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Todays Top Tip: Sealing Cowl Heat Barrier

goatflieg

Well Known Member
I'm sure others have tried this, but I wanted to share my positive experience.
Yesterday I spent seven hours cutting and applying the aluminized heat barrier recommended for the interior of the bottom cowl, which I bought from Aircraft Spruce. It is recommended that the seams and edges be sealed with high temp RTV, but before I did I conducted some tests using aluminum tape. The results were promising, so I went ahead and sealed all the seams and edges with the aluminum tape. I used a plastic roller (bought for fiberglass layups, but never used for that purpose) to firmly press the barrier material onto the epoxy layer applied to the raw interior the day before. When I used the roller to also apply the aluminum tape, it worked perfectly to bond the tape and blend it into the panels. I'm hoping the glue on the aluminum tape will hold up to the heat exposure; it is designed for HVAC applications so it should. In any case, the results are far better than expected. It's been awhile since I had a genuine "Yee Hah" moment in the shop... but this was one of them.
(Darn it... Google Photos is acting up again... my shared folder isn't sharing any more. Working on the problem)
 
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ACtC-3dzZ9EgTG1YEq9Qdld9e8ZGNWGsQ6WcmAO1_3DymOAHRCOFldb0mo4bM7bt3xHneElYmP_RD4LFlRAiG2tCrx6mRz2LutLQtVHsV6X8kgEhtUjs63OuFoOXtn0umOcl46DSUpyVqmd0ikeJRI_dLBk5=w900-h600-no

OK, so it seems my shared folder settings are all correct, but when I use the "share photo" icon above, it instead shares a link to the photo. The links work for me, but I need to know if they work for anyone else. Also wondering why they don't pop up as the image like they used to. Doug, if you have any suggestions, please advise.
 
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Photos

I can see your photos fine. The results of your work look very professional. Good job.
 
I think it looks great and should last a long time, heat, fluids will take a toll over time but I see this lasting a long time. We shall see. Nice work.
 
Beautiful job! One word of warning for folks doing this in the future however - there is a huge difference in quality in aluminum tapes. I did this to myRV-8 when it was new, and the tape eventually started peeling off, and I had to do it over. It’s enough work, doing a whole cowl, to make it worthwhile to check the specs on the tape you’’re going to use so to make sure its good for a couple hundred degrees.

Paul
 
Any reason not to do the entire surface in HVAC tape only?

In fact, why not high-build prime and sand flat, then tape only?

It seems to me a shiny flat aluminum surface would retain less heat than the serrated one that reflects onto itself.
 
Very nice job and good looking !!!


What part # from Spruce did you use and can you say what quantity was necessary? They offer different aluminised heat barriers...


Thanks
 
The part number is 08-00600; here's a link with description:
https://www.aircraftspruce.com/catalog/eppages/heatbarriers.php
I'm pretty sure the composite material will do a much better job of dissipating and reflecting heat than plain tape. I'd think the tape might reflect some heat but would absorb and transfer more than the composite. I did get the good aluminum tape... I think. We'll see.
As for my photo issues, thanks to hgerhardt for sharing them. I still don't understand what is happening. This is a different issue than I've ever experienced. The links worked, and none of the other photos I've shared here have disappeared, so I don't think it's an access issue. I've never used the photo icon and had it convert the address to a working link before. I've had a lot of strange buggy issues with electrons today; computer, TV, DVD player, even my phone. Tiny, pesky, rogue critters. Time to have the roof redone in tinfoil...
 
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.....As for my photo issues, thanks to hgerhardt for sharing them. I still don't understand what is happening. .......

I opened your links and right-clicked on each photo and selected "copy image location". Took that and used the standard
with the info pasted between. But what it took to make it work was delete the part after the picture size (....Wt=w900-h600-no?authuser=0). Never seen that as a problem before, but there ya go.
 
I had a feeling that suffix had something to do with it, as it was on all addresses. Now I have to figure out why Google Photos is suddenly putting it there. This test accurately depicts the effect all this nonsense has on me.
ACtC-3cOW2y57sMVPRu_pwO6yiCkKWb4DE8kfSHNkdRyzygU2lwLrq5sk-MvPvWHypS1U6UmWOdLeAgOtXuCK3qFVoQ-SPpna4IcHoFjIDXIuvIgdv8HExOJ80kbzIsq3_ZjZ9XCVs6qFhRbjRzgiWspUZvB=s432
 
In fact, why not high-build prime and sand flat, then tape only?

Be careful about the surface finish under tapes and heat barriers. As a general rule, a hard, high gloss paint is best for maximum adhesion of all the self-stick materials.

Some time back our own Pierre reported an inflight loss of cooling air flow when a section of self-stick heat barrier detached and partially blocked the cowl outlet.

