Wankel engine?

[TIMTS]

Have anyone thought of putting one of these engines in a helicopter?
Its lighter and smoother than a recip engine, and apparently powerful as well.

[Graviman]

The new Mazda Renesis engine (RX8) is a good candidate, but not sure if anyone is aero rating this. Other recent projects:

http://www.wankel-ag.de/seite1_e.html

http://www.mistral-engines.com/index.htm

I think Norton still build drone engines in Gloucester (UK), but only found this site:

http://www.nortonmotors.co.uk/about%20us.htm

The main problem with the rotary is the need to supply oil to lubricate the rotor, which in combination with an awkward shaped combustion volume, means that it will eventually fall foul of emissions requirements. I think the general view is that if you need improved power to weight you are better turbo boosting a piston engine. This limits the appeal of the rotary for new engine designs.

The best site for the Mazda rotary is:

http://www.rotaryengineillustrated.com/renesis.php

My guess is that rotary offers maybe double power-to-weight over piston, but new materials technology forever helps piston power-to-weight. If you find out anything please post!

Mart

Edit: Wankel-ag.de site address

[NickLappos]

It is interesting to see how the bumf for a given technology/engine/antitorque system has such endurance, and so little in the way of hard engineering.

The wankle died when the first oil crisis made fuel economy top priority, and I know of no major improvements that have raised it into the piston engine pack. Fuel economy is critical for pistons, since they exist only because the extra weight they have is offset by the lesser fuel they burn because range is the operating parameter. I have heard 9and can't find right now) that wankles eat about 10% more fuel per HP than a piston.

BTW, I saw that previous post where the erstwhile engineer had a rotating piston engine (a variable ratio displacement rotary engine, I think) where he could get a zillion HP out of a 125 lb engine. Yes, and also it runs on cornstalks and sea water.... If only engineering were so simple!

[IFMU]

Norton spun off the company UAV engines. Their website is here:
http://www.uavenginesltd.co.uk/

Also, a quote from their site:
"Please note that UEL do not supply engines for powering manned aircraft (or any other applications.)"

Having had some experience in the rotary wing UAV field with that engine, I wouldn't argue with their statement.

There was a recent article in one of the US homebuilding magazines that compared 4 RV8's. Two had rotaries and two had Lycosaurus engines. The main differences that I could see were:
1) the rotaries were thirstier
2) the rotaries were louder.

This agrees with my personal experience. My ears are still ringing 7 years later.

-- IFMU

[Graviman]

Agreed about myth perpetuation, Nick. The latest Mazda offering almost looks competetive in fuel efficiency terms - it gets ~24mpg (pretty lousy considering i'm used to 55mpg :uhoh: ). Like all design problems, there is a tradeoff in deciding whether the engine is aimed at more power or efficiency. In the rotary this comes in the form of rotary piston width.

Ideally the rotary piston should have the same width as tip-to-tip distance. This then approaches an "oversquare" (bore/stroke>1) piston engine for surface_area/volume. The problem then becomes breathing (ie power), since a gasoline rotary needs the ports in the sidewall to avoid the "valve" overlap that causes unburnt fuel emissions. Direct inject allows cylinder wall ports, but only diesels actually inject the fuel near or during combustion. The maximum compression ratio is too low for diesel combustion though.

Put in simple terms every engine design is a compromise for the given requirements and constraints. The rotary engines biggest area of compromise is the fluid dynamics during combustion. For this reason it is a concept which will always be there, but will never really be competative. For my money a good piston layout (eg radial for aircraft) beats rotary every time, and turbos are the way to boost power.

Mart

[Ian Corrigible]

Could have sworn that someone stuck a Wankel in a B47 or H269 at one time, but can't find any details.

The Swiss gave it a try with the Berger BX-110 (http://avia.russian.ee/helicopters_eng/berger_bx-110-r.html).

http://avia.russian.ee/foto/berger_bx-110.jpg

I/C

[slowrotor]

As IMFU has noted above, last month Sport Aviation magazine ran an article about RV-8s, both rotary and lycoming, flown side by side. The rotary used quite a bit more fuel and was much louder.
Helicopters really dont need more noise. I suppose a better muffler could be fitted.
I watched and heard a wankel powered Coot amphibian. I was annoyed by the sound.

