What are the design considerations for aircraft hydraulic systems?

Hydraulic systems power flight controls, landing gear, brakes, and other actuators. Design considerations: Pressure - Typically 3000 or 5000 psi (higher pressure = smaller actuators, weight savings); Redundancy - Minimum two independent systems for transport, three for critical functions, segregated routing; Power sources - Engine-driven pumps, electric motor pumps, RAT (Ram Air Turbine) for emergency; Fluid - MIL-PRF-5606 (mineral) or Skydrol (phosphate ester); and Architecture - Central vs. distributed, load demand systems. Sizing: Flow rate for simultaneous demands, reservoir for transients, and accumulator for peak loads. Safety: Fire resistance (Skydrol), leak detection, automatic shutoff. Analysis: System schematic, failure modes (loss of pressure, leak), and performance simulation. Certification: FAR 25.1435 hydraulic requirements. More Electric Aircraft trend: Replacing hydraulic actuators with EHAs (Electro-Hydrostatic Actuators) eliminates central hydraulic system but adds electric power demand.