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Have you ever wondered, what is takes to get plane
up in the air? If so, here is the explanation.
First of all, we need to understand the forces that
work on a plane. There are four types of forces on a plane
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Thrust: Force that pushes the aircraft forward
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Weight: Force that pulls the plane downward
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Drag: Its kind of friction that tries to stop
plane from moving forward
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Lift: Upward force that keeps the plane in
air
For an airplane to fly, following
2 conditions must be true:
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Thrust > Drag
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Lift > Weight
Thrust is delivered by engine and
is directly proportional to its horse power. Drag is usually a
by product of aircraft shape, wings and other add on. It is also
directly proportional to the speed of the plane. Pilot can increase
the drag by lowering the flaps, increasing angle of attack (increasing
rate of climb or pulling the nose up) etc. However, if engines
are running, Thrust will always be greater than drag.
Lift is the most important factor
in flight and is created by movement of air over wings. This means
that for a plane to fly it’s wings needs to be moving through
the air. A wing produces lift because it is a certain shape. If
you cut through a wing and look at it side ways you will see the
shape that is called an aerofoil. As air flows over a wing the
air on the top of the wing travels faster than the air crossing
the bottom of the wing. When the air goes past the wing, the shape
of the airfoil turns the air downwards. The difference in speed
of the air and the turning of the air means that there is a pressure
difference between the top and bottom surface of the wing. There
is low pressure(or effectively a vaccum) on the top of the wing
and high pressure underneath the wing. Due to this vaccum, wings
get tend to move up, thus providing the necessary lift to the
aircraft.
How can you increase lift?
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Lift is directly proportional to speed of
the plane. Faster the plane, greater the lift.
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Higher the airdensity, higher the lift.
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Wing - area and shape plays a pivotal role
in generating more lift for an aircraft.
Forces in various stages of flight:
| |
Aircraft Position |
Forces Acting |
Plane Position |
Control Surfaces and Flaps |
| 1 |
Stationary |
Weight >
Lift |
The plane is on the ground |
|
| Lift = Thrust = Drag
= 0 |
All other forces are 0 |
| 2 |
Moving down the runway |
Weight >
Lift
|
The plane is still on the ground
|
The flaps are deployed
to increase the lift that the wings produce. |
| Thrust >
Drag |
The plane is accelerating (getting
faster)as it goes down the runway |
| 3 |
Take off |
Lift = Weight
|
At the exact moment that the plane
leaves the ground
|
The elevators are raised,
pushing the tail down and the nose up for takeoff.
The flaps are still deployed |
| Thrust >
Drag |
The plane is still accelerating |
| 4 |
Climb |
Lift > Weight
|
The plane ascends
|
The elevators are still
raised, pitching the plane upward for the climb.
The flaps are slowly withdrawn as the plane rises |
| Thrust >
Drag |
The plane accelerates
horizontally |
| 5 |
Cruise |
Lift = Weight
|
The plane stays at the same height
|
The elevators are returned
to their neutral (flat) position. |
| Thrust = Drag |
The plane descends at a constant speed
vertically |
| 6 |
Descend |
Weight >
Lift
|
The plane descends |
The elevators are lowered |
| Drag > Thrust |
The plane is decelerating horizontally |
| 7 |
Landing |
Weight = Lift
|
The plane touches down |
The elevators are lowered.
The flaps are deployed to give the
plane
more lift as it is traveling
slowly |
| Drag > Thrust |
The plane slows to a stop |
Source: www.raes.org.uk, www.d155.org,
NASA, www.berkeleyscience.com
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