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Saturday, August 17, 2019

asymmetric blade effect



By ALI AL ANSSARI
During take-off or landing in a tail-wheel aircraft, the propeller shaft will be inclined upwards with respect to the horizontal. Consequently, as the aircraft moves forward, the down-going blade of the rotating propeller covers a larger path than the up-going blade, for each rotation.
This fact means that the linear velocity of the down-going blade is higher than that of the up-going blade, and its angle of attack is also greater. Therefore the downgoing blade will generate more thrust than the up-going blade.
 The difference in thrust on the two sides of the propeller disc will generate a yawing moment to the left for a clockwise rotating propeller.
Asymmetric blade effect will be greatest at full power and low airspeed with high angle of attack. N.B. 
Torque Reaction, Gyroscopic Effect and Assymetric Blade Effect will all cause the aircraft to swing in the same direction: to the right for a propeller rotating anti-clockwise, as seen by the pilot, and to the left for a clockwise rotating propeller.
Gyroscopic Effect and Assymetric Blade Effect are most marked on tailwheel aircraft on take-off. During take-off, all effects will either be exacerbated or countered by a cross wind.



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