Paul: Do you have any more info on the Powersport design, regarding the
internal spur gear
Perhaps any drawings on such a redrive
Le Roux Breytenbach
(South Africa)
It has some drawbacks that were recognised in the early 1930's when
Allison first
proposed the design to the US Army Airforce. The pinon or the ring gear
must be cantilevered
or over hung. That leads to undesirable deflections that tend to
increase the critical spacing
between the gears. Much material must be added to stiffen them and
reduce these deflections.
That leads to a extra heavy gear box solution.
The power transmission capabilities of a set of gears is directly
proportional
to the length of the line contact between gears. For a given gear width
a six pinion
planetary is six times stronger than any single set of spur gears.
The vast majority of aircraft piston and turbo prop engines have had
planetary
gear sets. The V12 fighter plane engines were the exception but the
life expectancy was short.
Vee's for Victory quotes.
"Allison was quite adamant about not overpowering the V-171O-C15 engine,
stating that "on account [of] extreme over-load on [the] over-hung pinion at
the higher horsepower's involved" in operating at take off manifold
pressures
up to the critical altitude of the engine. The limitation was not the
bearing, but rather the bending stresses developed in the front cheek
of the crankshaft as a result of the high loads transmitted to the
crankshaft extension carrying the pinion gear. "
"With the opportunity to completely redesign the engine
following the, Type Test in 1937, these features were incorporated in
th, "E"
and "F" series engines, which used straight cut "external" spur gears. As
developed, the ElF design followed closely the 1935 concept, and resulted in
lighter and more compact reduction gears than the original "c" gear set.
This
created a higher "thrust line" that reduced frontal area. "
Paul Lamar
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