Helicopter Dynamics · AERO

Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium

CASA Ref: CASR Part 61 MOS Schedule 3 AD(H) 1.3 · FAA Ref: FAA-S-ACS-15 Area I Task E (Helicopter Aerodynamics)

Scenario & Physics Summary

How automatic blade flapping and cyclic feathering compensate for differential airspeed between advancing and retreating blades in forward flight.

Interactive 3D Visual Plates & Scenario Media

Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium Plate 1

Plate 1: Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium

Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium Plate 2

Plate 2: Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium

Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium Plate 3

Plate 3: Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium

Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium Plate 4

Plate 4: Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium

Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium Plate 5

Plate 5: Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium

Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium Plate 6

Plate 6: Dissymmetry of Lift: Cyclic Feathering & No-Roll Equilibrium

Aerodynamic & Operational Physics

Advancing blade experiences V_rot + V_fwd; retreating blade experiences V_rot - V_fwd.
Increased airspeed on advancing blade creates excess lift, causing blade to flap UP.
Flapping up reduces Angle of Attack (AoA) via induced downwash. Retreating blade flaps DOWN, increasing AoA, maintaining 360° lift equilibrium across the rotor disc.

CASA & FAA Exam Gotcha Alert

CASA / FAA Exam Trap: Flapping reaches maximum up-displacement 90° later at the nose due to phase lag / gyroscopic precession, not directly over the advancing side.

Frequently Asked Questions & Exam Explanations

What compensates for dissymmetry of lift in forward flight?

Automatic blade flapping combined with cyclic feathering balances lift across advancing and retreating sides of the rotor disc.

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