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Will insulating the FF make the cockpit warmer or cooler?

ao.frog

Well Known Member
Hi.

I'm looking for a way to make the cockpit warmer and considering to insulate the FF, but came to wonder if that might have the opposite effect? Maybe the FF is getting warm during flight and by insulating it, I'll get a cooler cockpit?

For the record: I've installed ailreon boots, taped shut all those little holes in the cockpit, have a kind of "seal" along the canopy-rail etc etc, but still the cockpit is rather cold when the OAT drops below -10*C.

I'll also install some insulation on the fuse-sides where I can. I have CAD interior so it schould be room enough for that a number of places.

But for now; will insulating the FF give a warmer or cooler cockpit? My gut feeling tells me that the FF gets warm during flight?

Ofcourse I could find a way to crawl or bend over and feel the FF during flight, but why go through that troublesome exercise when a quick post to the great VAF-forum does the same job? :D
 
....will insulating the FF give a warmer or cooler cockpit? My gut feeling tells me that the FF gets warm during flight?

The firewall gets warm in flight. If it is warmer than the existing in-cockpit temperature, insulating it will make the cockpit cooler.
 
Yeah, that's a problem

... but still the cockpit is rather cold when the OAT drops below -10*C.
Those pesky laws of physics do get in the way - again :rolleyes:
Insulation slows the rate at which heat transfers, but unless you can add more heat than your aluminum heat sink (the whole plane :eek:) draws it away, it's a losing battle. My son added a second heater muff to get more heat into his cabin. Every little bit helps.
As Dan noted, more than likely the firewall will be warmer so insulation there will slow that heat getting into the cabin.
One convenience of my liquid cooled engine is the heater core in the cabin that keeps things comfortable even at -10C :cool:
 
Flip side is the benefit of the insulation. It will reduce noise in the cockpit and will make the cockpit cooler in the summer.
 
In Norway...

... it's very rare that the cockpit is too hot during summer. Setting the cabin heat to off and opening the fresh air-vents partially makes the cockpit nice and cool for about 95% of the normal summer-weather.

Noise is not a factor either, because both my wife and me have Halo headsets and LOVE them. We also have exhaust-turndowns installed to reduce drumming, and finally the 2-blade M/T-prop is rather quitet compared to other props at our homefield.

By the way; I also have a feeling that the dual P-mags makes the engine more quiet, since they fire twice as often as regular mags, thus making noise more "even" (not pulsating)
The X-over Vetterman exhaust-system has a great influence also I think.

Ofcourse, I'm just guessing here, but people on the ground says our RV is more quiet than most other planes. They say the sound is deeper in a way....
When I flew the test for the "Noise Certificate" (required in Norway), the reading said 69 db. (measured at 1000' at max cruise power) and that's pretty good I think.

But thanks for the note; it's always a good thing to consider all aspects of a modification.
 
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Side wall insulation

Alf,

If you haven't already put insulation on the side walls, it definitely helps. I used 1/4" aircraft grade (fire retardant) insulation/sound deadener and then covered it with cloth (also a/c grade). Cut one inch strips of posterboard and make templates of each panel with a hot glue gun, then cut the foam and cover. They will fit perfectly and help with the cold cockpit. I also changed from an internally controlled cabin heat box to the firewall-side controlled box and ran a scat tube to the eyeball vent mounted on the bottom of the instrument panel. It brings much warmer air right to you.

Hope this helps. It was -27 F in Durango, CO last week!

Jim
 
Alf,

I don't have any insulation on the inside of the firewall, just some sound deadening paint. I also have a heater system that shares the ducting with fresh air, via a mix valve on the hot side of the firewall, and that air (hot or cold or in between) comes via scat tubes to the Stein vents under the corners of the panel.

So all the warm air comes at the occupants from those vents...end result is that hands and upper body are pretty comfy, but toes and feet sometimes get chilly, with no heat down there from a standard heat box. It was that way at -5C here in Reno today on a quick hop.

From all the above, I'm thinking that perhaps not enough heat builds up in the firewall (in the winter) to effectively radiate much heat into the cockpit, but I haven't placed insulation there to try to measure if there is a difference. Summer may be a different story, when we battle heat soaking of everything, inside and out. FW insulation may prove more effective then, but Dan has a great thread on heat and fire protective insulation on the hot side of the firewall. (And it sounds like summer heat is not a factor for you there).

I did install DIY side panels, and I think that makes a difference in cold transfer into the cockpit.

All this is very unscientific opinion only, of course. Good luck, and if you find a solution that works in Norge, let us know, so us Vikings on this side of the globe can copy!! :)

Cheers,
Bob
 
How about using a cheap indoor-outdoor thermometer with a wired sensor taped to your firewall? They are available here for about US$10, and will record max-min temps. Seems easier than trying to point an IR thermometer at the correct spot on your firewall while flying.

Jim Berry
RV-10
 
Sound Insulation

What about sound insulation, is it worth making up something to attach to the cabin side of the firewall, keeping in mind the requirement for fire retardant and fume properties.
 
Just a little information

This is probably not very helpful but here it is anyway. We have an RV-6A.

