(11 Dec 2016, 4:53 pm)G-CPTN wrote But aren't the eFans driven by electricity (when required) rather than a constantly-running hydraulic motor?
This would result in lower parasitic drag - allowing 'more' power to drive the bus.
While I'm not definitely sure, The E-Fans will be driven by electricity, But the Electricity to power it comes from the bus electrics, Which needs the Engine's to deliver electricity to the battery otherwise the bus will be stranded.
That energy taken from the engine compromises the overall power the engine can deliver to the running axle, Creating drag.
Another similar example of this can be a car air-conditioning.
