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Aviation History
1912
1912 - 0032.PDF
AN AEROPLANE STUDY. By MERVYN O'GORMAN. I, AT the request of the Editor of FLIGHT, the following notes are given on^the utilisation of the chart* which I sketched out in the discussion of Mr. A. E. Berriman's excellent lecture on aeroplanes at the Society of Arts, on November 29th, 1911, published in FLIGHT, January 6th, 1912. Probably the most " actual " way of indicating the effect of the chart for aeroplane study is to show how it may assist us to criticise design in connection with some specific desirable objects such as long distance flight, fuel economy, quick rising, slow flight, weight lifting. In all aeronautical work, long distance flight is a question of not increasing the load of fuel to excess. It is not quite common know ledge that after the carburettor has teen tuned up to the finest possible point it is still possible to get waste of petrol by apparently nsignificant matters ofliandling the aeroplane, such as flying at the wrong air-speed, or by matters of design, such as using inadequate or excessive sail area. * Accordingly, fuel consumption (per mile or per hour), which differs with a given aeroplane so as to be more at very slow speeds, less at intermediate speeds, and more again at high speeds, is a suitable example to begin with. 2., Speed Range.—Very little timing of aeroplanes in straight flight has been done in this country, so that the existence of a con siderable range of possible flight speeds is not much appreciated. The range of speeds is in some machines fairly large, say 20 per cent. This need not be, but is, however, about the maximum. As instances of available speed ranges, a particular Bleriot machine can be quoted which had a range of flight speed from * I cannot trace that this method was given by M. Soreau in 1Q03 as stated in the published discussion at the Society of Arts. Accordingly I wish to mention that the particular chart herewith was prepared by Mr. Watts of H.M. Aircraft Factory, at the instigation of Mr. Graen. Mr. I^anchester, who does not claim it, has pointed out to me his study of an aerofoil in " Aerodynamics," showing that he had foreseen the possil ilities of this method ; this and much more we owe to him about 45 m.p.h. to 54 m.p.h. ; it had, of course, a large engine. A particular Breguet had a range from 46, or thereabouts, to 53. A particular Deperdussin had a slowest speed, estimated in the neigh bourhood of 45 and a maximum of 55. Specially designed machines can easily be given a greater speed range, and much of the possible range may be lost by having an engine that is not susceptible of control. These examples are, however, sufficient to establish the fact that such a speed variation is not only practicable, but is normal practice. 3. These may be called the available speeds. Theoretically more range can be obtained even from these aeroplanes by flying yet slower with the engine at full power and the aeroplane "cabre." Also, matters that are still considered quite small—as such things are viewed at present—may quite well account for a loss or gain of 5 or 6 per cent, of the upper limit. A complete absence of irregular air movements is necessary before a slow test of any duration can be made and even then it is risky to fly as slowly as possibly can be done, since no margin of power is then available for recovering if any loss of speed should result from warping or steering for balance. The risk then is chiefly the risk of "pancaking." Fortunately the chart shows that this particular limit of slowness does not conduce to fuel economy. See point P on curve 5 where both more horse-power is used, i.e., more fuel per minute, and less ground covered per minute than at point Q say. 4. A "Given" Aeroplane.—It is more practical to consider the matter from the opposite end and to suppose that we have, as most entrants will have, the aeroplane " given." To begin with there is a choice of engines within the limits of their adaptability to the particular fuselage. With a more powerful engine of the same weight as before, the intercept of curve 5 by curve 6 would show an increased range of flight speed, since curve 6 would be raised higher up on the chart. 5. The Small Engine.—At the outset it is quite possible to 300 -1 C URV WEIGHTS .- 1— - SURFACE I_RRTE OF es or RESISTANCE'AND RWER TOTAL 1150 LBS. EMPTY 770 PILOT, PASSENGER AND BALLAST S4& •• OIL AND FUEL 134 223 SQ-FT CLIMBING M-O FT/SEC REQUIRES. 5-3 pp. llN •3-5 32
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