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Aircraft control surfaces
Aircraft flight control surfaces allow a pilot to adjust
and control the aircraft's flight attitude.The main control surfaces of a fixed wing aircraft are
attached to the airframe on hinges or tracks so they
may move and thus deflect the air stream passing over
them. This redirection of the air stream generates an
unbalanced force to rotate the plane about the
associated axis.
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PRIMARY CONTROL SURFACE
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AILERONS
The Ailerons, located on the outer part of the trailing edge of the wings,
control the roll or bank of the airplane. The two ailerons (one on each wing),
work in opposite directions to each other.
The ailerons are movable parts on the wing. They are controlled by the
stick. When you turn the stick (just like a steering wheel in a car) to the left,
the ailerons move as such that the right aileron goes down and the left
aileron goes up. This makes the airplane turn left. When you turn the stick
to the right, the right aileron goes up and the left aileron goes down. This
makes the airplane turn right.
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Elevators are control surfaces, usually at the rear of an aircraft, which
control the aircraft's orientation by changing the pitch of the aircraft, and
also the angle of attack of the wing. In simplified terms, they make the
aircraft nose-up or nose-down.
The elevators are the horizontal part of the tail. You control them, just like
the ailerons, with the stick. But to move the elevators, the pilot has to pull orpush on the stick. Pulling the joystick back will move the elevator up,
causing the nose of the aircraft to point up. Similarly, pushing the joystick
forward will move the elevator down and pitch the nose down.
ELEVATORS
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On the trailing edge of the vertical stabilizer is the Rudder .The rudder istypically mounted on the back edge of the fin in the empennage..
Centering the rudder pedals returns the rudder to neutral and stops the yaw.
This controls the yaw or the left/right sliding movements of the aircraft. On a
real aircraft, this is controlled by the foot pedals.
When the pilot pushes the left pedal, the rudder deflects left. Pushing theright pedal causes the rudder to deflect right. Deflecting the rudder right
pushes the tail left and causes the nose to yaw right.
RUDDER
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Secondary control surface
The secondary flight controls are: flaps, trimming devices, spoilers, slats,
slots and speed brakes.
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Flaps Flaps: The flaps are found on the trailing edge of the wing. They are
usually the surface inboard in relation to the ailerons. Unlike the ailerons,
they move collectively rather than inversely. When extended, their trailingedge is moved downward in relation to the fulcrum near their leadingedge. Depending on the aircraft, they may be manipulated manually orwith electric actuators/hydraulics. The effects of flaps on lift listed aboveare long term effects if the airspeed is maintained.
Types of flaps
1- Plain flaps: this flap rotates on a simple hinge.
2- Split flaps: the upper and lower surfaces are separate, the lowersurface operates like a plain flap, but the upper surface stays immobile ormoves only slightly.
3-Fowler flaps: this flap slides backwards before hinging downwards,thereby increasing both camber and chord, creating a larger wing surfacebetter tuned for lower speeds.
4- Slotted flaps: a gap between the flap and the wing enables high
pressurized air from below the wing to re-energize the boundary layerover the flap. This helps the airflow to stay attached to the flap, creating alower stall speed. There are also double slotted flaps and triple slottedflaps.
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Spoilers are plates on the top of a wing which can be extended upward into
the airflow to reduce lift and speed.
They are mostly used on landing, because they cause a dramatic loss of liftand hence the weight of the aircraft is transferred from the wings to the
undercarriage, allowing the wheels to be mechanically braked with much
less chance of skidding.
The difference between airbrakes (speed brakes) and spoilers is that
airbrakes are designed to increase drag while making little change to lift,
while spoilers greatly reduce lift while making only a moderate increase indrag.
Spoiler
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Speed breaks
Speed brakes are not a common sight on civilian aircraft, although the Bae
146 has speed brakes. Some military jets have speed brakes (e.g.
Blackburn Buccaneer, Su-30,...). The meaning of speed brakes is, as the
name says, reduce speed during landing.
