Heels not only have to be the right height but in the right position: not too far back, but under the centre of the heel so they support your weight properly, following the natural line of your body.

Finally, dangling the control pod well below the aerostat shifts the craft's centre of gravity downward. This means it does not need additional stabilisers, which add weight.

Upstanding toothbrush makes use of a weight at the end of its rounded handle to create a centre of gravity at the handle base.