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Firewall Material

Posted By:
Dan Malone
Homebuilder or Craftsman
18
Posts
1
#1 Posted: 6/1/2011 08:08:23

I am building a composite amphibian which has the engine mounted in a pusher configuration  mounted on top of the wing.  I am wondering what firewall material to use.  stainless, fiberfrax,  ceramic....  I am worried that fiberfrax will absorb oil and fluel drips and then become more of a fire hazard.  Anyone have experience with the newer/other materials that are listed at Aircraft Spruce?  Any input/ opinions would be greatly appreciated.

 

Thanks Dan M



Dave Prizio
Young Eagles Pilot or VolunteerHomebuilder or Craftsman
118
Posts
29
#2 Posted: 6/1/2011 11:10:25

Stainless steel, or titanium if you have the budget for it, should serve as your main firewall. However, the composite structure must be protected from heat by Fiberfrax or a similar material. The Fiberfrax can be protected from oil with a thin layer of aluminum applied over it. Thus you have a sandwich of stainless steel/Fiberfrax/aluminum. The aluminum will be on the engine side and can be quite thin, say .020"  It is sacrificial in case of fire, and is merely there to protect the Fiberfrax.

In testing Glasair found that they needed 1/2" of Fiberfrax to keep temperatures on the cabin side of the firewall low enough to make them comfortable. You must remember that even though the stainless will stop the flame it will not stop heat. If the temperature of the cabin side of the stainless steel firewall exceeds about 700 degrees F the composite structure can burn.

Lancair makes a preformed firewall blanket for their kits that has a bonded protective coating over the insulating material. I don't know if any other kit manufacturers do the same, but they should.

When you look at other materials besides Fiberfrax be sure that they are fire rated for 2000 degrees plus. Many of these materials are heat/sound insulators but not suitable for firewall protection.  Also be sure to use caulking rated for 2000 degrees, not high temp RTV which is only good for 500 degrees continuous exposure.



Doug Belbin
Homebuilder or Craftsman
8
Posts
1
#3 Posted: 6/5/2011 05:05:34

Dave, sounds good, where does one get a 2000 deg caulking? Brand and number please, i am searching for that now. I actually got my firewall wrong, Stainless then sound/heat deadener then glass fuselage. Stainless to the motor, your caulking is of great interest I was going to use hi temp RTV.


Doug



Doug & Lisha Belbin - Yippyio on Vans wings - Australia - http://www.yippyio.net
Dave Prizio
Young Eagles Pilot or VolunteerHomebuilder or Craftsman
118
Posts
29
#4 Posted: 6/6/2011 11:45:31

Aircraft Spruce has a product called 3M Fire Barrier 2000. You can also use 3M CP-25WB+, which is available from online sources . Another good product is Flamesafe FS 1900 sealant. Glasair sells it, but it is also probably available from online sources.  The magic number you want to look for in a firewall product is 2000 degrees F. If it isn't rated for that temperature you should try to find a product that is instead. High temp red RTV is only rated for 500 degrees continuous or 600 degrees short term. 

Note than many firewall blankets, etc. are not rated for 2000 degrees. These products are OK for firewalls that are supported by metal structures, but  they are not really adequate for firewalls supported by wood or composite structures.



Doug Belbin
Homebuilder or Craftsman
8
Posts
1
#5 Posted: 6/8/2011 19:19:21

All noted. Thank you Dave - dunno about rebuilding the firewall now, ummmnm I guess one more rebuild is just anuvver day longer to first flight.

Do I die of old age waiting to fly, or go down in flames? That is the question, currently rummaging in my old bucket of nuts and bolts to see if I find an answer.

Once again, thanks Dave, still looking for help on lube-ing rod ends

Cheers



Doug & Lisha Belbin - Yippyio on Vans wings - Australia - http://www.yippyio.net