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Thread: firewall material for composite planes (no wood)

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    firewall material for composite planes (no wood)

    looking for what material i can use on the vision for the firewall. plans call for a wood firewall with an aluminum skin. I really have no ambitions of puting any sort of wood in this plane. is there something else i can use, and just add phenolic or aluminum embedded for the hard points for the motor mounts?
    Last edited by slociviccoupe; December 23rd, 2011 at 08:08 PM.

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    Super Moderator orion's Avatar
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    Re: firewall material for composite planes (no wood)

    You're not going to believe this but wood is actually not a bad choice. Yes, it's flammable but by the time the wood firewall burns through, the rest of the plane will already be an ash pile since the resin will burn much faster than that. Some years back I tested a firewall made of glass (with Vinylester) and end grain balsa (Baltek core) - just that alone worked pretty well since as the balsa burned it simply charred and bubbled up and pretty much insulated the rest from the torch flame. My end configuration was the balsa/glass sandwich with a Silica fabric on the engine side. The Silica fabric is the same stuff the welding fire curtains are made from. The Silica is attached to the laminate with a high temp Silicone (applied with a notched trowel). A thin sheet of stainless went on top of the Silica and a quilted fire blanket (similar to that used in NASCAR I believe) went over that. A pretty fireproof combination and overall not very heavy.
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    Re: firewall material for composite planes (no wood)

    yeah, whatever the firewall is made out of will be covered in an aluminum or stainless sheet, fire isn't really my biggest concern its just the fact of putting wood in an airplane that has no wood in it except for the firewall. i know its awesome at its strength to weight properties but its still wood. still suseptable to rot. even the best sealed piece of wood laminated between layers of glass can rot. even worse when there are multiple pass through points that will have to be sealed.
    Im trying to see if there are alternatives other than wood. added bracing on the inside or aluminum or phenolic inserts isn't a problem either. interested to know what lancair and other full composite planes are using for a firewall for where the engine mount is atatched. not just what is being used for fire protection.

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    Registered User Hot Wings's Avatar
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    Re: firewall material for composite planes (no wood)

    Orion is right, wood is hard to beat. Fully encapsulated with glass and resin it should not rot in our lifetime. Where you plan to perforate the firewall with bolts, or other, you can remove the wood in that area and fill with flox before skinning to keep any moisture from reaching the wood.

    If you still don't like the idea of wood maybe some high density PVC foam could be substituted? It's not going to have the same heat resistance that the wood does and will need more insulation, resulting in more weight.

    Also stainless isn't needed unless you just want it for looks. There are fiber materials available that have equal or better flame/heat resistance that weigh less.
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    Registered User Tom Nalevanko's Avatar
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    Re: firewall material for composite planes (no wood)

    I would use a 1/4" 2/Core/2 honeycomb covered with some Fiberfrax and a stainless steel sheet. This would give you good anti-fire capability at low weight. This was the setup in my Stallion and in many Lancairs, I believe.

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    Re: firewall material for composite planes (no wood)

    ill take that into consideration. where would i find that material. also the points for the motor mount to the firewall. is there inserts in the core material that keep it from crushing when the motor mount bolts are tightened to the firewall. And its standard core construction but with just different materials.

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    Re: firewall material for composite planes (no wood)

    How about this?:


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    Re: firewall material for composite planes (no wood)

    the coating is fine and dandy, im not worried about fire or heat. just wondering what material im going to use for the bulkhead that makes up the firewall for the vision aircraft. per plans its wood and i would hate to put wood in this plane as the rest of it if foam and fiberglass. whatever core material i use will have layers of glass on both sides, a thin sheet of aluminum, stainless, or a fire blanket material. A subaru ej25 will be infront of it so not as much firewall heat as an air cooled motor. Whatever material is used for the fwd bulkhead that makes the firewall and engine moto mounting point has to be strong as it will also support the fwd nose gear.

