Airflow and Aerofoils

Question 1

What are the two types of aerofoil sections?

Answer 1

Symmetrical aerofoil and Cambered aerofoil

Question 2

For which type of aerofoil is the Chord and Camber Line the same?

Answer 2

Symmetrical aerofoil

Question 3

Explain the term Angle of Attack

Answer 3

The angle between the Chord line and the Relative Airflow or flight path

Question 4

Explain the term Angle of Incidence

Answer 4

The angle between the Longitudinal Fuselage Datum and the Chord Line

Question 5

What direction is the Relative Airflow?

Answer 5

Opposite in direction to the aircraft’s flight path

Question 6

What’s the formula for calculating the Thickness to Chord Line Ratio?

Answer 6

(Max Thickness / Chord Length) x 100%

Question 7

What’s the formula for calculating the Fineness Ratio?

Answer 7

Chord Length / Max Thickness

Question 8

Explain the term Viscosity

Answer 8

Viscosity is a fluid’s resistance to flow

Question 9

What happens to gas Viscosity if the Temperature is increased?

Answer 9

Gas Viscosity will increase

Question 10

Name the type of drag that is reduced when streamlining an aircraft

Answer 10

Pressure (Form) Drag

Question 11

From Bernoulli’s theorem, what does Total Pressure equal?

Answer 11

Total Pressure = Static Pressure + Dynamic Pressure

Question 12

If the airflow Velocity increases as it passes around an aerofoil, what happens to the Total Pressure, Static Pressure and Dynamic Pressure?

Answer 12

Total Pressure remains constant, Static Pressure decreases and Dynamic Pressure increases

Question 13

What’s the Separation Point?

Answer 13

The point on the aerofoil where the Boundary Layer breaks away from the surface, causing Turbulent Wake

Question 14

In which direction does the Separation Point move when the Angle of Attack increases?

Answer 14

The Separation Point moves forward on the upper surface, towards the Leading Edge

Question 15

Explain the effect on Velocity, Dynamic Pressure and Static Pressure in the Stagnation Region of an aerofoil

Answer 15

Total Pressure remains constant. Total Pressure = Static Pressure + Dynamic Pressure. As the airflow slows in the Stagnation Region, Velocity and Dynamic Pressure will decrease causing Static Pressure to increase

Question 16

What happens to the Stagnation Region as the Angle of Attack increases?

Answer 16

The Stagnation Region will increase in size and move under the Leading Edge

Question 17

What’s the Boundary Layer?

Answer 17

The layer of air that starts from zero at the surface of an object and accelerates up to the Relative Airflow

Question 18

What are the two types of Boundary Layer?

Answer 18

Laminar Flow and Turbulent Flow

Question 19

What’s the Transition Point?

Answer 19

The point in the Boundary Layer where it changes from a Laminar to a Turbulent Boundary Layer

Question 20

Which type of Boundary Layer has more Kinetic Energy?

Answer 20

The Turbulent Boundary Layer

Question 21

What’s the advantage of having more Kinetic Energy in the Boundary Layer at a high Angle of Attack?

Answer 21

It will delay the separation up to a higher Angle of Attack, increasing the Stall Angle

Question 22

What are the characteristics of a Turbulent Boundary Layer?

Answer 22

A Turbulent Boundary Layer is an erratic path of molecules, thicker than a Laminar Boundary Layer, less likely to separate and with less Pressure Drag

Question 23

What are the characteristics of a Laminar Boundary Layer?

Answer 23

A Laminar Boundary layer is thinner than a Turbulent Boundary Layer, with a gradual increase in Velocity Profile and less Skin Friction

Question 24

What’s the point called at which the Total Air Reaction (TAR) acts?

Answer 24

The Centre of Pressure (CoP)

Question 25

Define the term Lift

Answer 25

Lift is the component of the Total Air Reaction (TAR) that acts perpendicular to the Relative Airflow

Question 26

Define the term Drag

Answer 26

Drag is the component of the Total Air Reaction (TAR) that acts parallel to the airflow

Question 27

What happens to the Separation Point when the airflow starts to stall?

Answer 27

It moves forward on the upper surface of the aerofoil towards the Leading Edge

Question 28

What happens to Lift and Drag when the aerofoil stalls?

Answer 28

Lift will decrease and Drag will increase

Question 29

What happens to the Centre of Pressure (CoP) when the aerofoil stalls?

Answer 29

It moves backwards on the upper surface towards the middle of the aerofoil