Flight control and cable system

A classic example of a control system is the negative feedback loop that controls the thermostat in your home. This loop, shown above in the block diagram, works continuously, many times a second, much more quickly and smoothly than a human pilot could. Turnbuckles A turnbuckle assembly is a mechanical screw device consisting of two threaded terminals and a threaded barrel.

Pulley wear patterns Fairleads may be made from a nonmetallic material, such as phenolic, or a metallic material, such as soft aluminum.

The above illustration shows how the basic elements of an autopilot system are related. When properly maintained, a tensiometer is 98 percent accurate.

Cable tension is determined by measuring the amount of force needed to make an offset in the cable between two hardened steel blocks called anvils. The cables run over pulleys, which are mounted on a bearing fastened to a structural member.

However, the grid method is sometimes used on large aircraft. The drawing shows a considerable redundancy of the flight control system: the inboard and outboard ailerons, elevators and rudder are controlled by both the primary and secondary computers and operated by the three hydraulic sub-systems; the high lift devices are controlled by their specific computers and operated by the three hydraulic systems Blue and Green for the leading edge,Yellow and Green for the trailing edge ; the vertical stabiliser, having a secondary role, is controlled only by the secondary computers and operated by two hydraulic sub-systems.

The unit consists of a compression spring and a locking mechanism that allows the spring to make correction in the system only when the cable system is in neutral.

Modern flight control system

Figure So while the flight controls are trimmed, the cable is tensioned nicely and accommodates varying circumstances. The rod end, or clevis, permits attachment of the tube to flight control system parts. The hydraulic circuit powers the actuators which then move the control surfaces. The diameter of the wire determines the total diameter of the cable. Straight shank terminal dimensions Test the cable by proof-loading locally fabricated splices and newly installed swage terminal cable fittings for proper strength before installation. The flight control system must be adjusted rigged to obtain these requirements. The overall aim is towards more- or all-electric aircraft and an early example of the approach was the Avro Vulcan. For simplicity, only one control surface — the rudder — is shown, although each control surface would have a similar arrangement. These movements must be synchronized with the movement of the flight deck controls. With hydromechanical flight control systems, however, the load on the surfaces cannot be felt and there is a risk of overstressing the aircraft through excessive control surface movement. A two-axis autopilot manages elevators and ailerons. Push-pull tubes are generally made in short lengths to prevent vibration and bending under compression loads. All of the control surfaces require specific hardware, spacers, and bearings be installed to ensure the surface does not jam or become damaged during movement.

These movements must be synchronized with the movement of the flight deck controls. The adjustments to the jacks necessary to level the aircraft are indicated on the grid scale. The thimble, bushing, and shackle fittings may be used in place of some types of terminal fittings when facilities and supplies are limited and immediate replacement of the cable is necessary.

aircraft flight control system

Aircraft control cables are fabricated from carbon steel or stainless steel.

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FLIGHT CONTROL MECHANISMS