1. 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.
Lesson Objective: Know the principles of basic aeronautics.
Samples of Behavior/Main Points
1. Describe the theory of flight.
2. Describe airfoil design.
3. Describe the effects of relative wind.
4. Describe the effects of angle of attack.
5. Identify the four forces of lift.

2. Overview 1. Theory of Flight 2. Airfoils and Flight 3. Relative Wind
4. Angle of Attack
5. The Four Forces of Flight
In this lesson we will discuss:
1. Theory of Flight
2. Airfoils and Flight
3. Relative Wind
4. Angle of Attack
5. The Four Forces of Flight

3. 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.
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.
It was discovered that air could be compressed; that it contains a number of gaseous elements, primarily nitrogen and oxygen; and that it is essential in burning wood, coal and other materials.
Later studies revealed that air has mass and weight and, at sea level, it exerts pressure equally in all directions at just under 15 pounds per square inch (psi) of surface area.

4. 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.
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, which is a surface designed to obtain a reaction from the air through which it passes.
As air passes over the curved surface of an airfoil, it flows faster than the air passing the flat surface below.

5. 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.
Bernoulli principle
A principle of nature discovered by Swiss mathematician, Daniel I. Bernoulli. He observed that moving air exerts less pressure than still air.
The Bernoulli principle states "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.

6. 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.
Aristotle
The first useful studies of motion are attributed to Aristotle. He believed that there were two kinds of motion: natural and violent.
Natural motions were those occurring without human effort such as the rotation of the Sun and Moon.
Violent motion resulted from the application of force to move an object.
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.

7. 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.
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.

8. 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.
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.

9. 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.
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." Simply stated:
When you hit something, it will pick up speed.
The heavier the object is, the less rapidly it will pick up speed.
The object picks up speed and continues to move in the same direction from which it was hit.
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.

10. 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.”
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."

11. 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.
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.

12. Theory of Flight Acceleration Velocity
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.
Acceleration, Velocity, Force, and Mass
Acceleration is the rate of increase in the velocity of something. Represents a change in velocity.
Velocity is the rate of motion in a given direction. The change of rate of motion in a given direction per unit of time.

13. Theory of Flight Force Mass
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.
Force is the power or energy exerted against a material body in a given direction. Force has both magnitude and direction.
Mass is 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.

14. 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.
The Forces of Flight
A plane is in the air and four forces in balance with one another hold it there.
The four forces are lift, weight, thrust, and drag. These forces operate in pairs: thrust and drag; lift and weight.
Weight is a measure of gravity, which is the attraction of the Earth for all bodies on or near it. Lift operates to overcome weight, and weight serves to keep the aircraft from rising any higher than the pilot wants it to go.
Thrust is a force that gives forward motion to the aircraft. The propeller or the jet engine produces the thrust. Drag is the force that is opposed to thrust. It opposes the forward motion, of the aircraft. The resistance of the air to the aircraft passing through it causes drag.
When weight and lift are equal, the aircraft flies level. When thrust and drag are equal, the aircraft flies at a constant rate of speed. Each of these four forces is both an asset and a liability. They are forces to use and forces to overcome.
The thrust of the engine produces the drag of air rushing past the aircraft. Without this drag, an aircraft would be like a car without brakes or steering equipment. Weight, too, can be an asset. It provides stability and control. Fuel capacity and payload (generally, passenger or cargo) contribute to weight.
Thrust and lift, the two helpful forces, must also be kept within the limits of usefulness and safety. An aircraft can be designed with decreased drag, but this decreased drag may also decrease lift.

15. 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.
Airfoil Design
Defined as any part of the aircraft that is designed to produce lift. An airfoil has a leading edge, a trailing edge, a chord, and camber.
Leading Edge - The “front” of the airfoil, the portion that meets the air first.
The shape of the leading edge depends upon the function of the airfoil. If the airfoil is designed to operate at high speed with a minimum amount of lift, its leading edge may be very sharp, as on most current fighter aircraft. If the airfoil is designed to produce a greater amount of lift at a relatively low rate of speed, as in a Cessna 152 or a Piper Arrow, the leading edge may be thick and fat. Actually, the supersonic fighter aircraft and the light propeller-driven aircraft are really two ends of a spectrum. Most other aircraft lie between these two. The leading edges of their airfoils may have a compromise shape, designed to provide a moderate amount of lift at relatively high speeds. Trailing Edge - The trailing edge is the “back” of the airfoil, the portion at which the airflow over the upper surface joins the airflow over the lower surface. The design of this portion of the airfoil is just as important as the design of the leading edge. This is because the air flowing over the upper and lower surfaces of the airfoil must be directed to meet with as little turbulence as possible, regardless of the position of the airfoil in the air. Chord - The chord of an airfoil is an imaginary straight line drawn through the airfoil from its leading edge to its trailing edge. When you look at an airfoil, you can see its leading edge and its trailing edge, but you can’t see its chord, because this line is imaginary. Camber - The camber of an airfoil is the characteristic curve of its upper or lower surface. The characteristic curve is measured by how much it departs from the chord (a straight line) of the airfoil. A high-speed, low-lift airfoil, the type found on the F-4, has very little camber. A low-speed, high-lift airfoil, like that on the Cessna 152, has a very pronounced camber. The upper camber refers to the curve of the upper surface of the airfoil. The lower camber refers to the curve of the lower surface of the airfoil. When the curve is away from the chord, the camber is said to be positive. When the curve is toward the chord, the camber is said to be negative. The camber of an airfoil causes an increase in velocity and a consequent decrease in pressure of the stream of air moving over it.

