CHT for Cyl 2 and 4

[Andy95W]

2 hours ago, Ghostrider said:

My G3 in flight

That one is real nice.  (I agree with Bob BTW- 13.3 volts is a bit low.)

[DXB]

14 hours ago, Ghostrider said:

then What CHT's do people see on the C's ? with a monitor on all 4?  if 420-440 is normal on climb and 396-400 in cruise for the left bank (2 and 4) then so be it.. but I want to know this is normal.  I get they are all high.. but HOW high....

 

Thanks

FWIW, I have a '68 C with full 8 temp probe setup that serves as primary for CHT.  I have gotten the baffle as tight as I can get it over the past two years.  My initial fuel flow in WOT climb is 17-18 gph, and I have excluded other causes of high CHTs like timing, oil cooler/vernatherm valve function, intake leaks, and exhaust leaks blowing on a probe.  I have pulled reconditioned 3 cylinders for exhaust valve or ring issues under my ownership in the past 3 years.  Even after such invasive engine work, the overall CHT profile has remained exactly the same, with only minor improvements coming from meticulous  work on my previously leaky baffle.  I have bitched ad nauseam about my CHT issues on this site, and I am now convinced it is an intrinsic flaw in the baffle design on the C.  

In my case, #2 and #3 run similarly hot in climb - in the summer I can usually limit them to under 430 on a hot day if I drop nose to 120mph as soon as practical, but keeping those two below 400 is a lost cause.  In cruise in summer, #2 is the only problem child, running 20-30 hotter than the next hottest cylinder, even though this is far from the leanest cylinder.  At 22.5/2500 while cruising at 7500msl,  it typically makes me burn an extra gph than necessary (10.5 vs 9.5)  to keep my #2 CHT from climbing beyond the 380s.  This problem is less limiting outside of the summer months.  

@Sabremech was busy optimizing a beautiful and potentially economical new cowl and baffle design for our C models and pursuing an STC for it.  This seems like the way to go, but I have not kept up with his progress recently.

[Sabremech]

1 hour ago, DXB said:

FWIW, I have a '68 C with full 8 temp probe setup that serves as primary for CHT.  I have gotten the baffle as tight as I can get it over the past two years.  My initial fuel flow in WOT climb is 17-18 gph, and I have excluded other causes of high CHTs like timing, oil cooler/vernatherm valve function, intake leaks, and exhaust leaks blowing on a probe.  I have pulled reconditioned 3 cylinders for exhaust valve or ring issues under my ownership in the past 3 years.  Even after such invasive engine work, the overall CHT profile has remained exactly the same, with only minor improvements coming from meticulous  work on my previously leaky baffle.  I have bitched ad nauseam about my CHT issues on this site, and I am now convinced it is an intrinsic flaw in the baffle design on the C.  

In my case, #2 and #3 run similarly hot in climb - in the summer I can usually limit them to under 430 on a hot day if I drop nose to 120mph as soon as practical, but keeping those two below 400 is a lost cause.  In cruise in summer, #2 is the only problem child, running 20-30 hotter than the next hottest cylinder, even though this is far from the leanest cylinder.  At 22.5/2500 while cruising at 7500msl,  it typically makes me burn an extra gph than necessary (10.5 vs 9.5)  to keep my #2 CHT from climbing beyond the 380s.  This problem is less limiting outside of the summer months.  

@Sabremech was busy optimizing a beautiful and potentially economical new cowl and baffle design for our C models and pursuing an STC for it.  This seems like the way to go, but I have not kept up with his progress recently.

Getting ready to start on an F model in the next couple of weeks. This will give me the data I need on the E & F models. As long as my FSDO will do field approvals, I'll keep installing my mod that way as I can get them done now versus who knows how long for an STC.

Thanks,

David

[neonbjb]

How is your lower cowl sealing?

A misconception many have with aircraft engine cooling is that it is all about sealing up the baffling / doghouse / whatever - when that is, in fact, only half the equation. The goal is to create a pressure differential between the upper and lower cowling which forces the air through the cylinder cooling fins. When I purchased my M20C there were huge holes in the lower cowling - the worst of which was a cooling hole for the old generator which had had it's hose disconnected but was not plugged. This meant the poor plane had a ram air hole in the lower cowling which was pressurizing it with air and completely defeating the pressure differential. Another big offender for my plane was the alternator install did not have proper baffling surrounding it which resulted in large holes allowing air around the prop and into the lower cowling. Finally, there were considerable gaps between the oil cooler's mounting plate and the cooler itself.

