AERODYNAMICS The principle of flight is made up of four fundamental forces: lift, weight, drag, and thrust. These forces work together in a delicate balance to determine an aircraft’s trajectory, with lift and weight opposing each other and thrust and drag doing the same. GEORGE CAYLEY Cayley founded the science of aerodynamics and is generally credited with the invention of the airplane. He has also been called the world's first aeronautical engineer. GEORGE CAYLEY Born in 1773, Sir George Cayley essentially created the science of flight. Using scientific methods and keeping careful and detailed notes, Cayley became the first to identify the basic problems of heavierthan-air flight, the first to carry out basic aerodynamic research, and the first to discover that curved surfaces produce more lift than flat ones AERODYNAMICS What Are the Four Forces of Flight? The four forces of flight are lift, weight, thrust and drag. These forces make an object move up and down, and faster or slower. The amount of each force compared to its opposing force determines how an object moves through the air. AERODYNAMICS AERODYNAMICS What Is Lift? Lift is the push that lets something move up. It is the force that is the opposite of weight. Everything that flies must have lift. For an aircraft to move upward, it must have more lift than weight. A hot air balloon has lift because the hot air inside is lighter than the air around it. Hot air rises and carries the balloon with it. A helicopter’s lift comes from the rotor blades. Their motion through the air moves the helicopter upward. Lift for an airplane comes from its wings. LIFT LIFT is the man made force which counteracts gravity. Special shapes, or airfoils produce the force called LIFT and allow an airplane to rise in the air. AERODYNAMICS How Do an Airplane’s Wings Provide Lift? The shape of an airplane’s wings is what makes it possible for the airplane to fly. Airplanes’ wings are curved on top and flatter on the bottom. That shape makes air flow over the top faster than under the bottom. As a result, less air pressure is on top of the wing. This lower pressure makes the wing, and the airplane it’s attached to, move up. Using curves to affect air pressure is a trick used on many aircraft. Helicopter rotor blades use this curved shape. Lift for kites also comes from a curved shape. Even sailboats use this curved shape. A boat’s sail is like a wing. That’s what makes the sailboat move. AERODYNAMICS Subsonic speeds—slower than the speed of sound. Supersonic speeds—faster than the speed of sound. WHAT IS THRUST? Thrust is the force that is the opposite of drag. It is the push that moves something forward. For an aircraft to keep moving forward, it must have more thrust than drag. A small airplane might get its thrust from a propeller. A larger airplane might get its thrust from jet engines. A glider does not have thrust. It can only fly until the drag causes it to slow down and land. THRUST Thrust is the man-made force, which counteracts drag. Thrust is produced by an engine or power plant, which pulls the airplane forward through the air. DRAG WHAT IS DRAG? Drag is a force that pulls back on something trying to move. Drag provides resistance, making it hard to move. For example, it is more difficult to walk or run through water than through air. Water causes more drag than air. The shape of an object also affects the amount of drag. Round surfaces usually have less drag than flat ones. Narrow surfaces usually have less drag than wide ones. The more air that hits a surface, the more the drag the air produces. Drag is the force exerted on a moving body, which tends to reduce its forward motion. WHAT IS WEIGHT? WEIGHT Gravity is a force that pulls everything down to Earth. Weight is the amount of gravity multiplied by the mass of an object. Weight is also the downward force that an aircraft must overcome to fly. A kite has less mass and therefore less weight to overcome than a jumbo jet, but they both need the same thing in order to fly — lift. Gravity is the force of attraction by which all objects tend to fall towards the center of gravity. In straight and level flight, at a constant speed, LIFT exactly equals GRAVITY and THRUST exactly equals DRAG. If we alter or change any of the man-made forces, a change will take place in the movement of the airplane. If LIFT is increased to be greater than GRAVITY, the airplane will climb and theoretically keep on climbing. If the LIFT is reduced, the airplane will descend or go down and also keep on going down. When THRUST is increased, the airplane will start to go faster, but since DRAG will also increase, the airplane will only increase it’s speed until THRUST will again equal DRAG. The reverse will take place when THRUST is decreased. The airplane will slow down until THRUST again equals DRAG . WHO IS DANIEL BERNOULLI? Daniel Bernoulli was an 18th-century Swiss mathematician and physicist known for his contributions to fluid dynamics, studying how fluids move and behave. He is particularly famous for his principle, which explains how a fluid’s pressure and velocity are related. DANIEL BERNOULLI This principle is vital for understanding how air moves around objects, including airplane wings. It is crucial for understanding the principles of flight. HOW LIFT IS PRODUCED Bernoulli’s Theorem At least 50% of the lift created by an airfoil is due to Bernoulli’s theorem of physics, which states “as the velocity of a fluid(air) increases, its internal pressure decreases”. Air, as we know, is a fluid. Air will try to flow from high to low. Since the air travels faster over the airfoil, a low pressure area is created. “as the velocity of a fluid(air) increases, its internal pressure decreases”. AIRFOIL An airfoil (American English) or aerofoil (British English) is a streamlined body designed to produce lift when moving through the air. Airfoils are used in the design of aircraft wings, helicopter rotor blades, propellers, and other applications where lift is required. HOW LIFT IS PRODUCED Any object moving through the air will not produce lift. The object must be of a special shape. Only then will it have the capability of producing lift. This special shape is called an “airfoil”. Leading Edge camber Trailing Edge chord HOW LIFT IS PRODUCED ■ Leading Edge - Most airfoils have a rounded leading edge which the oncoming air can move smoothly around. ■ Trailing Edge - Most airfoils have a very pointed, sharp trailing edge, behind which the two air streams (above and below the wing) can