16. 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.
Relative Wind
The movement of the aircraft through the air creates the relative wind; thus the flight path and relative wind are parallel, but act in opposite directions.
The term relative wind means the wind that is moving past the airfoil and that the direction of this 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 and the speed of the airfoil through the air.

17. 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.
Angle of Attack
The angle of attack is formed by the chord of the airfoil and the direction of the relative wind or between the chord line and the flight path.
The angle of attack is not constant during a flight. It changes as the pilot changes the attitude of the aircraft.
The angle of attack is one of the factors that determines the aircraft’s rate of speed through the air.

18. 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
According to Bernoulli’s Principle, there is increase in the velocity of air as the air flows around an airfoil shape.
Because the camber of the upper wing surface is greater than that of the lower surface, air flowing above the wing will be increased more than air flowing beneath the wing.
The Bernoulli’s Principle also states that an increase in the velocity of a fluid, such as air, results in a decrease of pressure within that fluid. As a result, the reduction in air pressure above the wing will be greater than the pressure reduction along the lower wing surface.

19. 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.
Lift can be increased in two ways: by increasing the forward speed of the airplane or by increasing the angle of attack.
The pilot can increase the forward speed of the aircraft by applying more power. This increases the speed of the relative wind over the airfoil.

20. 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.
Lift Variables
The pilot must have some way to control the amount of lift the airfoils generate.
If the pilot didn’t, the aircraft would either constantly stall or climb.
There are variables acting on the amount of lift generated.
Angle of attack
Velocity of relative wind (speed of the aircraft)
Air density
Airfoil shape
Wing area
Airfoil platforms
High-lift devices.

21. The Four Forces of Flight
Angle of Attack
Angle of Attack Again
Changing the angle of attack can change the amount of lift generated as the airfoil moves through the air.
Airflow over an airfoil is normally smooth with no turbulence. In the case of an airfoil with a flat or approximately flat undersurface and when the lower surface is parallel to the relative wind, there is no impact pressure on the lower surface.
The whole lift force comes from reduced pressure along the upper surface (pressure-differential lift).
When the wing is tipped up so that the lower surface makes an angle of 5 with the relative wind, the impact pressure on the undersurface contributes about 25 percent of the total lift.
When it is tipped up to 10, the impact pressure on the lower surface produces about 30 percent of the total lift.
A small force acts on each tiny portion of the wing. This force is different in magnitude (size) and direction from the force acting on other small areas of the surface farther forward or rearward.

22. 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.
It is possible to mathematically add all of these small forces, taking into account their magnitude, direction, and location. The sum of all the tiny forces over the surface of the wing is called the resultant, since it results from adding all the forces together.

23. 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).
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).

24. 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 angle at which lift stops increasing and begins to decrease is called the burble point.
This angle may also be called the stalling angle or the angle of maximum lift.
When the angle of attack is increased beyond the burble point, the resultant decreases in magnitude and its angle back from the vertical becomes bigger.
At the various angles just described, the direction of the resultant has had an upward and backward direction.
As the angle of attack is increased, more and more lift is generated. This increase in amount of lift continues up to a certain angle of attack (the burble point, mentioned previously) which depends on the type of wing design.
Most aircraft wings have a burble point of somewhere between 15 and 20°, but this is built into the aircraft.
When the air no longer flows smoothly over the top surface of the airfoil it is called burbling. When burbling is taking place on a surface, there can be no decrease in pressure below the atmospheric pressure.

25. 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 point at which the amount of lift generated is no longer sufficient to support the aircraft in air is called the stalling point, and the maneuver in which the pilot does this is called the stall.

