Rotaries, and a vent.

[rv6ejguy]

Originally Posted by rtry9a

Ross,
What you say is true (also applies to the Eggenfellner drive, doesn't it?) but in addition, I believe there is an inherent strength and weight advantage with a planetary gear set over spur gears or belts- they have a lot more contact surface between the 6 driven/drive gears and torque is distributed concentrically around the shafts which likely reduces some of the torsional vibration.

It's probably relatively easy to match up the flywheel to the PRSU input drive as long as it is centered, and, because it uses steel plates instead of a bell housing, you can likely drill your own mounting holes to match your engine.

Yes, this reasoning also applies to Eggenfellner's gearboxes and we have a massive thread now on that. Egg does not sell to anyone not using his engines however.

The planetary drive can be made very strong if enough pinions are used. The newer Ford 6 pinion carrier is much stronger than the 4 pinion one. Any drive system can be made to handle a lot of power. Aero engines in the 4000hp range have used both planetary and spur type gearboxes successfully in racing. The planetary setup is small and light but has two two things against it as used with the Ford gears- it offers zero thrust line offset so limits which engines fit under the cowling of which aircraft, especially those with top induction. Secondly is reverses prop direction possibly limiting prop choices in the higher hp ranges.

The Ross drives used the same early planetary gear set and were not good boxes by any measure with several design and machining problems. Once corrected, many people have reported good service with them. Any box design needs to be right irregardless of gear type or it can fail.

I know that one of Tracy's gearboxes has been applied to a gas turbine engine and despite no TV, it did not last even one hour (bearing issues). Testing on different applications is always prudent.

[rtry9a]

Good point on the thrust line- I'd never thought much about that "problem" since it is not relevant to rotary engines (intakes on the side, though it is common to wrap intake tubes over the top of the engine).

"Secondly is reverses prop direction possibly limiting prop choices in the higher hp ranges"

Not necessarily true- depends on how you set up the planetary gearset. Tracys RD-1C has normal rotation w/ 2.85 ratio and the -1B has 2.187 ratio w/reverse rotation. Both use the same 6-gear planetary set from Ford.

[rv6ejguy]

Originally Posted by rtry9a

"Secondly is reverses prop direction possibly limiting prop choices in the higher hp ranges"

Not necessarily true- depends on how you set up the planetary gearset. Tracys RD-1C has normal rotation w/ 2.85 ratio and the -1B has 2.187 ratio w/reverse rotation. Both use the same 6-gear planetary set from Ford.

Aha. I did not know that. I stand corrected.

The thrust line thing is a big deal on most piston engines including Subarus on airframes designed for opposed engines. Eggenfellner has to change the water manifold and fab a lower profile intake to get his non-offset drive setups to fit under most cowlings and many other Sube guys have had to do similar things with other planetary drives like Ross, RWS and the Geared Air Power units.

This can be a lot of work for non-fabricator types. Offset drives like RFI, Marcotte, Auto Flight and EPI give these users other options.

[Rotary10-RV]

Originally Posted by rv6ejguy

Aha. I did not know that. I stand corrected.

The thrust line thing is a big deal on most piston engines including Subarus on airframes designed for opposed engines. Eggenfellner has to change the water manifold and fab a lower profile intake to get his non-offset drive setups to fit under most cowlings and many other Sube guys have had to do similar things with other planetary drives like Ross, RWS and the Geared Air Power units.

This can be a lot of work for non-fabricator types. Offset drives like RFI, Marcotte, Auto Flight and EPI give these users other options.

Ross,
The zero thrust line offset can be a problem for rotaries too. Most of the guys like to wrap the intakes over the top of the engine. This puts the intakes away from the exhaust in a cooler area. You must design very carefully to fit the tubes in on a "over the top" intake. You can do it, since you need only pass the actual intake tubes over. The max area allows only about 2-1/2" though. The Powersport engine used a internal gear set-up just like the Marcotte, but straight cut rather than helical. Properly done this is a very good way to do things. I like the small offset offered and the rotation comes out "right". The way the planetary gearset works is that in the higher gear ratio (lower numerically) the power is taken from the ring gear and the planets are fixed. In the 2.83:1 ratio box the same gears are used but the power is taken from the planet carrier and the ring gear is fixed. This setup allows the standard rotation, and has really started to takeover on the rotary since they love to rev. Both Tracy's RD-1C and the Mistral planetary hold the ring gear and take power from the planet carrier giving standard rotation from the rotary. Both of these planetaries have zero thrustline offset though. Not impossible, but you must plan carefully.
Bill Jepson