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Will a Rotax 462 from a snowmobile make a good engine?

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corbenpilot

Well-Known Member
Joined
Nov 24, 2007
Messages
49
Hi, for what its worth I was invloved for many years back in the beginnings of the ultralight movement. All of the 2 stroke engines to my knowlege were/are derived from snowmobiles or industrial engines. The Cuyuna's, Hirths, and Rotax engines used in Ultralights were all based on the snowmobile powerplants. I'm presently rebuilding an old Rotax 343 for use on a Weedhopper I'm getting ready to put together. Course' I must reduce the RPM of the propeller as it would spin too fast by using a gear or belt reduction unit. Almost all 2 strokes turn at a high RPM so as to acheive the high H.P. for the low weight they are.

The only direct drive designed slow turning 2 stroke engines I've ever known for an ultralight was the Chotia 460 designed and built by Weedhopper of Utah back in the 80's. I owned two of the buggers and they ran great though they were not elegantly constructed. They turned so slow that they actually sounded like a 4-stroke engine.

Using a smaller or thinner prop won't really work well as the overall area of blade is so small that they are really inefficient and produce low thrust pounds. I remember well the early direct drive Lazairs with their tiny splinter props. They needed two engines to get airborn and the one a friend of mine owned he claimed it marginal at best.
 

thetford

Member
Joined
Feb 15, 2009
Messages
13
Location
Birmingham, Alabama
Direct drive on a two stroke Rotax (and/or Kaw. 440) is a BAD plan! The engine was not designed to handle the forces of a direct mount prop. One aspect of the gearbox engineering is that it absorbs the appropriate amount of forces. The other big factor is prop tip speed as Jake pointed out... the props available for ultralight use will not withstand very much supersonic use. Personally I would not want to be flying when the prop disintegrates in mid-air!
 

Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,360
Location
AMES, IA USA
IF YOU LOOK ON THE BACK OF THE ROTAX ENGINE THERE IS A BLACK DATA PLATE, THAT GIVES THE BORE & STROKE AND CC OF THE MOTOR. IF YOU LOOK AT THE PTO(CLUTCH) END YOU SHOULD SEE EITHER 4 OR 8 HOLES AROUND THE CRANK. PROVISION 4 OR PROVISION 8 CASE. PRO4 WAS IN THE 80s, AND PRO8 WAS IN THE 90s. ROTAX UL MOTORS ARE USUALLY RATED AT 6500RPM. SLED MOTORS ARE RATED MUCH HIGHER, USUALLY 7950RPM. IF YOU GOOGLE "ROTAX DYNO" YOU SHOULD GET SOME HITS ON SOME DYNO SHEETS POST ON THE NET. A ROTAX 670 MAKES 90HP AT 6400RPM.
RICH GILLEN
 
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