Coning is a phenomenon which affects

helicopter rotor On a helicopter, the main rotor or rotor system is the combination of several rotary wings (rotor blades) with a control system, that generates the aerodynamic lift (force), lift force that supports the weight of the helicopter, and the thrust ...

discs, where the blades describe a

cone In geometry, a cone is a three-dimensional figure that tapers smoothly from a flat base (typically a circle) to a point not contained in the base, called the '' apex'' or '' vertex''. A cone is formed by a set of line segments, half-lines ...

shape as they rotate. For a helicopter on the ground, as the blades rotate, they describe a horizontal disc due to

centrifugal force Centrifugal force is a fictitious force in Newtonian mechanics (also called an "inertial" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It appears to be directed radially away from the axi ...

. However, as the helicopter generates lift, the blades are pulled upwards into a cone shape.Central Flying School: Manual of Flying
Volume 12: Helicopters
Section 1-17. Coning results from the balancing of centrifugal and aerodynamic forces. The coning angle depends on

RPM Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or r⋅min−1) is a unit of rotational speed (or rotational frequency) for rotating machines. One revolution per minute is equivalent to hertz. Standards ISO 80000-3:2019 def ...

, gross weight and

g-force The g-force or gravitational force equivalent is a Specific force, mass-specific force (force per unit mass), expressed in Unit of measurement, units of standard gravity (symbol ''g'' or ''g''0, not to be confused with "g", the symbol for ...

. The ratio of aerodynamic forces to inertial forces is called the Lock number. Excessive coning can occur if the RPM is allowed to drop too low or the helicopter is operated at an excessive gross weight, or under turbulent conditions or if the helicopter experiences excessive g-force. An excessively coned disc will generate less lift due to reduced disc area. If rotor RPM drops too low, the centrifugal force will reduce until is no longer sufficient to balance the lift, and the rotor blades fold up with no chance of recovery. Coning is not to be confused with bending stresses within the blade. These are caused by tips of the helicopter rotor blades moving faster through the air than the parts of the blades near the hub, generating more lift. Helicopter rotor blades may be designed with washout (twist) so that lift is relatively uniform along the blades.Central Flying School: Manual of Flying
Volume 12: Helicopters
Section 1-11. However, the two phenomena are related. Some helicopters such as the

Bell UH-1 Iroquois The Bell UH-1 Iroquois (nicknamed "Huey") is a utility military helicopter designed and produced by the American aerospace company Bell Helicopter. It is the first member of the prolific Huey family, as well as the first turbine-powered hel ...

are designed with "pre-coned" blades, which are curved downwards but lay more flat in flight.

References

Helicopter aerodynamics {{aircraft-stub

See also

References