Quantcast

Making a firewall

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

Mad MAC

Well-Known Member
Joined
Dec 9, 2004
Messages
664
Location
Hamilton New Zealand
One would probably better if using two skins, to just ditch the insulation and just use a 1" air gap that is externally vented (if the cockpit is well sealed, cabin air sucked in the bottom and vented out the top).
 

Little Scrapper

Well-Known Member
HBA Supporter
Log Member
Joined
Jan 3, 2014
Messages
5,734
Location
Wisconsin
Open cockpit. I’ll probably stick to a single sheet. It’s worked well for decades so I don’t want to overthink this and create more work than required.
 
  • Like
Reactions: TFF

wktaylor

Well-Known Member
Joined
Sep 5, 2003
Messages
219
Location
Midwest USA
Be careful... ALL fibrous insulation wicks in moisture [water, water-vapor/condensation]. Without a protective jacket or exceptional ventilation, AVOID prolonged CONTACT with most metals.

Any aluminum structure exposed forward of the firewall...and attached to the backside of the firewall... is subject to heat damage in a fuel/oil-fed fire or exhaust system failure.
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
11,732
Location
97FL, Florida, USA
Any aluminum structure exposed forward of the firewall...and attached to the backside of the firewall... is subject to heat damage in a fuel/oil-fed fire or exhaust system failure.
Good point. There is at least one documented case where aluminum sheet, covering a 1/2” fiberfrax board firewall, burned through before an immediate landing could be completed from an oil fire on takeoff. IIRC, the fiberfrax remained intact.

BJC
 

tralika

Well-Known Member
Joined
Oct 19, 2009
Messages
92
Location
Wasilla Alaska
You might consider using titanium rather than stainless. You can buy a 24" x 36" sheet of .020" from McMaster-Carr for $162. More expensive than stainless but I saved over 5 pounds on my firewall. Certified aircraft can use as thin as .016" titanium.

McMaster-Carr

The melting temperature of titanium is higher than stainless but from a practical standpoint you could probably use aluminum. A fire in flight hot enough to melt a firewall is going to be forced down and out of the engine compartment. In a tube and fabric aircraft there is no protection on the bottom of the fuselage so by the time it burns through the firewall the passenger area will be compromised. Not pleasant to think about but true.
 

Will Aldridge

Well-Known Member
Log Member
Joined
Oct 30, 2009
Messages
955
Location
Northern Utah
A fire in flight hot enough to melt a firewall is going to be forced down and out of the engine compartment. In a tube and fabric aircraft there is no protection on the bottom of the fuselage so by the time it burns through the firewall the passenger area will be compromised. Not pleasant to think about but true.
This thought has crossed my mind(kitfox owner here). Any fire is going burn the belly of the plane because that's where the cooling air exhausts out of the cowling. So in that scenario is there any point in using anything heavier than aluminum for a firewall since you'll already be getting toasted? Parachute out immediately if there's a fire being the only other option?
 

mcrae0104

Well-Known Member
HBA Supporter
Log Member
Joined
Oct 27, 2009
Messages
3,434
You might consider using titanium rather than stainless. You can buy a 24" x 36" sheet of .020" from McMaster-Carr for $162. More expensive than stainless but I saved over 5 pounds on my firewall.
Wait. If I assume 0.032" Ti vs. 0.032" SS, on my particular (single seat) design I save 18 oz. You must have a BIG firewall!
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
13,610
Location
Memphis, TN
Annealed Ti is supposed to be pretty easy to form. Any weight saved is saved; if you can afford it.

