Pilots use several controls in conjunction to move an aircraft in its three axes of flight. Between the throttle, rudder pedals, and yoke, the pilot has direct control over the aircraft's primary control surfaces. Of these control instruments, the yoke is most likely to vary in design and function between aircraft. In this blog, we will discuss how the yoke functions to control the aircraft and how it may differ among designs.
The yoke connects directly to the airplane's ailerons and elevators by either a cable, hydraulic, or fly-by-wire system. In smaller, usually propeller-driven aircraft, the yoke is connected to these control surfaces through a series of cables and rods. With this configuration, there is minimal mechanical assistance between the pilot's input and the control surfaces, making its use impossible in larger aircraft. As a result, most commercial and cargo aircraft rely upon hydraulic or fly-by-wire systems for connection. Hydraulic systems implement non-compressible fluid to efficiently and reliably provide actuation between the yoke and control systems, while fly-by-wire configurations use a flight control computer.
Ailerons are found on the trailing edge of wings and control roll by increasing lift on one wing while reducing it on the other. On the other hand, elevators are used to control the plane's angle of attack. Situated on the horizontal stabilizer, elevators modulate the amount of downward force applied to the tail. This force is inversely proportional to the angle of attack, with an increase causing the aircraft to accelerate upwards. When operating the yoke, the pilot may maneuver it in one of four directions. Homologous to the turning action in a car, the pilot may rotate the yoke left or right to control the ailerons and roll. They may also push or pull the control mechanism to adjust the plane's angle of attack.
Since the yoke is the most critical flight control element in the cockpit, it is usually situated directly in front of the pilot. While retaining the same function, yokes may vary in design between an "M," "U," or "W" shape. In larger aircraft, such as commercial jets, the yoke is mounted directly on the floor, while smaller aircraft favor an instrument panel-mounted design.
While yokes remain the primary control instrument in most civilian aircraft, many military and other fly-by-wire planes use a side-stick system. Side-sticks work the same way as a yoke but exist as a single joystick positioned on the pilot's side. Given their tremendous success in military aviation, many airline manufacturers have considered replacing the yoke control system with this variant. For example, every Airbus aircraft after 1985 has used a side-stick control system instead of a yoke.
Despite its newfound popularity, yokes still pose several safety and practical advantages over the side-stick design. Chiefly, yokes are designed to move in unison, with any inputs by one pilot being felt by the other. This design prevents the pilots from sending conflicting inputs to the flight surfaces, which could potentially result in the loss of aircraft control. Additionally, side-sticks may only be handled with one hand, limiting the pilot's capacity to control other cockpit components with the non-stick hand. Finally, yokes are much less sensitive compared to side-sticks, allowing for more precise and less choppy aircraft movement.
In high-fidelity aircraft simulators, such as those used in commercial or military training, the ordinary joystick is replaced by a simulated yoke. This sophisticated yoke is designed to provide the user with real-time tactile feedback, similar to what they would experience during an actual flight. They may also feature ancillary buttons, such as the radio microphone, autopilot control, and trim, as many real-world yokes have these features embedded.
While communication failure between the yoke and primary flight control surfaces is unlikely, there are still several maneuvers that the pilot could perform to ensure a safe emergency landing. If elevator control was lost, the pilot could immediately adjust the trim up or down to provide a slight change in pitch while also modulating thrust. Similarly, if one or both ailerons were to fail in flight, the pilot could prevent the aircraft from spiraling out of control by carefully adjusting the rudders and elevators.
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