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Wankel engine?

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Wankel engine?

Old 24th May 2006, 01:46
  #21 (permalink)  
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from around 200hp up, you can figure that a complete Rotary installation will match a same power Lyc-dry.

Rotapower is an unknown on continous high power.
It's like a drag-racer using a 1500 hp fuel dragster with a 7l-V8 and claiming any V8 can do the same in an airplane...

As far as I know Rotapower is used in Jet-skis, etc.
duty cyle is more like a car, about 30%.
Aircraft are more like 80-100%.

Check up on Turbo Diesels again.
Once the hp gets a lot over 160hp, the engines become very heavy.

What does the Wilksch put out -180hp?
I bet it is not going a lot bigger!
Look at the Thielert: The small engine is a great success, but no word of the new 360hp wonder!!
By now it is 300hp at 600lbs dry....

The Rotary comes in at higher hp levels.

The 190hp about matches the Lycoming with the installed weight.
From here on it outperforms any piston on the market for power/weight/TBO/cost.
Cost is about the same as piston, but the TBO makes it a cheaper deal!!

I know the Rotary is not all perfect, but a very good alternative and new theme on an old tale!

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Old 24th May 2006, 20:31
  #22 (permalink)  
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There is a limit on maximum practical piston size in a turbodiesel, which in 4-cyl is approaching ~200BHP (that's why i only chose 4-cyls for the comparison). In theory you could take your 160 BHP 4-cyl Wilksch and double up on the number of pistons to make a 320 BHP V8. So the BSFC and kW/kg stay the same, although cost goes up linearly with power. In fact the 650 BHP (Cosworth/Mahle) VW R10 V12 diesel Lemans series machine boasts the highest specific power in a diesel car, and Ricardo/JCB have pushed further for a landspeed attempt - both are 4-stroke but are very secretive about weights. The same constraint will also apply to Avgas engines - it is all to do with combustion time.

Actually the SI diesel rotary does point to a possible future. You need to get the diesel to about ~600K before it will combust, but have to keep combustion below 2000K to avoid NOx. Running high boost, even with intercooling, will increase the inlet temp requiring a reduction in compression ratio. I had hoped to spark a nice technical debate on a rotary dedicated forum:


If you can design the crank mechanism to handle the pressure there is in principle no limit to the amount of turbo boost you can have. The same is true of Avgas, but the need to avoid knocking limits the possible efficiency. The ability to actually inject fuel during combustion is the main reason for my preference for diesels. My reservation about rotaries is entirely down to the combustion chamber fluid dynamics in such an awkward shape.


Last edited by Graviman; 31st May 2006 at 19:13.
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Old 25th May 2006, 09:45
  #23 (permalink)  
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Keeping up with the latest (courtesy of NASA Tech Briefs) brought me to this interesting development -
Difficult to find out much about it, but it would be interesting to know what others think. Is this going to be another Dynacam engine???


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Old 25th May 2006, 19:34
  #24 (permalink)  
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Shawn, there was a suggestion this thread was merged with:

This engine is a clever concept, but i'm not convinced. It needs complex seals, bearing in mind the 25:1 compression ratio. These will require rotary level of development, but for pressures of two to three times greater. Oil emission will be much worse than rotary.

The mechanism also looks much too flimsy for the sorts of powers discussed. By the time it is beefed up, i'm betting the weight is nearer those V8s that are mentioned. I would imagine compacting the mechanism is on the menu.


Edit: To address Delta3's comments about rotary seals.

Last edited by Graviman; 26th May 2006 at 20:38.
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Old 26th May 2006, 05:35
  #25 (permalink)  
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The best power-to-weight piston engine is the radial layout one.
But why is there no modern up-to-date-tech turbo radial engine on the market for small heli's and fixed wing? is to expensive in production to be able to compete with other piston engines?

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Old 26th May 2006, 16:32
  #26 (permalink)  
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Agreed, RotorRookie. The disadvantages of number of spark plugs to change disappear if you are running a turbodiesel radial, where the injectors last the life of the engine. The other advantage is a good spray pattern for the injectors, and a compact/light crank mech.

A loop scavenge 2-stroke radial turbodiesel is:

The maximum power version is 300BHP, which would get to ~441BHP if a uniflow scavenge 2-stroke radial was developed. So on the table prepared earlier:

Zoche Aerodiesel radial: 1.8kW/kg
Concept radial turbodiesel: 2.7kW/kg

So we have a clear winner!

For automotive,where emissions are king, poppet valves have outlived sleeve valves and rotary valves because they work and don't leak oil. This is why all mass prod cars are 4-stroke, and i don't really see why similar power/weight is not achievable...


Last edited by Graviman; 26th May 2006 at 16:52.
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Old 26th May 2006, 19:49
  #27 (permalink)  
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Aren't we running circles here ?

