Question on Rotary Wankel Engines

[Lionheart]

Hey all,


A quick question on Wankel Rotary engines. If one wanted a very powerful engine, 3 rotor size, would one make the rotors 'deeper' (thickness) or would you keep them about 3 inches thick and increase the overall diameter or face profile size? (You can make the rotors thick, or you could make them larger in diameter).

They now have aircooled rotory engines, such as the Sachs for snowmobiles and some older bikes, and in India, they are looking at running Wankels, aircooled, in their tiny 3 wheel cart cars.

A high performance version of one of these with an aircooled system would be really nice in a plane, (if it could be made quiet).

That Sachs engine is amazingly simple. One moving part like on a turbine. Basic castings, smooth, aircooled... What an amazing powerplant. Now that they have the seals tehcnology down, creating an aeroengine from one should be pretty easy, I would think...

Here is a Sachs Wankel;

http://farm5.static.flickr.com/4056/4270531004_8709ddb29d.jpg



Bill

[wombat666]

The short answer is to add an extra rotor Bill, at least with the MAZDA engineering philosophy.
:mixedsmi:

[Naki]

A local Long Eze had a Mazda rotary of aorund 600hp installed ...wow was it noisy ...you could hear it miles away...the owner must of thought it wasn't powerful and noisy enough :icon_lol: so now he's installed a jet engine from a Vietnam era drone/UAV with 2000lbs thrust giving a 1:1 power to weight ratio..

http://i96.photobucket.com/albums/l193/Naki_04/DSCF8704.jpg

http://i96.photobucket.com/albums/l193/Naki_04/DSCF8703.jpg

[Piglet]

Making the engine in an aircraft quiet is no problem, it's the prop moving air that's the challange...
Even jet engines are not that noisey, it's the air and exhaust velocities that make the noise.

[Lionheart]

A local Long Eze had a Mazda rotary of aorund 600hp installed ...wow was it noisy ...you could hear it miles away...the owner must of thought it wasn't powerful and noisy enough :icon_lol: so now he's installed a jet engine from a Vietnam era drone/UAV with 2000lbs thrust giving a 1:1 power to weight ratio..

http://i96.photobucket.com/albums/l193/Naki_04/DSCF8704.jpg

http://i96.photobucket.com/albums/l193/Naki_04/DSCF8703.jpg



Now that is COOL! Almost looks like something from Star Wars....


Roger that Wombat on rotor sets.


Roger that Tim on engine sound. The Wankel has a loudish 2 stroke sound to it. They tend to pop and stuff when at high RPM, changing RPM ranges. They are amazing engines. Really low vibration. Sort of a mix between a piston and a turbine jet.


Bill

[Naki]

I actually took those pics with with you in mind Bill...I will start another thread with some pics of other aircaft at a recent NZ air show which I think you might be interested in. There was a thread with all the airshow pics in Newshawks but it sort of got buried when SOH went offline for a few days..but i need to get to bed as its approaching midnight here and I have to work tomorrow...

[Lionheart]

Thanks Naki,

That would be awesome man. I found more pics of that plane online just now.

His paint scheme even looks a little 'Star Wars' looking, lol... If he had 4 super small turbines, two on each wing root, one on top, one on the bottom, it would look real close to a X-Wing, lol..

Must be fun...



Bill

[Bjoern]

Even jet engines are not that noisey, it's the air and exhaust velocities that make the noise.

Most old aircraft look silly with those hush kits fitted...

Unless it's a modern version (~ RX-8 era) I wouldn't use a Wankel at all. They're quite thirsty compared to their piston brethren.

[HighGround22]

.
Hmm. "Wankel Rotary Engine". Seems to me there was a Monty Python skit involving that term . . . . or is my memory faulty (pun unintended).

[MaddogK]

Ya'd prolly wanna go with the extra rotor as increasing the rotor size will increase the rotational mass and actually decrease the power output as those rotary's run best at high RPM's. Mazda's didn't start to breath till about 7K RPM and IIRC the tach on those RX7's went to 12K +.

[tigisfat]

I wouldn't go with the extra rotor, I'd easily say the best idea is to buy an aftermarket reinforced apex seal and add more boost from twin turbochargers, one small and one large. I'd actually gut an RX-7 with twin turbos and then swap the core for a 3 rotor, the ones from the mazda station wagons.

The other thing to remember about rotaries is that they need plenty of RPMs. I'd turn the one above to about 11,000RPMs. that'd be good for about 550-600hp.

[Ken Stallings]

Unless you countered the rotation with additional rotary compressors, would not a rotary engine's natural rotation cause a corresponding oscillation in the aircraft, either in the pitch, roll, or yaw?

Ken

[kilo delta]

Most old aircraft look silly with those hush kits fitted...

Unless it's a modern version (~ RX-8 era) I wouldn't use a Wankel at all. They're quite thirsty compared to their piston brethren.

The RX-8 also has a massive thirst for engine oil iirc.

