Definition
The aerodynamic force acting on a helicopter rotor blade during autorotation that keeps the rotor turning when engine power is no longer driving it. As air flows upward through the descending rotor disc, it strikes each blade in a way that produces a small forward-acting component of lift. This forward component overcomes blade drag and sustains rotor RPM, allowing the pilot to maintain control and flare for landing without engine power.
Plain English
When a helicopter loses engine power and starts descending, air rushing up through the rotor keeps the blades spinning on their own. The push that keeps them turning is called autorotative force.
Context Anchor
Used in helicopter training, especially when learning autorotations and how rotor speed is maintained during an engine-out descent.
Derivation
From 'auto-' (Greek, meaning 'self') and 'rotation' (Latin 'rotare', to turn). Literally 'self-turning' — the rotor turns itself, powered by airflow rather than the engine.
Why Pilots Care
Maintains rotor speed and lift during an engine-out descent, allowing a controlled landing instead of an uncontrolled crash.
Grounding Statement
Picture a helicopter gliding down with no engine: air flowing up through the rotor disc keeps the blades spinning, and that spinning is what gives the pilot lift to flare and land.
Intuition Check
Autorotative force is not engine power. It is an aerodynamic force from airflow through the rotor that helps keep the blades spinning.
Example Sentence 1
After simulating an engine failure, the instructor lowered the collective immediately to preserve autorotative force and keep rotor RPM in the green.
Example Sentence 2
Lowering the collective increased autorotative force by allowing more air to drive the blades.