[Graviman]

Anything about weight comparisons Slowrotor? I've come to the conclusion that radials weigh about the same as rotaries for any given naturally aspirated power. Basically excess crank&block mass is removed.

I remember reading a paper by Mercedes that compared their own developed uniflow 2-stroke diesel to it's 4-stroke diesel baseline - they must have spent quite a bit of cash in development. Despite the myths, the 2-stroke actually faired no better in terms of power! The reason was you needed about 1.8 times the air to scavenge, and a sizeable proportion of stroke was given to scavenge. This seems to be born out by the Wilksch Airmotive and Deltahawk turbo-diesel engines, which while being good performers weigh about what i would expect a comparable 4-stroke turbo-diesel to weigh.

http://www.wilksch.com/ ; http://www.deltahawkengines.com/

I suspect rotary engines are the same. The truth behind the myth is that they have slightly higher RPM capability, but the power-to-weight does not reach legendary performance. ;)

Mart

[chevvron]

Surely a diesel Wankel would get round the lubrication, economy and emissions problems?
Mercedes did develop a 3 or 4 rotor one for its C111 concept car in the late '60's, and I remember an article in Diesel Car magazine about one too.

[slowrotor]

Graviman,
The weight always depends on who is marketing the product.
I would guess that when you include a reduction drive built strong enough to be as reliable as direct drive and a cooling system and a proper muffler the weight could be similar. I dont recall what was said about the weight.

[Dave_Jackson]

Back in February there was a conversation with a Richard Sohn. The subject was the Blokow Bo-103 single-bladed rotorcraft, since he had worked on the controls for the flying version many, many moons ago.

He now owns or runs a small airport in Florida. During the conversation the subject of Wankel engines briefly came up. As I recall, he said that there were approximately a dozen Wankel driven rotorcraft and aircraft at the airport, plus a Wankel development association. The subject of high fuel consumption was mentioned and he said that the Wankel is an idea engine for rotorcraft since rotorcraft engines run at a constant rpm. He said that the fuel consumption of a Wankel varies greatly over the normal automobile operating range but the fuel consumption is the same as a reciprocating engine at its optimal rpm.

[Graviman]

Surely a diesel Wankel would get round the lubrication, economy and emissions problems?

Fraid not, Chevvron. In a 4-stroke an oil film adheres to the cylinder wall, and actually survives combustion - although this is how the diesel combustion particulates get into the oil. The inlet/exhaust flow doesn't interfere with this oil film, so remains clean. In either 2-stroke or rotary the oil film is constantly swept into the ports, so either escapes directly in the exhaust or becomes a product of incomplete combustion.

That said emissions on aircraft are nowhere near as strict as autos - i'm not sure what the exact requirements are. The problem with rotary diesel is mainly a maximum 12:1 compression ratio, limiting autoignition - good injection mixing is also harder to arrange.

... fuel consumption of a Wankel varies greatly over the normal automobile operating range but the fuel consumption is the same as a reciprocating engine at its optimal rpm.

Compared to an avgas Lycoming i can believe it, Dave - Low RPM gives more time for heat transfer into the cooling system. If a new engine project was being started specifically for a helicopter (ie high RPM) i think rotary would be in the concept investigation, but various factors would rule it out - total loss lubrication for the rotor seals would be my worry, since there are various ceramic coatings that can help with heat loss.

The VW soln for aluminium bores... (http://www.plasma-group.co.uk/keronite.html)

Mart

[KikoLobo]

The skycar project, managed by Dr. Moller at www.moller.com

features a "Wankel" type engine, in that there is rotary technology included, some other features are incorporated, however its not the same.

