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Microlight » Gyroplane Technical Knowledge » Dissymmetry of Lift

Dissymmetry of Lift

The situation where one side of the rotor disk has more lift than the other side.

Advancing and Retreating Blades

As an aeroplane moves forward in the air, both wings come in contact with the oncoming airflow and have an equal Relative Airflow (RAF).

Rotary wing aircraft moving forward in the air, like gyroplanes and helicopters, have blades that;

  • move forward, Advance, into the oncoming airflow, increasing its RAF; and then 
  • move backwards, Retreat, away from the oncoming airflow, decreasing its RAF.

So if the tip speed of the rotor is approximately 300 mph and the forward speed of the aircraft is 50 mph, then;

  • the Advancing blade has a RAF of 350 mph; and 
  • the Retreating blade has a RAF of 250mph.

The increase in RAF = an increase in lift.

In a anti-clockwise rotating rotor blade, looking from above, the advancing side is to the right and the retreating side is on the left.

The lift is greater on the advancing side and the gyrocopter would roll to the retreating side, which is Dissymmetry of Lift.

Dissymmetry of lift is caused by the airflow created by aircraft airspeed.

If the gyrocopter increases its speed, dissymmetry of lift increases.

Eliminating Dissymmetry of Lift

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