Explain what effect an increase in airspeed has on lift, as well as on drag, both induced and parasite - Essay Example

Aerodynamics Assignment Aim This assignment will discuss the effect of airspeed on lift and drag. Lift and Drag Lift is the component of force perpendicular to the direction of oncoming airflow and drag is the force (resistance) parallel to the airflow direction (Dole and Lewis, 2000). These are depicted at Figure 1. Figure 1. Airfoil Forces Lift increases with the square of speed. This is shown by the lift equation: Lift= CL x (? p V2) x wing area (s), where CL is the coefficient of lift and p (rho) is density (Dole and Lewis, 2000).

Assuming that in level flight, CL, p and s remain constant, then as speed is increased lift will increase. This equation is derived from Newton’s second law of motion whereby the net force on an object is equal to its rate of momentum change (Dole and Lewis, 2000). Thus, as air flow increases across an airfoil section, the rate of change of momentum is increased across the upper areas of the wing section, increasing lift (Dole and Lewis, 2000). Bernoulli’s principle states, an increase in the speed of a fluid occurs simultaneously with a decrease in pressure.

This is seen in the equation: Pressure+1/2 density(rho) V2= constant 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: Drag = Cd x(1/2 pV2) x area, where Cd is the coefficient of drag. 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: Pressure x cross sectional area x velocity =constant (Dole and Lewis, 2000).

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. Induced drag is due to the production of lift (Dole and Lewis, 2000) and is at 90 degrees to the lift vector. The angle subtended by the vector is known as the induced angle of attack (FAA, 2001).

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 were thrust not increased, the forward motion of the aircraft would gradually decrease to such a point that there was insufficient lift to sustain upwards movement and the aircraft would stall. The stall pitches the nose down, creating increased airflow over the wing section and once again lift is increased as speed increases, enabling the recovery from the stall (FAA, 2001). References Dole, Charles. E. and Lewis. James. E. (2000). Flight Theory and Aerodynamics: A Practical Guide for Operational Safety (2nd ed.). New York: Wiley-Interscience.

Federal Aviation Administration (FAA). (2001). Aerodynamics for Naval Aviators. Newcastle, WA: Aviation Supplies & Academics, Inc.