|The "W" shaped control yoke of a Boeing 737.|
The pilot 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. When the yoke is pulled back the nose of the aircraft rises, when the yoke is pushed forward the nose is lowered. When the yoke is turned left the plane rolls to the left and when it is turned to the right the plane rolls to the right.
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.
|This section does not cite any references or sources. (May 2010)|
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.
Most Yokes are connected, and provide instant indication to the other pilot when one makes a control input. This is in contrast to some fly by wire control sticks that allows each pilot to send different, and sometimes greatly conflicting inputs such as was experienced on Air France Flight 447, the Airbus A330 Rio-Paris flight that crashed into the sea in 2009.
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.
- Crane, Dale: Dictionary of Aeronautical Terms, third edition, page 563. Aviation Supplies & Academics, 1997. ISBN 1-56027-287-2
- Mc Clellan, J. Mac (May 2008). "New Gulfstream, p. 52". Flying Magazine 135 (5): 52–57. Retrieved July 7, 2012. "... sidesticks don't provide visual feedback and actually don't move much at all as they respond to the pressure applied by the human pilot ... in the G650 when you grab the yoke and move it, the one on the other side will respond just as it does on a conventional airplane."
- "Is Flight 447's 'Fly-by-Wire' Aircraft Technology Safe?". Fox News. 2009-06-12. Retrieved 2013-05-29.
- Ross, Nick (2012-04-28), The Daily Telegraph (article), "It seems surprising that Airbus has conceived a system preventing one pilot from easily assessing the actions of the colleague beside him. And yet that is how their latest generations of aircraft are designed. The reason is that, for the vast majority of the time, side sticks are superb. ... Boeing has always begged to differ, persisting with conventional controls on its fly-by-wire aircraft, including the new 787 Dreamliner, introduced into service this year. Boeing's cluttering and old-fashioned levers still have to be pushed and turned like the old mechanical ones, even though they only send electronic impulses to computers. They need to be held in place for a climb or a turn to be accomplished, which some pilots think is archaic and distracting. ... Whatever the cultural differences, there is a perceived safety issue, too. The American manufacturer was concerned about side sticks' lack of visual and physical feedback. Indeed, it is hard to believe AF447 would have fallen from the sky if it had been a Boeing. Had a traditional yoke been installed on Flight AF447, Robert would surely have realised that his junior colleague had the lever pulled back and mostly kept it there. When Dubois returned to the cockpit he would have seen that Bonin was pulling up the nose. ... It is extremely unlikely that there will ever be another disaster quite like AF447. Crews have already had the lessons drummed into them and routine refresher courses on simulators have been upgraded to replicate AF447 high-level stalls. Airbus has an excellent safety record, at least as good as Boeing, and the A330 is an extremely trustworthy aircraft. Flying is easily the least dangerous way to travel, far safer than a car. But while more of us take to the air each year, a single crash is enough to damage confidence."
- Ross, Nick; Tweedie, Neil (28 April 2012). "Air France Flight 447: 'Damn it, we're going to crash'". The Telegraph. UK. Retrieved 30 April 2012.
- "Learning To Fly In A Cirrus SR22". planeandpilotmag.com
- "Gear Up: One Big Airplane Training in US Airways' newest A330 simulator". flyingmag.com
- Picture of the Canadair CL-600-2B19 Regional Jet CRJ-200ER aircraft
- Picture of the Lockheed C-130H Hercules (L-382) aircraft
- Picture of the McDonnell Douglas DC-9-32 aircraft
- Picture of the Beech 58 Baron aircraft
- How Helicopters Work
- "Fly-by-wire - A CIVIL AVIATION FIRST". Airbus / Innovation / Proven concepts / In design / Fly-by-wire. Airbus. Retrieved 6 July 2012.
- Flying the Airbus side stick - the one with the fastest thumb wins!