An all aluminum 20B should be about 300 pounds. P-port with turbo
should give an easy 600HP. To get a higher HP capability gear box
I would use the Allison HT 640/HT 650 series planetary with approximately
3.5:1 ratio. This transmission was designed for use in 5 ton trucks
and buses. These transmissions are readily available and so are spare
parts. Probably a lot cheaper than the helicopter PSRU. The design
would mimic the current Ross/Tracy box with dimensions changed
to accommodate the Allison part dimensions. The weight should be
close to the helicopter box and the length should be similar.

Dale Davies

The helicopter box is surprisingly light with magnesium castings
at only 45 pounds..

The drawback is; it is $30,000.

Paul Lamar


Dale,
 Do you know which planetary of the Allison has the 3.5:1 ratio ?
Kelly Troyer


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