Wankle Engine

The Wankel rotary engine was designed by Dipl. Ing. Felix Wankel (Germany) and first used in the N.S.U. automobile (nowadays part of Audi AG) with very limited success. It was not fuel-efficient, and used much oil due to leakage around the rotor assembly and was shelved as a viable engine design. At that time N.S.U. was a very small carmaker with little capital and was later acquired by Audi AG.

During the late 1970's the Mazda (Japan) company built a light pickup truck with this motor, and soon followed with the RX-7 sportscar. The pickup truck died a quick death (butt-ugly some said; I thought it was ugly myself and maybe a bit weird).

The engine design was used to market the Mazda RX-7 sportscar line as a unique feature and with some success. Mazda (later Ford/Mazda) had the capital to improve the design of the engine to the level of performance that it has today. However, it is still not fuel-efficient due to blow-by of the rotor-to-chamber fit.

In operation it is a very smooth engine, but it must achieve much higher revolutions/minute than a piston engine to deliver comparable horsepower and torque. And as I recall the torque was a shortcoming of the design, as it could not be altered with bore x stroke and valve timing/duration modifications since it had none of these components!. So the torque "curve" was relatively flat throughout the speed range of the engine. Computerized fuel injection and ignition management have allowed further progress with this design, just as they have for the piston engine.

Even today, it is still a bit unique and at least it has seen some success with the Ford Mazda automobile company.

Ing. Robert Forbus

There was also a snow Mobile built by Arctic Cat and Skidoo which used the Wankel. On a packed track they were hard to beat loose snow was different, had a tough time getting them over 8,000 RPM and guite unreliable. Thanks

The Wankel's poor efficiency comes not from seal leakage, but from a lousy volume to surface ratio. The extra chamber surface robs heat from the combustion that would normally go into expansion. A sphere would be best. Wankel's sealed well after breakin.

High revving over square piston engines suffer from the same thing. They make great race engines, but poor econo-boxes. Also, it might be difficult to get high compression ratios from the Wankel design. I owned an RX7 till it was stolen - a Very fun machine.

The "high" oil consumption (1qt / 3Kmi) was intensional as they purposely injected oil into the carb bowls to keep the apex seals happy, not unlike what is done with 2 stroke MC engines.

Al D.

I once had a Mazda RX2 with a twin rotor Wankel B18 engine. It was the fastest 4 door family sedan that you could imagine. It would burn rubber in all four gears and rev over 10 grand. It had a 1 HP starter motor and glow plugs for cold weather starting. It had 4 sparkplugs (with tri-tips) twin coils and a 4 barrel carburator. And there lies the problem with Wankels. I once took the air cleaner off and watched the gas flow as I revved the engine. It was like watching a toilet flush! That small car never got 20 mpg. Maybe it was the way I drove it (quarter mile in the low 13's) but I don't think the design can be made fuel efficient. There's just too much blow by on the rotor tip seals.

ever heard of the mazda RX8?? considering that only one company has ever really put serious money into developing it, the "renesis 13B" as they call it (in the RX8) is pretty damn good. over here in oz, there are some ridiculosly fast 20B triple rotors (from the Cosmo, a big coupe if i remember correctly) for those not concerned about fuel consumption. have seen a race prepped 20B with triple turbos run 6 second quarter mile! we're talking more than 1500hp to do that even in a purpose built chassis.

Because the blowby is proportionally less at high rpm, the Wankel was once considered for small airplanes but I don't think it ever got off the ground (pun intended!)

I remember reading an article in a Kit-Plane magazine about using the Wankel for an airplane engine. In a magazine that assumed the enthusiast had high mechanical skills, they stated to ...not disassemble the engine for rebuilding -- you'll never get it back together again.

I vaguely recall reading about the Wankel in the early 60's in Popular Mechanics. They talked about it being so cheap to make, it would be a disposable engine. A few years later in High School geometry, the text book had a depiction of how to drill a square hole, which brought to mind the Wankel concept.

O.S. Engines made a wankel. Here is a link to their page. http://www.osengines.com/engines/osmg1400.html

They have made it for nearly 20 years.

