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Wankel/rotary - why dont we see more in experimental aircraft ?


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There have been many wankel/rotary small lightweight power planets for sale in the past 10 years

water cooled, for running gensets et, UAVs, designed for 100% load for 500 hours before seals overhaul.

 

120HP (peak) engine is 32kg, (4500RPM) (twin rotor) ....

team with rotax reduction gearbox....

 

or hybrid :  run an alternator-generator to battery, and electric motor to prop/.

Wankel engine runs the system at 75% power.  

30 minutes in the batteries enables solution for wankel engine failure.  and also provides power boost for takeoff. 

 

 

 

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True

Same as twostrokes Not gas guzlers really  ! .

61 mpg Hummel Ultra Cruiser. Now thats economical.

spacesailor

 

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1 hour ago, RFguy said:

There have been many wankel/rotary small lightweight power planets for sale in the past 10 years

water cooled, for running gensets et, UAVs, designed for 100% load for 500 hours before seals overhaul.

 

120HP (peak) engine is 32kg, (4500RPM) (twin rotor) ....

team with rotax reduction gearbox....

 

or hybrid :  run an alternator-generator to battery, and electric motor to prop/.

Wankel engine runs the system at 75% power.  

30 minutes in the batteries enables solution for wankel engine failure.  and also provides power boost for takeoff. 

 

 

 

Do you have a link for that 32kg 120hp engine?

 

This one in an RV4? Is pretty impressive. 

 

 

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There's a very extensive thread on Wankel somewhere. I would summ it up as not enough torque, but Torque x rpm - horsepower, but when you use the rpm that produces suitable horsepower, the fuel demand doesn't suit the expected hourly consumption for Recreational Aircraft, and as a secondary issue it works well in intermittant engine applications because it can cool down between power bursts and produce reasonable seal life, but in the constant power application of an aircraft the most rapid seal deterioration occurs.

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Direct Injection 2 strokes may be better than a wankel for fuel economy but they can do a bit better than a 2 stroke normally. They can be hard to muffle (Noise). but in my  research are more reliable than a 2 stroke . Definitely a proposition for a genuine sport plane. Nev

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Thruster, I will dig out the links for you.(embedded)  some of those came from marine engine developments, and also there are compound cycle wankels that have an extra rotor tjat post processes the exhaust gasses. 

I'm attempting to have a conversation with some of the vendors and will write up tomorrow most likely. 

 

There is this mob, been around for a while, not sure how much of their production is vaporware, but their claims and weight setc certainly stack up to that reported in peer reveiwed journals. https://freedom-motors.com/freedom_530cc.html    seems that have been through turbulance of non delivery for their stakeholders.

 

there's another mob that are quite active :  https://www.aieuk.com/    their website seems unavailable this evening.   they are active and have engines off the shelf to purchase. 

 

and there are a few German mobs who also have engines available off the shelf to purchase. 

 

all those options are still  about half the weight of a 13B even with all ancilliaries. I guess you build em different when weight doesnt natter so much. 

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At 32kg for a genset powerplant, the current rotary still too heavy, considering that you still have to add the generator, and the batteries for primary hybrid power.

 

But ...... Mazda are well on the way to producing a new Wankel - which is reportedly about 1 litre capacity - and which is going to be the genset powerplant/range extender for the 2022 Mazda Hybrid cars.

 

Mazda are being exceptionally coy on the actual final design of this new version of the rotary, but we should know more by the end of this year. A small, lightweight rotary range extender could be the answer for a hybrid electric aircraft.

 

https://www.mazda.com/en/innovation/stories/rotary/newera/

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Way back in the 80’s, I wrote the “experts report” for the IPO of a new engine on the ASX.

 

‘’All I can say is that a new engine type is up against an engine that has has a hundred+ years to get the wrinkles out. It isn’t easy to compete with that.

 

There is a HUGE difference between a test bench pampered performance and the actual performance after an engine has been sitting unused and neglected in a hangar for a month and is required to reliably produce full rated power after a ten minute warm up……and to do this month after month and year after year.

 

Good luck to the alternative engine builders! You are going to need it.

Edited by walrus
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Posted (edited)
8 hours ago, onetrack said:

At 32kg for a genset powerplant, the current rotary still too heavy, considering that you still have to add the generator, and the batteries for prim

It's close

60kW generator - 8kg,

Batteries 20 minutes at 50% power  is 36MJ  - 62 kg (LiPO4 - they don't catch fire ever) . 

However   genset powerplant of 32kg DOES need cooling anclliaries (Total 5kg). = 37kg

 

We are up to 37+8+62 = 107kg. Not too far off. 

 

The mazda is another compound rotor design. There are many. Nothign special, just well commercialized.

 

 

 

Edited by RFguy
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TURBS

so you are saying the seal problems have not gone away, same old problems , need substantially derated engines for high continous output ?

