Recreational water craft engines (even racing version rarely) get
more than
a few hours a year. There is no reason to believe the materials and
technology
in these engines is any better than the Rotax aircraft engines.
Rotax engines
have a TBO of 1500 hours and then you must replace most of the parts
such as
crankshaft and connecting rods. Piston engine parts fatigue and
rotary engine
parts do not.
http://www.rotaryeng.net/Rotar-v-Piston.html
The Rotax 912 engines weigh about 150 pounds which is a pretty good
power to
weight ratio. Better than an O-200 AC engine. An all aluminum P-port
120 HP
Mazda one rotor would weigh well under 100 pounds.
The current cost of a 912 is about $20,000 US.
A brand new RX8 engine is $5800 retail and about $3800 wholesale if
you are a
car repair shop.
Paul Lamar
Paul,
I helped modify a Kawasaki Z1 900 engine for use in a BD5. The engine
had modified cases and weighed less than 140 pounds without the
transmission. I quit the project when the owners wanted to do
modifications to the output that wouldn't stand the HP the engine was
capable of. Even with the ill-advised mods. the plane taxied and even
left the ground for some short hops. The mods they did failed and the
owners ran out of money. I don't know if they tried to fly it again
later. I believe this engine would have performed fine as it was capable
of 100% operation. About 100 HP with open exhaust. Air cooled, roller
bearing bottom end. At the bikes release they ran 3 production examples
flat out for 24 hours. They set the FIM record for speed and distance
for motorcycles in '72. There were no failures on any of the bikes. This
is a very tough engine. The biggest problem for use in an aircraft would
be the need for a 3:1 or higher for a reasonable prop speed. Making a
light enough PSRU woould be the toughest part.
Bill Jepson
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