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SCOPE…..

1) 4 Forces of Flight

2) Bernoulli’s Principle

3) Airfoil/Aerofoil Shape

4) How a Plane is Controlled

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While an aircraft is flying, there are 4 forces acting on it:

THRUST, DRAG, LIFT and WEIGHT.

Thrust VS Drag while Lift VS Weight. Refer to the pictorial below:

Centre of Gravity, cg

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THRUST

- A force that is created by the aircraft’s propulsion system, engines.

- It is a push or pull that moves the aircraft forward.

- For aircraft to start moving, THRUST = DRAG.

- For aircraft to accelerate, THRUST > DRAG.

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DRAG

- Opposes THRUST and acts the opposite direction of THRUST.

- It is the resistance of air due to aircraft movement.

- The aircraft body itself also contributes to drag.

Discussion

How does the aircraft body contributes to drag?

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LIFT

- Generated by airflow over the aircraft body.

- Wings of aircraft produces most of the aircraft’s lift.

- To be able to take off / go airborne / pitch up, LIFT > WEIGHT.

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WEIGHT

- Opposite reaction of LIFT.

- It is a vertical downward force towards the ground.

- Includes mass of aircraft, fuel, cargo or any loads on aircraft.

- Weight distribution in aircraft is not constant. i.e. Passengers walking about, fuel consumption.

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David Bernoulli is a Swiss scientist in the 18th century. He discovered that as the velocity of fluid increases, its pressure decreases.

Venturi Tube

1 2

As the fluid enters the narrowpart of the tube, it speeds up.This decreases the fluid pressure.As the molecules speed up, it usesmore energy, thus less energy isused to exert pressure.

1

The speed of the fluid decreases as itexits the narrow part of the tube. Thereis more energy to exert pressure asless energy is used for the speed ofthe molecules.

2

HOW IS THIS

APPLICABLE TO

FLIGHT?

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In most aircraft, you will see this shape if seen from the wing tip. There’s a lot of different types of airfoil shape, which is designed for the aircraft, depending on its role.

To facilitate better understanding of how aircraft wings generate lift for the whole aircraft, we will look at the most common design of airfoil.

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Cross-section of the wing…

For easier understanding, Bernoulli’s principle will be used to explain how airfoil shape generates lift.

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Movements of an aircraft plays along 3 axis. Different movements about or along different axis will bring about different kind of movements.

AXIS MOVEMENT

LongitudinalLongitudinal RollRoll

LateralLateral PitchPitch

VerticalVertical YawYaw

From the above, we get 3 different kinds of moments:

Rolling, Pitching and Yawing moments.

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How LIFT is produced…

1

3

4

2 Airflow is separated.

1

Air particles accelerate as itgoes along the upper camber, dueto the longer distance it has to travelas compared to that of lower camber.As the velocity of air increases,the pressure against the uppercamber decreases.

2

Velocity of air remains about thesame as before. Thus, pressureexerted against the lower camberwould be greater then the pressureexerted on the upper camber.

3

Since pressure against the uppercamber is more than that against thelower camber, the wing is beingpushed upwards by the higherpressure.

4

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Rolling Moment

- It is a rotation about the longitudinal axis

- Controlled by ailerons

When the starboard (right side of aircraft) aileron is up:

- Port (left side of aircraft) aileron will move downwards.

- Greater pressure at the bottom of port wing compared to top; pushing the port wing upwards.

- Greater pressure on top of starboard wing compared to bottom; pushing the starboard wing downwards.

OUTCOME?

Aircraft will roll to the right.

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Pitching Moment

- It is a rotation about the lateral axis

- Controlled by elevator

When the elevator is up:

- Pressure on top of the tailplane is greater as compared to the bottom.

- This pushes the tailplane down.

OUTCOME?

Aircraft will pitch up.

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Yawing Moment

- It is a rotation about the vertical axis

- Controlled by rudder

When the rudder is moved to the left:

- Pressure on the left of the vertical stabiliser is more as compared to the right.

OUTCOME?

Aircraft will yaw to the right.

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Find out how these flight controls work:

1) Elevons

2) Ruddervator

3) Spoilerons

4) Flaperons

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