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Aviation History
1913
1913 - 0780.PDF
Edited by V. Some Model Experiments. STEVENS (Upper Tooting, S.W.) E. MK. H. G. V. STEVEN ) sends us the following: "I note in a recent issue of FLIGHT that you desire readeri to send details of any [practical] experiments they may have made. In a previous communication I mentioned that I was then carrying out some experiments with a steam aeroplane plant, and that when these experiments were completed I would send you par ticulars. The following is a brief description of the plant :— Engine, single cylinder, double acting, slide valve, # in. by $• in., df gunmetal, ordinary marine type, but lightened ; weight ioj ozs. Boiler, flash type, 8 ft. of A-in. brass tubing, coiled in a spiral and fired by an oidinary petrol lamp, home made, weight 2% ozs. The water container of tin [i.e., sheet iron tinned] supplying water to the coils under a pressure of about 50 lbs. per sq. in. Total weight, ready for running, 1 lb. 5 ozs. " As you see, 1 made a big mistake in using brass tube for the boiler coils, which, of course, quickly burst, after a thrust of about 4 ozs. (on a normale type propeller, 16 ins. in.diam. and 20 ins. pitch) was obtained. On substituting steel coils for the brass and using a highsr air pressure, I obtained ultimately a thrust of 12 ozs. on several occasions; theoretically sufficient for 331b. model; but this, in my opinion, in view of later results, is nothing like enough. At any rate, on obtaining this thrust, I made a suitable monoplane for the plant, canard type, 5 ft. 1 in. span and 4 ft. 2 ins. length, total surface 588 sq. ins., loading 12 ozs. per sq. ft. Total weight 3 lbs. 1 oz. After several fires due to the too close proximity of the lamp and coils to the wooden frame or fttse/aqi; I got several fairly good runs up a garden path, and judged that it would be worth while taking it to an adjoining common and testing it, minus wings, to get an idea as to its running speed and thus determine if it would be worth while making wings. This was done, and the model made several exciting trips up and down a gravel path ; bumping about terribly (the chassis was unsprung). The speed was perhaps 12 miles an hour, insufficient for flight—I would advise a thoroughly sprung chassis on power models. Such is a very brief account of my experiments, which extended over some four months, working in spare time. The lamp was especially troublesome. I hope soon to start a new plant, and shall use a much stronger and lighter engine, together with a more powerful generator. I think that unless a model is fitted with a plant capable of giving a thrust of quite half its weight it is useless to expect good results. "In a series of tests with rubber models I have noticed that the thrust of the propeller was far in excess of one-quarter their weight, indeed in a model weighing 4 ozs. the propellers gave a static thrust of over ih ozs. When the power was reduced so that each propeller gave only £ 01. thrust, the model refused to lift from the ground and Ry.'f Referring to the above very interesting experiments Mr. Stevens certainly made a great mistake in not testing his model in the open when fitted with wings. The fact that the plant would drive the unwinged model along more or less bumpy ground at a velocity less than the flying speed, is no criterion that the complete one would not have risen off a good and level surface. It is the air lift on the wings which, by reducing the ground friction, permits the model to accelerate and ultimately fly. Off a good surface, given a really efficient model—efficient, that is, in possessing minimum head resistance and maximum lilt—a static thrust of one quarter the total weight of the model is sufficient to cause it to rise. I say nothing about rapid climbing, but it will fly it. Mr. Stevens will find a pump feed far preferable to a pressure one, being, when properly adjusted, practically quite constant; it is also less in weight, since the water reservoir can in this case be made extremely light The type of engine and valve (rotary) used by Mr. H. H. Groves is also tetter suited to aeronautical work, although it is most interesting and instructive to know what can be done with other types. Mr. R. V. Tivy also writes : «' I have for the last six months been building and testing a 20-01. rubber-driven model with 'Weiss' wings. I hnd it is impossible to get any but short flights out of this model, as a rubber drive does not lend itself at all to scale models I am now having a steam engine built (of which you shall have particu fen in due course), and shall be very fortunate if I get any flights before the M. E. Exhibition. '" Thus M m will take me a year to carry out, and you can hardly expect to have your columns filled with the results of JOHNSON, M.A. such experiments. Everyone I know who is anxious to do experi mental work has practically no spare time at all. " Referring to the description of my Olympia model, the action of the automatic cambering tail is rather too complicated to be described, and I am fitting a somewhat similar tail to the ' Weiss' model I am exhibiting next October at the M.E. Exhibition, when those of your readers who are interested will be able to examine it." Some Suggested Experiments with Models. We publish an illustration (from a photograph) of the machine flown by Mr. G. P. Bragg-Smith, in the K. and M.A.A. weight- carrying competition. The total weight (including 4 ozs. dead weight) was if lbs. ; span, 52-5 ins.; length, 54 ins. ; chord of upper main plane, 8 ins. ; of the lower curved plane, 6 ins. ; the lower plane being given an increased camber in order to equalise the lift on the two planes. The propeller had a diameter of 19 ins., and the blade area was considerable. Elevator dimensions, 18 ins. by 3 j ins. ; distance between trailing edge of elevator and leading edge"of top main plane, 27 ins. ; distance of propeller from trailing edge of same, i2-5 ins. ; gap in centre, 8'S ins. The most interesting item by far about the model was the arrange ment of the planes, which, instead of being staggered in the usual manner, were so arranged that whilst the entering edge of the top plane was two inches forward of the entering edge of the lower, the trailing edges of the two planes were in the same vertical plane ; Mr. G. P. Bragg-Smlth's weight carrying model. the lower plane being given, as already stated, an increased camber to make up for its lesser area. The designer claims for this arrangement that it has all the advan tages of the staggered form of planes, without some of the latter's disadvantages. The manner in which the air leaves the planes, as is well known, is of the greatest importance—much more so, in many respects, than the manner in which it impinges on it; and it will be noticed in this arrangement the air leaves both planes in the same vertical plane, just as in ordinary biplane with non-staggered planes. Now, here is an experiment which any reader of FLIGHT who can build a decent model can carry out, and the results would not only be interesting, but quite possibly of value in full-sized practice, viz., to build three models (some 4 ozs. to 8 ozs. in weight), all biplanes, and all exactly similar—save that in one the planes are non-staggered, in the second model they are staggered, and in the third Mr. Bragg-Smith's arrangement has been adopted. Having built the models, submit them to a series of tests in actual free flight, and note carefully each flight re steadiness, stability, gliding angle, duration, &c. The type chosen need not necessarily be that illustrated in the photograph, which is patented, although we do not think the inventor would offer any objection to the building of such for an experimental purpose of this character. The models would, of course, require to be very carefully built with constant recourse to the balance to see that the various items not only looked equal but •were actually so. The same propeller could be used on each model and the rubber motors interchanged, and various other precautions 806
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