§ 31. The following are the chief particulars of this interesting machine:—The engine is a four-cylinder one, and weighs (complete with double carburetter and petrol tank) 5½ lb., and develops 1¼ H.P. at 1300 revolutions per minute.
Fig. 22.—One-Cylinder Petrol Motor.
(Electro from Messrs. A.W. Gamage's Aviation Catalogue.)
The propeller, 29 in. in diam. and 36 in. in pitch, gives a static thrust of about 7 lb. The machine has a spread of 8 ft. 2 in., and is 6 ft. 10 in. in length. Total weight 21 lb. Rises from the ground when a speed of about 16 miles an hour is attained. A clockwork arrangement automatically stops the engine. The engine air-cooled. The cylinder of steel, cast-iron heads, aluminium crank-case, double float feed carburetter, ignition by single coil and distributor. The aeroplane being 7 ft. 6 in. long, and having a span 8 ft.
§ 32. One-cylinder Petrol Motors.—So far as the writer is aware no success has as yet attended the use of a single-cylinder petrol motor on a model aeroplane. Undoubtedly the vibration is excessive; but this should not be an insuperable difficulty. It is true it is heavier in proportion than a two-cylinder one, and not so efficient; and so far has not proved successful. The question of vibration on a model aeroplane is one of considerable importance. A badly balanced propeller even will seriously interfere with and often greatly curtail the length of flight.
§ 33. Electric Motors.—No attempt should on any account be made to use electric motors for model aeroplanes. They are altogether too heavy, apart even from the accumulator or source of electric energy, for the power derivable from them. To take an extreme case, and supposing we use a 2-oz. electric motor capable of driving a propeller giving a static thrust of 3 oz.,[23] on weighing one of the smallest size accumulators without case, etc., I find its weight is 4½ oz. One would, of course, be of no use; at least three would be required, and they would require practically short circuiting to give sufficient amperage (running them down, that is, in some 10 to 15 seconds). Total weight, 1 lb. nearly. Now from a pound weight of rubber one could obtain a thrust of pounds, not ounces. For scale models not intended for actual flight, of course, electric motors have their uses.
CHAPTER V.
PROPELLERS OR SCREWS.