Ground leaning has been an active discussion topic since the 172, and with this new simulation, we're given more relevant real-life cues to that than ever before. Previously when flying from at or about sea level airports, our ground leaning was basically based on pulling the mixture back until the engine starts coughing, and then advancing some. Let us see what happens in the current simulation before the engine starts to starve from the lack of fuel.
Here we are idling at 800 rpm with full-rich mixture. Note carefully the position of the fuel flow and the engine rpm gauge.
Now, the only change I do is pulling back the mixture. Note what happens.
Note the rpm rises some 50 to 70 revs per minute without me adjusting the throttle at all.
What's going on here? For many real life aviators it is probably all clear but it has not been all obvious in the simulator before.
The engine's idle mixture setting (throttle full back and mixture full rich) is adjusted in a specific way by the tech. The resulting mixture is very rich. This is to allow for cold starting and initial warmup of those big air-cooled jugs where a portion of the fuel going into the cylinders condenses on the cool walls of it and doesn't participate to the combustible mixture. But warming up, this mixture can be too rich for nice, clean burning and may result in fouled plugs etc. This is why we are recommended to lean the engine for ground operations.
But while doing that we actually change the mixture setting from the very rich towards and through the best power for that very low throttle setting. This will cause a noticeable increase in engine's rpm before it starts falling back down again if you lean far enough. This effect will give you a great cue for your ground leaning, so you don't need to hunt for the cough point of the engine.
Not only that, this is an important piece of realism. For best results and a good compromise, the idle mixture is usually adjusted by the book so that approximately 50 rpm increase in engine speed is noted while leaning from full rich. It is a part of checking the engine to note for such a rise and having that present in the simulator is convincing in that the things progress under that hood!
-Esa
