Heatshielding Question

[cattflight]

Originally Posted by DanH

Mike, please do post a source for the 0.010" SS sheet. It could be handy in some applications, in particular a belly overlay.

It's not that the outgassing requires a huge vent...see below



A subtle detail is that the aluminum tape is expected to melt in the event of a significant fire. The hot part of the firewall will be the centerline, down low, near the cowl exit, as fire tends to follow airflow. Thus, you kinda want some of the SS foil overlap seam in that location, so the aluminum tape has the opportunity to melt and open a vent.

Got it. Makes sense. Thanks, Dan.

[ppilotmike]

Originally Posted by DanH

Mike, please do post a source for the 0.010" SS sheet. It could be handy in some applications, in particular a belly overlay.

Dan,

Below is my source for the 0.010" SS sheet:

Frank Li
American Metals Company
PO Box 41
200 Obringer Lane
Sarver PA 16055
Phone 724-625-8666
Email: fli@metalshims.com

Please let me know what style of pop rivets you used. I've change my mind about using the structural rivets that are part of the actual firewall. I will likely put some SS pop rivets in on say a 6" OC spacing, just to hold the sandwich to the firewall. Also, I'm planning to vent the Fiberfrax off-gas via the edges of the sandwich and also the seams around the recessed box.

[Wayne Gillispie]

I installed a temperature limit switch near nose gear leg attachment. I set it at 230*F. Normally, 220*F is about max operating temp across the switch unless at 16,500 near gw in high AOA and in thin air. The NC switch opens and energizes an LED on the panel in case of fire. My fuel flow max warning is set at 27 gph. I installed an 1/8" layer of fiberfrax on inside of firewall and tunnel bottom. The best thing to do is build, inspect and maintain so that you lessen the chance of fire. Have a warning or two so that you are not flying along for 5 minutes while flames lap at your aluminum/fiberfrax/stainless before starting an emergency descent. We are way more likely to die in a LOC accident than an in-flight fire.

[tgmillso]

I have a couple of questions for the crew. I did my belly insulation using 0.005" TI (from Titaniumgoat) and 1/16" frax, using 3/32" rivets around the perimeter and Mk319BS monel rivets in the center. The perimeter was also sealed with sikaflex pro to limit the chance of water egress, and the aluminum belly skin was primed externally prior to the application. The center rows of rivets were wet riveted in place using firebarrier 2000+. I was pretty happy with how things turned out. I'm now working on the firewall, and have a couple of questions.
1. Using the fourier's law, it appears that the doubling of insulation thickness results in a halving of heat transfer into the cabin. At a 65degC engine compartment temperature and 20degC cockpit temperature, for 1/16" frax 1.55kW is transferred into the cabin, and 0.77kW for 1/8" frax. The only downside is that I see the 1/8" frax is going to be much harder to handle during the installation, especially sealing the perimeter and in the firewall recess. Has anyone used 1/16" frax instead and if so, what were the results? I figure if it is ok to protect the aluminum belly, then it must be adequate to protect the aluminum rivets in the firewall. I figure the thinner insulation would give a neater finish by limiting pillowing and thus the risk of catching a tool on it in the future and tearing it.
2. For a new build, could you just sandwich the foil around the perimeter between the flanges and the cowling hinges? I figure this would eliminate the problem of having the risk of the firebarrier 2000+ separating around the perimeter and the foil coming away in the future.

Below are some pics of my belly skin install.

[Dorfie]

[
Please let me know what style of pop rivets you used. I've change my mind about using the structural rivets that are part of the actual firewall. I will likely put some SS pop rivets in on say a 6" OC spacing, just to hold the sandwich to the firewall. Also, I'm planning to vent the Fiberfrax off-gas via the edges of the sandwich and also the seams around the recessed box.[/quote]

Mike,
I used 1/8 large head SS pull rivets. (I will have to get the exact detail of the rivets at the hanger). Also got 1 inch steel washers plated with 1/8 hole (Lowes) through which the rivets were installed. That distributes the force of the rivet nicely. I did not need 6 inch spacing and used much larger spacing. Also the items that mount to the firewall serves as anchors of the sandwich.
Johan

[ppilotmike]

Here's some pictures of how my belly shield turned out. I think it looks great and will virtually disappear when it gets painted. I used 1/16" fiberfrax materials, sandwiched between 0.010" stainless steel sheet and the aluminum belly skin. My heat shield comes back about 18" from the firewall, it's sealed with 3M Fire Barrier 2000 and is riveted, using slightly longer rivets (to allow for the SS thickness and FF thickness) to the understructure, during my build. With the 1/16" FF and the 0.010" SS sheet, there was very little pillowing, as you can see.

https://photos.google.com/share/AF1Q...pTdEhiOFBKMUlR
https://photos.google.com/share/AF1Q...pTdEhiOFBKMUlR

I plan to use 1/8" thick Fiberfrax and the same 0.010" SS sheet to make a heat shield on my firewall (engine side, of course!), per Dan Horton's suggestions. It will be held in place using SS pull rivets, spaced out at 6 to 9" OC, plus all the other connections through the firewall, and sealed up with 3M Fire Barrier 2000. I will also be using SS heat box valves, in lieu of the aluminum ones Vans provides. All in all, this should provide a bit of extra protection, in case of an in-flight fire, for not much added cost, work or weight, IMO.

[tgmillso]

Johan, to your point, my perimeter rivets are just regular AN426AD3-3.5 rivets, and the two rows of interior rivets are Mk319BS as they are monel and thus much higher temperature capable than the AN426 rivets. The holes were first drilled in the 0.040" belly skin, then the titanium was sandwiched between that and some particle board flooring, pressing down hard on the skin so that the holes drilled cleanly. The layer was clecoed to the board as I went along. After drilling the center holes to 7/64", they were then dimpled using a #40 dimple die (as that was the only size I had that fitted) but they worked fine.
So how about sandwiching the stainless foil between the cowling attach hinges and the firewall flanges? Anyone tried this approach?

Tom.

[DanH]

Originally Posted by tgmillso

So how about sandwiching the stainless foil between the cowling attach hinges and the firewall flanges? Anyone tried this approach?

I'm sure it can be done, but 6 years in service says a fillet of Firebarrier around the perimeter (2nd drawing, post 5) works fine to fasten and encapsulate the edge of the sheet.

SS foil is razor sharp. Forming a good 90 degree flange to trap under the hinge material may involve bloodshed. For sure you don't want an exposed edge anywhere when finished.

[tgmillso]

Fair enough Dan. I don't want to make this any harder than it needs to be.

T.

[koupster]

Anyone see a downside to attaching a belly shield with #6 stainless screws such as MS21207 100? FLAT HEAD TYPE B SCREWS? My 6 is flying and I'd like to do the attachment from the outside only. Don't see readily available stainless pull rivets smaller than 1/8". The #6 screws would require a smaller hole.

Cheers, David
RV-6A KBTF