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I'm considering adding cabin heat (or at very least the firewall hole) before I close in the glareshield. Looking for thoughts on whether my plan makes sense. The plane is an Ohio based tailwheel, turbo aerovee powered Sonex-A still under construction.
Since I have the top mounted oil cooler, and it's now considered acceptable to not install the bottom oil cooler inlet scoop in the cowl, I'm thinking of running a round SCAT tube inlet from that location on the front face of the cowl. I also want to get some blast tube air for the gascolator and fuel line. I'm thinking 2" or 2 1/2" diameter SCAT from the inlet, running back to a Wye that splits to a 2" (to the heat muff) and a 1" or 1 1/2" SCAT tube for the blast tube.
My plan would be to put a heat muff on the turbo exhaust down tube (the lower removable section) with screen door springs wrapped around the exhaust tube to increase heat transfer. This way, during summer flying, I could just switch out the heat muff down tube, for a plain exhaust tube without the heat muff, saving weight and heat retention issues. The SCAT would just be spliced together giving an extra source of fresh air in the cockpit.

On the firewall, I'm either going to to buy or make a stainless steel diverter valve like this one from plane innovations.
http://www.planeinnovations.com/product ... ve-hbv-02/

Installed orientation of this photo: right side is up, left side with the inlet tube would be down on the firewall, bottom is cabin side.

This diverter valve design will keep all of the controls on the pilot side, and keep it simple for penetrations. I would mount this on the passenger side, right above the rudder pedal tubes, and below the tank. Run a solid bar from it to below the panel for operation. There should be enough room on the firewall between the turbo exhaust and the firewall for the diverter valve and tubing to fit.
If I make my own diverter valve, I may just make the flapper and hinge from SS (directly attached to the firewall), and form the box from Aluminum for ease of construction. From a fire point of view, it shouldn't matter as the firewall and closure would still be all stainless, and would remain whole even if the diverter box melted off the firewall.

Concerns running through my head.
A.) Am I going to get enough heat from that short tube section to make this worth the time/expense?
B.) Is the exhaust tube joint going to leak causing fume issues? To some degree, I could mitigate this by welding the muff to the tube (but that makes the muff steel vs. alum). A welded heat muff shouldn't be a big issue since it should be inspectable from the inside.
C.) With the heat muff installed, and diverter valve closed, the diverter is going to dump more heat directly under the turbo...exactly where we don't want it...but this may not be an issue for cold weather flying when the heat muff would be installed. Might still be an issue for the shoulder seasons.
D.) Performance issues with the inlet in the front of the cowl...would a NACA scoop on the side or bottom of the cowl be a better choice? That's more expensive/ time consuming...
E.) Is a 2 1/2" inlet overkill vs. just use 2" SCAT throughout? Since the air will expand on heating, a 2" feed, even with some drawn off for the blast tube may be sufficient.
F.) Any ideas on where to buy a Wye like I'm describing? Thinking I'm going to have to fab something from some thin wall aluminum tube.
G.) Will the weight of the heat muff and tubing be too much for the exhaust extension connection springs, and will I need to add additional support for the system?

Anyone done anything like this, particularly with a turbo?

Thanks,

Gregg Short
Sonex 715
Burbank, OH

Your idea will probably work but you should consider mounting the valve box lower on the fire wall, nearer the cabin floor, and with the scat tube at the top. Air into the scat tube must run always so the heat muff doesn't overheat as well as the exhaust pipe it covers. The valve as shown in the picture is allowing the heat into the cabin through the open side (not seen in the picture). When the valve door is moved it covers the open side and allows the air to flow through the opening and into the cowl. Having the opening pointed down allows the heated but unused air (summertime) to exit the cowl bottom vent and not add to the heat in the engine bay. I used the right side exhaust pipes and tried to include the junction of the left crossover pipes under the muff. A cheap auto parts store push pull cable actuates it. I don't have a spring wrapped on mine but may do that in the future to see if it raises the heat output.
As for a "y" tube here's one : http://www.aircraftspruce.com/search/se ... =&pageno=2
For an inlet i used a hole in the baffle in front of the right front cylinder, that way I don't have to disconnect anything to remove the cowl.

Bill,

Thanks for your thoughts. I'm not sure you are correct on the usage/orientation of this particular heat box. While I don't have it in hand, I'm almost 100% sure that the bottom of the picture is the firewall side, and where it mounts via 2 bolts. This particular model is designed for cabin side operation, and the cabin heated air would come out the bottom of the photo . It's the dump side exit that is not shown in the picture, which is 90 degrees to the right of the 2" SCAT tube connection. Hinge is on the right side of the photo. If I moved this particular unit down on the firewall, then the operation would impact the pax side rudder pedals. I agree that locating it lower on the firewall would make it dump quicker from the cowl. If I make my own valve, I could connect some 2" line to the dump side, and run that down the firewall and out the bottom of the cowl...which could be added later if a problem existed.

Gregg Short

I actually just (finally) installed my heat Friday. My setup is similar to Bill.

Inlet on front right baffle - Scat tube to muff (with stainless steel mesh inside) on right exhaust pipe - Scat tube to diverter box like you have pictured (scratch built) with inflow on top, out flow out the bottom - Through hole in lower right firewall where I have a small diverter to direct air at left side as well (Idea from Tony Bingelis FWF book). Diverter box is operated by a hardware store bought choke cable. I also made the whole thing so I can quickly remove the system and cover the firewall opening for summer operations.

I tested it out Saturday on a quick local flight and Sunday on a 180mi X/C. It really put out a good amount of heat, better than expected.

