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Aviation History
1909
1909 - 0333.PDF
JUNE 5, 1909. by guessing, and then follow on by modifying the values chosen until a reasonable agreement is obtained. A full-sized machine of the Voisin type may weigh 1,400 or 1,500 lbs. fully loaded, but then, on the other hand, there is no reason to suppose that a successful flyer could not be built weighing only a fraction of this amount, perhaps as low as 400 lbs. It depends so much on engine development, and the skill with which the framework is constructed. Co'efficients of Traction. As to the power required, there is no very certain figure which can be used as a basis. The exact value will, of course, vary with each machine. It is reasonable for the purposes of estimation, however, to take the co- efficient of traction as equivalent to one-sixth the total weight, in which case a machine weighing 1,500 lbs. would need a thrust of 250 lbs., and one weighing 400 lbs. would need a thrust of just under 67 lbs. Such evidence as is available seems to show that this is well outside practical achievements, but it is important not to under-estimate. The horse-power is derived from the thrust by multi- plying by the speed of flight. Thus a thrust of 250 lbs. sustained at 40 m.p.h. is equal to 10,000 mile-lbs. per hour, which in turn is equal (dividing by 375) to nearly 27 h.p. This represents the net energy represented by flight under the assumed conditions; it is, of course, necessary to allow for losses in the transmission of that energy. There will be losses in the mechanical trans- mission itself, and in the propellers, but where so little is known, it is reasonable to take some round figure, such as 50 per cent., which results in multiplying the net horse-power by two in order to find the size of the motor required. In the case under consideration, the estimate would obviously be for a good 50-h.p. engine. Similarly, at the other extreme ot the scale, where we have assumed a total load of 400 lbs., with a thrust of 67 lbs. at a speed of, say, 35 m.p.h., this would represent 6^-h.p. or, say, a good 12-h.p. engine as a suitable estimate for the job. It will be observed that the small value in this latter instance lends a certain fascination to this aspect of the problem of flight. Reserve Power for Ascents. In the foregoing, no account has been taken of the reserve of power required for ascent. It is a factor of which it is extremely difficult to take note, and at the present stage of the art, when the majority of experi- menters would be satisfied with achieving horizontal flight, at any rate for a start, it becomes a moot point whether a special allowance should be made initially if by doing so the whole prospects of a certain type of machine are upset. To discard any such allowance is not necessarily ignoring the importance of this factor in the problem. It is merely placing a very proper faith in the designer's and constructor's skill to come well within allowances already estimated. Any power which can be saved over and above that necessary to horizontal flight is available for ascent, and if the designer has any reliance in his figures at all he will naturally anticipate a reserve of a few horse- power if everything goes through as he wishes. If he meets with unexpected difficulties, then the possible reserve may be swallowed up, and the machine not be altogether a success. But, on the other hand, neither is a machine altogether a success when a designer decides to instal an engine which is bigger than he really wants in the first instance. Propellers. Of the propellers and their design and construction we do not propose to say anything in this article, except that of all parts of the flyer they must be as good as it is possible to make them. The propeller is, on the whole, a job which no amateur need be ashamed to " put out," for not only will faulty construction spoil all chances of success, but if characterised by weakness as well, will be a grave source of danger to the experimenter. Launching. The question of launching, too, is one a little outside the scope of the present article. It is, of course, an important factor to be decided at an early stage in the design, as it is likely to affect the total weight of the machine. The governing factor is, of course, in the main the nature of the ground which it is proposed to use as an aerodrome. BLERIOT'S LATEST FLIGHTS. BY way of celebrating the inauguration of the Bleriot monument, which has been erected at Toury in commemoration of the cross-country flight of M. Bleriot on October 31st last year, and illustrated in last week's FLIGHT, this intrepid aviator proposed to repeat his flight from point to point on the day of honour. Unfortunately, en route he ran short of petrol, with the result that after accomplishing 14 kiloms. of the distance between Toury and Artenay and back, he had to cut short his flight at Chateau Gaillard, a great disappointment both to himself and those associated with the erection of this memorable monu - ment. On the Friday previous, M. Bleriot had flown at Issy with his small monoplane No. XI, a distance of 4 kiloms., during which, whilst quite near the ground, he made some remarkable turnings and grace- ful curves. View of the new Bleriot Monoplane, showing the disposition of aviator,motor, &c, and the curvature and struts of the main frame. 335
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