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  #21  
Old 01-31-2019, 11:01 AM
NinerBikes NinerBikes is offline
 
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I know it wouldn't apply to a Rotax motor, but in car engines, they put in heavier flywheel's or dual mass flywheels, to smooth the pulses out of the compression and combustion strokes, especially on turbo diesel motors. VW, Audi, Porsche do this, a lot.

Those pulses are probably what tear up the dogs.

Also when you are descending when landing and you throttle back, the propeller indeed gets feathered and sloppy, being driven by the wind, not the motor, with not much or no thrust being created by the prop. Hence the slop, if your dogs are worn.

Last edited by NinerBikes : 02-13-2019 at 11:47 PM.
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  #22  
Old 01-31-2019, 12:04 PM
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Piper J3 Piper J3 is offline
 
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I don’t agree with your assertion that prop gets “feathered” when engine is throttled back for landing.

A wind milling fixed-pitch prop creates a lot of drag. When the engine is throttled back the prop back-drives the engine, and in doing so, holds the dogs nicely against each other -so not chattering. This is why engine is running faster in glide than idle speed when stationary on the ground.

The key to gearbox longevity is engine minimum operating speed. Rolling elements – bearings, gears, etc. can take a lot of abuse under dynamic load but suffer badly if abused statically. The reason for the 1800 RPM idle speed is Rotax deems this to be the minimum speed where engine power pulses don’t hurt the gearbox.

That being said, I have my idle speed set at ~ 1700 RPM. This allows better aerodynamic drag and helps reduce float on landing. I have to manually operate minimum throttle to stay above 1800 RPM on the ground. Works very nice…
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Last edited by Piper J3 : 01-31-2019 at 12:21 PM.
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  #23  
Old 01-31-2019, 02:39 PM
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randylervold randylervold is offline
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Anyone know if the 912iS idle is even adjustable being controlled by the computer and all?
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  #24  
Old 01-31-2019, 04:15 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by randylervold View Post
Anyone know if the 912iS idle is even adjustable being controlled by the computer and all?
Yes it is.

There is an idle stop screw on the throttle body.
Van's recommends the same idle speed stop adjustment for the ULS and the iS engine (1650 RPM), with and then follow the standard operating procedure of manually keeping the engine speed above 1800 RPM at all times.
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