The Tupolev A-3 (as featured on yesterday's project) is an aerosledge - it has skis instead of wheels. For propulsion, it is powered by a rear-mounted, nine cylinder radial aircraft engine driving twin propellers. This is referred to as a "push motor" as it literally pushes the vehicle across the frozen tundra, as opposed to a front mounted single engine airplane, whose motor "pulls" the plane through the air.
That's amazing, agree with Graham, your cropping is always disciplined and the right selection for the viewer. Composition spot-on, Danny, shape and colour balance!
And now I know what an aerosledge is.