History of aicraft piston engines

It is standard on the douglas dc 7 and the lockheed

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ol the air after leaving the supercharger, have been generally used with turbo-superchargers, and with 2stage geared types. Such coolers are shown in figures 64 and 65. The Merlin e ngine (fig. 64) used a water-cooled aftercoolcr w ith its own separate r adiator and circulation system. T he culmination of the supercharger art is represented by the Wright T urbo-cyclone R-3350 engine shown in figure 47. This engine, introduced a bout 1946, has three exhaust-driven turbines geared into the power system, as well as a 2-speed centrifugal geared supercharger. It is standard on the Douglas DC-7 and the Lockheed Super Constellation, the last l arge piston-engine passenger-transport planes built in the United States. Vibration Control P owerplant vibration presents two kinds of problems in aircraft. One is e xternal vibration, or vibration of the power plant with relation to the airplane itself. T he other is internal vibration, that is vibration of parts within t he powerplant. Considerable external vibration from engine and propeller was accepted as normal in the early days of aviation. In my experience it b ecame of concern first in 1920, w ith the Hispano-Suiza V-8 300-hp engine, a l arger version of the original model. This engine, like all V-8s up to that t ime, h ad cranks at 180°, which gave a strong second-order horizontal v ibration. It also had an unusually large torque variation, due to its large cylinders and high mean effective pressure. Pilots complained of discomfort with this engine. A bout 1921 the Wright Aeronautical Corporation, which produced t he 300-hp Hispano engine, built one with counterbalanced cranks at 9 0°, t hus eliminating the horizontal shake. Vibration-measurement at t hat time was in a crude state, and the improvement obtained was demonstrated on the test stand by the fact that, with the 90° shaft, a penny would remain on the crankcase, whereas with the 180° shaft the penny w ould quickly bounce off. T he next test was to mount two engines in similar Thomas-Morse fighters, one with the 180° shaft and one with the 90° shaft. A number of e ngineers ran these engines on the ground, and a number of pilots flew t hem. The consensus was that there was no noticeable difference in vibration of the airplane. Probably, the engine torque variation was so large in b oth cases as to obscure the improvement in sidewise shake. In any case, 73 the 90° shaft was not approved, although it soon b ecame s tandard on V - 8 engines for nonaircraft use. Such was the state of vibration analysis in 1922! R eduction of engine vibration became essential in the e arly d ays of commercial aviation when passenger comfort became important. In this case, radial engines were used. Charles S. Draper and George Bentley m ade a serious study of the shaking forces and movements of radial engines in 1937-1938. One solution lay in flexible engine mounts to reduce the transmission of vibration to the airplane structure. This involved a problem of C t droop" d ue to gravity when the engine was...
View Full Document

Ask a homework question - tutors are online