Re: RE: RE: RE: RE: Effective AOA on prop blades?

From: <RLBailey_at_care4free.net>
Date: 02 Oct 2013 10:36:49 +0100

This discussion reminds me of an episode about 10 years ago when 2 well known F1D fliers proposed an F1D layout which was designed to keep the prop shaft aligned with the direction of flight. Some tests appeared to show a significant improvement. The only flier to get any real success in UK was Ron Green who is sadly no longer with us. Despite much determined effort I had no success with these; the rest, as they say,is history!

Far more to this topic than meets the eye!

Bob

On Oct 1 2013, leop_at_lyradev.com wrote:

















Obviously, the explanation and examples assumed straight ahead, level flight. Depending on the diameter of the turning circle, the forward airspeed is different on the sides of the plane but that just goes into calculating the advance for the various prop radii if one wants to get into that much detail. The upward (or downward) tilt of the propeller also affects, to a greater degree, the AoA of the blade. For nose up prop angles, the "downward" moving blade (the one on the right side for the usually indoor direction of prop rotation) sees a larger AoA than the left side. This difference creates a thrust difference which help turn the plane. This is called the "P-factor." This is accounted for in the differing pitch angles for the left and right side of the prop, plus and minus 2 degrees in your example. So, the equations work in these cases if one realizes that the airspeed and pitch angles change with the circle diameter and nose angle respectively. LP ---In Indoor_Construction_at_yahoogroups.com, wrote:and doesn't the prop on the outside of the circle see a lower AoA (when the nose is flat)? ---In Indoor_Construction@yahoogroups.com, wrote: But what if the nose is up by two degrees ;-) ? ---In Indoor_Construction@yahoogroups.com, wrote:
A short
time back, I posted about using the Advance Ratio to understand some aspects of
propellers. The advance of a propeller
is just how far forward the plane moves in one revolution of the prop. One definition of the Advance Ratio is just
this distance divide by the diameter of the prop. This is similar to the P/D ratio (pitch
divided by prop diameter) that we often speak of. The advance of a propeller is just:Airspeed
/ (prop angular speed)
In usual
units: advance = air speed
(inches/minute) / prop rpm
One can calculate
the angle of the prop blade at each radius using the pitch of the prop:
tan(angle)
= pitch / (2pi x radius).
One can calculate
a similar angle using the advance, A :
tan(advance
angle) = advance / (2pi x radius).
The advance
angle is the apparent angle of the air as seen by the prop blade at each
radius.
Since
the pitch angle is the angle of the prop blade, the difference between the pitch angle and the
advance angle is the angle of attack (at each radius):
AoA =
arctan (pitch angle) – arctan(advance angle)
I hope
this answers your question. Post if this
is too confusing or if you have other related questions.
Leo
---In Indoor_Construction_at_yahoogroups.com, wrote:Greetings.
Let's say I know RPM and the angle a blade is formed at.
I am finding all sorts of references to the effective angle of attack
changing as airspeed changes. But nothing as far as how you calculate it.
Can someone point me to the math equations for calculating the effective AOA?
Regards.
Mike Kirda

Received on Wed Oct 02 2013 - 02:36:51 CEST