There are effectively two bulkheads between the engine and the cockpit of our airplane:

- One is formed by baffling extending from the upper cowl in a vertical plane at the rear of the engine, then curving back to the bottom of the firewall, with vertical wedge baffles coming in from the sides of the lower cowl to the curved portion of the rear baffle at the width of the cooling air outlet and horizontal baffles just below the split line of the lower cowl completely isolating the cowl into three zones.

- The other is the firewall.​


Inlet air for cabin heat, when not blocked off for racing, passes through a ~2 inch port at the rear of the cooling air plenum (the top of the plenum is the inside of the upper cowl) down to a heat muff on the right exhaust pipe then back up to a control valve (box) mounted high on the firewall. When the cabin heat is off, the heated air is dumped through a duct (SCAT tubing) out a small vent under the fuselage directly above the engine cooling air outlet. When the cabin heat is on, the heated air comes through the other valve port into another duct inside the cockpit behind the instrument panel on the left side to a "Y" which divides the heated air into two more ducts. One goes down to the foot area of the passenger side and the other goes to another valve (box) on the pilot side behind the instrument panel. When the windshield defroster is off the heated air in this branch goes through a duct to foot area of the pilot side and when it is on the heated air is routed through a duct to the a 2 inch screened hole to the left side of the windshield.

Obviously we get no positive heat transfer directly through the firewall into the cockpit with this setup - it is all from the heat muff.

In the cockpit I have the inside of the firewall covered with aluminum foil backed thick black foam rubber glued with 3M upholstery adhesive (I think it is 377) to the firewall between all of the aluminum angle reinforcements. I used aluminum tape for closure between panels over the reinforcement angles.

On the cockpit floor I have a different type of foam rubber (equalling the height of the reinforcement angles) glued there with 3M upholstery adhesive. Over to top of this I have carpeting glued to the foam.

On the sidewalls of the cockpit and baggage area I have thin white foam rubber (~1/4 inch thick) and/or upholstery material glued directly to the sidewalls and all exposed structure except the upper longeron (where we enter and leave the cockpit) the baggage compartment bulkhead and baggage compartment floor.

On the baggage compartment floor I have carpet that is secured in the rear corners by the bulkhead screws and in the front by the flap actuator crossbar.

The purpose of all this upholstery is to look good, stay quiet and warm in that order. The surface temperature getting to 0 F here in northwest Arkansas is very rare but we do fly in the winter (with a coat) and we have yet to be cold once we close the canopy. I conclude from this that the upholstery/insulation is effective in helping to keep the cockpit warm but the contribution of the firewall insulation is unknown.

Bob Axsom
 
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insulation materials

....and as Bob notes, Dan has a lot of good info on insulation.
the usual caveat is that 'aircraft materials' can be misleading, meaning that they have a certain burn rate in the aft cabin of an airliner, and may not be suitable for firewalls!
My tests on the 3M #77 and similar solvent based spray adhesives are that they burn like crazy at low temps, and many of the common black foams start to melt, and give off toxic white smoke in a disturbing way.
Latex contact cement was far superior in every way I could find, except for not coming in a spray can!
 
I'm only aware of two guys with fully-ducted cooling air flows (Bob being one), and for them the air on the engine side of the firewall may be relatively cool.

For the rest of us, the air contacting the engine side of the firewall is within a range of 100F to 200F, the daily variable being ambient temperature.

The cooling calcs I've been using incorporate a heat transfer efficiency factor,......

efficiency = temperature rise / (CHT - ambient temperature)

......a measure of how much cylinder heat is transfered to the moving air. Your goal as a builder is to make this number as high as possible with good tight baffles. The evidence suggests a factor of 0.25 is average for the RV fleet.

This thread is about a 10C day, or 50F. I'll guess Alf's CHT at 300F in cruise, so.....

(300 - 50) x 0.25 = 62.5F rise

and

62.5 rise + 50 ambient = 112.5F at the firewall face.

Same cooling setup on a hot day climb might be:

[(400 - 100) x 0.25] + 100 = 175

Obviously these numbers are higher than cockpit temperature. Heat always flows from hot to cold. Insulation slows that flow.

BTW, I'll be instrumenting my own -8 at some point to confirm under-cowl pressures and temperatures. In the meantime, somebody point a non-contact IR thermometer at an uninsulated firewall and report. Don't forget to tape a target or you'll get some error trying to read shiny metal.

Whoops...just realized Alf said minus 10 (-10), or 14F. Doesn't change the basic facts, but it would push firewall-forward air temperature below 100F.
 
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It ...

...sure looks like the cockpit will be warmer by not insulating the FF.

By the way; the temp I was referring to was -10 (minus) * C, which equals around 14*F. Then the figures will be not quite so good, but warmer than the cockpit temp.

And when I climb alittle on a -10*C winterday to get favorable winds, the OAT at FL 100 can easily be -20*c (equals -4*F)

For example like it was in this situation:



OAT is -21*C as seen in the upper R/H corner.




Under those circumstances, it's important to dress well:




Thanks for all the inputs. I'll try a max/min termometer by the FF on the next flight.
And during annual in June, I'll install insulation along the FWD cockpit-sides and inside the CAD sidepanels.

Hopefully, next winter, the cockpit will be alittle warmer...
 
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