Physics

Bernoullis Principle of Lift



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More than a century before the Wright brothers' first flight, a Swiss mathematician named Daniel Bernoulli developed a theory on how it could be accomplished. Based on Newton's 2nd law of gravity Bernoulli showed air will always travel faster over a curved top surface, such as an airplane's wing, than it will travel over a flatter bottom surface.

Bernoulli published his now famous equation in 1738 with details on the flow of fluids in terms of speed, pressure, and potential energy. In its original form it's still confusing to scientists and mathematicians to this day, so it was later clarified and in honor of its author, renamed "Bernoulli's principle." His work was so powerful and influential that even today we consider Bernoulli to be the "father of mathematical physics." There's no documentation telling us everywhere he thought his principle would apply, but we do know it took someone another 165 years to see its use for flight.

Edward Huffaker, started his career as a professor in the late 1800s and moved his way up in the working world to a post under Samuel P. Langley, the 3rd Director of the Smithsonian. Langley and Huffaker were both intensely interested in exploring the possibilities of flight. Both built gliders for others to test, and both had working relationships with the Wright brothers, though Huffaker's was considerably more strained.

In 1893 Huffaker wrote to Langley suggesting the Bernoulli principle could be the answer to a wing's lift in flight. They conducted airfoil experiments together and in July of 1901 Huffaker was photographed with the Wright brothers at Kitty Hawk. Finally in 1903 the Wright brothers made their legendary flight, and history credits Huffaker with part of that success by recognizing how to apply Beroulli's principle to flight.

Despite Bernoulli's principle having become a staple of aerodynamics, it hasn't been the answer to all questions. So people like Jef Raskin, one of the creators of the Macintosh computer, was already challenging Bernoulli's principle before he left middle school. He argued with his science teacher the principle didn't explain how a plane could fly upside down since that put the curved surface of the wing on the bottom and its flat surface on top.

Raskin was right, and soon after we learned the "angle of attack" was an added element to keeping a plane in the air. To understand what an angle of attack is all you have to do is stick your hand out of the window in a moving car. Change its angles and you'll see the angle of your hand has a lot to do with how the wind "lifts" it up or down. The same is true of an airplane where a change in the direction of its nose also changes its angle of attack. So it became evident as time has passed there was more to keeping a plane in the air than just Bernoulli's principle.

We could hardly fault Bernoulli for this. He couldn't be expected - in 1738 - to foresee all that today's aerodynamics encompass. Bernoulli's principle did give us a primary element of flight, but not why it works. Without this why we still don't know precisely what keeps airplanes from falling out of the sky. Aeronautical engineers and physicists continue their heated debate over this issue - perhaps if Bernoulli were alive today he'd be able to help them out.

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