Wow - as a RL pilot it was fascinating reading all the advice, each post had both correct and incorrect info for the real world (not really sure about IL2 as it doesn't seem to respond as I expect it to). In RL when adjusting a constant speed (constant engine speed - rpm) prop (most allies and even the most 109s) one never thinks in terms of prop pitch but rpm. If you want to go fast or climb fast you have to have the lever full forward, 100% rpm (redline). In a dive with the prop set at 100% rpm the governor maintains redline rpm and you can have the throttle firewalled and the redline won't be exceeded until the speed gets massive as the max pitch setting will usually take some time to reach. Below about 1200/1400 rpm the governor gives up as it hits it's own limits and consequently the prop is at its default position flat against the low pitch stop. No prop lever jockeying will adjust the blades in this realm, that's why when you want to cycle the prop on a plane you have to rev the engine (it's done on runup, often right after mag check). Max performance being at 100% rpm on all aircraft (some WEP setups simply increase the rpm slightly) combat pilots (in combat) would firewall the prop and forget it, adjusting speed with throttle. If you want to use the car/gears analogy, the best I can come up with is the prop percentage would equate to the rpm range percentage the automatic transmission shifts at. 100% will shift your tranny at redline, 85% will shift it at 85% of max rpm, etc. That's the best I've got - lol. Prop blades have a rather shallow and narrow range of effective angles of attack so making a noticeably large increase will not only drop the revs a bunch but the blades lose a lot of their efficiency so the performance drops a bunch. I was in a two speed C190 once playing with this and at a slow speed with a high MAP I switched the prop to to cruise (higher pitch) and the plane actually slowed done a bit (and MAP went through the roof - yikes - always increase prop then throttle, decrease throttle then prop - but, game don't care).

Mixture, newer aircraft have better auto mixture control and that simply doesn't need to be adjusted (unless on an older plane leaving a smoke trail). Haven't found a need at all in game for the 120% mix setting. On airplanes equipped with this it substituted for water injection as the carb (actually, a pressure carb or throttle body injector) was upstream of the supercharger and was used during overboost to provide additional manifold air cooling to prevent detonation. Plug fouling could be a major problem with this setup so water injection was prefered (thats why the 190D 1944 was converted to the 190D 1945 as soon as possible).