Variable-buoyancy propulsion

In engineering, variable-buoyancy propulsion is the use of a buoyancy engine to provide propulsion for a vehicle.[1] The concept was first explored in the 1960s for use with underwater gliders, but has since been applied to autonomous aircraft as well.[2]

Principle

Variable-buoyancy propulsion is based on the ability of a vehicle to change its buoyancy from negative to positive and vice versa (for aircraft, this means alternating between being heavier and lighter than air). While positively buoyant, the vehicle rises vertically or near-vertically; at the top of the climb, buoyancy is turned negative and the vehicle, normally fitted with hydrofoils or wings, glides forward while descending.

The process can be repeated for as long as the buoyancy engine can operate, and allows for highly energy-efficient albeit generally slow propulsion. The vehicle's trajectory typically presents a sawtooth-like profile.

References
  1. "UK team trials new ultra-endurance air vehicle". University of the Highlands and Islands. 23 April 2019. Retrieved 22 May 2019.
  2. Macdonald, Kenneth (23 April 2019). "New aircraft rises 'like a balloon'". BBC News. Retrieved 22 May 2019.
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