Intercylinder Baffle Mod - Mixed Results

[Toobuilder]

I've been thinking a lot about cooling for the last few years and I'm convinced the standard intercylinder baffles are a target of opportunity for improvement. Understanding that they are "good enough", I can't help but look at all the evidence that supports other, more effective cooling schemes. Even the lowly VW Beetle has a more elaborate/extensive shrouding scheme. Compared to aircraft, air cooled cars have very little volume to work with, so they need to use all the fin area they can. That's what my research tells me, anyway.

So with the goal of being able to reduce the overall air moving through the Rocket's cowl AND still cool effectively, I removed the standard Lycoming parts and fabricated cylinder shrouds. Following NACA research, these shrouds are large in initial volume and shrink down to the fins toward the exit. I also fabricated blocker plates which prevent any (and I mean ANY) air from going anywhere other than through the fins on the cylinders or heads.









Pressed for time and unsure of the results, I decided to only do one half of the engine (cyls 2,4,6). Flight test revealed a significant increase in temps on all three of these cylinders, roughly proportional to their normal order of imbalance (ie. 2 coolest, 6 warmer, 4 warmest). Discouraging at first, but comparing the other side (1,3,5) to my normal baseline, these all ran significantly cooler. In retrospect, I should have seen this coming. Given the choice between the torturous path through the cooling fins on one side, the available air took the easy way out through the seive like qualities of the stock baffles.

So, with a bunch of flying coming up in the next few weeks, I have removed the modification and restored the stock baffles - albeit with some careful tweaking and sealing to ensure minimal leakage. Flight test has revealed my cooling is slightly better than normal. Rather than discouragement, I'm back to the drawing boards for a more elegant, optimized cylinder shroud system. Next time I'll do both sides and report the results.

[Kyle Boatright]

Nice job Michael, regardless of the unsatisfactory results.

It wouldn't surprise me if you made a set of these for the other side and saw all around improvement. I'd love to see that trial (hint, hint)...

[Toobuilder]

There will be a "version 2.0", trust me. The next set will go "over" the pushrod tube to allow a more favorable convergent duct volume geometry. Right now, I'm limited by the angle between the bottom of the tube and the point where the shroud lays down on the cylinders (tangency). Without doing a compound curve, my initial plenum volume is pretty low and the shroud just follows the fins around for most of the barrel diameter. Not optimum, but was easy to fabricate for a quick test.

I did fabricate a complete set of the original configuration, but like many things I do I figured out a better solution late in the game.

Anyway, sucess or failure, it will be reported here for the collective good.

[rv6ejguy]

We learn something from every experiment. Thanks for posting.

[crabandy]

Thank you for posting, it certainly does me some good!

[DanH]

Mike, could you quantify "significant increase"?

My limited understanding of such things says the exits need careful shaping, somewhat like the baffle entrance seen here.

I think you're right about simply re-routing the air to the other side.

[Toobuilder]

Originally Posted by DanH

Mike, could you quantify "significant increase"?...

On my way home before the mod I collected temp data as a baseline. The condition was in stable cruise flight at 8500, LOP, 60 degrees OAT. The temps 1-6 were fairly typical for this flight condition and as follows:

328, 314, 354, 354, 340, 354.

The test flight revealed the following: (OAT= 67)

304, 318, 333, 381, 326, 375

The term "significant increase" may been hyperbole, but the misbehaving cylinders were much more difficult to keep under control in climb. #4 in particular settled on 425 quickly after takeoff. While this temp is not a big deal as a transient condition, I know that my local ambient temps are going to skyrocket in the next few weeks as we roll into summer.

[longline]

I remember someone posting "optimal" upper and lower deck baffle gaps. My fallible memory seems to indicate that the optimal gap between the two baffles on a cylinder was greater in the upper deck than the lower deck. Can you compare these gaps somehow between the modified baffles and the other baffles, given that there is a flare around the push rod tubes on the modified baffles?
Interesting data points?.

[Mike S]

I tried something similar a few years back, not as elegant as what Mike did, mine were simple flat plates blocking off the big gap between the cylinder fins on the top side----------I did not wrap the material around the fins.

Same result--------temps went up. I have no idea why this happened, as the theory seems sound, that forcing air to pass through the fins will lower temps, but theory be damned--------temps went up.

Here is a shot of the paper templates as I was working on the project----finished metal parts were identical.



I do believe that the cylinder wrap setup like Mike has is the correct way to go, just need to find, and kill the bugs in the setup.

[TS Flightlines]

Back in my racing days, we went to the track to test theories. When we had the results, if they matched the theory we were good. If not, we believed the results and conjured up a new theory.
I think Michael is on to something here. But not everyone uses the same cowling, same engines, plenums (?). If it were all standardized it would be great, but them it wouldnt be experimental.
Keep it up Michael (and others) we all think outside the box.
Tom