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Slats are aerodynamic surfaces on the leading edge of the wings. Whendeployed, there exists a hole between the wing and the slat, this allows theair to flow from below the wing to its upper surfaces. This way the wing stillprovides enough lift when flying with a higher angle of attack. The slats aremostly used when landing or when doing operations at low speed. Duringnormal flight, they are retracted. There are two types of slats:
-automatic: the slat lies flush with the wing leading edge untilreduced aerodynamic forces allow it to extend by way of \
springs when needed. This type is typically used on light
aircraft.-Fixed :the slat is permanently extended. This is sometimes used on
specialist low-speed aircraft (these are referred to as slots)
or when simplicity takes precedence over speed.-powered : the slat extension can be controlled by the pilot. This is
commonly used on airliners.
Slats
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Slot is a span-wise gap in each wing, allowing air to flow
from below the wing to its upper surface. This allows the
wing to provide lift up to a higher angles of attack than
would be possible without the slot.
In this manner they allow flight at higher angles of attack
and thus reduce the stall speed. But the slot producesmore drag in normal flight. A way to overcome this, is
making slots retractable and then you have slats.
Slots
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Lift augmentation
Generally refers to leading and trailing edge devices which means
flaps, slats and etc which deployed during take off and landing.
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Flaps
Flap are lift augmentation devices normally deployed during take-
off and landing.
When lowered, it increased the camber of the wing thus
increasing lift and drag.
Advantage:-Lower the landing speed.
-Drag created will shorten the landing run in stopping the aircraft.
-Provide the steeper angle of approach aircraft on landing.
There are several of flaps:- plain, split, slotted and fowler.
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Trailing edge flap
Plain flap -simplest method to change the camber of airfoil
-same size as the aileron and hinged so can deflect.
Split flap -when lowered, the shape of the upper surface of the wing is
unchanged and it creates more drag because of its turbulentwake.
Slotted flap -flap permitting a smoother flow of air over the flap.
- the advantage is longer delaying boundary layer separation
and maintaining a high degree of lift.
Fowler flap - increase the upper camber as well as the wing area.
- Increase in lift for this type of flap is up to 90%
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Leading edge flap
Used to augment low speed lift is especially on swept wing aircraft.
Prevent leading edge separations that take place on thin sharp edge wings
at high angle of attack.
Type of leading edge flap
1-Krueger flap- consists of two basic sections; flap assembly and
hinged fairing.
2-Droop flap - folds down when the trailing edge flaps are lowered
allows the wing to reach a higher angle of attack
before the airflow breaks away from its upper surface.
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Slots and SlatSlats
main advantage is that it controlboundary layer on top of the wing
and increase the lift by 60% Are employed for the low speed
operation other than takeoff oflanding
the state are three position unit:-retract, extend, and full extend.
Slots
Built into the wing structure nearthe wing tips leading edge.
Slots guide and accelerate airfrom below the wing anddischarge it over the uppersurface to re-energize the existingairflow.
Maybe fix, controlled, automatic or
blown.
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Trim tabs
Tabs used to trim any out-of-balance forces and permit a hand-off flight at
normal speeds. These tabs are mounted on aircraft primary controls and
can be operated from the cockpit either by hand wheels or electrically. Also
called trimmers.
are small surfaces connected to the trailing edge of a larger control
surface on a aircraft. The angle of the tab relative to the larger
surface can be adjusted to null out hydro- or aero-dynamic forces
and stabilise the boat or aircraft in a particular desired attitude
without the need for the pilot to constantly apply a control force.
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When mounted on a control surface (such as an elevator or rudder), the trimtab allows the pilot to easily adjust the position of the control surface, and toadjust the large force generated by the control surface.
The trim tab acts as a servo tab. Because the center of pressure of the trimtab is further away from the axis of rotation of the control surface than the
center of pressure of the control surface, the moment generated by the tabcan match the moment generated by the control surface. The position of thecontrol surface on its axis will change until the moments from the controlsurface and the trim surface balance each other.