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Ubet_I
04-14-2004, 06:03 PM
Hello all! I am a bit confused with the pitch settings. The lower the percentage the more the prop bites? Hence more speed with lower rpm? And when in a dive what is the best pitch stting for recovery from a dive? Thanks all.

Ubet_I
04-14-2004, 06:03 PM
Hello all! I am a bit confused with the pitch settings. The lower the percentage the more the prop bites? Hence more speed with lower rpm? And when in a dive what is the best pitch stting for recovery from a dive? Thanks all.

Monza27
04-14-2004, 06:11 PM
http://mywebpages.comcast.net/Tailspin/documents/CEM_IL2FB.htm

That should help.

JG7_Rall
04-14-2004, 06:11 PM
Lower percentage=More "bite"

Lower RPMs don't necessarily mean more speed.

Prop pitch is generally used to keep RPM's at a constant rate. When you climb or dive your RPM will be effected so you adjust the percentage (climb=higher dive=lower) to maintain a constant RPM. You want a balance between not too slow and not over revving your engine.

S!

Hutch

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IKP_Hawk
04-14-2004, 06:32 PM
Scroll down the recent thread by Flying_Nutcase.

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El Turo
04-14-2004, 07:15 PM
Simplistic answer for IL2FB:

Most Allied aircraft will have a system wherein you control the RPM, not really the pitch. You tell the engine what RPM you want, and it will automatically adjust the pitch to meet that RPM as best as it can.

That means setting your "pitch" to 100% will give you maximum RPM, which is in most cases going to be the peak of your power curve as well.

At lower RPM/pitch settings, you will have a bigger "scoop" of air being pulled by the prop, but not as often (RPMs are lower)... which means that you are moving less VOLUME of air and thusly not producing as much thrust/speed/acceleration.

Analogy time:

Think of a man in a rowboat with a normal sized oar... then replace that oar with a HUGE paddle. He is going to be pulling much larger volume of water with each stroke, but will most likely not have the strength (HP) to be able to pull enough water as quickly to match the efficiency and total output of the regular sized oar. This is an extreme example of why a "bigger bite" at low-pitch settings doesn't necessarily mean more output.

The only instance this is different is in a high speed dive, wherein a low RPM/pitch setting will benefit you by way of decreased prop-drag (blades are flatter in relation to oncoming wind).

With variable props (Axis fighters on "manual" control), you are DIRECTLY controlling the prop pitch and therefore have better fine-control but also have a much smaller tolerance for error. You'll have to keep an eagle's eye on the RPM gauge to make sure you do not overspeed the engine and blow/damage it... which can be done rather easily if not monitored during an engagement.

Callsign "Turo" in IL2:FB & WWIIOL
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Fennec_P
04-14-2004, 07:30 PM
So....

high % = fine = high RPM

low % = coarse = low RPM

El Turo
04-14-2004, 07:42 PM
More or less, yeah.

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Callsign "Turo" in IL2:FB & WWIIOL
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michapma
04-15-2004, 12:36 AM
I've tried to provide a good explanation here:
http://people.ee.ethz.ch/~chapman/il2guide/cemguide/proppitch.htm
Be sure to look at the section "Controlling rpm" and "Power settings" as well.

H_Butcher is quite right, down to a detail. The man pulling the oar does not have the strength to pull the oar when the oar is grabbing more water (larger volume), and this corresponds to torque, not horsepower. It is important to realize that power is torque (the force the man and water put on the oars at a distance to its point of rotation) times speed (how fast the oar moves). With an aircraft engine and propeller, coarsening the blade angle loads the engine, and the whole system (prop and engine together) slows down. The pistons might be pushing harder on the cylinders (torque), but they are not rotating them as fast as before (rpm), and although the prop is grabbing more air each revolution, as H_Butcher points out it is not doing that revolution as fast as before. The thrust the prop produces is roughly the amount (mass) of air thrown back per second times the speed at which the air is thrown back.

The nice part of that is that the blades and engine operate more efficiently at higher blade angles/lower rpm, and the aircraft has significantly less drag at airspeeds corresponding to less engine power (full engine output power is usually designed to occur at maximum rpm of the engine). So for full power, you want full rpm (redline), and for economical and normal power, you want less rpm (and less manifold pressure).

These engines are extremely powerful, operating at very high manifold pressure. The pilots of these aircraft did not go flying around at full rpm and full manifold pressure all the time like we like to in the game. Full power (much less WEP) was reserved for takeoff, combat and go-arounds and other emergency situations. They also didn't have the luxury of spawning and getting a factory-fresh engine. Their engines were their lives, and they took care of them. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

H_Butcher is also right in that you have to consider what plane you are flying. Most of the Allied planes use constant-speed propellers (CSP). In these you are setting rpm, not prop pitch. The governor alters prop pitch to hold the rpm steady. Most German planes use a sort of whatc could be called an aeromechanical prop, which is fully automatic. In both cases there are limitations depending on airspeed, and rpm cannot be held constant. A very few of the older aircraft (maybe only just the TB-3?) have no prop adjustments, they have a fixed-pitch prop.

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