This engine was designed to go into the sky car project, you can check the sky-car which is a vehicle that features vertical take off characteristics at :

www.moller.com

and the engine it uses (wankel type) at :
http://www.freedom-motors.com/

[Graviman]

I had forgotten about Freedom Motors, thanks KikiLobo. That site certainly highlights one of the advantages of rotary over 2-stroke:

By operating on the 4-stroke principle, a rotary can have very good control over air to fuel ratio, this makes it suitable for the oxidation&reduction catalyst used for the emissions test. If the engine is to run as a diesel (Chevvrons question) then we are back to a "lean" air-to-fuel ratio. This means you cannot run the reduction part of the catalyst, but NOx only suffers if the combustion temperature gets above 2000K. The oxidation catalyst can still be used to remove any unburned hydrocarbons - i'm just oldschool in that i believe in not producing them to begin with.

My main concern then, for diesel or kerosine usage, is the limitation in compression ratio. I am definately convinced that efficiency is the only way forward for a helicopter powerplant...

Mart

[3top]

Hi all,

interesting thread. Also interesting how all the old misconceptions of the Rotary prevail!

If you want to get smart about Rotaries in aircraft I suggest to visit the following sites and to join the newsletters.

http://www.flyrotary.com/

http://www.rotaryeng.net/

Especially on the last one you will find a wealth of data and info on and about the Rotary in general and especially if it comes to adaption to aircraft. Also the owner of the list is working on a turbo compound system for the rotary.

Nick mentioned fuelburn.
I think that's not that important. Turbines are lousy at low levels - but they are light. So is the Rotary.
Moving parts - only 3 major parts moving around, not up/stop/down/stop/up/stop/.....(reciprocating...:) )
There is no catastrophic failure mode - no valves to break, rods to throw, cranks to shear, pistons to burn.
What it does is loose power, maybe can't restart, .....

Also, a comparison with any piston engine is useless.
It has aspects of 4-stroke and 2-stroke engines, but it is impossible to compare displacements. It is of course a 4-cycle engine, but it is taking the charge around the neighborhood. A piston engine has cylinders and all cycles stay within the cylinder.

At the end of the day it all comes down to how much to you feed it, what do you get out in return.

Rpm comparison is also irrelevant.
Though the excentershaft turns let's say 6000 rpm, each Rotor only does 2000 rpm at this stage (rotors turn at 1/3 excentershaft speed)
At the same shaft/crank speed a piston engine has less time to complete combustion per combustion cycle than in a Rotary.
There was a real Diesel rotary once, built I think by John Deere or Curtiss-Wright: It had a bigger Rotor that was driven as a compressor - feeding the actual power producing rotor with compressed air, so the pressure for diesel-ignition (self-ignition) could be reached - wasn't too efficient...

If you want to just burn Diesel/Jet-fuel you will have to wait a little longer until Mistral,
http://www.mistral-engines.com/
is ready to certify their Kerosine burner!!
It will be spark-ignited. Prototyps are running already.
Their first gasoline-engine is being certified as we speak, FAA to be immediately followed by JAR.
190hp NA,
next year follows the Turbo-intercooled version 230hp,
then a 3-rotor NA and turbo.
After that the K-series (Jet-A/Diesel).

The CEO went through this, because he nearly crashed because of "faulty quality-control at Lycosaurus"!

Also the more powerful the engines become the better the power/weight ratio of the rotary.

Where we are at a concise switchover point from piston to turbine around 400 hp, the Rotary has an easy potential to push this beyond 600 hp.

Of course even the Rotary will never match the power/weight ration of a turbine - but on the other hand it will also never match the $$$/SHP ration of it either!!

Don't bet on the Moller Skycar OR his Rotary any time soon.
So far (...about 30 years now) it has been mainly Vaporware for blind investors!
It is not so big a deal to build your own Rotary.
But it is if you want to make it safe and last!!

Mistral has their hardware flying (Embrey-Riddle operates a Turbo-Arrow on their behalf for R&D....). From their present state of development they project a 3000 hr TBO, at a very low overhaul-cost, compared to other aircraft engines.
Also their engine (or any Rotary for that matter) has a very high safety margin - e.g. the 360hp turbo could be brought up to 420hp easily for "emergency-power" (...for 30 min) if needed. It is recommended to inspect the engine after that, though there should be no reason for any replacements.

