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01-21-2007, 01:01 PM

jobst.brandt@stanfordalumni.org wrote:

>Mark Hickey writes:
>
>>> As a classic car buff, I learned fast that total production is a
>>> BIG factor in whether or not you can afford the thing. My Corvairs
>>> went to nearly two million copies and many service parts are shared
>>> with all Chevy sixes (1955~1980) so they are cheap to run and hop
>>> up. Every piece you want is available and cheap. These mills are
>>> currently powering brand new sport planes (November cover Sport
>>> Flying) 38 years after 'death'.
>
>> That reminds me of one of the actual real advantages of a rotary, at
>> least for aircraft use. If you lose the cooling system on a
>> water-cooled aircraft motor, you can get into big trouble - you
>> won't get far before the piston engine gets too hot to continue
>> running, and then if you're not within gliding distance of a
>> suitable landing place, you're gonna make the evening news.
>
>That sound like the introduction of the Wankel to cars, offering great
>advantages that seem not to have materialized. In spite of the fewer
>parts and claimed lighter weight, it does not compete economically
>against the piston engine, from manufacture to life on the road.

You're preaching to the choir - I agree with you entirely. There are
few cases where the Wankel is an advantage...

>> A rotary OTOH will continue to run virtually forever (at a somewhat
>> reduced power level) until you can get the plane safely on the
>> ground. It'll be a "throw-away" at that point, but would have
>> potentially saved the aircraft and the pilot/passengers.
>
>Could you explain how that works? This engine has a cooling problem
>when working normally. I don't believe there is a working air cooled
>version for that reason.

There's no "air cooled" rotary, for the reasons you state. My point
isn't that the rotary is capable of normal operation without a working
cooling system, just that a rotary will continue to run even when it's
gotten so hot that it's essentially ruined. That doesn't help with
the overhaul costs, and doesn't matter much in a car - but in an
airplane it could save your life. A piston engine that gets too hot
simply can't produce enough power to continue to turn.

>> Another benefit of the rotary is that they have a very smooth power
>> output at the crankshaft. This has huge benefits for an aircraft,
>> and the PSRU (Propeller Speed Reduction Unit) which gears down the
>> prop speed allowing the engine to run in its efficient RPM range
>> without sending the propeller tips into the (noisy and inefficient)
>> supersonic range (that's the noise you hear when aerobatic planes do
>> vertical dives). The lack of extreme "power pulses" puts a lot less
>> stress on the PSRU and propeller (which can be destroyed by the
>> pulsating power output of a piston engine in certain situations).
>
>It has three ordinary power pulses per rotation of the rotor and has
>an output roughly like a two-stroke per chamber.

Which is a lot more pulses (and smoother pulses) than the typical four
cylinder opposed motor it would replace in an airplane.

>http://www.answers.com/topic/wankel-engine
>
># Unlike a piston engine, where the cylinder is cooled by the incoming
># charge after being heated by combustion, Wankel rotor housings are
># constantly heated on one side and cooled at the other, leading to
># very high local temperatures and unequal thermal expansion. This
># places high demands on the materials used. A further problem caused
># by the shape of the seals in Mazda engines is that carbon particles
># can become trapped between the seal and the casing, completely
># jamming the engine and requiring a partial stripdown to rectify.
># Such engines should never be started and run unless the engine will
># reach operating temperature; most such instances of jammed engines
># occur when a car is started and moved a few meters, e.g. from a
># garage to a driveway. In these situations it is better to manually
># push the car.
>
>This is only a short piece of a fairly exhaustive and positive
>analysis of the Wankel. After reading this, the question arises, why
>these engines are not in general use. As I said, it sounds much like
>the recumbent bicycle description. If it is really so good, why
>aren't they taking over the market?

Way back in the '70s, there were those who felt that the rotary could
be refined to produce efficiencies on par with a piston engine. 30-40
years later, that's obviously not gonna happen. It remains a good
solution for a couple very narrow niche markets - your recumbent
analogy is very appropriate.

