The fundamentals of aircraft controls are explained in flight
dynamics. This article centers on the operating mechanisms of the flight
controls. The basic system in use on aircraft first appeared in a readily
recognizable form as early as April 1908, on Louis
Blériot's Blériot VIII pioneer-era monoplane design.
Aerodynamics is the study of forces and the resulting motion
of objects through the air. The basic aircraft's parts that involve in the aerodynamics
are the following
·
Fuselage
·
Wings
·
Flap
·
Aileron
·
Empennage
·
Stabilizers
·
Rudder
·
Elevator
Studying the motion of air around an object allows us to
measure the forces of lift, which allows an aircraft to overcome gravity, and
drag, which is the resistance an aircraft “feels” as it moves through the air.
Everything moving through the air (including airplanes, rockets, and birds) is
affected by aerodynamics.
Basic concept of Aerodynamics
Formal aerodynamics study in the modern sense began in the
eighteenth century, although observations of fundamental concepts such as aerodynamic
drag have been recorded much earlier. Most of the early efforts in
aerodynamics worked towards achieving heavier-than-air
flight, which was first demonstrated by Wilbur and Orville Wright in
1903.Aerodynamics is a sub-field of fluid dynamics and gas dynamics, and
many aspects of aerodynamics theory are common to these fields. The
term aerodynamics is often used synonymously with gas dynamics, with
the difference being that "gas dynamics" applies to the study of the
motion of all gases, not limited to air.
Since then, the use of aerodynamics through mathematical analysis,
empirical approximations, wind tunnel experimentation,
and computer simulations has formed the scientific basis for
ongoing developments in heavier-than-air flight and a number of other
technologies. Recent work in aerodynamics has focused on issues related
to compressible flow, turbulence, and boundary layers, and has become
increasingly computational in nature.
FLIGHT BEGINS WITH AIR IN MOTION
As an airplane moves through the air, its wings cause
changes in the speed and pressure of the air moving past them. These changes
result in the upward force called lift. To understand lift, you first have
to understand how air (a gas) behaves under certain conditions. So here we will
start by Bernoulli principle:
“The
Bernoulli principle states that an increase in the speed of a fluid occurs
simultaneously with a decrease in the pressure exerted by the fluid. When a
fluid flowing through a tube reaches a constriction or narrowing of the tube,
the speed of the fluid passing through the constriction is increased and its pressure
is decreased”
HOW DOES THIS CREATE LIFT?
A wing is shaped and tilted so the air moving over it moves
faster than the air moving under it. As air speeds up, its pressure goes down.
So the faster-moving air above exerts less pressure on the wing than the
slower-moving air below. The result is an upward push on the wing
Now we have the factors that effects the lifting:
WHAT FACTORS AFFECT LIFT?
The size and shape of the wing, the angle at which it meets
the oncoming air, the speed at which it moves through the air, even the density
of the air, all affect the amount of lift a wing creates. Let’s begin with the
shape of a wing intended for subsonic flight.
WHY DOES A WING HAVE A ROUNDED FRONT?
Air divides smoothly around a wing’s rounded leading
edge, and flows neatly off its tapered trailing edge. You might
think a sharp leading edge would be better. However, air cannot turn a sharp
corner, so tilting a sharp wing even slightly would disrupt the smooth airflow
over the wing. This would cause a loss of lift and increase drag. A rounded
leading edge divides the airflow smoothly, even as the wing is tilted up or
down.
WHY DOES A WING HAVE A SHARP REAR EDGE?
If the trailing edge were rounded, the higher-pressure air
flowing along the lower side would try to follow the rounded surface and spill
upward into the lower-pressure air above the wing. A sharp trailing edge
prevents this upward spill, because air cannot make a sharp turn. Instead, the
air flowing off the top and bottom surfaces rejoins smoothly.
HOW DOES TILTING A WING AFFECT THE AIR FLOWING OVER IT?
Tilting the wing upward increases lift—to a point. If you
tilt it too much, the airflow pulls away from the upper surface, and the smooth
flow turns turbulent. The wing suddenly loses lift, a condition known as a
stall. You can reestablish a smooth airflow by tilting the wing back to a more
level position.
Air flowing past an object pushes harder against the front
than the back. This difference creates a backward force called pressure drag.
DOES DRAG INCREASE WITH SPEED?
As an aircraft's speed increases, drag on the aircraft
generally increases much faster. Doubling the speed makes the airplane
encounter twice as much air moving twice as fast, causing drag to quadruple.
Drag, therefore, sets practical limits on the speed of an aircraft.
HOW DO YOU REDUCE PRESSURE DRAG?
The air pressure against the leading side of an object is
higher than the pressure in the randomly churning eddies of the wake on the
other side of it. Streamlining reduces this pressure difference.
Friction is the resistance that happens when two things rub
together—like air against an airplane. Friction is partly what causes drag.
Air friction, or air drag, is an example of fluid friction.
Unlike the standard model of surface
friction, such friction forces are velocity dependent. The velocity
dependence may be very complicated, and only special cases can be treated
analytically. At very low speeds for small particles, air resistance is
approximately proportional to velocity and can be expressed in the form
where the negative sign implies that it is always directly
opposite the velocity.
For higher velocites and larger objects the frictional
drag is approximately proportional to the square of the
velocity:
where ρ is the air density, A the cross-sectional area, and
C is a numerical drag coefficient.
The spirals of air that trail off the tips of an airplane’s
wings also contribute to drag. These wing tip vortices steal
energy from the motion of the airplane, creating vortex drag.
HOW DO WING TIP VORTICES AFFECT AN AIRPLANE?
The pressure imbalance that produces lift creates a problem
at the wing tips. The higher-pressure air below a wing spills up over the wing
tip into the area of lower-pressure air above. The wing’s forward motion spins
this upward spill of air into a long spiral, like a small tornado, that trails
off the wing tip. These wing tip vortices create a form of
pressure drag called vortex drag.
Vortices reduce the air pressure along the entire rear edge
of the wing, which increases the pressure drag on the airplane. The energy
required to produce a vortex comes at the expense of the forward motion of the
airplane.
Improvements in aerodynamics also hold great potential. Take sharklets
for example: At a height of 2.4 metres, the latest generation of these
curved wingtips reduce fuel consumption by around 3.5 per cent. They are
used within the Airbus A320 family and its successor generation, the
A320neo. German airlines have ordered 70 aircraft with this wingtip
modification. Some older aircraft can also be retrofitted with these
sharklets.
