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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.
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.
 A 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.
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.
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.
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
  Cargo/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
  When 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
  There 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
  The 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?
 Yes, 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.
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:
- Student
Program for Aeronautics Resources for Knowledge (SPARK), University
of Idaho, Moscow, ID
- Aeronautics and Aviation Science Careers and Opportunities, Massachusetts
Corporation for Educational Telecommunications, Cambridge, MA
- Aeronautics
Learning Laboratory for Science, Technology and Research (ALL STAR),
Florida International University, Miami, FL
- Aviation Academy 2000,Wooddale High School, Memphis, TN
- Internet-based
Curriculum on Math and Aeronautics for Children with Physical Disabilities,
InfoUse , Berkeley, CA
- K-8
Aeronautics Internet Textbook, Cislunar Aerospace, Inc., Vallejo,
CA
- Lego
Data Acquisition and Prototyping System, Tufts University, Medford,
MA
- Silver State Helicopters
Follow these links to programs which provide curriculum,
interactive materials, activities, and more!
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