Mark Hickey
Habanero Cycles
http://www.habcycles.com
Home of the $795 ti frame

01-21-2007, 01:01 PM	#124 (permalink)
Mark Hickey Guest Posts: n/a	Re: OT Interesting video jobst.brandt@stanfordalumni.org wrote: >Mark Hickey writes: > >>> As a classic car buff, I learned fast that total production is a >>> BIG factor in whether or not you can afford the thing. My Corvairs >>> went to nearly two million copies and many service parts are shared >>> with all Chevy sixes (1955~1980) so they are cheap to run and hop >>> up. Every piece you want is available and cheap. These mills are >>> currently powering brand new sport planes (November cover Sport >>> Flying) 38 years after 'death'. > >> That reminds me of one of the actual real advantages of a rotary, at >> least for aircraft use. If you lose the cooling system on a >> water-cooled aircraft motor, you can get into big trouble - you >> won't get far before the piston engine gets too hot to continue >> running, and then if you're not within gliding distance of a >> suitable landing place, you're gonna make the evening news. > >That sound like the introduction of the Wankel to cars, offering great >advantages that seem not to have materialized. In spite of the fewer >parts and claimed lighter weight, it does not compete economically >against the piston engine, from manufacture to life on the road. You're preaching to the choir - I agree with you entirely. There are few cases where the Wankel is an advantage... >> A rotary OTOH will continue to run virtually forever (at a somewhat >> reduced power level) until you can get the plane safely on the >> ground. It'll be a "throw-away" at that point, but would have >> potentially saved the aircraft and the pilot/passengers. > >Could you explain how that works? This engine has a cooling problem >when working normally. I don't believe there is a working air cooled >version for that reason. There's no "air cooled" rotary, for the reasons you state. My point isn't that the rotary is capable of normal operation without a working cooling system, just that a rotary will continue to run even when it's gotten so hot that it's essentially ruined. That doesn't help with the overhaul costs, and doesn't matter much in a car - but in an airplane it could save your life. A piston engine that gets too hot simply can't produce enough power to continue to turn. >> Another benefit of the rotary is that they have a very smooth power >> output at the crankshaft. This has huge benefits for an aircraft, >> and the PSRU (Propeller Speed Reduction Unit) which gears down the >> prop speed allowing the engine to run in its efficient RPM range >> without sending the propeller tips into the (noisy and inefficient) >> supersonic range (that's the noise you hear when aerobatic planes do >> vertical dives). The lack of extreme "power pulses" puts a lot less >> stress on the PSRU and propeller (which can be destroyed by the >> pulsating power output of a piston engine in certain situations). > >It has three ordinary power pulses per rotation of the rotor and has >an output roughly like a two-stroke per chamber. Which is a lot more pulses (and smoother pulses) than the typical four cylinder opposed motor it would replace in an airplane. >http://www.answers.com/topic/wankel-engine > ># Unlike a piston engine, where the cylinder is cooled by the incoming ># charge after being heated by combustion, Wankel rotor housings are ># constantly heated on one side and cooled at the other, leading to ># very high local temperatures and unequal thermal expansion. This ># places high demands on the materials used. A further problem caused ># by the shape of the seals in Mazda engines is that carbon particles ># can become trapped between the seal and the casing, completely ># jamming the engine and requiring a partial stripdown to rectify. ># Such engines should never be started and run unless the engine will ># reach operating temperature; most such instances of jammed engines ># occur when a car is started and moved a few meters, e.g. from a ># garage to a driveway. In these situations it is better to manually ># push the car. > >This is only a short piece of a fairly exhaustive and positive >analysis of the Wankel. After reading this, the question arises, why >these engines are not in general use. As I said, it sounds much like >the recumbent bicycle description. If it is really so good, why >aren't they taking over the market? Way back in the '70s, there were those who felt that the rotary could be refined to produce efficiencies on par with a piston engine. 30-40 years later, that's obviously not gonna happen. It remains a good solution for a couple very narrow niche markets - your recumbent analogy is very appropriate. Mark Hickey Habanero Cycles http://www.habcycles.com Home of the $795 ti frame