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Aeronautical Engineering study materials
Aeronautical Engineering study resources

Aeronautical Engineering: Aeronautics: Aerodynamics, Aircraft Structures, and Propulsion

Aeronautical Engineering · Work through your exam, one topic at a time.

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Aeronautics: Aerodynamics, Aircraft Structures, and Propulsion

Aeronautics here spans three coupled areas: aerodynamics (how lift, drag and moments arise), aircraft structures (how loads are carried and margins proven), and propulsion (how thrust is produced and paid for in fuel). Questions often cross boundaries, so expect a load case that must become a stress and then be checked against a material allowable.

Aerodynamics

  • Lift L = q S C_L with q = ½ρV²; drag polars combine parasite and induced terms: C_D = C_D0 + C_L²/(π e AR), with AR = b²/S.
  • Compressibility: above the critical Mach number wave drag rises sharply; sweep delays the rise.
  • Reynolds number sets boundary-layer state, and therefore stall behaviour.

Structures

  • Bending stress σ = M c / I; in thin skins, shear flow and buckling often govern before yield does.
  • Ultimate load is typically 1.5 times limit load; fatigue and damage tolerance address repeated and accidental damage.
  • The V-n diagram defines the certified flight envelope.

Propulsion

  • Thrust is momentum change plus a pressure term; at subsonic speeds, higher bypass ratio improves propulsive efficiency.
  • TSFC is fuel flow per unit thrust; core thermal efficiency rises with turbine inlet temperature, limited by materials and cooling.

Worked example

Wing: S = 30 m², b = 15 m, V = 80 m/s, ρ = 1.225 kg/m³, C_L = 0.5, e = 0.85. Dynamic pressure q = 0.5 × 1.225 × 80² = 3,920 Pa. Lift L = q S C_L = 3,920 × 30 × 0.5 = 58,800 N. Aspect ratio AR = b²/S = 225/30 = 7.5. Induced drag coefficient C_Di = C_L²/(π e AR) = 0.25/(π × 0.85 × 7.5) = 0.0125. Induced drag D_i = q S C_Di = 3,920 × 30 × 0.0125 ≈ 1,470 N. Sanity check: D_i/L = C_Di/C_L = 0.025, so induced drag is 2.5% of lift - plausible for a lightly loaded wing.

Traps

  • Using the 2-D lift-curve slope for a finite wing.
  • Ignoring density altitude when converting IAS to TAS.
  • Confusing shaft power with thrust power.
  • Checking only yield while buckling or fatigue governs.
  • Treating bypass ratio as a pure efficiency number without the flight-speed context.