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Lynx AFCS Engaging Controller (space model)

Technical Information

Catalogue No: C1001
Category: Flight Control
Object Type: Model
Object Name: Lynx AFCS Engaging Controller (space model)
Part No: 29-007-02
Serial No: None
Manufacturer: Marconi-Elliott Avionic Systems Ltd
Division: Unknown
Platform(s): Lynx
Year of Manufacture: circa 1980
Dimensions:
Width (mm):
146 
Height (mm):
134 
Depth (mm):
142 
Weight (g):
823 
Location: Main Store
Inscription(s):

Engaging Controller
29-007-02
Mod Record
────────────────
[Dymo label]
25/019

Notes:

The British Army ordered over 100 Westland Aerospatiale Lynx for a variety of roles, from tactical transport to armed escort, antitank warfare , reconnaissance and casualty evacuation. The Lynx AH.1 first entered service with the Army Air Corps (AAC) in 1979.
This is a model of the Engaging Controller which forms part of the Mk34 AFCS system which provides attitude stabilization in the pitch and roll axes. Stabilization demands are fed to limited authority series actuators which in turn drive the main powered flying controls. In the yaw axis the system operates as a yaw rate damping system to stabilise the aircraft during manual and automatic flight. The Engaging Controller provides pilot control for the engagement of the total auto-stabiliser and the disengagement of each auto-stabiliser lane in each axis, also the engagement of each autopilot mode (with the exception of the Cable and Transition modes). Facilities are also provided for pitch, roll and heading trimming. All switches are illuminated on engagement.


Marconi-Elliott Avionics of Rochester designed and produced a modular AFCS, under subcontract to Westland Helicopters, for the utility, Royal Navy and French Navy  versions of the Lynx. A modular, or building-block, system is needed because the aircraft has to operate in several roles.  The auto-stabilisation system is common to all three variants, with a range of auto-pilot facilities being added to meet specific requirements. The basic version, as fitted to the utility Lynx, has holds for airspeed, heading and barometric altitude.  In the Royal Navy aircraft these have been supplemented by a radio altitude hold, and in the French naval variant automatic transition between cruise and hover) and sonar cable hold (operating in both angle and height) are fitted. The heart of the Marconi-Elliott AFCS is the autostabiliser system, which provides attitude stabilisation in pitch and roll. Demands are fed to actuators which in turn drive the main powered flying controls.  In the yaw axis the equipment operates as a rate-damping system to stabilise the helicopter during both manual and automatic flight. All autostabilisation channels are fully duplicated, with monitoring circuits to indicate any discrepancy between the two lanes.  The auto-stabiliser is active throughout the flight envelope, including operation under autopilot control. A unique feature is a simple control loop to provide additional pitch stability by sensing normal acceleration and applying a collective pitch demand to counter the pitch rate divergence and instability induced at high forward speeds with an aft centre of gravity. This system—collective acceleration control (CAC)—has also reduced pitch stick activity, and hence workload, particularly in turbu-lence and during manoeuvring.  The autopilot modes of barometric altitude, radio altitude, radio altitude acquire, heading hold and airspeed hold operate individually or together. For example, barometric altitude, heading and airspeed hold can be used at the same time. Transition and sonar hover require simultaneous control in pitch, roll and collective axes, and the heading-hold mode would normally also be engaged. All autopilot control signals are fed to limited-authority series-mounted actuators and also to full-authority paralleled actuators, which operate to prevent the series units from becoming saturated with control demands during manoeuvres under autopilot control.  All autopilot channels are duplicated in the collective axis, but are simplexed in pitch, roll and yaw.

The AFCS consists of the computer AFCS, computer acceleration control, pilot’s controller, test controller, sonar transition controller, parallel actuators, yaw-rate gyros and stick-position transmitters. Overall system weight varies between 30lb and 50lb, depending on the variant. Mean time between failure (MTBF) is quoted in excess of l.000hr and built-in test equipment facilitates first- and second-line fault diagnosis.

Design work on the Marconi-Elliott AFCS began in late 1969 and the first equipment, comprising the computer acceleration control, was aboard the prototype Lynx on its maiden flight.  Basic development work had been completed by March 1972, when transition-mode equipment was ready for flight-testing.  

The British Army ordered over 100 Westland Aerospatiale Lynx for a variety of roles, from tactical transport to armed escort, antitank warfare , reconnaissance and casualty evacuation. The Lynx AH.1 first entered service with the Army Air Corps (AAC) in 1979. The Mk34 AFCS is fitted to the Army variant.

Four Rotary Actuators form part of the Mk34 AFCS system which provides attitude stabilization in the pitch and roll axes. Stabilization demands are fed to limited authority series actuators which in turn drive the main powered flying controls. In the yaw axis the system operates as a yaw rate damping system to stabilise the aircraft during manual and automatic flight. The Rotary Actuators provide a rotary output of nominally ±60deg for autopilot functions. They are controlled directly from the pilot’s stick switch in pitch and roll for trim adjustments in those axes.

See FLIGHT International, 8 November 1973

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