Choice of Flap Setting for Take-off, Climb and Landing

Flap Setting for Take-off

Flaps are used during takeoff to increase the lift coefficient (CL) of the wings, allowing the aircraft to achieve the necessary lift in available take-off distance with maximum weight/payload.

Take-off distance depends on unstick speed and rate of acceleration to that speed.

The unstick speed (Vr) is the speed at which the aircraft rotates (or lifts off) during takeoff.

Now selection flap setting brings the following dilemma:

  • Selecting a flap setting that maximizes CLmax helps to reduce Vr, allowing the aircraft to become airborne at a lower speed.
  • However, using larger flap angles also introduces higher drag. This reduces acceleration and increase the distance required to accelerate to unstick speed.
  • Lower flap angle can decrease the drag and increase acceleration, but it increases the target Vr.

In summary, the choice of flap setting for takeoff involves a trade-off between lift and drag. Pilots aim to select some optimum flap setting that allows for shortest possible take-off distance. Aircraft’s performance charts or performance application assist in determination of optimum flaps setting.

Flap Setting for Climb

Aircraft in a clean configuration typically have the best lift-to-drag (L/D) ratio compared to configurations with extended flaps. The clean configuration refers to retracting or minimizing the extension of flaps, which reduces the drag produced by the aircraft.

Once the aircraft is safely airborne and has cleared any immediate obstacles, transitioning to a clean configuration allows it to optimize its performance for the climb phase. By retracting flaps, pilots can reduce drag, increase airspeed, and climb more efficiently. However, it’s important to note that the decision to retract flaps and transition to a clean configuration during climb depends on various factors, including aircraft type, weight, altitude, and specific operating procedures. Pilots must follow manufacturer-recommended procedures and consider operational requirements to ensure safe and efficient climb performance.

Flap Setting for Landing

Landing distance depends on touchdown speed and deceleration. Flap setting for landing is quite simple. Dilemma of take-off flap setting (tradeoff between unstick speed and rate of acceleration to that speed) doesn’t exists for landing.

Lowest touchdown speed is given by highest CLmax (obtained at large flap angle). Large flap angle also gives high drag which is good for deceleration. For landing, largest possible flap angle is used.

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