Aircraft Control Surfaces

8/7/2019 Aircraft Control Surfaces

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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.

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Aircraft Control Surfaces