How many people are interested in a GOOD safe psru for the rotary?

Good to hear that you're getting close. Tracy Crook's retirement effectively stopped new rotary projects due to the uncertainty around getting a reliable gearbox. When will you tell the rotary list(s)? Do you have a price in mind, yet?

Sorry to hear that you have to sell the kit. Have you considered using one of the micro-funding sites to raise the money?

Charlie

 

Charlie, My partner and I are a bit old-fashioned. While I have thought about the possibility (of go-fund-me or something similar) we both feel you should have a finished product, (that actually works), before you promote it. For example I consider Ross' question about hours, numbers, and aircraft early in this post to be VERY REASONABLE for a product you are going to put your behind on the line to use. The original Powersport did a tremendous amount of work and testing, 1000's of hours and plain old hard work before they were ready to start selling the engine and gearbox. Just before Everett's crash. This testing is why Steve is dead set against the use of the truck planetary lifted from a regular transmission. They tested and built planetaries made to order and having much tighter tolerances than the typical automotive unit, and still had failures. They built the dampered e-shaft which did work reliably, but cost a ton. We are internally honest with ourselves, and realize that no one is going to spend certified engine money on an experimental package. No matter how good it is if it costs the same amount as a Lyc or Conti. It needs to have a track record of success. I don't blame them as it makes their flight test easier, and resale much easier if it comes to that. So I am waiting on the sale of some of my stuff to be able to afford to produce things the way we want to. Thanks for your interest. Also thanks to everyone who have liked this thread as it gives me a real idea of if there might be a market for these things, or if I am doing this for our own personal use.
Bill

 

Charlie,
and to some of the guys interested in versions for a V8, The cross section is for 6DP gears capable of handling 600HP continous. More centerline offset than I would like. I'm trying to get my gear guys back off Merlin gears to some smaller 8DP gearing or even 10DP. (Bigger numbers are smaller teeth for the non-engineering guys) That unit is 44 pounds with the heavier gears at 2.8:1 ratio. I'm working on the smaller gear version trying to get the weight below 40 pounds with the headroom to go to 450HP. I am STILL waiting for some final cost estimates.
Bil

 

Will 2.8 the the only ratio available? I've got Tracy's 2.85, but I've kinda wished for something closer to 2.4 for my rotary, to get a bit closer to a 'standard' prop. (Just works better for airframes designed for Lycs, and easier for prop carvers; when they're forced to deal with non-standard diameters, they often get it wrong.) Just about any V-8 install will need a much narrower ratio, as well. If I ever finish the rotary -7, I'd really like to try an LS motor on something, and that drive configuration looks like a good fit for a V-8.

 

Higher centerline offset is beneficial for most piston engines, even opposed ones like Subaru with the intake manifold on top. Plenty of room to move the engine down but not much to go up usually. Vee engines will require even more, probably a minimum of 8 inches.

 

Ross,
You are correct of course. The Rotary really needs at least a couple of inches of offset to allow the intake tubes to go over top of the motor. More than that and supporting the gearbox needs to be additionally supported. I've included a top mount on the version I pictured in cross section.
Bill

 

Charlie,
WE have a 2.4 ratio on the prototype. The rotary works best with regards to wear between 6 and 7000 RPM. This is why we were planning on 2.8:1. We figure that 6000 RPM will make a great high speed cruise setting. Very good power can be made by 7000 with the right intake length and a free flowing exhaust. The prototype gearboxes have been 2.2 and 2.4:1. Those gear sets have a center distance of 2 inches. That could probably be made OK for the V8's or Subaru engines, but as has been commented those engines could use even MORE offset. I would have no problem doing other ratios, but it is taking so long to get started I wouldn't promise any different ratios until the Rotary project is well proven. It must also be mentioned that there would not have any testing for torsional vibration on those engines unless someone wanted to pay for it.
Bill

 

Yup I'd concentrate on the rotary box first since most of the testing is done and it's a captive market right now. Make some money and then you can explore other possible markets if warranted.

