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specific question about climb out cht

erikpmort

erikpmort

Well Known Member
What is YOUR personal limit for how hot you will let your CHTs get before you put the nose down, richen up etc when climbing out?

AND

How long can you climb at say 100 kts at max power settings without exceeding that number?

I know there are a lot of variables with the second one, but just trying to get a feel for how much RVs have to manage temps on climb out.

AND one more

What Engine gauge is the one that causes YOU to make a change- if its not CHT (mine is cht, my oil stays plenty cool which is less than 185 this time of year)

btw- i have read plenty of posts on what the acceptable limits actually are... i'm trying to make this more specific

THANKS!
 
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I chicken out at 420. I've only seen that once however, and that was a hot day and after a quick refuel stop and extended climb. In that case I knew I was very close to ToC and was going to go LOP, which I have found to be very effective at reducing temps. Within minutes I was well under 350 and dropping.
 
415

I have a hot #3 that I have been troubleshooting this year, it used to be #1 and I removed the baffle plate and the problem moved to #3. Always runs up into the 400's on take-off and I have to power back and flatten the climb. Normal CHT's in cruise are fine (320 -340) although the right side runs about 20 deg hotter than the left.
 
erikpmort said:
What is YOUR personal limit for how hot you will let your CHTs get before you put the nose down, richen up etc when climbing out?

AND

How long can you climb at say 100 kts at max power settings without exceeding that number?
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I don't like to let CHTs above 420, and am uncomfortable with anything over 400.

Mid-winter at light weight, I can and have climbed straight from a field at 1300' MSL to 12,500' at around 90kts. Late summer at gross weight requires a different profile for engine cooling considerations.
 
Faster

If you guys will try 120 knots/138 MPH, you'll have better forward visibility, cooler cylinders and still be climbing over 1,000 FPM. We cruise climb the -10 around 130 knots/145 MPH and works well all the time. With a FP cruise prop, you'll turn more RPM's, making more power as well.

Best,
 
pierre smith said:
If you guys will try 120 knots/138 MPH, you'll have better forward visibility, cooler cylinders and still be climbing over 1,000 FPM. We cruise climb the -10 around 130 knots/145 MPH and works well all the time. With a FP cruise prop, you'll turn more RPM's, making more power as well.

Best,
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That's exactly what I do. Vx, if needed until clear of obstacles, then lower the nose to 120 knots until 1000' AGL. After that I typically set up a 500 Ft/min cruise climb to whatever altitude I need.

The OP didn't mention if they have a carb or fuel injection. WOT on the carb just dumps fuel to maximize cooling. (I don't know about FI.) If you pull back on the throttle, the fuel flow goes down but the CHT's may go up as a result. Typically it is best to keep everything full in while climbing. However, when I start the cruise climb portion of my ascent profile and increase my forward speed, I will pull back the throttle to 75%.
 
pierre smith said:
If you guys will try 120 knots/138 MPH, you'll have better forward visibility, cooler cylinders and still be climbing over 1,000 FPM. We cruise climb the -10 around 130 knots/145 MPH and works well all the time. With a FP cruise prop, you'll turn more RPM's, making more power as well.

Best,
Click to expand...

Oh, for sure. However, I think the OP's question was more about limits and such rather than normal operations.
 
My target number for high CHT is 400 and it is not unusual to see 403-405 at which point I lower the nose to bring them down. Once they come to 390 range, I can resume my climb and will stay that way usually till I have arrived at my target altitude.

My CHT has been the only limiting factor in extended climb as my oil temp has always been very good, even on the cooler side.
 
My CHT alarm point is set at 400, and it has only tripped once (at 402F) on a l-o-n-g hot climb last summer. If I see 390 on long summer climbs, I flatten it a bit and throttle back (still ROP) to stay under 400. Flattening the climb means 600-900 fpm, otherwise the Nine will climb all day at around 1500.
I only see those higher temps with a passenger and near full fuel. Solo with full fuel let's me climb at any rate in any summer OATs.
 
thanks

very good info thanks- I believe it is also my #3 that is the hottest- cools down quick when I lower the nose or pull the power back a bit but id like to be able to full power climb longer without issues. especially considering its not a hot time of year. I haven't tried a full rich full power climb though- is that advisable at my altitude? I usually lean on the ground for peak rpm then richen a couple 1/4 turns. My altitude is 4500. Thanks
 
Bavafa said:
My target number for high CHT is 400 and it is not unusual to see 403-405 at which point I lower the nose to bring them down. Once they come to 390 range, I can resume my climb and will stay that way usually till I have arrived at my target altitude.

