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Aviation History
1914
1914 - 0205.PDF
If your lubricant contains any grease or vaseline, it will, of course, quickly ruin your rubber. Harmless recipes have been given in back numbers. The rubber must be well lubricated. After you have been out flying your model, remove the rubber and keep it in an air-tight tin. Never leave it in the sun any longer than you can help. Keep the tin in a cool place. Use valve tubing over your rubber and propeller hooks. You get rather better results weight per weight with strip than square-sectioned rubber, but the writer's experience is that the latter is more durable. Don't join your rubber by tying knots in it, but by means of thread. Overlap the two ends for about an inch, get someone to pull or stretch these as far as possible and tie •when stretched. Trim the ends with a pair of scissors. A Large Triplane Model. A correspondent, Mr. L. S. Wyatt, sends us the following interesting particulars of a somewhat uncommon type of model. The model is all steel except the motor rods, which are bamboo. Chief dimensions : Total length 40 ins., span 01 main plane 30 ins. of the volume referred to is a veritable mine of information con cerning all sorts and kinds of experimental scientific apparatus, which cannot fail to be of the greatest use to anyone carrying out any scientific work, no matter of what kind. How to Determine the Static Thrust of a Propeller. A correspondent writes asking the best way to ascertain the above. One of the best is probably the following : Mount the propeller on the shaft of an electric motor, of sufficient power to give the pro peller up to 1,500 r.p.m. if of fine pitch. If coarse, say half that number ; a suitable accumulator or other source of electrical energy will be required ; also a speedometer or speed counter, as well as a voltmeter and ammeter ; a stop-watch is also very useful. Place the motor on a pair of scales or on a suitable spring balance (the former for preference), the axis of the motor vertical, with the propeller attached. Rotate the propeller so that the air current is driven upwards. When the correct or desired speed (as indicated by the speedometer and a watch) has been attained notice the difference in the readings if a spring-balance is used, or, if a pair of A few of Mr. L. S. Wyatt's models. Chord 4-5 ins. Gap 4 ins. Elevator, span 12 ins., chord 3*25 ins., gap 3 ins. Propellers 10 ins. in diameter and 22-inch pitch. Middle plane set at negative angle ; the others at a slight positive angle of incidence. Motors, twin gear of 12 strands of J-inch strip rubber ; centre of gravity 2 ins. in front of the leading edge of the main planes. Average flight 150 yards off the ground. Weight I lb. 2 ozs. The model is very stable and flies quite straight. Mr. Wyatt also sends the following particulars of another triplane constructed by him : Length of fuselage 38 ins., A-frame design, material bamboo. Span of two top planes 30 ins., of the lower 22 ins. Chord 475 inches. Double elevator 12-5 by 3^25 iins. The trailing edge of the elevator is mounted on two wire bridges, the front pair of uprights being carried down through slots, for elevation purposes. Diameter of propellers 10 ins., pitch 22 ins., each worked by J-inch gear wheels. Four strands of ^-inch strip rubber to each wheel, making 16 strands in all. Weight 15 ozs. As in the other model, everything is steel save the motor rods. The wheels are turned from solid blocks of red fibre. Four of them weighing J oz. The model rises after a run of about 15 ft. and flies rather low for an average distance of 100 yards. I am fitting floats for trials off the river Ouse. This is my 25th successful motor. Aero Silk for Models. We have received from Mr. G. P. Bragg-Smith some samples of his latest aero silk fabrics for models. Mr. Smith informs us that Mr. Louch, whose model made the as yet unbeaten records of 2 mins. 49 sees., was covered with this fabric, and that it is also used by Messrs. Slatter, Houlberg, and several other record holders. Personally, the writer has almost invariably used one of these fabrics, and found them perfectly satisfactory in every respect. We certainly know of none better. Messrs. J. J. Griffin and Son's Catalogue. The above firm, of Kemble Street, Kingsway, London, send us a copy of one of their catalogues of scientific apparatus. The book, which consists of over 1,000 pp., and an enormous number of illus trations, is entitled " Scientific Handicraft," and deals fully with all kinds of scientific physical apparatus as well as tools. As we have before remarked, the science of aeronautics is so intimately bound up both in theory and practice with the other physical sciences, that a more or less intimate knowledge of other branches besides those of an aerodynamical nature are essential if real progress is to be made. The only real, safe and sure knowledge is that founded on experience, based on experiment. For experiments we must have apparatus either purchased or home made. In the pages scales, place weights in the scale pan until the downward thrust of the propeller is exactly balanced. This gives you the thrust in ounces or pounds. Note carefully the voltage and amperage. Let us suppose the former 8 and the latter 10 = 80 watts ; remove the propeller and note carefully the number of volts and amperes consumed in running the motor alone ; that is, to excite itself and overcome friction and air resistance, suppose this to be 8 volts and 2 amperes = 16 ; the in creased load when the propeller is on is therefore 80- 16 = 64 watts. All this increased power is not, however, expended on the propeller. The lost power in the motor increases as C2R, where R is the resistance of the armature and C the current. If we deduct 10 per cent, for this, then the propeller is actually driven by 56 watts. Now 746 watts = 1 h.p. .• number of revs, per min. ® KITE AND MODEL 56 746 = A p" aPProx at the observed ® • ® ® AEROPLANE ASSOCIATION. Single screw, hand-launched Duration Twinscrew, do. ... £~ Single screw.rise off-ground. gjf^™ ™nscrew,do Son Single-tractor screw, hand- f Distance launched \ Duration Do. Off-ground gfe Single screw hydro., water Single-tractor, do., do. Twin screw, do., do. Official Notices. British Model Records. D. Driver... R. Lucas ... G. Hayden off ff "1 " [-Duration Duration Duration W. E. Evans W. E. Evans L. H. Slatter J. E. Louch C. C. Dutton J. E. Louch C. C. Dutton J. E. Louch L. H. Slatter C. C. Dutton L. H. Slatter 85 sees. 590 yards. 137 sees. 290 yards. 64 sees. 365 yards. 2 mins. 49 sees. 266 yard*. 91 sees. 1 190 yards. 94 sees. 35 sees. 29 sees. 60 sees. Gift of Trophies.—The Council desire to thank the President and his wife (Sir John G. Shelley and Lady Shelley) for their gift of valuable trophies for competition during 1914. Sir John's is for power-driven aeroplanes, and Lady Shelley's is for power-driven hydro-aeroplanes ; both trophies are to be won outright, and are not challenge trophies. They will be on show at Olympia. Kite Section.—The committee of the Kite Section desire to thank Major B. Baden Powell for the gift of a kite winch And cable for use with the No. 1 Section of the Volunteer Kite Squadron. 'Wellcome Scientific Expedition.—A letter has been received from the Sudan stating that good kite work has been done by a member of'the expedition, and some very interesting photographs, &c. have been obtained. Fuller details will be published, and a lecture given, if possible, on his return to this country This will be interesting news to the Kite Section. Aero Show.—As a great number of letters have been received on the loading question, the Hon. Secretary wishes to state for the guidance of exhibitors 205
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