History of aicraft piston engines

Another contribution to reduction of engine vibration

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: mounted at its rear, as in t he case of radials. T here was also the problem of decoupling the several modes of vibration in order to avoid numerous critical speeds. This problem was solved by t he m ount patented by Edward S. Taylor and K. Browne, which has been widely used since. The principle employed is an arrangement of links which h ave the effect of supporting the engine at its center of gravity, although t he actual flexible mounts are at the rear. Otto C. Koppen has used very flexible decoupled engine mounts in light airplanes with good effect since a bout 1939. Another contribution to reduction of engine vibration was t he adoption by Wright and Pratt & Whitney, in the late 1930s, of secondorder rotating weights to balance the second-order shaking component c haracteristic of the master-rod system in radial engines. I nternal vibration of reciprocating engines has been most serious in the propeller-crankshaft system. This type of vibration originates chiefly from the torque variation inherent in piston engines and may be destructive w hen resonance is involved. The Liberty engine of 1917 h ad a torsional r esonant speed of 1900 rpm with the usual propeller. Its rating at 1700 r pm was close enough to cause accessory-gear breakage, as previously m entioned (p. 30). Serious trouble with torsional vibration was experienced in the 1920s in dirigible airships using long shafts between engine and p ropeller. This type of vibration also held back the development of metal p ropellers, to be discussed later (p. 77). A very critical case of crankshaft-propeller vibration appeared with t he introduction of the geared version of the Wright 9-cylinder 1820-cu-in. r adial engine in 1935. This problem was quickly and brilliantly solved by E . S. Taylor and R. Chilton, who developed the pendulous counterweight, which effectively counteracted the principal torque components of the e ngine and prevented breakages in the drive system. The basic concept was that of E. S. Taylor, for which he received the Reed Award in 1936. C hilton contributed the mechanical embodiment. This type of device has been used in large radial aircraft engines ever since, and also in many 74 n on-aircraft powerplants. After the first engines so equipped had been t ested, it was found that these inventions had been anticipated in France, b ut the credit for practical application should go to Taylor and Chilton. I t should also be mentioned that the Packard Diesel engine of 1928 (see p . 59) was equipped with spring-loaded pivoted counterweights designed t o reduce torsional vibration. These, however, could be effective only at one speed, whereas the Taylor-Chilton design was effective over the entire speed range. A nother important torsional vibration problem was that caused by t he gear-driven supercharger rotor. Various types of flexible coupling have b een used in the gear train to avoid serious trouble. F urther consideration of vibration problems is included under the h eading, Propellers, below. Propellers G ibbs-Smith credits the Chinese with first use of the air pr...
View Full Document

This document was uploaded on 01/19/2014.

Ask a homework question - tutors are online