[Bjoern]

The RX-8 also has a massive thirst for engine oil iirc.

Would buy one nonetheless. I suppose you can afford the extra oil as an engineer. :icon_lol:

[Lionheart]

Unless you countered the rotation with additional rotary compressors, would not a rotary engine's natural rotation cause a corresponding oscillation in the aircraft, either in the pitch, roll, or yaw?

Ken

Hey Ken,

I havent never heard of this.

The Rotary engine is unique in that its vibration is extremely low. The only thing it has issues with in vehicle applications is torque. It acts like a huge lever in the Z axis when mounted with the shaft going front to rear. Thats why it failed so badly as a motorcycle engine, though the BMW still has the crank mounted fore/aft as well... They seem to deal with it.


One of the reasons I like the Rotary engine for aircraft is low vibration and continuous power curve. Its almost like an electric motor or turbine. I do not care for running one at 7K RPM though. Man, thats a high amount of R's... If they can sustain that though, and that is their perfect 'constant' then I guess thats what it is.


I have this design for a little triangle plane. Ive been dreaming on it for perhaps 20+ years now. It has a Wankle in it, 3 rotor, and you can drop the engine out the belly on a rack to examine it (change the oil, plugs, tune it, etc), and then heave it back up into the craft. The Wankle would feature lever like clamps so that you could literally disassemble the engine in sections and examine the innerts. Its a wild thought and probably too radical, but with technologies in machining getting so perfect, I figure such things could be done.

Thus... In an afternoon, you could add a module section (rotar and chamber) into your engine, clamp it together, (very elaborate double or tripple redundency interlocking lever system), and push it back up into the craft, start it up , and you have another 75+ HP.



Bill

[tigisfat]

Unless you countered the rotation with additional rotary compressors, would not a rotary engine's natural rotation cause a corresponding oscillation in the aircraft, either in the pitch, roll, or yaw?

Ken

Because the effect is minimalized like many other forms of propulsion such as jet engines.

[tigisfat]

Hey Ken,

I do not care for running one at 7K RPM though. Man, thats a high amount of R's... If they can sustain that though, and that is their perfect 'constant' then I guess thats what it is.


The sweet spot for most rotaries is barely tapped yet at 7,000rpms. You'd just have to plan the appropriate gear reduction, as with almost all automotive engines used in aerospace. There are so little moving parts in a rotary there is little besides proper apex sealing tht holds them back from high rpms. the clunky and cumbersome valve train is the source of many problems at high rpms for automotive engines.

[kilo delta]

I've heard that the RX-7 suffered from the tips of the rotors wearing....leading to compression problems after only 60k miles...and an expensive repair bill.
While I always liked the look of the RX8, with it's rear suicide doors and decent performance (in the 231bhp model)....... I don't think that I could live with a car that on average manages 16/17 mpg (unless it was a tuned BMW M3 or M5!!!!;) :icon_lol:)

[Lionheart]

The engine seals were with the early versions. That was long since fixed and improved, perhaps 15+ years ago.



Bill

[JoeW]

Back in the 70's I had a friend that had an RX3 coupe. He removed the governer and that car was amazing. Small and light, it performed like it had a 400 hp V8. He would turn up 8 grand easily and 10 grand in second and third was was amazing ............. It was like a turbine.
I often wondered why they weren't used more. Still do!

[kilo delta]

The engine seals were with the early versions. That was long since fixed and improved, perhaps 15+ years ago.



Bill

I'm not sure that the rotor tip issue was ever fixed on the RX-7.....the RX-8,however doesn't suffer from this particular problem.:)

[Ferry_vO]

IIRC Diamond has made some aircraft with a Wankel engine? (I believe it was a version of their Katana)
Torque isn't much of an issue with Wankel engines, as the rotating mass is relatively small, I don't think the diameter of a Wankel rotor is much bigger than the diameter of a rotating crankshaft.

[Ken Stallings]

Because the effect is minimalized like many other forms of propulsion such as jet engines.

But jet engines rotate in a circular motion with the weight evenly distributed over the perimeter of the circular motion. Therefore, the jets engines are smoother than horizontally opposed piston engines. The firing sequence of piston engines are designed to attain a more symetrical sideways force, with each piston cancelling out the sideways torques of the previous firing piston. Further, each piston in effect becomes a somewhat circular rotation of its own.

The rotary engine has one piston so to speak with its triangular shape providing three separate burn chambers.

You may be right, the displacement in any direction may be small enough as to be insignificant. I just don't know. But my biggest concern is that a car sitting on the ground has its weight resting on the ground and that can dampen the oscillating forces. An aircraft in the air enjoys no such natural dampening force and therefore if an oscillation starts to take place, if the rotary engine's piston was set up at a certain RPM, it could cause a harmonic type of oscillation in which a small oscillation builds upon itself and eventually could overcome the control surfaces' ability to maintain stable flight.

Cheers,

Ken