Reduction drives

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AIRCAB

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IIRC, RWS uses a flywheel attached to the eccentric shaft flange, with several elastomer bushings around the periphery. Then the gearbox input shaft has pins that mate with holes in the elastomer bushings. Similar arrangements have been done with with other systems.

Tracey Crook appeared to have a reliable system. He showed up at AirVenture with complete regularity... I have never heard numbers on fleet size, fleet hours, and failure rates. Using his inertia and bushings is probably a pretty good starting point.

I will not be selecting your equipment for you. I am planning an O360 for my bird.

BIllski
Thank you Billski, you're my man on this. I have a Mazda Renesis Rotary engine and will have a Tracy Crook PSRU. I can use your help on coming up with a damping device bolted right to the flywheel that will in-turn drive the PSRU.

Who are these other guys who have come up with successful dampers?
Thank you Billski, you're my man on this. I have a Mazda Renesis Rotary engine and will have a Tracy Crook PSRU. I can use your help on coming up with a damping device bolted right to the flywheel that will in-turn drive the PSRU.

Who are these other guys who have come up with successful dampers?
Paul Lamars site, Rotaryeng.net may be helpful. You may have to sign up to his email feed. A lot of Peru design issues have been discussed there. He designed the drive coupling for the 500HP Time to Climb record holder.
 

Russell

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Just my personal experiences here … I have owned two different manufacturers of planetary type gear drives. First was a Ross and the second was a GAP, the GAP was far easier to completely dissemble and reassemble for repairs. If I recall correctly the Ross used a Ford C6 planet set and the GAP used a Ford E4OD planet set. My electric MT Propeller was driven by a Subaru EG33 six cylinder.

I had multiple problems with both planetary drives. Most problems were correctable. The problem that I was never able to overcome was planet bearing failure. The tiny needle bearings in the planet gears would start to fail after about 20 hours (see photo). Calculated rotational speed of the needles at cruise speed comes to over 100K RPM. I came to the conclusion that the Ford planetaries were designed for about a 10% duty cycle. I have been told that rotary and smaller piston conversions have had better results with planetary drives.

I have since installed a Marcotte drive with internal spur gears and have been getting better results.
Russell Sherwood - Glasair IRG/Subaru EG33
 

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wsimpso1

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Paul Lamars site, Rotaryeng.net may be helpful. You may have to sign up to his email feed. A lot of Peru design issues have been discussed there. He designed the drive coupling for the 500HP Time to Climb record holder.
Well aware of Paul Lamar's list, abandoned it long ago. As for my powerplant - used O-360 with EFII.

Billski
 

GESchwarz

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GE,

With the RWS drive, you should have received a roughly square aluminum damper plate with a rubber 'donut' in each of the four corners.....

Charlie
Thank you Charlie. I have not received the package yet. Neil said it will be available in a month or so. For the past 10 years I have been totally focused on the airframe construction. Just now I am getting up to speed on the firewall fwd.
 

GESchwarz

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How important is it that the rotating inertia be equal on both sides of the damper? If it is, should I be using a Mazda flywheel meant for a manual transmission/clutch, instead of the much lighter one used for an automatic transmission.

As it is, the prop may have a lot more inertia than the rotary engine with the automatic transmission flywheel.
 
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Lendo

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GE,
If you could identify the Rubber/ Polyurethane Donut hardness, I believe it's fairly soft, you could make your own. I believe Tracy suggested Soft and out Wide, which makes me wonder about the Automobile smaller Diameter Dampers.
George
 

wsimpso1

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How important is it that the rotating inertia be equal on both sides of the damper? If it is, should I be using a Mazda flywheel meant for a manual transmission/clutch, instead of the much lighter one used for an automatic transmission.

As it is, the prop may have a lot more inertia than the rotary engine with the automatic transmission flywheel.
There is no need for identical inertia, but the bigger the difference between engine side and prop side inertia, the bigger the job of achieving an adequately low natural frequency becomes. Usually the prop is much larger inertia than the engine, even with the prop inertia being corrected for the gear ratio of the PSRU. So moving inertia from the engine side to the prop side of the isolator is directionally wrong. Usually, you can reduce the natural frequency significantly with some added inertia on the engine side, but you will have to add a lot of inertia to the prop to have the same effect. Ross has written about this with his Subie - he is RV6EJGuy on here and has a great web site at SDSEFI.com.

