Using Continental Baffle Design on a Lyc

Bubblehead · #1 03-25-2011, 09:53 AM

I took a lot of pictures of baffles and oil coolers last year at Oshkosh looking for ways to improve cooling. Here's a picture of what I have been told is typical baffling for a Continental engine. I like the idea of putting the baffle seal at an angle to eliminate some of the geometry issues from bending the seal to about a 90 degree angle. It would seem to make the corners a little easier and tighter too.

Has anyone tried this? If so, what was learned? Is there an easy way to make some 45 degree additions to existing baffles?

Here's a picture.

scsmith · #2 03-25-2011, 12:49 PM

Another interesting feature of some Continental baffles is that the front part of the engine is sealed BELOW the crankshaft, rather than over the top. This may address 2 problems.

First, the shaping of the baffling around the front and over the top of the engine is tricky because of the transition of the diffuser ramps, and I think many with poor cooling have leaks around here that they don't even know about.

Second, the external pressures around the spinner-cowl gap vary circumferencially, but in particular, are fairly high around the lower quadrant of the spinner. Since this area opens into the lower plenum on a typical RV/Lycoming style baffle, this tends to raise the lower plenum pressure some with air leaking into the lower plenum from around the spinner. I've seen some nice seals of various concepts to try to reduce this.

But it does beg the question - would we do better, or easier, to try to seal under the crankshaft rather than over? It seems difficult with the starter and alternator there - maybe that's why Continental's can do it and we can't? Maybe I answered my own question

.....but with some cleverness, maybe????

Bubblehead · #3 03-25-2011, 01:32 PM

scsmith - that was where I was heading next. When I improved the baffle seal over the top front of the engine with just a little work my temps dropped significantly. There is more to be gained there.

I also like the way the Continental baffles sit along the sides. Here are two pictures.

I think the rear baffle is a no-brainer for a trial of the 45 degree bend. If that works then maybe tackle down the sides. Either way the front of the engine would be trickly.

Bubblehead · #4 03-28-2011, 11:10 PM

There are probably guys sitting watching it rain at Sun N Fun or waiting for MVFR to get there that have time to post on this. Surely someone has some thoughts about this! (and I'll keep calling you Shirley until I get some opinions!

DanH gives EVERYTHING a lot of thought and Mel has seen at least one of everything. Maybe they have some thoughts.

az_gila · #5 03-28-2011, 11:22 PM

Quote:

Originally Posted by Bubblehead

.....
I think the rear baffle is a no-brainer for a trial of the 45 degree bend. If that works then maybe tackle down the sides. Either way the front of the engine would be trickly.

If the idea is just to get the baffle material to "tuck-in" in the inward direction, then only a 5 to 10 degree bend is needed and air pressure will take care of the rest.

No need for a 45 degree bend, it won't really make the seal any better...

DanH · #6 03-29-2011, 06:36 AM

Agree with Gil. The Continental install in the photos clearly shows some leaky spots, so mere seal angle isn't a cure-all.

Steve, I seriously considered a Continental style under-the-shaft baffle system, but couldn't see how to fabricate it around the Lycoming alternator/starter location. Which is not to say it can't be done.

FWIW, here's a nice illustration, Mooney Acclaim. Wouldn't that combustion air intake location be wonderful?

Bob Kuykendall · #7 03-29-2011, 11:06 AM

Quote:

Originally Posted by scsmith

...But it does beg the question - would we do better, or easier, to try to seal under the crankshaft rather than over? It seems difficult with the starter and alternator there - maybe that's why Continental's can do it and we can't? Maybe I answered my own question

.....but with some cleverness, maybe????

I think that you have identified the main issue: Continental seems to favor rear-mounted starters and accessories, cleaning up the fronts of their motors. I know that on the 206 I used to commute on, the starter was on the accessory case, and the alternator was belt-driven from a pulley on the accessory case. There was nothing driven off the front of the crank except the propeller.

Sealing under the crank on the Lycoming would probably mean a complicated partition that allows the front halves of the starter and alternator to be in the high-pressure intake plenum, with their back halves in the low-pressure exhaust plenum. That seems doable, even accounting for the fact that the alternator position changes with belt tension adjustment. And it would provide a guaranteed path for alternator cooling air. But it would seem iffy as to whether the benefits outweigh the trouble.

Thanks, Bob K.

Bubblehead · #8 03-29-2011, 02:39 PM

So perhaps a hybrid application with a Lycoming front end over the top of the case and Continental style on the sides and back.

I think Gil had it right - you don't necessarily need 45 degrees. 10 or 20 might be fine.

I have some pretty thick baffle seal. Perhaps a more pliable seal would help too.

DanH · #9 03-29-2011, 03:45 PM

Think about the geometry of a tipped up seal strip at the curved rear corner, then look at the second photo in post 3.....when the cowl pushes down on the seal edge, it wrinkles. You improve the situation by installing the seal more parallel to the cowl surface.

az_gila · #10 03-29-2011, 05:12 PM

Quote:

Originally Posted by DanH

Think about the geometry of a tipped up seal strip at the curved rear corner, then look at the second photo in post 3.....when the cowl pushes down on the seal edge, it wrinkles. You improve the situation by installing the seal more parallel to the cowl surface.

I think you would get wrinkles either way.

Cut slits and make overlaps to let the baffle sit better on the cowling - a bit like fluting ribs...