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    Re: firewall material for composite planes (no wood)

    Just checking the Long EZ plans and it has birch plywood with glass, fiberfrax and SS. Good enough for Burt.......

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    Registered User Tom Nalevanko's Avatar
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    Re: firewall material for composite planes (no wood)

    You could probably purchase from Lancair the basic 2/C/2. Yes there are phenolic inserts that you put in for the bolts as anti-crush points. Say 2" x 2", depending on the size of the contact area of the motormount at the bolts. The sheets are 2 ply fiberglass and the core is phenolic honeycomb, I believe.

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    Re: firewall material for composite planes (no wood)

    hopefully lancair is more friendly than say vans aircraft. for people wanting to use products they use for planes that aren't theirs.
    ill try them and see what they say.

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    Re: firewall material for composite planes (no wood)

    Quote Originally Posted by slociviccoupe View Post
    hopefully lancair is more friendly than say vans aircraft. for people wanting to use products they use for planes that aren't theirs.
    ill try them and see what they say.
    Why should they be. After research and testing they know what works. You want to go in a different direction - why should they help. Just don't be surprised if your results are not satisfactory.....

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    Registered User Lucrum's Avatar
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    Re: firewall material for composite planes (no wood)

    Quote Originally Posted by slociviccoupe View Post
    ...its just the fact of putting wood in an airplane that has no wood in it except for the firewall...
    Not trying to tell you what to do, but that doesn't seem like a choice based on logic and or engineering. Even multi-million dollar all metal corporate jets usually have at least some wood present in the interior.

    Another way of looking at it, how often will bystanders on the ramp ask you what the core material of your firewall is?
    Last edited by Lucrum; December 26th, 2011 at 06:03 AM. Reason: spelling
    ...If you forget this, you will be subjected to a four phase aeronautical process that dates back to the early 1900ís. Stall, spin, crash and burn. Phase 4 requires some amount of fuel on board at time of impact.

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    Registered User Tom Nalevanko's Avatar
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    Re: firewall material for composite planes (no wood)

    I did not have a Lancair and bought lots of parts from them. They were very helpful.

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    Registered User SVSUSteve's Avatar
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    Re: firewall material for composite planes (no wood)

    yeah, whatever the firewall is made out of will be covered in an aluminum or stainless sheet,
    Why not just go with a stainless covered with something that itself is burn resistant? That's the option I am going for with my design. Remember, just because something doesn't burn through does not mean that it isn't going to radiate heat through to ignite things in the cockpit. Backing a piece of wood up with a piece of metal will actually DECREASE the burn through time of the wood since it concentrates the heat. The same goes for most insulated fuselage panels due to the insulation concentrating the heat on the outside surface (the one next to the fire) rather than allowing it to radiate through. It seems counterintuitive but this has been demonstrated by US Army crash survivability research as well as FAA and NASA research. This is one of those circumstances where careful selection of materials and consideration of the interactions between various materials is very important.

    not just what is being used for fire protection.
    I would point out also that the firewall also plays a huge role in the crashworthiness of a design. You want to make sure it is going to stay in place and not be shoved back into the cockpit under any conceivably survivable crash scenario. Also, angling the lower portion backwards (towards the tail) will help to minimize the tendency to "plow" when landing on a "soft" surface such as soil or water. Such plowing will reduce the length of deceleration and increase the forces applied to the occupants.

    If you still don't like the idea of wood maybe some high density PVC foam could be substituted?
    You might want to also consider what happens when the various foams are heated (pyrolysis). The fire might not make it into the cockpit before you're on the ground but the same may not be able to be said for the toxic pyrolytic byproducts (hydrogen cyanide, CO, hydrogen fluoride, phosgene, etc).

    There are fiber materials available that have equal or better flame/heat resistance that weigh less.
    But they tend not to hold up as well as steel or higher grade aluminum in terms of impact resistance which is a consideration that is sadly overlooked in many aircraft designs, even the commercially built ones.

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