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ALC-104: Helicopter - General and Flight Aerodynamics
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This course provides an in-depth look at helicopter flight and rotor aerodynamics.

As seen in Figure i-2, there are four forces acting on a helicopter in flight:Figi-1.JPG

  • Lift - The upward force created by the effect of airflow as it passes around an airfoil.
  • Weight - Opposes lift and is caused by the downward pull of gravity.
  • Thrust – The force that propels the helicopter through the air.
  • Drag – Directly opposes lift and thrust and is the retarding force created by development of lift and the movement of an object through the air.

Additionally, there are certain additional physical characteristics and effects that are unique to a helicopter and its rotor system while in flight:

  • Pendular Action – Helicopter fuselages tendency to oscillate as a pendulum longitudinally and/or laterally.
  • Coning – Main rotor blades rise to form a “cone” owing to production of lift. Coning is balanced by centrifugal force produced by spinning blades.
  • Coriolis Effect – Rotor blade tendency to accelerate and decelerate as its center of mass moves due to flapping.
  • Ground Effect – Affects rotor efficiency by reducing induced rotor flow
  • Gyroscopic Precession – Main rotor act as a gyroscope, and is has precession properties.


The main rotor provides lift as well as thrust forces, and it is the “positioning” of the force generated by the rotor that allows for vertical, forward, and lateral flight. Helicopters are capable of both hovering flight, during which thrust and lift forces are coincident, and translational flight, during which the lift force is “tilted” to the desired direction of travel to generate thrust in that direction, as seen in figure i-2.Figi-2.JPG

During forward flight, additional aerodynamic effects are felt such as

  • Transverse Flow – reduced airflow at front of rotor causes right rolling tendency.
  • Dissymmetry of lift – difference in lift between advancing and retreating blades.
  • Retreating blade stall – At sufficient forward airspeed, retreating blade will stall. This sets the limiting speed Vne.

All certified helicopters are capable of controlled descent should an engine failure occur. The transmission allows the main rotor to continue turning under the force generated by the relative wind. This wind-driven flight is referred to as autorotation.

Related Media for this Section
View the file FAA-H-8083-21 Rotorcraft Flying Handbook Glossary.pdf
Glossary of Terms used in this Course
FAA-H-8083-21 Rotorcraft Flying Handbook Glossary.pdf (59.92 KB)

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