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Aviation History
1911
1911 - 0726.PDF
[pjGHT AUGUST 19, 1911. CORRESPONDENCE. The name and address of the writer (not necessarily for publication) MOST in all cases accompany letters intended foi insertion, or containing queries. Hollow Spars for Aeroplanes. Correspondents communicating with regard to letters which they have read in FLIGHT, would much facilitate ready reference by quoting the number of each such letter. Aeroplanes in War. (1304] With reference to the letter No. 1284, the calculations which Mr. Atkinson requires of me are hardly necessary if he would read through the following. First the barometer has to be set for the sea level reading, which is to be taken as "normal" for the day; then the aeroplane's position has to be fixed accurately, a difficult matter in hilly country. Provided that the "normal" barometer reading has not altered which it may), and assuming there is no instrumental error, the exact position is known, then there will be no error ; but since a small error will occur probably in each of these, and an error of the barometer means 100 ft. in height, it is most probable that the height will be at least 100 ft. in error. This will produce an error of anything up to 40 ft. in the bomb-dropper according to the height at which he is flying and speed relative to the ground. I mentioned an error of 8 ft., as that would occur when the aeroplane was flying out of rifle shot as slowly as can be reasonably expected and against a slight head wind, a circumstance which tends to reduce the error. For the smaller the horizontal velocity of the bomb through the air, the more nearly will it keep that velocity throughout which can be allowed for more accurately. Also, since lor a given error in height the amount by which the shot will miss decreases with the height, there is a certain accuracy in high flying which is modified by the unavoidable instrumental error of trie speed-registering apparatus and the personal error of the gunlayer. So it would seem that a range of about 3,000 ft. would be most suitable for the bomb-dropper as being a good mean working range. At present gyroscopic gear of any sort is too heavy for an aeroplane, but undoubtedly will be of the utmost use in the near future. D. H. T. Monoplane Construction. [1305] I am shortly going to build a small man-carrying mono plane, and would be glad if your readers would make suggestions on the following points :— I. Would a supporting surface of 162 sq. ft. main planes and 56 sq. ft. tail plane be enough, the span of former being 27 ft., chord 6 ft. ? My weight is 122 lbs. 2. Should the length of the aeroplane be the same as the span, or shorter ? 3. Would the curve in the accompanying sketch be too deep ; the plane has square ends? 4. At what angle should the main planes be fixed to the body ? Salisbury. D. ALLON PITT. Aeroplanes and Gusts. [1306] I have read the, to me, remarkable article by S. L. Walkden, published in your issue of August 5th, and would point out that, when an aeroplane is travelling in a horizontal flight-path, the force of gravity must be of necessity exactly balanced by the upward lift of the planes ; it is therefore impossible that a downward acceleration can exist, and consequently the whole of Mr. Walkden's argument and diagram exist only in his imagination. BELTON T. HAMILTON, M.I.A.E., A.M.I. Mech.E. Aeroplane Efficiency. [1307] Can any of your able contributors say whether the present knowledge of aerial locomotion permits of anything approaching an accurate determination of the mechanical efficiency of a given aero plane? It would appear from the horse power consumed in the propulsion of the simplest of monoplanes that there must be a great waste somewhere. How does this come about ? When it is stated that such and such a propeller has an efficiency of 80 per cent., what is the basis of the determination? I should be greatly obliged to see this matter put clearly by someone who has had actual experience in testing. Newcastle-on-Tytte. A. NOEL FERGUSON. [1308] I have been asked to take an interest in the invention of a mechanical device by means of which spars of any length and thickness and of various kinds of wood can be bored accurately through from end to end. The spars can be hollowed out to any of the diameters used for aeroplane work, and if need be tapered to a point. I am satisfied that hollow spars can be quickly and cheaply made by means of this simple invention, but before going further in the matter would like to have the opinion of your readers as to whether there is likely to be a substantial demand for same in the event of the spars being placed on the market. Edinburgh. A. J. Another Propeller. [1309] I have always been greatly amused when 1 have read about people making a new machine with engines of 40-50, even 60-h.p. By using such a power to carry one or two men they prove that their machines are badly constructed, or that they are using bad propellers. Hundreds of propellers have been designed, but always with the idea that they must be screws. I think it is a mistake. I have studied birds for years, and I must say that I have found that Nature has given them the " ideal" propellers, which are their wings. Thinking that it will interest your readers, I am enclosing the Mr. E. White and his Propeller. photograph of my propeller, made exactly on the principle of birds wings. It gives twice as much result as the ordinary screws; that is to say, 20 lbs. thrust per h.p. Of course, my propeller requires great care and study to build, on account of its shape, curves and flexibility; but, on the other hand, it requires only half-size engine for a given thrust, which means less weight, less petrol, less area. Wimbledon. E. WHITE. Vortex Principle of Flight. [1310] Those of your readers who have followed this corre spondence will readily appreciate my position when I say that Mr. Dring's peculiar methods of controversy leave me no option but to make this my last contribution to the discussion. Mr. Dring has brought forward a theory of insect flight which conflicts absolutely with the exact evidence collected by all the com petent authorities who have investigated the subject. The work of scientific investigators such as Marey, Pettigrew, Von Lendenfeld, Bull, Ritter, and others he has thrown aside, without producing tangible evidence against it. Conversely, the whole of his article and letters will be searched in vain for any scientific proof of the claims he advances for his " vortex propeller," and my reasonable requests that he should place before your readers the above essential proofs he has ignored. BERTRAM G. COOPER. 728
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