Aircraft Aerodynamics, Structures and Systems
What you must know
This domain covers aircraft structures (fuselage, wings, empennage, landing gear), structural design concepts (stress, strain, tension, compression, shear, bending, torsion), and aircraft systems: hydraulic, pneumatic, fuel, electrical, flight controls, air conditioning and pressurisation, ice and rain protection, and landing gear. You should understand system architecture at a descriptive level: reservoirs, pumps, accumulators, valves, and the purpose of each.
Traps to watch
- Stress versus strain: stress is force per unit area; strain is deformation per unit length. They are related by Young's modulus.
- Shear versus tension: a rivet in a lap joint carries shear; a bolt in tension carries pull-out load.
- Hydraulic accumulators: they store energy and damp pressure pulses; they do not pump fluid.
- Pressurisation: cabin altitude is controlled by outflow valves; a failure to close them prevents pressurisation.
- Redundancy: systems often have multiple channels; know which is primary and which is standby.
Worked example
A hydraulic system has a reservoir, engine-driven pump, accumulator, and system pressure of 3000 psi. The accumulator stores energy for peak demands and smooths pressure fluctuations; it is not a source of continuous flow. If the pump fails, the accumulator provides only limited emergency actuation.
Rule of thumb
Identify the load type first (tension, compression, shear, bending, torsion) before selecting the structural or fastener answer.
Aircraft Aerodynamics, Structures and Systems (Advanced)
What you must know
This section extends the previous domain into advanced aerodynamics and system integration: high-lift devices (flaps, slats), spoilers, boundary layer control, mach effects and critical mach number, sweepback, and stability and control (static and dynamic stability, dihedral effect, tailplane design). Systems content includes fly-by-wire concepts, autopilot and flight director basics, and the interaction between aerodynamics and structure (flutter, aeroelasticity).
Traps to watch
- Flaps versus slats: flaps increase lift and drag and are usually trailing-edge; slats are leading-edge devices that delay stall at high AoA.
- Spoilers: they spoil lift and increase drag; they are not primary lift devices.
- Critical mach number: the free-stream Mach number at which airflow somewhere on the aircraft first reaches Mach 1; sweepback raises it.
- Static versus dynamic stability: static stability is the initial tendency to return; dynamic stability is the behaviour over time (oscillation damping).
- Dihedral effect: positive dihedral increases lateral stability but can cause Dutch roll coupling.
Worked example
An aircraft with swept wings has a higher critical Mach number than a straight-wing design, delaying shock-wave formation and reducing drag rise. However, sweepback reduces lift coefficient at a given AoA, requiring higher AoA or high-lift devices for take-off and landing.
Rule of thumb
Leading-edge devices (slats) delay stall; trailing-edge devices (flaps) increase lift and drag; spoilers destroy lift. Match the device to the phase of flight in the question.