Not So Baffling?..

Ironflight · #1 07-16-2014, 02:51 PM

Baffle seals age slowly, and the effects of temperature and wear change CHT?s a little bit over a long time. Season after season passes, we go from winter to summer over and over again, and the overall rise in temperatures goes un-noticed until one day you realize that you?re compensating with increased climb speeds on every flight. Suddenly, you realize that the seals have been doing their duty for close to a decade and it is time for a re-do! Such was the case with the Valkyrie, my 1800+ hour RV-8?.so last weekend I decided it was time for new seals. As most builders remember, cutting and trimming baffle seals takes time and a lot of effort ? not something we remember fondly. But I?ve got good news ? replacing existing seals can be quick and easy! Here are a couple of notes from my project ? which really only took about five hours.

Crinkly! Yup ? these seals have taken a set and are heat checked ? ready to replace.

Use a center punch to pop the mandrels out of the pulled rivets ? a few clicks and they?ll come out with vigor!

After pulling off the old seal, use a sanding disk to grind off the shank ? sand it down flush to the baffle aluminum.

With the shank ground down, pull the tail off with a pair of dikes ? the holes will still be perfect!

Take each segment off one at a time. Lay them on the new material on top of a sacrificial wooden surface, then drill through the holes and cleco to the surface. Press down to flatten and cut with a new razor nice ? and the new piece will be perfect ? ready to remount.

All of the edge seals were done in about three hours ? only the center seals still to go!

Remember how complex those center seals were to figure out the first time around? The good news is that you don?t have to figure them out the second time ? just copy them!

Center section complete! If the cowl is hard to put back on, you?ve done it right ? the new seals need to compress and conform ? and that means you?ll get good results.

The results? Subjectively, duplicating a flight done the day before the replacement, with similar OAT?s (about 90 degrees F at 5,000?), I?d say that CHT?s ran about 20 degrees F cooler than with the old seals. The baffles themselves were in great shape, and although I went over the hole baffle, found very few things that needed additional caulking with RTV. Don?t be afraid to change seals if you seem to be running hotter than before ? it?s just not that hard.

(Look for a complete story on this in an upcoming issue of Kitplanes. I just figured this might help someone through the heat of summer!)

Paul

Jerry Fischer · #2 07-17-2014, 06:53 AM

Mr. Dye. excellent narrative too.

David Paule · #3 07-17-2014, 07:33 AM

The red silicone baffle seals on my C-180 are 20 years old and have 610 hours. They show some wear but are as flexible as they day they were installed. There is no cracking where they bend.

Please bear in mind that it was 20 years ago or more, but I got the material from Denver Gasket and Packing, 10943 Leroy Dr., Northglenn, CO 80233-3615, (303) 452-4600.

I plan to use the same or similar material for my RV-3B, when I get that far.

Dave

Lemmingman · #4 07-17-2014, 08:24 AM

I noticed in your pictures that the seals seem to have a nice inward bend. Once the cowl is replaced it will lay nicely and pillow outward as air is forced in. Is that the result of the cut, the material, the workmanship or does it "just work"? It would be unfortunate to do all the work, get to the last rivet and find out the material wants to lean outward.

Ironflight · #5 07-17-2014, 08:54 AM

Quote:

Originally Posted by Lemmingman

I noticed in your pictures that the seals seem to have a nice inward bend. Once the cowl is replaced it will lay nicely and pillow outward as air is forced in. Is that the result of the cut, the material, the workmanship or does it "just work"? It would be unfortunate to do all the work, get to the last rivet and find out the material wants to lean outward.

Initial fitting is part of it, but you'll also see that I tack the rear corners togetehr to encourage the seals to tilt inward. Other than that....magic!

I use the black stuff that Van sells partly because it comes in sheets versus strips , and I find I can make bigger single pieces that way. I like the orange silicone stuff as well, but it usually is found in 3" rolls, which is harder to fit on some of the more extreme curves (and the forward baffle). I figure that close to a decade is good life anyway.

Bill Dicus · #6 07-17-2014, 11:20 AM

Thanks for your post, Paul. My baffles are new but will need replacing sometime. How did you tack the back corners together? I might add to my current baffling even though it's working very well (just on taxi testing). Thanks in advance for any info and as well for the great post. Bill

Ironflight · #7 07-17-2014, 12:42 PM

Bill, I tack the corner with a baffle seal rivet, backed up with a washer. If the stack is too thick, use a long-reach pop rivet and a washer on each side.

pierre smith · #8 07-17-2014, 12:48 PM

......and if you'll cut the new rubber seal material across its narrow dimension, it will have a natural inward curve....the way it was rolled.

Best,

David Paule · #9 07-18-2014, 03:19 PM

I called the company now known as Die Cut Technologies (formerly Denver Gasket and Packing) to ask about the availability of silicone rubber sheet. It is available is widths which would be convenient for us.

Their phone number is (303) 452-4600.

There's a minimum order of $100.

It's available in the orange we're used to, black or white. Some other colors might be available for more money.

The salesman, Francis, wasn't entirely sure what specific material I'd used twenty years ago so he couldn't give me actual prices and sizes. But we agreed that I could send him a sample if anyone is interested in getting it. I've some in my hangar and could cut off a piece easily enough. Please send me an email (click on my name above and then use that for this) if you are interested in it. Of course if you ordered it, it would come as a sheet - it would not be die cut and there would be no installation plans. It would simply be some raw material. You'd have to make patterns and do your own cutting and fitting.

He suggested that Viton would be a suitable alternative with higher performance but at a much higher cost. I don't know any more than that.

I don't have any connection to them except for having been a customer a long time ago.

And Aircraft Spruce sells it in 1/8" x 36" by the foot, with a fiberglass insert, but it's not exactly cheap.

Dave

Doug · #10 07-21-2014, 07:23 AM

Paul,

I seem to remember when you changed the cylinders for brand new Lycoming units you observed an increase in CHTs across all cylinders. Was this on Valkarie?

If so, do you think this could be attributed to the baffle seal condition (given you account a 20 deg F drop with the new seal)?

Did you observe these high CHTs drop anytime over the first 100 or so hours on these cylinders?

I am curious because I have had a hot cylinder that has now at 200 hours has dropped to be in line with the other that defied all attempts to modify the cooling arrangement in the early hours. I have a theory for this behaviour but would be interested to hear if you have observed something similar.