PRINCIPLES OF FLIGHT 3 WWW.GOFLY.ONLINE Y ONLI NE FLI GHT SCHOOL Washout Washout is when the wing is designed so that the angle of attack reduces from the wing root to the wing tip. This causes a lower angle of attack at the wing tips which ensures the wing root stalls before the wing tip, making the stall less severe. Flaps Flaps are a lift generating device on an aircraft’s wings which work when extended, by changing the camber, or shape, of the wing. The use of flaps lowers the aircraft stall speed. By creating more lift the aircraft can takeoff and land at a lower speed, and the result is less runway is required for both takeoff and landing. Slats and slots A slot, normally located on the trailing edge, is used to deflect air from below the aircraft to the upper wing to reduce the stall speed and allow the aircraft to fly at lower speeds for shorter takeoffs and landings. Slats, like flaps, are a liftgenerating device that are found on the leading edge of a wing and, when extended, they increase the camber of the wing and produce more lift, allowing the aircraft to takeoff and land at a slower airspeed. Trim tabs A trim tab is a small control surface attached to the primary control surfaces. Trim tabs can be located on ailerons, rudders and the elevator. Most training aircraft only have trim tabs on the elevator. A trim tab is basically a secondary flight control surface which allows the pilot to reduce the pressure on the control column. As an example of how they work, let’s look at an elevator trim tab. During a climb the elevator is angled into the airflow and experiences a dynamic pressure which acts to force the elevator back to the neutral position. To counter this force, when the pilot chooses the desired elevator position, the trim tab can be set to create an opposite lift force to maintain the position of the elevator. The elevator will now stay in this position without any input from the pilot. Factors Affecting Lift The following factors all affect an aerofoil’s production of lift. Air density The higher the density of the air, the more lift that is produced by the wing. As a very general rule, if we halve the air density we halve the amount of lift the wing can produce. The higher the altitude, the less dense the air, so as an aircraft flies higher its wings will produce less lift. Higher air density results in more lift. Surface area The larger the surface area of the wing, the more lift that can be produced. As a general rule, if we double the size of the wing, we double the amount of lift available. The same can be said for drag. As the surface area of the wing increases so does the drag, and in general, if we double the size of the wing, we double the drag. Larger surface area results in more lift. Angle of attack Angle of attack is the angle between the wing chord and the relative airflow. As we increase the angle of the attack of the wing, the lift produced will also increase until lift reaches its maximum at the critical angle of attack. Higher angle of attack results in more lift, at least up until the critical angle of attack is reached. Angle of incidence The angle of incidence is the angle between the wing chord line and a reference axis that runs along the fuselage. The angle of incidence cannot be changed on an aircraft, as generally the wings are rigidly attached to the fuselage, and has no effect on the production of lift. Velocity As the velocity/airspeed of the aircraft increases, we get more airflow over the wing, and therefore more lift being produced. Higher velocity results in more lift.
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