RV heaters

[Bryan Wood]

Has anybody tried wrapping the heater muffs with aluminum foil help insulate it so that it gets warmer? What do you think, will loosely crumpled aluminum foil wrapped around the heat muff help, and will it stay put with air passing thru the inside of the cowl at cruise? How about with aluminum tape around the outside the foil? Just an idea. Experience has taught me that with this group my original ideas are rarely original at all. Feedback appreciated.

Thanks,

[gmcjetpilot]

Originally Posted by Bryan Wood

Has anybody tried wrapping the heater muffs with aluminum foil help insulate it so that it gets warmer? What do you think, will loosely crumpled aluminum foil wrapped around the heat muff help, and will it stay put with air passing thru the inside of the cowl at cruise? How about with aluminum tape around the outside the foil? Just an idea. Experience has taught me that with this group my original ideas are rarely original at all. Feedback appreciated.

Thanks,

My undergrad work involved a lot of heat transfer work. The short answer is probably no, but try it. Wrap it and use a thermometer of the proper temp range in the Cabin and see if there's a difference. Try it, may be there is a secret. The other thing you can try is insulate the heat muff with some thermal wrap. That may make a small difference? Some may say wrap the whole pipe, except for the heat muff area. That may further increase the heat transfer into the heat muff, but per another thread, most feel that wrapping the exhaust has negative effect on the exhaust pipes life, increasing chance of cracking. Basically the pipes COOK. Also it is not cheap, adds weight and you have to replace it from time to time as the wrap wears out.

Here is what you can do, make sure the air entering is coming at the exhausts down stream end and the exit is at the upstream or forward end of the heat exchanger. This "reverse" flow increases efficiency.

Second is add surface area in the heat muff. The tried and true method is a door spring spiral wrapped around the exhaust pipe. I highly recommend aircraft exhaust technologies. They can spot weld small studs on the pipe which increase the temp.

If you are getting cold it could be many things, like its just too darn cold outside. With thin sheet metal, minimally insulated and air leaks its almost impossible to make the cabin warm and toasty like your car. However make sure you do reduce air leaks in and provide an aft air exit in the cabin. This will draw the heat in and promote airflow in thru the cabin. If the cabin is air tight you can't get air into it. You have to have a some transfer of air for flow.


Of course the problem is accentuated when you are flying high or at reduced power.

[Bryan Wood]

Thanks George, I'll start addressing the leaks and reverse the way I have the scat tubes hooked up. Do you think the difference from the direction of flow in the heat muff will increase the efficiency enough where my wife will be able to detect a difference? She is pretty amazing and easily functions as my engine analyzer, tank switching annunciater, and traffic spotter. Unfortunately she is also the thermometer for the inside of the cabin with an audible warning system when temps dip.

Best,

[Bob Axsom]

The heat muffs often if not always have larger opening at the input than the output so you probably will have to reverse the installation of the muff on the pipe as well as switch the hoses. In dealing with the leaks, the aileron pushrod boots did the most good for my wife as a late mod. One thing I did with my slider was seal it very well, especially with a 3/16" bar stock rib I made for the side skirts. The inner surface of the ribs ar parallel with the the convex outer surface of the side rail extrusions about 1/2" abovet the canopy deck. I have rubber glued to the bottom of the ribs that extends out horizontally and seals against the extrusion.

Bob Axsom

[Bryan Wood]

Bob,

Sometime when your visiting your plane could you take a few shots of it and post the way that you sealed the side rails. This sounds good and I'd love more info.

Thanks,

[terrykohler]

here in Michigan, many of the RVs use two muffs to generate sufficient heat. Best approach is to pipe them in series, that is preheat in one and bring to full temp in two.
The other absolute necessity are pushrod boots that block air coming in underneath the seats. If you don't have these, I would install before a second muff. Cost is practically nil.

[robertahegy]

We went flying last Sunday morn in 25 deg.F temps (surface) and found the standard Van's heatmuff on our 0-360 with standard 7A heat system to be more than adequate. I have the inlet up in the left front of the cowl cooling inlet connected to 2" scat tube and runs to the right oulet exhaust pipe where the muff is mounted. Then scat to the heater valve. Nothing special, just what the Van's diagrams showed. Works great. We've flown in temps down to 15 F with fine heat output. Usually have to close up the valve somewhat.

Roberta

[MrNomad]

Originally Posted by terrykohler

The other absolute necessity are pushrod boots that block air coming in underneath the seats. If you don't have these, I would install before a second muff. Cost is practically nil.

Any chance you could send a picture of these pushrod boots or part # or just a description?

[AlexPeterson]

My experiences with the last five MN winters and flying my 6A: I have been thorough at sealing the cabin with all the typical things, and then some. One heater (counter flow as described in George's post) is enough when OAT's are in the 25F and up range AND the sun is shining. The sun makes a huge difference that is a little hard to believe until you've experienced it. Things get much tougher as the temps approach 0F and no sun. I have had (until recently, more in a minute) two heaters, both on the aft most section of the left and right pipes. I pick up the air for these from just behind #3. Controlling the amount of air passing through the heaters is important - too much air and it is cool, too little makes for nice warm air, but too little volume to displace drafts coming in. The coldest I've flown in was -10F, and it was not particularly comfortable...

However, I have been a bit irritated with the four segments of 2" scat tubing wandering around the back of the engine, as it makes inspection and simply working on the back of the engine tougher. Also, the left pipe/heater is almost impossible to position in such a way that it won't either hit the cowl or engine mount. I had Rick Robbins (Robbins Wings) make a heater with 1.5" inlets and outlets, and I mounted it on the front crossover. I pick up the air for this on the left inlet ramp, go counterflow through the heater, then just under the cylinders but above the induction tubes to the firewall. Also, I wrapped the scat tube with some silicone impregnated fiberglass fabric, not unlike the scat tube material, in order to insulate it somewhat as it carries the heated air to the cabin. (Note: it is my understanding that newer style Vetterman crossovers may not be long enough to mount a 9" heater.) I have a test piece of this fabric around that heater, to see if it will survive being 1/2" away from the other crossover pipe. If it takes it, I will insulate the heater also. There is a big difference in the intrusiveness of the 1.5" vs 2" scat.

Yesterday, I was able to do a comparison between the 1.5", crossover mounted, single cylinder fed heater and the tail pipe, two cylinder fed, 2" heater. OAT was 25F, sun shining, and I really couldn't tell a difference between the two. I was quite curious if the reduced mass flow through the crossover pipe (one cylinder) and the tail pipe (two cylinders) would make a difference, and it apparently does not. I would fly for 10 minutes with one heater, then the other and so on.

My next step may be to put a second crossover heater, and use it to feed the tail pipe mounted current heater, on the right side, in series. I'll post more if I do this.

[sportpilot]

I would think that aluminum being a very good conductor would not hold heat in, on the other hand it would transfer heat away from anything it touchs. I guess thats why they make heat sinks and condenser cores from aluminum.