Sam James Cowl/Plenum Cooling

Hi all,
Well I flew N727MM for the first time Saturday, and I was delighted/discouraged.
Delighted in the fact the airplane handled almost perfectly with just the slightest hint of a right wing heavy condition.
Discouraged in that I couldn't fly very long due to high CHT's. I mean like 440 for a short time. Oil temps weren't overly high.
I have an overhauled O-360, 9:1 pistons, Sam James cowl/plenum.
I understand there have been some issues with SJ cowl, so my question is, what have some of you done to mitigate the high temps, other than fly fast?
Can larger inlet rings be fitted to the cowl without major surgery? BTW, I have a new SJ cowl that I will be doing the surgery on.

My temps were high to begin with as well with the SJ cowl and plenum, and I had to be careful to pick the days to fly when the ambient temp was tolerable. 440 is quite high, and I saw temps of 415-425 for a short while while breaking in the engine. Now with 58 hours on it, my temps only climb to near 400 in a long climb on a hot day. Typical cruise CHT's are 300-330 now.

Might be a combo of the overhauled engine and hot temps on Saturday? Also, you could try blocking off a small portion of the oil cooler to force more cooling air over the cylinder fins. ([EDIT] This is only if your oil temps aren't reaching 190+ already)

One thing that helped bring my temps down was to make sure the plenum was sealed completely around the engine...meaning the baffles had some leaks that I fixed, and the nose of the plenum to the case had a terrible gap that I sealed up.

Not the same problem as you, but for reference:
RV-7, IO-360, 9 to 1's Emag/Pmag, james long cowl and a tight plenum. i ran warmer for the first 5 hrs or so. I did my initial flights in OAT of 20*F and had trouble getting the temps up. Now in the heat of summer, I've never had CHT over 400, also oil temp runs cool 195-202, even in OAT of 85*F ....but slow flight(<120kts) will send the oil temp right thru 220 in about 10minutes. then once I land my engine stumbles and has even died. it appears that i am boiling the fuel out of the injection lines while taxiing. I have to keep the rpm up for good fuel flow while moving very slow.

anyway just a reference for others with a james cowl. Good luck

I'd love to know the heat transfer efficiency value for those installations. It is mostly a fin/baffle/sealing issue, and more or less independent of the cowl scheme (ie inlet and exit type).

Paul Lipps posted a suggestion for temp probes some time back. They work great; I have two and move them around the enigne compartment as desired.

Pauls wrote:
For those who want to measure the cooling air at the bottom of the cylinder might I recommend the National LM135,235,335 familyof integrated citrcuits. They put out an analog voltage scaled to 10mV/K(C) over a range of -50C to 150C, and they only require an 11k resistor from 14V and return to power them. The output is easily read on a DVM and 20C would appear as 2.93V, corresponding to 293 deg. Kelvin.

I have a K to F conversion cheat sheet if anybody wants it.

Plenum

Another thing to look for is to make sure you follow Sam's instructions for the air exit gap spacing on the underside of the cylinders and inter-cylinder baffles. Too much or too little of a gap here will cause high CHT's. Also, make sure that the baffles curve properly and fit tightly to the cyl. barrel and cyl. head fins so no air is lost out the sides.

If unsure of the distance spacing of the gap, call Sam

Had similar issues. James cowl and plenum. Mounted a second oil cooler in series and oil temp stays where it should during slow flight. Also keeping the electric pump on after landing in 95+ OAT stops vapor lock during taxi.

hydroguy2 said:

Not the same problem as you, but for reference:
RV-7, IO-360, 9 to 1's Emag/Pmag, james long cowl and a tight plenum. i ran warmer for the first 5 hrs or so. I did my initial flights in OAT of 20*F and had trouble getting the temps up. Now in the heat of summer, I've never had CHT over 400, also oil temp runs cool 195-202, even in OAT of 85*F ....but slow flight(<120kts) will send the oil temp right thru 220 in about 10minutes. then once I land my engine stumbles and has even died. it appears that i am boiling the fuel out of the injection lines while taxiing. I have to keep the rpm up for good fuel flow while moving very slow.

Click to expand...

Some ideas

I just started flying my -4 with James cowl. Initial break-in temps were into the 400s, but with 30 hours on it I consistently see temps under 375 on climbout even on hot days (O320 FP). I can even fly formation with my friend's stock Stearman (at 80mph) with no buildup in oil temp.

Some things I tinkered with initially:

1)Ensure you have a clear path for hot air exiting the cowl. I had an exhaust brace for my 4-pipe exhaust obstructing a significant part of the outlet.
2) carefully inspect the baffling and ensure a tight seal against the crankcase. Seal with rtv if necessary. I reworked a significant amount of the plenum perimeter to get a good seal against the crankcase and baffling.
3) ensure that the baffles wrap nicely against the cylinder fins. If a fin isn't completely wrapped due to baffle misalignment, rework the baffle. I used the Vans baffle kit and had to do a lot of work to get a good fit around all cylinders with the bottom gap specified by James. For example, my rear #3 baffle had an unbent tab at the cylinder base, leaving about a 1 sq. in. opening for air to blow by.
4) add a temporary lip on the cowl exit to increase airflow during break-in. 2" long and about a 30 degree angle is what I used (though probably excessive)
5) make sure your carb is running rich enough (discussed amply in other threads). My carb was old and had been sitting around dry for years. An overhauled replacement ran noticeably richer and cooler.
6) keep climb speeds up to promote good airflow
7) I haven't tried it, but trimming back the cowl exit for a larger opening may help.
8) I haven't tried this, either, but removing your heat muff and blocking the heat duct may improve flow over the cylinders during break-in.
9) set up a manometer to ensure appropriate pressure recovery in the plenum and adequate pressure drop across the cylinders. I actually set this up on mine, but haven't collected any data since the temps came down during break in.
10) install fairings and wheel pants to minimize drag. This allows the engine to receive more cooling at a given power setting due to higher airspeed.
11) ensure the flow path from the inlet openings into the plenum is relatively straight and smooth. During construction, I had to hack off and relocate the plenum inlets to match them to the location of the inlet rings.
12) if front cylinders are running in the normal range, build baffles in front of them to help duct inlet air toward the rear cylinders.
13) if oil temps are high, look at ducting to the oil cooler. I spent a lot of time during construction to find a system that I was happy with, but I ended up with a generous, approximately 2" x 6" unobstructed opening above the #4 cylinder to supply oil cooler air. My oil temps are spot on in the 190s, but I'm utilizing the full flow of my ducting to achieve it.
14) try to find a cooler time of day to put the first 10 hours on it. After that, see if slightly reduced power settings help through the final stages of break-in.


