The focus of power

As Dr Neil Calder discovers, the drivers behind the supply chain for aircraft electrical power systems are changing as more subsystems become electrical.

The opportunity to realise the pure concept of an all electric aircraft is slipping with the in-service date for the next Western-built single aisle airliner, but there are other chances for the application of some of the smaller-scale technical outputs from recent development work. In terms of a radical engine, radical wing or complete aircraft system, this may be true, but the equipment under the skin of the aircraft can use the new technology so there is an incremental upgrade path.

Newly evolved turbofan engines, such as the Pratt & Whitney PW1000G, Rolls-Royce RB285 and CFM LEAPX are demanding some very individual solutions as the focus for power distribution shifts from a central controller to a more on-the-pylon set of solutions, which are inherently more customised and are more dissimilar to each other than the previous generation of twin-spool engine. Decentralised power generation means the power is both generated and used in the pod for applications like electrical actuation for thrust reversers and variable area nozzles, electrical nacelle icing protection or sensor clusters. This provides application opportunities for some of the new power system elements, not least because there has been talk about re-engineering the B737, A320 aircraft, as their intended replacements are delayed.

There is something new and high tech in each of these engine pods associated with the evolved turbofans. Even if we are still waiting for open rotors, laminar flow wings, rear mounted engines and so on, there are aspects of electrical technology, including power generation and safety critical loads that are going on current Russian, Japanese and Chinese regional aircraft, and particularly evident in the COMAC 919 application of electrical nacelle icing protection.

In materials technologies, effort is focused on high temperature, high power electronic switches, and not semiconductors that are a few microns across for data switching, but more like transistors the size of a finger nail that handle 800A. High temperature SiC and MOSFET variants of these are giving better reliability (the perennial issue with semiconductors) and mean that the weight of the equipment required to cool the transistor is less. With SiC power electronics, what was classified military technology in the 90s has undergone a couple of generations of development and is now commercially available in fields such as oil and gas drilling and automobile power train. Diamond as a thermally robust substrate material is also on the horizon although this has been about “five years away” for the last 15-20 years!

Whatever technologies are being developed at device and equipment levels, the high ground in power system integration is being contested within the supply chain. Out of nine equipment work packages for the B787 electrical power solution, only two were placed outside the direct commercial control of UTC, the engine OEM, and these for very specific reasons of unique capability: thermal mats for icing protection from Ultra Electronics in Cambridge and AC to DC power control from Thales. There was no pretence that the other remaining elements of the Hamilton Sundstrand offering were the best technical solutions.

The tenth, undeclared, work package of integration and optimisation at an overall system level remained in-house and this rather sets the scene for future supply chains in this area. Commercial, as well as technical control emanates from this point. Whoever has control of this aspect is in a position to offer other line items that aren't the best, aren't the highest performing, most reliable or most efficient, but are the most commercially expedient to the integrator.

This puts the rest of the world industry - UK, French, German and other parts of the US industry - on notice for being under threat because unless someone can offer a version of this super-bundle to Boeing and Airbus for use on aircraft in the future, then the contracts will go to those who have this overarching position rather than those who have the leading technology. As the whole aircraft system progresses to a more integrated, more electric offering then the systems integration becomes the critical factor not the specific equipment within that.

In terms of national effort this places the US in a very strong position. The Franco German capability is strengthened by activities such as the GETI project and Thales Liebherr strategic research cooperation in power optimised aircraft. The UK's inability to establish the Aviation Power Up project funding is threatening the otherwise world-class capabilities which exist. Aviation Power Up is about the UK achieving that and is why it is a single project with fifteen partners set within the National Aerospace Technology Strategy. The completed EC projects POA and MOET have had the same intention of maintaining capability in the overall architecture which is now seen as the minimum threshold for any nation to have strategic industrial interests in this area. Without that level of integration capability, organisations previously well established as tier one equipment suppliers become tier two players in a more commodity-based market without a direct line of communication into the airframer.

In the Clean Sky Joint Technology Initiative, all the significant European players are active. The electrical systems aspects of this have been spread about into all the nooks and crannies of the larger programmes, although there are some discernable larger bubbles of activity. In the rotary wing part there is a package in developing a direct drive, electrically powered tail rotor, and in replacing the gas turbine engine with a diesel engine which means completely re-engineering the way in which the electrical power is extracted, the sort of equipment used and the way in which it is used. The other bubble is in looking at the more electric aircraft rather than the all electric aircraft, somewhere between the conventional solution and the utopian vision.

As the capability of electric power systems is increasing, then the whole system takes on a more integrated nature. This provides a natural push away from a system comprised of discrete power source, distribution and load elements and towards a more inherently integrated solution. Consequently the relationship between the various supply chain players is experiencing a transformation. The ability to offer this all-up systems solution will define the high ground to a greater degree in forthcoming new aircraft programmes and significant upgrades.

https://ktn.innovateuk.org/web/aeroanddefktn
 

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