QCAA Aerospace Systems cheat sheet

Four forces in steady level flight: lift = weight and thrust = drag; any imbalance produces acceleration, so a turn requires extra lift (load factor n = 1/cos φ).

Lift equation L = ½ρV²SC_L: lift rises with air density, airspeed squared, wing area and lift coefficient; doubling airspeed quadruples lift at fixed C_L.

Drag equation D = ½ρV²SC_D, where C_D = C_D0 + C_L²/(πAe); induced drag falls as aspect ratio A and Oswald efficiency e rise.

Stall occurs at the critical angle of attack, not at a fixed speed; a heavier aircraft stalls at a higher speed because more lift is needed at the same C_Lmax.

Bernoulli and Newton give complementary lift explanations: faster upper-surface flow lowers static pressure, while downwash means the wing pushes air down and air pushes the wing up.

Load factor n = L/W; limit load is the maximum expected in service and ultimate load is typically 1.5 × limit load before structural failure.

Stress σ = F/A and strain ε = ΔL/L; Young's modulus E = σ/ε describes stiffness in the elastic region, and yield is the onset of permanent deformation.

Fatigue is cyclic loading below ultimate strength causing progressive cracking; safe-life and fail-safe (damage-tolerant) design are the two management strategies.

Brayton (gas turbine) cycle: compression, constant-pressure combustion, expansion, exhaust; thermal efficiency rises with pressure ratio and turbine entry temperature.

Thrust from a jet engine F = ṁ(V_jet − V_aircraft) plus a pressure term; specific fuel consumption is thrust-specific (TSFC) or power-specific (PSFC).

Turbofan bypass ratio = bypass mass flow / core mass flow; high bypass improves propulsive efficiency and reduces noise at airline speeds.

Rocket equation Δv = I_sp·g₀·ln(m₀/m₁); a higher mass ratio or higher specific impulse gives greater velocity change.

Hydraulic systems transmit force by Pascal's principle: pressure is equal throughout a confined fluid, so force scales with piston area (F₁/A₁ = F₂/A₂).

Electrical systems use AC (typically 115 V, 400 Hz) for weight and transformer efficiency, with DC supplied via transformer-rectifier units and batteries for essential loads.

Pitot-static instruments: airspeed from total minus static pressure, altitude from static pressure, and vertical speed from rate of static-pressure change.

Airspace classes: Class A is IFR-only above 18 000 ft; Class C and D require ATC clearance; Class G is uncontrolled, with VFR visibility and cloud-clearance minima applying.

Command words matter: 'describe' needs features, 'explain' needs cause-and-effect links, 'evaluate' needs judgement weighed against criteria, and 'calculate' needs working and units.

Show formula, substitution and answer with units; marks are allocated to method, so an unlabelled numerical answer can lose marks even if correct.

Graph interpretation: gradient equals rate of change (e.g., climb rate on an altitude-time graph), and area under the curve equals an accumulated quantity.

Unit checks: 1 knot = 0.514 m/s, 1 ft = 0.3048 m, 1 nautical mile = 1852 m, and 1 hp ≈ 746 W; convert to SI before substituting into equations.

Significant figures and uncertainty: report to the precision of the given data and quote uncertainty as ± half the smallest scale division for analogue instruments.

Extended-response structure: state the principle, apply it to the given system with data, then state a limitation or assumption to secure the highest band.

Multiple-choice strategy: eliminate options with wrong units or impossible magnitudes first, then compare remaining options against the governing equation.

Diagrams earn marks: free-body diagrams need labelled force arrows from the body, and system schematics need labelled components with flow direction.