109 prop pitch (rpm) and the supercharger

[Crumpp]

Can we all specify exactly when we are referring to prop rpm, when we a re referring to engine rpm, and when we are referring to both?

What is referred to as propeller rpm is actually measuring engine rpm but you use the propeller governor to control it in a constant speed propeller. In a direct drive, meaning the propeller is bolted right to the crankshaft, fixed pitch propeller the engine control is just the throttle which sets the rpm.

In a variable pitch propeller, the throttle controls manifold pressure and the propeller controls are used to set the engine rpm. What is confusing people is at the limits of the propeller blade movement, it will change rpm. So if you pull the power to idle from cruise, your rpm will change too. You are not controlling rpm with manifold pressure though, it is just an effect because they are dependant upon each other.

The rpm and manifold pressure settings found in the Operating Notes correspond to a specific point of maximum efficiency. This point is based on the speed of the aircraft.

First of all, what is a propeller?

It is just a wing that moves in a circle. Like any wing, it has limited range of angle of attack from zero lift to maximum lift coefficient. It is also subject to critical mach effects like any wing.

All propellers reach peak efficiency for a give pitch angle at a specific velocity. Just like the wings on the airplane have a point of highest lift to drag ratio, a propeller is no different.

That is why fixed pitch propellers come in "cruise" and "climb" propellers.

A variable pitch gives the pilot the advantage of being able to use a wide range of peak efficiencies by adjusting the pitch angle of the blades and the speed at which the propeller rotates. It allows us to adjust the angle of attack and dynamic pressure our rotating wing requires to keep it at the point it can transfer the most thrust force to the air.

The "popping the clutch" analogy was very good for what the German pilots were doing. The engine has a finite amount of power and thrust it can generate. The point of maximum thrust production is defined by a velocity and the most efficient engine setting. We cannot produce extra power from nothing and just changing blade angle is NOT going to change that point of maximum efficiency or necessarily get us there quicker.

Popping the clutch in your car does not increase the cars power or speed it can attain. Done correctly, you gain an increase in acceleration to the maximum point of efficiency. Done poorly, you loose traction and it takes longer to reach the point of maximum efficiency.

[Crumpp]

Are you Crumpp in alias?....you seem to have much the same charm, no need to get patronising.

Bongodriver, he is just right. Can you accept that?

[bongodriver]

Originally Posted by Crumpp

Bongodriver, he is just right. Can you accept that?

as soon as I'm shown data that says a prop turning at 1500 rpm is going to be efficient.....yes I would happily accept it, it's all I'm asking for and not a tirade of sarcasm.....so you can stick your little blue face up your rectum.

[Al Schlageter]

bongo, what is the prop tip speed of a 3.1m prop at 2400rpm and 1500rpm?

[Crumpp]

Originally Posted by bongodriver

as soon as I'm shown data that says a prop turning at 1500 rpm is going to be efficient.....yes I would happily accept it, it's all I'm asking for and not a tirade of sarcasm.....so you can stick your little blue face up your rectum.

Maximum helical tip velocity is an important parameter for propeller selection. In the absence of specific data from the prop manufacturer, it is safe to assume that (a) the maximum prop efficiency will be about 87% (for any metal prop a non-governmental agency can afford), and (b) that the prop efficiency begins to decrease dramatically when the prop is operated at a helical tip velocity in excess of 0.85 Mach. That occurs because the local air velocity over the surface of the prop (near the point of maximum airfoil thickness) will reach Mach 1, and create a shock wave, separating the flow and dissipating prop energy.

http://www.epi-eng.com/propeller_tec..._propeller.htm

You should probably spend more time reading such things as the Pilot's Handbook of Aeronautical Knowledge instead of lurking on gaming sites if you are professional pilot who does not know this kind of basic stuff.

Just saying, it would be safer for you and your passengers.

[Crumpp]

I am simply pionting out that what you said about how to fly a Bf109 is in conflict with what Steinhilper said about how to fly a Bf109

But is not in conflict and agrees with what is related in the anecdotes.

If you understood how an adjustable pitch propeller works in conjunction with the engine, you would see that.

It is useless to discuss it with you. Have a nice life, Tagert.

[Crumpp]

P. Ponk Aviation
Propeller Efficiency Calculator

To produce maximum thrust at full power your tip speed should fall between .88 and .92 mach. To move between .88 and .92 mach usually takes a change of about 110 to 120 RPM. This of course varies depending on your particular propeller and the temperature.

If your tip speed is less than .88 mach you should increase RPM to achieve maximum thrust. If your tip speed is greater than .92 mach you should reduce RPM to achieve maximum thrust. Do not exceed the published operating limitations of your engine or propeller.

Over .92 mach the airflow begins to detach from the propeller which decreases efficiency and dramatically increases noise. To improve performance and public relations you should consider reducing RPM so as to fall within the .88 to .92 mach range. Your propeller will be producing maximum thrust which is good for you, and less noise which is good for all of us.

http://www.pponk.com/HTML%20PAGES/propcalc.html

[ACE-OF-ACES]

Originally Posted by Crumpp

But is not in conflict and agrees with what is related in the anecdotes.

If that is true..

Why get so upset and say I was attacking you?

Brings to mind the old saying..

thou dost protest too much

[bongodriver]

Originally Posted by Crumpp

http://www.epi-eng.com/propeller_tec..._propeller.htm

You should probably spend more time reading such things as the Pilot's Handbook of Aeronautical Knowledge instead of lurking on gaming sites if you are professional pilot who does not know this kind of basic stuff.

Just saying, it would be safer for you and your passengers.

I dont need some walt without a pilots license telling me what I should concentrate on thank you.