Airflow and Aerofoils Flashcards
What are the two types of aerofoil sections?
Symmetrical aerofoil and Cambered aerofoil
For which type of aerofoil is the Chord and Camber Line the same?
Symmetrical aerofoil
Explain the term Angle of Attack
The angle between the Chord line and the Relative Airflow or flight path
Explain the term Angle of Incidence
The angle between the Longitudinal Fuselage Datum and the Chord Line
What direction is the Relative Airflow?
Opposite in direction to the aircraft’s flight path
What’s the formula for calculating the Thickness to Chord Line Ratio?
(Max Thickness / Chord Length) x 100%
What’s the formula for calculating the Fineness Ratio?
Chord Length / Max Thickness
Explain the term Viscosity
Viscosity is a fluid’s resistance to flow
What happens to gas Viscosity if the Temperature is increased?
Gas Viscosity will increase
Name the type of drag that is reduced when streamlining an aircraft
Pressure (Form) Drag
From Bernoulli’s theorem, what does Total Pressure equal?
Total Pressure = Static Pressure + Dynamic Pressure
If the airflow Velocity increases as it passes around an aerofoil, what happens to the Total Pressure, Static Pressure and Dynamic Pressure?
Total Pressure remains constant, Static Pressure decreases and Dynamic Pressure increases
What’s the Separation Point?
The point on the aerofoil where the Boundary Layer breaks away from the surface, causing Turbulent Wake
In which direction does the Separation Point move when the Angle of Attack increases?
The Separation Point moves forward on the upper surface, towards the Leading Edge
Explain the effect on Velocity, Dynamic Pressure and Static Pressure in the Stagnation Region of an aerofoil
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
What happens to the Stagnation Region as the Angle of Attack increases?
The Stagnation Region will increase in size and move under the Leading Edge
What’s the Boundary Layer?
The layer of air that starts from zero at the surface of an object and accelerates up to the Relative Airflow
What are the two types of Boundary Layer?
Laminar Flow and Turbulent Flow
What’s the Transition Point?
The point in the Boundary Layer where it changes from a Laminar to a Turbulent Boundary Layer
Which type of Boundary Layer has more Kinetic Energy?
The Turbulent Boundary Layer
What’s the advantage of having more Kinetic Energy in the Boundary Layer at a high Angle of Attack?
It will delay the separation up to a higher Angle of Attack, increasing the Stall Angle
What are the characteristics of a Turbulent Boundary Layer?
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
What are the characteristics of a Laminar Boundary Layer?
A Laminar Boundary layer is thinner than a Turbulent Boundary Layer, with a gradual increase in Velocity Profile and less Skin Friction
What’s the point called at which the Total Air Reaction (TAR) acts?
The Centre of Pressure (CoP)
Define the term Lift
Lift is the component of the Total Air Reaction (TAR) that acts perpendicular to the Relative Airflow
Define the term Drag
Drag is the component of the Total Air Reaction (TAR) that acts parallel to the airflow
What happens to the Separation Point when the airflow starts to stall?
It moves forward on the upper surface of the aerofoil towards the Leading Edge
What happens to Lift and Drag when the aerofoil stalls?
Lift will decrease and Drag will increase
What happens to the Centre of Pressure (CoP) when the aerofoil stalls?
It moves backwards on the upper surface towards the middle of the aerofoil
