Both Daniel Bernoulli (1700–1782) and Sir Isaac Newton (1643–1727) lived before the wing was invented, but their science explains what we now take for granted. When I took my basic flight training 40 years ago, Bernoulli’s principle ruled in explaining the miracle of flight: An increase in the speed of a fluid (air) creates a simultaneous decrease in pressure. To understand how this applies to flight, look at the profile of an airliner wing (called its camber): The leading edge is much fatter than the trailing edge, and the top side of the wing is slightly bowed whereas the underside is flatter. Air speeds up as it flows over the top of a wing and the air pressure drops. The higher pressure below then lifts the wing (and the airplane) upward since air moves from high–pressure areas to low–pressure areas – as any meteorologist knows.
Still, Bernoulli’s principle does not explain the lift felt by your hand when you hold it out the window of a moving car, or why some aircraft are able to fly upside down. This is where Sir Isaac Newton comes in with his third law of motion: For every action there is an equal and opposite reaction. As airflow is forced downward, it pushes your hand – or any wing – upward, which is what enables certain aircraft with symmetrical airfoils, such as stunt planes, to roll over and fly inverted. A fast–moving wing, then, creates a low–pressure zone to rise up into while also generating enough force to lift a plane off the ground – it’s a modern phenomenon that has both Bernoulli and Newton in the equation.
