Flight Controls, Hydraulics, and Landing Gear
Core concepts
Understand primary flight controls (ailerons, elevators, rudder) and secondary controls (flaps, slats, spoilers, trim). Know cable, push-pull rod, and torque tube systems, including tension regulators and fairleads. Hydraulic systems include reservoirs, pumps, accumulators, relief valves, check valves, selector valves, and actuators. Know the difference between open-center and closed-center systems, and how an accumulator stores energy and dampens pulses. Landing gear includes struts, torque links, shimmy dampers, brakes, and anti-skid. Understand gear retraction geometry, downlock mechanisms, and the purpose of squat switches.
Traps in questions
A common trap is confusing a check valve (one-way flow) with a relief valve (limits pressure). Another is assuming an accumulator provides continuous pressure rather than stored energy for peak demand. Questions may ask about shimmy: shimmy dampers control nosewheel oscillation, not steering. Also watch for gear warning systems: squat switches prevent gear retraction on the ground and disable certain systems in flight. Read carefully whether the question asks about extension or retraction sequence.
Worked example / rule of thumb
Rule of thumb: hydraulic force equals pressure times area (F = P × A). A 2,000 psi system acting on a 2-square-inch piston produces 4,000 pounds of force. If the load is 4,000 pounds, the piston area must be at least 2 square inches. Always check units: psi times square inches equals pounds. For accumulators, precharge is typically set below system pressure so the accumulator can supply flow during peak demand.