Martin Morgan wrote:

I've been reading a number of comments about how much better an engine would
be "direct drive". While I agree that gearboxes are expensive I would also
say that many successful engines use them without problems.

In Australia the Rotax 912 is certified. This engine gives much better
thrust than equivalent engines because of the gearbox. They spin larger
props slower... I have never heard of a 912 gearbox giving trouble, and
these engines are regularly going to 2 tbo's (2400 hrs) before being worked
on (and then not the gearbox!).

Personally I am happy to use a well designed gearbox and let the engine spin
at a more efficient speed. I read somewhere a long time ago that propellors
were most efficient below 1700 rpm. I can't verify this but I know they are
certainly quieter at those speeds, and most current engines haven't a hope
in hell of being efficient that slow.

 So, bowing low towards Mr Crooks house, I join the "higher reduction ratio"
bandwagon. (more RPM, more POWER, bigger PROPS... ok I'm a petrol head.)

Martin
Pitts Pilot

  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.

Bill
Long EZ builder & pilot
BSME, MSME

 
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