Basic Aeronautics

Know the principles of basic aeronautics.

1. Describe the theory of flight.

2. Describe airfoils and flight.

3. Describe the effects of relative wind.

4. Describe the effects of angle of attack.

5. Identify the four forces of flight.

Overview

1. Theory of Flight

2. Airfoils and Flight

3. Relative Wind

4. Angle of Attack

5. The Four Forces of Flight

Theory of Flight

• Aerodynamics• The science relating to the effects produced by

air or other gases.• The term comes from the Greek words aero

meaning air and dynamics meaning power.• Ancient Greeks described air as having the

qualities of moisture and heat. It was observed to shift in response to heating and cooling.

Theory of Flight

• Aerodynamics• A lifting force is required for heavier-than-air

flying. An object can be pushed upward by applying muscle power, an explosion, a hoist, or other means of force.

• It cannot remain aloft without decreasing the air pressure from above and increasing lift pressure from below.

• Increasing the speed of the object can increase the flow of air.

• The flying object must be shaped to form an airfoil.

• Air flows faster over the curved surface of an airfoil.

Theory of Flight

• Aerodynamics• Bernoulli principle

• “As the air velocity increases, the pressure decreases; and as the velocity decreases, the pressure increases.”

• A major part of the knowledge base needed in the design and development of aircraft.

• Contributed to the work of G.B. Venturi, an Italian scientist, who first noted the effects of constricted channels on the flow of fluids. A round tube, such as a nozzle or jet engine, designed to increase the speed of flowing gases and liquids is called a venturi.

Theory of Flight

• Aerodynamics• Aristotle

• The first useful studies of motion are attributed to Aristotle. He believed there were two kinds of motion: natural and violent.

• He concluded, and later stated as a natural law, that the velocity or speed of an object depends entirely on the force being applied to it and the resistance it meets. This law was later proven to be inaccurate.

Theory of Flight

• Aerodynamics• Galileo Galilei

• Observed that an object in horizontal motion would continue to move at the same speed with no additional force.

• This truth was accepted by Sir Isaac Newton and became the first of three laws of motion stated by Newton.

Theory of Flight

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

• “A body at rest tends to remain at rest, and a body in motion tends to stay in motion, unless an outside force acts on the body.” It is sometimes referred to as the Law of Inertia.

• One of the most common places people feel this law is in a fast moving vehicle. If you were standing inside a train and it suddenly stopped, you would continue to move forward even though the train had come to a stop.

Theory of Flight

• Newton’s Laws of Motion• Second Law of Motion

• “The acceleration of an object as produced by a net force, is directly proportional to the magnitude of the net force in the same direction as the net force and inversely proportional to the mass of the object.”

• Hitting a golf ball is a common example of Newton’s second law. The golf club is a force that causes the ball to move (overcoming inertia), and picks up speed (acceleration) and since the golf ball is relatively light, it picks up speed rapidly.

Theory of Flight

• Newton’s Laws of Motion• Third Law of Motion

• “Whenever one body exerts a force upon a second body, the second exerts an equal and opposite force upon the first body.” Simply stated, For every action there is an equal and opposite reaction.”

Theory of Flight

• Newton’s Laws of Motion• Third Law of Motion

• This law is exemplified by what happens if you step off a boat onto the shore. As you move forward toward the shore, the boat tends to move in the opposite direction.

Theory of Flight

• Acceleration

• The rate of increase in the velocity of something.

• Represents a change in velocity.

• Velocity• The rate of motion in a given direction. • The change of rate of motion in a given

direction per unit of time.

Theory of Flight

• Force• The power or energy exerted against a

material body in a given direction. • Force has both magnitude and direction.

• Mass• The quantity of material (matter) contained

in a body, while weight (which is often confused with mass) is really the amount of gravity being exerted on a quantity of matter.

Theory of Flight

• The four forces in balance with one another hold the plane in the air.

• The four forces are lift, weight, thrust, and drag.

Airfoils and Flight

• Airfoil Design• An airfoil is designed to produce lift. An

airfoil has a leading edge, a trailing edge, a chord, and camber.

Relative Wind

• The movement of the aircraft through the air creates the relative wind.