In about 1972 ?? a friend of mine in high school got one of the 4 door sedans probably the one mentioned above. I got to drive it a couple of times and I would have to concur with the above post. That thing would tear the tires off at just about any speed. You could just slam the wheel and stomp on it and you went in that direction. It was unbelievable, since otherwise it just looked like another junky foreign compact. Needless to say with the kind of driving it encouraged it didn't last very long. I'd have to say it was a lot of fun while it lasted!

I believe that some small Wankel motors from a Motorbike(?) UK made(?) were used to power a small airship about 25 years ago.....I seem to remember a program from the UK about it..... so it did fly at least once...!

Mazda UK had a racing version of the RX-7 in the late 70's, that could blow off cars (in the next bigger engine class), coming out of the corners, and late brake them into the corners.....Tom Walkinshaw (F1 manager for one of the teams today I believe) was the pilot in question in that car!! Exact dates I have forgotten. I actually drove the tuned road version once, it was quite docile till you put your foot down......eyebrow ports were the tuning aid of the time for Wankels if I remember correctly, fuel consumption was not good! OK for a race car, just not for the road.

Norton produced a Wankel powered road bike, and campaigned for a few years the famous race bikes on the UK domestic race scene. The race bikes where phenomenally fast in a straight line, but because of gyroscopic effects of the spinning mass of the engine; they ran twin rotors, they where always a nightmare to change direction. I last saw a Norton race at the Isle of Man TT, when the late Steve Hislop rode a white liveried bike (sponsored by the spectators!) in an epic, in fact terrifying, race against Carl Fogarty on a Yamaha. The Norton won the senior race by the way, 'cause Fogarty rattled his bike to bits!

When these bikes took part in the British championship, the rules where held to the international TT specs to enable them in, as it depended on how you measured the engine as to how much displacement they had. They where also run as a total loss oil system, very like a 2 strokes, with the lost oil bunt off in the exhaust. Any riders who got behind them used to get toasted by the flames!

Mazda RX7's and RX8's are fairly commonplace cars on the road in the UK. Norton motorcycles also had a motorcycle out not too long ago and it won a few races. The bike was scrapped due to poor sales but I believe the engine from it is still sold for boat and generator use etc. The mazda's are old favourites over here though. The RX8 came out here relatively recently . Have a look on the mazda website.

Wankel Engines or Rotaries as we call them in the Caribbean enjoy quite a following and a high degree of success in motor racing in the Caribbean. They are currently the fastest cars in Barbados, Trinidad, and Guyana. As an engine for a road car they might be uneconomical (mileage) but they are extremely popuar for racing down here!

George Chin (degsc@yahoo.com)

The other reason it is not more widely manufactured is that more efficient (power) and economical (fuel efficiency) designs, and there are several, have been patented but not yet produced due to other challenges inherent in high power-density engines.

One of those closest to commercial availability is the RandCam, check regtech.com - one version of which (a ceramic/diesel version, I believe) is going through 2nd or 3rd generation use in the US Navy's SWARM program for small, expendable UAV's, and will immediately be licensed out by the US sister-company (RegiUS?) for small engine use, probably for things like weed-wackers and lawn mowers first. I'd look for a hydrogen 'burning' version down the road, since the parent company has a large interest in a point-of-use hydrogen-separating tech as well, which would eliminate that pesky hydrogen-gas tank and refueling issues.

In fact, I need to google that whole subject and do some followup due diligence for my investment club and see if it's time to consider one of the public-traded shares (there's several layers of private ownership, and half has been 'donated' by the major developer to that Jehovah's Witness cult, though they probably claim they don't invest in military tech...or at least that's what I remember from my original research into RandCAM several years ago).

Of course, if you want to wait awhile for any evidence of a manufacturable 'real' prototype, there is the toroid motor out at angellabsllc.com - no idea if they'll find a way to deal with the heat rejection needed by this dense of a design, though the motion itself could make a great pump someday.

Moller International, http://www.moller.com/, apparently produces at least two variations of a wankel-rotary engine for powering their skycar, and I believe they may also be used to power snowmobiles? They are very powerful for their weight, which seems to be their primary advantage at up to 2 hp/lb?