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Air Flow and #6 CHT temp Tip

rvanstory

Well Known Member
For months I've tinkered with several things to try to get my #6 cylinder CHT under 400 in climb. All other cylinders were great, but #6 in this heat wave would get to 415 in climbout (at 130 KIAS).

I had already removed both front air dams during phase one for cooling. Last week, I decided to test adding the air dam back to #2 cylinder. For a "TEST" I just used aluminum tape. It made ALL the difference I needed. In climb at 120 KIAS (steeper than normal for me) #6 CHT stayed below 400.

Today, put back in a permanent air dam on #2 cylinder. Same result on test flight. #6 CHT under 400 on climbout AND #2 to #6 CHT spread was within 2 degrees during cruise phase. PERFECT!!

If you're still building your 10, I'd re recommend making your air dams "removable" instead of riveting them in. I think it'll make it much easier for you to tinker with it as needed.
 

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That's great! Gotta be a load off your mind. But you got some 'splaining to do! I'm trying to figure out why that worked. While we're here, what made you try putting the baffle back in after all that time? If you can't explain the theory, maybe one of the resident voices of knowledge will chime in.

I've got a similar issue with my IO-360 and the #4 cylinder getting hot, but only during the initial climb from the runway. The original air dams on the front cylinders from Van's are still in place. I'm not trying to hijack your thread...just trying to learn more about how that worked.
 
On my ~42 hour engine, the two hot cylinders are 3 and 6. I already have an air dam on #2 and have raised its temp to parity with #1. Surprisingly #'s 4 and 5 are the low ones, with #4 being 40F cooler than #6. In cruise, I'll see something like this, leaned:

#1: 380
#2: 380
#3: 390
#4: 355
#5: 360
#6: 390

I spent part of Sunday using jeweler's files to remove casting flash on #3 and #6, but I haven't flown it since. I assume I'll get a little improvement from that effort.

The real question is how to rob air from #'s 4 and 5 to better cool the rest. I haven't worked through that at this time.

The good thing is the airplane is relatively efficient, given that I haven't yet balanced the injectors. (FYI, 1 and 4 are the ones that go lean first). I'm seeing 170-171 knots at 9500' (DA well above that) and ~61% power (per the G3X) burning ~13-13.5 GPH. I figure that'll only get better when I balance the injectors.
 
That's great! But you got some 'splaining to do! While we're here, what made you try putting the baffle back in after all that time? If you can't explain the theory, maybe one of the resident voices of knowledge will chime in.

There are others on this forum that may can explain it better than me. But I tried it because I was told the dams were there to force more air FROM the front (#2) to the back (#6). (Sometimes needed if front cylinders run too cool). #2 was cool enough that raising its temps a little didn't concern me.

Not sure WHY it worked, but it seems to have done the trick for me.

My main point to others in build phase, is to install these with screws and nuts or nut plates so they are easy to remove and replace. Will make "experimenting" much easier.
 
There are others on this forum that may can explain it better than me. But I tried it because I was told the dams were there to force more air FROM the front (#2) to the back (#6). (Sometimes needed if front cylinders run too cool). #2 was cool enough that raising its temps a little didn't concern me.

+1

The purpose of the dam is to move cooling air from the fwd cylinder rearwards and let it flow to the rear cylinder(s).

Larry
 
The best configuration of air dams in front of Cyl 1 & 2 seems to vary from plane to plane. Mine are removable and over 200 hours I have cut them back and finally removed them completely. The best configuration for me seems to be no dams.

This is a pretty typical flight for me on a hot day ( for Michigan ) : https://apps.savvyaviation.com/flights/6026851/f6c7ae22-2ab5-48df-8207-43e9720021bf

The Cyl temps get near 400 shortly after takeoff and settle nicely in cruise running LOP. There is a significant spread in temps, but only during climb-out.

I noticed the OP has Cyl 2 & 6 running quite a bit hotter than the rest with the air dam in front of Cyl 2. I am not saying that is a problem, just not sure why.
 
Removing casting flash definitely helped #6 on my engine. #3 wasn't helped as much and now stands alone as the hottest cylinder.
 
What did that change do to your oil temp?

-Marc

There are others on this forum that may can explain it better than me. But I tried it because I was told the dams were there to force more air FROM the front (#2) to the back (#6). (Sometimes needed if front cylinders run too cool). #2 was cool enough that raising its temps a little didn't concern me.

Not sure WHY it worked, but it seems to have done the trick for me.

My main point to others in build phase, is to install these with screws and nuts or nut plates so they are easy to remove and replace. Will make "experimenting" much easier.
 
2 and 6 are my hottest as well. Seems to be the common complaint. Can it be prop rotation makes 2/4/6 worse that 1/3/5 ?

A key part of airflow into the upper plenum is related to the bulge that Van's has you install on the upper cowl to smooth the incoming air. There doesn't seem to be a natural place for it to fit exactly and the instructions are vague. It is my speculation that small variances in the installed location of that piece account for the variability that we see in the field. Just a guess. If they could add several knots by reshaping the wheel pants, it would stand to reason that differences here could change the turbulence seen at the inlet and therefore air distribution.
 
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This is where I really like the design of the RV14 air dams, they are installed with nutplates so you can easily remove and adjust them. If I was building again, I'd make sure to make them removable.
 
Having same issue , around 25 deg higher than all other cyliinder
Has anyone tried to open another fin hole in the bottom cowl? to help air flow?
Also, changing the angle of the fins? maybe pointing them up?
 
Wonder if the big duct for oil cooler on the left side is why 2/4/6 are hotter as too much air escapes there vs going past the cylinders ?
 
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