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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
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...
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This document was uploaded on 01/19/2014.
- Winter '14
- The Land