What's the current situation with tunnel heat?

[kirkbauer]

I have done exhaustive searching here on VAF about the RV-10 tunnel heat issue, but it is difficult to figure out how it will (or won't) affect my new RV-10 that I'm building. This is because a lot of the information is fairly old and it's difficult to determine what has changed.

Here is a summary:

• Per the plans, there is no insulation on the firewall. I have seen people insulate the firewall which should obviously keep some heat out of the tunnel. I plan to insulate the hot side of my firewall.
• It also seems that heat can enter from the bottom since the exhaust is directly under the tunnel. But it also seems that Van's modified the exhaust kit at some point that might mitigate this issue.
• I have also seen people put a stainless steel plate on the outside of the airplane to protect the fuselage from the exhaust heat. How necessary is this?

Here are my plans:

• As I said above, insulate the hot side of the firewall
• To protect against exhaust heat, insulate the floor of the forward tunnel
• Since it will be a trivial additional effort, insulate the forward wall of the tunnel (the cold side of the firewall)

The last step is probably unnecessary with insulation on the hot side of the firewall, but again, if I'm going to insulate the floor I might as well add a little extra on the firewall.

If I'm going to insulate the inside of my tunnel, I think the following are important criteria:

• Must provide effective heat insulation
• Must not be flammable or generate smoke
• Must not harm the aluminum (e.g. attracting moisture)
• Bonus: fire resistance (as an extra layer of protection, since the fuel lines are in there)

I am considering a few options (the blue text are links to the items I'm considering):

• A lot of products out there provide protection from radiant heat, but I don't think that will be helpful inside the tunnel. I think I need insulation.
• Heatshield Armor: I saw some other people used Lava Shield, which again is for radiant heat. But the same company makes this product that I think might be useful for insulation
• SealTech: It looks like it provides insulation and doesn't attract moisture
• Silicone Sponge: Or a similar type of product

 

[rocketman1988]

I have done exhaustive searching here on VAF about the RV-10 tunnel heat issue, but it is difficult to figure out how it will (or won't) affect my new RV-10 that I'm building. This is because a lot of the information is fairly old and it's difficult to determine what has changed.

Here is a summary:

• Per the plans, there is no insulation on the firewall. I have seen people insulate the firewall which should obviously keep some heat out of the tunnel. I plan to insulate the hot side of my firewall.
• It also seems that heat can enter from the bottom since the exhaust is directly under the tunnel. But it also seems that Van's modified the exhaust kit at some point that might mitigate this issue.
• I have also seen people put a stainless steel plate on the outside of the airplane to protect the fuselage from the exhaust heat. How necessary is this?

Here are my plans:

• As I said above, insulate the hot side of the firewall
• To protect against exhaust heat, insulate the floor of the forward tunnel
• Since it will be a trivial additional effort, insulate the forward wall of the tunnel (the cold side of the firewall)

The last step is probably unnecessary with insulation on the hot side of the firewall, but again, if I'm going to insulate the floor I might as well add a little extra on the firewall.

If I'm going to insulate the inside of my tunnel, I think the following are important criteria:

• Must provide effective heat insulation
• Must not be flammable or generate smoke
• Must not harm the aluminum (e.g. attracting moisture)
• Bonus: fire resistance (as an extra layer of protection, since the fuel lines are in there)

I am considering a few options (the blue text are links to the items I'm considering):

• A lot of products out there provide protection from radiant heat, but I don't think that will be helpful inside the tunnel. I think I need insulation.
• Heatshield Armor: I saw some other people used Lava Shield, which again is for radiant heat. But the same company makes this product that I think might be useful for insulation
• SealTech: It looks like it provides insulation and doesn't attract moisture
• Silicone Sponge: Or a similar type of product

Don’t insulate the cabin side of the firewall; there are numerous threads on this. It can be a huge safety risk. See DanH’s testing on this.

I have a Barrett IO540 with CAI and a Custom AircraftExhaust system. I have had ZERO hot tunnel issues. It never even gets warm. No insulation on the firewall at all.

