Soft Field take off

Soft field Take-off

Objectives

  • How to take off on a soft runway surface.
  • How to take off with an obstacle.
  • How to get the best angle (vx) and best rate climb speed (vy).

Why?

  • A lot of runways require this technique.

Link

Questions review

  • How to take off on a soft runway surface.
  • How to take off with an obstacle.
  • How to get the best angle (vx) and best rate climb speed (vy).
  • What are factors that affect takeoff performance?

Ground effect

  • Ground effect is caused by ground interference with airflow patterns around an aircraft when the aircraft is within one wingspan of the surface. As the wing encounters ground effect there is reduction in the upwash, downwash and the wingtip vortices.
  • The result is a reduction in induced drag. Thus, for a given angle of attack, the wing will produce more lift in ground effect than it does out of ground speed.
  • Consequences: At a height over wing span the ground effect disappears and if you lift-off too soon the plane may come back on the ground due to decrease lift and increase drag.

Soft field take off without obstacle

  • cockpit check
  • 10 degrees of flaps (check POH)
  • Roll back to the runway without stopping the airplane then:
  • No brake
  • Full power gently
  • Control column full back pressure.
  • Lift and hold nose up, wheel off runway
  • Rotate as soon as possible
  • Accelerate in ground effect until Vx or Vy speed.
  • Climb at Vy speed (check POH) until safe altitude and speed.
  • Retract flaps.
  • Accelerate to Vy

Soft field take off without obstacle

Same procedure as soft field take off with obtacles, except:

  • Climb at Vx speed (check POH) until clear the obstacle.
  • CONSIDERATION:
    • Close to stall speed.
    • Add speed if the wind is gusty.

Review questions

  • Why do we keep the plane rolling from taxi to takeoff rather than stopping?
  • Why fly in ground effect?
  • What will happen to climb rate if the nose is pulled up and airspeed falls below Vy or Vx?
  • What is the main difference between soft field take off with obstacles and soft field take off without obstacles ?