 

Charlie, We are looking at using 7000 RPM as a practical redline. For mildly set up engines that may be all there is due to intake restriction. 7000/2.8=2500 prop rpm. That puts you in the meat and potatoes range of the prop spectrum. Also if you build a real fire breather rotary, (say for RENO), you could run up to 8 or 9000 RPM with a multi-blade smaller diameter prop. The perfect balance point for rotaries is 6000. Mazda instrumented engines and found that the forces just balance out perfectly at that RPM. You shouldn't fear running your rotary at that speed, it isn't like a piston engine in regards to wear. Speeds far above 7000 RPM are safe but don't have the great almost no-load on the bearings balance that 6000 RPMs has. Tooth line speed in the gearbox is fine at that RPM and the tapered roller bearings are fine too when using oil for lube. Those are the reasons for the choice. It actually would be easier for me to build a shorter ratio like 2.4:1 but to cover the rotary spectrum a bit more reduction looks best. I would also like to sell to the Subaru crowd as the Subie makes a good engine for many planes too, but all our research has been on the rotary.
Bill

 

2.8 reduction at 6000RPM puts you around 2150 at the prop... a nice quiet cruise setting. Interesting....

 

Back in the late 90s I had a Bushmaster (V6 STOL) without an engine and was planning to put in a rotary. Had one built by Bruce Turrentine, built my own lightweight gearbox (C6 transmission based), etc. Changed jobs and ended up selling the plane, gearbox, and engine.

But...

Still have the engine mount that I need to sell. It is designed for a stretched Piper Pacer/Tri-Pacer, etc and would make an *excellent* testbed for anyone doing a rotary conversion. Was professionally welded by Snowline Mfg in Bend OR. Those are the guys that made weldments for Columbia, Aviat, etc. Includes 4130 fittings that use cups for rubber cones to isolate the mount from the engine. It's the right length with a 13b using Tracy's W&B numbers to duplicate the proper CG for an IO-360 powered stretched Pacer so if you use it on a Short Wing that's not stretched you can mount the battery in the tail to offset (much easier than adding weight fwd of the CG).

So someone make me a reasonable offer so I can give this mount a good home

 

Bill,
We have a little thread (here:https://www.homebuiltairplanes.com/forums/showthread.php?t=30244 ) where we've been yaking about/comparing the cost and weight per HP of various "ready to fly" and "almost ready to fly" 4-stroke aero engines. Originally the scope was limited to new engines, but we've added Corvairs now. I know you aren't done with your work, but thought it might be interesting to get some idea of the weight, cost, and HP of an inexpensive "mild" Wankel conversion using your eventual PSRU. We won't add it to the chart (since it can't be bought yet), but:

1) Do you plan to sell engines complete with your PSRU, or would it be up to the buyer to get/prep an engine?
2) If you won't be selling engines ready for aircraft use, do you know of anyone who dies this? I think I read that Bruce Turrentine was no longer in this biz.
3) Do you have a number (WAG, no one should count on this) for cost, weight, and HP for a "cost conscious" twin rotor P-port: (e.g. Holley carb with mixture control block, simple electronic ignition, your PSRU, coolant and radiator)
Maybe 180HP, 275 lbs, $____ ?
4) HP, weight, cost for a more sophisticated twin rotor? (Full-up programmable ECU with engine monitoring, etc):

Thanks.

 

Vigilant,
The weight I can easily do using a basically stock 13B we weighed the engine we put on the dyno at 240 pounds. that didn't include the radiators and H2O which will add about 11-15 pounds. Had all the rest in place. Alternator, Airflow Performance mechanical fuel injection, and intakes (P-ported) and exhaust. I'm planning to set up to do the p-ported housings, and of course the reduction drive. Still don't have costs nailed down. I plan to sell the gearbox by itself for those who would like to DIY. The HP will be 200 HP easily. We have yet to test the 1-3/4" intakes but the engine we showed on the dyno using the smaller 1-5/8" intakes made 195 HP @ 6500 RPM. Racing beat p-port using 2" intakes and a Weber carb made 240 on their dyno. The Airflow Performance injection (mechanical aircraft injection) is leanable and should be better than a carb at the same inlet diameter. The slightly smaller intakes will be more tractable at low RPMS. We were able to idle the 1-5/8" intake version would easily idle at 1000 ENGINE RPM. The gearbox having so little backlash allows the engine to run as if it is direct drive. No rattling or other problems, unlike the planetary versions.
Bill

 

Where can I find a PSRU and Engine Controller for my Renesis???

