Rotaries, and a vent.

[rv6ejguy]

Originally Posted by Roddzilla

Also, why don't some of you really smart guys design us a bulletproof PSRU??? I'll sign a release of liability and pitch in some cash... (you listening Ross and DanH??)

Thanks!

DR

I'd love to but I'm too busy with other aviation projects currently plus the RV10 and of course posting here.

[Mike S]

Originally Posted by Roddzilla

Also, why don't some of you really smart guys design us a bulletproof PSRU??? I'll sign a release of liability and pitch in some cash... (you listening Ross and DanH??)

Thanks!

DR

Molt Taylor used a device in the drive of some of his designs, used a wavy disc in a toroid full of steel balls, IIRC. Absorbed the TV and allowed him to use long driveshaft to a rear prop.

Unfortunatly, I dont remember the name of it.

BUT, I'll bet someone out there in VAF land will.

I wonder if a similar device would help with the PSRU TV issue???

[rzbill]

Molt used the Flexidyne dry fluid coupling concept.

http://www.dodge-pt.com/pdf/brochure...s/dmr_1513.pdf

[Mike S]

Bill, thanks, yes that is what I was thinking of.

From the things I have read/observed both on this forum, and elsewhere, it sounds like one of these units could be helpful in controlling unwanted vibrations in a PSRU.

Hopefully Dan Horton will jump in here--------------he seems to be the resident expert in the field of TV.

[rtry9a]

Unless I missed something, Tracy's PSRU IS bulletproof and represents the state of the art as far as affordable units are concerned- it has not failed to date and it is designed specifically for the Rotary engine. Why is another design needed?

[DanH]

I'm gonna jump in here a moment and then go away.

I appreciate all the nice comments about my writing on torsional issues, but I am not an expert.

I'm just a homebuilder like most of you. Back in 1998 I found myself with a Gold Lindy for an airplane I was afraid to fly (or at least too nervous to have fun). The purchased redrive I was using was a torsional and mechanical disaster. Those of you who frequented the old Airsoob group will remember.

I was lucky enough to find an excellent mentor (and great friend to this day); Steve Crow, Caltech PhD, former professor and dean, and all-round very smart guy. Steve had a project of his own, our interests were complimentary, so we worked together on both. He got data and I got an education. More important, I got a whole new perspective. I'd been a mechanical crazy all my life, but too much was based on the classic TLAR approach. Steve showed me I was capable of real engineering, despite the limitations of an Alabama high school diploma. No more TLAR for me. For someone as deeply wrapped in experimental airplanes as I am, it was a life-changing experience. Still, I'm not a pro, and I try to keep my limitations in mind. You should too.

Torsional vibration is a tough subject when taken in depth. The most complete work on the subject was published in 1940, Ker Wilson's "Practical Solutions to Torsional Vibration Problems". Practical Solutions is a three-volume set that stacks up about 9 inches high. I'd love to have a set of my own, if anyone knows of one for sale. Then maybe I'd be an expert after a few years to digest it all. <g>

[rv6ejguy]

The advantage that Tracy has with most of his drives is that they are used primarily on one engine- 13B Mazda and with props generally in the same range with regards to moments of inertia. The fact that many are flying and have accumulated many thousands of hours collectively PROBABLY means that there are no serious torsional vibration concerns with this package.

However putting the same drive on say a 4 or 6 cylinder Subaru throws that premise out the window as these are very different engines. There may be no issues again with the Subaru or there may be. There is not enough time on this combo to draw any conclusions. If Tracy has run the calcs or done actual instrumented TV testing, then we'd have more confidence that his drive would also be safe on various Subaru engines.

What we are saying here is not to assume that there are no hidden TV issues on any drive that has not been tested for TV. We are not singling out any one drive. TV is insidious and can cause both slow and instantaneous failures to engines, PSRUs and propeller systems. Many people have never heard of torsional vibration and have little appreciation of it.

If you are looking for a good track record on Wankel PSRUs, Tracy is at the top of the list along with Powersport. Tracy's drives have a lot more flight time, Powersport's has had detailed TV testing done. I'd feel pretty confident using either design on a 13B powered aircraft.

Drives that are fitted to a variety of different engines like the Marcotte that I use are more of an unknown quantity.

[Mike S]

Wow Dan, thanks for the honesty. I have been reading your posts on the TV subject for quite a while, and just assumed-----yes, I know what the word breaks down to-------you worked in the field.

Sorry to have put you on the spot like I did.

[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.

You might be interested in the following from Tracy's website:

"Looking for a redrive for an alternative engine but NOT a rotary? We also sell the drive WITHOUT the adaptor plate. Several builders have fabricated their own plate to allow them to use the RWS drive on a non-rotary powered plane. Here is a photo of Troy Wright's RD-1C drive installed on his Ford V-6 engine for a Fokker DVii plane. Contact us if you want a quotation for a drive minus the adaptor plate."

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.

[Rotary10-RV]

Originally Posted by Mike S

Molt Taylor used a device in the drive of some of his designs, used a wavy disc in a toroid full of steel balls, IIRC. Absorbed the TV and allowed him to use long driveshaft to a rear prop.

Unfortunatly, I dont remember the name of it.

BUT, I'll bet someone out there in VAF land will.

I wonder if a similar device would help with the PSRU TV issue???

Mike,

The ramp and ball system you're talking about is a impact protection cam. It's used in lots of motorcycles with shaft drive as a shock absorber. It isn't as good with TV though. The truth is that because this device is not a damper it can actually make the tortional vibration worse. It is another spring device designed to lessen impact on the gears. The link to the device used by Molt Taylor is an example of a true dampening device, and it looks good. The engineering problem is always to find the smallest, lightest and cheapest way to do it. You also have to design within the dampeners capacity, and as we slide up the HP scale it gets harder and harder not to just blow things up!
Several people are using the final drive for a helicopter (Bell 47) designed to handle over 1000HP. The only problem there is cost!
I'm not a Mistral customer at present, but they will sell some parts and I may eventually buy their PSRU. The Mistral PSRU is a purpose built design. It uses straight cut (spur) gears throughout. The biggest advantage is that the PRSU is designed to handle a CS prop from the start. It isn't cheap at around $6800 last time I checked, but the ability to use a standard CS instead of a super-expensive electric may make it worth it.
Bill Jepson

PS... DODGE® FLEXIDYNE® is a dry fluid drive that provides smooth, controlled
acceleration with a reduced current draw. Because of its unique concept in
principle and design, it can handle difficult drive problems and is compatible
with standard NEMA Design B motors commonly used in industry. It is not,
however, recommended for use with variable-speed drives, internal combustion
engines, or multiple-speed electric motors.
I've included this from the Dodge PDF on the Flexidyne coupling as an FYI. These manufacturers understand how tough a job this can be.
Bill