C of G issues?

[Don Patrick]

I'll give Van's a call later in the week, but thought I would check with the brain power here first.

I have a Superior IO-360 parallel valve that came off of a Lancair Legacy along with the prop. The prop is a hartzell HC-F2YR-1F, which has an extended hub.

I was looking at replacing the prop, but have been convinced to keep it and just modify the cowl. I have a good fibreglass guy to do it.

In relation to the extnded hub. I believe it is roughly 4.5 inches in extension compared to the compact hub.

I'm concerned that there may be a CofG issue as a result of the extended hub.

Does anyone have a similiar setup in an RV-8? My battery is mounted in the back as well.

Any input would be great.

Thanks


Don

[Toobuilder]

That's a rare hub and is worth good money to someone who needs it (like a Rocket guy). My first inclination would be to see if you can exchange it for the conventional HC.

That said, your CG will certainly move forward but I believe that you can load the back end of the airplane during the build to compensate. If all else fails, a couple of pounds of steel on the HS will likely be all you need. You will have a higher polar moment than most 8's, so the spin characteristics are going to be a little different, but hey, guys are flying with 540's on the nose, so you are likely OK.

The cowl mods can be simple (er) or complex, if you really want to take advantage of the longer hub by lengthening the inlets and making a really nice divergent duct.

[airguy]

Originally Posted by Toobuilder

If all else fails, a couple of pounds of steel on the HS will likely be all you need.

I'll point out that the elevator counter-weights for the newer 7A (Part number E-714) are a convenient 2.5 pounds each and could be bolted just about anywhere, and being lead instead of steel you can put them in the back tailcone area without worrying about screwing up the magnetic field for your tail-mounted magnetometer.

[Tom Martin]

Don
You should be able to do some calculations on the standard Van's Weight and Balance document, with and without the longer hub distance.
Having a forward C of G is not a bad thing for a tandem seat aircraft. If necessary you can always placard your plane with a few pounds in the baggage for solo operation. Also moving the ELT to the aft tail deck would likely balance out any difference the prop makes.
I think this will make a very attractive cowling.
Negatives are potential reduced G loading for aerobatics because of the longer hub.