1. Wankel versus MYT : same sealing problems ?

2. (Diesel) in line versus radial : why did aviation petrol engines abandon radial designs despite of the weight and cooling advantages ?

3. Two stroke loop > Two stroke uniflow > Four stroke : why are all racing engines moving to Four stroke ?. I would put uniflow in between 2 and 4-stroke: better but not fully efficiency, but added weight, height and complexity in line with 4-stroke.

From the specs it appears to me that Zoche could power for instance a R44 type heli, without applying unproven techniques, need we more ?

The key may still be (proven) reliability, given the fact that even the current 'antique robust' engines are quite oversized. Imhb, that is what Thielert among others will need to prove.

Don't read me wrong if this may look like a argument for no change, I am driving 7 years the wonderfully efficient CDI-engines with lots of torque and would not want to go back..

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Old 26th May 2006, 20:37
  #28 (permalink)  
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I am enjoying this discussion - it provides me with the sanity check i often need as an engineer!

My own particular interest in applying turbodiesel engines to helicopters is to avoid the costs assoiated with gas turbines. This includes fuel and manufacturing, due to the materials required to raise TET. I actually see the turbodiesel as just another combustion chamber variation. I also appreciate that this is the objective of the rotary engine.

To answer your questions:

"1. Wankel versus MYT : same sealing problems ?"

See ammendment to post on MYT above. It's not an impractical engine, but i suspect that many of the issues that lead to the criticised Cummins example engine have been overlooked.

"2. (Diesel) in line versus radial : why did aviation petrol engines abandon radial designs despite of the weight and cooling advantages ?"

Probably because Frank Whittle and Hans Von Ohain showed the world a better way. The turbo charger has direct ancestry to the gas turbine, and is making aerodiesels viable. This new breed of aerodiesels are reintroducing the possibility of large multicylinder engines - no spark plugs to maintain...

"3. Two stroke loop > Two stroke uniflow > Four stroke : why are all racing engines moving to Four stroke ?. I would put uniflow in between 2 and 4-stroke: better but not fully efficiency, but added weight, height and complexity in line with 4-stroke."

About right. The Mercedes paper (SAE 981032) does not give weights, but compares loop scavenge, uniflow scavenge and 4-stroke (4 valve). The uniflow is shown to have similar specific power to the 4-stroke. The 4-stroke of course will not suffer any piston/ring lubrication oil getting into the combustion chamber. In practice 4-stroke is currently about 66% specific power of uniflow 2-stroke, but advanced turbo charging concepts will nullify that advantage.

"From the specs it appears to me that Zoche could power for instance a R44 type heli, without applying unproven techniques, need we more ?"

Well as you say the reliability needs to be proven. The general theme of the thread, while discussing the rotary engine, has been to explore future engine developments. I would say that Zoche points the way for big 4-stroke turbodiesel radials. Increase the boost, and reduce the size (and improve efficiency).

"... I am driving 7 years the wonderfully efficient CDI-engines ... and would not want to go back.."

It would take a serious development for me to trade up my VW diesel!


Last edited by Graviman; 11th Jun 2006 at 13:20.
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Old 27th May 2006, 01:17
  #29 (permalink)  
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I WAS a big fan of the Zoche Aerodiesel, but it seems it is just another "Moller-Skycar"!!

Eating up government funding but producing nothing in the long run!

He comes to Oshkosh every year and the same old engine gets rustier every time!
He produces essentially the same engine for stationary compressors, fire pumps, etc.
However the Aerodiesel seems to have a problem with reaching the projected TBO (2000 hrs). It is a lighter version of the stationary diesels, AFAIU.
This is going on for some 15 years at least.

Mistral is on it since less than 3 years and are certifying their first one this year!!

There are plenty of exciting engines out there, but if they never make it out of "Dreamland" into reality AND have a marketing and production effort behind it.

Dynacam was a good engine concept, but never got the marketing or production effort.
Same with the Quasi-turbine....

I am afraid the MYT http://www.angellabsllc.com/index.html
is in the vapor ware catagory, at least with the power claims he is making.

Then there are:

Pivotal Engine, http://www.pivotalengine.com/index.html
Rad-Cam Engine, http://www.rad-cam.com/
Rand-Cam Engine, http://www.regtech.com/
Split Cycle Engine, http://web.archive.org/web/200012160...com.au/eng.htm

All interesting concepts, ...I am afraid that's where they will get stuck, ....unfortunately.

Non of them has A real new advantage over existing engines. Plenty of claims but none that come through so far in production - plenty of problems though to get into production!!

That's why I bet that Mistral is going to make it!
You need to read up on the history of Mistral and how it came to be.
Basically Mazda did most of the basic R&D over decades of spending millions on their road engines, which today are some of the toughest machinery you can buy.