• The term relative wind means the wind that is moving past the airfoil and the direction of the wind is parallel to the flight path and relative to the attitude of position of the airfoil.

• The pilot controls the direction of the relative wind.

Angle of Attack

• Formed by the cord of the airfoil and the direction of the relative wind or between the chord line and the flight path.

• Is not constant during a flight. It changes as the pilot changes the attitude of the aircraft.

• One of the factors that determines the aircraft’s rate of speed through the air.

The Four Forces of Flight

• According to the Bernoulli Principle, there is an increase in the velocity of air as the airflow around an airfoil shape; therefore, there is an increase of the relative wind as it flows above and below the surface of the airplane wing.

The Four Forces of Flight

• Lift can be increased in two ways• Increasing the forward speed of the airplane.• Increasing the angle of attack.

• The pilot can increase the forward speed of the aircraft by applying more power.

The Four Forces of Flight

• Lift Variables• The pilot must have some way to control the

amount of lift the airfoils generate.• There are variables acting on the amount of

lift generated.

The Four Forces of Flight

• Angle of Attack

The Four Forces of Flight

• Angle of Attack• The sum of all the tiny forces over the

surface of the wing is called the resultant.

The Four Forces of Flight

• Angle of Attack• This resultant has magnitude, direction, and

location. The point of intersection of the resultant with the chord of the wing is called the center of pressure (C/P).

The Four Forces of Flight

• Angle of Attack• The angle at which lift stops increasing and

begins to decrease is called the burble point.

The Four Forces of Flight

• Angle of Attack• The point at which the amount of lift

generated is no longer sufficient to support the aircraft in air is called the stalling point.

The Four Forces of Flight

• Velocity of Relative Wind• The velocity of the airfoil through the air is

another important factor in determining the amount of lift generated.

• If an airfoil is made to travel faster through the air, greater pressure differences between the lower and upper surfaces of the airfoil result.

The Four Forces of Flight

• Lift Variables• Velocity of Relative Wind

The Four Forces of Flight

• Air Density and Lift• Lift varies directly with density. If flying at

18,000 feet where the density is about half that at sea level, an aircraft will need to travel 1.414 times as fast as it would at sea level to maintain altitude.

• If something reduces the lift by half, we will have to increase the speed so that the square root of the new velocity is twice the square of the original velocity.

The Four Forces of Flight

• Airfoil Shape• It is extremely important to preserve the

characteristic curve that the designers built into the airfoil.

• Dents, mud, and ice are three common things that can spoil the built-in shape of the airfoil and interfere with the performance of the entire aircraft.

The Four Forces of Flight

• Wing Area and Lift• The greater the surface area of the wing, the

greater the amount of lift that will be generated.

• Gliders and sailplanes are very good examples of how a large wing surface generates lift.

The Four Forces of Flight

• Weight• There is a point in the relationship of airfoil

to angle of attack where lift is destroyed and the force of gravity (weight) takes command.

• Some of the most powerful jet fighter types and aerobatic sport airplanes can, for a short time and distance, climb straight up without any significant help from their airfoils.

The Four Forces of Flight

• Weight• There is another situation where lift can no

longer overcome weight.• The atmosphere becomes less and less dense

as altitude increases. • The airplane must be constructed of the

lightest weight materials that can be used. • The weight of whatever the airplane carries

also receives very careful consideration.

The Four Forces of Flight

• Weight• Where the weight, or useful load, is placed

in the airplane is another factor that has a pronounced effect on how well an airplane will fly.

The Four Forces of Flight

• Thrust and Drag• Thrust is the force that propels the aircraft

forward. • An airplane cannot gain altitude or maintain

straight and level flight unless its engine is producing enough thrust.

• Without the needed thrust, weight has more influence than lift and pulls the airplane toward the ground.

The Four Forces of Flight

• Thrust and Drag• Drag is present all the time and can be

defined as the force that opposes thrust. • The friction of air particles rubbing against

all parts of the airplane causes part of the total drag.

• The shape of something may create low-pressure areas and turbulence that retard the forward movement of the aircraft.

Summary

1. Theory of Flight

2. Airfoils and Flight

3. Relative Wind

4. Angle of Attack

5. The Four Forces of Flight