Wankel engine?
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Wankel engine?
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.
Its lighter and smoother than a recip engine, and apparently powerful as well.
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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
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
Last edited by Graviman; 20th May 2006 at 15:39.
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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!
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!
UAV Engines
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
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
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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 
). 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
). 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
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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.
I/C
The Swiss gave it a try with the Berger BX-110.
I/C
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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.
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.
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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
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
Last edited by Graviman; 21st May 2006 at 19:08.
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.
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.
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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.
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.
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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.
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.
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Originally Posted by Chevvron
Surely a diesel Wankel would get round the lubrication, economy and emissions problems?
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.
Originally Posted by Dave Jackson
... 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.
The VW soln for aluminium bores...
Mart
Last edited by Graviman; 21st May 2006 at 08:46.
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Moller
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/
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/
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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
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
Last edited by Graviman; 21st May 2006 at 19:07.
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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/Flugze...elicopter.html
And a sexy helo it was!!
Back lurking,
3top
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....
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/Flugze...elicopter.html
And a sexy helo it was!!
Back lurking,
3top
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....
Last edited by 3top; 21st May 2006 at 23:47.
Originally Posted by 3top
There is no catastrophic failure mode - no valves to break, rods to throw, cranks to shear, pistons to burn..
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
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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
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
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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).
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).
Last edited by Graviman; 23rd May 2006 at 21:04.
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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,
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,
Join Date: Nov 2004
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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
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
Last edited by Graviman; 23rd May 2006 at 22:00.