Date: Sun, 12 Apr 2009 23:49:03 -0400
Reply-To: Mike <mbucchino@CHARTER.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike <mbucchino@CHARTER.NET>
Subject: Re: Only ONE drive wheel?
Content-Type: text/plain; charset="iso-8859-1"
Just to set the record straight, this is not completely true.
The propeller is 'biting' the air, and is completely unaware of it's position relative to anything. Air is everywhere around it, and it has absolutely NO reference to up, down, fore , aft , left or right, or which side the ground is closest to Gravity, alone, as a factor impacting the rotation, is practically nil, compared to the many other forces working on the blades.
Yes, the sudden movement causes a short-duration, somewhat-bigger 'bite' in one direction, but it has nothing whatsoever to do with the location of the ground.
What is a much larger factor there, is "gyroscopic precession", which may have been what you were alluding to regarding taildraggers. For the un-initiated, it means that if you push against one side of a rotating mass, the force applied will output 90 degrees in the direction of rotation. This is the same force that allows a child to use a stick to tap-steer a rolling hoop. A stick tapped on the left of the 12 o'clock position of the hoop as it rolls forward, will result in a turn towards the left (when the 'top' of the hoop continues to rotate to the 'front'). Try it, if you want a fun lesson in physics.
The larger the mass, the greater the force. It's both harder to affect, as well as more severe reaction once affected. An aircraft prop has lots of mass and lots of rotational speed, so it makes one hell of a gyroscope. ANY sudden control inputs to change direction (up, down, left right), will cause some hard-to-control output reactions, but a good pilot knows this and plans ahead for it with compensational control adjustments.
Mike B.
> However, when the pilot rotates the nose of the airplane skyward, the
> angle of the propeller and the crankshaft changes relative to the earths
> plane. Given that most modern American made aircraft engines rotate to the
> right as seen from the pilots seat, the propeller blade on the right will
> be going down while blades on the left will be going up. Because of the
> change in the angle relative to the ground, the propeller blade on the
> right going down takes a much bigger bite of the air, than the blade on
> the left coming up. This produces much greater thrust on the right than
> the left, and the airplane tries hard to turn left all through the climb
> to altitude.
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