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Actuation System for Civil Aircraft Flaps

Application

An actuation system for civil aircraft flaps. Locally situated hydraulic pump and motor are controlled by a complex electronic system module.

Key Features

The control boxes are awkward in shape to fit within the air frame envelope and require a mixture of power (110 amps at 415 volts) and signals (requiring electrical
discrimination).

Timescales

Target for the first unit was six months.

Complex cable exits

Screened with Nomex jacket

Scenario

There are four different shaped boxes on the aircraft housing similar electro-mechanical interface control systems. This meant that the hardware architecture for each box decreed different shaped pcbs for each similar function, a different assembly method and
varying types of interconnect.

The boards tended to be sandwiched inside the box. One was fitted, secured into place, followed by the next one and so on and so forth with typically eight major boards per assembly.

Space was tight, clearances were limited and following a series of customer reviews, the following novel principles were established:

1. The Header Principle: Instead of the conventional two part connector system to join PCBs, which is space greedy, Tekdata Interconnect employed a ‘header’ principle. This used a block housing protruding pins which are terminated to the cables. The headers are then flow soldered to the pcbs during assembly creating a one time interconnect which enables the pcb to be tested as a sub assembly prior to fitting. The headers were all designed as two part mouldings, followed by encapsulation to create the cable strain relief. Due to the tight packaging requirements and current capacity, over twenty individual designs were used from 3 to 40 way in various shapes and sizes. Cable entry was also important with sometimes more than one being required to direct the cable with the minimum impact on module air flow restrictions.
2. PCB Interconnect: The high specification rectangular connectors fitted to the cable assemblies do not have standard hardware to protect the delicate pins on the
   plug mouldings. Tekdata Interconnect devised a series of encapsulated moulded backshells that incorporated the following features:
   • Extended shells for pin protection. Sometimes only one side was possible, due to 90° connector pcb mounting.
   • Low Profile custom shapes included cable feed as a dog-leg to allow jackscrew access.
   • Due to the high packing density of cables within the modules, additional ty-off features were incorporated into the hood/shell to allow passing cables to be secured without the need to modify the module casing.
   • Multi-exit mouldings were also used (as per the headers) to ensure that the cable pathways were optimised.
3. Cable Paths: Nomex and Peek jacketing are used to increase the wire bundle flexibility (wire gauges included 28, 26, 24, 20, 16 and 8 awg). These jackets are braided over tinned copper braid where necessary (RFI/EMI segregation being a key issue). Velcro wrap helped to secure the cables in position.
4. Power Wiring: The 8 awg wire for the high power was restricted in its landing areas. Catalogue item tags were either unavailable or too large. Tekdata designed and produced two types of tags and modified three additional tags to ensure fit.
5. Temperature sensor: special temperature sensors were required to be developed due to space constraint.

The Actuality of the Development

This was a major undertaking involving design, prototyping on the hoof, drawing, modification, tool design, manufacture and commissioning, review, first article reporting, and of course first production units. Composite imitations of the final cases were used and
Tekdata modelled cables and cable runs using quickly available material in the first instances.

The headers were modelled solid in aluminium as a first off, whilst it was necessary to make the connector shells in plastic to ensure that the clearances were acceptable in both the mated and unmated states. 3D drawing helped in creating the space envelope for the fixed components, eg headers and connectors. However, the modelling was essential with the wiring looms to ensure, for example, that the hinging necessary for the complex assembly could be accommodated. The models enabled 2D form boards to be created, and 2D drawings established.

A matrix spreadsheet was created to enable individual component tracking to be maintained and for all parties to realise the critical areas in the development and production path.

Summary

Over one hundred different cable assemblies were created per system, some very complex, others apparently simple, involving approximately fifty mouldings and forty cable variants.

At its peak into preproduction, Tekdata Interconnect Systems involved four toolmakers and a variety of sub-contractors. Target timescales were achieved (just!)