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Aviation History
1911
1911 - 0341.PDF
APRIL 15, 1911. E/UGHI] CORRESPONDENCE. *»* The name and address of the writer not necessarily for publication) MUST in all cases accompany letters intended for insertion, or containing queries. 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. NOTE.—Owing to the great mass of valuable and interesting corre spondence which we receive, immediate publication is impossible, but each letter will appear practically in sequence and at the earliest possible moment. to your readers, I submit same for publication. An interesting feature about the curves representing X is that the second differential, apparently at a maximum between aspect ratio 1 and 2, again seems to increase between 4 and 5. Lagos, W. Africa. R. FLEISCHBERGER. A Question of Sparking-Plugs. [JI37] With reference to Messrs. Lodge Bros, and Co.'s letter in your issue of April 1st, we have examined our advertisement of March 25th and find that we did not directly claim that Mr. Sopwith was using our plugs, although we were certainly under the impression that he was. We should have substituted the word "magneto" for " ignition," which would have made everything perfectly clear. THE BOSCH MAGNETO CO., LTD., J. A. STEVENS, Secretary. Aspect Ratio. [1138] I have read with interest L. B. Desbled's elucida tion of the aspect ratio, and as one interested in aviation fully recognise the value of the information he gives. j liM^'olu, iv.t .<i ny (Vt reference several values * f. J 0 N i •< r 4 > £ £ ^ '~ ! _•—"~ 1 ! j, R Fleischbs-rg Values of A. with tang a = Theory and Practice. [ir39] I read your article under the above heading with an interest the greater because I have followed the full course of your preceding articles upon " Can we Fly Faster for Less Power ? " The fourth of this instructive series, in your issue of October 22nd, 1910, was of especial interest, because it confirms the efficiency of the Crucifer body, and because, according to your article, " The whole question of efficiency at high speeds is, of course, primarily governed by the question of body resistance, which should be considered as a separate resistance and as an independent factor in the calculations, which must be reduced to a minimum by the use of suitable shapes and casings," as urged in this fourth article. By the aid of the charts in your issues of July 9th and October 22nd, 1910, I have been enabled to make certain deductions as to the importance of shape, which so fully confirm the accuracy and momentous- ness of your statement that I venture to write them to you, trusting that they will be of interest to you and your readers. Your charts enabled me to make a comparison of the factors of flight resistance at certain speeds, which disclosed the remarkable extent of the normal pressure experienced by the ordinary biplane of the Voisin or Wright type. 1 " ' I assumed such an aeroplane with its load to weigh 1,000 lbs., and its passengers and other principal masses to expose together 20 superficial feet area to normal pressure. The charts indicated that this machine would absorb, approximately, 35t-h.p. to enable it to travel the air at 40 m.p.h. Of this total— Skin friction absorbs ... _. ... 2j-h.p. The load absorbs ... .. 20 „ Normal pressure absorbs .. .. 13I ,, But, for increase of speed the chart discovered that the increase of power required to overcome normal pressure is very unfavourably dispropor tionate ; for, at 90 m.p.h., Skin friction will absorb ... .,. 15 h.p. The load will absorb — — ... 45 „ Normal pressure ... ... ... 120 ,, ... 180 ,, + ! « + 0-667 o-333|o-36o o-6oo 0-40010-391 0-556 0-44410-408 o-5ooo-5oo;o'444 0-4280-572^-492 0-3330-66710-552 0-2000-80010-693 O |l I -O-20OI-20o!l-56 -o-333i'333;2'24 -0-428 1-42813-05 - 0-500 t -5004-00 -05561-5565-08 -o-6oo 1-6006-25 —0-667 1-6679-02 0800 0-750 0-718 o-666 o-6oo 0-500 °'333 0 -0-5 1 -i'S - 2 -•3 -3 i-4 — 00 137° 3'4Q 3-00 iz'43 1-647 1-253 0'02 0"04 0-06 o-i 3H2 3-i3 2-76 J3-47 |3-22 2-90 i 2-40 11-653 3-18 2-66 1-99 1455 11-467 1-260' 3'22 2-96 2-67 2-31 1-667 1-275 1-113 i-n8i 2-41 2-27 '•93 i-5°2 1-136 of the variables in his equation for h, as also the value of A itself for various aspect ratios and tangents. As the above table and diagram may be of interest Total From these figures the tremendous potency of tin- normal pressure experienced by the principal masses, as a factor of flight resistance, is evident ; and your insistence upon the necessity for enclosure of these principal masses and upon the importance of the shape of the enclosing body, that high speed may be attained, has the amplest justification! The Crucifer shape combines a hemispherical head and a conically tapering body with a short cylindrical trunk between them. Current aeronautical literature assumes that the experi ments of Colonel Renard, M. Canovetti and others, con clusively establish that this form of vehicle is the best for rapidity of progress through either air or water. But, that the value of the reduction of pressure which may be effected by its employment should be appreciated, the pressure it experiences and that sustained by the normal plane and other forms and combinations of forms of equal cross-sectional area, which were submitted in experiment to direct air resistance, are compared below :— Normal thin plane, 100 ; thin disc, 90 ; cone, base forward, 67-J ; two cones base to base, 18; sphere, 16; Crucifer body, hemisphere followed by short cylinder and cone, 3J. > Crucifer body pressure is seen to be only 34 per cent, of the normal. Therefore were this body, with a cross-sectiona 343
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