A couple of notes I discovered. I want to make it so it is directed to the left side better, still working that out. Also, I need to make some kind of boot/cover for the wing root opening because that draft is really substantial, even with rubber gap seal on the wing/fuselage joint. I was able to really notice it with the contrast of the warmer air coming in from the front right.

I think if I get that all sealed up it will keep it comfortable in there down to 20f, which is as cold as I want to go fly in anyway.

I would love to know if anyone has gotten heat from a VW to work. I have tried for 3 years with no success. I have heat coming off of one exhaust. Maybe 2 would be better, but the heat coming off of a single VW exhaust, and into the cabin, has been something just north of zero. I'm using the same firewall "valve" as Gregg, down by the rudder pedals. Here are the links to some my attempts shown on my Kitlog pages. I've tried a lot more things than you see here, all with no positive results.

http://www.mykitlog.com/users/display_l ... 80&row=156
http://www.mykitlog.com/users/display_l ... 82&row=143
http://www.mykitlog.com/users/display_l ... 37&row=142
http://www.mykitlog.com/users/display_l ... 25&row=131
http://www.mykitlog.com/users/display_l ... 91&row=130
http://www.mykitlog.com/users/display_l ... 58&row=121
http://www.mykitlog.com/users/display_l ... 44&row=114
http://www.mykitlog.com/users/display_l ... 401&row=48
http://www.mykitlog.com/users/display_l ... 402&row=47
http://www.mykitlog.com/users/display_l ... 887&row=46
http://www.mykitlog.com/users/display_l ... 163&row=43

Mike Smith,

Are you getting plenty of air without heat rise, or just a bit of air with some heat? Just looking at your heat muff, it would seem that there is a lot of room for the air to move around the corners of the heat muff and bypass the springs/ exhaust pipe. I wonder if you add a baffle between the two sides maybe 1/2" - 1" larger diameter than the pipe, if that wouldn't help force the air to pickup more heat from the pipe. From my knowledge of heat exchangers, the surface area is important, and forcing the air across the surface is crucial. The springs tend to slow down the air, and increase surface area, but if the air is just jumping around the springs, then you're still not getting it done. I know Tony Bingelis talks about using multiple propane torch canisters for the heat muff...that's a lot more area than you've got covered (longer flow length)...and restricted in a lot closer to the pipe than what you've got going on...

BTW, the heat valve that you used is different than what I'm planning on using. You used a Heater Bypass Valve – HBV-01 which is engine side operated vs. the HBV-02 which is cabin side operated. Same basic flapper idea though. You can attach a cabin hose to the HBV-01 (good for running to a back cockpit) , but not the HBV-02 version...for the Sonex, I don't see that as an issue. I plan to just add a cabin side deflector plate like Mike Beck discusses, which will be slotted for the actuator arm.

So no Turbo drivers have tried the Turbo exhaust pipe as a heat muff source? Seems to be the most logical spot as you get all 4 cylinders worth of heat. I realize that the turbine wheel is taking some of heat and energy from the system, but four cylinders should make up for any other losses. I'm just concerned that there will be enough flow length with this location...

Thanks for all the input so far!

Gregg Short
Burbank, OH
N715SX

This heat muff worked pretty well on the AeorVee when I was running it. I think you might have better luck getting heat if you have a different ram air entry point like an opening up front on the bottom of the engine cowl. The location at the back of the engine baffle may not be giving you enough positive pressure IMHO.

OneTallShort wrote:Mike Smith,

Are you getting plenty of air without heat rise, or just a bit of air with some heat? Just looking at your heat muff, it would seem that there is a lot of room for the air to move around the corners of the heat muff and bypass the springs/ exhaust pipe. I wonder if you add a baffle between the two sides maybe 1/2" - 1" larger diameter than the pipe, if that wouldn't help force the air to pickup more heat from the pipe.

In the latest muff the holes entering and exiting the muff are much smaller than the scat tubing, to slow down the air. I get good air flow into the cabin. I have different intake baffle plates with holes varying from 1/4" to 2". I have tried all the sizes in between. If I go with a large intake opening then there is too much air flowing through the system and little heat pick up. If I go with a small hole then the heat and air flow are better, but there just isn't that much heat being generated. The joints on the muff are as tight as they can get without welding them. Welded connections would mean the device would have to be slid onto the exhaust with no way to easily remove it or check the exhaust underneath it. And no way to add surface area inside by things like springs, etc.

So I obviously don't have the answers, and I hope someone else has success. But I've asked the question before and have yet to hear a response from anyone that has had success getting usable heat from a VW aircraft engine. Just remember how well a 1970 VW bug stayed warm in the winter... it didn't!

lgsievila wrote:This heat muff worked pretty well on the AeorVee when I was running it. I think you might have better luck getting heat if you have a different ram air entry point like an opening up front on the bottom of the engine cowl. The location at the back of the engine baffle may not be giving you enough positive pressure IMHO.

My positive pressure is off the map. I have to make smaller inlets to keep the air from rushing into the cabin. So it's not a problem with positive pressure.

Was you muff custom made, or purchased somewhere? If you had some success with it I'd love to know about it. On a 30 degree day here, mine is worthless.

Loren,

That's a very clean and cool heat muff. Is it ~3" extruded aluminum tube for the main body? I'm guessing that there is a second hinge line on the other side so it can be split in half. Looks like a split shaft collar on the end with a thumb screw for tightening to the exhaust pipe. Not sure I understand how the end flange splits/ attaches to the main tube body. The end plate seems to be welded to the split shaft collar. But how is that assembly attached to the main body?

Did you need to wrap a spring on the inside?

I am planning something similar, but attached to the turbo exhaust...

Thanks,

Gregg Short