Airflow And Aerofoils Flashcards
Name and label the two aerofoil sections.
- Symmetrical Aerofoil
- Cambered Aerofoil
On which type of aerofoil are the chord and camber line the same?
Symmetrical Aerofoil
Explain the term ‘Angle of Attack.’
The angle between the chord line and relative airflow or flight path (free stream airflow).
Explain the term ‘Angle of Incidence.’
The angle between the longitudinal fuselage datum (LFD) and the mean chord line.
Is the free stream airflow opposite in direction to the aircraft’s flight path?
Yes
What is the formula for calculating the thickness-to-chord ratio?
Thickness-to-chord ratio = Max thickness / Chord length × 100%
What is the formula for calculating the fineness ratio?
Fineness Ratio = Chord Length / Max Thickness
Using Bernoulli’s theorem, explain the effect on velocity, dynamic, and static pressure as air flows over the top surface of a cambered aerofoil.
As the airflow accelerates over the upper surface, the velocity increases, causing the static pressure to decrease.
What is the separation point?
The point on the aerofoil where the boundary layer breaks away from the surface, causing a turbulent wake.
Which way does the separation point move as the angle of attack increases?
Forward on the upper surface towards the leading edge.
What is the boundary layer?
It is a layer of air that starts from zero at the surface of an object and accelerates up to the free stream airflow.
What are the two types of boundary layers?
- Laminar
- Turbulent
What is 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?
Turbulent boundary layer
What advantage is there in having more kinetic energy in the boundary layer at high angles of attack?
It delays the airflow separation up to a higher angle of attack (increasing the stall angle).
Give three differences between turbulent and laminar boundary layers.
- Turbulent: Thicker, erratic path, less likely to separate, more drag.
- Laminar: Thinner, smooth flow, gradual velocity increase, less drag.
Define the term ‘Lift’ in relation to airflow and total air reaction.
Lift is the component of total air reaction that acts perpendicular to the airflow.
Define the term ‘Drag’ in relation to airflow and total air reaction.
Drag is the component of total air reaction that acts parallel to the airflow.
What happens to the separation point when the aerofoil starts to stall?
It moves forward on the upper surface to the leading edge.
What happens to lift and drag when the aerofoil stalls?
Lift reduces and drag increases.
What happens to the center of pressure when the aerofoil stalls?
It moves backward on the upper surface toward the middle of the aerofoil.
Explain the term ‘Viscosity.’
Viscosity is the fluid’s resistance to flow (or internal friction).
What happens to gas viscosity as temperature increases?
It increases (opposite to liquids).
What type of drag is reduced when streamlining an aircraft?
Pressure (form) drag.
Explain how streamlining a flat plate to an aerofoil shape reduces drag.
The rounded front reduces velocity drop and static pressure buildup, minimizing resistance. The elongated rear reduces separation and turbulence, lowering drag.
From Bernoulli’s theorem, what does total pressure equal?
Total Pressure = Static Pressure + Dynamic Pressure
If airflow velocity increases as it passes around an aerofoil, does total pressure, static pressure, or dynamic pressure increase, decrease, or stay the same?
Total Pressure: Stays the same
Static Pressure: Decreases
Dynamic Pressure: Increases
