Simple solution to hot tunnel

[Wayne Gillispie]

Originally Posted by DanH

Two tiny points...

The "fire-breathing" test setup is merely the FAA standard, nothing radical at all.

As demonstrated by an unfortunate RV-10 owner right here, the floor will probably burn through below the tunnel in the case of a fuel-fed fire, igniting a poor insulation choice. Choose carefully.

And melting our brake lines.

[N427EF]

I don't expect an answer and I am sure we could all learn something from that accident .
Would like to know what happen and lead to the fire in the first place.

As demonstrated by an unfortunate RV-10 owner right here, the floor will probably burn through below the tunnel in the case of a fuel-fed fire, igniting a poor insulation choice. Choose carefully.

[flion]

Search the forum, it's in here.

I like Jack's solution; not only does it positively cool the tunnel but also vents it in case a leak puts fumes in there.

[Bill.Peyton]

I used fibre frax on the cabin side of the firewall and the floors, including the tunnel, two layers of 1/8". I also installed the stainless heat valves. Everything else is stock. My tunnel is cool to the touch. I believe that the newer exhaust system with the outlet extension pointed downward, is probably one of the reasons the tunnel issue has gone away.

[Geico266]

Originally Posted by JackinMichigan

I am about 1/3 along on my RV-10 and have also read all the stories about the hot tunnel. I have put a good amount of insulation on the firewall hoping this would help. I also insulated the tunnel itself to reduce interior noise (not good for a hot tunnel).

Anyway, I ran an air intake from using a 1" tube from the passenger NACA duct over to the front of the tunnel with a open/close valve. Also, made a fiberglass exhaust duct which looks like a mini hood scoop (1 x 3") but mounted in reverse and installed near the rear of the tunnel as an exhaust vent.

I didn't post this because I figure there would be too many nays..

Oh, I also plan on putting a temperature thermocouple in the tunnel to monitor the temperature.

How did your experiment work out?

[cderk]

I did nothing to my RV-10 other than put a firewall blanked on the engine side of the firewall... i have not noticed that my tunnel is hot.

[DanH]

Regardless of product used, consider the difference between insulating outside the structure vs insulating inside the structure.

Insulating outside (notably the engine side of the firewall, and the outer surface of the belly skin) slows heat transfer to the entire airframe.

Insulating inside allows the airframe to heat, while attempting to slow energy transfer from the hot airframe parts to components in the human space. It may slow radiant and convective transfer, but it does nothing for the metal-to-metal conductive path.

When someone talks about insulating inside the tunnel, I get a mental picture of them wearing their raincoat inside their clothes.

That's comfort insulation. Engine fire is a different subject. Assume a fuel or oil fed fire. If you insulate the inside of the tunnel floor without external surface shielding, I can pretty much guarantee you'll melt through the belly skin immediately aft of the firewall. Simple enough; temperature rise of the aluminum skin is a function of energy-in less energy-out. Insulating inside the skin blocks the energy-out path.

[mturnerb]

Originally Posted by DanH

Regardless of product used, consider the difference between insulating outside the structure vs insulating inside the structure.

Insulating outside (notably the engine side of the firewall, and the outer surface of the belly skin) slows heat transfer to the entire airframe.

Insulating inside allows the airframe to heat, while attempting to slow energy transfer from the hot airframe parts to components in the human space. It may slow radiant and convective transfer, but it does nothing for the metal-to-metal conductive path.

When someone talks about insulating inside the tunnel, I get a mental picture of them wearing their raincoat inside their clothes.

That's comfort insulation. Engine fire is a different subject. Assume a fuel or oil fed fire. If you insulate the inside of the tunnel floor without external surface shielding, I can pretty much guarantee you'll melt through the belly skin immediately aft of the firewall. Simple enough; temperature rise of the aluminum skin is a function of energy-in less energy-out. Insulating inside the skin blocks the energy-out path.

I'm familiar with techniques for insulating the firewall, but how do you insulate the outer surface of the belly skin?

[DanH]

Originally Posted by mturnerb

I'm familiar with techniques for insulating the firewall, but how do you insulate the outer surface of the belly skin?

Posted multiple times. Search is your friend.

[Kyle Boatright]

Originally Posted by mturnerb

I'm familiar with techniques for insulating the firewall, but how do you insulate the outer surface of the belly skin?

Sheet of fiberfrax under a thin sheet of stainless.