A last example:
Mazda won LeMans 1991 with a 4-rotor, non-turbo - outright. The win was such a threat to the rest of the club, that Rotaries where outlawed immetiately!
If you take any LeMans engine apart after the 24-hr race it is ready for a total overhaul or the junkyard.
--- Mazda hardly could find any sign of wear.
that machine developed some 720 hp...

Just read a little into the Rotary, and you will find out what a good engine design it is!

All the old-wife-tales are long solved:
High fuel-consumption - seal breakage - oil-consumption - idle problems, etc. are a thing of the long gone past...

Mistral matches or betters Lycomings fuelburn....

By the way, Citroen built a rotary powered helicopter!!
check this:
http://www.der-wankelmotor.de/Flugzeuge/Citroen-Helicopter/citroen-helicopter.html

And a sexy helo it was!!



Back lurking,

3top:cool:

PS:
At the present stage Turbo-Diesels loose their appeal for aircraft around 160-180hp. After this they become too heavy. See the Thielert - the 160hp one is a hit. the "360hp" is up fro mthe planned weight and down to 300 hp. At 600+lbs I prefer the 720Lycoming at 400hp.
Better wait for the Mistral....

[IFMU]

There is no catastrophic failure mode - no valves to break, rods to throw, cranks to shear, pistons to burn..
3top,

This is not true of all rotaries. One of my buddies has a chunk of rotor on his desk from one of those UAV engines rotaries. Apparently a tooth on the gear on the rotor fatigued off. It eventually found itself somewhere bad, and steel is incompressable. Capow!!! It was pretty catastrophic, I can assure you. This is not to say the same failure mode hasn't been addressed in either that rotary or other makes. However, any machine can and will fail you, be it rotary, piston, or turbine.

-- IFMU

[3top]

IMFU,

a) I guess it depends on definition of "catastrophic"
b) Rotaries do have some areas, that need more attention than pistons - well filtered air, for an example.
c) Drone engines are notoriously failure prone. Hardly any one is made for more than 50 hrs life. That is what they are made for - cheap and expandable.
d) If you want to kill a Mazda Rotary, you will have to do something wrong. If you just slightly care for your motor (like you should anyway, piston, rotor or turbine), the Rotary will not fail in a catastrophic mode.
Accelerate a piston past its rpm range and you got a handgrenade. Push a Rotary past its redline, and nothing happens. Push it way beyond the redline and your seals might go, but it probably still runs until you shut it off.

Again Drone engines should be compared to Drone engines.
I bet that piston drone engines have a higher failure rate than rotaries...

3top

[Graviman]

3Top,

Interesting post. You sound well informed about rotaries, so forgive me if i offer some constructive criticism. I am actually in agreement about the mechanical reliability of a well designed rotary engine. Piston sideforce during reversal is the biggest headache in piston engines, causing most of the durability limitations.

Not sure that rotary fuelburn can be dismissed out of hand, since it will contribute to the running cost of a privately owned machine. The rotary only really burns Avgas well, since the modifications for A1 are to make it burn more like SI Avgas. This means that a rotary "diesel" never has any hope of approaching the efficiency of a piston engine. With emerging piston diesel combustion technologies CI particulates are becoming a thing of the past. Regardless of existing legislation i feel that engine designers have a responsability to consider CO2 emissions.

Not sure you can dismiss comparison with piston so easilly either. To my mind a two rotor rotary is equivalent to an inline 4, in that there are 2 bangs per crankshaft revolution. The displacement comparison is always a problem, so the best solution is to consider any engine as an airpump. In this way a 2 litre inline 4 pumps 1 litre per per crank revolution, and a twin rotor with 1/2 liter per rotor section (ie 3 litre by convention) also pumps 1 litre per crank revolution. The rotary combustion chamber does not offer an easy shape for either SI laminar-to-turbulent swirl for flame propagation, or DI swirl for air/fuel mixing, so i would say piston makes better use of its litre (without considering heat loss through surface_area/volume).

