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CHTs over 400 degrees F

I have no issue with people reading all that. I am pretty sure I have done so myself. It is great stuff and these guys have done a great job dragging piston GA into the 20th century, never mind the 21st. And still many refuse to believe any of it…

However, most people will soon end up with their eyeballs rotating at 2400rpm and wondering how powered flight is at all possible when these engines are on the margin of self destruction

Administrator
Shoreham EGKA, United Kingdom

However, most people will soon end up with their eyeballs rotating at 2400rpm and wondering how powered flight is at all possible when these engines are on the margin of self destruction

And that’s a myth!

complex-pilot wrote:

I do not wish to make this personal.

Let’s all keep our cool.

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.

Lots of people here have read lots about engine management and failure modes. Also much of what Deakin et.al. teaches in the APS course. Taking that course — online or otherwise — does not mean that you understand these things better than everyone else here. Perhaps you do or perhaps you don’t. But please try to sound a little less condescending,

ESKC (Uppsala/Sundbro), Sweden

C’meon ladies, please!

Back to the original question by our poster:

So the question is – How bad is 430 degrees? Also is this a linear function from 400-500 degrees? Or more of an exponential function? I am guessing it must be an exponential /logarithmic function so the 480-500 degree range is REALLY bad but perhaps 410-430 is not worth worrying about?

Lycombing only answers for this thread as every engine must be different.

Is it all clear as mud now?
Have you found all answers to your question?

Last Edited by complex-pilot at 14 Oct 15:29

Well as the OP I found it all very useful, so thank you all! I’ll help my engineer tidy up the slightly worn baffles at the next Annual and report back in 4 months.

As an aside, I always find it amazing how some topics I start end up with lots of replies (like this one with 24 posts). Some do even better (like “How not to hand start a plane” with 71 posts.

The one I found quite amusing “How not to hand prop a plane (again)” was totally ignored. Perhaps I need to find a 1930’s black and white cine movie on leaning techniques – that’ll be click bait for EuroGA.

United Kingdom

A small gap in the baffles makes a big difference to CHTs. Even 3mm gap between a (metal) baffle and the cylinder head fins can give you an extra 20-30F. For years, my plane would climb with 420F showing on a hot day. Nowadays it rarely goes over 380F even in Greece.

But also a big tip is to get the fuel servo (if injected) adjusted for the full rich fuel flow to be right at the top of the tolerance band. For example most TB20s are set to about 23 GPH, but if you set the servo to 25 GPH that drops the climb CHTs perhaps 30F. It has no effect on cruise flow because one leans for peak egt ot LOP. I don’t know if carbs have an equivalent tweak.

As an aside, I always find it amazing how some topics I start end up with lots of replies (like this one with 24 posts). Some do even better (like “How not to hand start a plane” with 71 posts.

That’s because you post on interesting topics

The one I found quite amusing “How not to hand prop a plane (again)” was totally ignored.

I found the post. Yes; the timing must have been such that it got missed, and once a post ends up too far down, it gets lost, because way over 90% of people use only the Active Threads link. I tend to highlight such posts (if interesting etc) but sometimes I miss them too. I moved it to the existing hand propping thread – to here. It is a pretty scary video to watch…

Administrator
Shoreham EGKA, United Kingdom

To the OP: I have the same problem in climb-out with my 180 HP carbureted Lycoming. 3 & 4 cylinders go over 400 regularly. I climb to altitude in steps, throttling back and flying S&L for periods to keep the temperatures under control. But there is no realistic way to climb without going over 400. I would love it not to be so but it is.
I agree that there may be issues with baffles which I may replace.

Last Edited by WhiskeyPapa at 14 Oct 22:21
Tököl LHTL

It’s quite common I think with carburetted Lycomings – one cylinder of mine always runs hot, and we completely renewed the baffles a few years ago (which helped a bit), and they are in good condition. We also had a small mod done to the cowling to improve airflow. That cylinder also has the highest EGTs as well which indicates it has to do with mixture distribution. The mixture distribution in carburetted engines is far from perfect so you do what you can do, but other than that – all I can do is reduce power in the climb to keep the CHT from getting too high. The same was true of the Grumman Tiger my wife owned in the United States – despite baffling in good condition the (carburetted) engine had one cylinder that ran hotter than the rest by a good margin (and had a higher EGT in the climb) – I think the same one as mine (she had a CHT probe on every cylinder, I have only probes on the back two).

I suspect most people never find out on carburetted engines because there’s either no CHT probe at all (my Cessna 140 didn’t even have an EGT probe let alone CHT), or just one probe as standard – but I bet most of them have quite a temperature spread between the coolest and hottest CHT.

Andreas IOM

Also which is the hottest cylinder, varies. Mine used to be #6 and now (since the baffles were fixed some years ago) it is #3.

Administrator
Shoreham EGKA, United Kingdom

I usually manage to run my O-470-50 below 400 in climb, sometimes as high as 420 but that’s rare. It’s always one or two cylinders, most remaining much cooler. In cruise my cylinder 4 usually sits at about 390 with all the rest 345 – 380. A bit frustrating.

Last Edited by Katamarino at 16 Oct 11:24
KPJC and Kent, UK
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