Definition
A hinge used on a helicopter rotor head that allows the rotor blade to change its pitch angle (the angle at which the blade meets the oncoming air). Pitch change is controlled by the pilot through the collective and cyclic controls.
Plain English
The hinge on a helicopter rotor that lets each blade twist to change its angle, which is how the pilot controls lift and direction.
Context Anchor
Seen in helicopter rotor system descriptions, especially when learning how blade pitch is changed for lift and control.
Derivation
Alpha' is the Greek letter often used in aerodynamics to represent the angle of attack — the angle between the blade and the relative wind. The hinge is named for the angle it controls.
Why Pilots Care
It reduces stresses on the blades and hub, lowering vibration and extending component life.
Analogy
Think of a window blind slat that twists to change how much air or light it catches. The alpha hinge lets a rotor blade twist in a controlled way, though the rotor system is much stronger and more precise.
Intuition Check
Alpha Hinge does not mean the first or most important hinge. Here, alpha points to the blade’s air angle, and the hinge lets that angle be changed.
Example Sentence 1
The alpha hinge allows each rotor blade to rotate about its long axis when the pilot moves the collective.
Example Sentence 2
Proper function of the alpha hinge helps keep rotor vibrations within limits during flight.