Prop Extension

So everyone asks, why? Legitimate question. Let me cover some of the basics here. This is a small tail Lancair 360 with the short engine mount. I already have a bit of an aft center of gravity. Not terrible, but not great. So one thing on my mind is to move the C.G. forward.

First, the thing with the longest moment arm forward of the C.G. is the prop, easy. Second, since I will be building a new cowl from scratch anyway, I won’t have to re-do any work already done, like extend an old cowl. And lastly, pointy is better from a looks standpoint and a speed standpoint. (I hope)

Saber Manufacturing had a 2.25″ constant speed extension in stock. This extension bolts to the crankshaft flange and the prop bolts to the extension. An o-ring seals crankshaft side and the prop o-ring seals on the extension. What makes my install really long is that I already have the “long hub” Hartzell prop. HC-F2YR-1F/F7068-2 to be exact. This was standard for most Lancair 320/360’s, but an RV guy will look at you like your crazy. Either way, I have tested it to 4.5 G’s and 3,000 RPM with no side effects.

On a side note, I performed a dynamic prop balance before I left for Reno. It had never been done on this application. In all, I was rather shocked. The first test started at .74 IPS. For reference, most average planes on the ramp are about a .5 IPS. After a few runs at cruise RPM of 2500, we were able to balance it down to .02 IPS, I’d call that good enough.