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Hot air control box-firewall insulation

D

Dorfie

Well Known Member
I have read that some heat insulating materials are used between hot air control boxes and the firewall to reduce heat conduction and thus reduce the hot tunnel issues.
I am interested to know which materials have been used. Specifically interested in the temp the material must withstand.
I think that the red silicone baffle seal material has been used, but max temp seems to be 425F. http://www.aircraftspruce.com/catalog/appages/siliconecowlseals.php?clickkey=65885
Is this OK? I don't know how hot it gets there, but would think hotter than 425F.
Thank.
Johan
 
Use google search "site:vansairforce.com DanH +firewall "

Dan had some very well researched and tested work on materials, coverings for firewalls.

Be cool!:D
 
I used black baffle material between the stainless valves and firewall, with reflecting insulation on the firewall extending beyond the tunnel. Insulation in the tunnel.

I have two "loose"thermocouples, one FWF and one in the cabin. Both readout on the Skyview EMS. Before the insulation my tunnel temp ran at 180 degree F and over 200 with the rear heat on full blast. (The SCAT tube is must run around 220 when the heat is on) I turned the heat off before it got to the top, my ADSB receiver and transponder are in the tunnel. Afterwards it is still too high, 100 -120, but much better.

With the FWF thermocouple placed between the two air valves it was consistently between 220 and 240. I can see why we have an issue with only thin stainless between there and the tunnel.

I have an idea to build a aluminum "box" that would cover over the tunnel area and provide it with reflective insulation on the outside and some cool plenum air flow on the inside to keep the heat away. If done properly, it would also help smooth out the cowl exit airflow. With all the motor mount tubing and the gear leg and shock absorbers, the airflow must be a mess. When I was Crew Chief for Reno air racer "Bad Intentions" we did a lot of sheet metal under the motor to help get hot air out.
 
rleffler said:
If you purchase the stainless steel heater boxes from (http://www.planeinnovations.com/heater-bypass-valves/product/41-heater-bypass-valves-hbv-03.html), they ship a tube of biotherm that functions as an insulator.
Click to expand...

Bob,
I've got the stainless valves as well as the tube of biotherm. My sense is that the biotherm will simply be squeezed out when the valves are bolted on, and there will still be metal to metal contact.

I think there is still the need for a layer of some sort of non or poor heat conducting material between the valves and firewall.

Has anyone come up with a bypass valve higher up in the scat between the exhaust shroud and heater valves? That seems like it will keep the high exhaust heat away from the valves. One will then engage this bypass only when cabin heat is called for.

Anyone thinks this stuff might work?
http://www.mcmaster.com/#thermal-insulation/=rt93b7 Product number 93315K51
It compresses a lot, was thinking of folding it a few times. I have this available, planning to use for insulation purposes, covered with foil. Someone before me posted about this as a way to insulate the tunnel, but cannot find that post now.

Thanks.

Johan
 
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Same here

Fiberfrax sandwiched between firewall and heat box
And firewall sealant to close the edge.
Not to drag the thread into a tunnel heat issue but along with several other insulating techniques I believe the insulation between heat box and firewall
Is making the most effective contribution to a cool tunnel.
FWIW my tunnel temps have never been an issue, hand warm at most.
 
http://www.aircraftspruce.com/catalog/appages/brown95182_36.php?clickkey=5747 We used this with fiberglass reinforced. I agree with above comments in that it needs insulation separation to prevent heat transfer into the firewall and on to tunnel. We also over sized the four bolt holes in this material to insert spacers to prevent the valves from distorting when torquing bolts. The spacers need to be slightly thinner than material to allow crush on material. We then sealed the perimeter of the valves/ material with Dow sealant. I have material left over I can send you so you don't have to purchase minimum from ACS.
 
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Jackm said:
http://www.aircraftspruce.com/catalog/appages/brown95182_36.php?clickkey=5747 We used this with fiberglass reinforced. I agree with above comments in that it needs insulation separation to prevent heat transfer into the firewall and on to tunnel. We also over sized the four bolt holes in this material to insert spacers to prevent the valves from distorting when torquing bolts. The spacers need to be slightly thinner than material to allow crush on material. We then sealed the perimeter of the valves/ material with Dow sealant. I have material left over I can send you so you don't have to purchase minimum from ACS.
Click to expand...

Jack,
That will be great. Min purchase is quite expensive! It has a good temp tolerance of 550F. Is it also a poor conductor of temperature? (which I think is the main objective, and I do not know how to verify that)
Sent PM.
Thanks.
Johan
 
Here is a link to DanH's succinct summary for engine or cabin side insulation. He tested the insulation and sealants and has solid testing foundation behind this short post.

http://www.vansairforce.com/community/showpost.php?p=477570&postcount=27

To avoid using the link here is what DanH Says - - -

"For the cabin side, ceramic wool batting sealed in folded seam aluminum foil envelopes, with a mechanical attachment method. No glue please. Stainless foil is not necessary on the cabin side. All you need is HD Reynolds Wrap from the grocery store.