My final concern is that the seals need the continous addition of oil into the combustion chamber for lubrication. An oxydation catalyst will remove hydrocarbon emissions, but work better if the engine is designed to reduce emissions from the outset. The 4-stroke is definately a compromise, but the piston/ring lubrication oil stays well away from the valves/ports. Centrifugal oil conditioners now exist to remove particulate contamination. This oil loss is my main concern with 2-strokes and rotaries.

The 400 to 600 HP range for helicopters is an interesting region. It may be that rotaries can offer a good infill, but my take is that variations on the turbo charged piston theme are equally promising. For diesel the main limitation is definately combustion initiation. Getting piston engine mass down is definately an area for development, with the block being the biggest contributor. At the moment i would estimate piston to have 1/2 the power-to-weight of rotary...

Mart

Edit: Correction about 2-stroke oil injection (actually better than normal engine oil for emissions).

[3top]

Hi Mart and all,

I am as well informed about Rotaries in aircraft or aircraftuse as roaming 2 forums about the matter permits.
At this time (unfortunately) no practical experience with Rotaries yet....

I only dismissed Rotary fuelburn as a concern comparing it to pistons.
Mistral matched and bettered the equivalent Lycoming numbers. Mistral published their dyno numbers to max. power. Lycoming stays quiet above 75%.....

Though the Rotary used to use more fuel, this is not true anymore. The RX-8 is at least even with the competition.
What I hear it is just incredibly hard not to floor the pedal and hear+feel the engine!:) -
You control the consumption and fun!

However the Renesis was specifically made for the RX8 and it seems Tuners/Racers have a hard time to find extra horses without a Turbo. The exhaust is too restrictive.

As the Renesis was developed for the road it surpassed fuel-consumption and emissions requirements for 2005 already in 2002.
So there is no real disadvantage anymore in that regime.
Of course the aviation rotary - Mistral - will be a totally different animal than the car version (Mistrals principal engine dimensions are identical with Mazda, although by today there are no interchangeable parts anymore....).

I think the last car that tried aircraft engines was Tucker - tried to use a Lycoming or a Franklin.
Can't really compare aircraft pistons with car engines either....


If you want to get detailed about displacement definitions, I recommend to visit Paul Lamar's site mentioned somewhere in my last posts.
There is various ways, depending what was the issue at hand:
# Mazda was ingenious to get the 2-rotor rated as a 1.3l (chamber volume 650cc) for tax- reasons
# Someone else made it a 2.6l for thermodynamics
# Some make it a 3.9l for swept volume of all chambers

How would you define it?
A 2l 4-stroke piston will pump 2l on one revolution, but only pump 1l through the engine.
A 2l 2-stroke engine pumps 2l through everytime.

There is always arguments, depending on the viewpoint.

You are right the Rotary will never be a true diesel (Self-Ignition/Compression-Ignition), but the idea behind a Kerosene/Diesel/Jet-A burning Rotary in Aviation is not increased efficiency, but fuel availability.
As it is always going to be spark ignited the K-Rotary doesn't have to be as sturdy as a true diesel. Those torque-spikes from a diesel do need a sturdy (speak heavy) block!!

2-stroke oil in rotaries:

I really don't know where you picked that up!
It is true that some people that converted Mazda Rotaries for aircraft use do mix the fuel with 2-stroke oil, but this is not the rule. These individuals just feel it's easier than to mess with the original injection-pump, which takes the oil from the engine sump.
Others use a separate oiltank and the stock or aftermarket oil-injection pump.
Others leave the stock system alone, save for exchanging the crappy stock plastic lines for something better.
These plastic lines cause all the bad reputation, when they crack from old age and heat and start to leak, leaving the seals without oil. However you need a really old junker to find that.
If I ever get to build my own motor, i keep the stock system with a possible aftermarket pump, good lines and most important: good oil in the pan.
Synthetics are the rage.
The oil consumption is a fraction what a Lycoming throws out the breather on a good day!!
I doubt you would have to ever top off a well built Rotary between oil-changes.....

