Simple solution to hot tunnel
 

I have about 10 hours on my RV-10, and like a number of other builders, had an extremely hot tunnel. It was so hot that on my last flight a week ago, I couldn't even touch the side near my right leg after only about 10 minutes in the air. Since I have the fuel lines running through the tunnel, and my transponder's black box is located in it, I grounded the plane until I found a solution.

I came home and searched this website, and found that I wasn't alone. Two suggested solutions caught my eye: 1) replace the aluminum heater bypass valves that Vans provides with the stainless-steel valves made by Plane Innovations; and 2) add firewall insulation (or other thermal barrier) to keep engine heat and exhaust heat out of the tunnel area.

There seemed to be a lot of variations on the threads suggesting solution #2, and nothing seemed clear-cut or used by the majority. So I tried two heat barriers offered by a racing car supply company called "Heatshield Products" which is located here in San Diego. (I've used one of their products -- the "Lava Shield" -- to protect the fiberglass engine cowling from the exhaust pipes in my RV-6A, and that worked very well.) Their website is www.heatshieldproducts.com.

I ended ordering 12 square feet of "Lava Shield", and 12 square feet of "HP Sticky Shield", which are rated at 1200 F and 1100 F, continuous, respectively, and 2000 F intermittent for both products. (I probably only needed about 8 square feet.) The Lava Shield is cardboard-thin, easily cut with a scissors, and has a stick-on backing. The HP Sticky Shield is a little thicker (1/8 inch thick), but also is easily cut with scissors and has a stick-on backing. The stick-on backing makes installation easy.

I put the Lava Shield on the firewall side of the tunnel, and between the firewall and the new stainless-steel heater bypass valves. I also placed it on the floor of the tunnel. I placed the HP Sticky Shield on the cabin-side of the firewall, covering the bottom half inside the cabin. While I was at it, I put Lava Shield on the inside of the fiberglass engine cowling, where the exhaust pipes came close. It took me about a day to do all of this, since the plane is built, and it's a bit tough fitting my hands through all that engine stuff to replace valves and insert heat shield.

Well, I just flew her about two hours ago. It was a sunny, warm (80 F) day, and I climbed to 6000 ft to see what would happen. Eureka! The tunnel stayed cool to the touch, even when engine cylinder temps briefly touched 400 F.

So, my friends and fellow RV-10 drivers, I wish to report a successful fix to that tunnel problem, that can be retrofitted to your plane with just a day's work.

Jerry

Hot tunnel
 

Hi
Thinks how many times you will be using the heater in the plane,I disconnect the scats from the firewall valves ,I do have the Ss ones,redirect the hoses to the bottom .
Never a problem again
If I will decide to go north in winter ,it's 5 minutes to reconnect
Good luck
Hugo

Jerry,
Thanks for the wright up, I will defiantly look into doing this and thanks for posting the link.
Tim

It would be interesting yo see how these products hold up to Dan Horton's fire breathing dragon test rig.

Just a thought - do you risk getting firewall forward fumes or CO into the cockpit? Don't know how good the seal is on the heater box, even the after market ones.......

A little square of UL181 foil tape should cover those two holes nicely along with a CO detector.

I used 1/8" fiberfrax with good results too. I leave both of mine connected with no overheating. Probably could get by with one connected to a wye fwf. Being at 38 Deg latitude and enjoying flying high on most xc flights, we usually use heat on most flights. Good to assist defrosting on those cooler humid mornings.

My solution was a little different
 

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.

We have used, and have sold, Heatshield Products for several years with good results. They make good stuff at a very reasonable price. I particularly like their HeatShield Mat.

It works well on the engine side of the firewall and also works well to reflect exhaust heat away from the cowling. Easy to cut and install too. A bead of high temp silicone or ProSeal will make a very tidy installation on the cowling too.

For Mike Starkey, no, this stuff will not hold up to Dan Horton's fire breathing dragon set up. It isn't intended to be fireproof. It's intended to insulate and reflect heat.

I use this on the engine side of my firewall(s) but would have no qualms about putting it in the tunnel of an RV-10, although there are undoubtedly many ways to insulate that area.

I am building an RV-6 currently and the firewall will get the usual layer of HeatShield mat to help keep the heat out of the cockpit. The floorboards will also get some insulation, but i haven't made up my mind which product will go there yet.

Heat, sound, paint, and trim products

Jerry,
I have a similar set up in my 10 and absolutely no tunnel heat issues.
I fly in shorts most of summer as does my wife and passengers and most everyone comes in contact with the side walls of the tunnel and it is just a little warm.
Like you, I have used the aftermarket stainless steel heater valves and sandwiched fiberfrax insulation between the heater box and the fire wall, then sealed with Pro Seal.
On the inside is a piece of fire wall heat shield against the firewall as well as on the floor. I do have a double floor in the tunnel to accommodate the insulation.

I do have a reverse 1" NACA that I was going to install if needed but it is definitely not needed.
Seems that the hot tunnel issue has pretty much disappeared and I am not sure exactly what has changed since the early models had tunnel heat problems.

My installation was not designed to be fire proof just insulation against excessive heat.

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.