Noting that Bernoulli’s equation above is used for non compressible flows (low mach numbers) (FAA, 2001), the equation shows that as velocity increases, if the equation is to remain balanced, pressure must decrease. Thus, as airflow increases across the upper surface of a wing due to speed, lift is increased due to the drop in pressure above the wing.
Drag is derived from Newton’s third law whereby, for every action there is an equal and opposite reaction (Dole and Lewis, 2000). The action of the airfoil section on the incident airflow creates an opposite reaction, drag. Drag increases as speed increases (FAA, 2001). This is seen in the equation:
The continuity principle translates that in any steady state process, the rate at which mass enters a system is equal to the rate at which mass leaves the system. To be balanced, an increase in oncoming airflow must be balanced by forces resisting (drag). The continuity equation is:
Parasitic and induced are two kinds of drag. Parasitic is the resistance of the aircraft to the air through which it moves (Dole and Lewis, 2000) and increases with the square of speed. It is seen practically whereby as speed decreases, angle of attack is increased and increased thrust must be applied to maintain lift and offset the increased drag.
For an airfoil section to have a net upwards vector, lift generated must exceed the resultant forces of drag and weight. Other factors affecting lift include the coefficient of lift, which is related to wing section profile (Dole and Lewis, 2000).
A practical example of the concept of lift and drag in operation is that as an aircraft elevator moves upwards (control yoke is moved backwards), to maintain the continuity principle, rate of airflow over the wing upper surface increases, which, using the lift equation and Newton’s law, increases lift. This however creates increased drag and so