FAA Private Pilot Helicopter (PRH)Helicopter Aerodynamics and SystemsEasy
A mechanic explains to a new helicopter owner that the main rotor system uses only a flapping (teetering) hinge, with no lead-lag hinges, and the two blades are rigidly connected to the mast so that when one blade flaps up, the other flaps down. What type of rotor system is being described?
- ARigid rotor system
- BFully articulated rotor system
- CHingeless rotor system
- DSemirigid rotor system
Show answer & explanationAnswer & explanation
Correct answer: D. Semirigid rotor system
A semirigid rotor system, typically used on two-bladed helicopters, allows the blades to flap as a unit via a single teetering hinge but has no lead-lag hinges; the blades are usually underslung to reduce Coriolis effects.
Why the other options are wrong
- A. Rigid rotor systems allow feathering but restrain flapping and lead-lag through blade flexure, not a teeter hinge.
- B. Fully articulated systems have separate flapping, feathering, and lead-lag hinges for each blade.
- C. Hingeless systems use flexible blade roots instead of mechanical hinges for flapping and lead-lag.
Semirigid Rotor System
A two-bladed rotor design in which the blades are rigidly mounted to the hub but the hub itself can teeter (flap as a unit) on a single hinge.
- Also called a teetering rotor
- No individual lead-lag hinges
- Blades are usually underslung to reduce vibration
Memory trick: See-Saw Semirigid teeters together