Billski
 

Lendo

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Russell,
I had a good look at the Marcotte PSRU and it appears a robust design, I like the Spur gears as well, although with the Powersport PSRU the spur gear was internal to the Ring gear, which made the gear expansion rate travel in the same direction, without the need of greater lash to accommodate the gears expanding into one another -makes sense to me.
George
 

Vigilant1

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I know that if I had purchased a RWS PSRU, a very valuable thing to me would be the track record of these drives. It is good, and folks know what works with them. The field is littered with failed PSRUs, and the 13b has proved challenging in this regard. So I would change nothing from what Tracy Crook recommends and which has been proven in service. It would be ill advised (IMO) to deliberately make myself a guinea pig when the road to success is so clear--and hard won.
 
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AIRCAB

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The Bell 47 gearbox was used in the TTC 500HP project. In the 15 years I have been recieving Lamar,s emails, there is constant talk about improvements to the RWS (Tracy Crook) Peru. I was fortunate to get a AS350 heli reduction unit, good to 1500HP .
 

GESchwarz

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There is no need for identical inertia, but the bigger the difference between engine side and prop side inertia, the bigger the job of achieving an adequately low natural frequency becomes. Usually the prop is much larger inertia than the engine, even with the prop inertia being corrected for the gear ratio of the PSRU. So moving inertia from the engine side to the prop side of the isolator is directionally wrong. Usually, you can reduce the natural frequency significantly with some added inertia on the engine side, but you will have to add a lot of inertia to the prop to have the same effect. Ross has written about this with his Subie - he is RV6EJGuy on here and has a great web site at SDSEFI.com.

Billski
Thanks for the tip on SDSEFT.com I was suggesting that more inertia be added to the engine side, since the rotary engine is so small
 

rv7charlie

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Specific to the rotary:

Just about everything I might mention on this forum can be sourced directly from the Flyrotary email archives.
(I'm using 'damper' as a convenient term for the soft elements in the drive coupler.)

Renesis rotors: They are significantly lighter than the old 13B rotors, but are not aluminum. I honestly can't remember for sure, but they may have switched from cast iron to steel for the Renesis in order to make them lighter.
Flexplate vs flywheel: 13B, Renesis, and 20B have all run successfully using the flex plate. Biggest issue, as I mentioned earlier, is that flexplates have been known to crack, even in the car (I've got a cracked one that's never flown). Drive integrity/damage related to the dampers has never been an issue, to my knowledge. Damper life seems to be in the hundreds of hours, varying with HP extracted from the engine. One of the Flyrotary email list members (where most of the actual fliers hang out) has contracted to have another run of the dampers made, at a slightly higher durometer than the originals (increased lifespan with higher HP). They're from in the same facility, in the same molds, as the originals Tracy sold. Unfortunately, I think that the entire buy is spoken for at this point.

GE, if it helps ease your mind, the last version of the drive that Tracy sold before retirement used an aluminum racing flywheel (~8 lbs, IIRC) and no dampers at all (direct splined connection between the flywheel & input shaft). It has a slightly different input shaft, due to different mating to the flywheel, but the same sun gear, planetary, output shaft, etc. It was limited to wood (low inertia) props. He's been flying that version on his Renesis powered RV4 for many years. His 20B powered RV8 is still running the flexplate system, AFAIK.

Russell, Interesting failure. AFAIK, no one using Tracy's drives on a rotary has had any issues with the core planetary gearset. Different impulse patterns? Alignment issues? Something else?

Charlie
 

cheapracer

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Why hasn't anyone used a Robbo R22 dual V belt and sheave reduction? Proven, been around a long time etc.

Plenty of improvements in belts since they were first introduced as well.

R22.jpg
 

rv7charlie

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Well, my 1st thought is that there are no gyro loads on that system.
All mechanical issues aside, fitting that support structure on the nose of an a/c would be a bit tricky to cowl efficiently.
 

cheapracer

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All mechanical issues aside, fitting that support structure on the nose of an a/c would be a bit tricky to cowl efficiently.
Of course I wasn't refering to the entire Robbo setup, just the drive package.

The setup is not much different to gears in terms of support. Wider 'gears' (sheaves) obviously, but no need for oil proof housings.
 

BBerson

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The helicopter has a big overrunning clutch in the upper sheave (or lower?) which can cancel half the torsional vibration forcing from the rotor in theory. I don't know if it does in practice.
 

cheapracer

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The helicopter has a big overrunning clutch in the upper sheave (or lower?) which can cancel half the torsional vibration forcing from the rotor in theory. I don't know if it does in practice.
Understandable with that amount of rotational mass that could tear an engine or the driveshafts apart.
 
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