Greetings once again fellow simmers!
I have what to most will be a basic question, even though I’ve been a flight simmer for years…I’ve never really had to ever control the mixture level (probably as I have had to switch to ‘hard’ settings following aquisition of the flybywire Airbus to avoid conflict).
I’m flying the Beechcraft Baron and I can’t get the aircraft above 10 to 11 thousand ft without the engines dying and then getting to stall speed.
I put the aircraft temporarily into AI flying mode, and instantly the engine note soared and back came all the power…
I noticed the mixture control had been reduced to 47% - hitherto it had been on 100%…is this the culpritt??
I have mixture set to 100% on takeoff - what general settings should I use once I’m climbing? When to reduce say to 50%?? - any hard and fast rules would be appreciated!
Thank you!
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My 2 cents worth, but I’m not surprised. The air density is greatly reduced at 10K +. Reducing mixture is an attempt to maintain stoichiometric ratio (1 part fuel, 14.7 parts air). Fuel reduction maintains the ratio and consequent engine power. In the Bonanza, it seems to like 35 to 37 percent…
Piston powered aircraft rarely use the stoichiometric fuel ratio. Mixture is either set slightly rich or slightly lean to prevent peak EGT and detonation.
To answer the OP, the procedures for leaning differ from aircraft to aircraft but generally mixture is leaned using Exhaust Gas Temperature (EGT). Lean until peak EGT, then enrich mixture until EGT drops by … degrees for best power mixture or lean further until EGT drops by … degrees for best economy fuel mixture. Amount of degrees or divisions is described in the POH.
I remember that the aircraft type I used to fly even had a procedure for leaning without EGT which meant leaning until the first engine malfunctioning signs (rough running), then enrich slightly until symptoms have disappeared 
.
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And why is the EGT at maximum value? Could it be peak of combustion?
Peak EGT is generally slightly more rich than the stoichiometric ratio as in practise not all air and fuel is efficiently mixed and burned. Peak EGT is indeed the point of maximum combustion, in other words the point where all the fuel is utilised and nothing (or hardly anything will go to waste). Rich or lean from this point will both result in a lower EGT as the excess (air when running lean or fuel when running rich) is not burnt and just cools the engine down.
Running rich has a larger effect on temperature as the unburnt fuel evaporates and therefore cools the engine down more efficiently. Thats why most aircraft uses a rich mixture at high power setting. Too rich or too lean both decrease performance. Additionally a rich mixture may cause carbon deposits to built up in the cylinders from incomplete combustion which may cause pre-ignition or dirty spark plugs.
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Absolutely! 14.6 rich, 14.8 lean. Works on the ground, works in the air… 
For the OP. A correctly leaned mixture on a normally aspirated engine at 13000 ft over the Channel from Calais to Dover. Mixture full rich we would have never made it up to FL130. If we would suddenly have selected mixture to full rich the engine would immediately quit.
To fly all the way up to the aircraft ceiling requires two important things, first of all proper leaning of the mixture to get maximum power from the engine. Secondly you need to understand that the Vy speed decreases with increasing altitude while the Vx speed increases until Vx = Vy at the aircraft ceiling. Climbing with the sea level Vy or Vx speed as published in most POHs will never get you there.
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Just an addendum. Actually in use, I’m more used to ratios like 1.7 pounds of air to 1 pound of fuel. This is quite rich, but we didn’t care about replacing plugs or carbon deposits as the engine was rebuilt after every run. Without understanding of altitude and fuel ratio, we never would have reached 300+ MPH in less than 4 seconds.
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The simplest way for a casual simmer to use the mixture would just be to set it full below 2000 and once above, just set it to wherever the engine sounds the loudest or fastest. Swipe the mixture across the range to get a reference for where the sweet spot is. At higher altitudes you’ll hear the engine get quieter/slower near the min and max ranges of the lever, and a sweet spot around the middle. Anywhere in there is fine if you don’t care about IRL procedures or efficiency. MSFS doesn’t care about knocking or CHT overheating lol.
If you’re feeling more advanced, then lean for max EGT like others have said. That’s what I usually do.
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Yes, I agree… There is some variance allowed as to what mixture setting to use, I lean toward economy, seeing that AvGas is so inexpensive at this tme.
google : how to use mixture in a C172. watch some RL movies about it and then use the info in MSFS.
Mixture usage starts at 3000 feet and above
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While there is a lot of technical discussion here, to me it sounds like TO is not aware of the basic relation of fuel and air mixture vs. performance.
So I’d recommend reading some articles on it, explaining the basics, e.g. this one:
https://www.aopa.org/training-and-safety/students/solo/special/the-fuel-air-mixture
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