Yoke (aircraft)

Aircraft Yoke
The "W" shaped control yoke of a Boeing 737.

A yoke, alternatively known as control column, is a device used for piloting in most fixed-wing aircraft.^[1]

Principle

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.^[1]

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.^{[citation needed]}

Styles

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.^[2]

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^[3][4] 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.^[2]

Ancillary functions

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.^[5][6][7][8]

Alternative control systems

Yokes are not used on all aircraft. Helicopters use a cyclic^[9] 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.^[10]

There are also computer input devices designed to simulate a yoke, intended for flight simulators.

Image gallery

• 

  Collection of control yokes at Boeing Future of Flight Museum: 747, 707, B-29, Trimotor.

• 

  The cockpit of Concorde, which has an "M"-shaped yoke mounted on a control column.

• 

  The cockpit of an Embraer ERJ with an "M"-shaped yoke.

• 

  "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

See also

• Aircraft flight control systems

References

1. ^ ^{a b} Crane, Dale: Dictionary of Aeronautical Terms, third edition, page 563. Aviation Supplies & Academics, 1997. ISBN 1-56027-287-2
2. ^ ^{a b} New Gulfstream, Flying Magazine, Vol. 135., No. 5, May 2008, p. 52
3. ^ Learning To Fly In A Cirrus SR22
4. ^ Gear Up: One Big Airplane Training in US Airways' newest A330 simulator.
5. ^ Picture of the Canadair CL-600-2B19 Regional Jet CRJ-200ER aircraft
6. ^ Picture of the Lockheed C-130H Hercules (L-382) aircraft
7. ^ Picture of the McDonnell Douglas DC-9-32 aircraft
8. ^ Picture of the Beech 58 Baron aircraft
9. ^ How Helicopters Work
10. ^ Flying the Airbus side stick - the one with the fastest thumb wins!