PRINCIPLES OF FLIGHT 5 WWW.GOFLY.ONLINE Y ONLI NE FLI GHT SCHOOL Factors Affecting Drag The following factors all affect an aerofoil’s production of drag. Angle of attack Drag created as an aerofoil produces lift is called ‘induced drag’. As the angle of attack of the wing increases, so does the induced drag. Higher angle of attack results in more drag. Velocity Velocity affects the total aerodynamic force, meaning both lift and parasite drag increase with an increase of the velocity of the airflow over the wing. Parasite drag is all drag that is not associated with the production of lift. Interestingly, in relation to lift and drag forces, if we double the velocity of the airflow we quadruple the lift and parasite drag being produced. Higher velocity results in more drag. Shape The camber and thickness of a wing affects the amount of drag that is produced. As a general rule, a thicker wing produces more lift and therefore more induced drag. Also, a thicker wing produces more parasite drag as there is more of the aircraft structure exposed to the relative airflow. Damaged aerofoil surface Damage such as dents, scratches, or surface imperfections on the wing can disrupt the smooth flow of air over the surface, leading to increased skin friction drag. These irregularities create turbulence, which increases the drag. Damage that disrupts the boundary layer flow over the wing surface can lead to boundary layer separation that affects both lift and drag. Damage to the aerofoil surface results in more drag. Lift and Drag There is an effect on the lift and drag produced by an aerofoil with changes in the following factors Airspeed Lift is directly proportional to the square of the airspeed. Therefore, increasing airspeed will increase lift, and decreasing airspeed will decrease lift. This relationship holds true as long as other factors like angle of attack remain constant. Both parasitic and induced drag will increase as airspeed increases, up to a certain point. Angle of attack Lift increases with an increase of the aerofoil’s angle of attack, up to a certain point called the critical angle of attack. Beyond this point, lift decreases, and the wing stalls. An increase in angle of attack results in an increase in drag. Flap Settings Flaps are lift generating devices, and when deployed they increase the camber of the wing, allowing it to generate more lift at lower airspeeds. Therefore, deploying flaps will increase lift. Flaps also increase drag significantly. They increase both parasitic drag due to the increased surface area exposed to the airflow, and induced drag due to the increased lift being generated.
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