FAA Private Pilot Helicopter (PRH)Helicopter Aerodynamics and SystemsMedium
A mechanic is explaining rotor hub components to a new owner. Which hinge allows a main rotor blade to rotate about its own spanwise (longitudinal) axis so that its pitch angle can be changed?
- ADelta hinge
- BLead-lag hinge
- CFeathering hinge
- DFlapping hinge
Show answer & explanationAnswer & explanation
Correct answer: C. Feathering hinge
The feathering hinge (or feathering axis in semirigid systems) permits the blade to twist about its own length so the pitch angle can be varied by collective and cyclic inputs.
Why the other options are wrong
- A. A delta hinge is an offset flapping hinge used to couple flapping with pitch, not the primary pitch-change axis.
- B. The lead-lag hinge allows fore-and-aft movement in the plane of rotation.
- D. The flapping hinge allows up-and-down blade movement, not pitch change.
Feathering Hinge
A hinge or axis on the rotor hub that allows each blade to rotate about its spanwise axis, changing its pitch angle for collective and cyclic control.
- Also called the pitch-change axis
- Works with pitch horn and pitch links driven by the swashplate
- Distinct from flapping (up/down) and lead-lag (fore/aft) hinges
- Present in fully articulated and semirigid systems
Memory trick: Feather = twist the blade like turning a feather in your fingers.