As we have already seen due to the Coanda effect, as the airflow hits the front of the wing due to the curvature of the aerofoil - or angle of the wing- in relation to the airflow, it causes a drop in pressure that produces lift and also sucks or accelerates more airflow over the top of the wing, which accelerates the airflow over the top of the wing. Bernoulli's principle states that ‘when a fluid increases its speed, there is a reduction in pressure’. This curvature of the airflow over the wing is actually what causes the drop in pressure. Lift and Bernoulli's principle There is also another reason why the aerofoil produces lift and this is due to Newton's third law of motion. Newton's 3rd law states: ‘For every action, there is an equal and opposite reaction’. Due to the Coanda effect the airflow is deflected down at the back of the aerofoil. This creates a force deflecting down at the rear of the wing. Due to Newton's third law, an opposite force must result from this downward force and this upward force is lift. Lift and Newton's laws This deflection of the airflow causes a drop in static pressure above the wing. Even if we had a straight non-curved wing, if we angle the straight wing in relation to the relative airflow, a drop in static pressure will occur. This is one reason why paper aeroplanes can produce lift even though they have no curved upper surface. Ch.2 - How an aircraft generates lift
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