1. SCOPE

This document describes the necessity, functional & Physical parameters, need for an extractor of avionics LRUs for airborne applications. This extractor needs to be integrated with the avionics LRUs and is going to be integrated in a fighter aircraft and which is intended to withstand all stringent environmental conditions. This is specially designed to engage and disengage an Avionics LRU from an Arinc standard mounting tray without damaging the Shell connector pins.

2. NEED

A Typical Avionic equipments (Standard ATR size) integrated on various Aircrafts/Helicopters using mounting trays. The mounting trays are permanently fixed to the Aircraft/Helicopter frame and the Avionic equipments are integrated or removed as and when required by a special locking system which is an integral part of the mounting tray. The mounitng tray acts as an interface between the Avionics equipment and the Aircraft/Helicopter. These mounting trays are subjected to high vibration levels (8g) and shock loads which are experienced at different stages of the mission of aircraft.

In modern days, Avionics equipments needs to be integrated with the aircraft functionally with different types of signals based on the functionality of the LRU. Traditionally aircraft signals will be fed through the bulk head connectors on the front panel of LRU. When more number of signals are to be connected to the LRU, a normal bulk head connector will not be able to provide the signals in the stipulated space available for the unit. In these cases Arinc connectors with varying shell sizes will be used to connect the aircraft with LRU.

A typical shell connector consits of pins in different shells ranging from 300 to 500 numbers. In general, mounting tray consists of one shell connector to which all the signals from the aircraft are connected. The connector on the mounting tray needs to be connected with the connector in the LRU for electrical integration. Once the LRU connector aligns with the mounting tray connector a specific amount of force is required for full mating. In the same way since the connector contains more number of pins a specific amount of force is required to disengage the connector or LRU from the mounting tray.

Hence a special purpose extractor need to be designed for proper engagement and disengagement of LRU shell connector from the mounting tray on the Aircraft. It is designed and fabricated using the state of the art technologies with high ridigity. It suits to the Arinc 404 military specifications as per MIL 810 environmental standards and as well as airborne application requirements. This special design will serve most rigorous environmental hazards for all mission operations of the aircraft.

The Extractor assembly is designed as an assembly of 7 parts. Strength and rigidity of the mounting tray are improved by providing Stainless steel brackets on front and rear side. Aluminum brackets are riveted to the tray to provide additional strengthening and for mounting holes. A specially designed structure is attached at the rear end of the tray for firm fixing of the triple Shell connector. The challenges for the design:

a) Compact Size
b) Firm fixing of extractor to the tray
c) Strengthening of extractor to withstand stringent environmental conditions
d) Functional characterestics

3. FUNCTIONAL PARAMETERS

The LRU is intended to monitor the functionality of some of the critical systems in the aircraft. The size of the equipment is of standard Vz ATR size (318x193.5x124.0mm) and weighs 8Kg. So 8Kg of load which is having a triple shell connector on the rear side is to be extracted from the mounting tray without damaging the connector pins. Further to the unit weight, 61.2Kgf of force is required to disengage or engage the triple shell connector from the Arinc Mounting tray connector, 0.2Kgf is required to disengage on each pin of the connector for 318 pins. Further the equipment along with the extractor has to undergo various stringent environmental tests as per MIL810 standard. One of the most critical is Arrestor landing shock test, where the equipment's structural ridigity is to be tested for 30g, 15ms half sine shock pulse. The extractor assembly and its parts are shown below.

4. BILL OF MATERIAL:

5. BRIEF DESCRIPTION OF THE PARTS:

Extractor block: This component forms the main component in the total asembly by holding Extractor, Bearing and Threaded nut. Guiding pins guide the total assembly movement enabling the Extractor block along. Block is free component in final assembly, the provided slot at the top of block engages with the rigid designed portion of LRU. Also the criticality of travelling distance of extractor is maintained by fixing the space in the block.

Support Block : Support block holds total Extractor assembly with mounting tray. Guide pins are precisely located for disengagement and engagement of the extractor.

Extractor: Major driving component for the translation motion of assembly and in turn provides the smooth engagement/disengagement of connector with LRU. For easy operation, extractor is provided with knurled hexagonal head.

Guiding Pin : These act as rails for the lengthy extractor and enables foolproof functionality and whereby LRU translation is achieved accurately.

Protective bush : It is being a non metal made of Nylon acts as an isolator between two metals (i.e., Statinless steel and aluminium ) and avoids the wear and tear of the metals during operation.

Thrust Ball bearing : For holding of the extractor and as well as free rotation is provided by incorporating this bearing in the assembly.

Threaded Nut: Translatory movement of extractor in a controlled manner in either directions is provided by this component.

Principle of Operation:

Hexagonal head of extractor constitutes the prime force mover of total assembly. The total force required to disengage the coupled pins with LRU as per data sheets is 61.2Kgf. Required translational force is obtained from the extractor by applying very low rotational force on the hexagonal portion of extractor. This movement of mechanism forms the main principle of operation of engaging and disengaging LRU with shell connector pins. As explained earlier, the extractor being a free body which is independently operating results in uncontrollable movement damaging connector pins. To obtain a controlled and precise movement and to enable the smooth engagement and disengagement of the pins additional provision like bearing/threaded nut & guide pins are provided. Guide pins make the movement of the extractor assembly in a defined direction and with out any offsets. Initial movement of extractor doesn't impart any movement to LRU, this is utilised for guide pin alignment and then the actual engagement and disengagement of pins starts safeguarding the connector pins. The idle travel of the extractor assembly to the actual movement of LRU occurs at the junction where extractor block touches the LRU body. A second level guiding is provided by introducing a rigid block in LRU and a cut through in the extractor body.

7. AIRBORNE CERTIFICATION:

As a part of qualification programme, components for airborne applications needs to undergo various environmental tests as per MIL-810. Various environmental tests, Dynamic loading tests and highly accelerated tests were conducted on the Avionics equipment including the Extractor assembly. After successful completion of the below mentioned tests, CEMILAC has certified the equipment fit for Airborne applications.

Annexure-ll CLAIM:

I claim that

(1) The Extractor assembly serves the purpose of safe engagement and disengagement of triple shell connector in the LRU from the shell connector in the Mounting tray.

(2) A total load of 61.2Kgf is smoothly imparted by simple rotation of extractor.

(3) Controlled, guided and efforless assembly and disassembly of LRU in the Aircraft.

(4) The design is of no wear and tear of pins in the connector as well as there is no damage due to the physical movement of assembly, by which the number of engagements and disengagements with the connector using extractor assembly is innumerable.

(5) The material & physical dimensions is shown in the table 1.

(6) Fig.3 displays the mechanism for the movement of extractor for a desired result ie. engagement and disengagement of connector.

(7) The extractor assembly serves the purpose for more than 20 years.

(8) The Extractor assembly withstands all the environmental tests as per MIL810 standard.