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Date: Thu, 28 Jul 2011 18:59:37 -0400
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Subject: Re:  Engine Baffles
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John -

Your question was unclear as to whether you were looking for a fire shield,=
 cooling airflow control, or thermal protection.  Please defer to answers f=
rom guys who know the real answer to your question.  However, here are some=
 things to think about.

First things first.  I am referring to the firewall as the protective layer=
/layers that protects the airframe from fire.  I am referring to the bulkhe=
ad as the structural element that carries the loads.  They are not usually =
the same part.  Normally they are layered.  But usually we call the bulkhea=
d "the firewall", even though it is incorrect to do so.

1)  Fire shielding -- Thin stainless steel sheet (0.023 thick) is commonly =
used for aircraft firewalls.  The purpose of this element is to protect loa=
d-carrying structure from direct flames.  The qualification test is to expo=
se it to a 2000 F flame for 15 minutes, or something very similar to that (=
I'd have to reread the advisory circular).  If the sheet doesn't burn throu=
gh, it passes.  In a metallic airplane, or even a tube-and-rag airplane lik=
e a Citabria, the fact that the back side of the steel gets close to 1000F =
does not matter.  The load carrying bulkhead or tubing can still hold toget=
her.  Heat shielding is not needed.

2)  Heat shielding (thermal insulation) -- Those of us with composite airpl=
anes need to keep firewall backface temperatures low enough for the bulkhea=
d to maintain its structural integrity.  This is typically something like 1=
80-200 F.  The Lancair 320/360 that I have has a plywood bulkhead with fibe=
rglass cloth reinforcement.  I do not know what the critical temperature is=
 but it is probably similar, since the plywood bulkhead is attached to the =
fuselage with fiberglass.  Later model Lancairs have fiberglass honeycomb b=
ulkheads, as I understand it.  For either of these aircraft a heat shield i=
s needed. In the early days our firewall consisted of an 0.023 stainless fi=
re shield on top of 3 plies of Fiberfrax heat shielding.  Later models used=
 a quilted ceramic blanket that appears to be aluminized on one side (the h=
ot side) and covered with a red RTV impregnated cloth on the other.  (That'=
s probably not what the outer lyes really are, but that's what it looks lik=
e.)  (I took one look at Angier Ames' beautiful quilted firewall and took m=
y steel/fiberfrax out and replaced it.  I saved 3.5 pounds in the process, =
too.)

3)  Engine baffling -- These are the aluminum sheets that direct cooling ai=
r thru the cylinder head cooling fins.  These don't get very hot and take v=
ery slight loads, so aluminum works fine. =20

I'm not entirely sure why I barfed out all these words but they might help =
someone.  Have fun at Oshkosh for me this week if you are there.  I plan to=
 join y'all next year -- maybe even fly there in my own Lancair!  (Don't pa=
nic -- I have threatened this before...)

- Rob Wolf


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<font color=3D'black' size=3D'2' face=3D'arial'>
<div>John -</div>


<div>&nbsp;</div>


<div>Your question was unclear as to whether you were looking for a fire sh=
ield,&nbsp;cooling airflow control,&nbsp;or thermal protection.&nbsp; Pleas=
e defer to answers from guys who know the real answer to your question.&nbs=
p; However, here are some things to think about.</div>


<div>&nbsp;</div>


<div>First things first.&nbsp; I am referring to the firewall as the protec=
tive layer/layers that protects the airframe from fire.&nbsp; I am referrin=
g to the bulkhead as the structural element that carries the loads.&nbsp; T=
hey are not usually the same part.&nbsp; Normally they are layered.&nbsp; B=
ut usually we call the bulkhead "the firewall", even though it is incorrect=
 to do so.</div>


<div>&nbsp;</div>


<div>1)&nbsp; Fire shielding -- Thin stainless steel sheet (0.023 thick) is=
 commonly used for aircraft firewalls.&nbsp; The purpose of this element is=
 to protect load-carrying structure from direct flames.&nbsp; The qualifica=
tion test is to expose it to a 2000 F flame for 15 minutes, or something ve=
ry similar to that (I'd have to reread the advisory circular).&nbsp; If the=
 sheet doesn't burn through, it passes.&nbsp; In a metallic airplane, or ev=
en a tube-and-rag airplane like a Citabria, the fact that the back side of =
the steel gets close to 1000F does not matter.&nbsp; The load carrying bulk=
head or tubing can still hold together.&nbsp; Heat shielding is not needed.=
</div>


<div>&nbsp;</div>


<div>2)&nbsp; Heat shielding (thermal insulation)&nbsp;-- Those of us with =
composite airplanes need to keep firewall backface temperatures low enough =
for the bulkhead to maintain its structural integrity.&nbsp; This is typica=
lly something like 180-200 F.&nbsp; The Lancair 320/360 that I have has a p=
lywood bulkhead with fiberglass cloth reinforcement.&nbsp; I do not know wh=
at the critical temperature is but it is probably similar, since the plywoo=
d bulkhead is attached to the fuselage with fiberglass.&nbsp; Later model L=
ancairs have fiberglass honeycomb bulkheads, as I understand it.&nbsp; For =
either of these aircraft a heat shield is needed. In the early days our fir=
ewall consisted of an 0.023 stainless fire shield on top of 3 plies of Fibe=
rfrax heat shielding.&nbsp; Later models used a quilted ceramic blanket tha=
t appears to be aluminized on one side (the hot side) and covered with a re=
d RTV impregnated cloth on the other.&nbsp; (That's probably not what the o=
uter lyes really are, but that's what it looks like.)&nbsp; (I took one loo=
k at Angier Ames' beautiful quilted firewall and took my steel/fiberfrax ou=
t and replaced it.&nbsp; I saved 3.5 pounds in the process, too.)</div>


<div>&nbsp;</div>


<div>3)&nbsp; Engine baffling --&nbsp;These are the aluminum sheets that di=
rect cooling air thru the cylinder head cooling fins.&nbsp; These don't get=
 very hot and take very slight loads, so aluminum works fine.&nbsp; </div>


<div>&nbsp;</div>


<div>I'm not entirely sure why I barfed out all these words but they might =
help someone.&nbsp; Have fun at Oshkosh for me this week if you are there.&=
nbsp; I plan to join y'all next year -- maybe even fly there in my own Lanc=
air!&nbsp; (Don't panic -- I have threatened this before...)</div>


<div>&nbsp;</div>


<div>- Rob Wolf<br>
<br>
</div>


<div style=3D"CLEAR: both"></div>
</font>
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