Frozen Tundra and Cabin Heat

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Post by maules.com »

Chris, for 42 yrs I've been tracking and stopping the air leaks. Don't wait till summer as you will not bother then and next winter will be upon you. Just follow the list I published above. All can be accomplished by you inside a single day.
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Post by andy »

Flyhound, I wanted to address something you said about partially applying the heater controls. Jeremy, maybe you could weigh in on this since you've got much more experience that I have.

I used to think that it was okay to pull the heater controls out part way to control the amount of heat coming into the cabin. That was before I flew to Idaho and discovered a leak between one of my exhaust headers and the muffler pipe. It immediately set off my CO detector. When you pull the heater control partially out, the metal fitting on the end of the duct hose doesn't slide all the way up and align with the port on the firewall. That means that any exhaust gas floating around in the engine compartment can get sucked into the cabin through the gap between the hose rim and the firewall port. Now when I apply cabin heat I pull the heater control completely out so there's no gap and add cold air from the vents as needed to control cabin temperature.
Andy
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Post by Chris in Milwaukee »

maules.com wrote:Chris, for 42 yrs I've been tracking and stopping the air leaks. Don't wait till summer as you will not bother then and next winter will be upon you. Just follow the list I published above. All can be accomplished by you inside a single day.
Great plan. :). Thanks a ton for the list.

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Post by maules.com »

Andy, the heater slide valve is a bypass valve so when heat is off air still flows, though not into the cabin. It is important to adjust the cable so that when control knob is in to panel, the valve is fully closed and when knob is out the holes align for full flow of hot air. If valve is partially open the unopened portion of the slide valve should be blanked off by the valve's back sheet.
There is not a perfect seal and sometimes the valves are bent or warped and sometimes I see cold and heat valves mixed up and sometimes the knob can be pulled too far thus allowing engine compartment air into the cabin. So the trick is to adjust cable travel at both ends so the valve slide only can travel where it is intended.
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Post by Chris in Milwaukee »

maules.com wrote:#1, remove cowling and check routing of all heat and cool hoses to appropriate firewall valves.
Check muffler shrouds are fastened reasonably tight. Use a 7"hose clamp to control vibration of shroud.
One shroud is dedicated for carb heat, the other for the cabin. A third is on the tailpipe and piped to another firewall valve. The heat valve is bypass type whereas the cool valve is not bypass.
#2, address the Complete cabin which is a low pressure area in flight thus sucking cold air in at any tiny gap.
Door knob slots are a big gap though they don't look it. Seal with tape or silicone.
Door frame fit and sealing strips are a common leak. Ace hardware self stick.
Landing gear attach points under fairings need sealing with tape or insulation.
Wingroot. Remove top and nose fairings and fully seal with insulation being sure not to foul cables and pulleys. Make sure no gaps. Tape around aileron cable through fabric area. Then broad masking tape all around the wing root, top bottom, front and back, between wing skin and fuselage.
Behind rear cabin bulkhead seal with insulation the headliner back piece fully up to the fabric skin on top. Close the left sidewall gap. Then fully close the gaps among cable groups under floor. Allow no air to move into cabin.

This will make a cozy cabin provided you do it carefully, do not have crushed scat hoses and have no restrictions over the heat duct outlets.
Going to tackle these sealing items shortly. Is the insulation in the wing root and other areas just standard fiberglass insulation, or is there something else that is preferred?
Christopher Owens
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Post by maules.com »

Wijnsoort insulation looks just like underfloor and rear bulkhead insulation which looks like household hot water heater jacket material. Vynyl backed fiberglass blanket.
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Post by Chris in Milwaukee »

Wow, that must have hurt when you typed it :)

Thanks for the clarification. I'll go find some.

~Chris
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Re: Frozen Tundra and Cabin Heat

Post by drak130 »

ALCON,

I realize I may be jumping the gun here, what with heat indexes in the 100s here in NC, but anyone have any hints or techniques on how to seal up the removable bulkhead? I have managed to seal up the doors and the wing roots but still getting quite a bit of air from around the edge between the bulkhead and the sidewall on the side where the door is.

I have searched the forum but can't find this specifically addressed. From previous posts I gather that the cabin is a "low pressure" zone so I need to seal against air coming in vice air being drawn into the tailcone (thus pulling air in from all the other cracks and seams). I typically fly solo so have not been able to blow smoke.

Before I start brute forcing a fix, does anyone have an elegant solution? I was thinking of just doing like a big plug of insulation attached to the bulkhead but because of all the bracing back there it looks like that won't work. The insulation would keep the bulkhead from fitting snuggly.

Thanks for any help!

Tim

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Re: Frozen Tundra and Cabin Heat

Post by maules.com »

Drak, Maule used to hold the rear bulkhead panel in place with a chanel across the top and one sheet metal screw on each side half way up.
With the M7 the rear #5 seat backrest became the bulkhead panel and it was held with velcro, however the velcro would not stay adhered to the vinyl.
Then the M7 was sold with optional rear seat and thus a vinyl covered sheet of aluminum was attached again with unsuccessful velcro.
On my own M7s I attach a little swivel latch onto the vinyl covered trim pieces at top corners. I have also been known to attach a metal tab to the seat back or panel and sheet metal screwed it to the metal frame former (Do Not Drill Into The Tube). Ace hardware soft foam door/window seal self sticks to back of panel or frame.
Also, without fouling the top and bottom pulleys, insulation is stuffed lightly into gap between fabric and floor, fabric and headliner, and fabric and left side.
Voila, no air coming from tailbone.
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Re: Frozen Tundra and Cabin Heat

Post by andy »

When Maule Flight rebuilt my MX-7-180 in 2010, they changed the way the bulkhead panel fits. There's a channel on the top side but no screws. The vinyl covered bulkhead fits under the channel and is sized just right for the bottom to press into the floor carpet and flex backward to seal against the sides. I don't get any significant air leaks. I also have the rear seat auxiliary heat vent under the sling seat for use in winter so that offsets any cold air coming from the bulkhead area. I understand that not every Maule has the rear seat heat option but it helps keep it much warmer in back. The right side exhaust pipe has to be equipped with a heat muff with air intake from the top side of the engine compartment and outlet hose to the rear seat vent.

How about putting adhesive door seal on the back edges of the bulkhead panel?
Andy
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Re: Frozen Tundra and Cabin Heat

Post by drak130 »

Jeremy and Andy,

Thanks for the input. Interestingly my rear bulkhead is thin plywood covered in leather. I don't have the U-channel either. The main problem is that along the edge where the bulkhead/seatback meets the door is a fairly large gap that cannot reasonably be filled with foam weather stripping. I like Jeremy's idea of securing it with a fastner for a tighter fit and weather stripping to make a seal. Will see what I can come up with while not screwing into a tube!

Thanks fellas
Tim

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