Benefits and drawbacks of a rotary

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

John Slade

Well-Known Member
Joined
Jan 5, 2003
Messages
157
Location
West Palm Beach, FL
I think a proven re-drive is the main obstacle to Rotary acceptance
I think Tracy Crooks redrive (http://rotaryaviation.com) is becoming a standard, at least for the RV and canard guys. There are quite a few flying and no failures of any significance yet. Tracy now has upwards of 1300 hours on his, and a few others are coming up toward 500 hrs or so. It's not "proven" to the extent that many would like, I know, but it's definitely looking good so far.
 

orion

Well-Known Member
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
Tracy's redrive certainly looks extremely promising and he has certainly done a lot of responsible work in bringing it to the current point of viability. My only problem with it, and many like it, is the rather crude method he uses in attaching it to the engine. If he only invested a few extra bucks and developed a better interface, it would look better, it might be lighter, and structuraly it would be superior to just bolting the redrive to the flat plate.

Assuming the size and bolt pattern is remotely even close, if he started with an automatic transmission bell housing off of a Mazda, most of the work would already be done. All he would then need to do is get a pattern tool made that would be capable of making cast wax housings, which would then be converted to aluminum through investment casting.

It would certainly go a long way to improving the look and presentation of his products.
 

John Slade

Well-Known Member
Joined
Jan 5, 2003
Messages
157
Location
West Palm Beach, FL
It would certainly go a long way to improving the look and presentation of his products.
True enough, but the redrive works well as it is, costs < $3k, and it's hidden under the cowl anyway. We have a practical and available solution. I'd rather see Tracy get on with data logging for his engine monitor and the planned auto-tune and split timing (for turbo) features for his ignition / injection computer.
 

lehanover

Member
Joined
Jul 12, 2005
Messages
10
Location
Hebron Ohio in summer. Zephyrhills Florida in wint
Entertaining

Well, the enthusiasim is here if not all of the data.

I have been racing rotary powered cars since 1980. I have produced, through ignorance, a small list of failures. A very small list.

The rotory is only smooth at idle (in stock trim) because of the weight of the flywheel/torque converter. It has two powerfull pulses per revolution but no reversals as with the (real) airplane engines.

The cheap easy and most often used method in industry, of taming this problem in any system is a soft connection in the transmission system. The spring system works well until the springs have been cycled to death. Then you have a hard connection for part of a revolution. Tracy uses soft plastic pucks to drive the gearbox.

A one way clutch to unhook the driveline during part of each revolution would last about an hour. My estimate. Belt drive and chain drive reductions will work fine, as they are not rigid connections. However the crank will not tolerate much of a side load.

Look in any undustrial power transmission book for the formulas if you want to run it all down.

If there is any fear left after that, replace the redrive pieces (from your Ford dealer) every 200 hours. If 1300 hours is not enough proof.

The weight of the flywheel determins where you will deal with the first order pulsations. The stock flywheel is very heavy.

The flywheel in my race engine is just 5 1/4" and bolts on over an old flexplate from an automatic trans. It just carries the starter ring gear.
About 4 pounds total.

If I idle it down below about 1,500 RPM it shakes the transmission so hard it sounds like a rock crusher. Normal race engine idle is 2,000 RPM. Again, not a problem for aircraft use.

The kids have been drifting and drag racing these engines for years.
A large pool of knowledge about power output and failure modes has been amassed.

The stock apex seals hold up just fine in even turbocharged operation.
The third generation RX-7 had twin turbochargers. Very few failures even in the hands of idiots.

Poor sealing.

Cured in about 73 with a change from 9 MM one piece apex seals to alloy 2 MM 2 piece seals. The second side seal was dropped at the same time. I use one piece carbon seals, and drag racing high boost turbo cars use ceramic and aftermarket alloy seals. The stock 2 piece alloy seals are more than adequate for aircraft use.

With any kind of maintanance you should get an easy 100,000 miles on a rebuild.

Tetonation is just about, not possible, in a non turbo rotary engine. Not a factor. In a turbo engine it is a big problem, only if you run without the stock management system, and make a few additional mistakes.

At the RPM used in aircraft, the rotary is hardly running from the stress and wear standpoint. We shift at 9,600 RPM for the 12A, but the 13B with lightened rotors will go over 10,000 RPM with good reliability.

The drag racers go over 12,000 RPM. It sounds more impressive than it is, because the heavy rotors turn only one third as fast as the crank.

About 1/3 of the total heat load is in the oil (oil cooled rotors) so the oil cooler needs to be about 1/3 the size of the radiator. Two GM air conditioning evap cores is enough for the water cooling. A stock Mazda or equil is required for oil cooling.

If there is no room for the stock distributor or crank angle sensor, a crank triggered system may be used. The engine will start and run fine with a fixed advance of 20 to 26 degrees.

I use MSDs on both leading and trailing systems. There is a bit more power available with a high energy system. Plus the plugs will stay clean longer. The engine will run on the leading system alone with almost no loss in power, and on the trailing only with about a 15% loss of power.

You need to run an air cleaner all of the time. It is just stupid to risk death over such a simple thing.


Lynn E. Hanover
 

orion

Well-Known Member
Joined
Mar 2, 2003
Messages
5,800
Location
Western Washington
Great summary Lynn. This is about the same info I've gathered over the years in my association with Dennis Hayes (Hayes Rotary Engineering) - nice to get the confirmation from an end user.

Personally I think the rotary is great for aircraft application - I just wish someone would take a more complete and optimized approach to its application (I don't have the time myself).

I do like the reduction drives offered by Mistral and Powersport, even given their rather high price tags. But given the critical nature of this potential "weak link", the extra cost is probably reasonable.
 

craftsven

Well-Known Member
Joined
Dec 20, 2006
Messages
65
Location
Manitoba/ New Mexico
Hi,

If you are interested in a good Mazda engine builder contact Yaw Power,
Mr. Paul Yaw he's located in Phoenix AZ.
A redrive similar to Powersport is manufactured by a company in Quebec, I can't remember the name, last contact I had with them the price was around $3500.

I just remembered the name: Marcotte, he now using the name Mega Power or something similar.

Sven

"Mistakes are the portals of discovery!"
 
Last edited:

Mac790

Well-Known Member
Joined
Jun 22, 2008
Messages
1,529
Location
Poznan, Poland
Seems that we had a vivid discussion about rotary engines fuel consumption (and not only), some says those engines burn more fuel, other says that those engines burn less fuel. I think this short article might answer it, or it might bring more confusion those planes (RV-8) had different frontal area, and small differences in HP, one thing is clear rotary engines are noisier.

Seb
 

Attachments

Group Builder
Top