Gearbox Problems 912iS

What type and diameter of prop are you using (i.e. moment-of-inertia)?

DUC Windspoon Propeller.  

Diameter  68”              1727 mm. 

Moment of Inertia.       3725 kg cm2

Max. Engine Power.     120 hp

Weight.                         4.05 kg

This is the only Prop allowed in the UK because we use it as a Tow Plane for Sailplanes (Gliders). Private Eurofox Aircraft are allowed a Woodcomp SR200 as an alternative.

Thanks - interesting that is a very low MOI compared to some prop types.  This kind of wear is often attributed to a MOI close to the upper limit 6000kgcm^2.  Do you have to idle more than usual in sailplane tow operations?  What idle rpm do you aim for?  I have heard some iS users intentionally keep above 2500rpm to minimise such wear.  Am I correct to assume this prop is a ground-adjustable pitch, i.e. if you do idle it might be at a lower rpm than might otherwise be the case?  My impression is that the most natural pairing is the iS with a constant speed prop.

Malcom,

Have you verified that the oil spray nozzle is clear and functioning?  

Unfortunately due to the nature of Sailplane Towing there is quite a bit of idling, we are very conscious of keeping the rpm at approx. 2000 rpm. 

The spare bar is cleae and working for all the good it does.