On one of the forums I just read about the imminent first flight of a Lancair ES with a Turbo-3-Rotor that was dynoed at 500hp - chamber volume is still 650cc.
So even if you are very conservative, a 4-rotor can easily hit the 600hp range and wouldn't even push it.
200hp from a 2-rotor without turbo is a good average....

Careful assembly and systems integration is of course mandatory - but there are good, sad and horrible samples with pistons just as many.

You mentioned pumping efficiency.
Once the Rotary is correctly tuned it will easily run at volumetric efficiencies higher than 1, and that without a turbo.
Of course that means you will have to run it at a specific rpm setting, but in Aviation in general and helicopters specifically this should not be a problem.
This only concerns pumping efficiency however - how the aerodynamics considering combustion work is a different game - one of the downsides of the Rotary.

If you are specifically interested in Rotaries for Aircraft, I really recommend you join the newsletters mentioned in a previous post.
As a primer go to http://www.rotaryeng.net/ and start reading all the tech-papers about THE ENGINE!
For installation details scroll to the technical topics.
Warning: There is other ways to do things, what is posted is only one way, though well worked out!

For certified engines, you want to follow Mistral's progress closely! http://www.mistral-engines.com/


Cheers,

3top,:cool:

[Graviman]

Just for interest, trying to choose 100-200BHP and similar configs (2 "bangs" per crank rev). Using maximum powers and installed weights:

Mistral G-190 Rotary: 1.0 kW/kg - Avgas

Freedom Rotapower: 1.65 kW/kg - Avgas

Wilksch WAM-160: 1.0 kW/kg - TurboDiesel

Deltahawk DH160-V4: 0.68 kW/kg - TurboDiesel

Lycombing 0-320 D: 0.83 kW/kg - Avgas

Assuming that the Freedom figures are dry, installed specific power is probably also about 1kW/kg. The Deltahawk suffers because it is a loop scavenge 2-stroke, with nowhere near the volumetric efficiency of the Wilksch uniflow scavenge. Being very mean a VW TDI cast iron lump is probably about 0.5 kW/kg, but an aero redesign would approach the lycombing 4-stroke.

The practical upshot is that rotary offers little benefit over say a 2-stroke turbodiesel. This is why i feel that turbodiesel piston is the way to go, albeit requiring development to reduce weight. To my mind push the turbo boost way up and go for a small, but very solid, piston 4-stroke...

Mart

[3top]

Gravimen,

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!

3top,:cool:

[Graviman]

3Top,

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:

http://www.rotaryengineillustrated.com/forum/viewtopic.php?t=16

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.

Mart

[Shawn Coyle]

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???


http://www.angellabsllc.com/index.html

Shawn

[Graviman]

Shawn, there was a suggestion this thread was merged with:
http://www.pprune.org/forums/showthread.php?t=226000

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.

Mart

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

[rotorrookie]

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?


http://en.wikipedia.org/wiki/H-19_Chickasaw

[Graviman]

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:
http://www.zoche.de/

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...

Mart

[delta3]

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..

d3

[Graviman]

Delta3,

I am enjoying this discussion - it provides me with the sanity check i often need as an engineer! :ok:

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! :cool:

Mart

[3top]

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....
http://www.quasiturbine.com/

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/20001216070700/www.splitcycle.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.

3top,:cool:

PS: Just for the curious:

This baby is never going to fly, but it is biiiiiiiiig!!
http://www.bath.ac.uk/~ccsshb/12cyl/

[Graviman]

3Top,

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:

http://www.axialvectorengine.com/AxialVector.htm

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.

Mart

Edit: 'cos i gots confused over names - Sorry folks! :8

[Graviman]

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) (http://en.wikipedia.org/wiki/List_of_Volkswagen_engines#70-90_hp_1.4_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.

Mart

[Graviman]

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

Rolls-Royce Helicopter Turboshaft Database (http://www.rolls-royce.com/defence_aerospace/products/helicopters/default.jsp)

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...

Mart

[2000hrsinVN]

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....;)