four forces of flight

Four Forces of Flight

• Lift• Weight• Thrust• Drag

Source: NASA Glen Research Center

Forces on an Airplane

Lift

• Lift is an aerodynamic force• Lift must exceed weight for flight• Generated by motion of aircraft through air• Created by the effects of airflow past wing• Aircraft lift acts through a single point

called the center of pressure.

Weight

• Weight is not constant– varies with passengers, cargo, fuel load– decreases as fuel is consumed or payload off-

loaded• Direction is constant toward earth’s center• May be assumed concentrated at the center

of gravity

Thrust

• Forward-acting force opposes drag• Direction of thrust depends on design• Propulsion systems produce thrust• Equal to drag in straight, constant speed

flight

Drag

• An aerodynamic force• Resists forward motion• Two broad drag classifications

– Parasite drag: drag created by airplane design– Induced drag: by-product of lift generation

• Acts through the center of pressure

What’s Missing?

CONTROL & PROPULSION

Scientific Method

Think about what the world still needed before controlled flight

could become a reality