Basic Aerodynamics& Theory of Flight

ByAhmad Ahsan

Course Outline• Introduction• Bernoulli’s Principle• Airfoil & Airfoil Shapes• Aircraft Structure• Flight Controls• Four Forces of Flight• Three Axes of Movement• Aircraft Control & Stability• Wings• Aerodynamic Forces of Flight• Simulation

The course has been designed based on the recommended outline of the US National Transportation Safety Board (NTSB Aviation Curriculum Guide) in addition to a number of other sources.

Responsibilities• Attendance

• Assignments

• Presentations

• Case Studies

• Project

Reference Materials• Textbook : Aircraft Flight: A description of the physical

principles of aircraft flight. Fourth Edition. RH Barnard and Dr Philpott

• FAA H-8083-25A Pilot’s Handbook of Aeronautical Knowledge

• FAA H-8083-15A Instrument Flying Handbook

• FAA 80T-80 Aerodynamics for Naval Aviators

• Glenn Research Center, NASA. grc.nasa.gov

• NASA Foilsim

Outline – Basic Aerodynamics• Introduction & Definition

• The Atmosphere• Theories

• Newton’s Laws of Motion• Bernoulli’s Principle

• Airfoil & Airfoil Shapes• Angle of Attack & Incidence• Aircraft Structure• Flight Controls• Four Forces of Flight• Three Axes of Movement• Aircraft Control

Definition• “Aerodynamics is a branch of dynamics that

deals with the motion of air and other gaseous fluids, and with the forces acting on bodies in motion relative to such fluids” Webster’s Dictionary

• Aerodynamics is made of two Greek words: aerios, concerning the air, dynamis, which means force

• “Aerodynamics is the study of forces and the resulting motion of objects through the air.”NASA

Definition

• In simple terms, we can describe aerodynamics as the study of objects in motion through the air and the forces that produce or change such motion.

• Understanding aerodynamics is the key to understanding how aircraft fly

• It is vital for safety to understand the basic principles of aerodynamics

• In order to understand aerodynamics, we will start with the environment of the aircraft – “The Atmosphere”

The Atmosphere• Air is a mixture of gases composed principally of nitrogen and

oxygen. An aircraft operates in the air, therefore, the properties of air that affect aircraft control and performance must be understood.

• These include, pressure, density, and humidity.

The Atmosphere• Pressure – Amount of force exerted

per unit area.

• Atmospheric pressure varies with altitude.

• At higher altitude pressure decreases.

The Atmosphere• Density is the amount of matter contained in a certain volume.

• Density of air is the amount of air molecules in a certain volume.

• It varies directly with the pressure and inversely with the temperature.

The Atmosphere• Humidity – Humidity is amount of water vapor in the air.

• It varies directly with temperature.

• Warmer is the air, more water vapor it can hold.

Newtons’ Laws of Motion• Newton’s First Law:

“Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.”

• Second law of motion states:“If an object moving with uniform speed is acted upon by an external force, the acceleration will be directly proportional to the amount of force and inversely proportional to the mass of the object.” The motion will take place in the direction in which the force acts, Hence F = m × a

Newtons’ Laws of Motion• Newton's Third Law of Motion (action and reaction)• The third law of motion states that for every action (force) there

is an equal and opposite reaction (force).

ActionReaction

Balloon

Air

Bernoulli’s Principle• Bernoulli's principle states that

“As the velocity of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases.”

• Hence high speed flow of air = low pressure of air• When a fluid flowing through a tube reaches a narrowing of the

tube, the speed is increased and its pressure is decreased.

• “Any surface, such as a wing, propeller, rudder, or even a trim tab, which provides aerodynamic force when it interacts with a moving stream of air.” FAA

•The mean camber line is a line drawn midway between the upper and lower surfaces

• The chord line is a straight line connecting the leading and trailing edges of the airfoil.

The Airfoil

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

Bernoulli’s Principle & Airfoil• The upper surface of an

airplane’s wing is designed to have a greater curvature or camber as compared to lower surface. This greater curvature causes air to flow faster over the upper surface.

• Due to higher speed, the pressure decreases.

• On the lower pressure, the lesser curvature causes decrease in speed and increase in pressure.

• This creates “Lift”

Aircraft Structure Aircraft Structure

Four Forces of Flight

DRAG

WEIGHT

THRUST

LIFT

Lift• Lift is the force created by the interaction between the wings

and the airflow. • It opposes the downward force of weight. • Lift is an aerodynamic force and is directly proportional to the

square of velocity. • It is produced by the dynamic effect of the air acting on the

airfoil. • It acts perpendicular to the flight path.• Aircraft lift acts through a single point

called the center of pressure. • Lift Equation: L=½ ρ V2A CL

LIFT

Weight• Weight is the combined load of the aircraft, crew, fuel,

passengers, and the cargo. • Weight pulls the aircraft downward because of the force of

gravity. • It opposes lift, and acts through the aircraft’s center of gravity

(CG)• Weight is not constant

WEIGHT

Thrust• Thrust is the forward force produced by the

powerplant,propeller or rotor. • It opposes or overcomes the force of drag.• Direction of thrust depends on design

THRUST

Drag• Drag is a rearward acting force that resists the motion of

aircraft through the air.• It is an aerodynamic force and like lift varies to square of

velocity.• Two broad drag classifications.• Parasite drag: caused by disruption of airflow by the wing,

rotor, fuselage, and other parts of structure. • Induced drag: produced as reaction of lift• Drag Equation: D= ½ ρ V2A CD

DRAG

Axes of Aircraft• The axes of an aircraft are three imaginary lines that pass

through an aircraft’s CG. • The axes can be considered as imaginary axles around which

the aircraft turns. • The three axes pass through the CG at 90° angles to each

other.• The axis from nose to tail is the longitudinal axis. • The axis that passes from wingtip to wingtip is the lateral axis.• The axis that passes vertically through the CG is the vertical

axis. Whenever an aircraft changes its flight attitude or position in flight, it rotates about one or more of the three axes

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

The Ailerons control movement on the lateral axis called

“rolling”.

Control around the Longitudinal Axis

The Ailerons control movement on the lateral axis called

“rolling”.

Control around the Longitudinal Axis

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 to the right

Moving rudder to the left forces tail to the right, nose to the left.

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

The Ailerons control movement on the lateral axis called

“rolling”.

Control around the Longitudinal AxisSources

• FAA H-8083-25A• FAA H-8083-15A• NASA Guide to Aerodynamics• Aircraft Flight:A Description of the Physical Principles of Aircraft

Flight• Kansas University Aerospace

The End