dynamically changing the pitch angle of each anti-torque blade while the blades rotate. Currently, the EDAT helicopter is flying as a technology test bed,


utilizing a seven-passenger Bell 429, configured with an EDAT tail boom encompassing four sets of shrouded anti-torque blades. Bell, reports Sinusas, isn’t disclosing plans for production of an EDAT helicopter but, rather, is testing technology that could be applied to a future production aircraft. Te OEM, he says, is currently “continuing to expand the flight envelope” and gather data at its Mirabel facility near Montreal. Te major technical challenge to making an all-electric or hybrid


propulsion system viable is the development of batteries with the required power density. In tandem with that, Sinusas says, there are range and payload issues. “Te first all-electric and hybrid-electric helicopters will probably


have to make some trade-offs of range and payload capabilities due to the weight of the existing batteries, at least for the short term,” he says. “Battery technology will have to make significant improvements in terms of being lighter weight and, therefore, comparable in weight to gasoline-powered systems.” In addition, unlike liquid fuels, which are consumed during com- bustion, thereby increasing payload capability, a battery essentially weighs the same whether empty or full. (Using the familiar E = mc2 formula, Tesla estimates the difference between the weight of a full and discharged Model S battery, for example, to be the equivalent of a grain of sand.) Fuel calculations for electric aircraft will look very different from those powered by avgas. Also required, reports Sinusas, will be built-in safety provisions that


are needed to protect a high-power electric system from lightning strikes. And since any next-generation electrically powered helicopter will likely be all digital, anti-hacking features will be needed. Other factors to consider, he adds, are vibration as well as the impact of HIRF (high-intensity radio field), a radio-frequency energy of a strength sufficient to compromise the performance of a device. “With HIRF, the energy emitters of concern tend to be large ground-


battery that drives electric motors directly powering the rotors. Tis eliminates the need for an engine powered by avgas or jet fuel, reducing both emissions and noise. In contrast, a hybrid rotorcraft can have multiple configurations,


but the key aspect of this solution is that at least some of the energy comes from a conventional fuel-powered engine. One example of a current hybrid rotorcraft project is Bell’s electrically


distributed anti-torque (EDAT) aircraft. As Eric Sinusas, program director, light aircraft, at Bell in Fort Worth, Texas, explains, this heli- copter uses a conventional fossil fuel–driven engine to power both the main rotor and the electric generators. “Te generators then provide electric energy—the same way a battery would—to power electric motors that drive the anti-torque system.” Te EDAT’s anti-torque system, says Sinusas, is unique in that it


controls thrust by changing the rpm of the fixed-pitch anti-torque blades. In comparison, a conventional helicopter controls thrust by


based systems, such as radio and TV transmitters, and radar,” he says. “Te concern with airborne systems is how that energy may affect sensitive electrical components.” But once the engineering challenges are met, says Sinusas, electri-


fication is expected to result in lower ownership costs, given that there would be fewer moving parts and lubricated components. “For an all-electric helicopter, there are fewer items to wear out. For example, gearboxes and driveshafts [would be] replaced by electric wiring.” Looking forward, Sinusas ventures that lightweight helicopters are


the most likely candidates for an electric propulsion solution, which would initially be hybrid. “Te hybrid-electric would have more range than an all-electric helicopter, at least in the near term,” he notes. “In fact, at Bell, we believe we can retrofit existing engines for application to a hybrid-electric helicopter, because there is nothing stopping them from integrating with a hybrid-electric system.” Putting aside the technology and engineering challenges, however,


2020 Q4 ROTOR 37


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