autorotation

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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 ?
After a couple of quick stop maneuvers, the instructor offered to demonstrate the first autorotation (auto) during high and hot conditions.
We recovered low on our first autorotation, and I didn't say anything.
The helicopter was at the 180-degree position and was cleared for an autorotation to touchdown.
After reporting the initial western entry point to the field, we did the landing checklist and got permission for a night autorotation.
At 25 feet, I thought about completing a full autorotation (to the deck) at night, or trying a "low Nr recovery" maneuver.
During my copilot's autorotations, I was uncomfortable because of the late, nose-high attitude he used to arrest groundspeed on each one.
I was having an internal conflict whether my comfort zone or his autorotations needed to be adjusted.
My squadron defensive-posturing instruction, which provides aircraft commanders guidance on conducting high-risk maneuvers, states, "High-density altitude and/or high gross-weight autorotations above 18,500 pounds gross weight should be avoided.
The bottom line is I made a series of poor choices and overestimated my ability to recognize, react, and recover from a poor autorotation flown by my copilot.
Later in the flight we were planning to perform practice autorotations and single-engine HODGE maneuvers, where the extra weight may have proven disastrous.
The Bell 505 s flight test vehicle one completed its first flight in November of last year, and the program has quickly progressed, performing additional flight tests and numerous practice autorotations.
These features, combined with the aircraft s high inertia rotor which delivers superior autorotation capability, and a newly designed cabin seating five passengers place safety, performance and affordability at the forefront.