Definition
The angle formed between the spanwise axis of a rotating helicopter rotor blade and the plane of rotation (the tip-path plane), produced when lift bends the blades upward against the downward pull of centrifugal force. The blades settle into a shallow cone shape during flight, and the angle of that cone is the coning angle.
Plain English
When a helicopter rotor is spinning and producing lift, the blades bow upward slightly instead of staying perfectly flat. The amount they bend up — measured from flat — is called the coning angle.
Context Anchor
Seen in helicopter rotor system discussions, especially when describing blade position, rotor loading, and rotor system inspection.
Derivation
From 'cone' — the shape the rotor blades trace when they bend upward in flight, like the sides of a shallow cone rather than a flat disc.
Why Pilots Care
Correct coning angle keeps blade stresses within limits and maintains proper rotor performance and stability.
Analogy
Picture an umbrella. Closed and spinning fast with no wind, the ribs sit nearly flat. As wind pushes up against it, the ribs bow upward into a shallow cone. The angle between flat and the bowed position is the coning angle.
Intuition Check
Coning angle is not blade pitch angle. Pitch angle is how the blade is twisted to bite the air; coning angle is how much the whole blade rises upward while it spins.
Example Sentence 1
As the helicopter lifted a heavier external load, the coning angle increased noticeably.
Example Sentence 2
An increase in coning angle can signal a drop in rotor RPM or an imbalance in blade weight.