Aircraft General Knowledge - Helicopter Airframe, Rotor Systems, and Engines
Airframe and rotor systems
A helicopter's airframe carries the dynamic components: the main rotor system, the tail rotor or anti-torque system, the transmission, and the engine installation. Know the difference between articulated, semi-rigid (teetering) and rigid rotor heads, and what each implies for flapping and lead-lag. Understand the swashplate: the collective changes blade pitch equally on all blades, the cyclic changes pitch cyclically to tilt the thrust vector, and the pedals control tail rotor pitch. Know that the freewheeling unit (one-way clutch) disconnects the engine from the rotor during autorotation.
Engines and systems
Most training helicopters use reciprocating piston engines; turbine engines appear on larger types. For piston engines, know the carburettor icing risk, mixture control, and the magneto check. For turbines, know that power is limited by torque and temperature (TOT/ITT), not by manifold pressure. Understand the governor: it maintains rotor RPM by adjusting engine power, and its failure requires manual throttle control. Know the electrical, fuel and hydraulic systems at a functional level.
Traps in questions
Questions confuse collective with throttle, or cyclic with pedals. Another trap is assuming the tail rotor only controls yaw: it also counteracts main rotor torque, and its failure has different consequences in hover versus forward flight. Watch for items that ask what happens when the governor fails versus when the engine fails.
Worked example
Rule of thumb: if rotor RPM decays and the engine is still producing power, suspect the governor or throttle linkage; if torque drops to zero, suspect the engine. In either case, lower collective promptly to preserve RPM.