Mixture Control

[Button]

I've just read some notes that say leaning of mixture should not be carried out with more than 75% power set - like in the climb I suppose.

I guess this could be engine specific but what's the general thoughts?

[Pilot DAR]

Generally this is the best practice, though if you are operating at high altitude, some leaning will be required. The objective is to prevent leaning to peak lean or more at high power settings. If you're leaned, but still well rich (150F or more) rich of peak, the eninge will be fine. At very high power settings, and very lean, the engine might be creating more heat than it can reject, and therefore suffer cooling problems. The risk of detonation plays a role it ths too, but is generally less a factor. Wasted gasoline is cheaper than an over heated engine.

Pilot DAR

[OneIn60rule]

Basically

If you are running at high power and lean the engine as you normally do, that could actually overheat the engine.

Remember what happens with the excess fuel you don't burn? It cools your engine.

So if you run it at high power and lean it and especially if you are climbing it with a lean mixture... you could do some harm. Hence climb with rich mixture in order to prevent overheating.

[Button]

Thnaks guys, so for aerotowing gliders to reasonably high altitudes at quite low speeds, leaving the mixture fully rich would be best?

[what next]

Hello!

...leaving the mixture fully rich would be best?

Best is always what the operating instructions of your engine say. Nothing else. Not anything that is written in generic flying books and certainly not what you can get from the internet!

Take the time to locate the manual for your specific engine and read it! And ask the mechanic who maintains your engine for additional advice and/or clarification.

Greetings, Max

[OneIn60rule]

In general

And this is just general!

Leaving the mixture rich in a climb is the correct answer.


1/60

[hatzflyer]

IF you are talking specifically glider tugging,whilst all that has already been said on here is basically true, there are slight differences to generall flying.
The aircraft will be fitted with a CHT guage ( or at least should be as that is a requirement for tugging approval). It is always advisable to fit an EGT as well.
There should be a prominent placard with CHT limits displayed on the dash,and a section in the POH relating to tugging which should be followed.

Also it is the tug masters duty to make sure that anyone using the plane is familiar with these limitations.

[Button]

I understand that the pilot's operating notes are the definitive reference, that's if they are specific enough.

What's the rule on take-off from a high altitude airfield, say Jo'burg?

[Big Pistons Forever]

The POH should tell you at what altitude full throttle will produce 75 % power undre ISA conditions. Any takeoff at this or higher Density Altitude should be done with the mixture leaned to max power. The easiest way to do this is at the end of the runup apply full throttle and then lean to max RPM (assuming fix pitch prop and carburated engine) and then slightly enrichen the mixture (move the lever about 1/4 the distance from full RPM to the full rich position). Use this setting for the takeoff. Regardless all hot and/or high operations require carefull monitoring of CHT and oil temp. As a very rough rule of thumb most engines will produce 75 % power up to a Density Altitude of about 7000 feet.

[poss]

The aircraft I fly states that after 5500 feet, when climbing, the mixture should be leaned. All aircraft are different, consult your POH.

[SNS3Guppy]

So if you run it at high power and lean it and especially if you are climbing it with a lean mixture... you could do some harm. Hence climb with rich mixture in order to prevent overheating.

You want to cool the engine? Fly faster, climb slower.

Lean of peak is cooler than peak. Rich of peak is cooler than peak. Running lean doesn't mean running hot.

Climbing with a rich mixture is appropriate sometimes, in some airplanes. Not all, and not at all times.

Most manufacturers suggest leaning above several thousand feet and at less than 75% power in order to idiot-proof the engine operation. You can't do much to hurt the engine if you're leaning with less than 75% power. Accordingly, manufacturers use this as a guideline generally in dictating when leaning is recommended.

Does this mean that leaning can't be accomplished at higher power settings and at lower altitudes? Of course not.

One should lean for density altitude.

Know your engine. If you're operating a Cessna 172 with an economizer (enrichment) valve, then you need to consider the effects of that valve in the carburetor when you lean. Especially if you reduce power. If you lean at full throttle in that airplane, for example, then when you reduce power, the mixture is leaned substantially more. You might experience a power failure, or be operating at peak...because the mixture is leaned simply by reducing power. It follows, then, that in the carbureted 172, a full power takeoff is an enrichened takeoff. One can (and often should) lean for field conditions when appropriate.

Know your aircraft, conditions, and what happens when you lean, and then act accordingly.

[bookworm]

I've just read some notes that say leaning of mixture should not be carried out with more than 75% power set - like in the climb I suppose.

Lycoming says "Use full rich mixture during take-off or climb." Elsewhere, the instruction was not to lean at more than 75% power without appropriate instrumentation, which is rather more permissive.

If you have an engine analyzer (and you trust its readings) I can't see any reason to avoid leaning in the climb entirely. Unless your injectors are so well balanced as to permit lean-of-peak operations at high power, it makes sense to stay well on the rich side of peak EGT. You can then use the CHT as the parameter against which you lean. If the CHT rises above target (somewhere in the 380 - 400 degF range), then you either need to enrichen the mixture or increase the airspeed to bring the CHT down.

[debiassi]

It always seems a contentious issue this one and sort of goes agains the POH for most piston aircraft but certainly leaning slightly as you get to higher altitudes allows the engine to develop more power which is sometimes valuable. Conditions also need to be considered. I once took of from Samedan which is the highest commercial airport in Europe. I was in an arrow and on the day, the density altitude was 6700ft. Taking off in these conditions and climbing whilst fully rich would be a big mistake in mountanous terrain. I also find that my Mooney climbs much better with comprehensive engine management including leaning in the climb whilst carefully monitoring, temperatures especially turbine inlet temp and fuel flow. In most cases, if not confident then fully rich is the safer option but a good understanding of the particular engine installation and exterior conditions does pay dividends.

[flyboy2]

Type specific leaning above 5000 ft

Hi
Although some of you are quite correctly stating what the piston engine manufacturers recommend, one must bear in mind that they wrote that advice for USA conditions.

In South Africa ( say Johannesburg altitude 5500 feet AMSL) most un-turbocharged/supercharged piston engines produce better power with a correct slight leaning procedure applied - before take-off.

When flying tubocharged engines use full rich mixture -as the engine behaves as if at sea-level. The only exception to that is when taking off at 10 000 feet, such as at Lesotho s Letseng airstrip.
There have been incidents in South Africa of "rich cuts" on final approach because the book states " mixture full rich", but the book doesn't know you are at say 7000 feet.

Use common sense & find out what works in such an area.
Many pilots never experience operations at such altitudes, so again use common sense and obtain guidance from SOP's.

Happy landings.

[SNS3Guppy]

Although some of you are quite correctly stating what the piston engine manufacturers recommend, one must bear in mind that they wrote that advice for USA conditions.

In South Africa ( say Johannesburg altitude 5500 feet AMSL) most un-turbocharged/supercharged piston engines produce better power with a correct slight leaning procedure applied - before take-off.

You mean you have different air in South Africa? Perhaps a different atmosphere, with a different combination of 79% nitrogen and 21% oxygen?

Think about what you wrote, and perhaps correct it. It did bring a smile, though.