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Lift, Drag, and Airfoils

Objective​

To understand basic aerodynamic concepts like lift, drag, and the nomenclature we use to describe it.

Motivation​

Forms foundational knowledge for more advanced aerodynamic topics and provides a useful mental model for pilots so they can better anticipate and understand the operation of an airplane.

Timing​

1 hour

Format​

Elements​

Basics​

  • Airplane component: Fuselage, wings, control surfaces
  • Newton's laws of motion: Momentum, Fnet = mass * acceleration, equal and opposite reaction
  • Four forces of flight, equal in unaccelerated flight
  • Theories of lift:
    • Bernoulli: low pressure above the wing
    • Newton: angle of attack
  • Airfoil and relative wind
  • Angle of attack
    • Different between flight path and relative wind
  • Lift equation
lift=12ρV2SCl2\text{lift} = \frac{\frac{1}{2} \rho V^2 S C_l}{2} Where:ρ=air densityV=velocityS=surface areaCl=coefficient of lift\text{Where:}\\ \rho = \text{air density}\\ V = \text{velocity}\\ S = \text{surface area}\\ C_l = \text{coefficient of lift}
  • Critical angle of attack, stall
  • Flight at slow airspeeds
  • Basic torque
  • Center of pressure vs center of gravity
    • Cl should always be behind Cg

Thrust and Drag​

  • Engine provides thrust
  • Drag works opposite
  • Parasite drag
  • Induced drag
    • Tilting of the lift vector
    • Wingtip vortices
  • Parasite drag vs induced drag
  • Best L/D, power required above and below
  • Ground effect

Wing Design​

  • Aspect ratio: Wing span to wing chord
    • Low aspect ratio: Concord, fighter jet
    • High aspect ratio: Glider
  • Wing taper: more lift and less drag
  • Wing loading: how much force each square foot of the wing needs to produce

References​

Pilot's Handbook of Aeronautical Knowledge pg. 4-1 Pilot's Handbook of Aeronautical Knowledge pg. 5-1