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Aviation History
1933
1933 - 0665.PDF
r,7 SEPTEMBER 28, 1933 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT Measurements were made, over a range of Reynolds number of »00,000— 1,600,000, of the drag of each model In the hare tunnel and also behind each of three screens placed at various distances from the model. The intensity of turbulence was roughly calibrated by means of resistance measurements on a sphere. Measurements were also made of the normal pressure at various positions along the surface of each model without a screen in the tunnel and for one position of the intermediate screen. In the bare tunnel the drag coefficient of the model with the higher block coefficient was found to be about 51) per cent, higher than tha* of the other model at a Reynolds number of 1,600,000. With increasing turbulence the drag coefficients for the two models increased and approached one another until they finally became equal for the highest degrees of turbulence obtained. The difference between the drag coefficients without the screen appears to be due to an earlier transition from laminar to turbulent flow in the boundary layer of the model with the bluffer nose, which is consistent with the distribu tion of normal pressure over the surface. This difference is eliminated by the introduction of artificial turbulence in the wind tunnel stream, which causes the transition point to move forward on both models. It is concluded that, for the full scale airship, where the boundary layer of either shape is probably almost wholly turbulent, there is nothing to choose between the two shapes from the consideration of resistance alone. • N.A.C.A. Technical Note 264. Figs. 3. 4 and 5. + Dryde.n and Keuthe. N.A.C.A. Reports 342. 392. % R. <fc M. 597. " The effect of up-wind disturbances in the air current of the channel upon the forces on models with special reference to the effect on the drag of an airship model." Relf and Lavenden. THE EFFECT OF A TRACTOR AIRSCREW OX BODY-WIXG INTERFERENCE. BV E. Ower, B.Sc, A.C.G.I.. R. Warden, Ph.D., M.Eng., and L. .1. Jones. R. & M. No. 1512. (35 pages and 13 diagrams.) November 25, 1932. Price 1>. 9d. net. Researehe-- carried out at various Institutions during the last few years have yielded much information on the mutual interference between the fuselage and the wings of aircraft when not affected by the airscrew slip stream. On analysis, this information has indicated certain general features upon which the interference seems mainly to depend, and has consequently enabled recommendations to be drawn up for the avoidance of the con struction of body-wing combinations having high interference drag. A full account of them and of the evidence upon which they rest will be found in the recently published report R. «* M. 1480.* It is, however, of import ance to know how, if at all, these recommendations need modification when the slipstream from the airscrew plays upon the junctions of wings and body where the major part of the interference has its origin. This is considered in the present report. Measurements of ifft and drag have been made on a streamline body with a tractor airscrew at the nose, and with wing roots of R.A.F. 31 section attached to it in various positions above and below its horizontal median plane, and at a constant axial distance from the nose. The body used was a smaller scale model of that used for the similar work done without airscrew and described in R. & 31. 1480. and the general proportions of the body- wing combinations were approximately the same as in the earlier work. The airscrew used was a four-biader of P/D ratio 0-7 and diameter 19-25 in. Measurements were made of net thrust, net torque, and lift of the various combinations for values of V/nD ranging from 0 to 1. In addition, measure ments of lift and drag were made with the airscrew removed. Although the relative merits of different combinations may be somewhat altered quantitatively by the slipstream, qualitatively no important modi fication was observed. The low tangential wing position on the body of circular cross section was still very distinctly the worst of those tested, while the best was that with the wing chord slightly above the centre line of the body. The slipstream effects a relative improvement of the had wing positions (but without rendering them actually superior to the good positions) and there is also evidence that it spoils positions in which the wings are high on the body. In general, the wings reduce the rotation in the slipstream by an amount which is greater the better the wing position as judged on the basis of its interfernece drag. In bad positions the wings may sometimes introduce additional rotation into the slipstream. In an Appendix the results are analysed by an application of the theory of airscrew-body interference developed by Lock and Bateman. and it is shown that a simplified form may be used to predict the net thrust with fair accuracy. * '"Some aspects of the mutual interference between parts of aircraft." —Ower. THE HEATS OF FORMATION OF NITROUS OXIDE AND CARBON DIOXIDE. PART I. Bv J. H. Awberv, B.A., D.Sc, and Ezer Griffiths, D.Sc.*, F.R.S. PART*II. Bv R. W. Penning, M.B.E., B.Sc., D.I.C., and F. f. Cotton, B.Sc. Work done tor the Department of Scien tific and Industrial Research. R. & M. No. 1513. (42 pages and 13 diagrams.) February, 1933. Price 2s. 6d. net. An investigation on the properties of fuels that is proceeding at the N.P.L. called for an accurate knowledge of the heat of formation of nitrous oxide. Since the published values of this constant differed widely, a redetermination of its value was undertaken with a view to obtaining as high an experimental accuracy as possible. The heat of formation of nitrous oxide has been determined by a continuous flame method at constant pressure (described in Part I) and by an explosion method at constant volume (described in Part II). Incidentally, values have also been obtained of the heat of formation of carbon dioxide from carbon monoxide and oxygen. In the constant pressure experiments, an adiabatic calorimeter was used to measure the heats of reaction, its extent of the reaction being determined by collecting and weighing the carbon dioxide produced. The results were converted into absolute values by calibrating the apparatus electrically. In the constant volume experiments, a number of mixtures were exploded in a specially-designed bomb calorimeter of the adiabatic type for the purpose of determining the reaction heats. The mass of oxygen or nitrous oxide taking part in the explosion was computed from pressure, temperature and volume measurements of the gas concerned, and its amount was adjusted so that the heat imparted to the calorimetric fluid was sensibly the same in all cases. The following are the comparative results of the experiments with those of other workers :— Author Date Heat of formation of N2O in kg.