The Silk_E_ Hybrid Propulsion System project offers a 21st century breakthrough in hybrid propulsion efficiency and cost, reducing turboshaft fuel consumption and CO2 emissions by 50%, reducing propulsion system cost by 70-90%, and enabling a new generation of eVTOL air taxis capable of 400mph international inter-city flight.

The urban air mobility (VTOL air taxi) market is still at feasibility stage and eVTOL solutions remain unproven. Uber Elevate is aiming for 400Wh/kg battery capacity and charging in five minutes to be able to offer a range of 100 miles, which it calculates makes Uber flying fleets feasible. Even assuming this is possible by 2025, the resultant aircraft would be limited to low speeds and two passengers. Range figures are further complicated by international aviation regulations, which dictate that aircraft must carry a 30-minute fuel reserve to reach an alternate landing strip in an emergency. Therefore, if the range of the aircraft is 100 miles at 100mph, the maximum trip length is 50 miles.

By contrast, powered by a 1200kW P&W PT6C-67C turboshaft engine, Transcend Air Corporation's Vy-400 aircraft is capable of carrying a payload of 1 tonne, cruising at 300-400mph with a range of 450 miles. But the downside of this approach is that the turboshaft turbine/ gearbox is inefficient (peak 25.7%, cruise 22.3%) and noisy and since the unladen aircraft weighs 2.2 tonnes (1 tonne more than an equivalent helicopter) and flies 3 times faster, even with a more efficient tilt wing architecture, the aircraft uses 50% more fuel than a helicopter per hour (50% less per trip).

The Silk_E_ hybrid propulsion system solves these problems because it combines 400KW from the power dense battery system with 800kW from the generator system, for 1200kW peak take-off distributed electrical power and then isolates 800kW from the generator for cruise power, with battery recharging in flight. Even accounting for losses, the R6 eco-engine/ YASA motors can provide cruise powertrain efficiency of 42.6% compared to the turboshaft/gearbox efficiency of 22.3%, thereby reducing fuel costs and CO2 by 50%.

The Silk_E_ hybrid propulsion system project is inspired by the manufacturing heritage of the North West and aims to revive the legacy of Rolls-Royce in its deprived inner-city birthplace in Manchester. The project can make a substantial contribution to the Northern Powerhouse initiative, eventually creating thousands of jobs, manufacturing hybrid electric propulsion systems fit for the 21st century in partnership with a global manufacturer.