Lesson 4 Developing the Concepts - Lift (Theory of Flight)

7/29/2019 Lesson 4 Developing the Concepts - Lift (Theory of Flight)

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Basic Aerodynamics

& Theory of Flight

By

Ahmad Ahsan


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The Airfoil


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The angle of attack is the angle between the chord line and

the average relative wind.

Greater angle of attack creates more lift (up to a point).

Angle of Attack


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Three Axes of Movement

Axis of Roll (Longitudinal Axis)

Axis of Pitch (Lateral Axis)

Axis of Yaw (Vertical Axis)

Three Axes of Movement

Longitudinal Axis

Lateral Axis

Vertical Axis


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The Aileronscontrol movement on the lateral axis called rolling.

Control around the Longitudinal Axis

The Aileronscontrol movement on the lateral axis called rolling.

Control around the Longitudinal Axis


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Rudder The rudder controls the

movement around vertical axis

called yawing.

Control around the Vertical Axis

Moving rudder to the

right forces tail to the

left, nose to the right

Moving rudder to the

left forces tail to the

right, nose to the left.

Rudder The rudder controls the

movement around vertical axis

called yawing.

Control around the Vertical Axis

Moving rudder to

the right forces tail

to the left, nose tothe right

Moving rudder to

the left forces tail to

the right, nose tothe left.


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Elevators are used to control

movement about the lateral axis

called pitching

Control around the Lateral Axis

Elevators are used to control

movement about the lateral axis

called pitching

Control around the Lateral Axis


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Four Forces of Flight

DRAG

WEIGHT

THRUST

LIFT


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Lift Lift is the upwards force created by the interaction between the wings and the

airflow.

Lift Formula: L= V2A CL

LIFT


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Lift Basic Concepts According to Newtons Laws, Lift is the reaction that results from the

action of forcing air downward by the airfoil(Jeppesen)

NASA has established through experimentation that pressure on lower

surface of wing is higher than upper surface (hence pressure difference

exists)

Lift results from the higher pressure below the wings surface and lower

pressure above the wings surface.

Lift acts perpendicular to the relative wind.


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Lift Basic Concepts Relative Wind or Airflow:

Relative wind is opposite to the flight path of the airplane.

Lift, drag, thrustdepend on relative wind.

Angle between chord line of wing and the relative wind isAoA.

Higher the AoA, more will be the lift produced (up to about 16 degrees).

Any thing that changes the profile (shape) of airfoil such as snow, ice,

dents, etc. WILL disrupt the airflow and cause LOSS OF LIFT.


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By

Ahmad Ahsan


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By

Ahmad Ahsan


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By

Ahmad Ahsan


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By

Ahmad Ahsan


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By

Ahmad Ahsan


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By

Ahmad Ahsan


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By

Ahmad Ahsan


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Lift Equation


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Important Factors

To increase lift, one or more of the four factors must be increased.

Lift is proportional to square of velocity, so increasing velocity two times

will increase lift four times (provided other factors remain constant).

Coefficient of lift increases with the angle of attack.

As air density increases, the lift also increases. To generate the same amount of lift at high altitude,

Aircraft must be flown at higher angle of attack or higher airspeed.

More concern is what decreases lift? As it is important to know which

factors can cause negative effect on aircraft performance.


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Controlling Lift Four main ways commonly used:

Most common is to vary the angle of attack. Advantage of this method is it alsolets you control airspeed and drag (to an extent)

Increase Angle of Attack = More Lift generated (to a point)

At a certain angle, airflow begins to separate, this is called CLMAX at this pointSTALL occurs.

The angle at which a wing stalls remains constant regardless of weight,

airspeed, bank angle, or pitch attitude.

Stall speed depend son a number of other factors, such as, G-loading, weight,

center of gravity location, etc. Above certain limits can cause damage.


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Controlling Lift Another way is through certain wing design features called High Lift Devices

Most common of these is trailing edge flap. It increases both lift and drag.

Flaps increase lift and reduce the stall speed allowing the wings to produce the

same lift at lower airpseed.

Leading edge devices can also be used, include fixed slots, slats (portion of

leading edge which move forward and down), and leading edge flaps.


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Trailing Edge Devices


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Leading Edge Devices


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The End

Lesson 4 Developing the Concepts - Lift (Theory of Flight)

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