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Engine management / leaning / peak / lean of peak (merged)

You can achieve 65% or less power below FL100.

Use the throttle lever

That's for sure! This is why my second question was: Or do you always cruise at <60% power?

LECU - Madrid, Spain

Early in flying I was told that fuel is the cheapest coolant you can use

I know that is said tongue in cheek but it happens to be technically wrong.

I recall this worked out somewhere, and the specific heat of vapourisation of avgas was of the order of 1% of the heat released by burning it.

So the often repeated thing about the ROP mixture being cooler because of the liquid avgas going into the cylinder and coming out unburnt is wrong.

The reason ROP is cooler is because the combustion is making less heat. The same reason that LOP is cooler.

Administrator
Shoreham EGKA, United Kingdom

The reason ROP is cooler is because the combustion is making less heat. The same reason that LOP is cooler.

At a high level correct, but missing some obvious but important points.

At LOP there is less chemical energy (because there is less fuel) in the charge, so when it combusts (and combusts fully breaking all of the HC bonds and forming CO2 and H2O) there is a 'high' energy per gram of fuel but 'low' total energy, no carbon to glow or foul things and a slower pressure rise.

At ROP there is much more chemical energy in the charge, but when it combusts it only partially oxidises (due to the lack of air vs fuel) so you get unburned Carbon, Unburned aromatics, CO, CO2 and Water - leaving a good junk of that chemical energy as potential energy in the exhaust stream rather than thermal energy in the cylinder (aka cooler combustion).

When you are trying to pull the maximum power out of the cylinders, cooling with fuel makes sense. When you are just cruising I prefer the price of air to fuel for cooling.

I do accept that in an engine burning a few gph of cheap fuel it is probably not worth worrying about.

EGTF

That is a comprehensive way of explaining LOP/ROP. I thought that was very good!

Everybody is free to manage mixture as they decide. There is no limit placed on a pilot of an aircraft other than some silly max CHT temperatures.

Another point is that peak EGT is the beginning of cooler CHT's, that's all.

LOP can be the fastest airspeed with cool CHT's for a conforming engine.

Is there only one way to operate an engine? I don't think so.

There is no limit placed on a pilot of an aircraft other than some silly max CHT temperatures.

If by silly you mean potentially very expensive...

EGTK Oxford

Peter you have obviously spent a lot of time studying this issue. Certainly more than I have. What you say seems to be at odds with the Advanced Pilots Course.

I run LOP and find it very reassuring to see the CHT on every cylinder below 350F. The Turbo GAMI injectors and the JPI monitor made this possible.

At the top of the climb I am below 350F on the hottest cylinder because like you I like full power climbs, with 34 USG/ hr there is plenty of cooling coming from unburnt fuel vaporisation.

As our leader on this forum I think you should go on the APC and report back to us.

G

I won't let any cylinder get above 400 deg C under any circumstances. If I have to pour fuel in to get the CHT's down then so be it. Ask anybody who overhauls engines and they will all say that controlling CHT's is the single most effective thing a pilot can do to reduce maintenance costs.

I used to fly a C 421 with the infamous GTSIO 520 engines. It was sold with 1400 hours SMOH, all original cylinders, turbo's and except for one tail pipe all original exhaust components. No magic here just care with the mixture lever.....

Wine, Women, and Airplanes = Happy
Canada

What you say seems to be at odds with the Advanced Pilots Course.

Which part do you think is at odds?

I am not aware that I disagree with anything from Deakin on engine management.

As our leader on this forum

I would prefer to not think of myself as a "leader" here

Sure enough it was my idea to set this forum up originally, to provide a decent to-the-point tech aviation site for European pilots. But I would really hate to think anyone here feels they cannot disagree with me. I am a mod/admin here but, unlike at least one site I can think of, I would never mod anything in that category. BTW I have not modded any postings here to date; I've deleted about 10 of which most were variously unpleasant or obvious trolls and the others were taking the micky out of the misfortunes of another aviation site.

Administrator
Shoreham EGKA, United Kingdom

Sorry JasonC, that my reply is not in sequence.

Yes, as you point out the POH CHT limits are not realistic, meaning they are way, way too high.

My max limit is at 380F, which by the way in 10 years of engine monitor use I have never got close to. My rule is that if I would see temps nearing that personal limit I would quickly do something about it by decending , going full rich, do anything to quickly reduce temps. That limit can vary from engine installation and cooling design.

As it has been demonstrated cylinder head castings loose 50% of their strength at 400F. Why is that important? That item relies on a shrink interference fit and a thread. In that order! You don't want to compromise one of them.

Avoiding high ICP's is essential in controlling CHT's, at tought by APS and that's done by staying outside the red box.

Avoid both and we can avoid in flight cylinder separation. Some excellent material is available from APS and also from Mike Bush.

Cost is a major go/no go factor today, clearly. With fuel prices around $12/USG and rising, it is a difference if you use 100-150 USG less per 100 hours. But that is not only a cost thing, it also means range. If I can fly at 7 gph with the same speed with John's recommendations as opposed to 9-10 GPH, that means $25-$35 per hour LESS money (here in Europe) at the same speed and it means I have one hour or so more endurance. At 52 USG tanks and 140 kts, that can well mean a huge difference of 150 NM more range.

If I do this and at the same time run a healthier engine, which has been proven with lower CHT/EGT as well as the stop of fouled plugs since ever we do this, then the conventional thinking simply has to make way.

The poster here who sais that most of us are conditioned to be scared of the mixture lever is only too right. And that is wrong. Very wrong. This to the extent that even some tech docs are written with this in mind to go "safe". Using fuel as coolant is outdated, expensive and won't safe the engine. According to what I read by John and Walter, the opposite is the case.

I am considering going for one of their courses even though I fly a carburetted engine. Actually, I have been talking to John to do one of them in Europe. Here in Switzerland, people seem to thrifty in order to pay for this, but maybe we could organize it somewhere else and get the about 50 people we need to make the expense worthwile. I'll help if people here are interested.

Best regards Urs

LSZH(work) LSZF (GA base), Switzerland
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