Aerodynamics CASA 8.2

Generation of Lift

• Lift is produced by air being deflected downwards by the wing.
• The angle of attack is the angle at which the wing meets the airflow.
• Increased angle of attack deflects air downwards more, increasing lift.
• However, there's a limit to angle of attack, exceeding it causes air to flow unevenly and decreases lift.
• Bernoulli's principle states that faster air creates less pressure.
• Air above the wing moves faster, creating lower pressure than the air below the wing, contributing to lift.

Stalling Angle

• A stall occurs when airflow separates from the wing's upper surface, causing a rapid decrease in lift.
• The airflow becomes turbulent with a greater angle of attack.
• Critical angle of attack, also known as the stalling angle, occurs at around 15 degrees and is when maximum lift is generated.
• An aeroplane can stall at any airspeed, flight attitude, or weight.

Generation of Drag

• Drag is caused by surfaces that deflect or interfere with airflow.
• It acts against the direction of flight.
• Induced drag is caused by the lift generated by the wings.
• It is directly related to the angle of attack.
• Higher angles of attack lead to higher induced drag.
• Wing-tip vortices are created by the spinning air.
• Parasite drag is all drag not related to lift production.
• It is caused by the disruption of airflow around the aircraft surfaces.

Types of Parasite Drag

• Form drag is resistance to motion due to the shape of the aircraft.
• It is created by any structure that protrudes into the airflow.
• Skin friction drag is caused by the roughness of the aircraft's surfaces.
• Interference drag occurs when different air currents meet and interact.

Total Drag

• Total drag is the sum of induced, form, friction, and interference drag.
• There is an optimal airspeed where total drag is at a minimum.
• The maximum range speed is slightly above the minimum drag speed, as flying at the minimum drag speed is unstable.

Lift Coefficient

• Lift is directly proportional to:
  • Shape of the aerofoil
  • Area of the aerofoil
  • Air density
  • Speed of the air
  • Angle of attack

Drag Coefficient

• The drag force is determined by the drag coefficient, density of air, velocity, and area.
• The drag coefficient is affected by the shape of the aircraft and other factors.

Aerodynamic Curves

• The aerodynamic curve shows a point of intersection at about a 4-degree angle of attack, known as the optimum angle of attack, where the lift-to-drag ratio is best.

Aerodynamic Forces

• The four aerodynamic forces controlling aircraft flight are:
  • Lift
  • Drag
  • Weight
  • Thrust
• In straight and level flight, lift equals weight, and thrust equals drag.

Wing Shape

• Planform is the shape of the wing from above or below.
• Common wing shapes:
  • Rectangular: cheapest to build.
  • Elliptical: most efficient.
  • Tapered: compromise between cost and efficiency.
  • Sweepback: highest speed.

Wing Geometry

• Chord: straight line connecting leading and trailing edges of an aerofoil.
• Wingspan: distance between the wing tips.
• Wing Area: projected area of the wing.
• Aspect Ratio: wingspan squared divided by the area.
• Mean Aerodynamic Chord (MAC): chord drawn through the center of the aerofoil area.

Wash In and Wash Out

• Wash out: greater angle of incidence at the root of the wing than at the tip.
• Wash in: greater angle of incidence at the tip than at the root.
• Wash out improves stability in stall conditions by stalling the root section first.

Icing Effects

• In-flight icing can disrupt airflow, reducing control and performance.
• Ice increases the stall angle and reduces lift.
• Uneven ice build-up can affect balance and roll control.