Heat Muff problem

OneCharlieKilo · #1 02-01-2009, 12:26 AM

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" :

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/Flight...TestingPg1.htm

Thanks for any advice!

jetjok · #2 02-01-2009, 01:59 AM

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!

OneCharlieKilo · #3 02-01-2009, 04:34 PM

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.

flion · #4 05-12-2009, 09:34 AM

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.

647jc · #5 05-12-2009, 09:55 AM

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.

Fredrik · #6 05-12-2009, 11:08 AM

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

flion · #7 05-12-2009, 03:48 PM

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.

Bill Dicus · #8 05-12-2009, 06:08 PM

Fredrik: Would you be able to post a picture of your mod? Thanks. Bill

Fredrik · #9 05-12-2009, 11:39 PM

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

Fredrik · #10 05-13-2009, 06:06 AM

Bill,

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

Regards,
Fredrik