Aircraft Motion
Physics of Aircraft
Lift
Drag
Weight and Thrust
Secondary Controls
Stability
Straight and Level
Climbing
Descending
Turning
Aircraft Design Features
The Stall
Practice Exam

Forces

Vectors

All forces are vectors, which means they have both a strength and a direction. For example, lift is the force created by the wings and its direction is perpendicular to the relative airflow. In straight and level flight, this direction is convenient as it is directly opposite the downwards force of weight. However, as soon as the aircraft is banked the lift vector is tilted and it is no longer opposite in direction to weight.

Components of Vectors

For convenience, we can break this vector down into two components. One vector that is directly opposite weight and one that is perpendicular. We now have a vertical component of lift and a horizontal component of lift. To keep this aircraft level, the total lift force needs to be increased until the vertical component is again equal to weight.

Any force can be resolved into two components in this manner.

We can also reverse this procedure to combine two seperate forces into one resultant force.

We will discuss turning in more detail later. For now, the important fact to remember is that any force vector can be resolved into two components at 90° to each other.

Newton’s Laws of Motion

Inertia
Newton’s first law states that, if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by a force.
Force = Mass x Acceleration
Newton’s second law describes the relationship between force, mass and acceleration. The bigger a force is, the greater the acceleration that it will cause. The bigger the mass of an object is, the greater the force that is needed to move it.
Every action has an equal and opposite reaction
Forces are always found in pairs – if two forces acting on an object are equal in strength and opposite in direction, the object will not move. If the force acting in one direction is stronger than the force in the opposite direction, the object will begin to move.