Yep, tunnel finally fixed. Should be an AD.

[VHMUM]

Ok the problem is fixed but I do not want to put whatever external on the belly (I understand flying 10s need something now) so keep thinking guys and see if we can do something else there.

Aparently Vic Syracuse has also fixed the problem so am desperately trying to find out what he has done...will post.

Chris

[osxuser]

Is it possible to exhange a section of the bottom skin with a stainless one built right into the airframe, then put insulation on the INSIDE and a false floor in the tunnel, also consider turning the exhaust tips down, it might help a little.

[Mike S]

I doubt that replacing a part of the skin would work, even if it was something that could be accomplished without a huge ammoount of work.

Stainless will conduct the heat into the passanger compt almost as well as aluminium-------think about cook ware-------------

The SS heat shield works beacuse of the air space between it and the fuse, and the air flow through that space.

Mike

[rv6ejguy]

Thanks Glen for finding the root cause of the heat , trying the Vans fix (unsuccessfully) and coming up with a flight proven fix.

For those non- 10 builders, the 10 uses a tall, structural tunnel running down the center of the forward fuselage to carry loads in lieu of upper longerons as on most other RVs. This is required because of the cutouts for the gullwing doors. Please don't punch this tunnel full of big holes! Not only might this compromise the integrity of the structure, it would only pass more heat into the cabin.

This tunnel contains almost the entire fuel system, brake lines, front and rear heater ducts, control rods etc. The fuel system is not easily moved to another location. Vapor lock and the potential for burns to the occupants have been documented on this forum by several RV10 fliers.

For those building 10s, serious consideration might be given to installing the fuel system components off the belly floor, a second false floor and insulation between them. Clearly, if you don't, you'll be forced to use a method similar to Glen's on the outside of the belly skin. Maybe not pretty, but proven functional and better than a dead stick landing.

Stainless has a fraction of the heat conduction of aluminum so this might help somewhat but think insulation as well.

Anyone else flying a solution, I want to hear about it.

[gmcjetpilot]

I agree moving fuel lines is not practical. Here is the LS from vans.

http://www.myrv10.com/Plans/updates/...unnel_temp.pdf

Here is one RV-10 builders compiled solutions on Van's site:

http://www.myrv10.com/tips/mods/HotTunnel/index.html

Apparently the brand of exhaust may have some effect (theory)? Also leaking cabin heat valves may add to the heat. If you have it insulated and cool air blowing in the insulated tunnel area I don't understand how that would not lower temp. Repeat I don't understand and make no claim to solve it, but apparently it happens and is difficult to remedy for some. Others don't have as much of an issue? The ideas above seem reasonable in addition to Glens suggestion.

[brenthg]

Here are several photos we took of our modification to N331JH. Take note that the silver mylar insulation taped to the bottom of the fuselage is temporary and it proved our point that the exhaust running down along the centerline was the biggest heating problem in the tunnel. This is the same insulation used on the firewall, too. Glen Thompson's idea to rivet a SS sheet over this insulation is a lot easier fix for the already built -10's, and I'm sure new builders and maybe even Vans will come up with several other solutions, too.

BOTTOM OF COWL

BOTTOM OF FUSELAGE

SIDE VIEW OF COWL VENTS

[rv6ejguy]

Holy cow! Thems is louvers! Looks good though.

[glenmthompson]

Yep, since I am "stuck" down here in Rio till tomorrow AM when we will depart for MIA, then to OSH, I sure am glad Brent got those pics posted that Jim took. One can see the side gills I wrote about a while back, those are painted and faired in, as they were installed before I painted the plane for Jim.
Those "silver" somewhat larger gills on the bottom of the cowl, Jim made and I installed last week temporarily with the observerd pull rivits. One should note the uneven spacing on the rivits. There was alot of 3D going on there and I wanted the edges to be somewhat "down". BTW, Jim says he can make these gills on his CNC machine pretty easy and with any dimensions to suit your particular wants, needs, desires and necessities!
Write him @ JIMRHG@adelphia.net.

Note the following please for those who have been unable/unwilling to thoroughly follow my tunnel threads before making condescending comments ( U know who U are):
########## The side gills made a SLIGHT", barely noticable difference in tunnel temps. In fact makes the fuselage side VERY hot.
######### Blowing one 2" scat tube of fresh air (Per Vans SB bandade) into the tunnel, cooled the tunnel sufficiently to touch the front, but still scald the paxs in the back.
#########Blowing 2 scat tubes (read NO CABIN HEAT NOW) cooled the front significantly, and made the back tunnel able to touch, but still VERY WARM.
Please note after this point, we have only ONE fresh air tube blowing into the tunnel!!!!!

######### The addition of the "silver" bottom gills, cooled the front tunnel significantly!...analysis......Tons of heat from engine cooling air and muffler heat leaves these gills and puts that heat out of the aft chin area and more to the sides, where we have an insulated cabin floor. As in, not below the stove, er, sorry, I mean tunnel.
######### Gills that then were added to the bottom skin in the aft tunnel area I think actually made the aft tunnel HOTTER, with the obvious entry of exhaust gasses at slower speeds.
######## NOW THE CREM DE LA CREM! We addded the above observed "insulation" to the belly, and the tunnel problem has been fixed!
We will be taking out all together, the fresh air blowing into the tunnel (remember the Vans bandade?) after OSH. Nope, tell ya what, we are gonna cover the hole before we leave for OSH tomorrow. Guaranteed not necessary now.


,
Now, to further explain my theories/observations...Listen guys, YOU MUST KEEP THE HEAT ON THE OUTSIDE OF THE PLANE!!!!! Don't like my SS suggestion? Cool, any ideas to "insulate" the bottom skin, as in, YOU MUST KEEP THE BOTTOM SKIN, AS IN THE BOTTOM SKIN, THE ONE THAT THE FUEL PUMP IS MOUNTED ON, COOL TO THE TOUCH. Sorry, but I guarantee you, if you have a hot bottom skin, you will have an RV "stove"
INSULATION INSIDE THE TUNNEL DOES NOT WORK! As in, install a " blanket" as we did last yaer, well before Vans suggested (per SB worthless bandade). Nope, nuh uh, does...not....work.....Any suggestions to such in any way, is a complete waste of time and weight. Insulate via a false floor? I think would work in an unfinished plane, but still will cause a scalding aft tunnel area problem, ...hence...My SS barrier/heat insulated heat shield recommendation.
Some kind of exterior barrier is required. period. Now, lets see some real ingenuity here! Put those RV minds to work!!!!!!!!
Glen

[brenthg]

Hey Glen,

Like I've been saying all along, it's always been the exhaust gas that's heated the tunnel, and maybe some additional heat from the firewall created by super-heated air in the cowl.

I believe you have the best possible re-engineered idea for the RV-10. Keep the heat out of the inside of the fuselage by fitting a heat shield to the bottom of the fuselage from the firewall to just aft of the passenger floorboards. Yeah, all you high powered aeronautical engineering types out there may have other ideas, but this is simple, common sense fly-by-the-seat-of-your-pants engineering that works. You can make it as complicated as you want, but simple works, too.

That's what NASA came up with to keep the Shuttle cool during re-entry. Makes sense, huh?

Brent - Son of N331JH

[rv6ejguy]

We use stainless heat shields extensively in our turbo RV6A including on the belly skin aft of the exhaust pipe which only diverges from the skin by about 5 degrees. The skin does not get hot at all.

I've videotaped tufts all over our 6A in flight. The flow is highly turbulent behind the bottom cowl exit. I'm pretty certain an external heat shield would not cost any knots aft of this location. Easy to clean the belly too!