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Aviation History
1912
1912 - 0227.PDF
Conducted by V. E. Scale Models. We herewith give the remainder of Mr. Ernest A. Vessey's communication on this subject :— " Provided that the argument set out in last week's issue is correct, the larger model may be successfully constructed to fill all conditions, provided gold-beater's skin is used to cover the planes, any difference in finished weight being made up by a compensating weight placed within the wing structure and with its centre of gravity coincident with the C.G. of the completed supporting surface. Supposing now that we wished to construct the smaller model recommended by Mr. Lanchester (two models being suggested, viz., £ and ^ full size), it is at once apparent that the only course open is to modify the internal structure oj the planes so as to compensate for the increased relation weight of the fabric. Theo retically this causes no serious difficulty, but in practice the question of strength and rigidity immediately becomes prominent, and the adjustment between the latter factors and the weight form a problem not easy of solution even by a process of trial and error. " For the sake of argument, let us suppose that the fabric used in the model is sufficiently strong and rigid to allow of planes built of it alone without any internal spars or framework whatever. Let us select mica, as used in the Lanchester gliders, for our fabric. This is about one-thousandth of an inch thick, and weighs approximately \ oz. per sq. ft. Let A = the total skin friction area of the full-size plane. L = the scale of the model in terms of full-size. W = the total weight of the completed full-size plane. Then if A is in sq. ft. and W in lbs. the total model area = AL2 sq. ft. And if mica, as above, is used for the model plane the total AL2 ,., weight = ozs. (2) But by the rule (see last week's issue) the total weight of the model plane must not exceed WL3 lbs. = 16 WLS OZ5. (3) In the limit the expressions (2) and (3) must be equal, i.e., , AL- 16 WL3 = . 4 A , . whence L = 64 W (4) by substituting known values for A and W the minimum scale allowed by this method of construction may be found. I have, unfortunately, not been able to obtain reliable values of W, but no doubt some reader of PLIGHT can supply them. It will be suffi cient, however, for the present purpose to find the value of W (total weight of the full-sized aerofoil), which permits of a T\, scale model being built on these lines ; assuming that the support ing surface is 200 sq. ft., whence A is 400 sq. ft., substituting these values in equation (4) we have ^ = j= w' wnence ^= I0° ^s-> which is, without doubt, considerably in excess of the weight per missible in a machine of this size. Assuming, however, that this value of W agrees with practice ; let us consider the strength of a model aerofoil constructed of mica in the manner described ; the scale of the model being T\; full size. The span of the full-sized JOHNSON, M.A. counterpart would probably be about 32 ft., whence the model span is 2 ft. Could such an aerofoil be constructed in the manner described, to tie of sufficient mechanical strength to support the model in flight, apart altogether from the consideration of the effect of landing shocks and collisions ? Obviously, no. We, therefore, arrive at the following conclusions. That if a model is to be built, which in flight will reproduce the performance of its full-size counterpart as regards everything except s]>eed, the smallest permis sible scale is ^ [1 to I, V.E.J.] full size, and that in such a model the best wing construction is a framework true to scale and following exactly in every detail that of the full-size machine. This apjiears to me to be a rather unexpected result, and one which will bear discussion. Inter-Club Contests. A suggestion has l>een made to us which, we must say, appears to be an excellent one if it can be successfully carried out, and there certainly seems no valid reason why it should not. It is that there should be this season a series of model club flying contests in very much the same way that we have annually cricket and football matches between, we suppose,-—reckoning both large and small— some thousands of different teams. True, there are not at present thousands of model aeroplane clubs in existence—there are quite a respectable number, however ; fully thirty at least, which are capable of putting a good team in the field ; quite a large enough number to commence with. Provincial footballers and cricketers think nothing" of running up to Town from Birmingham, Manchester, Sheffield, Liverpool, Bristol, &c, and even Edinburgh and Glasgow ; or Londoners of travelling so far afield as the above-mentioned places ; then why not aeromodelists ? According to the accounts which appear in our club notices, we have some decidedly " crack " flyers in the provinces, and it would be intensely interesting to see if they could or could not hold their own against some of the best London clubs. There is no question of prizes. A cricket team doesn't go from Yorkshire to play a team in Surrey for a. frize—but for the love of the game and the honour of winning. There might, of course, be a cup, or something of that kind, for the winner of the most inter-club contests at the end of the season. Will the secretaries of the London and also of the leading provincial clubs kindly communicate their views to us on this matter ; and if we can do anything to further such a scheme we shall only be too happy to do so. The Bragg Smith Mcdel Biplane. We publish this week two illustrations of the simplest form of this celebrated model—a form in every way suitable for the novice in model aeroplaning. The total weight of the model we found on weighing to be exactly 95 grammes, and the weight of rubber only 12 grammes, which in itself is a proof of its efficiency. Although the model is lightly built, it is extremely strong, and can be flown time after time without breakage, a fact which should appeal strongly to the beginner. The average length of flight, in the case of this par ticular model, is stated by Mr. Bragg-Smith to be about 100 yards, which is certainly not an over-estimation, and quite sufficient to commence with. We have been given to understand from vendors Two views of Bragg-Smith's model biplane. 227
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