Rotary Engine (Mazda/Wankel) conversions Hummmmmm!
 

As I have been rather long winded about the rotary in another thread I figured I would be true to my word and start a thread about rotary conversions. There are several types of aircraft already flying with a rotary engine. The list (and I'm sureI've left some out) RV's mostly 6's, Long EZ's several, The most interesting being that of Perry Mick who designed his own ducted fan and ran the rotary direct drive! Sadly or gladly he has since converted to a standard PSRU and pusher prop. Several of the Zenith designs are running rotaries. The biggest contributor to the rotary cause so far has been Tracy Crook (who fortunatly isn't). Tracy sells an engine control module with redundant controls for injection and ignition. Also two different PSRU's or re-drives as he likes to call them. Tracy has over 1000 hours on his RV-4 conversion. Tracy recently installed the new 2 rotor engine out of the RX-8 sports coupe called a Renesis by Mazda (Yea I know the name is weird but the engine runs verywell) He is also bulding an RV-8 as a test bed for another version of the rotary called the 20B which has 3 rotor chambers and was used on larger sedans in the japanese home market. the engine is a natural for aircraft since it is 50% larger. This is the engine about which I'm basing my own conversion. I'll be running the 20B engine in my RV-10 once completed. Mistral Engines in Florida is producing a 2 rotor that is to be CERTIFIED which will surely help the rotary in the eyes of the insurance companies. Fortunately Mistral is also going to sell parts to the homebuilder market. The reason I'm interested is that their PSRU is designed for high HP and is setup for the use of a hydraulic constant speed prop from the outset. In fact they are running this engine in a Piper Arrow now preparing for certification. The RV-10 has a wide speed range and I expect that using a CS prop is really almost a necessity. I would be interested in Tracy's unit which is much cheaper if it could accomodate a standard CS, but so far this hasn't been a priority with Tracy, he has a great deal of business already. An MT electric prop is always a possibility but is very expensive. That is a start for rotary conversions which IMO show a great deal of promise.
Rotary10-RV
Bill Jepson

Im with you- the Rotary looks to be an excellent aircraft motor based on reliability, durabiity, power to weight, and probably, fuel burn rates. My only comment is that the Renesis 2-rotor motor might be a better choice for your RV-10 at 230-259 HP output (in the recommeded power range, with less weight than the Lyc). You could always add a turbocharger if you need more HP later on. I dont think you will be able to convert the extra HP to speed in a 10 with the 20B, only burn excessive fuel and generate excessive heat in the process.

Cobra,
Reasonable comments to be sure. The 20B and 13B as well are NOT gas guzzlers in high power and high RPM use. The comment I made about the rotary being a better aircraft than car engine? The engine is more and more efficient at higher outputs, (relative to other engines), in fact Mistral is reporting slightly better fuel burn than a compareable output Lycoming. I have chosen the 20B as producing the required HP easily, rather than a higher tuning level needed for the 13B. On the weight issue the raw 20B weighs in at 295 lbs which still allows for 100+ pounds for plumbing and accessories. There are several current efforts to build and replace the iron end and intermediate housings with aluminum ones. If successful the weight savings will be drastic, 40 pounds on my engine! The 13B would save about 27 pounds. The rotary is progressing and getting better the more effort that is applied.
Bill Jepson

I've been lurking on the FlyRotary list for a while, and I'm kind of torn between going totally stone-age with a carbureted O-360 and 2 magnetos or building out the simplest possible Renesis installation, that is, NA 4-port with RWS redrive and ignition controller. The biggest issues that seem to be facing the rotary aviation community so far seem to be cooling, intake, and exhaust. This is because there's no best or only way to do any of them. There are plenty of ideas and examples out there and most of them work just fine, but each one is unique. This being my first homebuilt airplane, I'm not sure if I have the chops to put together a nonstandard installation which isn't recommended or endorsed by the kit manufacturer. On the other hand, I could take the savings from the rotary installation and put it in the panel.

Still (not)deciding.

PS, I don't mean to ruffle any feathers. I realize that a successful installation of this kind is cause for celebration and respect. I'm also hoping that by the time I'm ready to look for an engine, all the parts I need for a rock-solid plug and play rotary conversion will be available, and that will make the decision easier.

I too am thinking Renesis and I have some very specific ideas on how to approach the cooling challenges.
The oil is a major contributor to total engine cooling because of the heat transfer through the rotors. If you can get a handle on that, you can whip the whole problem. Focus on increasing oil flow through the oil cooler(s).

-mike

Both water and oil cooling are important on the Wankel. The heat exchangers and ducting are critical for success and low drag. Powersport has done a nice job of this on their 2 RV8 conversions with the single inlet, divergent, under spinner duct. Bill Kay could offer some advice on on heat exchangers. Don't underestimate the task of keeping one of these conversions cool.

Planning on a Renesis with a Catto 3 blade. I think that the cooling issues are being dealt with by several that are already flying (Tracy, Dave, Paul, among others). These guys are essential to those of us in the planning stages, and I do believe that there will be something close to a "plug n play" install avaibable in the near future (couple of years).

Keep thinking. We'll get there, and it'll be great!!

Cooling the Rotary
 

Fellow Experimenters,
Cooling the Rotary isn't much different than cooling any other water cooled engine. You need diffuser ducting to slow the air prior to the rads, (water or oil), and good exit area (an often ignored item) with low restriction. The rotary does have a slightly higher oil cooling component than the typical piston rengine, as a percentage of it's overall thermal package. About 20-30% for those interested. You will need 2-3 cubic inches of heat exchanger per HP on the water radiators. For oil I would try to use the standard Mazda coolers if they will fit. They are an excellent cooler when tested.
I'm building an RV-10 which has plenty of under-cowl area. My plan is to run 2 radiators toward the sides of the cowl with a standard Mazda racing oil cooler under the engine toward the rear. Near standard inlets will be ducted to the radiators and oil cooler. I plan to sweep the exhaust under the engine and exit centrally in a single centered outlet. Engine mount will be bed style supporting the engine in three points a la Questair Venture.
Bill Jepson

Bill,
Question concerning your cooling ducts that "slow down the air". Tracy Crook had problems with his ducting at first because turbulent airflows reduced the cooling efficiency, at least before he radiused his inlet ducts into a venturi. I think you misread the comment, the idea is to provide as much air as possible, without turbulence, until it gets to the radiators, not slow it down. Slow turbulent air does pass thru dense radiator cores well.

FWIW, my very sketchy plan at this point is to place twin radiators on each side of the engine then build a streamlined scoop underneath the spinner, much like the Rockets do, to provide air to the oil cooler and the intercooler. The heated air will leave by (and cool) the turbo/muffler/exhaust pipe around the front wheel strut, below/behind the motor.

[quote=cobra]Bill,
Question concerning your cooling ducts that "slow down the air". Tracy Crook had problems with his ducting at first because turbulent airflows reduced the cooling efficiency, at least before he radiused his inlet ducts into a venturi. I think you misread the comment, the idea is to provide as much air as possible, without turbulence, until it gets to the radiators, not slow it down. Slow turbulent air does pass thru dense radiator cores well.

Cobra,
I do NOT intend to induce turbulence in my ducting. If you build a smooth sided DIVERGING duct the airflow will slow (more area) naturally. There are several texts on this. There was a well established wedge shaped duct that give uniform flow. K&W testing heat exchangers.
Bill Jepson