In the military, shutting down one or two engines to save fuel is a relatively common practice. Crews flying maritime patrol aircraft such as Lockheed's Orion or Britain's Nimrod had the ability to shut down two engines while in high-altitude cruise, allowing them to increase endurance. Such practices are also common in the military helicopter world, particularly during long-range flights. But now helicopter manufacturers and engine suppliers are hoping they can sell a similar principle to the commercial world. Helicopter engine companies say there likely will be physical limits to the metallurgy and thermodynamics as they push to achieve greater efficiency from their products. Though they have not reached those limits yet, they have meanwhile begun to look at the potential for electric power to reshape helicopter propulsion. In France, helicopter engine producer Turbomeca has been bench testing what it calls "twin-engine power management concepts," trying out the principles of hybridization and experimenting with powerful electrical generators that could wake what it calls a "sleeping engine" to deliver power during key phases of flight such as the transition to a hover after cruise.
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