Back in the late 1940's, 1950's and 1960's over 9000 turbo compound
aircraft engines were built. They reached a TBO of 3000 hours in airline service.

As far as  turbo compound piston engines are concerned they  are very hard on
exhaust valves and much energy is therefore lost in the exhaust valves. Needless
to say the rotary has no exhaust valves so in theory it would be significantly
more efficient.

Paul Lamar


When my father was a Flight Engineer at United flying the DC-7C, the average time between in-flight shutdowns (on each airplane) was 400hr.

I also had a long conversation with a professor of mine who was a USMC C-119 squadron commander, he had buckets of trouble with the 3350TC, had to get a CW engineer in to consult and teach everybody how to operate the engines, and reliability got to an acceptable level.

It is probably more of a function of that particular design then that of the whole idea of compounding.

The heat efficiencies are just too good to overlook. It's a shame that the commercial GA manufacturers are completely hamstrung by 1) certification costs, and 2) a complete lack of want to change the product.

Jim Tiemann

As I said most of the trouble was with the exhaust valves.
When a valve broke it would take out the turbine blades.
The rotary has no exhaust valves.

Paul Lamar