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Aviation History
1913
1913 - 0194.PDF
\ftMn FEBRUARY 15, 1913. AERONAUTICAL ENGINES. Paper read by A. GRAHAM CLARK before the Institution of Automobile Engineers. (Continued from page 130.) The 60-h.p. Sturtevant Engine shown in Fig. 20 and Fig. XI, is in all respects, excepting that of the means by which the water circulating pump is driven, an engine of the standard car type, in which weight has been reduced by the employment of high grade materials. The ultimate tensile strength of the steels used is 56 tons per sq. in., while the cylinders and pistons are cast from semi- steel having an ultimate tensile strength of 18 tons per sq. in. It Fig. 20.—60-h.p. Sturtevant engine. may, however, be remarked that the high brake mean effective pressure indicates that an extremely high compression is used. With regard to the wearing qualities of the engine, it would seem to be desirable for the side thrust on the piston to be taken on bearing rings, rather than on the body of the piston itself. All parts other set, by taking off the leads to the cylinders from two different points on the periphery of the pump case. Steel pistons and cylinder walls are employed, but they are kept from coming into contact with one another by the use of two phosphor bronze bearing rings. It would, however, seem to be preferable to bolt or other wise secure the head to the barrel, rather than to rely upon a thread in cast iron for a part subjected to the full explosion pressure. Bosch dual ignition is fitted ; air is taken by the engine from the crank-case, and the remarks made anent a similar arrangement in the Dorman engine will also apply here. Desirable Qualities in an Aero Engine. Having dealt with the principal features of repre sentative types of engines, the qualities it is either desirable or essential that an aeronautical engine should possess will be considered. They are :— 1. Reliability. 6, Freedom from vibra- 2. High power/weight ratio. tion. 3. Economy in fuel and oil. 7. Accessibility. 4. Low air resistance. 8. Silence. 5. "Controllability." 9. Cleanliness. The need for the first requirement will at once be obvious, as the failure of the engine necessitates the im mediate descent of the machine, if of the heavier than air type, which, should it occur at an inopportune moment may be attended with disastrous consequences. Hence, reliability must be placed above all other considerations. High power/weight ratio and economy in fuel and oil consumption are desirable because of the increased radius of action possible with an engins possessing these qualities, while, in addition, the presence of excessive quantities ot oil in the cylinder is a fruitful cause of irregular firing, and consequently falling off of power. The importance of air resistance becomes more marked with increase in the speed, as the power absorbed in this direction varies as the cube of the velocity ; since many designers are raising the speed of their machines for the purpose of obtaining greater stability, the higher powered engines which result from so doing will render Fig. 21.—60-h.p. Sturtevant engine. subject to atmospheric influences are nickel plated as in the Hall- Scott motors. The 120-h.p. Wolseley Engine is illustrated in Fig. 22, from which the general construction is apparent. It should be observed that provision is made to prevent the diversion of the water into one set of cylinders in the event of a steam lock being formed in the Fig. 22.—120-h.p. Wolseley engine. it necessary that a greater amount of attention shall be paid to the question in the future. It may be remarked in this connection that the horse-power required to propel a fiat plate 3 ft. in diameter through the air is increased from about 6 to over 16 by increasing the relative velocity of the plate to the air from 50 to 70 miles per hour. I98
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