Definitions Flashcards
Datum
A reference point or base line from which measurements are taken.
Lapse Rate
The rate at which air temperature decreases with an increase in altitude. The standard lapse rate is approximately 2°C / 1000’
Standard Pressure Datum
In aviation, standard pressure refers to 29.92 inches of mercury (Hg), which is used to set altimeters for uniform pressure measurements.
ISA Lapse Rate
The International Standard Atmosphere (ISA) lapse rate is 2°C / 1000’, 1Hg / 1000’ providing a standard for temperature decrease with altitude increase.
Standard Temperature Datum
The standard temperature datum refers to the International Standard Atmosphere (ISA) temperature at mean sea level, which is defined as 15°C.
Bernoulli’s Principle
Bernoulli’s Principle states that as the velocity of a fluid (air) increases, its pressure decreases.
*Remember Venturi Tube
Airfoil
A structure designed to produce lift when air flows over it, such as an airplane wing or propeller blade.
Airfoil is 2D, Wing is 3D
Camber
The curvature of the airfoil’s upper and lower surfaces, which influences the amount of lift generated. A greater camber generally increases lift.
Mean Camber Line
Mean camber line is the line equidistant from the upper and lower surfaces of the airfoil.
Airfoils with more pronounced camber tend to produce more lift at lower angles of attack, whereas symmetrical airfoils (no camber) generate equal lift on both surfaces.
Newton’s First Law
When a body is in motion it tends to remain in motion.
Newton’s Second Law
A force must be applied to alter the state of uniform motion of a body.
Newton’s Third Law
Every action has an equal and opposite reaction.
Equilibrium
In flight, equilibrium occurs when all forces acting on the airplane (lift, weight, thrust, and drag) are balanced.
Angle of Attack
The angle between the chord line of the wing and the direction of the relative airflow.
This angle is critical for maintaining lift, but if too steep, it may cause a stall.
Boundary Layer
The thin layer of air that flows over the surface of an aircraft wing.
Proper management of the boundary layer is important to reduce drag and improve efficiency.
Types of Drag
- Parasite Drag: Is the term given to the drag of all those parts of the aeroplane which do not contribute to lift.
Includes form drag, skin friction, and interference drag all of which resist forward motion.
2.Induced Drag: Is caused by those parts of an aeroplane which are active in production of lift.
Increases with a higher angle of attack.
Drag
Drag is the resistance an aeroplane experiences in moving forward through air.
Euler’s Equation
Describes the motion of a non-viscous fluid.
These equations help describe how the airflow behaves around an aircraft, influencing its stability, control, and lift generation.
Coanda Effect
The Coanda effect refers to the tendency of a fluid jet (air in this case) to stay attached to a convex surface, such as an airplane wing, which helps generate lift.
Washout
Washout refers to the twist in an aircraft wing where the angle of incidence decreases from root to tip.
This helps delay stall at the wingtips, improving control at lower speeds.
Center of Pressure
The center of pressure is the point on an aircraft’s wing where the total sum of aerodynamic forces (lift and drag) acts.
It shifts as the angle of attack changes.
Longitudinal Axis
The longitudinal axis is an imaginary line running from the nose to the tail of an aircraft.
Movement about this axis is called roll, controlled by the ailerons.
Lateral Axis
The lateral axis is an imaginary line that runs horizontally across the aircraft from wingtip to wingtip.
Movement about this axis is called pitch, which controls the aircraft’s nose-up or nose-down attitude. The elevator controls pitch by adjusting the aircraft’s angle relative to the horizon, affecting ascent or descent.
Vertical Axis
The vertical axis is an imaginary line that runs vertically through the center of the aircraft, from top to bottom.
Movement about this axis is called yaw, which controls the direction the nose of the aircraft points, left or right. The rudder controls yaw by adjusting airflow over the tail, helping to maintain directional control during flight.
Angle of Incidence
The angle of incidence is the angle formed between the aircraft wing’s chord line and the aircraft’s longitudinal axis.
It is fixed and designed to optimize lift and performance.
Laminar Airflow
Laminar airflow is the smooth, orderly flow of air over an aircraft’s surface.
Maintaining laminar flow reduces drag, which improves fuel efficiency and performance.
Turbulent Airflow
Turbulent airflow occurs when the smooth, laminar flow breaks down, causing chaotic movement.
It increases drag and can reduce efficiency.
Wingtip Vortices
Wingtip vortices are spirals of air created by the high-pressure air beneath the wing meeting the low-pressure air above the wing.
These vortices contribute to induced drag.
Transition Point
The transition point is the location on the wing where the airflow changes from laminar to turbulent.
Its position depends on the airfoil shape, speed, and conditions.
Skin Friction Drag
Skin friction is a type of parasite drag caused by the friction of air particles moving along the surface of the aircraft.
Reducing surface roughness helps decrease skin friction.
Induced Drag
Induced drag is created by parts of the aeroplane involved in generating lift.
It increases with angle of attack and decreases with speed.
Parasite Drag
Parasite drag is the resistance experienced by the aircraft as it moves through the air.
It consists of form drag, skin friction drag and interference drag and increases with speed.
Form / Pressure Drag
Form drag, a type of parasite drag, is caused by the shape of the aircraft.
As air flows around the body, pressure differences create resistance. Streamlining the aircraft helps reduce this drag.
Interference Drag
Interference drag occurs when airflow around different aircraft components (such as the wing and fuselage) interact, creating additional resistance.
Reducing sharp intersections can minimize this drag.
Downwash
Downwash refers to the downward deflection of air behind an aircraft’s wing as a result of lift generation.
It contributes to induced drag but also stabilizes the airflow over the wing.
Relative Airflow
Relative airflow is the direction of the airflow in relation to the wing. It is opposite to the direction of flight and affects lift and drag generation on the aircraft.
Boundary Layer Separation
Boundary layer separation occurs when the airflow can no longer adhere to the surface of the wing due to adverse pressure gradients, leading to increased drag and potentially a stall.
Clean Configuration
In a clean configuration, an aircraft is in its most aerodynamically efficient state, with no flaps, slats, or landing gear extended, minimizing drag and maximizing speed.
Separation Point
The point at which the airflow pulls away from the wing.
Winglets
A winglet is a small, vertical or angled extension at the tip of an aircraft wing designed to reduce drag caused by wingtip vortices.
Feathering
Feathering means turning the blades to the extreme coarse pitch position, where they are streamlined and cease to turn.
This is typically done in the event of an engine failure to minimize drag and prevent the wind from turning the propeller (windmilling) and reducing drag on the blades. By feathering the propeller, the aircraft can maintain better performance and control during an engine-out situation. It also stops excessive vibration.
Fairing
A fairing is a smooth, streamlined covering placed over various parts of an aircraft to reduce drag and improve aerodynamic efficiency.
Fairings are commonly used on landing gear, wing-fuselage junctions, and other structural joints to minimize turbulence and resistance by smoothing out airflow over these areas. They contribute to better fuel efficiency and overall aircraft performance.