A closer look
Trying to strap a battery and a propeller to a drone and expecting it to cross the Atlantic Ocean is a fool's errand—it will die in two days. The RU27 'Scarlet Knight' accomplished the multi-month crossing using practically zero energy by completely abandoning standard propulsion. It 'flies' underwater using a buoyancy engine. The drone pumps a small amount of mineral oil between an internal bladder and an external one. Inflating the external bladder makes it positively buoyant, causing it to float upward. Deflating it causes it to sink. Combined with fixed wings, this simple up-and-down motion is translated into forward glide. It crossed an entire ocean by simply choosing to fall and rise over, and over, and over again.
