Cylinder Head Temperatures

[Helidesigner]

What kind of temperatures are people seeing on Bearhawks with 540 engines? After about two minutes at full power, ~85 kt climb, on an 80F day I hit 400F on #2 with the others about 15F to 30F behind.

Mark

[Battson]

Hi Mark,

I agree that #2 seems to be the hottest in many installations, mine included.

It all depends on airspeed and ambient temp, also leaning and RPM.
On a hot day, like 80F, with cowl flaps full open, at 75kts I can do about 5 minutes at WOT @ 2500RPM before it red-lines at 400F. Cylinder #2. If I climb at about 100kts it stabilises about 385F. Also using a lower RPM or richer mix helps.

At the moment (mid-winter) it's about freezing outside at 1000ft. With flaps open it stabilises about 370F for an 80kt cruise-climb.

In the cruise, I see about 350F for your 80F day, and if I run LOP it's more like 320F. In winter those reduce to 330F and 300F respectively.
On a long cruise descent, I often see them drop as low as 280F - 250F.

Jonathan

[bearhawk2015]

My #2 cyl also runs hotter, especially in a climb, it'll be around 400 in a long climb, but I usually pull power back after take off and hardly get above 1500 agl, cruising around they usually settle in around 360 degrees and 100 mph, and have about a 10-15 degree spread between all the cylinders

[bearhawk2015]

I think your temps are probably normal for the 540 installation

[marcusofcotton]

It all depends on airspeed and ambient temp, also leaning and RPM.
On a hot day, like 80F, with cowl flaps full open, at 75kts I can do about 5 minutes at WOT @ 2500RPM before it red-lines at 400F. Cylinder #2. If I climb at about 100kts it stabilises about 385F. Also using a lower RPM or richer mix helps...

Richer mixture??? Shouldn't you already be full rich for a WOT climb? (Assuming your not speaking of being at high elevation.)

[Battson]

My comment was a generality, but I can see how it reads the way you've read it.

Any time over 75% power Lycoming recommends using full rich mixture. However, throttle position is only one factor, many other things effect % power.

[Mark Goldberg]

400 degrees and a little above on a climb is not too bad. I have had to increase the bottom opening a little on my Patrol and more recently on my LSA. Bob says 1.5 more outlet area than inlet area.

Mark, you might be fine until you travel to Texas when its hot or the south in the summer. Mark

[DesertBearhawk]

What am I gonna see in Vegas when it's 115?

[Battson]

The main thing is to manage the engine power / mixture / RPM / airspeed / (cowl flaps?) to ensure the temperature stays below 400F. Much above that temperature, the aluminium which the cylinders are made of starts to become considerably softer with every degree hotter, and that isn't good for anybody except the guy selling spare parts!

[Helidesigner]

Thanks for the replies. It sounds like I'm on average. I think I will start performing cruise climbs more in the ~95 kt speed range and see where the temperatures stabilize.

[Mark Goldberg]

Lycoming says no continuous operations above 450 CHT. Mark

[Battson]

I think it's important to add the following note to the manufacturer redline limits, in the interests of caring for your engine: See the link below, article written by Mike Busch.

http://www.avweb.com/news/savvyaviat...g198162-1.html

"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.)