01-20-2007, 12:26 PM
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#102 (permalink)
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| Guest | Re: OT Interesting video
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.
> 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.
> 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.
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?
Jobst Brandt
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