Aircraft General Knowledge - Airframe, Systems and Powerplants
Airframe
A semi-monocoque fuselage uses skin, stringers and frames; the skin carries shear and pressurization loads while stringers stiffen it. Fail-safe structure provides alternate load paths so a crack does not cause immediate failure; safe-life parts are removed at a fixed life; damage-tolerant designs depend on scheduled inspections.
Systems
Hydraulic actuators produce force from pressure × area; accumulators smooth demand and supply emergency pressure. Electrical systems use AC generators, bus ties and transformer-rectifier units; loss of a bus is not necessarily loss of all electrical power. Pressurization is controlled by the outflow valve. Ice protection may be thermal (hot air), electrical or chemical.
Powerplant
The gas turbine follows the Brayton cycle: compression, combustion at near-constant pressure, expansion through the turbine, exhaust. Thrust is mass flow times the change in velocity. N1 is fan/LP compressor speed, N2 core speed, and EGT is a turbine temperature indication. FADEC schedules fuel and protects limits. A propeller converts shaft power into thrust; blade angle and RPM determine the operating point.
Worked example
A hydraulic piston of area 20 cm² is supplied at 200 bar. 200 bar = 20,000,000 Pa; 20 cm² = 0.002 m². Force = pA = 20,000,000 × 0.002 = 40,000 N. Reasoning: convert bar to pascals and cm² to m² before multiplying; fluid flow rate sets speed, not force.
Traps
Using gauge pressure as absolute; confusing N1 with N2; assuming a safe-life item is fail-safe.