# Principles of Flight Drag Lift Thrust and Weight

Flight is defined as the motion of an object in or through a medium, usually through the earth’s atmosphere or space. Flight is as a result of the four basic forces; lift, weight, thrust and drag. When one flies straight and level at a constant speed, the thrust will be equal to drag and lift equal to weight as well. Force is a very important requirement in flight; it is defined as a push or pull force.

Thrust is a force that opposes drag, whenever there is more thrust than drag; an airplane accelerates along the flight path until the increasing drag restores equilibrium. Thrust is a factor that limits the top speed of an airplane. converting rotational energy into thrust. The difference between thrust and power is fundamental to understanding of an aircraft’s performance.

Weight is defined as the force of an object due to gravity, which is a force that pulls everything towards the earth’s surface. Planes and other aeronautics need enough lift force to oppose the weight force. Lift force acts upwards against the weight and is caused by air moving over and under the wings of the plane. The weight is distributed throughout the plane or flying object but the effect is on a single point known as the center of gravity. The center of gravity is always located at the longitudinal centerline of the airplane.

Drag is a force exerted on an object moving through a fluid; it is oriented in the direction of relative fluid flow. It is also caused by moving any type of object through the air. Most flying bodies such as airplanes are streamlined or have a streamlined shape to be able to cut through the air in order to get a minimal drag. Drag increases as speed increases until a point reaches when the drag is equal to thrust, and an airplane will continue in a steady flight at a higher speed.If the thrust is greater than drag, the airplane will not climb. There are two types of drag; induced drag and parasite drag

Induced drag – This is the type of drag that is undesirable but unavoidable by product of lift and increases in direct proportion to increase in angle of attack

Parasite drag – This is the resistance of the air produced by any part of an airplane that does not produce lift.

Lift is an upward force created by an airfoil when moved through the air. It may be exerted to some extent by many external parts. There are three principal airfoils on an airplane; wing, propeller and the horizontal tail services. Lift is generated by motion of air passing over the aircraft’s wings; the direction of wings is perpendicular to the flight direction. Its magnitude will depend on several factors; shape, size and the velocity of the aircraft/airplane.