RV heaters

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,

Probably nothing

Bryan Wood said:

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,

Click to expand...

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.

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,

Be sure you ...

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

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,

Why not two heat muffs

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.

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

Pushrod boots?

terrykohler said:

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.

Click to expand...

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

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.

heat transfer 101

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.

Bryan Wood said:

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,

Click to expand...

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Above is a photo of the rib clecoed to my canopy skirt and the final skirt.

I have a power point package I made up on the mod that I will try to send to you. The rib development process is fairly importabt to get the exact profile of the fuselage where the side skirts come down to it. Basically marked off the canopy sill every 1/2" as I recall, make up a table that has a cell (block) for every mark on the canopy sill, us a square to measured the distance from the maximum horizontal extension of the roller track to the edge of the fuselage at every mark, record every measurement, layout the points from a straight line on some pattern material (I use file folders), connect the dots with a gentle curving line, cut out the pattern, tape it to to a piece of 3/16" aluminum bar stock (I got mine from Aircraft Spruce), transfer the pattern to the aluminum with a Sharpie pen, saw out the anuminum rib, file the sawed edge smooth, trial fit it making sure to accommodate the structure and closure fiberglass band at the front and the narrowing space at the rear end of the roller track extrusion (the rib terminates in this area), drill evenly spaced mounting holes through the rib from the curved surface to the inboard edge, measure the distance above the canopy sill to the point where the canopy roller track curved surface outward extension is at its maximum, mark a line with a Sharpie pen on the inside of tha canopy skirt at this height above the bottom edge, clamp the rib inplace on the inside of the canopy skirt so the line is visible in the holes, back drill the canopy skirt through the holes in the rib clecoing every hole as you go, removed the rib, debur all the mounting holes (rib and skirt), countersing the rib holes on both the inside and outside surfaces, dimple the skirt holes, , clecoe the rib to the shirt, buy long rivets and cut to the required length for each hole as you go, squeeze the rivets in place with the manufactured head on the outside of the skirt and the shop flush head (double flush riveting) inside the straight inside edge of the rib, take the pattern used to make the rib and tape it to a sheet of rubber (I bought rubber sheet from Aircraft Spruce) set back from the straight edge the amount you want it to extend beyond the edge of the rib to effect the seal against the roller track extrusion, drwathe curved pattern on the rubber with a Sharpie pen, cut out the rubber and glue it to the bottom of the rib with 3M weather strip adhesive, repeat this whole process for the opposite side of the canopy. It not only seals the side skirts opposite the roller track but it forces the canopy skirt to conform exactly to the contour of the fuselage and it does not deform in flight, meaning it does not get sucked out into the airstream to form a minor cold air scoop.

This leaves four canopy seal ares to deal with, the interface between the side skirts aft of the roller track, the windshield interface, the rear skirt and the center track hole.

Van's says to have a skag formed by the rear skirt extend below the side skirt and overlap the fuselage to close off the opening aft of the roller track. I found that a 1/16" x 3/4" x 3/4" angle turned up and riveted back to back on the upper fuselage longeron from the aft canopy pin anchor block to the inside of the upper fuselage skin closes the opening just as well with several advantages (no air scoop effect, full contact with no potential fuselage paint scraping on closure).

I used the soft white "P" strip bought from Aircraft Spruce cemented to the aft and rear side skirts and the intersection between the roll bar and the fiberglass band to seal these ares upon closure.

Finally I used Tracy Saylor's idea of a sliding follower plug on the rear center canopy track and an aluminum hat on the rear canopy skirts to close this hole (which sucks air in surprisingly). Mine is made of balsa wood covered with fiberglass, stainless steel pull eyelets (made from safety heavy gauge safety wire that extend all the way thorugh the block on both sides and double back into the block), and waxed flat nylon wire bundle lacing tape (string) tied from the eylets to the bolt securing the slider block (four pieces all individually tied). I had to evolve this through several configurations before I came up with the one that works every time and lasts.

Bob Axsom

You have no e-mail listed so I will send the PPT File to Doug, perhaps he can forward it.

pushrod boots

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

Click to expand...

Here is how I made the boots for my RV-6:

http://thervjournal.com/cold.html#boots

Highly recommended.