 

[Carl Froehlich]

My thoughts:
- Insulate the engine side of the firewall using the Dan Horton method FireFrax and SS clad. Do this and skip insulating the cabin side of the firewall.
- You left out what I consider the major tunnel heat source, the cabin heat control valves. These valves get blasted with heat muff air when the valves are shut. The heat then conducts to the firewall and the tunnel. For this I place a piece of KoolMat between the firewall and the valves. I then extend the KoolMat over the top of the valve and down such that the not used hot heat muff air gets directed down toward the cowl exhaust - not just bounce back at the engine driven fuel pump.
- I do not consider the exhaust to be a major source of heat in the tunnel if using the standard exhaust setups.
- Skip insulating the inside of the tunnel. No need and it can absorb gas when you pull the fuel filter for inspection.
- The SS plate on the bottom of the fuselage is for fire protection.
Carl

 

[Richard Connell]

Don’t insulate the cabin side of the firewall; there are numerous threads on this. It can be a huge safety risk. See DanH’s testing on this.

I have a Barrett IO540 with CAI and a Custom AircraftExhaust system. I have had ZERO hot tunnel issues. It never even gets warm. No insulation on the firewall at all.

Same here

 

[Jesse23]

Don’t insulate the cabin side of the firewall; there are numerous threads on this. It can be a huge safety risk. See DanH’s testing on this.

I have a Barrett IO540 with CAI and a Custom AircraftExhaust system. I have had ZERO hot tunnel issues. It never even gets warm. No insulation on the firewall at all.

2020 RV 10 - no insulation anywhere, no special SS panels, no heat issues and I fly in FL. Stock tunnel setup. Except Aerosport tunnel diverter (worth every penny) to flow around fuel valve. (See pic)

 

[Kyle Boatright]

I bought two 2x2 thin sheets of stainless. One was installed on the bottom 2' of the the firewall, the other was installed on the fuse bottom, as far forward as possible. I put fiberfrax under both and secured them with stainless pop rivets. The bottom one was sealed with proseal to keep moisture and oil out, while remaining paintable. The one on the firewall was sealed with stainless tape. I placed insulation between the stainless heater valves and the firewall. With all that, after flying for a while, the tunnel is probably 20F above cabin temp when in flight and the heaters off. You could install a bigger firewall shield or a bigger belly shield, but the two 2x2's seem to work fine.

If you're worried about heat inside the tunnel, why not cut a couple of openings in it to vent it? Maybe some wire mesh over a couple of 2" openings at the bottom of the tunnel near the firewall and another one or two on the top of the tunnel, under the panel.

 

[kirkbauer]

Carl, thank you as always for all of your help. And it is good to hear that others aren't having issues with heat.

I did have one question, you said:

For this I place a piece of KoolMat between the firewall and the valves. I then extend the KoolMat over the top of the valve and down such that the not used hot heat muff air gets directed down toward the cowl exhaust - not just bounce back at the engine driven fuel pump.

Do you have a picture of this anywhere by chance? It sounds like a great solution. I'm actually about to mount these valves right now -- on the final page of Section 27 (Firewall).

I just tried to find some pictures and that's also when I found out there are multiple options for stainless-steel replacements. I have already ordered this one from Aircraft Spruce -- do I need to reconsider?

Heater Bypass Valve For RV-10 | Aircraft Spruce

Heater Bypass Valve For RV-10 The all stainless steel heater bypass box was conceived while looking at aluminum hardware used for sealing the firewall on experimental aircraft. It didn't make much sense to try to seal a stainless steel fire

www.aircraftspruce.com

 

[Carl Froehlich]

Carl, thank you as always for all of your help. And it is good to hear that others aren't having issues with heat.

I did have one question, you said:



Do you have a picture of this anywhere by chance? It sounds like a great solution. I'm actually about to mount these valves right now -- on the final page of Section 27 (Firewall).

I just tried to find some pictures and that's also when I found out there are multiple options for stainless-steel replacements. I have already ordered this one from Aircraft Spruce -- do I need to reconsider?

Heater Bypass Valve For RV-10 | Aircraft Spruce

Heater Bypass Valve For RV-10 The all stainless steel heater bypass box was conceived while looking at aluminum hardware used for sealing the firewall on experimental aircraft. It didn't make much sense to try to seal a stainless steel fire

www.aircraftspruce.com

Those valves will work fine.

I’m now working the firewall. I’ll have photos of the KoolMat install in a week or so.

Carl