26. 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.
Another Lift Variable - 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, a greater pressure difference between the lower and upper surfaces of the airfoil results.

27. The Four Forces of Flight
Lift Variables
Velocity of Relative Wind
As the speed increases, the lift increases, within practical limitations. This increase in lift is not a directly proportional increase (that is, there isn't a one-for-one gain of lift for velocity). Actually, the lift increases as the square of the velocity.
An aircraft traveling 100 mph has 4 times as much lift as the same aircraft traveling at 50 mph.

28. 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 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.
Air Density and Lift
Air density is another variable factor that can influence lift. The first thing to note is that lift varies directly with density.
For instance, at 18,000 feet, where the density is about half that at sea level, an aircraft will need to travel times as fast as it would at sea level to maintain altitude. The number is the square root of 2.
If something reduces the lift by half, it has to increase the speed so that the square of the new velocity is twice the square of the original velocity.

29. 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.
Airfoil Shape as a Variable
Up to a certain point, the greater the camber, the greater the lift.
It becomes extremely important once an airfoil has been designed, to preserve the characteristic curve that the designers build 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.

30. 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.
Wing Area and Lift
If the pressure differential is only 2½ ounces per square inch (a very small amount of differential pressure), this will produce a lifting force of more than 20 pounds per square foot (144 square inches/square foot x 2½-ounces/square inch).
The greater the surface area of the wing, the greater the amount of lift that will be generated, within practical limitations if the proportions of the wing and the airfoil section stay the same.
Gliders or sailplanes are very good examples of how a large wing surface generates lift.
Lighter, stronger, materials are being developed, so that today’s aircraft can be built to withstand tremendous strains and yet not be heavy.

31. 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.
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, but these airplanes will eventually stall and start to fall toward Earth. The stalled condition is one from which recovery and continued flight is fairly easy.

32. 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.
There is another situation where lift can no longer overcome weight. This limit is called the aircraft's ceiling. At its ceiling, the aircraft's power plant is producing all possible power, and the airfoils are producing all possible lift just to equal the force of the aircraft's weight.
The atmosphere becomes less and less dense as altitude increases. The aircraft's ceiling is that point in the atmosphere where the air is too thin to allow further increase in lift.
The airplane must be constructed of the lightest weight materials that can be used. Most airplanes today are built of metal. Aluminum alloy is used extensively in aircraft construction because of its strength and light weight.
The weight of whatever the airplane carries also receives very careful consideration. Each airplane has a total weight limitation called the maximum allowable gross weight above which the airplane is unsafe for flight.

33. 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 pilot has to subtract the empty weight from the maximum allowable gross weight to find out how many pounds may be loaded into the airplane. This is the useful load.
Where the weight, or useful load, is placed in the airplane is another factor that has an effect on how well the airplane will fly.
This is because the center of gravity of the airplane must be within certain limits prescribed by the manufacturer.
These limits are based on where the center of lift (CL) of the particular design happens to be.
If placement of the useful load moves the center of gravity too far forward or too far aft of the CL, the airplane will be difficult, if not impossible, to control while in flight

34. 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.
Thrust and Drag
Thrust is the force that propels the aircraft forward. Thrust for aircraft is obtained from different types of engines.
An airplane cannot gain altitude or maintain straight and level flight unless its engine is producing enough thrust to propel (pull or push) the airfoils fast enough to produce the needed amount of lift.
Without this thrust, the airplane will continue to fly. It will not “drop out of the sky” as many people think, but its flight becomes a gradual descent toward the ground.
Without the needed thrust, weight has more influence than lift and pulls the airplane toward the ground. Helping the force of weight is drag.

35. 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.
Drag is present at all times and can be defined as the force that opposes thrust. Better yet, drag is the force that opposes all motion through the atmosphere and is parallel to the direction of the relative wind.
The friction of air particles rubbing against all parts of the airplane causes part of the total drag. In fact, airspeed can be increased several miles per hour if the surfaces of the airplane are kept highly polished.
The shape of something may create low-pressure areas and turbulence that retard the forward movement of the aircraft. Streamlining the aircraft will reduce form drag.
Parts of an aircraft that do not lend to streamlining are enclosed in covers, called fairings (or cowling for an engine), that have a streamlined shape.

36. Summary 1. Theory of Flight 2. Airfoils and Flight 3. Relative Wind
4. Angle of Attack
5. The Four Forces of Flight
In this lesson we discussed:
1. Theory of Flight
2. Airfoils and Flight
3. Relative Wind
4. Angle of Attack
5. The Four Forces of Flight