Ch.2 - How an aircraft generates lift This effectively means lift is reduced from the back of the wing first, and both the separation point and centre of pressure move forward as the wing reaches its critical angle of attack, which is normally around 16 degrees. As the angle of attack reaches the critical angle the separation point and centre of pressure move drastically forward, at this point the air becomes very turbulent on top of the wing. The airflow under the wing is generally still laminar. At the critical angle of attack there is a huge increase in turbulent air, and a large loss of lift. At this point the force of weight will be more than lift, and the aircraft will descend. The wing is producing the most amount of lift just prior to the critical angle of attack (16 degrees angle of attack). It is important to note that an aircraft can stall at any airspeed. The stall is caused by the aircraft exceeding the critical angle of attack. In relation to stalling, as an aerofoil increases its angle of attack the lift increases and so does the induced drag. There is an angle of attack that represents the maximum lift for the least amount of drag for the aircraft. This maximum lift for the least amount of drag is known as ‘best lift to drag ratio’ and is used to determine the aircraft’s best glide ratio. We do not use angle of attack indicators in most light aircraft. The pilot operating handbook will advise on the aircraft’s best glide speed which is the best glide ratio. If this speed (and corresponding angle of attack) is maintained, the aircraft will fly the longest range with no engine power (in a glide). Any speed either side of this number will increase the total drag and reduce the aircraft range. Best lift to drag and glide speed
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