Rotation of helicopter rotors by action of wind resistance rather that engine power
This article is about autorotation of rotary wing aircraft. It is not to be confused with Autorotation (fixed-wing aircraft) or Autorotation (airborne wind energy).
Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor.[1][2][3] The term autorotation dates to a period of early helicopter development between 1915 and 1920, and refers to the rotors turning without the engine.[4] It is analogous to the gliding flight of a fixed-wing aircraft. Some trees (for example maple trees) have seeds that have evolved wing-like structures that enable the seed to spin to the ground in autorotation, which helps the seeds to disseminate over a wider area.
The most common use of autorotation in helicopters is to safely land the aircraft in the event of an engine failure or tail-rotor failure. It is a common emergency procedure taught to helicopter pilots as part of their training.
In normal powered helicopter flight, air is drawn into the main rotor system from above and forced downward, but during autorotation, air moves into the rotor system from below as the helicopter descends. Autorotation is permitted mechanically because of both a freewheeling unit, which allows the main rotor to continue turning even if the engine is not running, as well as aerodynamic forces of relative wind maintaining rotor speed. It is the means by which a helicopter can land safely in the event of complete engine failure. Consequently, all single-engine helicopters must demonstrate this capability to obtain a type certificate.[5]
The longest helicopter autorotation in history was performed by Jean Boulet in 1972 when he reached a record altitude of 12,440 m (40,814 ft) in an Aérospatiale SA 315B Lama. Because of a −63 °C (−81.4 °F) temperature at that altitude, as soon as he reduced power, the engine flamed out and could not be restarted. By using autorotation he was able to land the aircraft safely.[6] Autorotation is the normal operating mode of autogyros; the distance record is 1653 km.[citation needed]
^Rotorcraft Flying Handbook(PDF). U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration. 2001. pp. 16–1. ISBN 1-56027-404-2. FAA-8083-21. Archived (PDF) from the original on 2013-04-20. a gyroplane rotor system operates in autorotation
^Bensen, Igor. "How they fly – Bensen explains all Archived 2014-06-26 at the Wayback Machine" Gyrocopters UK. Accessed: 10 April 2014. Quote: "air.. (is) deflected downward"
^Charnov, Bruce H. Cierva, Pitcairn and the Legacy of Rotary-Wing Flight Archived 2016-03-03 at the Wayback Machine Hofstra University. Accessed: 22 November 2011.
^"Autorotation", Dictionary.com Unabridged (v 1.1). Random House, Inc. 17 April 2007 Archived 17 March 2012 at the Wayback Machine
^USA Federal Aviation Regulations, §27.71 Autorotation performance Archived 2016-12-08 at the Wayback Machine
^R. Randall Padfield; R. Padfield (1992). Learning to Fly Helicopters. McGraw Hill Professional. p. 151. ISBN 978-0-07-157724-3.
Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through...
gyroplane, is a class of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. While similar to a helicopter rotor in appearance, the...
axis traverse to the wind so that Magnus-effect lift obtains during autorotation; the electricity is generated with end-hub generators. The LTA Windpower...
damage or failure when the rotor(s) are still intact and free to turn. Autorotation, in which airflow over the rotors keeps them turning and provides some...
uses an unpowered rotor, driven by aerodynamic forces in a state of autorotation to develop lift, and an engine-powered propeller, similar to that of...
basic flight conditions for a helicopter: hover, forward flight and autorotation. Some pilots consider hovering the most challenging aspect of helicopter...
referred to as "gyrodyne", between a rotaplane (with the rotor free for autorotation and an upward total axial flow through the rotor disc), on the one hand...
the R22 to enter autorotation and land in a controlled manner. Because the main rotor has very little mass and inertia, autorotation in an R22 requires...
Bristow Helicopters Flight 56C, forcing the crew to perform an emergency autorotation to a ditching in the sea. Despite the rough sea conditions, the 16 oil...
on a routine training flight. While making his second attempt at an autorotation with powered recovery, the aircraft was unable to recover power after...
pull it. Pateras-Pescara was also able to demonstrate the principle of autorotation. By January 1924, Pescara's helicopter No. 1 was tested but was found...
propel through water. Wing forms in nature Winged tree seeds that cause autorotation in descent A laughing gull, exhibiting the "gull wing" outline Bat in...
airflow. In these cases, the pilot's only recourse may be to enter an autorotation to break the rotor system free of its vortex ring state. In a tandem...
were still working and the pilots were forced to perform an emergency autorotation onto the rough seas. Emergency floatation devices on the helicopter allowed...
If there is a suitable landing spot within the aircraft's gliding or autorotation distance, an unplanned landing will often result in no injuries or significant...
result in substantial damage. With helicopters, a forced landing involves autorotation, since the helicopter glides by allowing its rotor to spin freely during...
crash was attributed to the pilot's loss of control during a power-off autorotation landing attempt; a contributing factor was failure of the throttle control...
continue rotating faster than the engine so that the helicopter can enter autorotation. A sprag clutch is used in the electric starter motors of modern motorcycle...