Aerospace engineering fundamentals
"Explain the four forces of flight." Lift (perpendicular to flight path, generated by wings via pressure differential and angle of attack), Drag (opposing flight, profile + induced + wave drag), Thrust (engines opposing drag), Weight (gravity opposing lift). Steady level flight: Lift = Weight, Thrust = Drag. "What is the difference between laminar and turbulent boundary layers?" Laminar: smooth, ordered — lower skin friction drag but susceptible to separation at adverse pressure gradients. Turbulent: chaotic mixing — higher skin friction but more resistant to separation. Wing design delays transition as long as possible on the upper surface (natural laminar flow profiles). At transonic speeds, shock-induced boundary layer separation is a critical design concern.
Aerospace structures questions
"What is fatigue and how is it managed in aerospace structures?" Progressive structural damage under cyclic loading below ultimate strength. Every aircraft pressurisation cycle stresses the fuselage. Management: damage tolerant design (slow crack growth, detected before critical), fail-safe design (multiple load paths), safe life design (component retired before fatigue life). Inspection programmes and structural health monitoring are critical in service. "What is the Von Mises yield criterion?" Predicts yielding when distortion energy reaches the value at yield in simple tension. Used for ductile metals under combined stress states. In 2D plane stress: σ_VM = √(σ₁² − σ₁σ₂ + σ₂²) ≤ σ_y.
Propulsion questions
"How does a gas turbine engine work?" Brayton cycle: intake (pressure rises), compression (20-50:1 pressure ratio), combustion (temperature rises to 1500-1700°C at turbine entry), expansion (turbine drives compressor and accessories), exhaust (thrust via nozzle). Turbofan: large bypass fan — bypass ratio 10-15:1 in modern civil engines — for better propulsive efficiency. "What is specific impulse?" Thrust per unit weight flow rate of propellant — the efficiency measure for rockets. LH2/LOX: ~450s vacuum. Kerosene/LOX: ~350s. Solid: ~250-300s. Higher Isp reduces propellant mass fraction needed for a given delta-V (Tsiolkovsky rocket equation).
Behavioral questions
"Tell me about a project on a safety-critical system." Show understanding of development assurance levels (DAL A-E per DO-178C), requirements traceability, independent testing and validation. "Describe a time you disagreed with a design decision." Professional challenge: raised concern with technical evidence, engaged with counter-arguments, escalated appropriately, committed to the agreed approach once decided.