Introduction to Aerodynamics

Definition and Scope

• Aerodynamics: Study of forces and moments on bodies moving through fluids, primarily air.
• Key Focus: Forces and moments (pressure, viscous stress) on the surface of bodies like aircraft.
• Goal: Determination of pressure and viscous stresses to predict motion of the body.

Aircraft Forces in Aerodynamics

• Forces on Aircraft: Lift, Drag, Weight, Thrust (Buoyancy force negligible)
• Straight Level Flight: Weight balanced by Lift, Thrust balanced by Drag.

Coordinate System for Forces and Moments

• X-axis: Along the relative wind (direction opposite to the aircraft's speed).
• Y-axis: Perpendicular to plane formed by X and Z axis; positive towards the starboard (right-wing) side.
• Z-axis: Normal to X-axis; upward but not vertical.

Components of Forces

• Drag: Along the relative wind (X-axis)
• Lift: Normal to the relative wind (not vertical)
• Side Force: In Y-direction; positive if towards the starboard

Moments on the Aircraft

• Pitching Moment: About Y-axis (raises/lowers the aircraft nose)
• Rolling Moment: About X-axis (one wing up, other down)
• Yawing Moment: About Z-axis (nose left or right)

Flight Dynamics

• Assumption: Body (aircraft) is at rest, fluid (air) moves.
• Forces in Symmetric Flight: Primarily Lift, Drag, and Pitching Moment.

Aircraft Components

• Key Components: Fuselage, Wings, Horizontal Tail, Vertical Tail, Engine.
• Functionality:
  • Fuselage: Main body housing passengers/cargo.
  • Wing: Major lift generator (95% of total lift).

Wing Geometry and Parameters

• Planform: Shape of wing in plan view (e.g., trapezoidal, delta-wing).
• Wingspan: Distance from wingtip to wingtip.
• Wing Area: Planform area extended to the center of fuselage.
• Aspect Ratio (AR): Span^2 / Wing Area
• Chord: Distance from leading edge to trailing edge of the wing section.
• Taper Ratio: Tip chord length / Root chord length

Sweep Angle and Twist

• Sweep Angle: Angle between Y-direction and leading/trailing edge.
• Twist: Change in chord plane across wing span affecting angle of attack at different sections.
• Dihedral/Anhedral: Wing tips above/below root in front view.

Airfoil Characteristics

• Airfoil: Cross-section shape of the wing.
• Important Terms:
  • Chord Line: Line from leading edge to trailing edge.
  • Thickness: Distance between upper and lower surfaces at any chord location.
  • Aspect Ratio: Relative measure of wing slenderness.
  • Camber Line: Line joining midpoints of thickness along chord.
  • Angle of Attack: Angle between relative wind and chord line.
• Designations: Symmetric (no camber) vs. Cambered (curved mean line)

Summary

• Understanding of basic aerodynamic concepts and aircraft components necessary.
• Definitions and terms introduced form the foundation for further study in aerodynamics.