Aeronautics

The Four Forces

It is important to understand that while in flight, there are always four forces acting on your unmanned aircraft:

• Weight;

• Lift;

• Thrust; and

• Drag.

Weight - the act of gravity on the aircraft, pulling it towards the ground

Lift - the upward force that counter acts gravity. This is created by the propellers pushing air downward (on a multi-rotor UAV), or by the high and low pressure areas created by air flowing over the wings (on a fixed wing UAV).

Thrust - what causes the aircraft to be propelled forward. This can either be from the propellers on the top of the aircraft being angled in one direction (on a multi-rotor UAV). In this instance, the propellers would be contributing to both lift and thrust. Thrust can also be created to a propeller mounted to the front or back of the unmanned aircraft that pushes air rearward and propels the aircraft forward.

Drag - the opposite of thrust. This is what causes the aircraft to slow down. This is generally created by different types of friction created by the aircraft structure itself. A very thin and aerodynamic aircraft will generate less drag than a large boxy aircraft, due to the different amounts of friction they create. Think of sticking your hand out the window of a car and the difference you feel between when you have your hand parallel with the ground or perpendicular to the ground.