Theory of Flight CASA 8.3

Aerodynamics of Flight

• Four forces act on an aircraft during flight: lift, weight, thrust, drag.
• Lift: Upward force created by airflow over and under the wings. Acts at a right angle to the airflow through the Centre of Pressure (C of P).
• Weight: Downward force caused by gravity. Acts through the Centre of Gravity (C of G).
• Thrust: Forward force that propels the aircraft through the air. Acts through the centreline of the engine or propeller.
• Drag: Backward force that opposes thrust. Acts at a right angle to lift.

Aircraft Components

• Fuselage: The body of the aircraft.
• Wings: Horizontal aerofoils producing lift. Ailerons and flaps are hinged to the wings.
• Tail: Provides stability and control.
• Engine: Provides thrust.

Primary Flight Controls

• Ailerons: Control roll by moving up or down, creating a rolling moment.
• Elevator: Controls pitch by moving up or down, creating a pitching moment.
• Rudder: Controls yaw by moving left or right, creating a yawing moment.

Aircraft Axes

• Lateral Axis: Extends wing tip to wing tip, rotation around this axis is called pitch.
• Longitudinal Axis: Extends nose to tail, rotation around this axis is called roll.
• Vertical Axis: Passes vertically through the centre of gravity, rotation around this axis is called yaw.

Lift and Weight

• Key aerodynamic forces are lift and weight.
• Lift opposes weight.
• In straight and level flight, lift and weight are equal.
• The shape of the wing creates high pressure under the wing and low pressure above, generating lift.

Centre of Gravity (CG) and Centre of Pressure (CP)

• Centre of Gravity (CG) is the point where the aircraft's weight is concentrated.
• Centre of Pressure (CP) is the point where the lift force acts.
• The designer carefully positions the CG relative to the CP to maintain stability.
• Ideal arrangement: CG forward of CP, thrust line lower than drag, creating opposing forces that balance.

Adverse Forward Centre of Gravity

Occurs when too much weight is towards the front of the aircraft.

• Increased fuel consumption.
• Increased power required.
• Increased tendency to dive, especially with power off.
• Increased oscillation tendency.
• Increased stress on the nose wheel.
• Increased danger during flap operation.
• Difficult to raise the nose during landing.

Adverse Aft Centre of Gravity

Occurs when too much weight is towards the tail of the aircraft.

• Poor stability.
• Reduced flying speed.
• Reduced range.
• Increased strain on the pilot during instrument flight.
• Increased danger of stall.
• Dangerous spin characteristics.
• Poor landing characteristics.

Centre of Gravity Limits

• Every aircraft type has its own CG limits, usually between 15% and 40% of the wing chord.
• Limits are established by design based on flight handling characteristics.

Straight-and-Level Flight

• In straight and level flight at a constant airspeed, Lift = Weight, and Thrust = Drag.
• To change equilibrium, use thrust to accelerate or climb, reduce thrust to descend.

Forces in a Climb

• When entering a climb, lift momentarily increases as the nose is raised.
• Airspeed gradually decreases as thrust is insufficient to counter the increased drag during a climb.
• More power is required to maintain a constant airspeed during a climb than in level flight.

Forces in a Descent

• Entering a descent decreases angle of attack, momentarily decreasing lift.
• Weight becomes greater than lift, causing the aircraft to descend.
• Thrust is reduced to allow gravity to pull the aircraft downwards.

Forces in a Glide

• Thrust is removed, lift and drag balance the weight.
• Best glide ratio is achieved at an angle of attack that produces the maximum lift/drag ratio.

Glide Ratio and Glide Angle

• Glide Ratio: Distance travelled divided by altitude descended.
• Glide Angle: The angle of the glide path, calculated using the tangent of the angle.

Theory of the Turn

• Centrifugal Force: The outward force experienced by a body moving in a curved path.
• Centripetal Force: The inward force that counters centrifugal force, keeping the body in a curved path.
• An aeroplane banks to turn, generating a horizontal component of lift (centripetal force) that pulls the aircraft towards the centre of the turn.

Sideslip, Skidding and Balanced Turn

• Sideslip: Occurs when the bank angle is too high, causing the aircraft to drift inwards during the turn - Skidding: Occurs when the bank angle is too low, causing the aircraft to drift outwards during the turn.
• Balanced Turn: Occurs when the bank angle is correct, with no sideways drift during the turn.

Wing Loading

• Wing loading is the weight of the aircraft divided by the wing area.
• Measured in pounds per square foot (lb/ft2) or kilograms per square metre (kg/m2).
• A lower wing loading results in a lower stall speed.
• A higher wing loading results in a higher stall speed.

Load Factor

• Load factor is the ratio of the load imposed on the aircraft structure to the weight of the structure itself.
• Measured in g (gravity units).
• In straight and level flight, the load factor is 1g.
• Aircraft are designed to withstand load factors greater than 1g during maneuvers and turbulence.

Load Factor Limits

• Each aircraft has a specified g limit to avoid structural damage.
• Certification standards ensure adequate strength to withstand load factors.

Effect of Load Factor on Stall Speed

• Increasing load factor narrows the safety margin above stall.
• The aircraft is closer to its stalling angle of attack during a turn due to increased load factor.

Lift Augmentation

• High-lift devices are used to increase lift during take-off, landing, and low-speed situations.
• They include trailing edge flaps, leading edge slats, and leading edge slots.

Trailing Edge Flaps

• Designed to increase lift and reduce stall speed.
• Allows the aircraft to fly at a slower speed while maintaining control.### Trailing Edge Flaps
• Trailing edge flaps are movable surfaces that alter the effective shape of an aerofoil
• Flaps are used to increase lift and drag during low speed operations, such as landing and take-off
• Flaps allow for slower approach and landing speeds, as the aircraft can fly slowly and at a fairly steep angle
• Deploying the entire set of flaps increases drag more than lift, so they are typically used for landing
• Deploying only part of the flaps increases lift more than drag, so they are typically used for take-off

Leading Edge Slats

• Slats are extendable high lift devices on the leading edge of the wings
• Slats increase both the surface area and the camber of the wing
• Slats are deployed outwards and downwards from the leading edge
• They increase lift during low-speed operations such as take-off, initial climb, approach, and landing

Leading Edge Slots

• A slot is a fixed duct for air to flow from below the wing to the top
• Air is directed over the surface in a high-velocity stream
• Slots are typically placed ahead of the aileron
• Slots can be automatically deployed at a predetermined angle of attack or mechanically deployed by the pilot

Effects of Flaps and Slats on Coefficient of Lift (CL)

• Flaps/slats increase both lift and drag
• On most installations, deploying half of the flaps/slats increases lift more than drag
• On most installations, deploying all of the flaps/slats increases drag more than lift

Explore the fundamental forces of flight and the components of aircraft in this quiz. Understand how lift, weight, thrust, and drag interact, and learn about the role of various aircraft parts such as the fuselage, wings, and controls. Test your knowledge on aviation mechanics and aerodynamics.