Mixture and Engine Pitch..

[Skoshi Tiger]

Originally Posted by Blackdog_kt

Let's start simple with the mixture. In order to have a well-running engine you need a specific proportion between fuel and air. However, the higher you go, the less air there is to burn. That means we need to reduce the amount of fuel in the mixture to maintain that optimum proportion or the engine will choke due to too much fuel, hence the mixture controls.

Just to add, a carburetor meters fuel through the volume of air that passes through it, one cubic foot of air at sea level has the same volume of air as one cubic foot of air at 20,000 feet.

Unfortuanately the fuel/air ratio is based on mass.

One cubic foot of air at sea level has a higher mass than One cubic foot of air at 20,000 feet, therefore to get the correct fuel/air ratio you need more fuel per volume at sea level than you do higher up.

Cheers!

[Azimech]

Also, there is a big difference between carburetted engines and the ones with mechanical fuel injection. All combat planes in IL2 have superchargers or turbochargers.

You will notice that some planes will start to produce black smoke and engine power drops/irregular RPM above a certain altitude. That altitude is the supercharger's critical altitude, usually around 5000 meters for most planes. This means that the supercharger cannot deliver the volume of air to the engine as requested. To keep it simple, the volume of air drops but the volume of fuel stays the same. That's why in IL2 on most planes you only need to adjust mixture above the critical altitude, although it's done in a very crude way.

Fuel injected systems like those on the FW190 and Bf109 adjust themselves automatically. And by the way the FW190 adjusts it's supercharger stage automatically as well; the Bf109 has the most elegant construction because the speed of that supercharger is adjusted the whole time by means of a engine-driven dynamic hydraulic clutch and this provides maximum boost until supercharger RPM and clutch RPM are equal. This is also less efficient than gear-driven superchargers because friction in the hydraulic clutch produces heat, and that's loss of engine power. In a car with older types of automatic transmission this loss increases fuel consumption by 20% compared with the
same car with a manual gearbox.

Turbochargers are a different story, their critical altitude (usually much higher) is the maximum allowable RPM: the higher the altitude, the more RPM the turbo has to make in order to supply the requested manifold pressure. In IL2 turbochargers are set automatically, in real life pilots had to adjust their engine RPM, manifold pressure AND turbo RPM while climbing or descending. As you climb, the pressure differential between the exhaust system and the outside air increases, which speeds up the turbo. Turbo RPM was/is regulated by a valve that controls the amount of exhaust gas that flows through the turbine.

[KnightFandragon]

And does the Jug, Corsair F4u1D, Spit 25LB, P38 L and J also auto adjust? I have my keys mapped but I cant get any of my planes to adjust thier mixtures...I even flew at 10000m and nope, it still wouldnt adjust. Prop Pitch worked on the Jug but that was it, I didnt try it on the P38 but didnt on the Corsair and Spit. THe Corsair mixture had 2 settings of 100% and 120% but the other 3 I couldnt change. Those were the only planes I was messing with but they didnt do anything, I do have complex engine management on, Ive flown with realism settings on for awhile, I just never messed around mcuh with these settings.

[Blackdog_kt]

Damn, i had a lot of typos on that long post of mine, i didn't have time to proof-read it before posting

Azimech and Skoshi are also correct in their information.

As for your last question i think most of the aircraft you are testing have automatic mixture controls in IL2, that's why you can't mess with it even though you have CEM turned on and the keys mapped. The P47 in reality has the semi auto system (cut-off/full rich/auto-lean/auto-rich) but in IL2 i think it's fully auto. As for the corsair, maybe it only has auto and emergency full rich settings (the 120% setting) in IL2.

If you want to run a quick mixture test fire up the quick mission builder, select a Yak-1 with no enemies, set the starting altitude to 5000m and when you spawn set the supercharger to high gear (does the yak-1 even have one? not sure) apply full throttle and get climbing.

You'll see almost immediately that there appears to be something wrong with the engine, it sounds strange and seems to not deliver enough power. Switch to an external camera and you'll see a trail of black smoke coming out of your exhaust stacks. Now switch back to cockpit view, lower the mixture to 80% or 60% (it's done in 20% intervals per key press in IL2) and you'll hear and see (instruments) the engine come back to its senses. Switching to the external camera you can also see the black smoke trails have disappeared.

That smoke is due to the excessive fuel being burned in an inefficient manner (or being almost unburned even). There has also been talk that due to the analog nature of auto-mixture systems, it took a couple of seconds for it to stabilize if throttle was applied abruptly. This had the effect that sometimes if the pilot quickly slammed the throttles forward, a brief trail of black smoke was produced until the auto-mixture system stabilized. In turn, this was used by pilots to judge if the enemy aircraft was suddenly going to high throttle settings, a clear sign that he is aware of you and is initiating combat.

[PE_Tigar]

Just to chime in - in reality, Corsair had double the engine controls than we have at the moment in Il2. Aside from prop pitch, compressor stages, throttle, cowl flaps (that we have), it had more complicated mixture control, inter-cooler flaps, oil cooler flaps and alternate air control (not sure about the purpose of this one, some a/c have it for instruments, in case outside static gets frozen over).

As for the situation in Il2 - a/c with automatic mix perform "perfectly" - like they have a manual system that is perfectly managed. If F2 or F4 outrun you in level flight in Spit IX 25 lbs. you might be doing something wrong. Try the following - full throttle and trim the plane properly keep the slip indicator and climb speed indicator zeroed with trim and see what happens. One other thing that might be hindering you - cooler flaps on Spit IX are on closed/auto by default, so if you were running for a long time on full throttle they might be open, thus lowering your airspeed.

[TheSwede]

Dont forget to change the prop pitch as well. When you go full throtthe and have picked up speed, then lower the pitch so the blades can "dig" into the air in a more efficient way.

Just like you change gear in a car when you hit the rev limiter.

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).

[Skoshi Tiger]

Originally Posted by zipper

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.

Hi and welcome to the board.

In game its something you learn to live with. You disregard the RPM message on the screen when your flying a plane with a CSU, you know the prop pitch message on the screen is just showing the position of the leaver, you need to use the RPM dial to set you RPM.

Originally Posted by zipper

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.

I don't know how faithfully IL2 models WWII aircaft but the game will allow you to set an rpm higher than the red line.

Cheers!