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Which statement is correct regarding the Lift Coefficient?
  • A
    It changes with density.
  • B
    It increases with an increase in angle of attack up to the critical.
  • C
    It changes with the velocity of the airflow squared.
  • D
    It is at its maximum value at the angle of attack with the maximum lift to drag ratio.

Refer to figure.
Lift is defined as the proportion of the Total Reaction vector (vertical component), which acts at 90º to the relative airflow and is given by the formula:

  • Lift = CL ½ ρ V2 S

Where:

  • CL, is the Coefficient of lift, dimensionless number, consisting of the blade shape, the profile shape of the blade, the angle of attack, the Mach number and the Reynolds number (viscosity).
  • ρ, is the air density.
  • V2, is the squared forward airspeed of the blade travelling through the air.
  • S, is the total surface of the blade.

Regarding the CL, the only variable that can be changed significantly during flight by the Pilot’s action is the angle of attack.

If the Pilot increases the angle of attack, then the lift coefficient and as a result the lift production increase, but only up to the critical angle of attack.

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