"Corky Scott" wrote in message
...
On Wed, 03 Dec 2003 02:05:35 GMT, Roger Halstead
wrote:


The life of a PSRU on a piston engine has to be complicated. It not
only has to handle linear torque and thrust, but virtually any other
imaginable angle as well. Then it has to be designed to avoid any
resonances with those power train pulses AND take the positive and
negative torque without beating the snot out of the gears which means
next to nothing for slack (which brings its own set of problems).
Helical, double helical, spur, planatery...each with it's own set of
pluses and minuses.

Most manufacturers seem to take the attitude that big is strong and
bigger is stronger. In order to resist the impulses and resonances
you mention, they just design huge gears to take the load.

BUT, didn't the big 12 and 16 cylinder Vs in WWII have PSRUs? Course
those engines had very short TBOs too. Then again they weren't
exactly babied either.

Yup, the Roll Royce Merlin uses a spur gear reduction drive, driven
off a torque tube. Those gears are some big. Every single one of the
big radials also used a reduction drive, but was a planetary type, not
spur. I think the low TBO was more due to the nature of the treatment
of the engine during combat than something inherent in the design.
But come to think of it, they still don't have a very high TBO even
now, when they don't have to be run up to military power for every
takeoff.

By the way, the Rolls Royce Griffon engine was sort of two 12 cylinder
engines siamesed together for a total of 24 cylinders. I'd hate to
work on that thing.

Also...How did the guys make out using the Olds chain drive in the
Legend? It "appeared" to work great for at least a short time, but
they were running 400 to 500 HP through a chain that was used in a
drive train that only had about 200 HP on the other end. When I
talked to the one guy at Oshkosh some years back he thought it had
plenty of reserve.
I always like that airplane. Last I saw it had a turbine up front.

Sorry, that should be NSI.

I know when he used the original "so called" chevy big block aluminum
based engine he felt the front web was the weak spot. Course that was
right after planting his IV_P off the end of the runway when the web
broke. (or did he make it back on that one?) At any rate the web
broke and it was a high pucker factor.

I hadn't heard that the web broke. The story I got was that they did
some computer analysis of the engine design and factored in the prop
forces that would be transferred to the block by the PSRU and decided
to add material to the block where the PSRU bolted on. Of course, Jim
could have told me this AFTER the engine broke, don't know.

Corky Scott
Corky,
Sorry, but the Griffon was a V-12 like the Merlin, just BIGGER:

http://www.home.aone.net.au/shack_one/rolls.htm

Rick Pellicciotti
http://www.spitfire.org