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Aviation History
1925
1925 - 0260.PDF
APML 30,, AERONAUTICAL RESEARCH COMMITTEE REPORTS FROM the number of enquiries we receive it appears that there is a desire in aircraft circles to know approximately the contentsof the various technical publications of the Aeronautical Research Committee. All the aircraft firms probably receive these reports regularly, whether or not they contain anything of immediate interest or utility. In the case of draughtsmen, however,and others interested in aeronautics, who can hardly be expected to purchase all the reports, the problem of deciding whether any publication interests him is often a difficult one. As it is obviously desirable that the knowledge of aeronautics should bemade available to all who take an interest in the subject, we have arranged with the Air Ministry to publish in FLIGHTsummaries of all the technical publications as soon as these are issued, or shortly before they are published. All A.R.C. publications can be purchased from H.M. Stationery Offices at Adastral House, Kingsway, London, W.C.2 ; 28, AbingdonStreet, London, S.W.I ; York Street, Manchester; 1, St. Andrew's Crescent, Cardiff; 120, George Street, Edinburgh, and through any bookseller. Reports and Memoranda, No. 935 (Ae. 156). Experi- ments to Measure the Variation, with Speed and Size, of the Forces on an Aerofoil of Thick Section (German Aerofoil, No. 420). By A. Fage, A.R.C.Sc, and \V. L. Cowley, A.R.C.Sc. January, 1925* One difficulty associated with wind tunnel work is to find the values of the corrections that have to be applied to the results of a model test carried out at a given speed and in a given size of tunnel for the purpose of predicting full-scale aeroplane performance. It is clearly impossible to carry out all wind tunnel tests at the highest velocity and with the largest model in the largest wind tunnel, and with a view to obtaining some estimate of the correction which should be applied, because it is not possible so to test each model, a number of experiments have been made on special wings over A wide range of size and speed. Several experi- ments of this nature have been previously made on thin aerofoils, but there is not a large amount of information available on the scale effect of thick sections. R. and M. 763 and 894 describe experiments on the thick section R.A.F. 19. The present experiments were carried out on the well-known German section 420, which was one of a series of thick sections tested at Gottingen Laboratory. Measurements of lift, drag, and centre of pressure were made on No. 420, at incidences ranging from - 8 deg. to 30 deg., on two models, a large model 10 ft. span and 2 ft. chord being tested in the Duplex tunnel at wind speeds 20, 40, 60, 80, and 100 ft./sec, and a model of standard size (3 ft. x 5 ft.) being tested in a 7-ft. tunnel at speeds 40, 60 and 80 ft./sec. The experiments on the large aerofoil—vl range 40 to 200 —showed a pronounced drop in the minimum drag coefficient with increase in vl. At the highest values of vl, there was no appreciable speed effect on maximum lift coefficient. The results for the two models when compared at vl = 40 and aspect ratio fi : 1, were in fairly close agreement on lift, centre of pressure, and minimum drag coefficients, but the drag curves diverged at the higher angles of incidence. A comparison of the National Physical Laboratory results (vl = 80), with others published by Gottingen showed close agreement on lift, except at the stall, where the values of the coefficients were 0-73 and 0-66 respectively. The N.P.L. value of minimum drag coefficient was about 12 per cent, greater than that measured at GQttingen ; elsewhere the drag curves were in fairly close agreement. The present experiments demonstrate that the scale-speed characteristics for this section differ appreciably from those of the thin section aerofoil R.A.F. 15 at maximum lift and minimum drag. Reports and Memoranda, No. 941. (M.N.8.) Measure- ment of Vertical Currents in the Lowest Layers of the Atmosphere during Sea-Breezes. By J. Durward, Meteorological Office, Presented by the Director of the Meteorological Office. August, 1923. Vertical currents in the lower layers of the atmosphere are important for aviation in several ways :— (a) They affect getting off and landing of aeroplanes, and a site with marked vertical currents arising from the local topography may be undesirable on that account as the site of an aerodrome. (b) They affect also the apparent performance of an aero- plane, and