Autorotation
[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.
[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.
[2] In all cases, a successful landing depends on the helicopter's height and velocity at the commencement of autorotation (see height-velocity diagram).
At the instant of engine failure, the main rotor blades are producing lift and thrust from their angle of attack and velocity.
Several factors affect the rate of descent in autorotation: density altitude, gross weight, rotor rotational speed, and forward airspeed.
Rate of descent is high at zero airspeed and decreases to a minimum at approximately 50 to 90 knots, depending upon the particular helicopter and the factors previously mentioned.
The specific airspeed is different for each type of helicopter, yet certain factors (density altitude, wind) affect all configurations in the same manner.
The specific airspeed for autorotations is established for each type of helicopter on the basis of average weather and wind conditions and normal loading.
[citation needed] A helicopter operated with heavy loads in high density altitude or gusty wind conditions can achieve best performance from a slightly increased airspeed in the descent.
Following this general procedure of fitting airspeed to existing conditions, the pilot can achieve approximately the same glide angle in any set of circumstances and estimate the touchdown point.
Driving region size varies with blade pitch setting, rate of descent, and rotor rotational speed.
This causes the point of equilibrium to move inboard along the blade's span, thereby increasing the size of the driven region.
The requirements for the award, as stated in Army Regulation 672-74, are, "An aircrew member must, through outstanding airmanship, minimize or prevent aircraft damage or injury to personnel during an emergency situation.
