I've got a doozy of a question...

[psunder]

What effect does changing the relative wind flow into propeller disk have? What I am wanting to know how does the efficiency of a power unit change as the AOA (and thus the relative wind into the propeller disk) changes...

[raptor22]

Of course you get decreased thrust in a non-stalled prop. But it really depends ont he exacct prop whether or not effeciency changes.

[psunder]

Of course you get decreased thrust in a non-stalled prop. But it really depends ont he exacct prop whether or not effeciency changes.

this was my thinking as well, however I am at a loss to explain why... would this effect be atributable to p-factor alone?

[Ollie]

http://aerodyn.org/Propulsion/propeller.html

[raptor22]

Not really due to p-factor. It is because the AOA of the prop decreases.

The effeciency-per-AOA is highly dependent upon prop geometry and airfoils.

--Alex

[psunder]

Not really due to p-factor. It is because the AOA of the prop decreases.

only on the ascending/retreating blade would it decrease... AOA and velocity would increase on the descending blade. this is really the crux of my question, does the increased "bite" of the descending blade offset the decreased "bite" of the ascending blade? if not, then what are the effects on system efficiency and to what are they due? does the system become (as I suspect) less efficient due to increased drag (both induced and parasitic)?

[vintage1]

Remember that power going into the airframe = thrust x speed.

When you measure static thrust, the actual power train is 0% efficient in terms of propelling the model.

All the power is going into noise, engine heat and moving air around.

At full speed, most of the power from the prop is going to overcome drag of the airframe at that speed. That may be as little as 1/20th of the weight of the plane.

Only in full climb and initial acceleration is the engine power actually going into adding energy to the plane, by the fact of its climbing and increasing potential energy, and increase of kinetic energy.

[raptor22]

only on the ascending/retreating blade would it decrease... AOA and velocity would increase on the descending blade. this is really the crux of my question, does the increased "bite" of the descending blade offset the decreased "bite" of the ascending blade? if not, then what are the effects on system efficiency and to what are they due? does the system become (as I suspect) less efficient due to increased drag (both induced and parasitic)?

Not true. The airmoves through the prop without the rpm's increasing too much.

Visualize it this way. The prop is moving 1 rpm, constant. The plane moves at 20 mph. The air is actually hitting the prop at almost as if the prop isn't moving at all. If you speed it up, it hits it at a smaller and smaller neg angle until you have a positive AOA and are actually getting a "bite" of air.

--Alex