Removable Aluminum panels all sides to the end of the cockpit, may weigh a bit more than fabric, but fire protection and accessibility are pretty good reasons to put up with it.
 

gtae07

Well-Known Member
Joined
Dec 13, 2012
Messages
2,009
Location
Savannah, Georgia
This thought has crossed my mind(kitfox owner here). Any fire is going burn the belly of the plane because that's where the cooling air exhausts out of the cowling. So in that scenario is there any point in using anything heavier than aluminum for a firewall since you'll already be getting toasted? Parachute out immediately if there's a fire being the only other option?
And that’s why you should place a stainless exhaust shield under there from the cowl exit aft. A 1/16 fiberfrax layer extending 18-24 inches aft, covered by a stainless sheet sealed and pop-riveted (or secured another way) around the edge, will go a long way to preventing that burn-through. I think that’s a much better solution than just fatalistically accepting “well, it’ll just burn through anyway so f*** it”.

Remember that an engine fire might happen on the ground. Or at an altitude too low to bail out. Or in any number of other situations where maintaining the integrity of the aircraft for more than a couple seconds is critical to the survival of the occupants. The FARs specify firewall parameters that way for a reason; I might not always agree with how prescriptive they are (i.e. how specific they are on “thou shalt do it this way”) but generally the things they’re trying to achieve are good ideas borne out of experience or good engineering judgment.

Properly constructing a firewall is not hard, expensive, or heavy. It’s a “safety mod” on the same level as properly installing a good five-point harness.
 

tralika

Well-Known Member
Joined
Oct 19, 2009
Messages
92
Location
Wasilla Alaska
Wait. If I assume 0.032" Ti vs. 0.032" SS, on my particular (single seat) design I save 18 oz. You must have a BIG firewall!
I went from .032" SS to .020" Titanium. I would have used .016" Titanium if I could have sourced it.

If anyone has built one of those planes with the passenger compartment protected by stainless steel on all sides I'd like to see the photos. I'd especially like to see it in flight.
 
Last edited:

crusty old aviator

Well-Known Member
Joined
Feb 17, 2014
Messages
238
Location
Grantham, NH
I don’t know if they qualify for “one of those planes,” but:
Fleetwings Seabird: all stainless construction...just like the Budd Conestoga
1587139161907.gif
1587139280157.jpeg
 
  • Like
Reactions: BJC

gtae07

Well-Known Member
Joined
Dec 13, 2012
Messages
2,009
Location
Savannah, Georgia
I went from .032" SS to .020" Titanium. I would have used .016" Titanium if I could have sourced it.

If anyone has built one of those planes with the passenger compartment protected by stainless steel on all sides I'd like to see the photos. I'd especially like to see it in flight.
You don’t need “stainless steel on all sides”.

What we’re talking about here is just a properly-constructed (and sealed) firewall, and shielding aft of cowl exits (the old Part 23 specifies “each part behind an opening in the engine compartment cowling must be at least fire resistance for a distance of at least 24 inches aft of the opening”).

Of course, there is the example of the A-10... ;)
 

Markproa

Well-Known Member
Joined
Feb 9, 2017
Messages
130
Location
Bellingen, NSW. Australia.
My plane has a plywood firewall with epoxy glass layer then painted with fire retardant paint. It is a diesel with well shielded exhaust and turbo so hopefully less likely to have an engine room fire.
 

vhhjr

Well-Known Member
HBA Supporter
Joined
Jun 29, 2003
Messages
92
From a practical standpoint galvanized steel is more than adequate and a lot cheaper than stainless or titanium. A 48" x 48" sheet of .019" is only $36 and has the same short term fire resistance as stainless. You may be able to get a piece of it from a local HVAC shop that makes duct work. Galvanized sheet may be left as is, polished or painted if the right primer is used.
Sheets
  • Yield Strength: 40,000 psi
  • Hardness: Rockwell B55 (Soft)
  • Heat Treatable: No
  • Specifications Met: ASTM A653
Thick.Thick.
Tolerance
Each Each Each
12" × 12"24" × 48"48" × 48"
0.012"0" to 0.006"8943K11$6.678943K12$16.56________
0.015"0" to 0.006"8943K1117.678943K1318.038943K23$32.37
0.019"0" to 0.006"8943K1128.688943K1419.178943K2436.03
0.024"0" to 0.008"8943K11311.528943K1523.668943K2541.90
 
Top