Pushrod boots

Flightline sells them for $19/ pair, for those of us too lazy to make them.

http://my.execpc.com/~erdmannb/construction.html

I made mine based on Ken Scott's article

Ken Scott had an article on them in Sport Aviation a while back. I made some changes in mounting but they are essentially the same as he described.


Bob Axsom

Got it

Thanks Bob, Doug forwarded it to me. It looks great.

Bryan

Boot Photos

Here are a couple of photos of my aileron pushrod boots at both ends of the travel. They are made with the material Ken Scott recommended in his article (I think it was called rip stop nylon) which I bought at a fabric store. There were some other little gaps etc. in this area that I sealed with RTV.

Bob Axsom

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Dual heatmuffs and a defroster on RV-7 goes where?

Hi all you warm and comfy RV-7 aviators.

I'm considering installing two heatmuffs on my RV-7 with a XP IO-360 Superior Engine. The exhaust is Weterman X-over system.

Where can I install two heatmuffs on this config?
Vans drawing shows only for a carburated engine?
I think one can be installed on the cyl 1 exhaust tube. Maybe another on cyl 4 tube?

Also: anyone installed a defroster system in a RV-7? Where and how? Maybe the second heatmuff can be used for routing defroster air only?

I've tried to search this site, but this tread is all I came up with?

Regards from Alf Olav Frog (who lives in the cold Norway with a wife who loves a warm cockpit...)

In front or behind #3?

Yesterday a friend came by to help with the baffles. He commented that he wished he had mounted the SCAT tubing behind the #3 cylinder rather than under the right side intake ramp.

Have any of you moved your intake from one place to the other? Did it make any difference?

Thanks!

I too am fighting the cold in my RV8. I ordered an extra heat muff from Van's with the intention of running 2 in series. There is a problem with the muffs from Van's in that they are for 1-3/4 pipes and the newer Vetterman tailpieces are 2". The Van's muff will work on the front crossover though, and that's where I have one for my carb heat with a dedicated inlet on the left front inlet ramp.
Today if the snow gets shoveled enough in front of the hangar I'll disconnect the carb heat muff and run 2 muffs in series, first from the front inlet, then from the aft baffle and see if there's any dif.
Also and maybe this is obvious to everyone but I've never seen it mentioned, is that getting your EGT's up has a profound effect on heater output temp. Example; 3000 MSL, 0 deg. F,Mixture rich, EGT's 1100 deg.s
heater air lukewarm at best.
50 deg.s ROP EGT's 1425 deg.s heater air is HOT.

While were on the subject of the back baffle...

I wish that I had done my differently. I think that I followed the plans, but I mounted my on the vertical part of the back baffle. The better position would be on the angled part of the back baffle. You may pick up a little heat off the cylinder in this position, but the biggest benefit is that the scat tube will not be interfering with the oil stick tube.

Kent

Installing the aileron push rod boots and weather stripping the tip-up canopy made a huge difference in our RV-9A, esp. the boots.

During my last flight in my -7A in early February, my OAT readout got as low as -7F at 6500' at night over western PA.

I installed one heater muff per Van's plans, installed 1/2" soundproofing foam on all sidewalls and the cabin side of the firewall, installed 3/4" soundproofing foam in the forward cabin floor under my feet, installed aileron pushrod boots and replaced Van's leaky plastic vent outlets with the large aluminum units from Stein Air. With the cabin heat full on, I was reasonably comfortable (i.e.: I could fly without gloves in a 50 - 60F degree cabin).

Incoming unheated air from the front was virtually nonexistent. However, the cool draft coming in from the rear aimed at the back of my neck told me that a suitable outlet needs to arranged. I think I'd read that the area directly behind the canopy is a high pressure area. That's the reason my slider canopy tends to be pushed closed inflight. It also forces outside air past my pretty well-fitted, yet poorly sealed aft canopy skirts and the "doghouse". It's pretty obvious that heated air doesn't just enter the cabin through it's inlet and then exit around the aft canopy skirts.

One of the things I'm looking to do to improve my comfort at -5F is to deflect the heater outlet more toward my feet on the floor. With the stock design, it feels like a good portion of the heat comes at you from just under the panel, with a fair amount going up behind the panel toward the avionics, which don't really need anymore heat.

The other thing I want to do is to find a way to better seal against incoming air from around the aft canopy skirt. Any ideas? OR put a suitable air outlet in place as has been discussed in these forums previously, but where? and how?

Thanks for your comments,

Mike