History of aicraft piston engines

22 f or official definitions of fuel terms including

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Unformatted text preview: es?" He answered in the a ffirmative! 20 O bviously, the sleeve-valve Napier Sabre and the Junkers Diesel also had unconventional cylinder arrangements. 21 A n important contribution to this art in the United States was the development of S tresscoat by E. S. Taylor and Greer Ellis in 1938. This method of showing stress patterns b y means of a brittle lacquer coating had been used by the Germans earlier, but was not used in this country until the work of the above-mentioned persons. Experimental stress a nalysis, using strain gages and photoelastic techniques as well as Stresscoat, has been g enerally used in aircraft-engine development since about 1940. 22 F or official definitions of fuel terms, including performance number, see fuel handbooks published by the American Society for Testing Materials, Philadelphia, Pennsylvania. 23 A s quadron of Martin bombers was the first combat group ever equipped with t urbo-superchargers ( 1923-1924). 24 T he NEC 2-cycle engines of 1909-1912 were equipped with Roots-type scavenging blowers, but these were not superchargers in the sense that they were used for altitude c ompensation. 25 W hen the cooler is used between stages of supercharging, it is called an intercooler, w hen it is used between the supercharger and the engine, it is called an aftercooler. 92 Appendix T he Rotary Radial Engine T he radial engine has been built in two essentially different configurations: t he static radial, which still enjoys widespread use; and the rotary ( rotating) radial, which passed out of use soon after 1918. The former m ay be considered a "conventional" engine, in which the pistons, reciprocate inside the cylinders of an engine firmly a ttached to the airframe. I n the rotary radial, however, the anti-propeller end of the crankshaft is attached to the airframe, and the cylinders and crankcase, to which of necessity the propeller is fixed, rotate around the crankshaft (see figs. 20 a nd 2 1). T he rotary engine functions internally in exactly the same manner as the conventional radial engine, but because of this arrangement the pistons do not reciprocate relative to the mounting structure, and therefore n o unbalanced forces result. Thus, in operation, the rotary engine is exceptionally free from vibration. As mentioned in the text (p. 25), the large flywheel effect of the rotating cylinders was important in relation to the t ype of control system used at the time. T he rotary radial engine shares with the conventional radial the a dvantages of compactness, short crankshaft, and adaptability to air cooling. O n the other hand it has the following inherent d isadvantages: 1. Severe limitations on rpm, resulting from high centrifugal forces c reated within the revolving engine and wind drag caused by the rotating cylinders. 2. Design limitations imposed by the rotation of all parts except the crankshaft. 3 . A n undesirable gyroscopic effect on the airplane during turns. 4 . L imitations on the lubrication system, which, owing to the design of the engine, resulted in high oil consumption and the t hrow...
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This document was uploaded on 01/19/2014.

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