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Aviation History
1912
1912 - 0293.PDF
MARCH 30, 1912. A I-H.P. PETROL MOTOR FOR MODEL By GEORGE BRENT. MANY attempts have been made to produce a reliable, vet sufficiently light, small motor for model aeroplanes but mostly without any degree of success, owing, no doubt, to the trouble of getting small working parts sufficiently light and at the same time reliable. The engine described herewith has been in constant use for several months, that is, it has had several runs every week, sometimes running every night; usually a run lasts about twenty minutes. As the accompanying drawings and photographs show, the engine is of the four-cycle, horizontal opposed type, having two east-iron cylinders of ij in. bore and ijf in. stroke. Each cylinder is cast in one piece, and as the engine is air-cooled, they are east with radiating fins. One b.h.p. is developed at 1,500 r.p.m. and the total weight of the engine, petrol tank and propeller is 7A lbs. In preparing the design of these motors, it was decided to "follow, as far as possible, the lines of similar full-sized aero motors. The pistons are similar to those used on large aero motors and are fitted with two rings ; the crank-shaft is turned out of two-inch special bar steel, and is carried in two phosphor-bronze bearings. There is no special feature about the connecting rods, these being of tin- standard type, but very strong and light. To enable the two cylinders to be exactly opposite one another, the connecting-rods are off-set in the pistons and are connected to the latter by gudgeon- pins. The aluminium c.ank-case is extremely simple, being cylindrical and vertically divided. The inlet valves are automatic, the exhaust valves being mechanically operated ; the cam-shaft is driven from the main shaft by two-to-one gearing. To assist the exhaust, and also the cooling, small holes are drilled round the cylinder in such a position that when the piston is at the inner end of its stroke, these holes are uncovered, thus permitting the hot exhaust to escape, and so relieve the amount passing through the exhaust valves. The commutator is also driven off the cam-shaft as shown in the drawing. No distributor is fitted to the commutator, as small ones are some what troublesome and very light coils are now obtainable at a reasonable price. The petrol tank is made of copper in stream-line form, and is usually fitted to the back of the crank-case, thus reducing the head resistance, but if desired it can be fitted in any other position. The action [/UGHf AEROPLANES. of the carburettor can be easily seen from the drawings ; it i> of the surface type and much simpler, lighter and quite as efficient as the spray type. Specially light and simple sparking-plugs are used that give very little trouble. The propeller is somewhat 001 of the ordinary having been specially designed for these engines, and patented. They are made entirely of aluminium and have a variable pitch, this lieing easily obtainable as the blades are graduated to that any desired pitch, within certain limits, may be given at once. They are made in four sizes, namely :— 15, 20, 25 and 30 ins. diameter. The results of a series of tests on a 30 in. propeller are shown on the accompanying diagram, and from it the thrust at certain speeds with a certain pitch can lie obtained. Taking the engine running at 1,540 r.p.m. with • pitch of 15 ins. the thrust comes out at (»| lbs., or moie than the weight of the motor and accessories. The designci of this engine is a Mr. W. t;. Jopson, a member of the Manchester Aero Club. Improvements are still being carried out with Ihis engine, and the designer hopes to reduce the weight by 1 lb. and still have sufficient Sectional elevation of the 1'b.p. petrol engine fcr models described by G. Brent. The disposition of the petrol tank and wtck carburettor is particularly noteworthy. It will be seen that metal journals are provided for the crank-shalt, which Is turned out of 2-in. bar steel. strength. (Ini' of these engines has been run for one hour, and it is proposed fo fit one to a quarter scale model Farnian, which the designer is constructing. The makers of these motors arc Messrs. Cook and Co., Standard Works, Altrin ham, Cheshire. TMRU5T T£S75 AtKlAL PGOPi'LLEK The interesting horizontal-opposed petrol motor for mcdel aeroplanes described by G. Brent. The top photograph shows the halUpeed shaft and the arrangement ot the valve mechanism. This engine is air cooled, develops 1-b.h p. at 1,500 r.p.m., and weighs 7£ lbs., including petrol tank and propeller. The bottom vi-w shows the engine 9 v propeller in situ. Ig 8" 1- * - u / 1 / > t / <^ / ^ / / 7* ; ~~] 1 A 1 / ' ' 1 1 I A / / 1^--—• AT iS40WPr _^^-H 1 \ fV 1020 ft PM • AT bttO EPfrl \ \ PITCH a, BLAOe&(iNtHES) iJiagram cf results obtained from tests of the 1 b.p. model petrol metor described by G. Brent, shewing the thrust in lbs. at varying speeds with propellers of different pitch. 293
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