Aircraft Aerodynamic Forces

There are various forces that act on an aircraft during flight which helps to ensure the aircraft stays in flight as well as being able to maneuver during flight as well as land. In essence there are 4 aerodynamic forces that affect an aircraft in flight.

  • Lift
  • Weight
  • Thrust
  • Drag

Lift – Moves the aircraft up

Weight – Pulls the aircraft down due to gravity

Thrust – propels the aircraft forward by pulling air in through the from of the propeller and pushing air away from the rear of the propeller

Drag – provides resistance (wind) to slow the aircraft down the opposite of thrust.

In an aircraft moving in a straight and unaccelerated flight, with no change in speed or direction, the four forces will be considered to be in equilibrium as the thrust and drag will be equivalent as well as the lift & weight being equal. Any changes to either four forces could result in a change in speed or direction.

Bernoulli’s Principal of Creating Lift

Daniel Bernoulli is a physicist who discovered the principal that as water is being forced through a restriction and speeds up, it’s pressure decreases as well as the inverse that as water coming out of being in a restricted state, the pressure increases.

In applying this from water to air, airflow over a wing acts in the same manner in that as air is forces over the opt of a wing, it speeds up and its pressure will decrease.

“Airfoil” – The shape of a wing or other lifting surface.

camber” – the curve of the airfoil

chord line” – an imaginary line connecting the leading edge to the trailing edge

relative wind” – opposite direction to your flight path

angle of attack” – the angle between the relative wind and the chord line.

– if the angle of attach become too great, then air cannot flow smoothly over the edge of the wing which will disrupt the production of lift.

critical angle of attack” – the maximum angle before lift is greatly reduced, drag is greatly increased and the wing becomes stalled

For the Cessna 172 Skyhawk and the Cessna 162 Skycatcher, the “critical angle of attack” is about 16 degrees with flaps up. Most smaller general aviation aircrafts are designed to stall with an angle of attack at around 15-20 degrees.