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Cyl #3 and #4 show hottest CHT, too hot for my taste during climb

Why would you not lean the mixture during a climb to 7000 feet?

I was just giving the lazy version

Of course you can use the constant-EGT method all the way from sea level to 20000ft. My writeup says as much, but very few people click on links in posts

With a turbo it is different – you normally climb with all 3 fully forward to 25000ft or whatever your ceiling is. Of course the engines mostly don’t make TBO then because while a NA engine runs at full power from the runway to about, ahem, 100ft, a turbo engine will be running at full power all the way up.

Administrator
Shoreham EGKA, United Kingdom

Of course the engines mostly don’t make TBO then because while a NA engine runs at full power from the runway to about, ahem, 100ft, a turbo engine will be running at full power all the way up.

That’s entirely the pilot’s choice, even turbo engines have power levers . A NA engine at the end of its excess power capacity requires very low airspeed and a steep pitch angle to get the remaining climb capability out of it which may come with very high CHT.

Of course turbo engines are more expensive and require more expensive maintenance thanks to our crappy aviation engine technology but they are so much more capable. I promise you would never want to go back (same holds true for pressurized cabin and a turbine I bet)…

A NA engine at the end of its excess power capacity requires very low airspeed and a steep pitch angle to get the remaining climb capability out of it which may come with very high CHT.

I have just checked the EDM data for the last flight with a FL190 climb and the hottest cylinder reached 360F.

I promise you would never want to go back (same holds true for pressurized cabin and a turbine I bet)

I am sure that’s true – until you are forced to by some other factor e.g. no longer being able to afford it, or getting fed up with the regular downtime. I know a TB21 owner whose % downtime I can only guess but from what I can see it is many weeks a year, and was 6 months at one stage. I am sure that in flight it’s absolutely brilliant to have that high altitude performance.

Administrator
Shoreham EGKA, United Kingdom

It’s simply a decision. I have an NA engine, because i wanted it. 90 percent of my IFR flying are up to FL120, 130 … 10 percent up to FL160.

Up to 100 the turbo offers very little advantage in the SR22, and since i don’t care about flying in FL250 and the NA engine is more robust i have exactly what i need. I don’t have to fly in wx in which only a turbo could get me on top, but if you need that the turbo is the way to go.

Climbs i do full power and i use the table on the panel for leaning 29 gph, 24 at 4000 ft, 21 at 6000… You can also use the EGT normalize feature and simply keep the EGT delta at zero with the mixer. And you can even do a lean if peak climb.

I closed all the tiny holes in the baffling and around it with sealant and where the baffles overlap in the corners we riveted them together. I do automatic IAS climbs with the autopilot and most times i use 110 KIAS, or 120 if it’s very hot. I have only once reached a CHT of 380 F if i remember correctly.

FWIW

Just to give you IO540 drivers some comfort:

My aircraft has two IO540s identical to yours. Ever since I fitted JPI I have realised that they run very hot indeed. My CHT warning is set to 475°F. My hottest cylinders are never less than 425°F and very often much hotter. 440°F in the cruise is not untypical.

I am on engines 3 and 4. Neither these nor the previous have ever shown any damage due to over heating (or indeed shock cooling).

Engines 1 & 2 were still going strong at 3000 hours, when one of them had a non-heat related failure (cylinder stud failed, probably because of over tightening at some stage). I used that as an excuse to change the engines, but I kept all eleven remaining cylinders as spares, and they are all in good condition.

I dream of cylinders which max at 400°F. You really are worrying too much!

EGKB Biggin Hill

I cannot tell for the Lycoming, but a big bore Conti would be ruined quickly with 450-475 F CHTs. But i think it’s common knowledge that Lycoming cylinders are more forgiving in that respect …

Is “shock cooling” really shock cooling or only a roundabout way of saying “poor metallurgy” ?

Flyer59,

…but this whole conversation is about the Lycoming IO540, is it not?

EGKB Biggin Hill

Yes, of course Timothy. I understood it more as a general discussion, but i am wrong.

Is “shock cooling” really shock cooling or only a roundabout way of saying “poor metallurgy” ?

I don’t think there is anybody to blame here, because in engineering there are tradeoffs and perfection cannot be achieved.

These engines use thin metal sections, to achieve a lower weight.

They don’t use water cooling, for simplicity (=reliability) and lower weight.

They cannot deliver the full rated power at stochiometric combustion (~peak EGT) because there is no way to remove the heat generated, but then neither can even the most modern car engines. And don’t forget that a typical car engine runs at ~30% power even on the motorway, and when they are used for competitions (where they might run at, wow, 60% power on average) they usually get shagged very very quickly.

They cannot deal with rapid temperature changes at high CHT values, because they use materials optimised for each job but these have differing expansion coefficients.

These engineering objectives cannot be reconciled. Maybe you could build a ceramic engine for some silly money which can do it…

The price we pay for this is that the engine needs intelligent management. And I am sure anybody with the IQ to get through the PPL exam(s) – which is by no means everybody – can get their head around it. There is a real issue that it was not until recently that people had the instrumentation.

Timothy – have you checked your EDM is not out of adjustment?

Administrator
Shoreham EGKA, United Kingdom
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