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When an aircraft is flying level and unaccelerated...

  • A

    drag equals lift and thrust equals gravity.

  • B

    thrust equals the sum of drag and gravity.

  • C

    thrust equals lift and drag equals gravity.

  • D

    thrust equals drag and lift equals gravity.

Refer to figure.
Thrust. The forward force produced by the aircraft's engines.
Drag. The aerodynamic resistance opposing the aircraft's motion through the air.
Lift. The aerodynamic force acting perpendicular to the relative airflow and supporting the aircraft in the air.

STRAIGHT AND LEVEL UNACCELERATED FLIGHT

During unaccelerated flight, the forces acting on an aircraft are in equilibrium, meaning they balance each other out and there is no net force causing acceleration.

  • In order to have an equilibrium in the longitudinal plane, thrust should be equal to drag. This balance ensures that the aircraft maintains a constant velocity.
  • In order to have an equilibrium in the vertical plane, lift should be equal to wight (gravity). This balance ensures the aircraft does not ascend or descend.

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