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. The tips of the helicopter rotor blades move faster through the air than the parts of the blades near the hub, so they generate more lift, which pushes the tips of the blades upwards, resulting in a slight cone shape to the rotor disc. This is balanced by centrifugal force. If rotor RPM drops too low, the rotor blades fold up with no chance of recovery.[1]: 2–16 [2][3]: 1–77 

Helicopter rotors are typically designed with washout (twist) so that lift is relatively uniform along the blades. However, because lift increases quadratically with airspeed, coning still occurs at higher RPMs.

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.[4]: 129 

The ratio of aerodynamic forces to inertial forces is called the Lock number.

  1. ^ "2. Aerodynamics of Flight". Helicopter Flying Handbook (PDF). Federal Aviation Administration. 2012. Retrieved 17 January 2022.
  2. ^ Croucher, Phil (2007). Professional Helicopter Pilot Studies. [S. l. pp. 2–17. ISBN 9780978026905.{{cite book}}: CS1 maint: location missing publisher (link)
  3. ^ "1". 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). Principles of Helicopter Aerodynamics with CD Extra. Cambridge University Press. ISBN 978-0-521-85860-1. Retrieved 7 July 2022.