-cal.15" per mol Berthelot Thomsen Carlton-Sutton Awberv and Griffiths Fenning and Cotton .. .. 1880 .. 1905 .. 1932 .. 1 1932 . . ! 1932 i 20.6 17.74 20.5 ±0-3 (at 20desj. C.) 19.5 (at 20 dcg. C.) 19.74 ± 0.07 (at 20 deg. C.) Author Date Heat of formation of CO? in kg.-cal.150 per mol. Berthelot and Petit . . Thomsen Roth and Banse Rossini Awbery and Griffiths Penning and Cotton .. .. 1 1889 . . 1 1905 .. 1931 1931 1932 1932 68.22 67.96 (at 18 dcg. C.) 67.86 ±0-1 (at 20 deg. C.) 67.623 ± 0 030 (at 25 dcg. C.) 67.57 (at 20 deg. C.) 67.655 ± 0-035 (at 20 deg. C.) SOME FULL-SCALE EXPERIMENTS WITH SERVO RUDDERS. By J. E. Serby, B.A. Communicated bv the Director of Scientific Research, Air Ministry. R. & M. No. 1514. (8 pages and 17 diagrams.) July 8, 1932. Price 9d. net. Servo rudders have been fitted satisfactorily to many aircraft.* To pro vide data for the design of servo rudders for larger aircraft and to cover the " flap " type servo design, a programme of tests was drawn up following on a report on the general aerodynamics of servo rudders (R. * M. 1105).f Both types of servo were tested in the wind tunnel, the tests covering two different sizes of servo chord and various lunge positions (B. & M. 1186).t A report (R. <£ M. 1187)§ on the theory of "follow-up" in servo system* was next made. It was then decided that flight tests on a flap-type servo rudder fitted to a large aeroplane were desirable in order to check the wind-tunnel tests, atid these form the subject of the present report. The cross-wind force coefficients and main rudder moments liave been measured on an all-moving rudder fitted with hinged flap type servo, for a range of servo positions. The maximum cross wind force coefficient (<L) obtainable with the rudder which was used in these experiments, and of which the aspect ratio was 2-4 is approximately 0-24 at an incidence of 14°. Shielding of the rudder by the tail causes a loss of rudder efficiency of 40 per cent, on the calculated values. The centre of pressure movement is large enough to l>e very important in large rudders with hinge positions set well back. The servo moments were extremely small. * R.A.E. Report B.A. 528.—•Full-scale tests of a servo rudder on a T).H. 10." (Unpublished.) t K. <i- M. 1105.—"The aerodynamics of a simple servo rudder svstem." — H. M. Garnei- and Flt.-Lt. Lockyer. J R. * M. 1186.—"Wind tunnel tests of various servo rudder systems." —K. V. Wright. § R. & M. 1187.—"On the use of follow-up mechanism in aerodynamic servo control systems."—H. M. Garner and K. V. Wright. FURTHER EXPERIMENTS ON THE SPINNING OF A BRISTOL FIGHTER AEROPLANE. By A. V. Stephens, B.A. Com municated bv the Director of Scientific Research, Air Ministry. R. & M. No. 1515. (22 pages and 18 dia grams.)' July 26, 1932. Price Is. 3d. net. The development of a method of determining completely the spinning motion of an aeroplane was described in R. & M. 1261.* In the same report the quantities defining eleven spins of a Bristol Fighter are given, and it is pointed out that although the control settings and loading of the aeroplane were approximately the same in each case, the characteristics of the spins varied widely. It was subsequently discovered that consistent results could be obtained if the spins were entered in a standard way. Recent experiments with dynamical models in the vertical wind tunnel have shown that although the transition from one type of spin to another may occupy a large number of turns, the final state is a definite function of the control settings and loading of the model. The spinning motions of the aeroplane were completely determined from measurements of the, vertical velocity and the components of angular velocity and linear acceleration at the C.G. A number of spins were analysed in which. (a) the aeroplane was normally loaded : (b) the longitudinal axis was loaded to increase the relevant momenta of inertia without changing the position of the C.G. ; (c) the lateral axis was loaded ; («f) the elevator angle was varied ; (e) the rudder angle was varied. It appears that the Bristol Fighter eventually attains a definite spinning attitude whatever method of entry is employed. Loading the longitudinal axis of the aeroplane induces slower and steeper spins, whereas loading the wing tips has the opposite effect and the difficulty of recovery is much increased. The generality of these effects is uncertain. Reducing the rudder angle invariably decreases the incidence of the spin, hut moving the elevators down increases the rate of spin and has little effect upon the in cidence. The outstanding difficulty in explaining the equilibrium of the spins lies in the balance of rolling moments (chord axes) and further work on this point is required. • " Experiments on the Spinning of a Bristol Fighter Aeroplane."—Wright. SOME POSSIBLE ADVANTAGES OF A VARIABLE-PITCH AIRSCREW. By W. G. Jennings, B.Sc. Communicated by the Director of Scientific Research, Air Ministry. R. tv M. No. 1516. (25 pages and 11 diagrams.) October 10, 1932. Price Is. 3d. net. The object of the present report was to investigate the improvement in aircraft performance, including take-off, range, etc., that might be expected 972 g
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