Uneven CHT Temperature Profile Stroker 340

[turbopilot]

Since my Carbon Cub arrived from the factory I have noticed a very uneven distribution of CHT temperatures in cruise. Here is a picture of my airplane in cruise.



You will note a 75F difference between #1 CHT (the coolest) and #3 CHT (the warmest). #1 cylinder is the furthest forward in the engine on the right side and with this installation has a large area of cooling fins right in the path of direct ram air. Looking to even out the temperatures (ie reduce the temperature of the warmest cylinder), used some aluminum tape to block direct airflow on #1 cylinder with the hope getting some more cool air to the back cylinders, #3 and #4.



Here is what it looks like with the foil in place.



As you can see the #3 CHT has come down by 20 degree while #1 has warmed up to a temperature comparable with the other cylinders.

Most engine installations I have seen place a baffle in front to the fins of the forward cylinders directly facing the airflow. Any reason we don't have on in the Carbon Cub?

[seastar]

Looks like we need some additional work on the baffels.
Thanks for the effort.
My airplane is supposed to be delivered at the factory on the 4th.
Probably too late to get anything done about this now.
How about a picture of your AL tape installation.
Bill

[Centmont]

Great information Bob....please keep us posted! Ralph

[rfriend]

Nice deductions and implementation Bob, I hope that there will be actions taken in the company to improve the airflow in future production due to your observations. Your work is appreciated. Future owner CC 141.

[turbopilot]

Nice deductions and implementation Bob, I hope that there will be actions taken in the company to improve the airflow in future production due to your observations. Your work is appreciated. Future owner CC 141.

Just my old home builder curiosity. In my airplane #1 is the coolest and #3 is the warmest (thus the limiting cylinder as temps climb). Looks like covering the front fins of #1 just allows cooler air to flow over #1 and help #3.

[Centmont]

This is a pretty small sample size. How many other Carbon Cubs have EGT montoring and see the same problem? If it is consistent, then the airflow really does need some tweaking...if it is not, then this could, for some reason, be unique to Bob's aircraft. If you are a Carbon Cub owner and see the same pattern, please weigh in. R

[turbopilot]

This is a pretty small sample size. How many other Carbon Cubs have EGT montoring and see the same problem? If it is consistent, then the airflow really does need some tweaking...if it is not, then this could, for some reason, be unique to Bob's aircraft. If you are a Carbon Cub owner and see the same pattern, please weigh in. R

I think CubCrafters may be way ahead of us on this issue. Got the idea from this CubCrafter picture doing tuff testing. Note something shiny in the right cowl inlet.

[seastar]

Without the Dynon panel that monitors all the cylinders no one would know the temps were uneven.
I wonder how many have been built with the capability to monitor all four?
Teething problems?
Bill

[Bill]

About CHT's, my SS is a bit of an odd ball, #92 was the first "production" model. It was built with a stock Lycoming A2B 150 HP (my choice NOT Jims). #92 has the same plenum & overall install as the first ones, don't know what changes have ben made to date.
So in some ways it is an orange in a basket of apples, but here are my numbers from today.
OAT 44F
2150 RPM @ 21.2 MP IAS 96mph alt 900 ft
EGT's all close to 1450
CHT #1 347 #2 336 #3 367 #4 390
I think with my OAT's, 390 is pushing it in a lazy cruse. I'll talk to Becky Tuesday morning.
Hope this helps someone, Bill......................

[randylervold]

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!