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Aviation History
1913
1913 - 0370.PDF
l/HGHTj longer on the journey, which in turn would involve carrying more fuel. A journey of 2,000 miles at 70 m.p.h. would occupy nearly 29 hours. Let us take 30 hours for the sake of round numbers. An engine working on a consumption of half a pint of petrol per h.p. hour for 30 hours con tinuously will, therefore, consume 15 pints of petrol per h.p. for the entire journey. Once again let us take round figures, and say 2 gallons, which represents a weight of roughly 15 lbs., rather less. Thus, starting with the machine that itself weighs 15 lbs. per h.p. in construction when empty, we must add thereto the weight of 15 lbs. per h.p. for fuel consumed on the journey. At the start of the flight, therefore, such a machine cannot be expected to weigh less than 30 lbs. per h.p. exclusive of the two pilots. The resistance to flight we have supposed to be 1 in 6 at 70 m.p.h. One-sixth of 30 lbs. is 5 lbs.—that is to say, there is a resistance of 5 lbs. per h.p. at 70 m.p.h. at the start of the journey. This resistance at this speed represents an expenditure of 350 mile lbs. per hour, or 94 per cent, of 1 h.p., which is an efficiency quite unattainable by any modern propeller. Owing to the fuel being consumed steadily throughout the journey, the weight in flight will decrease with the distance from shore. With the decrease in the weight there will be a decrease in the resistance. If the resistance were pro portional to the mean weight in flight, it would amount to one-sixth of 15 lbs. plus 7^ lbs.—that is to say, it would be about 375 lbs. instead of 5 lbs. resistance. At 70 m.p.h. this represents an expenditure of just over 260 mile lbs. per hour, or 70 per cent, of 1 h.p., which is a more reasonable figure for propeller efficiency. It will be recognised that the above elementary calcu lations assume the machine to be flying without a pilot. They arc also independent of the size of the machine, certain assumptions having been made in the light of the data at present available in respect to actual aero planes. A journey of 2,000 miles at 70 m.p.h. could scarcely be undertaken by one pilot; two men at least would have to be aboard the machine, which would have to be fitted with dual control. Their weight would amount to a least 300 lbs., and the problem of selecting the best type of aeroplane for the journey is very largely governed by this item. Thus, suppose the power is small, then the weight of the passengers represents a greater proportionate in crement to the resistance than when the power is high. Apart from this consideration, it is immaterial whether the machine be large or small, except in so far as the size may alter the figures chosen as the basis for the above calculation. In the light of modern data it would require an exceptional aeroplane and a very exceptional engine to improve materially upon the values chosen. It is interesting to consider the conditions represented by an attempt to perform the journey with a 100-h.p. engine. In this case the pilots' weight of 300 lbs. repre sents 3 lbs. per h.p., one-sixth of which becomes half a pound resistance per h.p. On the assumption that the mean resistance of the machine and petrol amounts only to 375 lbs. per h.p., this extra half pound, which remains constant throughout the journey, brings the resistance up to 4\ lbs. per h.p., which, at 70 m.p.h., represents about 300 mile lbs. per hour, or 80 per cent, of 1 h.p. It is easy to recognise, therefore, that the fundamental mechanics of the problem brings such a journey as this very near to the limits of present possibility. It is at any rate very clear that those who make a serious attempt for this prize are best advised to concen- APRIL S, 1913. trate their attention upon low body resistance, for whereas it may be a difficult matter to reduce the weight of an aeroplane to less than 15 lbs. per h.p., or the fuel con sumption of an engine to less than ipint per h.p. hour, it does seem reasonable to anticipate that we may ultimately attain to aeroplane designs that offer less than a resistance of 1 in 6 at 70 m.p.h. For a machine such as that outlined, the initial fuel supply assumes somewhat alarming proportions. Thus, as we pointed out, it is necessary to start with 2 gallons of petrol per h.p., which, for a 100 h.p. machine, represents 200 gallons, which would weigh about two-thirds of a ton. The machine as a whole therefore would weigh about a ton and a half. This represents a weight of about 33 lbs. per h.p., which is much greater than any figure characterising a successful machine in the Military Trials. The Cody, which weighed 2,680 lbs. in flight, had an engine rated at 120 h.p., which brought the load per h.p. to less than 24 lbs. To assume a more powerful engine in the above problem is merely to assume a proportionate increase in the total weight carried, with the exception of the frac tion represented by the pilots. Assuming the proved reliability of the engine, however, it would be desirable to use the largest that is available. Not only does the greater power render it more reasonable to expect the realisation of a low fuel consumption, but it reduces the effect of the pilots' weight. «> <0> 4» . .- , We hope that one outcome of the offer by Aeronautical ., „r., ,, ., . , . „ .* Lectures. *ne -£->alty Mail may be a great interest in the design of low-resistance bodies. Prof. Petavel, who is delivering a series of Howard Lectures on Aeronautics at the Royal Society of Arts, showed some very striking comparisons last Monday evening, which would have interested many of the constructors who were not present. They were models constructed to show to an audience the immense potential reduction in head resistance that might ensue from using stream line bodies and good fair-shaped struts. It is a study that should be very much to the fore in the constructor's mind, and particularly now that there is the stimulus of a ^10,000 cheque indirectly connected with it. Lectures such as those now proceeding at the Royal Society of Arts deserve to be well attended by the members of this new profession, as also do the meetings of the Aeronautical Society. It is quite evident from the interest that has been taken in its proceedings that it is successfully fulfilling some of the technical requirements of those scientifically interested in the movement. But, from the Council's report, which was presented at the annual general meeting last Wednesday week, it is apparent that it must have a largely increased member ship if it is to continue to carry on this useful work adequately. There are without doubt many readers of FLIGHT who would gain much from an association with this already historic yet so very modern society, and who would be only too pleased to feel that by joining its ranks they are being of real service to such a worthy institution. The phenomenally rapid progress in aeronautics has been due solely to the openness with which scientific and practical data have been discussed among members of scientific institutions like the Aeronautical Society and in the technical Press. We ourselves feel proud to think that FLIGHT has consistently done its best to further this end for a period that is already beyond four years. Time flies ! One hesitates even to let the imagination venture into the realm of aviation four years hence. Will the Atlantic have been flown by then, we wonder? 17$
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