Helicopter Dynamics

Dissymmetry of Lift & Retreating Blade Stall

FAA Ref: FAA-S-ACS-16 Area I Task F (Performance and Limitations)

Scenario & Physics Summary

Differential relative wind between advancing and retreating rotor blades in forward flight, creating left-roll tendency at high airspeed.

Interactive 3D Visual Plates & Scenario Media

Dissymmetry of Lift & Retreating Blade Stall Plate 1

Plate 1: Dissymmetry of Lift & Retreating Blade Stall

Dissymmetry of Lift & Retreating Blade Stall Plate 2

Plate 2: Dissymmetry of Lift & Retreating Blade Stall

Dissymmetry of Lift & Retreating Blade Stall Plate 3

Plate 3: Dissymmetry of Lift & Retreating Blade Stall

Dissymmetry of Lift & Retreating Blade Stall Plate 4

Plate 4: Dissymmetry of Lift & Retreating Blade Stall

Dissymmetry of Lift & Retreating Blade Stall Plate 5

Plate 5: Dissymmetry of Lift & Retreating Blade Stall

Aerodynamic & Operational Physics

Advancing blade relative airspeed: V_adv = V_tip + V_forward.
Retreating blade relative airspeed: V_ret = V_tip - V_forward.
At V_NE (Never Exceed Speed), the retreating blade reaches maximum critical AoA to compensate for low airspeed and stalls, causing nose pitch-up and roll toward the retreating blade side.

FAA Exam Gotcha Alert

Exam Trap: Retreating blade stall recovery requires lowering collective FIRST, then aft cyclic to reduce airspeed. Pulling back cyclic first worsens the stall.

Frequently Asked Questions & Exam Explanations

What are the symptoms of retreating blade stall?

Vibration, nose pitch-up, and an uncommanded roll toward the retreating blade side.

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