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CHTs over 400 degrees F

Absolutely agree with you here.

As you write:

But in some aircraft you will see +400 in the climb and it just has to be managed sensibly. Quote

For me that would include:

What are my EGT’s during climb? Are they the same as during full rich at sea level take off?
Is the mixture rich enough during take off?
Are all controlls really all fully forward?

And then:
Is the baffle and baffle seal installation perfect?
Any air flow restrictions?

The myth is not that high CHT’s over 400F can occur, the myth is to call it normal.

Last Edited by complex-pilot at 14 Oct 13:23

complex-pilot wrote:

Strange things such as sudden detonation can occur in a cylinder when CHT’s are over 450F and the oil temps are say over 220F.
The cylinder will self destruct in 1-2 minutes.
Hot oil and hot CHT’s are both required for the detonation process to begin.

Do you mean detonation or pre-ignition? From what I’ve learned (e.g. from Mike Bush) detonation does not usually cause quick catastrophic failures. while pre-ignition does.

ESKC (Uppsala/Sundbro), Sweden

Normal = usual, typical, expected. Unless there is data to the contrary, we will just have to agree to differ

Even when all the items above have been verified OK, it is not abnormal to see temps above 400F in the climb. I see it in my Tiger, the OP sees it in his Archer, and I’m sure many others do (or they don’t know). That’s why we were taught to keep the nose down in the climb for cooling, long before the days of digital engine monitoring.

A further thought re the original post: I find that if the initial climb is at “cruise climb” speed, the CHTs remain lower and easier to control, whereas if the initial climb is at Vy allowing the CHTs to rise above 400F, they are more difficult to control in the climb even if the nose is lowered. This could be installation specific.

Last Edited by NeilC at 14 Oct 14:01
NeilC
EGPT, LMML

Baffles make a huge difference. Most GA planes have shagged baffles, not helped by the crappy materials normally used.

Administrator
Shoreham EGKA, United Kingdom

Airborne_Again

Do you mean detonation or pre-ignition? From what I’ve learned (e.g. from Mike Bush) detonation does not usually cause quick catastrophic failures. while pre-ignition does.

There are 2 forms of detonation:

Mild detonation, which is harmless
Then there is heavy run-away detonation. If not spotted immediately it will lead to pre-ignition and will destroy a complete cylinder assembly in mere seconds. The speed of it is most alarming.

Pre-ignition can occur in a hot cylinder, when metal parts are very hot and by accident cause a self ignition due to that hot spot.
Temperatures are therefore kept below 450F, to avoid that. You also need hot oil temperatures, as well as as hot CHT’s to start heavy detonation.

Pre-ignition can also be started without detonation, btw.

So detonation can indeed be very bad for an aero engine, or for that matter any type of piston engine.

That is the reason modern cars have knock sensors fitted, to spot the onset of detonation and immediately auto adjust the mixture accordingly to avoid sudden destruction of an engine due to detonation.
We don’t have knock sensors fitted to our expensive aero engines and have to manage the situation manually.

Please be sure to understand, that our CHT gauges are measuring a single point on an air cooled cylinder, if the factory location for that sensor reports 400F, the hottest part of the same cylinder will be about 450F, which is near the top of the cylinder, near the spark plug!

So when managing CHT’s one should always remember that very important parts of a cylinder are much hotter than our instrumentation reports.

I took the online paid for course with APS and along many others also the first APS live class in Europe.
We had it demonstrated to us how to run an engine into heavy detonation, so we could see the symptoms for ourselves.
It was an eye opener for me for sure.

Not sure what Mike Bush teaches regarding detonation, but I would be very surprised if it differs from any of the above.

Last Edited by complex-pilot at 14 Oct 14:21

I am sure the APS course is good but they are in business to make money, and in reality the subject is much simpler.

It was GAMI and George Braly there who found that it is damn hard to cause detonation. They had to run a TIO-550 on a bench to something like 450F CHT and high or max power before they could do it. This is consistent with engine certification criteria.

Pre-ignition doesn’t happen in certified engines unless you are using the wrong fuel or have some protruding fragment in there (e.g. a metallic deposit which partly separates from the piston or the cylinder head wall) which goes incandescent and works like a permanently glowing spark plug.

I’ve read the same stuff as all the keen to learn people in this game Some notes here

Administrator
Shoreham EGKA, United Kingdom

t was GAMI and George Braly there who found that it is damn hard to cause detonation. They had to run a TIO-550 on a bench to something like 450F CHT and high or max power before they could do it. This is consistent with engine certification criteria.

That is a myth. Sorry.

It is very easy to run an air cooled aero engine into detonation, which then can lead switfly to heavy detonation.
I am afraid some might believe it is difficult, but under the right conditions (perhaps better to say wrong conditions) it is almost too easy to do.

It is also true to say that some engine types are more prone to it than others.

Pre-ignition:
One only needs a little tang of the heli-coil for the spark plug protruding marginally into the cylinder and the party starts very early on when hot CHT’s are achieved.

Anyway, please take the online course and then we can have an open discussion all again, perhaps George Braly might want to chirp in too.

Until then, all bets are off.

Last Edited by complex-pilot at 14 Oct 14:50

I have enough to do here and won’t go around to finding that article, among many which Mr Deakin wrote…

One only needs a little tang of the heli-coil for the spark plug protruding marginally into the cylinder and the party starts very early on when hot CHT’s are achieved.

which is what I said.

Anyway, please take the online course and then we can have an open discussion with all again, perhaps George Brawly might want to chirp in too.

Please, repeating that people should spend a load of money is not helpful.

BTW, Mr Braly signed up on EuroGA a long time ago

It is very easy to run an air cooled aero engine into detonation, which then can lead switfly to heavy detonation.
I am afraid some might believe it is difficult, but under the right conditions (perhaps better to say wrong conditions) it is almost too easy to do.

Can you educate people on how exactly to do this, on a certified engine?

Administrator
Shoreham EGKA, United Kingdom

I do not wish to make this personal.

Let’s all keep our cool, please.

There are organisations that teach us how to fly, be it VFR or IFR.

There are also organisations that teach us Advanced Piloting Techiques to operate our aero engines efficiently.

I would recomend anyone to use any of those organisations to hone their skills even further and not live on in ignorance.

Last Edited by complex-pilot at 14 Oct 15:28

If you don’t want to spend some money on APS (peanuts for an aircraft owner, with huge downside if things go pearshaped), at least read and reread John Deakin’s articles about engine management. Here is the link to the basics (there are many more):Pelican perch engine articles

EBKT
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