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Thermal Modeling and Analysis of an Aircraft Electronics Navigation Unit

White Paper This paper describes the thermal modeling and analysis of a Transformer/ Rectifier Unit (TRU) unit attached to civil aircraft for high altitude navigation.

Engineering Edge

Model Based System Engineering at the Aeronautical Development Agency

By V Krishna Prasad, Deputy Project Director, General Systems

Figure 1 Squadron of Light Combat Aircraft LCA) Tejas Series

The design of modern aircraft remains an extremely challenging undertaking. A combination of stringent and often conflicting requirements, expensive equipment with long lead times and highly co-dependent and integrated systems present engineers with problems of almost unimaginable complexity. Consider, for example, how a change to the design of the fuel system has implications for the flight dynamics of the aircraft; its structure; hydraulic systems and potentially even cooling and avionics.

These constraints are felt all the more keenly for those designing modern combat aircraft. Not only are the packaging requirements more stringent, both the range of operating conditions and the rate at which they are covered during operations is much more extreme.

The Aeronautical Development Agency (ADA) of India was established in 1984 to wrestle with such challenges during development of the Light Combat Aircraft (LCA), an extremely ambitious project aimed at producing an indigenously designed and built aircraft.

The task before the fuel systems group was a daunting one: while the most obvious requirement is to ensure reliable fuel feed to the engine, this must be met while ensuring that the stability of the aircraft isn’t compromised as tanks begin to empty. Meaning that the fuel tank pressurization and venting lines must be adequately sized and routed and the dynamic response of the system is well understood across a range of challenging mission profiles.

In order to meet these challenges, Mentor's Flowmaster® 1D CFD software was brought in by ADA as a complementary tool to existing theoretical and physical test procedures. Flowmaster allowed the group to achieve more accurate predictions of system performance at all stages of the design loop. This increase in accuracy translates to less uncertainty and consequently the ability to finalize on an appropriate configuration sooner. As a consequence, the overall design cycle can be significantly shortened.

Figure 2 Tejas cockpit

However, while significant, the benefits of using system simulation extended further than allowing the group to accomplish the same tasks to a higher degree of fidelity. A key benefit offered by Flowmaster was the ability to interrogate the virtual system in regions not easily accessible by instrumentation in physical prototypes. This ability streamlines the trouble-shooting of the snags that inevitably arise during the design of such complex systems. This in turn further reduces the physical test burden.

Figure 3 Drop Tank characterization in Flowmaster

These high level benefits are the result of incremental improvements at each stage of the design process. For example, an accurate characterization of the drop tank circuit enables you to arrive at the pressure range of the Pressure Transducer intended to be used for monitoring the health of the drop tank fuel transfer system. This allows component specification to begin, not only for the Pressure Transducer itself, but a range of up and downstream system components.

Perhaps not as obvious, but equally significant, is the fact that the impact of any mid-design changes can be readily assessed and accounted for. Where any work must be revisited, options can be explored and assessed quickly and with confidence.

Fourteen squadrons of the LCA, now in production as the ‘Tejas’ (‘radiance’), will ultimately enter service with the Indian Air Force (IAF), while a further 40-50 aircraft will enter service with the Navy as part of their carrier based air arm. Such a commitment underlines the capabilities of the Tejas and indicates that the design will continue to evolve as operational demands change.

Flowmaster will continue to play a role throughout this evolution at ADA.

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