Science Magazine

An Introduction to Flight

Posted on the 11 September 2011 by Nerdywerds @NerdyWerds
It's been over 100 years since man first achieved flight, it's time we understand how it works

Does December 17, 1903 have any significance in your mind? It should; it's the date the Wright brother's first achieved heavier than air human flight. The technology of aviation has advanced by leaps and bounds since that time. But the basics principles of flight are getting close to 300 years old. Daniel Bernoulli, a Dutch-Swiss mathematician published the book Hydrodynamica in 1738. In the book, Bernoulli formalizes "Bernoulli's principle", which is the foundation for aviation. We'll get into the fluid dynamics for which Bernoulli is famous later, but I'm just trying to illustrate a point at the moment; the mechanics of flight are too old to be as widely misunderstood.

Depending upon where you live, you can probably step outside right now and see a plane in the sky. Regardless of where you live, you've probably been in one of these sky chariots. The wonder of flight is truly an amazing feat. For the purpose of this article, we're not going to discuss the mechanical systems of an airplane; we're only going to be discussing the physics of flight. I've learned from experience that people tend to get a bit scared upon hearing the word "physics", but don't be. Physics has gotten a bad rap for being more difficult than it really is. As a bit of a caveat, this article is only concerned with the flight of traditional airplanes. We will not be discussing the flight of helicopters or other aerial crafts; but if you'd like me to, hop on the Facebook page and let me know. Without any further delay, let's get this baby airborne.

First off, we need to get a bit technical. Scientists classify gases and liquids as fluids. They classify them as such due to their flow properties. So whether it be water, milk, molasses or even air, all fluids have uniform mathematical relationships. Swimming through a pool or flying through the air actually have more in common than you might think. Even though the sky above our heads is not an aquarium, it is still full of fluid.

There are four basic aerodynamic forces that must be utilized to achieve flight; lift, weight, thrust and drag. The first two, lift and weight, are actually opposing forces. The last two, thrust and drag, as you might have ascertained, are also opposing forces.

First up are thrust and drag. Thrust is a force in aerodynamics that propels the airplane forward through fluid. Whether it be a pushing or a pulling force, as long as it is moving the vessel onwards, it's thrust baby! The Yang to thrust's yin is drag. Drag is, as we stated earlier, the opposing aerodynamic force to thrust. Drag is the friction on an object that impedes it's progress through a fluid. It's important to add the "through a fluid" part because the object doesn't have to be moving. Think about a bag caught in an updraft. The bag is just being affected by moving fluid. This gets us to another important; for an object to obtain flight, either it must be moving through a fluid, or a fluid must be moving around it. A plane flies through a fluid whereas a bag gets caught by moving fluid. For flight to be possible, the thrust must equal or exceed the amount of drag. When the equilibrium tips, and drag exceeds thrust, the object slows down.

If you've ever been on a 1,200 calorie diet, woken up at 4:45 AM to go to the gym or bought a treadmill, you're all to aware that every object on Earth has weight. Weight is a product of not only mass, but also of gravity. If you go to the moon, for instance, you'll weigh approximately 1/6th what you do here currently. In aerodynamics, weight is force which attempts to drag an object towards the Earth. Lift is the aerodynamic force trying to stymie weight's attempts to bring planes down. Lift is the force that holds an airplane in the air. In airplanes, lift is achieved thanks to a wing, also known as an airfoil. Lift, like drag, is only possible in the presence of a moving fluid. As I said earlier, it is irrelevant whether the motion is due to the fluid or the object. All that matters is the speed differential.

In an airplane, thrust is easy to identify; it's created by the airplanes turbines. Drag is the friction on the moving aircraft, and weight comes from a rather obvious place. Lift is where the marvels of science come in. The lift is achieved by the airplane's wings splitting the airflow. Some flows over the wing, the rest under it. The wings are designed and shaped in such a way that the air moving over them travels much faster than the air moving under it. The shape of the wing's top acts much like crimping a hose does; it narrows the path the fluid must travel through, so the resulting stream has much more force behind it. This is relevant because as air speeds up, its pressure drops. The air moving over the wing exerts a good deal less pressure on the wing than the air moving beneath it. This differential in pressures results in an upward force, or lift. Less pressure is being applied down upon the wing as is being applied upwards. Remember when I mentioned Bernoulli's principle earlier, well, that's what this is.

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