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Yaw Rate Platform

Technical Information

Catalogue No: C0900
Category: Flight Control
Object Type: Sensor/Transducer
Object Name: Yaw Rate Platform
Part No: 5051-A-1
Serial No: 118/66
Manufacturer: Elliott Bros (London) Ltd
Division: Unknown
Platform(s): VC10
Year of Manufacture: 1966
Dimensions: Width (mm): 222
Height (mm): 84
Depth (mm): 160
Weight (g): 1,998
Location: Rack RAA09 [Main Store]
Inscription(s):

Elliott
Yaw Rate Platform
Type No. 5051-A-1
V.A.A.S. No. 202(ET)
Ser No. 118/66
[Mod Status] 1 & 2
────────────────
[motor]
Type 11MS201
R.P.M. 8000
Freq. 400
ø1 115V
ø2 57.5/115V
Serial No 501281...
Vactric Control Equipment Ltd.
Morden, Surrey, England
────────────────
[gearbox]
────────────────
[resolver]
Stator
3 Phase
11.8V
...
CT1
...
[Bend]ix Corporation
[Montr]ose Division
Montrose PA
────────────────
[on the box]
FAL/199/028
Delicate instrument
Handle with care

Notes:

The given dimensions are for the unit alone; when in its wooden transport box its dimensions are: 262 x 98 x 191 mm, 2930g

The Yaw Rate Platform is part of the yaw damping system providing an input to the automatic damping when the autopilot is engaged.

The label on this unit's gearbox is missing and that on its resolver is either obscured or worn.

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.

The basic requirement for an automatic landing is that the equipment must survive a single failure and continue to operate. Fundamentally, this can be achieved by triplication of all equipment. But in providing and justifying redundant equipment in civil passenger aircraft, consideration must be given not only to overall safety, reliability and performance, but also to weight, installation difficulties, overall cost, maintenance problems and many other factors. Unnecessary redundancy must therefore be avoided.

It is essential that effective autopilot disconnection should occur in the event of a failure and that the pilot should be warned of the failure and the control runs automatically freed. The disconnection and warning unit can only be electrical and must be made truly fail-safe. In practice, failure of the system to disconnect following an autopilot failure will occur only if both the autopilot and the disconnection device fail. The likelihood of this is remote as it involves a product of small probabilities in the landing phase. The acceptance of an electrically actuated disconnect device permits further simplifications of the duplicate channel, with an increase in system reliability and a saving in weight.

The operation can be checked in a different way by comparing the demand of the second autopilot with the effective demand of the first which is obtained by suitably processing the actual control output with the approximate inverse transfer function of the servo motor control loop. This concept is called a "monitored-duplicate" system and is the design used by Elliotts on the VC10. The comparison concept is used throughout the Autopilot and the Flight Director system with the various flight parameters derived in a stand-alone units. Because the duplicate sensors are used for comparison and not for actual control, they can be considerably simplified and therefore made more reliable and lighter than those used in the autopilot; and the inherent differences make them less liable to fail from a common environmental cause.

Longitudinal and Lateral Computers have equivalent Comparison computers, the Vertical Gyro has a simple comparison unit and the Air Data Computer core elements are separated for this purpose. Not all the functional boxes are compared in this way; in some cases such as the Polar Path Compass the units are duplicated and are compared electro-mechanically but there is not a Comparison unit.

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