Ordinary fiberfrax under Vans self-stick foil, cut to shadow the headpipes. Base is sanded epoxy seal wipe, epoxy primer, and two-part single stage top coat. White is reflective and great for leak detection. No edge sealing, everything still locked down at 950 hours, and my under-cowl air temps are higher than most.

Cowl%20Insulation1.jpg
 
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weight considerations?

Nice looking interior cowl. Any idea on how much weight gain the before and after job resulted in?

For those that need a local source of 3M HVAC tape, Ferguson Plumbing/HVAC is in a large part of the country and they will sell most materials to individuals without commercial accounts...

For those wanting to keep the plane as light as possible, you may consider the approach I took... painted the interior with two light coats of 1,000 degree white grill paint in a spray can for phase 1 testing. After phase 1, I noticed 1 "hot spot" forming on the pilot side of the cowl right in front of the front exhaust pipe joint, I put a similar self adhesive heat barrier along the cowling area near both exhaust pipes with RTV sealant along the edges....total result was a few oz. in weight gain. After 175 hrs, I haven't noticed any other visual signs of hot spots.

I haven't bothered to do get my thermal camera out to scan the cowling after shutdown and get actual temps on different sections of the cowl....maybe a project to do later this week.....


Paul
RV7A / 0360
 
weight considerations?

Nice looking interior cowl. Any idea on how much weight gain the before and after job resulted in?

For those that need a local source of heat resistant HVAC tape, Ferguson Plumbing/HVAC is in a large part of the country and they will sell most materials to individuals without commercial accounts...

For those wanting to keep the plane as light as possible, you may consider the approach I took... painted the interior with two light coats of 1,000 degree white grill paint in a spray can for phase 1 testing. After phase 1, I noticed 1 "hot spot" forming on the pilot side of the cowl right in front of the front exhaust pipe joint, I put a similar self adhesive heat barrier along the cowling area near both exhaust pipes with RTV sealant along the edges....total result was a few oz. in weight gain. After 175 hrs, I haven't noticed any other visual signs of hot spots.

I haven't bothered to do get my thermal camera out to scan the cowling after shutdown and get actual temps on different sections of the cowl....maybe a project to do later this week.....


Paul
RV7A / 0360
 
Sorry gang; I don't know the exact difference in weight. A rough extrapolation based on information gathered from Aircraft Spruce: each square foot weighs 0.16 pound. I used about 14 sq.ft., plus the aluminum tape... I probably added about 2.5 lbs to the bottom cowl... which is a lot, I guess, because I chose to extend my coverage. The Skybolt flanges added more weight, I'm sure... and I'm not done adding weight; filler, glass, paint etc. Yes it will probably be heavier than most... and on the nose; not the best place for extra weight in an RV-8. Running a relatively light C/S prop; battery aft; relatively simple airframe. I'll just have to see.
 
Looks great Martin

I had a feeling that suffix had something to do with it, as it was on all addresses. Now I have to figure out why Google Photos is suddenly putting it there. This test accurately depicts the effect all this nonsense has on me.
ACtC-3cOW2y57sMVPRu_pwO6yiCkKWb4DE8kfSHNkdRyzygU2lwLrq5sk-MvPvWHypS1U6UmWOdLeAgOtXuCK3qFVoQ-SPpna4IcHoFjIDXIuvIgdv8HExOJ80kbzIsq3_ZjZ9XCVs6qFhRbjRzgiWspUZvB=s432

Martin,
Looks really good.
I may copy your efforts on my -4.

Daddyman
 
The only comment I'd add to what Dan and others have already said is that Proseal works great to seal down any raw edges. Proseal won't soften in the oily environment, but you may need to keep it reasonably distanced from the exhaust pipes.

Nothing wrong with proseal, but Loctite 598, aka Permatex Ultra Black (very high oil resistance), would be faster/easier.

That said, a finish-painted cowl needs nothing for insulation edge sealing beyond a strip of aluminum tape.
 
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actual cowl temps after shutdown

Ok for anyone interested.... the other day I got some temps from cowling with the thermal imaging scan gun after shutdown (pulled the plane indoors, so it was a few minutes after shutdown before I did the actual measurements.) Outdoor temps where about 76 degrees. It would be another budget league to obtain in flight temps in these areas...so after shut down the best data I have.

Top of cowl over cylinders = 127 degrees
Top of Cowl in the middle and not directly above the cylinders ~100 degrees
Lower cowl just below air intake ports = 112 degrees
Bottom and Sides of lower cowl = 100 degrees
Bottom of lower cowl along below the exhaust pipes = 90 degrees (this is where I have the heat shielding installed).


Does anyone know what temps our cowlings will start to be impacted by heat? Especially since it gets close to 130 degrees on that top cowling.

Interesting that there is only a 10 degree difference on where the heat shielding is installed on the bottom cowling, but I am sure it not a linear relationship as actual heat off the exhaust increases.....


Paul
 
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