Uneven CHT Temperature Profile Stroker 340

[turbopilot]

Bob,

Good work! The technique you used is a common one in the homebuilding community and is called a "baffle fence" and is used to balance front-to-rear temps. It has been on our list of fine tuning tweaks but we haven't gotten around to it yet. I asked Ben Hodges to try this some time ago as I suspected it would improve things but he's been very busy lastely. The aluminum tape is the most common and easiest method for testing, and frankly it can work indefenitely but it's not the best looking solution -- we need to find something less attention getting.

We we need to do is standardize a set of dimensions which would need to be done over at least several aircraft. If other owners would care to try this and then measure the height of the baffle needed to get the best f/r balance we'd appreciate it. I believe you'll find though that what the optimum height will vary a bit from plane to plane. No matter, I'll make sure that some sort of fence solution gets moved up in the R&D queue. We've made lots of little tweaks in the plenum system so far and now have oil temps well under control where the early ships were a bit warm, now we need to tweak this balance.

Thanks Bob!

Randy, fresh off the same task in a Cirrus TN22 Perspective. Combination of baffle changes and injector changes dialed in the CHT's to small differences. We started about 50 dF high to low and slowly worked our way down. Goal was to keep warmest cylinder south of 380 dF all the way to 17,500 up to a +15 C ISA day.

The Stroker 340 is still evolving I am sure we can get the CHT's lower with a little work.

[turbopilot]

Update on our continued testing to balance CHT temperatures. Been experimenting with various combinations of aluminum tape on the front fins of #1 and #2 cylinders.

We now have a pretty even spread operating at the placard max continuous power settings.



These temperatures happened with tape in the position shown below. Note I have put tape over the upper cowl inlets:



Next challenge is getting CHT's even in climb. Here is a picture taken after 2 1/2 minutes of climbing at 100 mph and full power. There is a 82 degree difference coolest to warmest cylinder. #4 is not getting enough air in a climb.

[turbopilot]

Just an update as I continue to understand the Carbon Cub. Weather has not been great on the Central Coast of California this week. Wet and windy so I not too much flying. Going to stay windy for a while.

For the last week or so I have been trying to make sense of the instruments on board particularly as they relate to POH values for cruise. Finally discovered that things were not making sense because I have a cruise prop and it looks like POH was done with a climb prop. So the previous posts I have made suggesting that I was running at the placarded RPM settings were misleading as the placard does not apply to my aircraft. Looks like the cruise prop turns around 150 to 200 RPM slower than the climb prop.

Able to make a flight today where I "backed" into the cruise RPM by setting up the fuel flow and manifold pressure which should correspond to POH limitation of maximum continuous power. So here is a screen shot of that attempt. Everything makes sense now with the prop turning around 200 RPM slower at this altitude than the placard limitation. The Dynon crudely calculates percent power by keying off the high RPM limit setting in the software which is set at 2,700 RPM. I need to change that and the percent power displayed should be close.



Running at the true horsepower limitation for maximum continuous power yields slight lower CHT's but not by much as compared to my previous screen shots in this thread with the engine running around 6 gph, +50 ROP. I would guess those screen shots were really taken when the engine was developing around 60% power.

My education continues.

[turbopilot]

Aluminum foil tape seems to do an amazing job of equalizing temperatures on the Stroker 340. Here is a run today with CHT's all within 5 dF of each other.

Note OAT was 52 dF which is very cold for southern California in May. Sure don't like that oil temperature at 150 dF. Anybody know if the vernatherm is adjustable on this engine? No mention in the maintenance manual or engine overhaul manual.

[TheCubWorks]

Hi can you take another picture of panel chts iin flight while appliying carburetor heat.
Sometimes patt of a cht sprrad is due to un even fuel distrubtion. The carburetor heat helps distribution for trouble shooting purposes.

[glickle]

Just a FYI during all this great tech testing by Bob et al , to add that I have just passed 200 hours on the CC 340 and running perfectly and while I do not have the glass cockpit monitoring, I can say that the cooling is sooo good that I still have about 3 inches of the oil cooler covered with the aluminum tape in 85 degree weather here in Florida to get my oil temps to run 180-200. I have also kept very accurate records of fuel and oil consumption over the 200 hours and it works out to an average of 7.3GPH fuel and .1 Qt/hr oil. Regards Gary

[turbopilot]

A little background about why I like to see CHT's south of 380 dF in all phases of flight. Most everything I know about aircraft piston engines I have learned from George Braly at Tornado Alley. Below is a graphic George uses in his APS classes. It plots the strength of aluminum used in aircraft engines versus operating temperatures. As the temperature of a cylinder increases above 200 dF it progressively suffers a loss of strength. At 380 dF a cylinder has lost 20% of it's strength. At the manufactures red line cylinders have lost 60% or more of their strength.

So why would engine manufactures allow such high CHT red lines? Complicated question with lots of trade offs. In the case of TCM they make more money selling after service parts than new motors. Selling the razor versus the razor blades. So this is obviously one answer. In my experience running TCM motors at high CHT's (ie using manufacturers recommendations for operating limits) the cylinders will normally fly out of the warranty period before failing. Could be the temperature limits are set with a financial consideration given to operating limits.

Whatever the answer no one really disputes that these motors should be operated at the lowest achievable CHT to enhance engine life and reliability. 380 dF seems like a fair compromise.

[seastar]

I added some aluminum tape to both front cylinders and the oil cooler.
This is the result.
I need to add some more.
Carbon Cub 010.jpg

[randylervold]

Little more on the right (#1 & #3), a little less on the left (#2 & #4). If you can get the f/r spread to within 20° you're there.