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What is Aeronautics?

Aeronautics is the science of flight. Scientists and engineers who study aeronautics learn about how and why airplanes fly. Using what they learn, they can design better, safer, and cheaper-to-build airplanes. To understand how NASA scientists and engineers begin this big job, we need to first learn how an airplane flies. Then we can answer a few other questions including:

When we are done here, we can jump into learning what tools are used to design an airplane.

How does an airplane fly?

Most of us have probably seen or felt wind blowing things like flags or kites around. But how is it possible that heavy airplanes (some weighing almost half a million pounds, or more than 200,000 kilograms) are able to be supported by air high above the ground?

The answer may sound strange at first, but it's actually the air that is pushing the airplane's wings and the rest of it up. The air under the wings pushes up more than the air on top of the wings pushes down. This "pushing" by the air is called air pressure. We can think of air pressure as air "press"-ing down or up against something else. On a windy day, you can actually feel the air pressure push against your body. The wings of an airplane "feel" a similar pushing, but there happens to be a bigger pressure under the wings and a smaller pressure on the top.

What's really amazing is why this happens. The special shape of an airplane's wing makes the air moving around it behave in a certain way. If we look at an airplane's wing from the side, we can see that the wing is a special shape called an airfoil.

Air flowing over airfoil

An airfoil is curved on the top and flat on the bottom, causing some of the air to go over the top and the rest of the air to go along the bottom. This shape looks simple, but it is the main reason airplanes can fly at all. Because of the airfoil's curved shape, the air moving under the airfoil moves at a slower speed than the air going over the top.

Daniel BernoulliA scientist named Daniel Bernoulli (Ber-NEW-lee), who lived more than 200 years ago, did work that proves slow-moving air causes a high pressure and fast-moving air causes a low pressure. Because there is a higher pressure "pushing" on the underside of the wing than on the top, the bottom pressure wins out overall and the wings (and the airplane attached to it) are pushed up, making the entire thing fly!

You can actually see this for yourself. If you take a strip of paper and blow over the top of it as shown in the picture below, the paper will rise.

Experiment to try

What happened? You lowered the pressure that was pushing down on the top of the paper, causing the pressure on the bottom side of the paper to push the paper strip up. The same thing happens when air pushes on the bottom side of an airplane's wing. The pressure that is pushing the airplane up creates a force called lift in the upwards direction.

For a further explanation of lift.

What forces act on an airplane?

There are four forces acting on an airplane in flight: lift, weight, thrust and drag.

Four forces acting on airplane

We already know that lift comes from the wings. What about the other forces?

Weight is a force caused by gravity. You've felt gravity every time you jump. Gravity is what pulls you and everything else back down to the ground. This "pulling down" by gravity is what causes you to have a "weight" that you measure when you step on a bathroom scale. An airplane's weight also pulls downward on it - directly opposite to the lift force that is pulling the airplane up. It's like the lift and weight forces are playing a game of tug-of-war. One pulls in one direction and the other pulls in the opposite direction. For level flight, lift and weight must balance each other out.

Thrust, caused by the airplane's engines, is the force that moves the airplane forward. If an airplane did not keep moving, air would stop moving over and under the wings. Without this movement of air, the wings could not create lift, and the airplane would start to fall back to the ground!

Drag is the force that tries to slow down a moving object. To lessen the drag that an airplane feels, most airplanes are made more aerodynamic, or streamlined, to reduce the amount of drag they feel. A streamlined airplane has smooth surfaces and no bumpy sections, causing as little resistance to the air as possible. Just like lift and weight are opposite forces, thrust and drag are opposites to each other too. For an airplane to keep flying, its thrust must be bigger than its drag.

Can I see any of this myself the next time I'm flying on an airplane?

Definitely! Now that you know what makes airplanes fly, you can look for certain things the next time you are aboard.

Looking out an airplane's window

Right before take-off, feel your back get pushed against your seat as the airplane builds up its speed before leaving the ground. As the airplane races down the runway, it's waiting until enough lift is created by the wings to lift the entire thing off the ground. If you are sitting by a window and can see the wing look at the way the ailerons (flaps on the back edge of the wing) move up or down when the airplanes banks or turns.

When the airplane gets ready for landing, try to listen for the sound of the landing gear being lowered below you.  Then, right before touchdown notice the large wing flaps in their down position.  The pilot lowers these flaps so he or she can more easily control the airplane at such a slow speed.  After landing, look at how the spoilers (big rectangular sections in the middle of the wing) pop up to create more drag to slow down the airplane even more!

What are the different types of airplanes?

