Aircraft-Mounted Accessory Gear Box For LCA

DRDO has designed and developed an Aircraft-Mounted Accessory Gear Box (AMAGB) for Light Combat Aircraft (LCA). AMAGB is a lightweight, single input, multi-output gear box, which takes its input drive from LCA engine through a power take off shaft at a rated speed of 16,810 rpm. AMAGB has a high power-to-weight (185 kW:43 kg) ratio and a  generator and one starter unit. Together, these cater to a major part of hydraulic and electrical power requirements of the aircraft and hence forms a crucial part of its secondary power system.

Design & Development

The design of AMAGB included: (i) installation study, (ii) preliminary design, and (iii) detail design for prototype fabrication. All these were subjected to critical project reviews at each stage. Installation studies were carried out and cleared in consultation with HAL. The software used for gear train optimisation, gear size selection, stress analysis of gear teeth and its webs, shafts stress critical speed analysis, and spline stress analysis has been developed indigenously.

The gears are made of electro slag refined 3.5 per cent Ni-Cr case hardening alloy steel. The gears are case carburised and ground to DIN 5 class of accuracy. Many gears are designed integral with the shafts for minimum weight consideration. ISO standard splines, precision gear grinding and cylindrical grinding have been successfully developed adhering to appropriate quality standards requirements. The shaft ends have been suitably designed to act as inner race of the bearings eliminating the inner race.

Two modules of external gear type lube pumps have been developed and assembled at the rear side of AMAGB casing. The pumps are driven by AMAGB gear train itself and provide sufficient flow and pressure requirement (20 lpm, 10 bar at 6000 rpm) to AMAGB lubricating system. Other items of AMAGB, such as drive pads, static deaerator, gravity die cast aluminium alloy components, lubrication jets and static oil seals have been developed successfully utilising manufacturing facilities available locally.

The casing for AMAGB is made of thin walled magnesium alloy (RZ-5) with integral reservoir and built-in mini cored oil passages. Solid/surface models of the casing were made on the IBM 3020 computer using CATIA software and stress analysed using ELFINI software.

The thin walled magnesium alloy casting with in-built lubrication passages and integral reservoir for proto type production has been developed and inspected as per MIL-STD 2175 class 1 using Mini Core technology. Seven prototypes of AMAGB have been built. These assemblies were carried out in a specially designed dust free assembly cubicles. Number of special assembly/dis-assembly tools were designed, manufactured and used during assembly of prototypes.

Testing

DRDO has also established elaborate test facilities—Combined Performance Test Rig, Attitude Test Rig and the Endurance Test Rig—for qualification testing of the AMAGB. The facilities include sophisticated microprocessor-based pre-programmed automated test bed and a servomotor controlled platform for simulation of aircraft manoeuvres, like rolling and pitching. Facilities to monitor test parameters through a multi-screen, graphical user interface and online recording of vibration data are built in the testing.

The AMAGB has successfully passed its maiden flight aboard India’s Light Combat Aircraft–Technology

Demonstrator 1 (LCA–TD 1). It has also successfully completed the first block of flight test of LCA–TD 1 (12 flights) flying to maximum altitude of 8 km.

The project is in its final stage, pending completion of the elaborate 1000 hrs of endurance test.

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