Supercharger / spotting AI

[JtD]

Originally Posted by Jumpy

1) Firstly, what's the deal with the supercharger? When flying the F4U I can see a noticable amount of manifold pressure gained if I toggle to speed 2 immediately at ground level. If more MP = more engine power, are there any side effects in switching to speed 2 right from the start and not at recommended 2000m?

2000m is probably an outdated recommendation. It's about true at high speed with lots of ram pressure when flying without water injection. With water injection, or at lower speeds, you need to switch earlier.

Higher MP doesn't always mean more power, because the higher gear supercharger consumes part of the extra power. So while MP might go up for the F4U at sea level, the engine actually delivers less hp until you're at about 1000m altitude, the exact figure depending on atmospheric conditions and your engine settings.

[majorfailure]

Originally Posted by The Stalker

1) Firstly, what's the deal with the supercharger? When flying the F4U I can see a noticable amount of manifold pressure gained if I toggle to speed 2 immediately at ground level. If more MP = more engine power, are there any side effects in switching to speed 2 right from the start and not at recommended 2000m?

With water injection activated, 2000m is to high to switch stages, try 600m and 2000m may even be to high without water injection.

In Il-2 you can usually switch charger stages a few 100m early or late without significant disadvantages in power output, and it doesn't matter what stage you use -you will never ever get your engine damaged even if you use stage 3 at tree top level or stage 1 at 10km.

[The Stalker]

Originally Posted by JtD

Higher MP doesn't always mean more power, because the higher gear supercharger consumes part of the extra power. So while MP might go up for the F4U at sea level, the engine actually delivers less hp until you're at about 1000m altitude, the exact figure depending on atmospheric conditions and your engine settings.

This is modeled in the game?

[JtD]

Yes, it is.

[Jumoschwanz]

Originally Posted by The Stalker

So what about the actual game? More power but no consequences?
I understand also that running something like power 100% on 60% prop pitch would also ruin the engine, but is not modelled and not the case in the game... Generally running much greater power than PP would damage real life engines also. Is that true?

Think of prop pitch like the transmission in your automobile. If you were to put a stick-shift automobile in high gear, 5th gear of a 5 speed for instance and then drive very slowly at speeds you would usually use 1st gear for, the engine would have a tough time. And if you floored the throttle while running really slow in high gear it would have a high risk of damaging the engine or drive-line parts.

The job of the pressure in an internal combustion engine has the job of pushing the piston down it's bore and spinning the crankshaft. Under normal operating conditions the design engineers expect the pressure to be able to push the piston down it's bore in a certain time and then exit through the exhaust system. If your automobile or aircraft is stuck in a transmission gear or prop pitch that keeps the engine rpm much lower than the designers had in mind then the very hot gases are in the cylinder for much longer and have more time to make the engine hot before they are pushed out and a very cool charge of fresh air and fuel are pulled into the cylinder. It is a delicate balance that engineers figure out for operators of combustion engines in advance, but they can be circumvented by "determined" individuals.

The heat produced by combustion is hot enough to destroy the materials the engine is made of, but it does not because the heat is supposed to be carried away by air or liquid coolant systems. Yes the fresh charge of intake fuel mixture is one of the engine coolants.

On a very hot day you might notice the temperature gauge in an automobile go up while you are sitting at a standstill in traffic and then go down while you are at cruising speed on the highway. Same as an aircraft engine, the cooling systems are designed to work best with air going over them. Going slow with little airflow but at high throttle and high pressure and heat in the engine can overheat the engine.

New computerized engine management systems have knock sensors in the cylinder heads that will automatically alter the mixture and ignition timing if the engine starts to experience pre-ignition or detonation. Before these management systems a lot more was up to the operator.

When the air fuel charge in the engine is ignited by the spark plug the gas in the cylinder increases in volume many times but is held in relatively the same space, you can imagine the pressure increase, it goes from roughly atmospheric, up to hundreds or thousands of pounds! Altering the point at which the ignition lights the fuel charge will alter the pressure in the combustion chamber. Early ignition will burn the fuel charge more completely but will put maximum pressure in the cylinder, if there is too much pressure before the piston reaches top dead center then a power drop and overheating will result, too little ignition advance and un-burned fuel will be pushed out the exhaust and wasted, so again it is a delicate balance with the ignition. Older engines had ignition lead altered by a combination of initial, mechanical and vacuum, currently this is almost all done with computers of course.

Lots to know and learn and it is a hobby unto itself.

[RPS69]

Nice post Jumo.
Extremely nice.

[Laurwin]

Originally Posted by The Stalker

This is modeled in the game?

Jtd is correct on that, I believe.

You can still though, switch back and forth between supercharger 1 and 2, to see if there's any notable increase in manifold pressure.

I'm not sure about low lever supercharger gear 2 myself, I don't seem to recall using it at low level AND having it increase manifold pressure significantly, and sustainably.?

What happens to your airspeed, rpm and manifold pressure if you go to supercharger 2, right at 600m altitude?

I think Jtf is of course correct about less horsepower available, this is true for regulard superchargers, which exist in aircraft such as F4U corsair.

From wikipedia:
P-47 on the other hand has turbosupercharger. Turbocharger is powered by a turbine that is driven by the engine's exhaust gas.

Regular supercharger is mechanically driven from the engine, often from a belt connected to the crankshaft

In real life this sort of regular supercharger operating procedure - switching back and forth between supercharger gear 1 and 2, would not be good for the safety of the engine (but this, is not modelled in game)