further information is required before the conclusions of this report can be fully confirmed by quantitative analysis of the motion in a spin, but there seems little doubt that the features in design which may lead to danger in spinning have now been recognised and the reason for the danger understood to a large extent. Other Work oti the Subjer'—Papers bearing on the subject of spinning to which reference is made in the above report are : — R. & M. 828.—A continuous rotation balance for the measurement of L, at small rates of roll.—Relf and Lavender. R. & M. 936.—A continuous rotation balance for the measurement of pitching and yawing moments due to angular velocity of roll (M,, and~N,,).—T. Lavender. R. & M. 831.—On the effect of sideslip on the aerodynamic forces and moments (including those due to the controls) for a model S.E.SA aeroplane.—H. B. Irving and A. S. Batson. R. & M. 787.—Lateral control of Bristol Fighter at low speeds. Measurement of rolling and yawing moments of model wings due to rolling.—F. B. Bradfield. R. & M. 944.—Measurement of pitching moments due to roll of wings of Avro 504K.—F. B. Bradfield. R, & M. 975.—Auto-rotation measurements on a model aeroplane with zero stagger.—Bradh'eld and Coombes. R, & M. 848.—Rolling and yawing moments due to roll of model Avro wings, with standard and interplane ailerons and rudder moments for standard and special larse rudder.— R. A. E. R. & M. 733.—Preliminary note on the effect of stagger and decalage on the auto-rotation of a R. A.F.I 5 biplane.—Irving and Batson. THE REPRESENTATION OF AIRCRAFT PERFORM- ANCE TESTS, USING NON-DIMENSIONAL VARI- ABLES, WITH SPECIAL REFERENCE TO THE PREDICTION OF THE EFFECTS OF CHANGE OF LOADING ON PERFORMANCE. By R. S. CAPON, B.A. PRESENTED BY THE DIRECTOR OF SCIENTIFIC RESEARCH. R. and M., No. 984 (Ae. 196). November, 1925. Price 4rf. net. In Bairstow's " Applied Aerodynamics," Chapter IX, a method of plotting a performance test, using non-dimen- sional co-ordinates, is described, which has a particular application to the estimation of the effect of change of load- ing on performance. The application to maximum rates of climb is stated not to be rigorous, however, and this also applies to the formula' of prediction of change in performance with change of load given in R. and M. (508. In the present paper the condition is investigated under which the application is rigorous to maximum rates of climb, air speeds for maximum rates of climb, and corre- sponding airscrew rotation rates ; a convenient formula for deducing the maximum rates of climb, maximum angles of climb, etc., for one loading from known values for another loading deduced ; and the applicability of the formula checked in so far as rates of climb are concerned by reference to results of tests at Martlesham. A slide rule is described which facilitates the computations. It is shown that dimensional theory may be applied rigorously when the engine power is proportional to any power, integral or fractional, of the airscrew rate of rotation, aiid that in this case maximum rates of climb and the corre- sponding air speeds and airscrew rates of rotation, as well as ii-aximum level speeds with the corresponding airscrew rates °f rotation, may be obtained at one loading from tests at -•• loading by a simple calculation. It is further shown ' : a close approximation the calculation reduces to 178/e that re-plotting the observed values of the above quantities at standard height H at a height H1 such that the ratio of the power factors at the heights H and H1 is equal to the ratio of the flying weights. It is proposed to check more accurately the validity of the method by further tests at two flying weights, first determining the power factors by an independent series of tests. ON THE SYSTEM OF VORTICES GENERATED BY A CIRCULAR CYLINDER IN STEADY MOTION THROUGH A FLUID. BY C. N. H. LOCK, M.A. R. and M. No. 986 (Ae. 198). (6 pages and 3 diagrams.) November, 1925. Price id. net. This paper deals with the Karman theory of the wake left behind the cylinder which takes the form of a double row of two-dimensional vortices, and suggests that the recent results obtained at higher values of the Reynolds number (see R. and M. 825)* may have a bearing on the application of the theory when there is a certain change with increase in speed in the resistance and frequency coefficients observed in the neighbourhood of (VL/c — 10). The note concludes not that the Karmin regime ceases to apply at the higher Reynolds number, but that the sudden drop in resistance at YL/D = 4>; 10' corresponds to the sudden increase of frequency and decrease of the distance between the rows. " R. & M. 825. " On Hit1 sound emitted by wires of circular section wlieuexposed to an air current." V>y K. F. IMS. ' Pliii. Mag. ser. 6 XLII, p. 173. NOTE ON THE MINIMUM SPEED FROM WHICH THE DIRECTION OF A GLIDING AEROPLANE CAN BE CHANGED TO A HORIZONTAL PATH FOR LANDING. BY F. W. MEREDITH. B.A. PRESENTED BY THE DIRECTOR OF SCIENTIFIC RESEARCH. R. & M. No. 993 (Ae. 204). June, 1925. Price U. net. Recent improvements in the control of aeroplanes at low speeds raise the question of the minimum speed at which it is safe to come in to land with an under-carriage which has usually not been designed to absorb the whole of the vertical velocity present during a glide. In the analysis of the present paper it has been assumed that the aeroplane is flying horizon- tally at the moment of contact of the wheels with the ground. so that the motion of approach to the ground is that at which the wings are giving the maximum possible lift. It is concluded that for a normal aeroplane the speed must be about 20 per cent, above the stalling speed, to provide the necessary excess lift for flattening out under the above hypothesis. THE AIR-BUBBLE VISCOMETER. BY GUY BARK. B.A., D.Sc. "Work performed for the Department of Scientific and Indus- trial Research. R. and M. No. 98S (M. 31). April, 1925. Price yd. net. It was desired to find whether, and under what circum- stances, the rise of a large bubble in a vertical tube containing liquid could be used as an indication of the viscosity of the liquid. The method has been used by Faust (" Zeits. Phys. Chem.," 1919, 39, 758) for very viscous oils ; by Abrams, Kavanagh and Osmond ("Chem. and Met, Eng.?' 1921, 25, 665) for oils of 0-15 to 0-9 poise, and by Gardner and Holdt (Circ. No. 128 of Paint Manufacturers" Association of the U.S., 1921) in varnish works for oils of viscosity between 0-5 to 5-5 poises. The effects of length of bubble and diameter of tube have been examined, and the rate of rise determined for several oils of known viscosity and surface tension, for water and for sircerin in different tubes. A dimensional analysis of the problem has been made involving certain assumptions which seem to be capable of verification, in any particular case, from the pppearance of the bubble.
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