Going to town with some silicone sealant, and baffling material in these areas dropped my CHTs by a little over 20 degrees at their hottest.

That being said, my M20C can still get up to 420 or so on #2 with a lot of heat soak and a steep climb. Just the nature of the beast on these planes for whatever reason.

[Andy95W]

37 minutes ago, neonbjb said:

How is your lower cowl sealing?

A misconception many have with aircraft engine cooling is that it is all about sealing up the baffling / doghouse / whatever - when that is, in fact, only half the equation. The goal is to create a pressure differential between the upper and lower cowling which forces the air through the cylinder cooling fins. When I purchased my M20C there were huge holes in the lower cowling - the worst of which was a cooling hole for the old generator which had had it's hose disconnected but was not plugged. This meant the poor plane had a ram air hole in the lower cowling which was pressurizing it with air and completely defeating the pressure differential. Another big offender for my plane was the alternator install did not have proper baffling surrounding it which resulted in large holes allowing air around the prop and into the lower cowling. Finally, there were considerable gaps between the oil cooler's mounting plate and the cooler itself.

Going to town with some silicone sealant, and baffling material in these areas dropped my CHTs by a little over 20 degrees at their hottest.

That being said, my M20C can still get up to 420 or so on #2 with a lot of heat soak and a steep climb. Just the nature of the beast on these planes for whatever reason.

+1

[Marauder]

How is your lower cowl sealing?
A misconception many have with aircraft engine cooling is that it is all about sealing up the baffling / doghouse / whatever - when that is, in fact, only half the equation. The goal is to create a pressure differential between the upper and lower cowling which forces the air through the cylinder cooling fins. When I purchased my M20C there were huge holes in the lower cowling - the worst of which was a cooling hole for the old generator which had had it's hose disconnected but was not plugged. This meant the poor plane had a ram air hole in the lower cowling which was pressurizing it with air and completely defeating the pressure differential. Another big offender for my plane was the alternator install did not have proper baffling surrounding it which resulted in large holes allowing air around the prop and into the lower cowling. Finally, there were considerable gaps between the oil cooler's mounting plate and the cooler itself.
Going to town with some silicone sealant, and baffling material in these areas dropped my CHTs by a little over 20 degrees at their hottest.
That being said, my M20C can still get up to 420 or so on #2 with a lot of heat soak and a steep climb. Just the nature of the beast on these planes for whatever reason.

This was one of the areas David did spend some time showing us when we saw his plane last year at Oshkosh. He spent a good amount of time address the area behind the prop and the area just in front of the engine. There is a lot of air lost to those holes and when Bob Belville and I looked at his design upclose, it is clear he was aware of the issue and addressed it.


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[Ghostrider]

19 hours ago, Marauder said:

 

 

This was one of the areas David did spend some time showing us when we saw his plane last year at Oshkosh. He spent a good amount of time address the area behind the prop and the area just in front of the engine. There is a lot of air lost to those holes and when Bob Belville and I looked at his design upclose, it is clear he was aware of the issue and addressed it.


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First Thank you for all the information and pointing out the Bus Voltage... I will look more closely at that.  I will also go look at the plane after I get off work to really look at the lower area of the cowl.  I have checked the seal but now I will look at holes in the lower area and around the oil cooler. 

If anyone wants to look at my flights and the temps or just data from the G3 here is the link

https://savvyanalysis.com/my-flights/1003338/c58cc8de-cab6-407e-b661-cffa918e3388

 

[DXB]

FWIW here's a pic of my lower cowl dropped to reseal around the starter and alternator.  The big gaps are closed with the riveted new baffle material placed by the A/P. I then meticulously sealed the smaller gaps, particularly around the tops of the starter and alternato,r with hand cut pieces of baffle material and silicone, requiring considerable contortion of my hands .  It's particularly a PITA to seal around the oil return tube that is between the alternator and prop.  I've spent many hours futzing around with this and other parts of the doghouse, and I'm convinced the baffle is tight now.  Sadly this effort and expense seems to have made little or no difference in my CHTs.  

