Airframe Systems: Hydraulic, Pneumatic, Fuel, Ice/Rain and Cabin
Hydraulic and pneumatic power
Hydraulic systems transmit force through confined fluid: pressure = force/area. A 3,000 psi system with a 1.5 in² piston gives 4,500 lbf. Accumulators store energy and damp pressure pulses; relief valves protect the system; filters keep contamination out. Skydrol-type phosphate-ester fluid needs compatible seals and careful skin protection. Pneumatic systems use engine bleed or stored gas for anti-ice, pressurisation and starting; water separators and pressure regulators matter.
Fuel, ice and cabin environment
Fuel systems need venting, boost pumps, crossfeed, quantity indication and sump drains. Ice protection may be thermal (bleed air), chemical (TKS) or inflatable boots; rain removal uses wipers or hydrophobic coatings. Cabin pressurisation uses bleed air, an outflow valve and pressure controller; a cabin altitude above about 10,000 ft needs oxygen for occupants. Air-conditioning uses air-cycle machines: bleed air is cooled, water removed, then delivered.
Worked example
A hydraulic actuator must produce 4,500 lbf with 3,000 psi. Required area = 4,500/3,000 = 1.5 in². If the pump supplies 5 gpm and the actuator volume is 30 in³, ideal extend time = 30 in³ / (5 × 231 in³/min) = 0.026 min, about 1.6 s, ignoring leakage and pressure rise.
Traps
Do not mix up accumulator precharge with system pressure; do not assume a fuel gauge is a quantity check for dispatch; do not use the wrong seal with phosphate-ester fluid; and do not treat cabin differential pressure as cabin altitude.