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-   -   Is 1/8" really sufficient for cowl-spinner gap? (http://www.vansairforce.com/community/showthread.php?t=31770)

alpinelakespilot2000 07-06-2008 11:55 PM

Is 1/8" really sufficient for cowl-spinner gap?
 
I have my cowl all fitting pretty well. The top cowl may actually fit too well. Once drilled to the firewall, I ended up with a strong 1/8" (somewhere between 4/32" and 5/32") gap between spinner and cowl at the top and probably 1/4" at the bottom. Between a little bit of future sag, and a little bit of filler on the bottom half, I'm assuming this will eventually even out to something around 3/16" all around. However, if I end up with no sag, is 1/8" between cowl and spinner really enough over the long term? Van's says anything 1/8" to 1/4" is OK, but I'm just checking for confirmation from those with experience that being on the smaller side of that range will work out. Definitely don't want the spinner ever catching on the cowl on startup or any other time the engine might shake a little.

Side note: From the archives, I see that many nosewheel folks and those with 3-blade props prefer larger gaps (1/4" to 3/8") for ease in removing and installing cowl. However, I have no nosewheel and only a 2-blade prop, so I'm pretty happy with the smaller gap assuming it's conservative enough already.

Thanks for any tips.

pauldan181 07-07-2008 01:30 AM

Hi Steve

I also wound up with a cowl-spinner gap similar to what you're seeing. After 60 hours now on my 8A there is no evidence that the spinner plate has ever touched the cowl. The engine has sagged a bit but the gap remains about 1/8" all around.

When you run the engine with the cowl off, watch the engine closely on start and shutdown. Most of the "shaking" is rotational with very little up/down or left right movement.

Hope this helps

Paul Danclovic

pierre smith 07-07-2008 05:51 AM

Thrust...
 
Quote:

Originally Posted by pauldan181 (Post 236986)
Hi Steve


When you run the engine with the cowl off, watch the engine closely on start and shutdown. Most of the "shaking" is rotational with very little up/down or left right movement.

Hope this helps

Paul Danclovic

.....will help increase the gap in flight as well, as the rubber mounts allow. With a C/S prop, the braking action at closed throttle might decrease the gap a bit, but not 1/8".

Regards,

Rick S. 07-07-2008 09:39 AM

I'm one of the nosewheel/three blade types and I needed about 3/8 of an inch. One thing about rotational movement is making sure the metal portion of the baffle has adequate clearance from the underside. IF it's too close the metal may contact the cowl with bad results.

rv6ejguy 07-07-2008 09:59 AM

1/8 with nose gear and a 3 blade prop WILL make for a miserable cowl removal experience. 2 blade and TW you are ok.

David_Nelson 07-07-2008 10:16 AM

3/8" it is...
 
Quote:

Originally Posted by rv6ejguy (Post 237068)
1/8 with nose gear and a 3 blade prop WILL make for a miserable cowl removal experience. 2 blade and TW you are ok.

Ross,

Thanks for the heads up on the spacing with a 3-blade prop!

LifeofReiley 07-07-2008 10:20 AM

I've got a Catto three blade and 1/8" spacing and do not have any issues with install or removal of the cowling. I think it really depends on how you final trim and fit the cowling.

N941WR 07-07-2008 10:59 AM

Steve,

I have about a 3/8 to 1/4" gap and it works fine. I also trimmed the lower cowling, per one of the RVator's to help with the removal of the lower cowling.

Which engine mount do you have? The conical mount on my engine sagged much more than I ever thought it would, about 3/8" or so. :(

rvbuilder2002 07-07-2008 11:12 AM

Quote:

Originally Posted by David_Nelson (Post 237075)
Ross,

Thanks for the heads up on the spacing with a 3-blade prop!

A three blade prop doesn't require more gap from the spinner...it requires a deeper slot (cut further forward) for the nose gear so that the cowl can be lowered down much further to clear the prop blades. I had probably the first RV "A" model with a 3 blade prop back in 1993. I just made an aluminum cover to screw over the slot in the cowl bottom.

BTW a 1/8" gap works fine (in fact an even 1/16" works with no rubbing on most installations) but the closer the gap, the higher the difficulty of removing and installing the cowl. Especially if there is an improper interface between the FAB and the induction air inlet.

LifeofReiley 07-07-2008 11:21 AM

Quote:

Originally Posted by rvbuilder2002 (Post 237101)
A three blade prop doesn't require more gap from the spinner...it requires a deeper slot (cut further forward) for the nose gear so that the cowl can be lowered down much further to clear the prop blades. I had probably the first RV "A" model with a 3 blade prop back in 1993. I just made an aluminum cover to screw over the slot in the cowl bottom.

BTW a 1/8" gap works fine (in fact an even 1/16" works with no rubbing on most installations) but the closer the gap, the higher the difficulty of removing and installing the cowl. Especially if there is an improper interface between the FAB and the induction air inlet.


Yep... what Scott said! :D


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