Finishing Cowling inlet ducts

crabandy · #1 12-05-2011, 06:21 PM

I just epoxied the upper cowling inlet ducts to the upper cowling on my RV 7 and was wondering how most people finished these.

-smooth the foward and trailing edge with filler
or
-smooth the foward and trailing edge with filler and fiberglass the sides closed.

I don't have the baffling kit yet and am not sure how the baffling mates to the upper inlet ducts.

Thanks,
Andy

Jeff A · #2 12-05-2011, 07:45 PM

No need to close the sides....the rubber baffle seals will cover the open areas. At least that's the way it is on the -8. I just finished my baffles last week. They are a lot of work, even using Van's kit.

Lars · #3 12-05-2011, 10:01 PM

Getting the baffle seals to contact the upper inlet ramps without sealing the sides (inside or outside or both) is tricky. There are previous threads about this, where folks have closed off the ramps with the result being better cooling.

This thread is definitive.

I closed off the outsides, as that was where I was having the most trouble getting the baffle seals to stay on the ramps, as opposed to sliding off the edge of the ramps.

I used foam in a can to fill the gaps (wouldn't do that again- I'd buy 2 part expanding foam, much more consistent) then shaped with X-acto knife and sandpaper, followed by glass. Melted the foam out with acetone afterward.

My fiberglass skills are pathetic compared to the real artists that post here, but I was able to get the baffle seals to lay down nicely and they seem strong enough. Not flying yet, so the truth remains to be seen.

MauiLvrs · #4 12-05-2011, 10:24 PM

Quote:

Originally Posted by Jeff A

No need to close the sides....the rubber baffle seals will cover the open areas. ...

If you don't close at least one of the ends .... cooling air will leak to the lower cowl ... without cooling

Jeff A · #5 12-06-2011, 07:25 AM

Quote:

Originally Posted by MauiLvrs

If you don't close at least one of the ends .... cooling air will leak to the lower cowl ... without cooling

Well, I guess I still have some work to do! Not sure if this thing will ever get finished!

MauiLvrs · #6 12-06-2011, 09:15 AM

Quote:

Originally Posted by Jeff A

Not sure if this thing will ever get finished!

Finished ... Who knows... Define finished... Flying ... YES

DanH · #7 12-06-2011, 09:46 AM

Perhaps the answer isn't quite as simple as "you must close at least one end".

If I had to pick the one build task most often done badly, I'd pick baffle rubber sealing around the inlets. Simply closing a ramp end doesn't necessarily get 'er done. Instead be creative and build whatever it takes to be airtight.

Think about this; in climb at 100 knots and 3000 MSL you only have ~5" H2O to drive cooling mass through the system.....less than 0.4" Hg or 0.18 psi. Lose just 1" H2O or 0.036 psi to a leak and you lost 20% of your cooling capacity.

crabandy · #8 12-06-2011, 10:32 AM

Thanks for the replies, I will probably wait till I get the baffles built. They are only $275 so hopefully they're within Santa's budget!

Lars · #9 12-06-2011, 12:06 PM

Quote:

Originally Posted by DanH

Perhaps the answer isn't quite as simple as "you must close at least one end".

If I had to pick the one build task most often done badly, I'd pick baffle rubber sealing around the inlets. Simply closing a ramp end doesn't necessarily get 'er done. Instead be creative and build whatever it takes to be airtight.

Think about this; in climb at 100 knots and 3000 MSL you only have ~5" H2O to drive cooling mass through the system.....less than 0.4" Hg or 0.18 psi. Lose just 1" H2O or 0.036 psi to a leak and you lost 20% of your cooling capacity.

I spent many 10's of hours fabricating/installing/reworking/reinstalling the baffle inlet seals- still not sure I got it right.

I want to figure a way- perhaps simply witness marks left by the seal material on the inside surface of the upper cowl- to gauge if I'm getting good sealing everywhere.

RV8R999 · #10 12-06-2011, 12:53 PM

The tricky part, and which makes closing the inlet ramps mostly useless, is the transition forward and outboard of cowl inlet flange where the two halves meet. If the rubber baffle material isn't fitted to lay flat up against the ramps they will form a tube allowing air to leak down through a vertical path at the very forward outboard portion of the cowl.