a region in which topographical conditions produced marked vertical currents to considerable heights would be undesirable as a region in which tests of aeroplanes should be carried out. (c) They affect gliding ; in fact, gliding depends entirely for its success on the utilisation of upward currents and a knowledge of the topographical conditions in which upward currents are marked and the height to which such currents extend is of fundamental importance for the development of gliding and of aeroplanes of low engine power. It was known that vertical currents must occur over con- siderable areas during sea-breezes, and it was thought desir- • Part of the above work was completed in January and part in November1024. Rewritten for publication, January, 1925. able to obtain some more exact idea as to their velocity and probable extent. The single theodolite " tail-method " of dcing pilot balloon ascents was adopted on selected occasions at Calshot during the summer of 1923. The report concludes as follows : — (1) The sea-breeze found has generally been less than 500 ft. thick ; but on one or two occasions it has extended to at least 1.000 ft. (2) The maximum upward velocity of the air found over any particular minute was 300 ft./min., whilst the maximum downward velocity was in the region of 180 ft./min. (3) Around Calshot the tendency seems to be in favour of encountering descending air. (4) In a good many cases descending air has been found at moderate heights, viz., between 1,000 ft. and 2,000 ft., especially when the balloons travel over water (as they generally do). Reports and Memoranda, No. 942 (Ae. 162). The Royal Aircraft Establishment Control Movement Recorder, Mark III. By D. A. Jones and H L. Stevens, of the R.A.E., presented by the Director of Scientific Research. October, 1924. For the improvement of aeroplanes and their flying characteristics, it is of first importance to be able to measure, not only the movements of the aeroplanes, but also the move- ments of the controls which bring about the various manoeuvres through which an aeroplane can be put. There are several methods of attaining this end, and, whereas the Americans have used one instrument on which a number of simultaneous records are kept, the Royal Aircraft Establish- ment have designed a type of recorder, one of which is fitted to each control. From many points of view, the R.A.E. method appears preferable. The recording instrument described in this' paper gives a contitruepbs record of the movements of any control surface of an aircraft during manoeuvres. It has been designed so that it can be directly attached to the surfaces, thus avoiding any eror due to elasticity in the control wires, etc. One instrument has been subjected to some 15 hours' flying, involving about 30 separate flights, and has given every satisfaction. A reproduction of a portion of one of the records obtained is attached to the report. For research work at the R.A.E. it is proposed to fit these instruments to all the control surfaces of an Avro, together with a gyro instrument to record the rate of turn about the three axes. Reports and Memoranda, No. 949 (Ae. 169). The Performance of Tandem Systems. By H. Glauert, M.A. Presented bjT the Director of Research. December, 1922. The vortex theory of aerofoils has been discussed in several previous papers published by the Aeronautical Research Committee. They are as follows :— R. andM. No. 723. " Prandtl's Aerofoil Theory."—Glauert. ,, 752. " Some Applications of the Vortex Theory of Aerofoils."—R.A.E. ,, ,, 889. " Experimental Tests on the Vortex Theory of Aerofoils."—Glauert. ,, ,, 901. " Theoretical Relationships for a Bi- plane."—Glauert. The theory lias many applications, and it is applied in the present paper to find the aerodynamic characteristics of a tandem system of monoplane aerofoils. It is shown that at small angles- of incidence the lift and drag of a tandem system of aerofoils is the same as for a monoplane of the same total area and span. If, however, the tandem system is arranged to secure equilibrium, and if the centre of gravity is fixed by the consideration that the system must not be unstable statically, the maximum lift coefficient obtained is very low, being less than 0 -40 compared with 0-55 for the monoplane. As a preliminary step for the above work it was necessary to obtain expressions for the upwash in front of, and for the downwash behind, a monoplane wing, Details of this analysis are contained in Part II of the report. 260
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