As the horizon returns for a moment to the horizontal - albeit with the blue bit at the bottom and the green above - it occurs to me what two-dimensional lives we normally lead. Actually, the thought comes a few seconds later, when the glider completes the loop and the Dunstable Downs are back where they belong, 3,000ft below. But the point stands: besides climbing the stairs and an occasional sensation-free airline hop, we don't make the most of the third, vertical dimension.

An aerobatic flight in a glider (we are talking here of the aircraft-without-a-propeller variety) redresses the balance. There is an exhilarating sense of liberation to looping, wheeling and corkscrewing across the sky, the horizon flicking up and down and side to side like interference on a detuned television.