We will start with a definition which is often debatable, but I will use the following for a starting point:

Flight is the process by which an object moves through an atmosphere (or beyond it, as in the case of spaceflight) without contact with earth’s surface. It needs enough upward force to counteract gravity.

A hot air balloon traps the raising hot air and lifts the basket up exceeding the pull of gravity. For horizontal flight, the object uses propulsion from a propeller or jet engine generating enough lift from the airfoil to counteract gravity.

Today we will discuss the force generated by an airfoil. This is explained by the Bernoulli Principal: the pressure in a stream of fluid is reduced as the speed of the flow is increased

Marriam-Webster Dictionary

Air is considered to be a fluid. An airfoil or wing typically has a flat bottom and curved top. As the air passes over the top of the airfoil, the speed increases and the pressure decreases thus generating a vacuum that pulls the wing upward. This is the same effect from a propeller that has the shape of an airfoil. The propeller has a lower pressure on the front thus pulling the aircraft forward or upward as in a helicopter.

A hot air balloon simply uses trapped hot air to ascend and has little or no control of direction. A rocket uses an engine that produces upward thrust to ascend with some limited directional control. A baseball pitcher uses his strength to propel the ball and can change its direction by inducing a spin allowing the Bernoulli effect to curve the ball. A knuckle ball has little or no spin thus causing an uncontrolled flight path. These forces can be easily demonstrated by spinning a beach ball in various directions.

The wing generates upward force on the fuselage but provides no directional control. The directional stability is provided by the appropriately named stabilizers. A horizontal and vertical stabilizer are typically at the back of the fuselage.

Entering our gallery, at the bottom of the ramp, is an exhibit showing the Bernoulli Principal. The ball spins and stays levitated because of the pressure differentials. Just across from the exhibit is a huge vertical stabilizer. This is equally curved on both sides stabilizing the aircraft direction but not generating any forces to either side. This is an actual vertical stabilizer taken from 747 and an excellent example of how large the 747 is.

There are many aerodynamic forces affecting flight especially as noted in Isaac Newton’s Laws of Motion. Newton’s Third Law; For every action there is an equal and opposite reaction, generates a problem. This article introduced the useful element of lift. Future articles will explain how to deal with ‘the opposite and equal reaction’ often called drag and how, by modifying the shape of airfoils and stabilizes in flight, the aircrafts can climb, turn and descent.

Art Krull

FoF Volunteer Ambassador