Aircraft design – lift/drag forces

Lift force- causes plane to lift away from earth surface

- difference in atmospheric pressure above aircraft wing described by Bernouli’s principle - low pressure above the wing caused by faster air movement over the wing, relative to below the wing which is subjected to usual atmospheric, high pressure.

- according to Pascal’s principle, all fluid pressure aims to achieve balance or equilibrium in the complete system. For this reason, the higher pressure below the wing pushes the wing into lower pressure region above the wing, hence causing the plane fuselage attached to the wing to be lift.

Drag force

- opposes forward movement of aircraft through the air

- drag friction is caused by many things, such as aircraft skin smoothness (), aircraft form/shape, air thickness (viscosity), air pressure, induced drag (caused by wing length & shape), parasitic drag, wave drag, and ram drag. Winglets are used to reduce wing induced drag.

Aeronautic drag forces.

* Drag is a mechanical force that is generated when solid objects move through fluids (…………….. and ………………).

* Different types of drag are produced depending on various factors

Parasitic drag is the total of form, wave, pressure, ram and friction types of drag

Form – shape of the solid

Wave – shock waves that occur when movement is close to speed of sound

Pressure – force against moving surface (Newtons 3rd law)

Friction – between moving surface – solid and fluid viscosity

Ram – slowing of free air when entering engines and cooling vents

Induced drag – produced by lift force of plane – vortex around wingtips

Streamlined objects have less drag.

Lift/drag ratio is best close to 4.

Drag is especially needed when trying to slow an aircraft down – to reach safe landing velocity, and to stop aircraft from rolling once landed on ground.

Wing ailerons, flaps, rudder, elevators, trim