Aerodynamics: Wing Performance Quiz

Aerodynamics - Part 1

• Aerodynamics is the study of forces and moments on bodies moving through the air.
• Objectives for this section include describing airflow around a body in relation to terms; boundary layer, free stream flow, laminar and turbulent flow, relative airflow, upwash and downwash, vortices and stagnation.
• Also, describing the terms camber, chord, mean aerodynamic chord (MAC), profile (parasite drag), induced drag, form drag, centre of pressure, angle of attack, angle of incidence, wash in/wash out, fineness ratio, wing shape and aspect ratio.
• Describing the relationship between weight, thrust, and aerodynamic resultant, and defining terms lift coefficient, drag coefficient, polar curve, and stall. The relationship between ground speed (GS), true air speed (TAS), and indicated air speed (IAS) must be described.
• Aerofoil contamination by ice, snow, and frost is also a consideration.

Airfoil (Aerofoil)

• The wing cross-sectional shape.
• Features of the airfoil include a leading edge, trailing edge, chord line, camber, and thickness.
• The wing is a structural component with sections known as ribs and spars to give strength.
• Airfoils are designed for the efficient production of lift.

Generation of Force

• Lift is the net force produced perpendicular to the relative airflow.
• Drag is the net force produced parallel to the relative airflow.

Free Stream Flow

• The clean flow of air when distant enough not to be affected by a body.
• Streamlines show the air flow direction.
• A streamlined shape produces less resistance.
• The amount of free stream air is directly related to the resistance applied to the airflow.
• Resistance to airflow is directly related to airflow and drag applied.

Friction

• Resistance felt by a body moving through air is called friction.
• Airflow slows down near the surface due to viscosity, creating a boundary layer.
• Drag is determined by the boundary layer's nature and thickness.

Boundary Layer

• Layers of air close to the surface of a body.
• Airflow slows down by friction due to air viscosity near the body's surface and increases as it moves away.
• Thickness of boundary layer is proportional to the object's velocity and depends on the type of airflow.

Laminar Flow

• Smooth, orderly motion of air particles sliding past each other.
• Laminar flow typically occurs at the leading edge of a surface.
• Flow transitions to turbulent as it travels across the body.

Turbulent Flow

• Chaotic, irregular air motion with rotating particles.
• Occurs after laminar flow as speed increases.
• Drag increases as the speed of the object increases.

Transition Point

• The point where laminar flow changes to turbulent flow.
• Transition point moves forward as speed increases and drag increases.

Stagnation Point

• The point where airflow comes to rest due to leading edge.
• The origination point of the boundary layer.
• Some airflow moves over, and some under the wing.

Separation Point

• Point where the boundary layer breaks away from the surface.
• Drag increases beyond the separation point.

Wake

• Unsteady rotational flow after separation from the wing.
• Flows behind the wing, dragged by trailing edge.

Boundary Layer Separation and Stall

• Boundary layer separation is where the boundary layer breaks away from the surface.
• Stall occurs when the airflow separates and lift rapidly decreases.
• Stall happens at specific angles of attack and is independent of speed.

Relative Airflow

• The direction of air flowing with respect to a wing.
• Relative airflow moves opposite to the horizontal flight path of the wing.

Coanda Effect

• A fluid will follow a curved surface.
• Viscosity of fluid causes this effect.

Upwash

• Upward airflow in front of a wing.
• Happens due to low pressure region, causing air to move towards it.

Downwash

• Downward deflection of air over a wing.
• Deflection causes upward force on the aircraft, making the downwash action more efficient.

Ground Effect

• Reduction in drag and increase in lift near the ground.
• Airflow pattern changes near the ground surface.

Vortices

• Rotating air eddies at the wing tips.
• Created when airflow over and under the wing meet.
• Form a large vortex on each wing tip.

Jet Engine Vortices

• Vortices generated by jet engines.
• Vortices can affect other aircraft in their vicinity.

Airfoil Nomenclature

• Terms and descriptions for defining shapes and parts of an airfoil (e.g., chord lines, camber) are included.

Types of Airfoils

• Different wing shapes and their associated use (e.g., symmetrical vs. cambered profiles).

High Lift Aerofoil

• Sections using high thickness/chord ratio.
• Well-rounded leading edge with pronounced camber.

General Purpose Aerofoil

• Sections with lower thickness/chord ratio.
• Used typically when high lift/speed are not necessary.

High Speed Aerofoil

• Characterised by thin aerofoil section with low camber.
• Used typically when high speed is necessary or a major requirement.

Aspect Ratio

• Measurement of a wing's span relative to its average chord.
• High aspect ratio means higher efficiency, but lower manoeuvrability.

Aspect Ratio and Maximum Lift Coefficient

• The relationship between high aspect ratio and reduced stall speed.

Aspect Ratio and Induced Drag

• The relationship between high aspect ratio and lower induced drag.

Wing Planform

• A variety of wing shapes for efficiency and building costs.
• Shapes include elliptical, rectangular, tapered, and sweptback.

Mean Aerodynamic Chord (MAC)

• An imaginary chord between the root and tip chords of a wing.

Angle of Incidence

• The angle between the chord line and longitudinal axis of aircraft.
• Fixed angle during manufacture.

Angle of Attack (AoA)

• Angle between the wing chord and relative airflow.
• A crucial factor for lift generation in flight.

Center of Pressure (CP)

• The point of application of lift on the aerofoil.
• Can vary depending on angle-of-attack and aircraft speed.

Pressure Distribution

• Pressure variation on an aerofoil at an angle of attack.
• Differences in pressure on upper and lower surfaces produce lift.

Lift Coefficient (CL)

• A measure of aerodynamic lift.
• Higher CL values mean more lift for a given airflow speed.

Resultant Lift

• Net force produced by an airfoil perpendicular to the relative airflow.

Drag

• Resistance to motion through air (or fluid).
• Two main types are parasite and induced drag.

Parasite Drag

• Drag due to shape or roughness, not directly related to lift generation.
• Three main kinds: skin friction, interference, and form drag.
• Resistance directly proportional to airspeed squared.

Skin Friction

• Drag caused by the roughness of the aircraft's surfaces.
• The thin layer of air clinging to the surface creates small eddies which contribute to drag.

Interference Drag

• Drag from the mixing of airflow streams over fuselage and wings.
• Example is the point where the wing and fuselage connect.

Induced Drag

• Drag as a result of lift generation, from wingtip vortices.
• Inversely proportional to airspeed.
• Angle of attack directly impacts induced drag (higher angle, higher drag)

The Polar Curve

• Graph of lift-to-drag ratio versus angle of attack.
• Relationship between lift, drag, and angle of attack.

Straight and Level Flight

• Lift equals weight, thrust equals drag.
• Thrust adjustments control climbs, descents, and accelerations.

Drag Curves

• Drag variation with speed.
• Minimum drag occurs at an intermediate speed.
• Induced and parasite drag are in play across the various speed ranges.

Stall

• Airflow separation from wing surfaces, resulting in a severe lift drop.
• Happens at a critical angle of attack, regardless of speed or attitude.

Test your knowledge of key concepts in aerodynamics, particularly focusing on wing performance and airfoil design. This quiz will challenge you with questions about lift, drag, flow characteristics, and more, essential for understanding flight dynamics.