OneCharlieKilo

OneCharlieKilo

Well Known Member
I'm about 20 hours into my Phase I flying now and on my most recent firewall forward inspection I found my heat muff looking like the end caps were "blown out" :

HeatMuff1.JPG



On initial installation, I tightened the hose clamps enough to keep the heat muff from rotating but there was no deformation of the end caps or anything else. Since the heat box is open on the bottom when not feeding the cockpit, it can't be an overpressure issue in the muff. Maybe the exhaust pipe is expanding at operating temperature more than the hose clamp, thus squeezing the end caps out....not really sure but if that's the case, I would think I'm not the first to do this or see this. Clearly I also need to remove the heat muff to inspect the exhaust pipe and make sure I'm not feeding exhaust into the cockpit.

Has anybody seen this before in other installations? Any ideas on what I did wrong here?

Some closer pictures of the damaged ends are posted towards the bottom of the page at:

http://rv6aproject.ckhand.com/FlightTesting/FlightTestingPg1.htm

Thanks for any advice!
 
Me Too!

Chris,
Initially, I had the same experience with my -6. The inlet is on the right side of the rear bafflle, and the airflow was quite fast. I installed a baffle to slow the airflow and have not had a problem since.
Yes, there is less airflow, but the air is warmer as it enters the cabin, so I did not lose any cabin heat.
I am quite sure that there are some folks here with way more experieince on this than I have, who can give you some tips. However, my simple fix seemed to work.
Also, I resisted the temptation to overtighten the clamps. On my heat muff, the flanges on the end caps are narrower the the clamp, and I noticed that excess constriction actually was pushing the flange out. I believe that a slight redesign of that particualar part would help tremendously.
Good Luck!
 
Thanks for the reply Mark. So you think it's a combination of too tight clamps and high airflow causing too high a pressure inside the heat muff?

I'll fix the end caps and see if slowing the airflow down helps.
 
Well, I just ran into this problem too; discovered it at my 50 hour inspection. How has that fix been working for you, Chris? I'm tempted to order a new set of rods along with the end caps and putting them at 90 degrees to the original (or maybe space 3 around since there is that close-to-the-exhaust side.
 
I also had this problem at 25 Hr inspection. I don't have a solution other than put it back in place and see what happens. Definite design / installation problem.
 
Me too

I had the same problem after only 10 hours. I think the the major cause is heat expand/contract and vibrations, that makes the ends creep out.
My solution was to reinstall the ends and crimp/fold the aluminium shroud at 90 deg. offset to the bolts. I just used a large, flat screwdriver for the job.

Regards,
Fredrik
 
Yeah, I think that's a better solution. I think I can rig up a little roller that will put a 1/16" 'flange' on the shroud edges and help keep the ends in.
 
Patrick, that is a really good idea. You could also make that flange if You put the shroud around a large pipe, and work the edges with a mallet.

I'll see if I can get away to the hangar and take a picture today.

Regards,
Fredrik
 
Bill,

Here's what I did (circled). As You can see it's constrained and can't creep out.

033_3.jpg


Regards,
Fredrik
 
Heater muff failure

Fredrik: Photos are helpful. Looks like a simple and effective fix. Many thanks and good luck. Bill
 
still haven't fixed mine yet

Well, I just ran into this problem too; discovered it at my 50 hour inspection. How has that fix been working for you, Chris? I'm tempted to order a new set of rods along with the end caps and putting them at 90 degrees to the original (or maybe space 3 around since there is that close-to-the-exhaust side.
Click to expand...

Actually, the weather is pretty mild where I live and fly right now so I haven't really needed cabin heat and haven't made the effort to take it apart and fix it. I'm at a little over 47 hours right now and am still pulling the cowl pretty often for inspection; it hasn't gotten any worse, still looks the same as the initial photo I posted.

But I like the suggestions posted in the last couple days and will try crimping the sides in to keep the end plate from blowing out again.
 
Ditto!

I just discovered the same problem after 20 hours. I straightened and reassembled the muff. We'll see what happens. I'll bend some lips in the shroud if necessary.

Jim Sharkey
RV6 - Phase 1
 
Heat Muff

Guys,
I had the same problem with my RV-7. To fix, I drilled a 1/16" hole in each end on the collar adjacent to the buldged area and ran a piece of .041 safety wire thru the inside of the muff then pulled back out to the opposite end making a loop then tightened the safety wire. You will have to keep the muff pulled back from the collar to get access to run the safety wire thru from front to back. Once it's run thru then attach the muff with the clamp. It's working fine on mine so far.
Charlie, Tucson RV-7
 
Note how Fredrik safetied his clamps. That is a very good thing to do on all of your clamps and only takes a few minutes.
 
Heat Muff Problem

:)I recall watching a video by George Orndorff, who makes instructional videos on building RV aircraft, so I finally found the part where he talks about the heat muff installation(RV Systems, Part 1). His tip was when you are drilling the holes into the heat muff, was to try to create some back pressure. You can do this by drilling 6 holes in the inlet of the heat muff and then drill only 5 holes(one less hole) in the outlet part of the heat muff. This may help your situation.
Steve G
RV6A
 
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