Chapter 4 Flashcards
Airflow
The flow of atmospheric air
Angle of attack (a)
The angle of airflow relative to the chord line of the aerofoil.
The angle of attach in (3D flow) is the angle between the aircraft’s longitudinal axis and the relative airflow.
Boundary layer
The volume of air around the surface which flows significantly slower than the free stream velocity. Defined as the area extending from the aircraft’s surface out to the point where the speed of airflow is 99% of the free-stream flow.
Camber
Is the distance between the chord and mean camber line
Cambered aerofoils
Also known as asymmetric aerofoils. Aerofoils with different curves on the upper and lower surfaces
Centre of pressure
The point of the origin of the total reaction is the average point from which the forces act.
Chord
The distance from the leading to trailing edge, measured along the chord line. The point of maximum thickness of an aerofoil usually occurs in the first 1/3 of the chord length.
Downwash
The downward floating air leaving the trailing edge.
Drag
The component of the total reaction which is parallel to the free stream flow.
Form drag
Caused by the pressure of the aircraft acting on the frontal cross-section profile of the aircraft as it moves. Increases with angle of attack.
Ideal flow
The flow of an ideal gas
Leading edge
The frontal area of the aerofoil where is meets the airflow.
Lift
The component of the total reaction which is perpendicular to the free stream of flow.
Mean camber line
An imaginary line half-way (equidistance) between the upper and lower surfaces of the aerofoil. Also known as the camber line.
Positively cambered aerofoil
When the mean camber line is above the chord line. Most wings are positively cambered.
Skin friction drag
Caused by surface roughness of the aircraft’s skin which traps and slows air molecules in the boundary layer. Caused directly from friction within the boundary layer. All effects take please within the r boundary layer.
Stagnation line
The dividing line between the upper and lower flows over and under an aerofoil
Stagnation point
The point on the aerofoil which coincides with the stagnation line.
Symmetric aerofoils
Aerofoils with identically curved upper and lower surfaces
Thickness - chord ratio
The ratio of the aerofoils maximum thickness to the length of its chord. Also knows as fineness ratio
Trailing edge (TE)
Rear edge of an aerofoil which is always sharp.
Upwash
The distinctive upward flow of air before the leading edge
