[Piwoslaw]

One of the problems with classic pusher trailers is that they can be unstable while pushing the vehicle, especially when turning, and especially single wheeled trailers. So, would it be possible to have a trailer with an engine that uses a flexible driveshaft to drive the rear axle of the towing vehicle?

I got this idea when looking at city busses in Warsaw, some of them are articulated, with the engine in the very rear (behind the third axle) driving the middle (second) axle, with the articulation between them.

So here is what we'd have: An EV, with electric motors driving the front wheels and a diff axle in the rear, plus an aerotrailer with a small engine. For city driving with no trailer, the diff axle would freewheel. For long distance trips the trailer would be hitched up and the a flexible driveshaft would connect to the differential. The engine in the trailer would be sized to just barely push the car up a slight incline at highway speeds, with a 3 speed transmission (with clutch) geared to hit the efficiency sweetspot at 45mph/70kph (in 1st gear), 55mph/90kph (2nd), 65mph/105kph (3rd). Higher speeds and hill climbing would be helped by the electric motor. Lower speeds would be in pure electric mode. Of course, there would also be a small generator for charging.

The downside of this is the extra weight and drag of the diff axle when in EV mode, but this should be made up for by stability when towing at speed. So would this work?