exhaust -cowl clearance

prkaye · #1 03-07-2010, 07:23 PM

My exhaust pipes (vetterman exhaust from Vans) sit quite close to my cowl. I've read on other threads about people putting various types of unsulation material on the cowl to protect it... does this work well? Or would I be better to cut my cowl and add blisters to increase clearance? Since I am painting before flying I want to do this modification now if it's going to be needed...

John Clark · #2 03-07-2010, 07:38 PM

I'm not sure what "quite close" is, but as a data point, my exhausts are as close as 3/4 inch from the cowl. The inside of the cowl is painted with white Jet-Glo and there is no heat shielding. In 300+ hours there is no damage or even discoloration of the paint.

John Clark
RV8 N18U "Sunshine"
KSBA

jsharkey · #3 03-07-2010, 07:44 PM

The LH exhaust on my RV-6 comes close to the cowl and was "browning" the fiberglass. I fitted the aluminum shield as recommended by Vetterman. It is bonded with a perimeter of RTV (or proseal) and creates an insulating air gap between it and the cowl. I drilled a couple of air vent holes. Not sure if they are needed - and might just accumulate crud eventually.

Jim Sharkey
RV-6 Phase 1

Kyle Boatright · #4 03-07-2010, 08:25 PM

Quote:

Originally Posted by jsharkey

The LH exhaust on my RV-6 comes close to the cowl and was "browning" the fiberglass. I fitted the aluminum shield as recommended by Vetterman. It is bonded with a perimeter of RTV (or proseal) and creates an insulating air gap between it and the cowl. I drilled a couple of air vent holes. Not sure if they are needed - and might just accumulate crud eventually.

Jim Sharkey
RV-6 Phase 1

I had similar browning of the cowl during the first 5 hours of so flying my RV-6. I used a product called Koolmat from Aircraft Spruce to insulate the area. The material is still holding up very well after 9 years and almost 700 hours. I have the koolmat over a substantially larger area than is shown in the pictures Jim included in his post. I don't know if protecting the larger area was necessary or not, but I'm happy with the result.

lostpilot28 · #5 03-07-2010, 08:58 PM

Hi Phil, mine was pretty close in a couple spots too...to give you an idea of how close, on each side of the engine, where the exhaust goes from 2 pipes into 1 there's a flange holding the pipes together with 3 bolts. The flange has made contact with the cowl while running (during startup, I'm sure). Either way, clearance is very small.

I just used the adhesive backed aluminum foil available from Van's. It does the job just fine, and it's light and inexpensive compared to the thicker heat shielding. I'm pretty sure that those are all overkill.

Bob Axsom · #6 03-07-2010, 09:58 PM

Well Man - shield it, space it, and don't paint before it's ready. There are probably builders out there that pussy foot around with their power settings and they are happy as a kitten lapping cream but why would you let that be a reason for you to paint you bird before you make sure this known vulnerable situation is not a problem on your airplane? Mine burned BADDLY, I don't mean some little toasty shading, darn thing burned black through the inner layer and the honeycomb core and browned the outer layer. I fixed it with a lot of work and a year later I had it painted and no more problems have occurred with the paint or the cowl. It is silly to risk all of your work in your unique configuration (your clearance, your exhaust, your engine, your temperature) where there are known vulnerabilities when experience shows it is not necessary. Not elegant but I'm trying to be honest with you.

Bob Axsom

LarryT · #7 03-07-2010, 11:14 PM

I just discovered the same thing about lack of left side exhaust clearance on the 6A I purchased flying. Could get a piece of paper between the ball joint and the cowl but probably not a piece of cardboard.

Would it be possible to reduce the length of the short pipe the crossover tube slides over just before the "Y" and shorten the dog bone connector? If I had 1/4 - 3/8" more clearance and added a heat shield I think it would be OK based on other posters comments.

prkaye · #8 03-08-2010, 05:30 AM

Thanks guys, it sounds like I will be able to get away with some kind of shielding, and not have to carve up my cowl. I'll measure the clearance today.
Kyle, how did you affix that Koolmat product?

jsharkey · #9 03-08-2010, 05:42 AM

Oh - it's the exhaust joint flange that gets the closest. Make sure it is rotated to align a "flat" with the cowl to maximize the gap. The hot bolt can radiate quite a bit of heat.

JimS

erich weaver · #10 03-08-2010, 10:52 AM

The sticky sided aluminum foil heat shield from Vans is easy and has worked well for me. However, it seems to be currently out of stock and back ordered. I placed an order for some more about 2 months ago that still hasnt been filled. Doesnt look like ACS carries it. Anybody have another supplier?

erich