Ch.2 - How an aircraft generates lift The attitude is also closely related to the aircraft airspeed. Let's look at what happens when an aircraft slows down in level flight. We know that lift is a factor of velocity, so as the aircraft slows down, the lift starts to reduce. If nothing changes the aircraft will start to descend. The only way for the aircraft to stay level is to create more lift by increasing the angle of attack. The pilot controls the angle of attack by altering the aircraft’s attitude by pitching the nose up or down with elevator control. An aircraft wing stalls when its angle of attack exceeds the critical angle. In most training aircraft this is about 16 degrees angle of attack. Now we will look in detail at the forces that act on the wing as it approaches the stall. Let's assume the aircraft is slowing down and trying to maintain level flight. As the relative airflow starts decreasing so too the lift decreases. To maintain level flight, the angle of attack will need to be increased. On top of the wing we have the centre of pressure. The centre of pressure is the average point where all the different pressure forces are applied on the wing. As the wing's angle of attack starts to increase, so does the lift and drag, and the centre of pressure starts to move forward. While the wing is still producing lift the airflow remains ‘laminar’, which means the airflow flows smoothly over the wing. As the wing approaches the critical angle of attack the airflow starts to become turbulent towards the back of the wing. The part of the wing where the laminar airflow starts to separate and become turbulent, is called the ‘separation point’. Angle of attack and stalling
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