Question

1. what are the four main forces acting on an airplane in flight? if the plane accelerates forward, which two forces must be out of balance? to fly on a level path, which two forces must be in balance?

Explanation:

• Four main forces:
• Lift: Generated by the wings, acts perpendicular to the flight path.
• Weight (Gravity): Acts downward due to the plane's mass.
• Thrust: Produced by engines, acts forward.
• Drag: Opposes the motion, acts backward (air resistance).
• Accelerating forward:
• According to Newton's second law ($F = ma$), for forward acceleration ($a>0$ in the forward direction), the thrust (forward - acting force) must be greater than the drag (backward - acting force). So, thrust and drag are out of balance.
• Flying on a level path:
• In the vertical direction, for a level flight (no vertical acceleration, $a_y = 0$), from Newton's second law ($F_y=ma_y$), the lift (upward - acting force) must balance the weight (downward - acting force).

Answer:

• Four main forces: lift, weight (gravity), thrust, and drag.
• When accelerating forward: thrust and drag.
• When flying on a level path: lift and weight.