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That type of seal will always have problems compared to round holes which are the easiest to seal. In supercharged form they will just keep on putting out power but chatter type wear of the outer case and heat at the ports limit the thing. NORTON the motorcycle people made an aircooled one that has been used in aircraft. More recently than that in the USA they were used in racing outboards which is similar to flying where you are flat out a lot.

  They will never be as thermally efficient as a four stroke as the combustion chamber has too much area to volume and always will inherent in the design. It can't run high compression ratios also but does respond to supercharging. Sun and planetary gears are the best for gearing the engine down. (better than a layshaft)  The motor is not likely to throw the internals all over the place like a reciprocating motor can easily do. Nev

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I'd be happy to swap some efficiency and lifespan for an engine that didnt have pistons trying to get out of the box....

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1 hour ago, RFguy said:

TURBS

so you are saying the seal problems have not gone away, same old problems , need substantially derated engines for high continous output ?

Yes, Facthunter’s post sums it up, a circle is easier to seal than something with corners plus a swept path combined with face seal.

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9 minutes ago, RFguy said:

I'd be happy to swap some efficiency and lifespan for an engine that didnt have pistons trying to get out of the box....

Most don’t get out of the box

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This is a terrific video, worth watching if you have time. 

the LiquidPiston engine. includes visit to the plant.

May 2021. new.

 

essentially the rotor has a port internally. 3 bangs per rev.

 

 

 

 

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1 hour ago, RFguy said:

This is a terrific video, worth watching if you have time. 

the LiquidPiston engine. includes visit to the plant.

May 2021. new.

 

essentially the rotor has a port internally. 3 bangs per rev.

 

 

 

 

I like it and the idea of 3 bangs

You can see it still has the two types of seal used by Wankel, the wiper seal around the two sides (front and rear here). Notice a little carbon build up out to the seal. The apex seals are reversed, mounted in the housing and scraping the apex.

The million dollar questions are:

1.  Will the three bangs allow a smaller fire, and therefore a cooler chamber, so lower temp to stop the seals burning away at full power?

2. What is the torque, rpm and power compared to a 4 hp 4 stroke. I think he gave us the hp, but with the rpm we can work back to torque and then perhaps see if it suits constant load applications such as aircraft.

 

 

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Posted (edited)

the torque etc question is what many  people who try electric power aircraft often dont do their sums- spec of 100HP at 8000 RPM etc , and of course at 2500 they'll be very disappointed... must use reduction gearbox for std prop. 

It looks very new right now. But some neat ideas.  ah yeah I see the seals on the casing.

 

I wonder what people are doing for innovation for engines  in marine service (high continuous loads). 
As a kid, my friends with Mazdas, we used to joke fill up with fuel, fill up with oil....

Edited by RFguy
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Posted (edited)

There is a bit of stuff here on their 30kW output 

https://www.sae.org/publications/technical-papers/content/2018-01-0885/

 

but they do say "final performance objectives'. they have not got there yet.

"The final performance objectives of the program are aggressive: 45% brake thermal efficiency; > 1 hp / lb power-to-weight; and the engine is targeted to fit within a 10”x10”x10” box weighing <40lbs."

 

1hp/lb is about the same as a Jabiru 6 cyl :-) . but thermal efficiency would be impressive if they make that. I guess if they can hold the hot gases as long as possible, do as much work as possible is the game....

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20 minutes ago, RFguy said:

the torque etc question is what many  people who try electric power aircraft often dont do their sums- spec of 100HP at 8000 RPM etc , and of course at 2500 they'll be very disappointed... must use reduction gearbox for std prop. 

It looks very new right now. But some neat ideas.  ah yeah I see the seals on the casing.

 

I wonder what people are doing for innovation for engines  in marine service (high continuous loads). 
As a kid, my friends with Mazdas, we used to joke fill up with fuel, fill up with oil....

Marine has the advantage of a continuous suppy of cold water, so a slight advantage over auto radiator temp but fuel consumption these days is a key factor becaise of the cost of petrol.

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Sniff i miss the 1200cc two stroke jet ski's.

 

marine were running direct injection outboards for a while but that has ceased, everything is now 4 stroke with forced induction for performance.

 

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1 hour ago, spenaroo said:

Sniff i miss the 1200cc two stroke jet ski's.

 

marine were running direct injection outboards for a while but that has ceased, everything is now 4 stroke with forced induction for performance.

 

That's a good point; they did that because they couldn't meet the ever tightening emission standards.

The wankel principle now has a much more stringent environmental performance to achieve than it did in its heyday.

 

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that's the reality unfortunately, engines are getting more efficient but less powerful thanks to emissions,
the new generations of bikes have the same power or sometimes less then the previous for the same capacity. and its all down to tighter regulations on emissions.
cant burn oil anymore to help with the performance

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Car Ute and Van engines are smaller and they are getting crazy outputs from them. The adblue seems to work too. NO stink. It's incredible what

 Torque comes out of a two litre Turbo Diesel.. Nev

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