Paul et al,

 I have what is probably a basic question.

 I have often read that a propeller induces adverse vibrations into a
 drive train and that a belt driven PSRU is the way to isolate those
 vibrations from the rest of the components and engine in general
 while allowing the propeller and engine to each operate in their
 most effective rpm range. Yet I also see a lot of planetary (and
 other?) gear drive units, especially in the information shared here,
 that would seem likely to transmit those propeller vibrations. So in
 the applications being discussed here how is a direct drive
 permissible? Is it because the aircraft (e.g. the time to climb) are
 limited purpose and limited life and thus not likely to be adversely
 affected in the time they are operational?

 Just curious and hoping to understand better. Thanks for any
 responses!

 Brad Chubb

 The planetary was universally used in aircraft engines for years.
 Only in WW II was a spur gear used in the water cooled V12's. All
 the radials had planetary gear box's including the largest aircraft
 engine ever made in quantity. That was the P&W R 4360 Wasp Major. It
 had 18 planet gears. The latests in large P&W turbo fan engines for
 airliners is a planetary gear box that is 98% efficient.

 Direct drive requires a lot of displacement for a limited amount of
 HP. The 2 rotor rotary engine is small displacement as aircraft
 engine go at 160 cubic inches. However the time to climb engine is a
 record amount of HP (650)  for it's weight of under 250 pounds with
 gear box.

 BTW The rotary is also a record amount of HP per cubic inch of
 displacement at 4 HP per cubic inch. The former record holder was
 the Offenhouser race engine at 3 HP per cubic inch.

 The TTC record holder Grumman Bearcat had 2 pounds per HP to lift
 while our TTC aircraft (Vans RV4 basically)  only has 1.5 pounds per
 HP to lift. Weight per HP is the name of the game in high climb
 performance. Ask any truck driver :-)

 We are about done with the installation and we are waiting until Dan
 Gray gets back from vacation to test run the engine on the aircraft.

 Paul Lamar


Paul,
I had one other question about the P&W planetary. Are there two outer gears
so they can put one on from each side? That was the only way I could think
of that I could think of to put them all together. there are splines on the
sun gear to fit the drive shaft. There are also on the outer ring gear but
they are split so it looks like they both come in from the outside.
Bill Jepson


I don't know. The device is on display at the P&W museum in Connecticut.

Paul Lamar


I can not remember from the last photos but if the planetary is built with
two carriers with opposing helix, then for removal the planet carriers
could be removed from each end. The two carriers could be through bolted.

Dale Davies

Dale,
I agree that the carrier's could be bolted together. But if you look at the
P&W planetary the Herringbone, ( double "V"), gears internally all appear
to be single piece. I'm not certain how the final assembly is done.

Bill Jepson

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