View text source at Wikipedia

Coning (aerodynamics)

This article is about the helicopter phenomenon. For the medical condition, see Brain herniation.

Coning is a phenomenon which affects helicopter rotor discs, where the blades describe a cone shape as they rotate. For a helicopter on the ground, as the blades rotate, they describe a horizontal disc due to centrifugal force. However, as the helicopter generates lift, the blades are pulled upwards into a cone shape.[1][2][3]

Coning results from the balancing of centrifugal and aerodynamic forces.[4] The coning angle depends on RPM, gross weight and g-force.[3] 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.[3] 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.[1]: 2-16 [5]

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.[6] However, the two phenomena are related. Some helicopters such as the Bell UH-1 Iroquois are designed with "pre-coned" blades, which are curved downwards but lay more flat in flight.[7]

See also

[edit]

References

[edit]
  1. ^ a b "2. Aerodynamics of Flight". Helicopter Flying Handbook. Federal Aviation Administration. 2012. Retrieved 17 January 2022.
  2. ^ Central Flying School: Manual of Flying. Volume 12: Helicopters. Section 1-17.
  3. ^ a b c "1-77". Fundamentals of Flight FM 3-04.203 (PDF). US Department of the Army. May 2007. pp. 13, 42–43.
  4. ^ Leishman, Gordon J. (24 April 2006). "4.6.1 Coning Angle". Principles of Helicopter Aerodynamics with CD Extra. Cambridge University Press. p. 183. ISBN 978-0-521-85860-1. Retrieved 7 July 2022.
  5. ^ Croucher, Phil (2007). Professional Helicopter Pilot Studies. [S. l. p. 2-17. ISBN 9780978026905.{{cite book}}: CS1 maint: location missing publisher (link)
  6. ^ Central Flying School: Manual of Flying. Volume 12: Helicopters. Section 1-11.
  7. ^ Leishman, Gordon J. (24 April 2006). "4.2 Types of Rotors". Principles of Helicopter Aerodynamics with CD Extra. Cambridge University Press. p. 129. ISBN 978-0-521-85860-1. Retrieved 7 July 2022. the Bell-Huey series of helicopters. Here, the blades are given a precone angle so that a downward (negative) bending component resulting from the centrifugal forces produced by the blade rotation eliminates the upward (positive) bending moment at the hub resulting from the aerodynamic loads.


Stub icon

This aircraft-related article is a stub. You can help Wikipedia by expanding it.