 

I'd be pretty happy to find a reliable PSRU of reasonable cost for my RX8 conversion.

 

We build and sell reliable PSRUs. Our highest time has gone over 5500 hours on a commercial airboat. It is rated to 1200 ft-lb peek impulse torque. Keep in mind that the moment of inertia, etc. on both sides of the gearbox is important for gearbox loads. Currently we do not provide a mounting solution for Wankel engines but we can custom manufacture to your CAD file.
Mark Kettering
aeromomentum.com

 

I'm looking for a reliable 2.4/1 PSRU that can safely handle 650 SHP.

 

Mark, thanks for chiming in. The field is littered with a lot of PSRUs that haven't worked well on Wankel engines. Maybe it is due to the very stiff eccentric shaft (crankshaft analogue), maybe due to the higher RPMs these engines can reach with little trouble, or maybe due to the torque pulse signature (though, for a twin rotor, it should look a lot like a 4 cylinder 4 stroke). Whatever the reason, it has been a problem, including shattered springs and flex plates, increasing gear lash over time, etc. The OP of this thread is attempting to test and field a "stiff" PSRU to avoid the challenges "soft" systems have encountered when applied to this engine.
Your "soft" PSRU might work fine on a Wankel (it seems to work very well on yoir inline 4 cyl engines), and if so there would be much rejoicing in the E-AB community. I'm just offering that the path has proven to be tough.

 

Hi Mark. I'm glad you decided to post. I've been over to your website several times and thought about contacting you. I'd be happy to send you a CAD file, or possibly even a running engine. A decent PSRU would be a boon to the rotary community. I do like the OP's 2.8 ratio, though.

 

Most of the issues listed about rotaries sound like things people hear from people who heard from people who....

I think that if you have a good data sample, you'll see that rotaries have no more issues with reduction drives than any of the other alternative engines. Ex: the old Ross drives (when built by senior Ross) seemed to work fine except for the fact that Ross failed to include an input shaft thrust bearing, to handle the thrust back into the engine shaft due to the helical cut gears in the planetary. The RWS follow-on does fine. Ex: the rotary is a 2-per-rev engine, like a 4 cyl 4 stroke. But, while a 4c/4s engine has a literal torque reversal on every rev, the rotary's power stroke lasts for significantly longer than 180 degrees, so the torque never reverses on a 2 rotor rotary. The overlapping torque curves look more like a 6 or 8 cyl engine.

It's worth remembering that one example does not (necessarily) define a problem. The old original Powersport shredded a coupling shaft on a dyno, but apparently, no one had checked on resonance issues with a 2 per rev engine running on a dyno that was set up for 4 per rev (8cyl) engines. Tracy Crook (RWS) proved conclusively that 'loose' systems (resonant point below min excitation frequency of the engine) can survive just as well as 'tight' (resonant point above highest freq of engine). P.S. also apparently shredded some drives by using heavy metal props. Well, if you don't design for high mass moment of inertia, you're probably going to shred some stuff. An additional data point on RWS drives that's not well known 'in the wild': Tracy's been running his Renesis powered RV-4 for several years, with no 'damper' (for lack of a better term) at all. There is enough lash in the gear set to keep resonance outside the critical range. He does specify no metal (high MMI) props, if the drive is operated without the 'damper' mechanism. Ex: shattered flex plates are very common, in most automotive engines regardless of make/model/type. I've got a 13B flex plate that's cracked; never been flown. And if you prowl the salvage yards, you'll see them on just about any auto trans car if you look around a bit. Ex: lash increasing over time is something you monitor, but it's something that happens in any gear set, including (and more critically) a 'zero lash' gear set. It is not, however, a significant issue in the planetary drives I'm familiar with, as long as proper use/maintenance is maintained.

Mark,

I hope you do enter the rotary market. But if you do, can you make sure the drive turns 'the right way'? Right hand rotation (tractor install, viewed from the cockpit) just makes more sense. It's easier to get a properly carved prop, and opens up the possibility of retaining a stock motor mount. I do like your drive ratio. 2.5 gets prop rpm in the 'normal' range, again making it easier to get a properly carved prop. It's really impressive how often the prop makers get it wrong, when dia & rpm get outside the 'normal' range for engines in this HP range (150-250 HP).

Charlie