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01-03-2019, 07:42 PM
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Join Date: Jun 2017
Location: Phillipston, MA
Posts: 2
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One or two air intakes for heat
I'm looking to install a second heat muff on my RV6A to increase the cabin heat. I live in the north and fly in the dead of winter. The current system with one muff is not sufficient and one of my worst flights involved me drinking out of a water bottle that had significant ice in it which formed during my 2 hour flight. In order to maximize heat gained in the cabin I'm wondering if it would be better to add a second air intake and make the second muff on a completely separate set of tubing all the way to the cabin OR if I should place a Y intersection (can be seen in the link below) just after the existing air intake before the existing heat muff and have one intake serving two heat muffs.
https://www.vansaircraft.com/cgi-bin...outing-devices
My theory is that I should have a second air intake because of the following. With the Y I would expect the incoming air volume to remain the same but the outgoing air to be hotter than it currently is due to the slower velocity through the muff. However as the air increases in temperature, it heats slower and thus I think the higher volume of cooler heat would effectively dump more joules of energy into the cabin and thus heat the cabin up better.
However, I believe (but don't know) that the exhaust temperature is in the thousands of degrees fahrenheit (is that number crazy?). If that is so, the decrease in heat transfer speed due to the warming of the intake air would be negligible since there is still a very large difference between a thousand and a hundred degrees. The Y would be a heck of a lot easier to install as well since I wouldn't need to create a new intake hole.
Thoughts? Suggestions?
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01-03-2019, 07:59 PM
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Join Date: Mar 2008
Location: Clarksboro, NJ
Posts: 829
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I have two RV6A's. one has the standard single heater, one has two standard heaters - one for the pilot, and one for the passenger. Each has their own muffler heat muff, their own firewall penetration, and their own air supply from the baffles. The plane with two heaters has 4 times the heat.
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01-04-2019, 05:22 AM
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Join Date: Aug 2014
Location: Bowie MD
Posts: 886
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What PA said. 2 heaters with separate firewall boxes. Go the extra mile and just do it - its a sure thing for more heat, and its there just waiting to be used. I have it planned for my plane and space set aside if I decide its needed. I also have oil cooler heat, but thats iffy in really cold climates because the vernaterm will limit oil flow and negate its usefulness.
__________________
Mani
Busby MustangII (FoldingWing) Pending DAR.
Don't be a hater; I'm a cousin with thin wings! 
N251Y (res)
Last edited by maniago : 01-04-2019 at 05:26 AM.
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01-04-2019, 05:54 AM
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Join Date: Aug 2016
Location: Asheville, NC
Posts: 2,104
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Would more thermal insulation in the cabin help?
__________________
(2020 dues paid)
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01-04-2019, 06:16 AM
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Join Date: Jan 2005
Location: SC
Posts: 12,887
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Before you change anything, try wrapping just your heater muff, not your exhaust, with exhaust wrap from an auto parts store.
This will help keep the heat in your existing heater muff and may be enough for you.
__________________
Bill R.
RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
Build the plane you want, not the plane others want you to build!
SC86 - Easley, SC
www.repucci.com/bill/baf.html
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01-04-2019, 06:21 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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My limited experience . . .
It is easy enough do do the experiment of two heat muffs in series before you undertake the task of another FW flap. I have one heat muff but the exhaust pipe inside has pin-fins welded to the pipe to enhance the heat transfer. I have flown in sub zero temps and it is sorta ok, but really sensitive to EGT's.
I did (1) insulate the external shell of the muff, (2) have pushrod seals for the ailerons, (3) restricted the heat flow to a 1" hole in the baffle. This provides some balance between total heat with high flow and temperature with lower flow.
More circulation within the muff will help collect more heat, but stuffing is not much good according to posts. Internal baffles that cause the air to zigzag, or spiral will help collect more exhaust pipe heat. Continental has a spiral flow baffle inside the muff. Even a few hose clamps with U shaped fins under them would greatly help heat transfer from the pipe.
Recently, I have sealed the spar gaps, but still have a cool draft at my armpit by the fuse. Not sure exactly where that comes from. Maybe the pleats in the back bulkhead wall, those leak too, or the aft corner of my tip-up.
I don't remember the poster but some Minnesota guys posted a good list some years ago. I think Alex Peterson was one, that listed all the leaks that were sealed. I use "site:vansairforce.com search1, search2" in google to search, it seem easier sometimes.
Good luck in your heat improvement project. Keep all posted with any data you get, and welcome aboard VAF!!
__________________
Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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01-04-2019, 06:54 AM
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Join Date: Aug 2010
Location: Wichita, KS
Posts: 1,958
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If you have a Vetterman crossover exhaust, you might consider contacting them about a muffler exhaust. I have their muffler system, and the cabin heat muff surrounds the muffler and is generally much larger than a standard heat muff. It puts so much heat in the cabin using only a single SCAT tube and one muffler shroud, that I cannot ever run the heat on full blast even on the coldest day (RV9A).
__________________
Kurt W.
RV9A
FLYING!!!
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01-04-2019, 07:40 AM
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Join Date: Mar 2006
Location: Edmond, OK
Posts: 194
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I have this "Y" tube configuration on my RV9. I do suggest connecting the straight end of the "Y" to the muff with the longest duct run to help balance the airflow. I do have the Vetterman exhaust/mufflers. I rarely have the heat knot more than 1/3 out on the coldest of days.
__________________
Dan Burdette
Skyview, ADS-B, Garmin 420W, TT Gemini AP
RV-9A, IO-320, E-Mag
Guthrie-Edmond Rgnl, OK (KGOK)
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01-04-2019, 08:08 AM
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Join Date: Jul 2007
Location: Delta, CO/Atlin, BC
Posts: 2,391
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Stuff some steel wool (stainless type that is used for kitchen scrub pads) into the heat muff. Increases heat transfer. May not totally solve the problem but helps a lot. I have two individual heat muffs, both with the steel wool. Generally has worked ok down to subzero temps as long as I'm not descending with the power pulled back.
__________________
Greg Arehart
RV-9B (Big tires) Tipup @AJZ or CYSQ
N 7965A
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01-04-2019, 08:08 AM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
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Before you dive too far into more plumbing, try making the existing heatmuff more efficient. Get a stainless steel pot scrubber and lightly pack it into the heat muff. This will have two effects:
- a significant increase in heat transfer to the cabin air
- slowing of the cabin air, again increasing cabin air temperature
If that does not work, I?d go with two heat muffs in series before adding another cabin heat box and such. You want higher temps, not more volume.
Carl
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