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Standby Yaw Damper

Technical Information

Catalogue No: C0827
Category: Flight Control
Object Type: Signal/Data Processor
Object Name: Standby Yaw Damper
Part No: 5074-A-1
Serial No: 010/63
Manufacturer: Elliott Bros (London) Ltd
Division: Unknown
Platform(s): VC10
Year of Manufacture: 1963
Dimensions: Width (mm): 100
Height (mm): 190
Depth (mm): 454
Weight (g): 5,460
Location: Rack RAA01 [Main Store]

Standby Yaw Damper
Type No. 5074-A-1
V.A.A.S. 227(ET)
Ser. No. 010/63
[mods] 1
Ref. No 6TK6577348


In order to enhance the basic stability of the aircraft against Dutch roll, each autopilot system incorporates a yaw damper which is operative when the autopilot is engaged. In the event of failure of both dampers a third completely independent (Standby) yaw damper is available which may be engaged at any time. The Standby Yaw Damper drives the upper rudder surface under conditions where the ELRAT (Emergency Ram-Air Turbo-Alternator) is operating.

This was an Elliott design and was delivered for the very first flight of the VC10 from Weybridge as yaw damping was deemed critical. This first unit was damaged on test before flight but was rebuilt in record time by the engineers at Borehamwood.

From the early days of the company it had been hoped to enter the civil aircraft flight control field, in order to reduce dependence on military projects. The late 1950s was a time of significant change in the automatic flight control field. Elliott made a major contribution to this evolution by the design and development of actuation systems which integrated the electronic control input with the hydraulics of the main flying control power actuator.

The opportunity to take this step came in the late 1950’s with the planning of the Vickers 'VC 10' for which Elliott Brothers secured an order to provide a complete automatic flight control system. This led to considerable shared responsibility with the airframe designs of the Vickers VC 10, where the main control surfaces were split into several separate units. From the outset, the 'VC 10' system was planned to make provision for fully automatic landing of the aircraft. For certification ever to be possible an extremely high standard of reliability was essential, and even in the case of failure of the equipment it was a requirement that the aircraft must not be subjected to violent manoeuvres. After a detailed study of possible alternatives, the solution chosen was to duplicate the whole of the major system, one half to be operative while the other was to be 'standing by', with a changeover mechanism of the utmost reliability to permit instant switching from one to another. By 1960 the basic development was substantially complete and the requirements for automatic landing were being explored in detail with full 'autoland' capability available from January 1963. Successful development of the 'VC 10' system resulted in the opportunity to supply broadly similar equipment for the British Aircraft Corporation 'BAC 111', which has been produced in substantial numbers. The automatic flight control system of the Standard and Super VC10 was designed to be capable of development to full blind landing. To meet this requirement the system had to be capable of failure survival and this includes associated services such as power supplies and flying controls. The method of autopilot failure survival chosen was to provide two monitored systems which are fail soft, i.e. there is negligible aircraft disturbance after a failure. Only one autopilot is used to fly the aircraft, and the two systems, including power supplies, are completely independent. Each autopilot has a comparison monitor which detects faults and, in flight, will disconnect the system if these faults are likely to lead to dangerous conditions. For autoflare the system provides for automatic changeover to the second monitored autopilot system, in the event of fault in the first. Under these conditions the second autopilot is primed and ready to take over. If for any reason the monitoring system fails to prevent an autopilot runaway, the control movement is limited to a safe amount by the yielding of a torque-limiting spring. Many of the needed components were already present in the autopilot fit on the Standard VC10s, to achieve the autoland capacity the system on the Super received some additional items. The system, supplied by Elliott Brothers (London) Ltd, was based largely on components of the well-proved Bendix PB-20 autopilot, made under licence by Elliott, and interchangeable with American built components as installed in Boeing 707s. However, the system as a whole i.e., the dual autopilot concept was novel, and designed entirely by Elliott.           

A comprehensive description of the VC10 systems will be found at this VC10 website.

A yaw damper is a device used on many aircraft (usually jets and turboprops) to damp (reduce) the rolling and yawing oscillations known as the Dutch roll mode. It consists of yaw-rate sensors and a processor that provides a signal to an actuator connected to the rudder. The use of a yaw damper helps provide a better ride by preventing the uncomfortable yawing and rolling oscillation. On some aircraft it is mandatory for the yaw damper to be operational at all times during flight above a specified altitude.

Modern digital yaw dampers are part of an integrated digital autopilot system. They use accelerometers and rate sensors to determine the aircraft's motion. It then runs the numbers through special algorithms to determine what rudder inputs need to be made in order to damp any Dutch roll and to coordinate a turn. It then provides those rudder commands to a servo or hydraulic system which operates the rudder. The yaw damper is also known as a Stability Augmentation System.

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