Mistral started right there to get it fine"R&D"'d for aviation - never mind a huge task by itself.
However the Rotary is the only engine you can take from the car to the airframe without having to change the layout of the basic components - like you have to do in a piston engine, or it will die in about 300-400 hrs (piston engines....).
Thielert being the exception and even he has to do everything new except the block ( ...and maybe the head, I wouldn't know OTBOMH)

If you want to know about the sturdyness of the Rotary, start to roam the Rotary racing sites/forums.
There is no piston engine ( same size, cumulative combustion chamber volume) out there that takes as much abuse with as little maintenance/overhauls.


PS: Just for the curious:

This baby is never going to fly, but it is biiiiiiiiig!!
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Old 28th May 2006, 21:03
  #30 (permalink)  
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I was only really using the Zoche to generate figures for turbodiesels, but didn't realise they had been going (or not) that long! For my money Wilksch are the guys to watch as they have a very conservative design, but in a good overall package. Again it seems to be happening at a sensible pace.
Interestingly the Dyna-Cam is still out there, but under a new guise:


I can't really comment on the Mistral specifically, but the rotary is very definately an extremely robust design so i see no reason for any problems. Certainly the pace they are working at indicates that they are serious about producing a product, rather than a concept.

I'm just a piston head, since i prefer heavier fuels - mainly due to their combustion characteristics. The point i was really trying to show was that Mistral G-190 Rotary compared similarly to the Wilksch WAM-160 in terms of power/weight. The better fuel consumption of the diesel then benefits the operator. This is not strictly a fair comparison since the Wilksch is turbo while the Mistral is not. The point being made is that better crank mechanisms will allow future turbodiesels to offer improved power/weight.


Edit: 'cos i gots confused over names - Sorry folks!

Last edited by Graviman; 29th May 2006 at 19:02.
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Old 29th May 2006, 19:00
  #31 (permalink)  
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VW Engine Database

Just to provide a baseline for comparison, i thought to include a link to the best VW engine database for weights that i have found on the web:

VW Engine Database (auto scrolls to 3-cyl TDI)

Unfortunately 4-cyl data is hard to find, however the automotive 4-stroke turbodiesel is as follows (using the best figures):
3-cyl: 0.52kW/kg
V6: 0.77kW/kg
V8: 0.9kW/kg
V12: ~2.4kW/kg - this is the engine used in the R10 LeMans racer!

A realistic figure for 4-cyl 4-stroke engine is probably about 0.6kW/kg. Interestingly VW are now looking along the lines of higher boost in smaller engines.


Last edited by Graviman; 29th May 2006 at 21:05.
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Old 11th Jun 2006, 13:02
  #32 (permalink)  
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RR Turboshaft Database.

For completeness, a comparison against turboshafts aimed at helicopter application:

Rolls-Royce Helicopter Turboshaft Database

AE 1107C: 4586 kW / 440 kg = 10.4 kW/kg

RTM332: 1897 kW / 228 kg = 8.32 kW/kg

T800: kW 1268 / 154 kg = 8.23 kW/kg

MTR392: 958 kW (Max Take-off) / 169 kg (dry) = 5.57 kW/kg

Gem: 746 kW (Max Take-off )/ 183 kg (dressed) = 4.08 kW/kg

250: 485 kW / 124 kg = 3.91 kW/kg

T63: 313 kW / 72 kg = 4.35 kW/kg

In practice figure on a increase on cost/power proportional to power/weight...


Last edited by Graviman; 12th Jun 2006 at 13:38.
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Old 12th Jun 2006, 07:37
  #33 (permalink)  
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Always had a fascination w/the RX2 and Wankels in general....

After a ride in an RX2 about the SEA environs with a priest friend of my new wifes', I started reading up on the cars and engines. Road and Track or Sports Car Graphic or other such did a 50K test drive with one, and reported that with the stainless exhaust, there was no wear apparent on the motor and no corrosion with the exhaust. Mazda developed the engine with a chrome liner in the combustion surface and ceramic seals with spring tensioners, further, that dyno tests they did indicated that the only limit in RPM appeared to be lack of air....

This made me think that perhaps two engines put together, i.e. working center two rotors with outer rotors being used as air pumps for the working middle might be a cheap way to hot rod one, given good engines sourced from otherwise totaled wrecking yard machines. Long (2 X) binding bolts to hold it all together and maybe some fancy welding on the crank (methinks the rotors each bolted together at the crank, and were interchangable, but I disremember) and use the front and rear end plate/bell housing from one of them to sandwich the works.... thought a simple stopped flapper valve to control air source and route the exhaust from the 'compressors' to the intakes, maybe rotating the outer banks 180 degrees to get proximity for the cold exhausts to the working intakes -- or not, if you tried high pressure injection like the jtronic from Volvo and wanted lots of mixing and cooling on the intakes - roughing the interbank intake runs for non-laminar turbulence and charge-shaping before passing the intake ports in the working banks. --That, or just mount a blower on a stock setup and over-pressure the heck out of it....
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