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Why do engine/aircraft manufacturers discourage LOP?

Airborne_Again wrote:

75%

At 75% the answer is YES you are close enough with reasonable operational tolerances and considering common and “acceptable” failure modes to doing damage (i.e. blocked injector), that also includes ROP, where a single EGT is used. Perversely ROP can mask this failure mode.

An important failure mode to consider is improper mixture settings will preclude the production of maximum power. This IS seen in hot and high operations, where mixture control is ignored. Both low and normal density operations should be properly addressed in flight training.

Last Edited by Ted at 14 Jul 11:38
Ted
United Kingdom

If the engine runs smoothly, probably not, in fact at 65% or below you cannot damage the engine with the mixture control. If it doesn’t run smoothly that means that one or more cylinders are developing less or more power than the rest of the engine. Think of a six-cylinder engine as six little independant engines flying in very close formation.

I also run a turbonormalised IO550, high speed cruise is about 82%, during the entire flight except take-off and climb. LOP is compulsory. Will have to pull the cylinders next year due to AD, will report on condition.

EBKT

@A_A without multi probe CHT, not EGT btw, how might you detect detonation due to magneto or valve timing issues?

Richard Collins was not a fan of LOP and he spent his time in SEP IFR.

Oxford (EGTK), United Kingdom

Airborne_Again wrote:

Do you run a risk (even remotely) of damaging the engine if operating at peak EGT or LOP on an aircraft which has a single EGT indicator because the cylinders are not peaking at the same time? At 65%? 75%?

If you correctly lean LOP or ROP I would not see a difference.

However (!), and that’s towards an answer to your original question: Do you know many pilots that are correctly leaning if they fly ROP (i.e. on peak egt or 50 deg below depending on engine)? In my experience of flying with others, people who lean mostly fly LOP while people who claim to fly ROP often just don’t care about leaning at all and therefore flying way ROP.
And as the Fuelflow-Band of flying ROP (basically w/o upper limit) is much broader than the one for LOP, engine manufacturers prefer that.

Germany

The Dr400 I flew, went everywhere ROP.
Before me it had made 2400hrs on the engine without any major work. As I joined the 4 person group it had 200hrs on a factory new engine. Lyco O-360

At 2400 rpm it was 120kts and 6hrs range there was no incentive to lean.
It was on 1400 hrs when we sold it and had nothing done to it at all that I can think of, and performed exactly as it should.
With my Cessna 6 pot Conti, I’ll run out of fuel between the pumps and the runway if I don’t lean.
I remain ROP at 80 deg below peak in cruise.
Eventually I will on longer legs go LOP.

United Kingdom

GA_Pete wrote:

I remain ROP at 80 deg below peak in cruise.
Eventually I will on longer legs go LOP.

The highest CHT occurs at roughly 75 degrees ROP. It generates the most heat for the engine and in IMHO is the worst place to operate. For ROP operation, I would recommend 125 to 150 ROP, especially at high power.

KUZA, United States

dirkdj wrote:

If the engine runs smoothly, probably not, in fact at 65% or below you cannot damage the engine with the mixture control. If it doesn’t run smoothly that means that one or more cylinders are developing less or more power than the rest of the engine. Think of a six-cylinder engine as six little independant engines flying in very close formation.

Sure, but suppose you set 75% power and lean to peak EGT on a single-cylinder instrument. Then one of the other cylinders may be be running 25-50°F rich of peak, which is the worst possible place to be. And the engine will run smoothly.

ESKC (Uppsala/Sundbro), Sweden

RobertL18C wrote:

A_A without multi probe CHT, not EGT btw, how might you detect detonation due to magneto or valve timing issues?

You probably won’t until it is too late. Yet lots of aircraft don’t even have a single probe CHT.

ESKC (Uppsala/Sundbro), Sweden

I used to lean my IO520BA in my Bonanza using an engine analyzer and its EGT indications. I no longer do this as I find it to be a waste of time. I use digital fuel flow for leaning.and for 65%, lean to 12.5 GPH. I use the analog fuel flow to set the mixture because it is fast responding and very repeatable, even if not accurate. IOW I know what i need to see as the analog indication, so 12 on the analog will settle out as 12.5 on the digital. I only use the engine analyzer to troubleshoot if the engine is running rough or other indication, such as a limit exceeded.

KUZA, United States

The early Piper Malibus were powered with a TCM TSIO520BE that was intended to be operated LOP by the manufacturer. Pilots were reluctant to do so at the time and were burning up their engines prematurely. It took TCM quite some time before they supported LOP operation and in the Bonanza manuals with the IO550B engine, the Bonanza POH has two mixture settings, best power at 20C ROP and best economy at 20C LOP. I think the 20C ROP is too hard on the engine and would prefer 80C ROP, but the fuel flow is higher.

KUZA, United States
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