- Yoke (aircraft)
Aircraft Yoke The "W" shaped control yoke of a Boeing 737.
The aviator uses the yoke to control the attitude of the plane, usually in both pitch and roll. Rotating the control wheel controls the ailerons and the roll axis. Fore and aft movement of the control column controls the elevator and the pitch axis.
Small to medium-size aircraft, usually limited to propeller driven, feature a mechanical system whereby the yoke is connected directly to the control surfaces with cables and rods. Human muscle power alone is not enough for larger and more powerful aircraft, so hydraulic systems are used, in which yoke movements control hydraulic valves and actuators. In more modern aircraft, inputs may first be sent to a fly-by-wire system, which then sends a corresponding signal to actuators attached to the control surfaces. Yokes may feature a stick shaker, which is designed to help indicate the onset of stall, or even a stick pusher, which assists in stall recovery.
Yokes come in a variety of shapes and sizes, the most common being of a "U" or "W" design. Some aircraft use an "M" style, such as Embraer and Concorde. There are some rarer exotic or archaic styles, such as circular designs much like a steering wheel.
In larger aircraft they are usually mounted on a post protruding vertically from the floor, referred to as a control column. In most other planes, they are mounted on a horizontal tube that comes out of the instrument panel.
Advantages and disadvantages
Side-sticks and centre-sticks are better for making rapid control inputs and dealing with high g-forces, hence their use in military, sport, and aerobatic aircraft. However, yokes are less sensitive (i.e., more precise) thanks to a larger range of motion and provide more visual feedback to the pilot.
Yokes take up more room than sidesticks in the cockpit, and may even obscure some instruments; by comparison, side-sticks have minimal cockpit intrusion, allowing for the inclusion of retractable tray-tables and making it easier to enter/leave small cockpits.
A yoke, unlike a side-stick, may be used comfortably with either hand. This can be useful if one needs to write or manipulate other controls in the cockpit. This advantage is shared with the centre-stick.
The yoke often incorporates other key functions such as housing thumb or finger buttons to enable the radio microphone, disengage the autopilot, and trim the aircraft. In addition, there may be a clipboard, checklist, or chronometer located in the yoke's centre.
Alternative control systems
Yokes are not used on all aircraft. Helicopters use a cyclic and the majority of military fighter aircraft use a centre or side-stick. Some light aircraft use a stick because some sport pilots prefer that control system. The latest Airbus family of passenger jets use a side-stick, not unlike a computer game controller, to actuate control surfaces.
The cockpit of Concorde, which has an "M"-shaped yoke mounted on a control column.
"W"/"U" style yoke in a Cessna 152 light aircraft, mounted on a horizontal tube protruding from the instrumental panel.
Circular, steering-wheel type yoke in a 1940s Lisunov Li-2
- ^ a b Crane, Dale: Dictionary of Aeronautical Terms, third edition, page 563. Aviation Supplies & Academics, 1997. ISBN 1-56027-287-2
- ^ a b New Gulfstream, Flying Magazine, Vol. 135., No. 5, May 2008, p. 52
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