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.

Tucker dealing with new parts.
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.

Prop Extension Installed
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.

  1. Mike Wynn
    Mike Wynn02-19-2013

    Hi Tom!
    Once again, my hat’s off to you for posting some very good info. Your photos help just as much.
    !. My prop hub is the same as yours. What is the spinner attachment screw spacing or how many are you using, please?
    2. Do you happen to have a side-view diagram of your plane showing the locations of the major components? Like you, I have the short mount [preferred] with a 210hp Lyc angle valve eng; same p-hub with the F7666A-4 blades and smal tail. H-pump and batts loation are not set as I am still concerned about t he CG location. Knowing your component locations will help a lot.
    3. Ever think about using the oil cooler (2ea.) heat as cabin heat? I am not a fan of CO in the cockpit!

    Thanks for your time, as always.
    And as always, when in Moab, UT you’ve got free taxi and B&B with us.

    Mike Wynn
    ~85% done

    • admin

      Not at my desk at the moment, but i’ll respond with detail when I am. Thanks

      (Update) Check your email, covered most of your questions. Thanks again!