Boeing 787 Flaps and Slats Boeing 787 full pilot training course,

 ADVANCE FLYING ACADEMY

The theory of flight explains how an aircraft is able to stay in the air and maintain controlled flight. It involves the understanding of the physical principles that govern the movement of an aircraft through the air. The basic forces involved in flight are lift, weight, thrust, and drag. These forces interact in various ways to control and sustain flight.

The Four Forces of Flight:

1. Lift:

   • Lift is the force that opposes the aircraft's weight and supports it in the air. It is generated by the wings as air flows over them. The faster the airflow, the greater the lift produced.
   • Bernoulli's Principle helps explain lift. The air above the wing travels faster than the air below the wing, causing lower pressure above the wing, and higher pressure below the wing, creating lift.
   • Angle of Attack (AoA): The angle between the chord line of the wing and the relative airflow also influences lift. As AoA increases, lift increases until a critical angle is reached, beyond which airflow separation occurs, and the wing stalls.

2. Weight (Gravity):

   • Weight is the force that pulls the aircraft down towards the Earth. It is balanced by the lift generated by the wings. To achieve and maintain flight, lift must always counteract weight.
   • Aircraft must generate enough lift to overcome their weight in order to become airborne, and they must maintain a balance between the two for sustained flight.

3. Thrust:

   • Thrust is the forward force that propels the aircraft through the air. It is generated by engines (jet engines, turboprops, or piston engines) and counteracts drag.
   • Thrust must exceed drag for an aircraft to accelerate. The engines are designed to provide enough force to overcome drag and move the aircraft at the desired speed.

4. Drag:

   • Drag is the resistance an aircraft encounters as it moves through the air. It is caused by the friction between the aircraft's surfaces and the air molecules. There are two types of drag:
     • Parasite Drag: This drag is caused by the aircraft's structure and is not directly related to lift. It consists of form drag (the shape of the aircraft) and skin friction (the friction between air and the aircraft's surface).
     • Induced Drag: This drag is caused by the generation of lift. As the wing generates lift, it creates vortices that increase drag. Induced drag increases with the angle of attack.

The Principles of Lift:

Lift is generated primarily by the airfoil (wing), and several factors contribute to its ability to generate lift:

1. Airfoil Shape: The wing’s shape (curved top surface and flatter bottom surface) is designed to create the pressure difference needed for lift.
2. Relative Wind and Angle of Attack: The angle at which the wing meets the airflow (Angle of Attack or AoA) is crucial. A higher AoA increases lift until the critical angle is reached (beyond which the wing stalls).
3. Bernoulli’s Principle: Air moves faster over the curved upper surface of the wing and slower along the flat bottom. This creates lower pressure above the wing and higher pressure below it, generating lift.
4. Newton's Third Law: Air is deflected downward by the wing. According to Newton's Third Law, for every action, there is an equal and opposite reaction, so the downward deflection of air causes the aircraft to be pushed upward.

How Aircraft Achieve Controlled Flight:

1. Roll:
   • Roll is the rotation of the aircraft around its longitudinal axis (from nose to tail). The ailerons control roll. When ailerons are deflected, one wing generates more lift, causing the aircraft to roll in that direction.
2. Pitch:
   • Pitch is the rotation of the aircraft around its lateral axis (from wingtip to wingtip). The elevator or stabilator controls pitch. Moving the elevator controls the aircraft’s angle of attack, which influences the pitch attitude.
3. Yaw:
   • Yaw is the rotation around the vertical axis (up and down). The rudder controls yaw. It moves to one side or the other to keep the aircraft aligned with its flight path.

How Lift and Thrust Relate to Weight and Drag:

To maintain flight, the forces of lift and thrust must counterbalance the forces of weight and drag. These interactions are described by the flight envelope, which outlines the safe operating ranges for an aircraft's speed and altitude. For example:

• Takeoff: Thrust is used to accelerate the aircraft down the runway, and lift is generated by the wings. The weight is initially greater than the lift, but as speed increases, lift becomes greater than weight, and the aircraft becomes airborne.
• Cruise: The aircraft maintains level flight where lift equals weight, and thrust equals drag. The engines maintain a constant speed to overcome drag, and the wings generate just enough lift to balance the aircraft’s weight.
• Landing: During landing, thrust is reduced, and drag is increased (using speed brakes or flaps). The aircraft descends and loses altitude, and the weight is slowly controlled by lift, until it touches down.

The Effect of Flaps and Slats:

1. Flaps: Flaps are devices that extend from the trailing edge of the wing to increase lift and drag. By increasing the wing's surface area and curvature, flaps allow the aircraft to generate more lift at lower speeds, which is particularly useful during takeoff and landing.
2. Slats: Slats are mounted on the leading edge of the wing. They are deployed to improve airflow over the wing at higher angles of attack, preventing premature flow separation and delaying the onset of a stall.

Stability and Control:

1. Static Stability: This refers to the aircraft's ability to return to a stable position after being disturbed. For example, if the aircraft’s nose is pitched up, a statically stable aircraft will return to its original attitude.
2. Dynamic Stability: This refers to the aircraft’s ability to dampen oscillations over time. A dynamically stable aircraft will eventually stop pitching up and down after an initial disturbance.
3. Control Surfaces:
   • Ailerons: Control roll (rotation about the aircraft's longitudinal axis).
   • Elevator: Controls pitch (rotation about the lateral axis).
   • Rudder: Controls yaw (rotation about the vertical axis).

Stalls and Spins:

1. Stall: A stall occurs when the angle of attack exceeds the critical value, causing airflow to separate from the wing’s surface and resulting in a loss of lift. Pilots recover from a stall by lowering the angle of attack and increasing speed.
2. Spin: A spin is a more severe form of stall, characterized by a rapid, uncontrolled descent. It occurs when one wing stalls more than the other, causing the aircraft to enter a rotational flight path. Recovery typically involves reducing the angle of attack on both wings and applying opposite rudder to stop the rotation.

Conclusion:

The theory of flight is built upon fundamental principles of aerodynamics that explain how aircraft can stay in the air and be controlled. It is a balance of forces—lift, weight, thrust, and drag—along with an understanding of airfoil design, control surfaces, and stability. Understanding these concepts is critical for both aircraft designers and pilots to ensure safe and efficient flight.

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