rejoin smoothly. ■ Chord - The imaginary line that connects from the leading edge of the wing to the trailing edge, and is usually discussed in terms of chord length. Generally, a longer chord length produces more lift. ■ Camber - The curvature of the airfoil. Generally, the upper surface of an airfoil is more curved than the lower surface, however this is not required. Airfoils with more camber generally stall at higher angles of attack. HOW LIFT IS PRODUCED The curved surface of the airfoil is called “camber”. A line, an imaginary straight line from the leading edge to the trailing edge of the airfoil, is called the “chord”. As you can see, the upper curve or camber of the airfoil is greater than the bottom, which is almost a straight line. upper camber upper camber lower camber lower camber HOW LIFT IS PRODUCED Bernoulli's Principle: This principle states that as the speed of a fluid (like air) increases, its pressure decreases Airfoil: Wings are designed with a specific cross-sectional shape called an airfoil. Now, let us imagine a piece or block of air striking the leading edge of the airfoil. The piece of air will split in half, one half will go over the top of the airfoil and the other half will go under it. Since that piece of air must come exactly together again when the two halves meet at the back of the airfoil. The pressure on the bottom of the airfoil will be higher. As a result, the air will push on the bottom of the airfoil trying to flow to the low pressure area on top. You will see that the top piece of air must travel farther, therefore, faster, than the piece of air, which travels under the airfoil (above). The pressure on the bottom of the airfoil will be higher. As a result, the air will push on the bottom of the airfoil trying to flow to the low pressure area on top. HOW LIFT IS PRODUCED How it works: When air flows over an airfoil, the curved upper surface forces the air to travel a longer distance compared to the air flowing under the flatter lower surface. To meet at the trailing edge of the wing, the air over the top must travel faster. According to Bernoulli's principle, this faster-moving air has lower pressure than the slower-moving air below. This pressure difference creates an upward force, known as lift. HOW LIFT IS PRODUCED HOW LIFT IS PRODUCED LIFT LOW PRESSURE HIGH PRESSURE HOW LIFT IS PRODUCED LIFT LOW PRESSURE HIGH PRESSURE FACTORS AFFECTING LIFT Shape of the airfoil Speed of the relative wind Angle of attack ANGLE OF ATTACK Relative wind – air which passes the airfoil. FACTORS AFFECTING LIFT ANGLE OF ATTACK: This is the angle between the wing's chord line (an imaginary line from the leading edge to the trailing edge) and the oncoming airflow. FACTORS AFFECTING LIFT ANGLE OF ATTACK: This is the angle between the wing's chord line (an imaginary line from the leading edge to the trailing edge) and the oncoming airflow. STALLS A stall is what happens when an airfoil can not make enough lift to keep the aircraft in level flight. Stalling is risky and can be dangerous during low-level flying. An airplane stall is a dangerous situation that occurs when the wing's angle of attack exceeds a critical point, causing a reduction in lift and potentially leading to a loss of control. Here's a breakdown of what happens during a stall: CAUSE OF STALL Critical Angle of Attack: Every wing has a critical angle of attack, typically around 15 degrees, though this can vary. Beyond this angle, the airflow over the wing's upper surface separates, becoming turbulent and causing a dramatic decrease in lift In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded. The critical angle of attack is typically about 15 degrees, but it may vary significantly depending on the design of the wing. CAUSE OF STALL The amount of lift produced by an airfoil is increased when we increase the angle of attack. If we increase the angle of attack more than 12-20 degrees, the airflow over the wing will break away and “burble”, then the wind will fill in the low pressure area and lift is destroyed. This condition is called a “stall”. The stall is a condition of excessive angle of attack. When the wings of an aircraft stall, the nose of the airplane will drop and a loss of altitude or height results until the airplane is brought out of the stall. BURBLE Smooth Airflow: Under normal flight conditions, air flows smoothly over the curved upper surface of a wing (airfoil). This smooth airflow is crucial for generating lift. Increasing Angle of Attack:As the wing's angle of attack (the angle between the wing and the oncoming wind) increases, the airflow over the top surface starts to become disrupted. Burbling: At a certain point (the critical angle of attack), the airflow can no longer adhere to the wing's curved surface. It separates, becoming turbulent and chaotic. This turbulent, separated airflow is what we call a "burble." RECOVERY: To recover from a stall, the pilot must decrease the angle of attack to re-establish smooth airflow and regain lift. STALL WARNER An aircraft Stall Warning System is that system which provides the pilot with advance warning of an impending stall. STALLS This type of sensor uses a small opening on the wing's leading edge. As the angle of attack increases, a low-pressure area forms, drawing air through a tube to a reed in the cockpit. The vibrating reed creates a sound, alerting the pilot. HE IS NOT KISSING THEIR AIRCRAFT FOR GOOD LUCK, MERELY TESTING THE STALL WARN AS PART OF PRE-FLIGHT CHECKS! First, let’s talk about what is meant by “wing.” Yes, those big rectangular things jutting out from a fuselage are wings of course, but when talking about stalls, we are looking specifically at the chord line of the wing. If you draw a side profile of a wing and extend a line from the leading edge to the trailing edge, you’ve just drawn the chord line. Why bother with a chord line, why not just say “the wing”? Watch what happens to the chord line of the wing as you add flaps, or aileron inputs. The chord line changes as you manipulate control surfaces! The only thing that causes a stall is exceeding the critical angle of attack. The airplane still produces lift, but it gets really inefficient. The airplane does not fall out of the sky. You are still flying. The only way to correct a stall is then to reduce the angle of attack. Spoilers: Primarily designed to reduce lift. They do this by disrupting the airflow over the wing's upper surface. Their main purpose is to slow the aircraft down.
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