Paul,
Since Brad is new to the list we might mention to him that belt drive
technology is such that modern toothed belts DO NOT isolate torsional
vibration, and sometimes make it worse. No one should think a belt drive
will stop torsional vibration. The previous post has it right. The prop is
nearly a constant load and the gearbox prop shaft, and eshaft are what
loads and unloads.

Bill Jepson
On Apr 15, 2016 8:11 PM, "rotaryeng@earthlink.net" <rotaryeng@earthlink.net>
wrote:



 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 think that F1 engines in 2005, in the final year of the 3.0-liter
 V-10 era, were making about 900 hp and weighed less than 200 pounds.
 That would be 4.5 hp per pound. Of course, they were spinning to
 19,000 rpm.

 Csaba Csere


 I also think they were allowed Beryllium Aluminium pistons made from
 surplus Russian atomic war head material. BeAl is .7 the density of
 aluminium and will tolerate 600 F. As I understand it, BeAl is now
 outlawed in F1 due to its toxic nature.

 We are turning only 6500 RPM now because of the current 3:1 gear box
 and the 84 inch diameter prop.  If we used a 4:1 gear box (available
 in one planetary) we could turn 11,000 RPM. Many Mazda RX7 road
 racing engines use that red line. If that  were the case we would
 have  1100 HP.

 Here is such a 4:1 planetary. This one may not be up to the required
 torque so it would have to be scaled up but I doubt it would weigh
 much more than the current 3:1 Bell 47 final drive.

 If we replaced the current 20 pounds of cast iron rotors and counter
 weights with 4.2 pounds of BeAl we could double the RPM and the HP to
 2200 HP roughly speaking. Of course the engine weight would be well
 under 200 pounds as well.


 Paul Lamar


Hi Paul, I seemed to have missed the discussion on using the jeep transfer
case planetary's for a PSRU . Are you proposing using the 4 to 1 unit?

Thanks, Steve Carlisle

Well we tried hard to buy just the planet carrier. No  luck.
Seemed the only way to get one was buy the whole transfer case.
No problem for a bucks up Reno racer but I doubt it would
live with a 1000 HP three rotor or even the time to climb engine.

I gave up. Too rich for my blood :-)

It has some what of a bad reputation for failing.

It might work for a NA 13B  p-port however.
If you used it you might get 300 HP at 9 to 10,000 RPM
with a reasonable diameter prop.

The sun works on one diameter of the planet gears and
the sun gear reacts the other diameters for 4 to one reduction.

Paul Lamar

Paul,
Since Brad is new to the list we might mention to him that belt drive
technology is such that modern toothed belts DO NOT isolate torsional
vibration, and sometimes make it worse. No one should think a belt drive
will stop torsional vibration. The previous post has it right. The prop is
nearly a constant load and the gearbox prop shaft, and eshaft are what
loads and unloads.

Bill Jepson

Good way of putting it Bill.

It also messes up the installation big time :-) No room for the cooling
system under the cowl. Here is a very early rotary powered airplane.

Paul Lamar

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