 

[Ghostrider]

19 minutes ago, DXB said:

FWIW here's a pic of my lower cowl dropped to reseal around the starter and alternator.  The big gaps are closed with the riveted new baffle material placed by the A/P. I then meticulously sealed the smaller gaps, particularly around the tops of the starter and alternato,r with hand cut pieces of baffle material and silicone, requiring considerable contortion of my hands .  It's particularly a PITA to seal around the oil return tube that is between the alternator and prop.  I've spent many hours futzing around with this and other parts of the doghouse, and I'm convinced the baffle is tight now.  Sadly this effort and expense seems to have made little or no difference in my CHTs.  

 

Is that a Power Flow Exhaust I see?  Performance Review???

[Andy95W]

18 minutes ago, Ghostrider said:

Is that a Power Flow Exhaust I see?  Performance Review???

Before you get a PowerFlow exhaust for your M20C, check with @pmccand. He will advise against it, and may sell you his for the right price.

[DXB]

1 hour ago, Ghostrider said:

Is that a Power Flow Exhaust I see?  Performance Review???

Nope - just the beautiful '68 original exhaust - still problem free.  I've heard the Powerflow can reduce CHTs anecdotally but want more data points before going down that road.

[MIm20c]

2 hours ago, DXB said:

 Sadly this effort and expense seems to have made little or no difference in my CHTs.  

Not the type of feedback I was looking for.  I was predicting a healthy improvement from sealing around the starter because of the pressure differential increase. 

[M20D6607U]

On 8/7/2017 at 11:03 AM, neonbjb said:

How is your lower cowl sealing?

A misconception many have with aircraft engine cooling is that it is all about sealing up the baffling / doghouse / whatever - when that is, in fact, only half the equation. The goal is to create a pressure differential between the upper and lower cowling which forces the air through the cylinder cooling fins. When I purchased my M20C there were huge holes in the lower cowling - the worst of which was a cooling hole for the old generator which had had it's hose disconnected but was not plugged. This meant the poor plane had a ram air hole in the lower cowling which was pressurizing it with air and completely defeating the pressure differential. Another big offender for my plane was the alternator install did not have proper baffling surrounding it which resulted in large holes allowing air around the prop and into the lower cowling. Finally, there were considerable gaps between the oil cooler's mounting plate and the cooler itself.

Going to town with some silicone sealant, and baffling material in these areas dropped my CHTs by a little over 20 degrees at their hottest.

That being said, my M20C can still get up to 420 or so on #2 with a lot of heat soak and a steep climb. Just the nature of the beast on these planes for whatever reason.

I have the old generator hole that is not plugged also. I will block it off. I talked to the service manager at LASAR and he said the design of the doghouse is flawed, and to extend the cowl door links and climb out full rich at 120 mph. I also found my carb heat was adjusted wrong and half deployed. My engine seems to cool quicker though still climbs to low 400's on takeoff.  My engine builder says it's not a problem. A lot of great advice here! I did install a JPI EDM 800 with fuel flow. Very nice unit. 

[jamesm]

Your Insight  G3 reports is similar to mine,  Cylinders 2 & 4 are usually are the cylinders  get the hot the  quickest. With me....  the  hottest  CHT 's that are  reported is not always related to  outside  air temp (OAT). A couple  flights a go in the middle of summer in some of the hotterst day's for  the PNW , all Cylinders  temps stayed in the green on climb out.   When compared that to some of the flights  that I did in the winter time where it was  cold  out . Where I had pre-heat the engine to start it. I had the CHT's  2 & 4 in the  yellow 430ish dof  range.   I was monitoring my CHT's every flight  but sort of stop doing it so frequently. I can say I opened up  the Cowl Flaps exit air opening that seems to help but it is not definitive. I would hope that my procedures and technique on climb out   aren't so erratic  causing the high CHT's . But on the other has  If it was my procedures and technique then I would know the source of the CHT problem.

I just wonder if it has more to do with how Insight   does their  sampling rates on  the G series engine monitors   for their thremocouples.  If you were to  compare  Insight Theromocouple  philosophy  to JPI or  EI engine monitors Theromocouple  philosophy.     Insight uses different ranges thremocouples , I think it is Type J  (blk) for CHT and  Type K (yel) for EGT whereas  JPI & EI   Engine monitors uses a one size fits all approach for their Theromocouple  philosophy. I believe JPI and EI  uses Type K (Yel) for both CHT and EGT thermocoulples .  Then EI does something goofy  their thermocouples by using the engine block as the ground return for their thermocouples.  Not sure how Garmin and others manufacture  do their Engine thermocouples.

 

 

James '67C

 

Edited August 13, 2017 by jamesm