How does an airplane fly?
Ever wondered how an A380, the biggest airplane in the world, stays in the air? To be honest, the exact and correct answer is really difficult. So I will keep it by the basic explanation. The most heard declaration (the law of Bernoulli) isn’t wrong, but still incomplete. In fact, there are 2 reasons why an airplane flies.
1. The law of Bernoulli
The law of Bernoulli is one of the reasons that an airplane can fly, according to him the wing profile does the work:
the upper part of the wing is curved and the bottom is approximately flat. This forces the air to stream much faster over the upper part (curved) than over the bottom (flat) of the wing. Because of the high speed of the air, there is less air above the wing. This creates a lower pressure above the wing than the pressure beneath the wing. This way lift is generated and the wing is pushed upwards.
2. More lift or upward pressure
Another declaration for the upward pressure or lift is much simpler. With a simple test, you can actually feel the lift. (At own risk!) Put your hand out of the window of a fast driving car. First hold your hand with the fingers tight so flat as possible. Your hand now cuts through the air as a knife through butter. Next hold your hand slant and mark the difference. Your hand wants to rise! This is caused by the streaming air that pushes against the underside of your hand resulting in upward pressure or lift.
By an airplane the air streams against the bottom of the wing in a certain angle and pushes the airplane upwards (you could also say that the wings push the air that they meet down, and according to the law of ‘action=reaction’, the wings are then pushed upwards by the air). This angle is called the angle of attack, it is the angle that is formed by the chord of the wing and the direction of the relative wind or in other words the angle between the wing and the horizon. The angle of attack changes in flight as the pilot changes the pitch (up or down) of the aircraft. The increase in angle of attack increases lift up to a point. A too high angle of attack results in loss of lift and causes an aircraft to stall.
If you feel how strong this force is in the experiment, then you could imagine how strong it is by a speed of 300km/h and by a wing surface of 845m2. No wonder anymore that the A380 stays in the air. But you must have a fast enough horizontal speed. That’s why an airplane has engines. For more lift, the wing profile can be adjusted, according to the phase of the flight (take-off, cruise, landing). This happens with flaps, slots, spoilers and ailerons, their functions are described in this article: secondary flight controls.
