Bill wrote:

How many R 912s have been run to TBO in the whole world?  I'd guess it is about
0.01% of the LyCon GXX-YYYs that have been and the gearboxes give problems.  This
does not mean that all gearboxes will give trouble, but I like the extreme
simplicity of direct drive.  Like Perry says - flying around with 3 moving parts
has a certain attraction.  Perry actually isn't counting the water & oil pumps, but
an aircooer would actually be 3 moving parts + the oil pump.  Parts that are not
used are free, never break or wear out, and weight nothing.  I like that.  A direct
drive air cooled rotary is by far the mechanically simplest realistic engine EVER.

Sure, the absence of parts is a good thing, in general.  But remember that making
decisions based on statistics is fraught with peril, and making decisions based on
MISUNDERSTOOD statistics is just plain dumb.

Fact: Every commercial passenger-carrying jet airplane flying today is using not one,
but *several* gearboxes in the engines.  You don't see them falling out of the sky
because of gearbox failures, do you?  What are the possible conclusions?

1. "LyCon GXX-YYY" drivers are not following proper engine management techniques for
their geared engines (and presumably the ATPs are).
2. "LyCon GXX-YYY" gearboxes are not as well built as P&W or RR gearboxes.
3. "LyCon GXX-YYY" engines are not well suited to drive gearboxes, but P&W and RR
engines are.

I say it's all three to an extent.

Russell Kent

The turbo jets do indeed have problems with the gear boxes. They need to be changed
far more often than the engine itself. I think Mark Wrathal may have some
hard data on that. Besides that, torque from a gas turbine is steady and that
from an intermittent combustion engine is well.....intermittent :-)

Now here is where we have an advantage. Torque from a two rotor is smoother
than a four cylinder and we are using rubber isolators between engine and
gear box unlike a lot of geared A/C engines that were and are direct drive.

Vance just sent me this little tidbit :-)

"I have always been fond of a statement made by John Bolster regarding British hill
climb and trials cars - "an ounce of rubber is often better than a pound of
engineering" - Vance"

Paul Lamar
 
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