Sealing baffes vs blast tubes?

[bret]

Been doing a lot of reading about the importance of sealing every crack and escape path for the cooling air coming into the cowl, or plenum, seams like having all those blast tubes for mags, alternator, ect, is contrary to sealing everything up with RTV? I might have one for the EFII fuel pumps and filters filters doghouse but that's it, how many do you have, and do you have cooling problems?

[JonJay]

Bret - I have what is probably considered typical, if there is such a thing;
Air for Heat (per plans)
Blast tubes for Alternator, Engine Driven Fuel Pump, and Mags.

I cool well under the Lycoming limits but need some care when the engine is already hot from flying, long taxi's, etc... to keep under 400 (my personal, time to do something, limit). Lower the nose a tad and all is fine.
I0-360, per plans baffle system.

So, I don't consider this to be a cooling "problem" but some would probably not consider that ideal. Some may tell you that if you can't climb full out on a 100 degree day and stay below 400, something is wrong..... Nobody I know and fly with meets than standard, but there are those that post they routinely do....

[flyboy1963]

I think the smart engineer types would agree, if you seal the 'leaks', then you'll have the excess pressure and airflow to direct it to useful places, and still achieve adequate cooling.

Interesting thought, when I pull carb heat on, I am 'stealing' whatever flows thru that scat tube from the air going in the left cowl inlet.
obviously not a cooling issue, but has an effect nonetheless.

Do you tape over your oil cooler in winter? If it's mounted or feeds from the back of the baffles, you now have a whole bunch more pressure pushing cool air thru your cylinder fins, right when you don't really need it.

P.S. Gardnerville looks reel Purdy! how do you stand all that scenery???

[bret]

Originally Posted by flyboy1963

I think the smart engineer types would agree, if you seal the 'leaks', then you'll have the excess pressure and airflow to direct it to useful places, and still achieve adequate cooling.

Interesting thought, when I pull carb heat on, I am 'stealing' whatever flows thru that scat tube from the air going in the left cowl inlet.
obviously not a cooling issue, but has an effect nonetheless.

Do you tape over your oil cooler in winter? If it's mounted or feeds from the back of the baffles, you now have a whole bunch more pressure pushing cool air thru your cylinder fins, right when you don't really need it.

P.S. Gardnerville looks reel Purdy! how do you stand all that scenery???

on the net somewhere there is a pic above KMEV up high, 18K or so, looking west, mountain range and then Lake Tahoe. On my list of things to do is get special permission to do a celling test in phase one and take one of these awesome photos!

[bret]

Ok, so back to the baffle thing, did you space out baffle on rear of 3 and in front of 2?

https://photos.flightaware.com/photo...5194c04791cf7c

[Bavafa]

Originally Posted by flyboy1963

Do you tape over your oil cooler in winter? If it's mounted or feeds from the back of the baffles, you now have a whole bunch more pressure pushing cool air thru your cylinder fins, right when you don't really need it.

P.S. Gardnerville looks reel Purdy! how do you stand all that scenery???

I do have a shutter over my oil cooler and love it as I can regulate my oil temp very closely. But to my surprise, I have found it has very little effect to my CHT if it is closed or wide open. Another surprise was my scat tubing for my heat muff which is not from the back of my baffle but at the right hand cowl inlet. I had expected if I close that in summer time, there is no air to the bottom cowl which will reduce the pressure and less competing air to the exist ramp. Closing it completely by covering the inlet had zero or no measurable effect on my CHT. My CHT numbers are more like Jon, typically hit 400 on longer climbs or if the engine is already rather hot.

[JonJay]

Originally Posted by Bavafa

I do have a shutter over my oil cooler and love it as I can regulate my oil temp very closely. But to my surprise, I have found it has very little effect to my CHT if it is closed or wide open. Another surprise was my scat tubing for my heat muff which is not from the back of my baffle but at the right hand cowl inlet. I had expected if I close that in summer time, there is no air to the bottom cowl which will reduce the pressure and less competing air to the exist ramp. Closing it completely by covering the inlet had zero or no measurable effect on my CHT. My CHT numbers are more like Jon, typically hit 400 on longer climbs or if the engine is already rather hot.

Same here with the shutter.
I suspect the plenum is being more than adequately charged and losing some air through things like scat tubes for cooling, heat, etc... isn't depleting that pressure too much. I also suspect that work could be done to improve the differential between the plenum and lower cowl on the stock design. If you open the shutter, that air then goes into lower cowl. You would think it would be double bad, but it has no affect, at least on mine.
Dan H. did a lot of testing, real testing. Without going to that degree you really can't fine tuning inlets, exhaust outlet area, etc....
So...., many of us simply built it per plans and find the cooling more than adequate for the type of flying and conditions we operate in.
Could it be better? Lot's of examples show it can be without too much trade off in cooling drag.
Much of this was really not messed with "back in the day" as the performance of the stock plans build airplanes was so good, why mess with it. Took me long enough to finish the airplane as it was.

[JonJay]

Originally Posted by bret

Ok, so back to the baffle thing, did you space out baffle on rear of 3 and in front of 2?

https://photos.flightaware.com/photo...5194c04791cf7c

I did not. I do have dams in front of 1 and 2 as they where cooling a bit too much from the ram air.
3 is not much hotter on a given day than any other cylinder.

[bret]

Interesting on your test closing off the heat muff, with no change? one thing I forgot to mention is that I am using the SJ long cowl, so I don't know if that makes a difference on how critical it is of the gap sealing and cooling tube leakage compared to the Vans cowl, a lot bigger intakes. excess air to waste?

[6 Gun]

Bret don't worry about cooling cylinders they will be way cool its the oil that's the problem with our set up get the best cooler you can I'm running a 13 row an wish I had room for the 17 row.
Bob