For the engine side, ordinary Fiberfrax felt (available Wicks, Spruce, etc) under stainless steel foil, attached with SS pop rivets and sealed around the perimeter with 3M Firebarrier 2000. Common 24" wide SS foil is fine, actually preferred. Overlap a mid-panel seam about 2 inches and cover it with one strip of aluminum foil sticky tape. In a fire the aluminum tape will melt away instantly and provide a directed escape path for the outgassing binder in the Fiberfrax.

The engine-side approach is much superior, but both are free of cabin smoke and insulate well enough to buy a lot of time without burns.

I'm not aware of any safe sound insulator for a firewall. The fire performance of some has been horrifying.

All firewall penetrations should be steel or insulated/protected.

Everyone is welcome to an opinion, but please, first read and understand the standards, then do some actual test work."
 
Johan.

Tunnel is cool on ours. I felt if we exceed 550deg at that location, we have big problems. I used fiberfrax on inside of firewall but my concern FFW was the fiberfrax would absorb liquids unless completely sealed. I am happy with our results and its is certified looking install.
Send me your address....will sent out no charge.
 
PM sent

Jackm said:
Johan.

Tunnel is cool on ours. I felt if we exceed 550deg at that location, we have big problems. I used fiberfrax on inside of firewall but my concern FFW was the fiberfrax would absorb liquids unless completely sealed. I am happy with our results and its is certified looking install.
Send me your address....will sent out no charge.
Click to expand...

Jack,
I sent you a PM with my info. Let me know if you did not get it.
Kind offer. Much appreciated.
Thanks.
Johan
 
We carry a few useful products to insulate the engine side of the firewall.

Heat and sound

The items we sell are not intended to be fireproof and they likely won't pass Dan Horton's fire breathing dragon testing. However, if applied to a fireproof stainless steel firewall properly, they will provide a bit of insulation to help keep your feet cool, or to prevent exhaust heat from scorching your paint.

Let me say this a different way so no one is confused: the stuff we carry is useful if there it radiant heat making your feet (and other body parts) hot. It is NOT intended to replace the firewall or any of the standard fire resistant, good building practices.

It is easy to install while building, but can be added to a flying plane also.

It is also very useful for reflecting exhaust heat away from your cowling (and expensive paint job).

YMMV. We have used this stuff on several airframes and like it for it's low cost, ease of use, light weight, and durability. And it does what we are asking it to do... reduce radiant heat.
 
I placed a layer of fiberfax across the whole front of the fwf and then a layer of stainless sheet on top of that and sandwiched everything together. I did cut out more material where the motor mount bolts on so as there would be no issue. By doing that it had metal to metal contact for bolting up the motor mount. Turned out really good and looks great.
 
Stamper,

I know it's been a while since this post. I'm at the point in the build where I'm going to insulate the firewall. Do you have any pics of your installation? I'm debating whether to mount the stainless heat selector boxes on silicone baffle layer and fiberfrax/ SS foil around it or just put the boxes over the fiberfrax/ SS Foil. Also wondering how you dealt with the inset in the middle of the firewall.

Thanks!
 
Hi Eric,

I installed the firewall doubler on my RV-10 using .016 stainless sheet and Fiberfrax.
Making the stainless box around the control cables was not difficult but stainless does not bend as easy as the materials we are used to working with.

The stainless/Fiberfrax sandwich used on the firewall and the tunnel ,along with the stainless heater boxes has resulted a very cool to touch tunnel and very little radiated heat at my feet.

My aircraft has a very effective A/C unit installed from Airflow-Systems and the low cabin heat from the firewall area was one of my goals.

I am very happy with how it looks and performs .

https://photos.google.com/share/AF1...?key=bUo4WlQxc2x2d0w5RWRUSjJuRzJyTlp0UUxFVnN3
 
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Don't forget the heat muff dump air

Firewall insulation is well worth the effort. I have it just on cabin side of the firewall as well as under the cabin floors and have had no heat problems.

I note that this thread has not addressed the issue of what happens when the cabin heat boxes are shut. You have very nicely heated air coming into the box and then redirected right back at the engine - in the vicinity of the fuel pump. So on a hot day we are adding heat right where we don't want it.

