Hybrid power will make helicopters safer and more productive

SCORES OF ELECTRICALLY powered vertical take-off and landing (eVTOL) aircraft are under development, heralding a future where air-taxis whisk people from one place to another. Provided their batteries are charged up using renewable power, these new flying machines will also travel in a green, planet-saving way. They therefore appear to be the nemeses of noisy, fossil-fuel guzzling helicopters. But not quite yet. As with all forms of electrically propelled flight, weight—and therefore range—are issues. In the interim, however, a touch of electrification looks likely to make conventional choppers not only safer but also more useful.

The idea is to turn them into hybrids so that, like hybrid cars, they are powered by a combination of an electric motor and a combustion engine (a jet turbine, in the case of most commercial helicopters). This will make them a bit greener, by improving fuel economy and thus reducing emissions, as happens in a hybrid car. But helicopter hybridisation brings other benefits too, especially when it comes to safety.

To test this out, Airbus Helicopters, part of the eponymous European aerospace group, has fitted a helicopter that it uses as a flying laboratory with an electrically powered engine-backup system. This consists of a battery and an electric motor connected to the helicopter’s main gearbox. In a recent series of test flights in partnership with the French Civil Aviation Authority, it was found that during simulated engine failures this set-up could provide the pilot with 30 seconds of electric-only power.

That might not seem much to shout about, but it is enough to give the pilot of a single-engine helicopter a much better chance of coping with an engine failure, by executing a tricky emergency-landing procedure known as autorotate. This involves maintaining a steady rate of descent, so that the air passing up through the rotors is sufficient to keep them spinning in a way that provides enough lift for the helicopter to “glide” to a safe landing—much as a sycamore seed gently windmills down to the ground. After further development work, Airbus plans to add the hybrid backup system to new helicopters.

The problem with adding bits of kit to an aircraft, however, is that it can reduce flying efficiency by increasing weight, thus requiring more fuel to be burned. But in this case the hybrid system can also be employed to boost a helicopter’s performance, and to do so by an amount that will more than overcome the weight penalty, says Tomasz Krysinkski, Airbus Helicopter’s head of research and innovation.

The performance gain comes about in two ways. First, the electric motor can, in normal flight, provide the rotor with additional torque when a bit of extra power is required. Torque is a twisting force which electric motors are particularly good at delivering, and they deliver it much more rapidly than combustion engines can manage. It is this occasional boost from the electric system that helps reduce emissions. Once it delivered, the battery would then be topped up again in flight, using power from the engine.

The torque boost also enables the second important benefit. This comes about because performance and safety affect an aircraft’s certified maximum take-off weight. By improving both, the hybrid backup system will allow a helicopter to carry heavier loads. The increase should amount to an additional passenger, says Mr Krysinkski, which would greatly increase a helicopter’s earnings potential.

To improve the system yet further, Airbus is working on extending the electric-only flight time to several minutes. This would still be a long way from what eVTOLs can manage, at least with existing battery technology. Helicopters can, though, fly much longer missions than eVTOLs, and are more versatile. They can carry heavier loads and are often required to operate in extreme weather conditions—as when undertaking air-sea rescues—and in hazardous circumstances such as firefighting. Hybrid technology can help with all that, too, and so should keep choppers airborne for a few more years to come. ■