My CHT has been the only limiting factor in extended climb as my oil temp has always been very good, even on the cooler side.
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That's pretty much how I limit my CHTs since I did the Dan Horton and Toolbuilder mods for the #2 and 3 cylinders. This typically means climbing out around 750 fpm except during the hotter parts of the summer. I'm not done experimenting with improving the cooling. My goal is to be able to do Vx climbs in hot weather and never have CHTs exceed 400.
 
420. I'd like to change that to 400, but my #6 Cyl has proven to be stubborn. I've been doing some baffle tweaking lately trying to get all 6 Cyl relatively close, I have managed to get all of them down with the exception of #6 which is still 30deg hotter than the rest.
 
400 is my own limit? Why? Oil burns on the cylinder walls at anything over around 450, and causes them to glaze. The further away you are to the point where oxidation of the oil occurs the better. This will start a chain of events where the rings will pump oil and come into contact with the cylinder walls thus causing cylinder wall wear. Eventually a ring can carbon up and cause a hotspot on the skirt of the piston. I have a few of these in my junk pile....
 
I'm a Mike Busch devotee and in an article on AVWEB http://www.avweb.com/news/savvyaviator/savvy_aviator_59_egt_cht_and_leaning198162-1.html (and possibly in Sport Aviation) he wrote the following with regards to CHTs:
Why do you recommend keeping CHTs at or below 380°F, while TCM sets its CHT red line at 460°F and Lycoming sets it at 500°F? Aren't you being excessively conservative? ​
Both TCM and Lycoming specify CHT limits (460°F and 500°F, respectively) that should be considered emergency limits, not operational limits. Allowing your CHT to get anywhere close to those values for significant periods of time will most likely result in premature exhaust-valve problems and increased incidence of cylinder-head fatigue cracking. I do not like to see CHT above about 400°F, which is the temperature at which the aluminum alloy from which your cylinder head is made loses one-half its tensile strength. (The strength decreases rapidly as the temperature rises above 400°F.) For legacy aircraft, I recommend a maximum target CHT of about 380°F just to provide a little extra cushion, and consider any CHT above 400°F to be grounds for "doing something right now" to get it down. (For modern designs like the Cirrus and Diamond, reduce those CHTs by 30°F or so.) The higher the power setting, the further away from 50°F ROP you need to stay to keep CHT at or below the target. As power decreases, this "zone to avoid" around 50°F ROP becomes narrower and narrower. When power gets down to about 60 percent, the avoidance zone disappears and you can run the mixture pretty much anywhere you please without overtemping or overstressing anything. (The APS folks refer to this zone to avoid as "the red box.") In my view, the best way to manage our piston engines is the same way we manage turbine engines: by limiting temperature, specifically by CHT (which is the best proxy we have for ICP). For best engine longevity, set the mixture somewhere that produces CHTs no higher than 380°F (or 350°F for modern designs). This can be very ROP, or slightly LOP, or even right at peak if the power is low enough. What's important is that you limit CHTs to a maximum target value. How you accomplish that is less important from the standpoint of longevity.
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I'm a firm believer in following his advice to do everything possible to keep CHTs below 400*F.
 
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If you are carbureted, your fuel distribution (therefore your CHT's) may vary greatly depending on whether you are WOT or partial throttle. I'm learning how to manage CHT's by going back and forth while in climb, though Bill Repucci's model above is pretty much what I try to do. On hot summer days (above 85F) #3 can get into the 400s, especially after a quick turnaround on the ground. I'm not real happy with this, but haven't entirely figured it out yet. It's not really a problem for me this time of year however, at least whenever OATs drop below 70F or so. Now my peak on #3 will usually stay below low 390s. Good luck.
 
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