High CHT's On Climb

[billnaz]

I echo what RVGUY says. In many cases I think we're victoms of too much information. I went through the same consternations durring my phase one with high chts on climbout. Did all the usual fixes and finally listened to an old sage and just powered back a little, and dropped the nose a bit when chts got to >400. They stablized and I was still climbing like mad (compaired to the old Piper). If cruise temps are OK, don't sweat those climb temps (within reason).

[frankh]

Originally Posted by DanH

So how? First, make sure your baffles really fit, hugging the cylinders and heads at all points so every bit of air passes between fins with maximum surface contact for the maximum possible distance. A standard set of Van's kit baffles don't fit right from the box. Many builders are happy when they get them trimmed to fit on the engine, and stop working.

Air not in in contact with a fin surface doesn't pick up any heat. The really sad thing is that the above baffle wrap is the one near the exhaust port.....the hottest part of the cylinder head. Remember delta-t? This is the area with the most potential for heat transfer.

Ok, so much for fixing stock baffles to work better. Now consider some of the work done by the canard guys, the sho'nuff fanatics of drag reduction. The fast guys don't use baffles like ours. Ours wrap only 60 or 70 degrees of cylinder. Some of theirs wrap 120-130 degrees.....and are often formed from glass and RTV so as to not leak anywhere along that wrap.

I was just thinking about this....We have the plenum (or top of the cowl) but the air reallly is not going through the cylinder fins..its bascially short circuiting the top fins apart from those that are in the direct blast of incomming air..and we usually put temp raising sheilds in front of those to balance the front and back cylinder head temps.

Seems the Long Ezy guys are onto something by covering a larger part of the circumference on top of the heads and barrels.

I woundered if we could do some experiments with aluminium tape stuck directly to the heads/barrels to improve cooling.

of course this would also make the total cooling path longer which will add more pressure drop, but then the pressure in the top cowl would be larger anyway.

Any thoughts?

Frank

[flickroll]

Think what I'll do, BEFORE the dreaded fiberglass work, is stuff some foam in the tunnel of the eyebrow and see if that helps. I THINK my baffle material is sealing well here. The 'foam test' will tell for sure.

[DanH]

Bill Woods, you out there buddy? Post some pictures of your baffles seals, in particular the intake area.

Frank, it is an easy experiment...go for it and report.

[frankh]

Sounds like a project for the next annual...Do it one day so the OAT's remain fairly consistent.

Frank

[JonJay]

Originally Posted by flickroll

Wonder how an aluminum plate RTV'd in the tunnel would do? I HATE glass work.......

Make a kidney shaped piece out of .020, bead of RTV, and pop rivet in place. Ten minute job, perfect seal.... I hate fiberglas work...

[kentb]

Originally Posted by DanH

.

Now how to fix it. In the above picture to I add RTV where you have the two arrows drawn between the baffle and the fin?

Originally Posted by DanH

.

Same question here, put RTV between the baffle and the fin?

Originally Posted by DanH

.

Same question?

Kent

[Bubblehead]

I did something similar to what Kent is suggesting when I reapplied my baffles to new ECi tapered fin cylinders. I did not want to rebuild the whole baffle system so I used hi temp rtv and made adapters to go between the baffle and the cylinders. For instance, for the front two cylinders I put a layer of duct tape on the front of the cylinder fins, then a layer of packaging tape. I wanted the tape to come off the cylinders without removing paint and for the tape to come loose from the RTV without pulling the RTV off the aluminum.

Once I had everything ready I gooped up the tape and the left and right front baffle halves with hi-temp RTV then assembled them to the side baffle plates and the engine. The next day I carefully pulled the front baffle halves off the engine. The RTV had set up nicely and made a tapered spacer for the cylinder. There were some voids and gaps but the basic contour and dimensions were there so I added more RTV and smoothed it out. I was worried that the second layer would not hold but it did!

The back baffle halves were harder but I was able to take some measurements of the gap between the bafle and the cylinders and use RTV and bid fiberglass to create a contour that matched the cylinder pretty well.

Here is a posting from Groucho that gave me the idea. I'd seen this on EZs years ago but had forgotten all about it until this post showed up. I did not apply the RTV/FG in a way that it would stick to the cylinders though. My baffles can be removed without peeling RTV off the cylinders.

http://www.vansairforce.com/communit...ad.php?t=26988

[DanH]

I was planning to saturate fiberglass cloth with high temp RTV to line the inner surface of the baffle wraps (additional plies for thickness where needed). John's method sounds good too....and there are probably 3 or 4 more ways to skin this cat.

[frankh]

I now remember Groucho's (Bryan's) post...I think this is definately an experiment coming on.

I do have a roll of very sticky aluminium tape that will conform well to the fins..so I expect to be able to run a few test cases (assuming the lower baffles already fit well ..I think they do).

So hopefully just the uppers will recieve the tape...fly adjust, rinse ,lather, repeat until the lowest cylinder head temps are seen for the same power settings assuming the same OAT.

Once i have have baffles that give me the best temps I simply replicate the alu tape with the RTV/BID layup, marking the edges of the required layups with a sharpie.

I just hope the openings in the lower baffles would not need to be opened up to reduce the pressure drop.

This could be cool!

Frank