autorotation


Also found in: Dictionary, Wikipedia.

autorotation

[¦ȯd·ō‚rō′tā·shən]
(mechanics)
Rotation about any axis of a body that is symmetrical and exposed to a uniform airstream and maintained only by aerodynamic moments.
Rotation of a stalled symmetrical airfoil parallel to the direction of the wind.

autorotation

autorotation
Airflow in auto rotation.
i. A condition in which a rotor of a helicopter is driven solely by the action of air ascending through its blades rather than by engine power. In helicopters, descending with the power off, air flows in the reverse direction upward through the main rotor, causing it to continue rotating at cruising RPM. To maintain the rotor RPM, the helicopter is allowed to descend by lowering the collective lever so that the relative airflow strikes the blade in a manner in which the airflow itself provides the driving force. Under these conditions, the rate of descent becomes the power equivalent, and the helicopter is said to be in a state of autorotation. The angle of descent in an autorotation is very steep. Autorotation landings are practiced to train pilots to enable them to land in case of actual engine failure. Various expressions used by pilots while carrying out autorotations are autorotative landing, touchdown autorotation, or autorotation to touchdown. All these mean that the pilot will land without applying power to the rotor. A 180° autorotation means one initiated from a downwind heading, with a turn into the wind; it commences well inside the normal traffic pattern. Low-level autorotation commences at an altitude well below the traffic pattern, usually below 100 ft AGL (above ground level), and is primarily used for tactical military training.
ii. The rotation of aircraft around its axes resulting from aerodynamic forces. An aircraft in spin autorotates (autorolls, autoyaws, and autopitches) because of aerodynamic forces.
iii. The tendency of an airfoil at high angles of attack to rotate to align with the relative airflow.
References in periodicals archive ?
The co-pilot (pilot flying) entered an autorotation while the pilot in command secured the engine control levers.
Given how annoying this can be in the iPad--some users lock out the automatic rotation--we're not sure we want an autorotation option in a GPS navigator/chart reader.
Preston coroner's court heard how they were practising autorotation manoeuvres, in which the engine's power is cut while the helicopter's blades keep rotating.
And they simply use a process called autorotation to spin through the air.
The Schweizer 269C-1 helicopter struck power cables attached to wooden poles 30ft off the ground at speed while performing an exercise known as autorotation.
From the result of the Table 5, the Null hypothesis is found to be invalid at critical value of t at 5% level of significance showing that there exists significant difference between automation and non autorotation (Structure, Task and People behaviour changes) creating more job insecurity among workers.
Aircraft rolled over while practicing full autorotation.
The X2 Technology Demonstrator is designed to establish that a helicopter can cruise comfortably at 250 knots, while retaining such desirable helicopter attributes as excellent low speed handling, efficient hovering, and safe autorotation, combined with a seamless and simple transition to high speed.
It said: "This would have led to autorotation and a steep nose-down attitude.
Consideration of autorotation in profile changing orthognatic surgery.
In 2003 Textron Systems unveiled its Selectively-Targeted Skeet concept, in which the warhead is fitted with a fabric Samara Wing, providing autorotation and a 30-degree axis inclination for area search.
Later, Flight Safety Officer training led to my investigation of a B-1 Class A mishap in which the investigators ironically became part of another Class A mishap when the UH-1 Huey that was ferrying us to the accident site made an autorotation forced landing in the Utah Test and Training Range -- fortunately I was prepared for that survival situation