✈️Intro to Flight Unit 5 – Aircraft Wing Design and Geometry

Wing Basics and Terminology

• Wings generate lift by creating a pressure difference between the upper and lower surfaces
• Leading edge is the front of the wing where airflow first encounters the wing
• Trailing edge is the rear of the wing where airflow leaves the wing
• Chord is the imaginary straight line connecting the leading and trailing edges
  • Mean aerodynamic chord (MAC) represents the average chord length of a tapered wing
• Span is the distance from one wingtip to the other
• Camber refers to the curvature of the airfoil, with upper camber on top and lower camber on the bottom
• Angle of attack (AOA) is the angle between the chord line and the relative wind

Airfoil Profiles and Selection

• Airfoil shape determines the lift and drag characteristics of the wing
• Symmetrical airfoils have identical upper and lower surfaces and generate no lift at zero AOA
  • Commonly used on horizontal stabilizers and vertical fins
• Cambered airfoils have asymmetrical upper and lower surfaces, generating lift at zero AOA
  • Suitable for most general aviation and commercial aircraft wings
• Laminar flow airfoils have a maximum thickness further aft to maintain laminar flow over a larger portion of the wing
• Supercritical airfoils delay the formation of shock waves at high subsonic speeds, reducing drag
• Airfoil selection depends on the aircraft's mission, speed range, and desired performance characteristics

Wing Planform Geometry

• Planform shape is the shape of the wing as viewed from above
• Rectangular wings have a constant chord length along the span
  • Simple to manufacture but less aerodynamically efficient
• Tapered wings have a decreasing chord length from root to tip
  • Reduces induced drag and improves spanwise lift distribution
• Swept wings have a leading edge that angles back from the wing root to the tip
  • Delays the onset of compressibility effects at high speeds
• Delta wings have a triangular shape with a highly swept leading edge
  • Provides good low-speed handling and high-speed performance
• Elliptical wings have an elliptical lift distribution, minimizing induced drag
  • Difficult to manufacture and rarely used in practice

Wing Loading and Aspect Ratio

• Wing loading is the aircraft's weight divided by the wing area ($W/S$)
  • Higher wing loading results in faster flight speeds but longer takeoff and landing distances
  • Lower wing loading allows for slower flight speeds and shorter takeoff and landing distances
• Aspect ratio (AR) is the square of the wingspan divided by the wing area ($b^2/S$)
  • Higher aspect ratios reduce induced drag but increase structural weight
  • Lower aspect ratios are more maneuverable but less efficient
• Winglets are vertical extensions at the wingtips that reduce induced drag by minimizing wingtip vortices
• Wing fences are vertical plates attached to the upper surface of the wing to control spanwise flow and improve stall characteristics

High-Lift Devices

• High-lift devices increase the maximum lift coefficient ($C_{L_{max}}$) of the wing during takeoff and landing
• Leading-edge devices (slats) extend forward from the leading edge, increasing the effective camber and delaying stall
• Trailing-edge devices (flaps) extend downward from the trailing edge, increasing both lift and drag
  • Plain flaps are simple hinged surfaces that increase lift and drag
  • Split flaps have an upper and lower surface that separate, creating a slot to further increase lift
  • Fowler flaps extend aft and down, increasing both the wing area and camber
  • Slotted flaps have one or more slots between the main wing and flap, improving airflow and increasing lift
• Krueger flaps are hinged leading-edge devices that extend forward and down, increasing camber and lift

Wing Structural Considerations

• Wing structure must withstand the loads imposed during flight, including lift, drag, and inertial forces
• Spar is the main structural member of the wing, running spanwise and carrying the majority of the bending loads
  • I-beam spars have a vertical web and horizontal flanges, providing good bending resistance
  • Box spars have a rectangular cross-section, offering torsional rigidity
• Ribs are chordwise structural members that maintain the airfoil shape and distribute loads between the spars
• Stringers are longitudinal members that run spanwise, providing additional bending resistance and skin support
• Skin is the outer covering of the wing, typically made of aluminum alloy or composite materials
  • Stressed skin design allows the skin to carry a portion of the loads, reducing the required spar size
• Ailerons are hinged control surfaces near the wingtips that provide roll control
• Spoilers are plates on the upper wing surface that disrupt airflow, reducing lift and increasing drag

Performance Trade-offs in Wing Design

• Wing design involves compromises between various performance aspects
• High-speed performance favors swept, thin wings with low aspect ratios
  • Reduces drag at high speeds but compromises low-speed handling and efficiency
• Low-speed performance and efficiency favor high aspect ratio, unswept wings with moderate thickness
  • Increases lift-to-drag ratio but limits high-speed capabilities
• Maneuverability requires lower aspect ratios and moderate sweep for quick roll response
• Structural considerations may limit the use of high aspect ratios or thin airfoils
• Environmental factors, such as icing conditions, may necessitate the use of thicker airfoils or anti-icing systems
• Noise reduction requirements may influence the choice of airfoil and planform shape

Advanced Wing Concepts

• Morphing wings can change shape in flight to optimize performance for different flight conditions
  • Requires complex actuation systems and flexible materials
• Forward-swept wings have a leading edge that angles forward from the wing root to the tip
  • Provides good low-speed handling and maneuverability but requires advanced composites to counter aeroelastic effects
• Blended wing-body (BWB) designs integrate the fuselage and wing into a single lifting surface
  • Offers improved aerodynamic efficiency and reduced fuel consumption but presents challenges in passenger accommodation and emergency egress
• Closed-wing designs, such as box wings or joined wings, have multiple lifting surfaces that create a closed loop
  • Reduces induced drag and improves structural efficiency but increases complexity and weight
• Active flow control techniques, such as boundary layer suction or blowing, manipulate the airflow over the wing to improve performance
  • Can delay flow separation, reduce drag, or enhance lift but requires additional systems and energy input