Good luck!

OK, So now I have about 4-5 hours, on the thing and still my CHT's are hot, but only on cylinders 1 & 2. 3&4 run around 370-380F. Go figure. I actually had an hour long conversation w/Sam at Osh and he said to check the gaps at the bottom of the baffles. (All are good), Seal the plenum, (I did that when I installed it), Make sure all the baffles are tight around the cylinders, (they are). My oil temps are not high at all, between 180-210 but I have to be real careful not to fly very long with high power settings even at cruise speeds or the CHT's on 1&2 get up to 425+. Trying to break in an engine is tough when you can't run over 2250 RPM for any length of time.
Other than adding water spray nozzles, any cooling gurus have any suggestions?

Electronic ignition? What are your EGTs and how much rise to do get when leaning? Back when I finished my 9A with 9:1 compression and Emag/Pmag I was high on CHT and EGT and got little to no rise when leaning. Wound up go up in jet size in the carb and problem solved. Was too lean when running full rich and after going up in jet size was able to run richer and cooling problems went away.

Scott

Merle
Most installations include "air dams" in front of #1 and #2. If yours has these risers you might want to trim them back or remove them. Also on the #2 cylinder cooling is enhanced if you place one or two washers under the screw on the front of the baffles. It is the screw that you can see on the outboard forward side of the cylinder and is used to hold the baffles tight to the cylinder. Spacing here will give you better airflow around that cylinder. Likewise on the aft #3 cylinder. seal the gap created around the washers as you want more air to go through the fins, not this space.

Well, I may have found my problem. I say may have because I am in the process of correcting it. I called Sam the other day while I was standing by the plane, and I asked him for some help with this problem. Seems you have to install the front baffle so that it hits the cylinder right at the "parting line" where the cylinders are cast. When I looked at mine they (both #1 & #2) were about hitting the cylinder cooling fins 3/4" higher than that line, so I was losing that fin area for cooling. I now have lowered those baffles to the parting line,(although it required additionnal fiberglass work) and hope to test fly it tomorrow.
I'll let you know how it turns out.

Well, I am still looking for answers to the cooling issue. The changes I made before my last post helped, but #3 & #4 are still running around 410-420 at cruise. I still can't run the engine above 2100-2200 RPM without getting those 2 cyl's above 400.
I am going to look at exit air issues next and see if I can optimize/augment that area of the equation.

Cooling solution?

Merle,

What did you finally end up doing or finding as the cause of the two cylinders running hot? Going through the same thing with a -4 right now and looking at options short of adding a cowl flap.

Thanks!

SJ Cowl and Plenum on RV10

Guys,

I've been through the ringer with my 10 and the SJ cowl and plenum. This is my 2nd SJ cowl, the first was with 5" inlet rings, then I had Will James make another with 6",, still very warm on left side, #2, #4 and #6. I relocated my large SW oil cooler 10361S to directly behind #6 as Sam recommended,, oil runs to 210-218 and my #2 is the hotest at usually 408. I've had it up to over 425 when breaking my engine in, however I CANNOT lean as I need the fuel to cool, so I see 17 gph at best and if at lower allitudes, I'm closer to 20 GPH.

I've got 158 hrs on my 10 now and after this next trip, I'm opening the inlets to 8" rounds that I bought from Alan Bikle at OSH 2010, mod the cowl and plenum to see what happens. I've also got an A/C compressor on the left side, so I"m not going to split line the 8" inlets, I"m going to have them higher on top by a couple of inches to allow room for the A/C compressor and cut-reshape the plenum for now. I've also got Chri Frisella of Bonehead Composite on line for the 4" NACA scoop that I'm seriously considering installing on the lower left cowl and re-locating my oil cooler again with it's own seperate inlet and exit air.

I'm determined to get this thing cooled and working,, some of my building and flying buddies tell me why not just order a standard Van's 10 cowl,,, I like the looks of the round inlets and this 2nd cowl is nicely fitted on my plane now, so I'm going to start the old plow boy method of trial and error. I cannot do any worse than what I've got now!

Kenny Gene
Wichita KS area
RV 7a 294TC (AWC 9-07) 680 hrs sold 11-11
RV 10 484TC (AWC 10-10) 158 hrs

Kenny Gene said:

Guys, I've been through the ringer with my 10 and the SJ cowl and plenum..(snip)...so I'm going to start the old plow boy method of trial and error.

Click to expand...

Perhaps some diagnosis is in order before cutting the patient. Why not get upper and lower plenum pressure measurements, and an outlet temperature?

BTW, can you see any of the AC installation looking through the left inlet?