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

Hi all, this LOP debate always evokes a lot of emotion. When Peter cruises at PEAK, what altitude would that be at? What oil and CHT's temps are achieved at PEAK when cruising at that altitude?

When Peter cruises at PEAK, what altitude would that be at?

Any.

I cruise at 65% or so.

At low levels, say below 8k, this is 23" 2400 11.5USG/hr.

Above that, the throttle is wide open so the MP is whatever you get.

What oil and CHT's temps are achieved at PEAK when cruising at that altitude?

Oil temp is regulated by the oil cooler bypass regulator, at about 170-175F.

CHTs vary between cylinders, and obviously scale with the OAT. Maybe 330-370F at ISA, low level. I have 106MB of EDM700 logs.

There is nothing "emotional" about this

It's just reasonable engine management, if one is paying for fuel, and maintenance.

Administrator
Shoreham EGKA, United Kingdom

Let's not get "emotional"....

65% hp is realistic above 8k, isn't it? For altitudes below 8k that seems low for a N/A engine. Have you tried 2500 rpm and WOT?

Just trying to get my head round only flying at peak egt everywhere, that's all.

65% hp is realistic above 8k, isn't it? For altitudes below 8k that seems low for a N/A engine. Have you tried 2500 rpm and WOT?

Just trying to get my head round only flying at peak egt everywhere, that's all.

Lyco authorise peak EGT at 75% or below.

So you are "entitled" to fly at 75% all the time, peak EGT.

However, it is believed by many (not all) that 65% gives you the best engine life, versus speed.

So I fly at 65%, which gives me about 140kt IAS. 75% would give me a little more speed, but less MPG.

It is completely normal to fly at peak EGT in cruise, at all levels. Except where more power is required which is at high altitudes, near the operating ceiling.

Altitude is nothing to do with this. You can take off, level off at 500ft, and set up for peak EGT. That's what I would do even if flying at 500ft.

Flying ROP when not needed is just wasting fuel.

Flying LOP means you are flying slower.

Administrator
Shoreham EGKA, United Kingdom

Well in the turbocharged Mirage, you can't fly at peak unless you pull power right back so your choices are ROP or LOP. I choose LOP at about 75% power which gives me TAS of 200kts. At ROP I can get 210kts. But I save 5 gals/hr and it is better for the engine.

With this stuff you decide what to do and take your chances.

EGTK Oxford

That's right, but the PA46 installation is a bit of a special case.

The generic stuff I wrote applies to most non-turbo installations.

Administrator
Shoreham EGKA, United Kingdom

Peter, thanks for the information.

How do you know you are at peak EGT?

How do you know you are at peak EGT?

Flames coming out of his exhaust, followed by bits of the exhaust valves...?

EGTK Oxford

Oha!

That is an individual technique; may be a slightly too narrow operating window for some.

As they say: There is not one right way to run an engine!

How do you know you are at peak EGT?

This

Flames coming out of his exhaust, followed by bits of the exhaust valves...?

No; that's what happens if you mix in too much Jet A1

There is not one right way to run an engine!

That's right. Most non-turbo installations can be simply run ~100F ROP. Historically that is how almost everybody used to fly, and many still do. There is nothing wrong with it; you just waste maybe 10-15% of fuel and get nothing in return.

Virtually all of UK PPL training is done with the red lever fully forward, but they never go above 2000ft The engine isn't going to actually stop running until maybe 10000ft.

If you read this you will see that after 800hrs of running 100% peak-EGT my engine was spotless and within new limits, except the exhaust valve stems which were just outside but were well within overhaul limits. I have the old valves here and you can measure them up

The tales you get from some old engine rebuilders about they can always tell a leaned engine (because it's knackered) are rubbish. Most of them have never flown a plane and have no idea about modern (post 1970s i.e. instrumented) engine management. You can certainly knacker an engine but you need to push the CHT really high (well past 400F while under power). GAMI found (TSIO550) that detonation was almost impossible to achieve below a CHT of 450F, plus some other aggressive factors. But 450F can be reached easily if one has no gauges and poor airflow. In the TB20 I could reach it in minutes after takeoff just by doing what I was taught in the PPL which is climbing at Vx or Vy.

It must be time for a shock cooling debate

Administrator
Shoreham EGKA, United Kingdom
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