Cabin heat

Flying back today into a frigid cold front I saw as low as 1*F at about 5000, mostly clear sky's. My wife said we were flying in a refrigerator. It was chilly and cabin heat was doing all it could. My heat ducting comes off the back of the baffling behind number 3 cylinder. The heat shroud covers two exhaust pipes (4 pipe exhaust) I am wondering if I am just not getting enough airflow from Sceet ducting from behind the number 3 cylinder. I am considering moving the ducting to front of the cowling on the inlet ramp, but wanted to get some feedback first.

Too much or not enough

Just a thought. You could be getting too much airflow as well... I.e. the air passes through the heat muff so fast it doesn't have time to warm up passing the hot exhaust pipes. Try closing the damper to see if the temp rises, (with an obvious decrease in volume. If so, you may need to find a means to add a catalyst to the system; I've read some people wrap the pipe with a coil spring of sorts inside the heat muff, this creates a greater surface area of hot steel for the air to pass over.

You could also add another heat muff, but that would be pretty involved...

This is one of those things that seems so individualized. Among the issues are how sensitive you are to cold. Also, what your exhaust/heat muff setup is like.

In my case I have a clone (made of stainless steel) of the standard Van's heater valve located in the stock location for my 180HP RV-7, per plans, drawing air via SCAT tube from the baffles behind #3 cylinder. But, I have Vetterman mufflers on my crossover exhaust, which unfortunately is only available for vertical draft sumps, as I understand it. I pick cabin heat off a heat muff surrounding one of the mufflers. My wife, described by one of her friends as She Who Has No Body Fat, is always cold. Last time we flew we saw about 10 degrees F OAT. The heat was off, she started griping, I instructed her which knob to pull. Wide open it went. That lasted about 30 seconds. Back to about 1/2" out from fully closed. Fully open it would have driven us out of the cockpit. Like having a heat gun trained at our legs.

You might try using two heat muffs in series. On my RV8 I go from one heat muff to the other, and then into the cabin. I have plenty of heat - in the front seat ( shouldn't be a problem in your -7). My GIB (wife) isn't so lucky. She's rather frosty in the back - even with a heated seat. Stop the air inflow and you've tackled half the problem. Wing root between the spar bars and web is a big source of cold air.... Plug it with some foam.

Ryan,

I switched from the cabin side controlled heat box to the engine side controlled box years ago. The big difference is the engine side box has a scat tube flange on the cabin side. I then ran a scat tube from the flange to a plastic vent located just underneath the left side of the instrument panel. I can aim it straight back so hot air blows to the rear cockpit or up at me. We can now fly when the temp is 0 F and both of us are warm. The difference is the air arrives at the vent at a much higher temp than it did when released at the firewall. I cannot hold my bare hand in front of the vent for more than five seconds...it is that hot! Both of us think it is the best mod we have made to the aircraft. BTW, I also get the air to feed the muff off the curved baffle under the #3 cylinder. My GIB does get some air blowing forward from the rear of the skirt (canopy shrinks when cold), so she wears a furry collar to keep the cold air off her neck. If you need some pictures just call me. Good luck.

Jim 970-769-9830

Another thought ...

Are you running LOP? I find the additional 150 to 200 degrees on the EGTs is reflected directly in the heater air dumping into the cabin. Makes a HUGE difference!

Was running ROP at the time.

sounds like I have some options, and likely the local of my current Scat tube behind the number three cyl is fine.

Jim I would difantly like to see some pics of your set up...or any others for that matter. Just looked up engine side control and pretty sure I have that already.

pics of my current set up.

Ryan,

I will go to the hangar in the day or so and send you some shots of my set-up. I get my intake air from the curved part of the baffle underneath the left rear cylinder...sorry, I thought that was #3. My thinking was that the air at the bottom of the engine would be warmer than the ambient temp on top. I helped a friend change his heat box, but he never got around to running the scat tube to the instrument panel. He didn't see much of an increase in cabin temp, so getting the hot air closer to you is important! Send your email address to jpthornton@frontierdotnet and I will send them to you direct.

Jim

heat

Ryan

Rick Robbins had me go with 1 !/2 inch scat from behind the #3 cylinder to the heat muff and into the plane. I have a 4 into 4 setup like you do and he feels that less volume with more heat is better. I also found that wearer stripping on the rear of the canopy made a huge difference. I spent some time closing the canopy and cutting small tapered pieces to make sure that the seal was as air tight as possible. No draft whatsoever makes a huge difference.

If it helps, I flew the airplane from Cleveland to Cincinnati a couple of weeks ago and the OAT was 9 on the ground and in flight it had warmed up to 15f by the time I had landed. I was fine (long underwear on) and my pax was ok as well (his feet we getting a bit cold after an hour)

Cabin Heat

On my 7A I have the scat tube opening behind the number 3 cylinder 1/2 covered with duct tape and I also reversed the scat connection on the hat muff. Goes from behind the number 3 cylinder to the rear opening on the heat muff . Forward opening goes to the cabin. The reverse connection makes the air coming in do a 180 degree reversal.
I fly out of Green Bay WI. and have no problem getting enough heat in the cabin.