Chapter 4

Question 1

Airflow

Answer 1

The flow of atmospheric air

Question 2

Angle of attack (a)

Answer 2

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.

Question 3

Boundary layer

Answer 3

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.

Question 4

Camber

Answer 4

Is the distance between the chord and mean camber line

Question 5

Cambered aerofoils

Answer 5

Also known as asymmetric aerofoils. Aerofoils with different curves on the upper and lower surfaces

Question 6

Centre of pressure

Answer 6

The point of the origin of the total reaction is the average point from which the forces act.

Question 7

Chord

Answer 7

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.

Question 8

Downwash

Answer 8

The downward floating air leaving the trailing edge.

Question 9

Drag

Answer 9

The component of the total reaction which is parallel to the free stream flow.

Question 10

Form drag

Answer 10

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.

Question 11

Ideal flow

Answer 11

The flow of an ideal gas

Question 12

Leading edge

Answer 12

The frontal area of the aerofoil where is meets the airflow.

Question 13

Lift

Answer 13

The component of the total reaction which is perpendicular to the free stream of flow.

Question 14

Mean camber line

Answer 14

An imaginary line half-way (equidistance) between the upper and lower surfaces of the aerofoil. Also known as the camber line.

Question 15

Positively cambered aerofoil

Answer 15

When the mean camber line is above the chord line. Most wings are positively cambered.

Question 16

Skin friction drag

Answer 16

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.

Question 17

Stagnation line

Answer 17

The dividing line between the upper and lower flows over and under an aerofoil

Question 18

Stagnation point

Answer 18

The point on the aerofoil which coincides with the stagnation line.

Question 19

Symmetric aerofoils

Answer 19

Aerofoils with identically curved upper and lower surfaces

Question 20

Thickness - chord ratio

Answer 20

The ratio of the aerofoils maximum thickness to the length of its chord. Also knows as fineness ratio

Question 21

Trailing edge (TE)

Answer 21

Rear edge of an aerofoil which is always sharp.

Question 22

Upwash

Answer 22

The distinctive upward flow of air before the leading edge