Franklin Cabin/Carb Heat - Fire Safety Hot Foot Conundrum

blimpy

blimpy

New member
I just discovered that the heat muff which supplies cabin heat ( pilot side control- which I think is rear seat heat)
also supplies Carb Heat.

A diverter valve ( flap) selects fresh air, or heated air for the Carburetor Intake.

Imagine my surprise when I saw that the cabin heat tube is also connected to the diverter box
under the carburetor.

In the case of a Carburetor Fire or Back Fire
It would seem that when carb heat is ON, and rear cabin heat is ON... there is a direct path into the cockpit
for Fire !

It would take a pretty long string of improbables to make this a problem,... but that is always how accidents happen.

Now I know why the standard drill is to shut all cockpit vents in case of fire .

---

Now, if having the pilot side cabin heat ON... diminishes the heat supplied to the carburetor...
that's not so good.

Hmmm :?: :idea: :roll:
 
My 14-13-2 runs flex metal ducting from the right side shroud into a Tee. One branch to the rear seat (lower left firewall) and the other to the forward passenger side heat outlet (upper right firewall). Cabin heat valves are on the firewall pass-throughs. One control on the pilot side (rear seat), the other on the passenger side. The left side shroud has 2" scat to the carb box. I believe all the metal duct and valves are original.
 
Ok, that is somewhat different than my '47 cruisair set up, which has the right muff feeding the cabin heat on the right,
and the shared feed from the left muff.

Both have the firewall mounted controls, of course.

blimpy
 
I think you may have discovered someone's "innovation" . I'll take a look at my setup today and confirm.
 
Just back from the hanger. My left side cabin heat has always been closed off with no connection. (since 1963 anyway) The left muff has a 2 inch inlet connection from the nose bowl and a 2 1/2 inch outlet to the carb heater box via a short piece of SCAT and a U shaped formed duct to the rear of the carb heat box. That's it, simple.

However, there is a hot air dump port on the heat box and it could conceivably have been connected to the left cabin heat valve. That would duplicate what you describe.

I dimly recall an early SB or AD regarding cabin heat to disconnect something or other. That may be it. So, you spotted something that definitely needs to be corrected. (10 points) 8) BTW. Ever get strong gas fumes in the cabin, say on start-up?

Also, a picture of the connection for the archives would be good.

ron
 
I believe the AD was to remove the original aluminum air valve (at the firewall) and replace with the steel ones that we see on all Cruisairs now. They must have figured out that a fire can melt aluminum. Also remember that there should be a fine mesh steel (not aluminum) screen where the valve bolts to the firewall. Flame will not travel through a fine mesh (so Im told). I have one of those old aluminum valves ,hiding in a box of junk. It was cast and looked nicer than the ones we have now. Oh Well, we are safer. _____Grant.
 
Ron, I'm gonna take a picture of the set up tomorrow, and I will try to remember to post it here.
Nope, never get any fumes in the cockpit, "magic" CO detector is always happy.
About the Only time I smell anything is through the side vents. Which is pretty amazing when you think about it.
all the leaking oil nicely misses anything Hot !

Grant, I'd have to look closely to see if I have the "fire screen. I know I don't have the matching tongs and shovel :wink:

My firewall valves are steel.

See, I told you my cruisair was "real original". :twisted:
 
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