I added a flap of Koolmat http://www.aircraftspruce.com/catalog/appages/koolmat.php?clickkey=31128
to help redirect this dump air away from the engine. It is mounted under the cabin heat boxes (between the firewall and the boxes, holes cut out for the boxes) and extends up and over the front of the boxes such that dump air hits it and is deflected down toward the cowl exhaust.

I also added an aluminum disc with a 3/4" hole to the heat muff SCAT hose coming off the engine to reduce the total air going to the heat muff. Even so, on the coldest day I have just one of the cabin heat boxes cracked open. My thought here is there is no need to rob the engine of cooling air if it is never used.

Carl
 
heat boxes- firewall protection.

I think everyone has great suggestions. i was part of the development of the plane innovations heat boxes, we designed the flap to keep the heat out, and it does it well, I dont have any tunnel issues, our tunnel heat is cabin temp. To Carls point there is nothing going through those boxes and its all going out the exhaust area, with very hot temps in between. I have probably the least expensive option out there and it has worked great without any blistering or other issues in 4 years. I used the boxes with the included sealant and there is nothing coming through that area, if you wanted more go to HD or Lowes and get the 3m fire sealant they sell for far less than any aircraft certified place. All my firewall area was sprayed with a ceramic material. if i was (and I did) to put my hand on the inside of the firewall, its warm maybe a little hot but never uncomfortable The weight is a few pounds, like 2-3 maybe as its really light material and completely fireproof. I did this as having a mat would make for some difficulties with all the items attached and I didnt want to have to work around (by cutting) those areas. I use the 3M for all openings to avoid any fire related issues ever getting back to the cabin, or best I can anyway.
I wouldnt get to worked up on the boxes, but if you do want something in the "metal to metal" I would do the 3m sealant or even the red RTV that can withstand 600F.

Pascal
 
ReidVaitor said:
...if you wanted more go to HD or Lowes and get the 3m fire sealant they sell for far less than any aircraft certified place.
Click to expand...

Lowes and Home Depot don't sell a suitable high temperature sealant.
 
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FLIR Testing

In-flight testing with my insulated firewall,showed that the hottest spots on the firewall are now the engine frame mounting bolts.
There is still an elevated temp area around the closed heat boxes so a diverted valve up stream of the heat boxes would help.

With two summers of North Australian flying,the cabin temps have been very comfy with the A/C consistently being able to have a 10 deg C drop at the vents over outside ambient temps. ( Happy wife = Happy life )

https://goo.gl/photos/Lo9W1kiobwgEUCr5A
 
Dustyone said:
In-flight testing with my insulated firewall,showed that the hottest spots on the firewall are now the engine frame mounting bolts.
There is still an elevated temp area around the closed heat boxes so a diverted valve up stream of the heat boxes would help.
Click to expand...

Love those FLIR photos. What thickness is the fiberfrax layer?
 
Hi Dan,

I used 1/8" Fiberfrax and Type 301 1/42b .016" Stainless Sheet. Thinner sheet would of been better,but it was all that was readily available to me at the time.

3M Fire Barrier 2000 was used to fill in any gaps.

Very happy with the smooth and maintenance free finish on the inside and out of the firewall.

I was inspired while I was building by Deems Davis (RV-10 ) and your though testing on your burn rig.

The FLIR camera is an attachment to the iphone from,
http://www.flir.com.hk/flirone/content/?id=62910

Very useful for finding failed insulation points and confirming where the heat flows around an aircraft.

Thank you to all that post their collective knowledge on this site to pass on to the next builder.

I'll be visiting Oshkosh for the first time this year and hope to meet many of you that are on these forums.


Cheers,
 
Dustyone said:
Hi Dan,

I used 1/8" Fiberfrax and Type 301 1/42b .016" Stainless Sheet. Thinner sheet would of been better,but it was all that was readily available to me at the time.

3M Fire Barrier 2000 was used to fill in any gaps.
Click to expand...

Question - What are the fittings you used for the control cables?
 
Ashley,

I'm very happy you bought that FLIR/ iPhone Camera! I have a ~$5 part in that thing! I would recommend that everyone buy one :)

It is a very cool toy!
 
Eyeball Firewall fittings

Hi Justin,

The Eyeball fittings are available from Aircraft Spruce.

http://www.aircraftspruce.com/catalog/appages/eyeballfw1.php?clickkey=3026635

They are well made and all stainless steel.They fitted my cables well,I can not remember the exact size,but just measure your cable diameter and order same. I wish my cables worked as well as the eyeball fittings,at just over 270 hrs (2yrs in July ) I am starting to get binding in my mixture cable. I insulated my cables as best that I could hoping to get a longer life from them but as others have reported a better quality cable with higher temp rating is required.

Eric,
The FLIRONE has been my favourite toy to buy this year! So many uses and ways to waste lots of time :)

Cheers
 
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