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Aviation History
1909
1909 - 0383.PDF
JUNE 26, 1909. was 0-27 lbs. This test was kindly made for the writer by Professor A. F. Zahm in the " wind tunnel" of the Catholic University at Washington, D.C., who, more- over, stated that the resistance of a live bird might be less, as the dried plumage could not be made to lie smooth. This particular buzzard weighed in life 4-25 lbs., the area of its wings and body was 4/57 sq. ft., the maximum cross-section of its body was o"iio sq. ft., and that of its wing edges when fully extended was 0-244 sq. ft. With these data, it became surprisingly easy to compute the performance with the co-efficients of Lilienthal for various angles of incidence and to demonstrate how this buzzard could soar horizontally in a dead horizontal calm, provided that it was not a vertical calm and that the air was rising at the rate of 4 or 6 m.p.h., the lowest observed, and quite inappreciable without actual measuring. To be concluded,) CORRESPONDENCE. %* The name and address oj the writer not necessarily for publication) MUST in all cases accompany letters intenaea for -'•: insertion, or containing queries. V ^ AERONAUTICAL ENGINES. To the Editm- of FLIGHT. SIR,—In FLIGHT of the 12th instant, in an article entitled " Some Points in Aeronautical Engines," by A. J. McKinney, he refers to extra exhaust ports uncovered by the piston, " the length, in the line of piston travel, being not more than 18 per cent, of the stroke." Now, if the stroke is 4 ins. the length will be nearly f in. for the port, but the piston rings usually used would be little more than J in. thick (or deep). Is it necessary to fit rings wider than the port (i.e., about § in. wide), or would the stiffness of the ring prevent it slipping into the port? Will you please give me the equivalent of " 15 or 17 mm." Would it be safe to build an engine with an auxiliary port considerably wider than the piston rings, and, if so, about what would be the limit in a line across the line of stroke to prevent the ring fouling the port, e.g., could you, on a 4-in. bore engine, have a port 2 ins. wide by I in. long with ordinary piston rings ? The ends being kept clear, would the rings pass it safely ? All good wishes for the future of FLIGHT. Yours truly, Sandgate. NOEL VERNHAM. ' [In order (o save delay we submitted Mr. Vemham's letter to Mr. McKinney, and are now able to append the latter gentleman's reply below.—ED.] To the Editor of FLIGHT. SIR,—In reply to Mr. Noel Vernham's letter on exhaust ports» the point raised is an interesting one. Though I gave the limit as 18 per cent., I should not recommend it as the maximum unless a non-return valve is fitted to prevent air being sucked in on the induction stroke. Apart from this, however, there are no mechanical difficulties in practice, providing that the port is not wider (i.e., in a horizontal plane, assuming the engine is a vertical one) than § in. That is, one can use exhaust auxiliary ports which are oblong or rectangular, always providing that the greatest dimension does not coincide with the plane of the piston rings. If the width (in the transverse direction) exceeds §• in., there is great danger of the ends . _ " of one, or more, piston rings expanding when passing over the port, which, of course, breaks them off immediately. When experiment- ing recently on an engine which had a bore of 82 mm., I found ports over § in. in width dangerous in this respect. Another result of my experiments was that two or three circular ports § in. in diameter, cut so as to be just uncovered at the lower limit of the piston travel, were preferable to one large one of corresponding area. By the way, the inner edges of the ports must be carefully cleaned after cutting the orifices, as otherwise the cylinder would soon be seriously scored. A point to bear in mind is that while the power is increased, and the engine, particularly when of the air- cooled type, keeps cooler, the lubricating oil tends to blow out. The auxiliary ports, then, should have a non-return valve and piping to convey the gases to the silencer. If Mr. Vernham would like to discuss the matter further, perhaps he would care to com- municate with me direct, as otherwise I fear I should take up too much valuable space in your journal. Truly yours, A. J. MCKINNEY. PROPELLER CHALLENGE. To the Editor of FLIGHT. SIR,—I am sorry Mr. Cochrane's reply does not give the revolutions per minute and brake horse-power of his §-h.p. electric motor. I should have liked to have tried my amateur hand to win the prize he so generously offers, but I cannot make the attempt without these particulars. 385 I am disappointed that what promised to be an interesting competition should fall through, but I suppose there must be some difficulty in ascertaining this necessary information. Mr. Sidney Hollands, according to his letter dated June 7th, prefers to enter a competition for larger propellers. I have a model motor boat, propelled by an air propeller 3 feet diameter, driven by a petrol motor. If he and any other gentleman would like to make 3-ft. screws for the purpose of a friendly competition, I shall be glad to test them, as I am already fitted up for the work. I cannot try them against my own, as mine is not designed to give the highest push possible when the boat is stationary, but to work most efficiently when the boat is travelling at a good speed. I have several times made brake tests of the motor, and I find the actual brake horse-power at the propeller is just 2 when running 1,100 revs per min. The propeller is at the back of the boat, and it revolves in a left- handed direction as viewed from behind, and, of course, competing propellers must be shaped to suit this direction. My propeller weighs 2 lbs., but the weight of competing propellers may be anything up to, say, 10 lbs. Yours truly, Shipley. ALFRED WALKER. To the Editor of FLIGHT. SIR,—I am greatly interested in Mr. William Cochrane's letter published in FLIGHT of June 5th. I admire his pluck in issuing such a broad challenge. His fan must be exceptionally good to inspire him with such confidence. As Mr. Cochrane gives no particulars regarding the size of his fan, the speed run at, nor the actual weight lifted, he places his competitors at a disadvantage. Most inventors consider their own pet ideas the best, and I must plead guilty to a weakness in that direction. Therefore, I am anxious to accept Mr. Cochrane's challenge under his own con- ditions, and at any time or place convenient to Him. I give some particulars of the weight-lifting capacity of some fans I have, but, following Mr. Cochrane's example, I make no mention of the speed, size, or horse-power used. I have a fan which weighs, without its bars, i\ ozs. This fan lifts, direct from the ground, 6 lbs. dead weight. Another fan, weighing, without its bars, 5^ ozs., lifts 20 lbs. dead weight. In both cases the weights are kept suspended after lifting. I should be pleased to hear from Mr. Cochrane re the above. - -> . I am, yours faithfully, ,_•.••.'••• . • -^'••'-• .••"• .;,:..,:.' . E. M. WILDEY. MR. ROE'S TRIPLANE. To the Editor of FLIGHT. SIR,—It may come as a surprise to your readers to learn that I have been making dozens of short flights with my British-built aeroplane during the last few weeks ; true, they are hardly more than jumps, being only 2 and 3 feet high and 50 or so feet in length. Personally, I would have preferred to let this fact leak out on its own accord by winning the ,£100 and ,£1,000 prizes for the 100 yds. and 1 mile flight respectively, but, to be candid, to carry 40 lbs. per h.p. has proved a bigger task than I calculated on, for my machine, with self aboard, weighs 400 lbs., and is driven by a 10-h.p. air-cooled J.A.P. motor cycle engine; but I am confident there is sufficient power, and there is every reason to believe I shall continue to get better results with further experiments. Although I have been trying various gear-ratios, pitches, width of blades, diameters, two and four bladed propellers, and have kept a careful record of each experiment, there still remains quite a number of varieties to be tried yet. Carrying 40 lbs. per h.p. seems easy enough on paper but rather different in practice. The reason the above announcement is made, is because I feel confident that the machine I am now experimenting with has
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