Propeller Mount

Roger Lee,
I followed the link from Byron Mills and found the Warp Drive extension.

I think the construction in the picture was to clear the cowling by extending the prop hub forward 3/4in. Although my machinist friend can make a correct extension , Warp Drive sells their 1.5in extension for $325. The materials and my retired friend’s time would be worth more than that.

I will be ordering the Warp Drive extension.

Your response gives me more confidence in my decision. Thank you.

Hi Bert,

You're definitely doing the right thing. That extension should be solid and not a stand off. Most of them you see are solid aluminum machined out to fit the prop hub and Rotax prop flange. The prop flange inserts usually will fit inside the spacer / extension so it can not rotate which would be really bad. I saw one that someone didn't use the extensions into the spacer and the prop broke all bolts clean off except one.

I guess this is just an open question. Should Bert be concerned with the Warp Drive prop’s already high MMI rotating that far forward of the engine, or are extensions common on the 912 and don’t cause any premature gearbox issues?

Thanks for that question, Jim.

The prop is currently 3/4in. forward of the drive flange and the shortest extension that Warp Drive shows, and I plan to buy, is 1.5in.

I have to cook today for the Super Bowl party or I would go to the airport (35-40 min. drive) today and check something. I will go tomorrow and reinstall the cowling to check the clearance between the prop and the nose of the cowling. I bet the extension was added to clear the back of the spinner from the cowling. If the prop clears the cowling OK, I will remove the spinner and mount the prop directly to the flange for now.

Since you presented the question, I would like to know if using the 1.5in extension might create problems with the gear box.

Sam, I believe you are right. I found the crack.