@rosborne979,
Yes Ros,
I wonder if going through the math would help people... or if people have too much difficulty accepting math that contradicts their intuitions (a common problem with teaching Physics).
I was thinking about setting up equations showing that the work done by the Propeller against a tailwind equals the work done on the wheels by the ground-- and then showing how this value can easily be greater then any frictional forces even when the car is going faster then the tail wind.
I am not sure if this would be worth the effort.
The tacking example is another perfectly good way of looking at it (as always with Physics, you can look at a problem in different ways and still get the same answer). Personally, I find the tacking example is a little more difficult to describe.