[gubby]

I think the key conceptual thing that's difficult to grasp is the propellor's interaction with the wind.

Forgetting the speed of the car vs the wind for a moment, the propellor is arranged so it is trying to push air into the wind (i.e. it is propelling the craft). So, whatever force the wind might impart on a simple flat disc of similar radius to the prop, the force the prop actually experiences is higher than that because it is pushing against the wind.

For me, this realisation that the prop is pushing against the wind, increasing the overall force, unlocked understanding how this craft is possible.