I was just wondering, what difference does changing the direction of the propellers on a plane had on the motion of it
Answer by ageekmom · Sep 28, 2010 at 03:32 PM
On most single-engine aircraft (in the United States, anyway,) most propellers spin/rotate to the right, from the pilot's perspective. Some single-engine (single propeller, non-jet) aircraft have what is known as a "variable pitch" propeller which allows the prop blades to change their angle in flight, thus affecting their "bite" to the wind, but they do not rotate "backwards".
If the aircraft is a multi-engine (multiple propellers), then it depends. One some aircraft, the propellers rotate the same direction; on others, the propellers rotate opposite one another ("counter-rotating props"). It depends on the airframe, the engines, and such. The same is true of jet aircraft engine turbines, I believe.
I'm not an aeronautical engineer or physics major so this is a layman's view as the wife of a pilot who flies small, single-engine (single prop) aircraft.
Answer by Justen Robertson · Sep 29, 2010 at 12:53 PM
The main thing is that the propeller has to spin in the direction the blades are made to spin. There's no physical reason they have to go clockwise or counterclockwise beyond that. Reversing the direction of the propeller spin will move air in the opposite direction, but it will not cause the plane to fly backwards because the wings won't create lift while moving backwards (it might roll backward slowly on the runway). Reversing them in flight would probably cause the plane to stall and crash as it slowed down, and might destroy the engine due to the competing forces of the air direction vs. the direction the reversed propeller is trying to push.
Answer by Marc · Dec 13, 2010 at 04:32 AM
There's no reason that they can't spin in the opposite direction.
However, an interesting effect of changing the direction of the blade (and reversing the design of the blade) would result in a change the climbing characteristics of single engine aircraft.
As it is now, all single engine aircraft have "left turning tendencies" during steep climbs (eg. takeoff). If the bade was reversed, the aircraft would have a right turning tendency.
Left turning tendencies are caused by two factors. One is due to rotating air from the propeller which spins around the body of the aircraft and hits the sides of the the aircraft and tail. The other (and more significant is due to the difference between the angle of attack of the blades:
During a climb the aircraft is pointing up and moving forward more than it's climbing. The relative wind is crossing the front of the at an angle. The blade that is moving upward's angle is near-perpendicular to the relative wind, and is not as efficient as the propeller which is moving downward, and attacking the relative wind at a greater angle. This results in a bunch of torque coming from the right side of the aircraft.
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