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From: "Bryan Winberry" <bryanwinberry@bellsouth.net>
To: "'Rotary motors in aircraft'" <flyrotary@lancaironline.net>
References: <list-4152974@logan.com>
Subject: RE: [FlyRotary] Re: The stalled propeller blade
Date: Fri, 5 Mar 2010 08:31:07 -0500
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In-Reply-To: <list-4152974@logan.com>

Bill,
All that sounds familiar from ground school.  It's only been about 30 years
and I haven't thought much about prop torque or P-factor....till now.
Cheers,
BW 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Bill Bradburry
Sent: Thursday, March 04, 2010 11:49 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: The stalled propeller blade

Bryan,
I think P-factor is the result of a couple of things...

One, the thrust line of the engine is at an exaggerated upward angle on
takeoff and climb and, on most planes, a slightly less up angle in cruise.
This angle is in relation to the forward motion of the plane.  This causes
the ascending propeller blade to have a lower angle of attack than the
descending blade.  That causes asymmetrical thrust with the most thrust on
the right side of the propeller.  That results in a turning moment to the
left.

Two, the air being pushed to the rear by the prop is swirling around the
fuselage in a clockwise motion.  That causes the swirling air to impinge on
the left side of the rudder.  That results in a turning moment to the left.

These two factors are greatest in takeoff and climb configuration, but they
never go completely away.  Most planes have the vertical stabilizer cocked a
couple of degrees to the left to counter these turning forces to the right
when the plane is in cruise.  This is called rigging.  If you are lucky, you
will not need rudder in cruise as a result.

There is a third factor in that when the propeller is rotating clockwise,
the fuselage of the plane tries to rotate counterclockwise. (opposite and
equal reaction).  This left rolling force is countered by a slightly higher
angle of attack on the left wing in relation to the right wing.  Rigging
again.  The higher angle of attack increases drag on the left wing and
results in a turning moment to the left as well. 

When you find a plane that "doesn't fly straight", rigging is a possible
cause. 

Bill B

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Bryan Winberry
Sent: Thursday, March 04, 2010 9:35 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: The stalled propeller blade

Dave,
Please don't attribute that statement to Lynn.  He was responding to me with
the same font.

And you are correct about the pitch of the plane changing the AOA of the
prop.  I seem to recall this being talked about in ground school many years
ago.  But still, fixed prop AOA isn't something we intentionally control
like a CS prop.   At least that's the way it seems to me. P-factor is just
something we have to put up with till we gain higher speeds on climbout.

I need to go to the basement and work on the project or I'll never get to
the prop part.

Thanks,
Bryan

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Dave
Sent: Thursday, March 04, 2010 8:01 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: The stalled propeller blade

Lynn Hanover wrote:
>
>  AOA, I think in terms of the wing producing max lift.  The AOA 
> changes with elevator input.  A prop is not unlike a wing, but I still 
> don't have a grasp of what is causing AOA change in a fixed pitch 
> prop.  But, usually I have to read things three or four times in order 
> to "get it".
>
Ok.. a "fixed" pitch prop can have a changing AOA.. heres how..

The pitch angle of the plane.. itself... along the crankshaft axis.. has an
impact on how the prop sees the oncoming air, and hence varies the angle of
attack of the prop blades.

An airplane flying at lower airspeeds in its regime will tend to fly nose
high..

An airplane flying at higher airspeeds will tend to be nose level or even a
tad nose down..

The same prop on the same plane at two different speeds will result in two
different pitch angles and therefore two different angle of attacks.. which
then have an effect on thrust.

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