Noob Question - CEM and Prop

[Charly_Owl]

Hello guys,

I'm kind of new to sims. So far, I'm having a great time: that's a true kickass hobby to be honest! I'm having a real blast with Il-2 '46 UP3, and I decided to buy CoD to support the company, despite its multiple bugs. I know the game's current state, but I have faith in the devs to eventually patch it right.

But that's not the point. This thread is to ask you a very specific question. I'm a newcomer here, so forgive me if these questions seem like really dumb, but I want to learn to know the planes I fly and how they really work. I'm kinda new to complex engine management. I just learned about trimming the plane in-flight, which helps considerably. However, I was wondering about CEM features and how they affect your flight.

1) About Mixture
How does increasing or decreasing the mixture affect my in-flight performances? Is it controlling the fuel flow so that engine's performance is better and generates more thrust? I'd like to have some explanations so I can understand how to use it efficiently in-flight, and for which cases I should use high % mixture vs low % mixture.

2) About Radiator
My best bet would be the opening of the radiator allows the engine to cool down a bit. Is it to prevent overheating or it has another utility I'm not aware about? Furthermore: what happens when an engine overheats? Does it blow up or anything?

3) About propeller pitch
I know they affect the thrust generated. But why would you want to increase or decrease prop pitch during a dogfight as I've seen in many youtube videos? I'm curious about the reasons behind it.

Once again, I'm sorry if my questions annoy you or seem like no-brainers. I just thought some sim vets like you could give me first-hand experience on the reasons behind using these features.

[Verhängnis]

1) Sets the amount of fuel added to the intake airflow. At higher altitudes the air pressure (and therefore the oxygen level) declines so the fuel volume must also be reduced to give the correct air/fuel mixture. This process is known as "leaning". Too much fuel and your engine can overheat, produce less horsepower and possibly explode. Methane for instance must have a proper fuel air mixture or it won't combust - in an aero engine it has to combust efficiently to produce the most power and not damage the engine. Basically your cordial - water ratio.

2) Radiator allows cold air to cool the fluids (Coolant) in the engine to maintain optimal temperature. Too little heat to start your engine - close the radiator, too hot, open it up or your engine will overheat, boil and you will have oil all over your canopy.

3) Propellor pitch ofcourse affects thrust output being how much air is 'caught' by the blades. More prop pitch, more air is caught = higher RPM, lower pitch = less air caught = lower RPM.
In diving or high speed engagements you will need to lower the prop pitch in order to avoid exceeding the engine RPM limits, if your engine 'over-revs' then it will damage the gears and shafts and you will destroy the shaft.

Atleast this is how I would describe these things.

[Charly_Owl]

Great! That pretty much explains it all. Thanks Verhängnis!

[Kodoss]

@Verhängnis:

Too much fuel and your engine can overheat, produce less horsepower and possibly explode.

This statement is wrong. Actually it's the opposite. Less fuel and your temp gets higher until it's decline again because it's get to lean. You can also use a little bit more fuel to cool down the cylinder walls, but you lose power by rising fuel consumption.

[louisv]

Think you are drving a bicycle, propeller pitch is like your speeds on a bike...

If you are climbing, go to easy speed...fine pitch

If you are going straight and level, you will gain speed by going to harder speeds...coarse pitch.

There are 3 types of props (and the 2 pitch on the hurricane), fixed, variable and CSP (constant speed prop). The CSP automatically keeps the same RPM all the time, so its like an automatic transmission, no need to change it as often (ex: spit IIa)...generally not during a digfight. With the variable (non-CSP), there is more work to do (ex: Bf-109)

[AdamB]

Originally Posted by louisv

Think you are drving a bicycle, propeller pitch is like your speeds on a bike...

If you are climbing, go to easy speed...fine pitch

If you are going straight and level, you will gain speed by going to harder speeds...coarse pitch.

There are 3 types of props (and the 2 pitch on the hurricane), fixed, variable and CSP (constant speed prop). The CSP automatically keeps the same RPM all the time, so its like an automatic transmission, no need to change it as often (ex: spit IIa)...generally not during a digfight. With the variable (non-CSP), there is more work to do (ex: Bf-109)

Basically a higher prop pitch increases the displacement of the air in front of the propellor towards that rear of the prop. It does this by spinning through the air at a greater angle (in relation to the prop and the direction of the air flowing through the prop) However increasing the prop pitch cause more drag because more airflow will be rebounding off the trailing edge of the prop thus you should only use a high prop pitch when ascending because youll have a lower airspeed so you need more pulling force from the prop to maintain the climb and because of the lower speeds the effect of drag is limited because the force of the air hitting the greater surface area of the prop is less because of thhe lack of speed. >>> the opposite occurs when decending.

Hope this answers it for you, im not sure this is a gr8 explination but then again us physics lot are never good at explaining. Just take my word.

Adam

[jf1981]

Originally Posted by Charly_Owl

1) About Mixture
How does increasing or decreasing the mixture affect my in-flight performances? Is it controlling the fuel flow so that engine's performance is better and generates more thrust? I'd like to have some explanations so I can understand how to use it efficiently in-flight, and for which cases I should use high % mixture vs low % mixture.

Hi,
In short, too rich mixture does not generate more power however send fuel that will not be burnt and hence wasted. On the other side, it will allow engine to run a little bit cooler.

In Cliffs of Dover, you will notice lower fuel consumption when leaning the mixture above 10/15 kft (> 3000 meters). Leaning the mixture in thin air allows the correct fuel/air mixture to be maintained however stay rich at full power because you may damage the engine particularly in a dive. It depends if CoD takes care of this possible engine failure case.

3) About propeller pitch
I know they affect the thrust generated. But why would you want to increase or decrease prop pitch during a dogfight as I've seen in many youtube videos? I'm curious about the reasons behind it.

An engine can run with higher torque at lower rpm which would result in the same as higher rpm with less throttle (or less torque) => in both cases same power. However if you can run lower in rpm you should have a better efficiency and so less fuel burnt, less noise also, one more point that CoD does'nt take care of, the engine lasts longer (better for maintenance).

In short for CoD : if you have a constant speed propeller (like Spitfire II for example), you better run at higher rpm during dogfight and take off, lower during cruise.
If you have a constant pitch propeller (like some BF 109) then also take care not to run the engine too high in rpm for example in a dive you should coarse the pitch or reduce throttle, because it will not take care of it, the pilot has to. If not the engine at overspeed may be failed !