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Aviation History
1910
1910 - 0102.PDF
l/LJGHf) MODEL DRAWINGS. [334] Could you, or any of your readers, advise me where I could obtain the working drawings of a Wright aeroplane and a Bleriot monoplane (models) ? Also the necessary materials for building same. I should prefer models of about 4 ft. span to be driven by elastic motor. Trusting you will be able to oblige me, as I am a constant reader of your excellent paper, FLIGHT. Canterbury. E. S. FLYER EFFICIENCY. [335] In vour issue Vol. I, p. 804, you publish a very interesting letter by Mr. Evans on "The Analysis of Flyers," in connection with which I should like to make one or two remarks. Mr. Evans considers the efficiency of a machine as (h.p. x sq. ft.) per lb., and obtains some very interesting figures by so doing; but I do not think we should consider the efficiency without taking the speed of the machine into account, and in connection with which I think the following table which Ihave worked out will be of interest:— FEBRUARY 5, 1910. TWO CORRECTIONS. [336] In your issue of January 15th, p. 37, theoretical efficiency is given = V-*- (V- 0-57;): this should be V -4- (V + 0-5 v). In January 22nd issue on p. 59 the momentum imparted down- wards to the air is given = breadth of plane x L x density x V» sin a. g Here evidently ' L' is a misprint for ' /.' Regent Street. A. G. H. [We thank our correspondent for drawing attention to the mis print in our article on Propellers. The efficiency should be as stated in the above letter. The other correction relates to an article by Messrs. J. P. Chittenden and L. H. Robinson, but it is- obvious from the context that the above correction is again in order.—ED.] DIHEDRAL ANGLE. [337] My idea of the solution of this problem is as follows :— The pressure on the planes must be at right angles to them, there fore the resultant force must bisect the angle, thus there is no- Name. Antoinette Bleriot ... Cody Curtiss ... Dutnont ... Farman ... Voisin Wright ... d sr .s Ar e 36S lbs . _c We h.p . 1,21050 JS m. p 42 150 7IS2545 780 2,200 80 43-8 272 7103047 115] 4023°4° 4201,3825037 4451,1505031-5 5381,2002539 S per £ 6i-8 66 62-7 69 Speed. Where Attained. Rheims, Aug., 1909 English Channel, July 25th, 1909 Aldershot, cross country Rheims, Aug., 1909 58-6 St. Cyr * 1 s : • fl iZ Mhra- fe ll i* 1 HP n 1,0401,210 4-08 484; 7151258 — 2,20O 2"2I 550 710 6-oo 242 402 6-8i 54 iRheims, Aug., 1909 1,2121,382! 3'56 46"2!Rheims, Aug., 19091 9801,150 2-39 57 |Rheims, 1909 (Tis- 1,030 i,2Co! 5'10 sandier) 1 I 1 These results have been based upon the following argument. The efficiency of a flying machine will vary directly as (1) the total weight supported, and (2) the speed of the machine; and inversely as (1) the area and (2) the h.p. So if— JJ = the efficiency of machine W = total weight in lbs. S = speed in ft. per sec. A = area in sq. ft. h.p. = horse-power TU W x S Then— -q — t— A x h.p. This efficiency is not, of course, the actual dynamical efficiency of the machine, for this can only be obtained by knowing the exact gliding angle of the machine in still air ; but it is a true efficiency of performance, and it shows whether the design is economical in power or not. From the last column it will be seen that the Bleriot comes out top by a long lead, which is just the same result as Mr. Evans got from his formula ; whilst the next three are fairly close togelher, and form a very interesting group, as they consist of one monoplane and two biplanes ; but as to why the Bleriot should give this remarkable high figure I leave to future discussion. Winchester. W. S. FLIGHT. [These tables of efficiency that various correspondents have sent us are extremely interesting, and contribute a great deal to the really serious theoretical side of the problem. We are for the moment publishing these tables and their accompanying letters without detailed comment, because we wish them to be, as we feel sure they are, attentively studied by others, from whom in turn we hope to receive further opinions and calculations. The deduction made by our correspondent as to the relative efficiency of the Bleriot is noteworthy, and without presuming to have in any way thoroughly investigated all the points of the table, one fact is prominent—viz., that the Bleriot is the only monoplane included that does not embody the dihedral angle in the design of its planes. Only quite recently we heard a prominent aviator give expression to his personal opinion that whatever merits the dihedral angle might possess, efficiency was certainly not one of hem. We merely mention this point as it would be interesting to ave the opinions of others on the same subject, especially in view f the figures given in the above table.—ED.] righting couple due to the dihedral angle itself, as has been explained. My theory is that the dihedral angle is a simple method of raising the centres of pressure c and d. The effective area of A and B is equal to a horizontal plane, e,f, thus when the dihedral angle tilts over, the weight, W, acting vertically downwards, brings weight to g, thus gf being greater than g e the plane must tend to right itself. I think the dihedral angle is not so efficient as a horizontal plane, as the area of A and B is greater than area of e f for the same support, thus causing greater skin friction and weight. Poplar. G. E. PAGE. P.S.—Could any reader kindly give me the pressure on a curved surface at an angle of incidence of 12° as a fraction of pressure at 90°, and say if this is too great an angle for gliding ? SURFACING, BY ROBERT-BAILLIE GALT. [338] Referring to the above method of fixing the canvas, &c.T to framework for planes, wings, tails, &c, p. 67, January 22nd, it is certainty the best I have yet seen suggested ; but there is one item in the description with which I disagree—i.e., the last paragraph, " most cloth will stretch when wet," &c. May I suggest that while calico, canvas and similar fabrics really seem to stretch when wetted, and to have shrunk when again quite dry, the actual " stretch " is almost infinitesimal. What happens is, the individual strands (both warp and weft) actually swell when wet, and the whole piece seems to stretch, and if nailed on or otherwise fixed in that condition the surface will assume the normal condition of the fabric, and when dry become loose and " baggy " between the fixings. In fact, the same result is found with an ordinary clothes-line, which while quite " taut" when wetted, becomes loose and " swingy " when quite dry. With your permission, Sir, and an apology to Mr. R. B. Gait, I beg to submit the following remedy for "bagging," which Ihave always found most satisfactory. By all means wet the fabric, but instead of "normal" water, dissolve half-a-pound of " papering size " in " hot," not "boiling," water, and when nearly cold add sufficient cold clean water to make up one gallon in all. Then "completely soak every portion of the fabric for a few minutes in the mixture, wring as dry as possible, pull out flat, stretch and fix as advised by your correspondent, and I feel sure that if carefully strained and nailed or sewn the result
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