You may be wondering why there are so many different types of airplanes out there. What makes them different from each other? We'll take a quick look at what makes each of the following airplanes unique:

Cargo/Transport Airplanes

GuppyFreighterCargo/transport airplanes have a lot of room inside them to carry things that would ordinarily be too large or too heavy to carry on other types of airplanes. Sometimes these planes carry trucks, packages, construction equipment, or even other airplanes! Since cargo/transport airplanes are so big they usually have large, powerful engines to help get themselves off the ground. Because of their large cargo bays, a few of these planes are a little unusual-looking. It's no wonder that the "Guppy" and the "Beluga" are named that way - they look like huge fish! Sometimes private shipping companies and the postal service use modified passenger jets as cargo planes. In those cases, most or all of the passenger seats are removed and large containers full of cargo go in their place. Pictured here are a Boeing 757 freighter and a Airbus Guppy.

Experimental Concept Airplanes

X-29X-36When engineers are designing an airplane, they often build one or two full-size airplanes of the design to see if it flies the way it should. Because the engineers are still experimenting with the design, these types of airplanes are sometimes called experimental concept airplanes or prototypes. A specially trained and very experienced pilot flies these airplanes, and then reports to the engineers. The research pilot can tell them what he or she thought were the good and bad features of the airplanes and what needs to be improved. Many times, experimental concept airplanes are quite unique-looking because they are trying out a strange, new concept or technological advance. Most experimental planes, like the X-36 and X-29 pictured here have names starting with "X" as in eXperimental.

Fighter/Military Airplanes

F-15F-16There are many different kinds of military airplanes. Transport airplanes carry armies, equipment, and supplies hundreds of miles to where they are needed. Reconnaissance, or spy, airplanes fly secret missions to photograph enemy territory. Fighter airplanes were used for the first time in World War I. Today, most fighters have advanced computer, navigational, and weapons systems and are able to maneuver quickly and precisely in case they have to participate in aerial combat. Some fighters are able to fly at supersonic (faster than sound) speeds for short periods of time, and other fighters use stealth technology to make themselves nearly invisible to enemy radar. The first letter in the name of a military airplane tells us what kind of mission it flies. For example, the F-16 and F-15 shown here are types of fighters. Similarly, a B-2 is a bomber, a A-10 is an attack airplane, and a C-7 is a cargo/transport airplane.

Passenger Airplanes

747ConcordeThe airplanes most people see most often are passenger airplanes. These are the type of airplanes that you are more likely to board at the airport or see or hear flying overhead. The earliest airliners in the 1950s were very noisy and could not travel very far without refueling. Today, people use passenger jetliners to travel all over the world for both business and pleasure. Most jetliners travel at about 600 miles per hour (965 kilometers per hour), and some can carry people and cargo for over 8,000 miles (12,874 kilometers) non-stop. Some airplane designers are working on passenger airplanes that carry more than 600 people or fly at supersonic speeds. Right now, the Concorde is the only supersonic passenger jet, traveling at twice the speed of sound (1,400 miles per hour or 2,250 kilometers per hour)!

By the way, do birds fly the same way airplanes do?

Eagle in flightYes, for the most part, birds and airplanes fly for the same reasons. If we looked at the shape of a bird's wings, we would see they are curved the same way airfoils on airplanes are. When a bird glides during level flight, it stays in the air just like airplanes do - its wings provide the lift. However, birds flap their wings up and down to go higher in the sky while airplanes must use a combination of control surfaces and their powerful engines. In the 19th century, before airplanes were around, some inventors tried strapping homemade wings to their arms and jumping off buildings to copy the flapping motion of birds - usually with deadly results. Unlike humans, birds have strong wing muscles that give them the power needed for flight. So, after millions of years of evolution, birds and insects continue to fly on their own, but humans will have to depend on machines like airplanes. For more information how birds, bats, and marine life fly, check out the Aeronautics Internet Textbook's chapter on the aerodynamics of animals.

Why does NASA study aeronautics?

NASA scientists and engineers work together with other researchers from several universities and aerospace companies to learn how to design better airplanes. What does this mean to the general public? Improved or more modern airplanes are easier to maintain, cost less to operate (which means a cheaper ticket for the passengers aboard), are safer to fly, and are better for the environment. NASA focuses on several areas including weather-related safety, aging airplanes, advanced structures and engines for airplane design, air traffic control, helicopters, airport and supersonic engine noise reduction, turbulence prediction, and the human factor.

An Aeronautics Glossary

Where else on the Internet can I learn about aeronautics?

As part of a national program in High Performance Computing and Communications (HPCC), NASA is working to empower educators and students to use the evolving National Information Infrastructure to meet their educational needs. Through grants and cooperative agreements, the following aeronautics-related educational materials have been developed:

Follow these links to programs which provide curriculum, interactive materials, activities, and more!


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