Alternatives for enhancement of transport economy in underwater gliders

An analytical flight survey was conducted of the net transport economy of the present generation of underwater gliders, referred to as legacy gliders. Net transport economy (NTE) is the total energy consumed. The analysis determined that legacy gliders operate in a scale regime equivalent to that of bats and small birds. Gliding performance of the legacy glider does not match the transport economy of its bird and bat counterparts because of the way it is flown, insufficient loading of the wing, excessive wetted surface area, and inefficiencies of the buoyancy engine. Legacy gliders are not flown in the most transport efficient manner. They are flown at steep glide angles in order to profile ocean water masses. If they were flown at the flattest glide slopes within present capability (L/D max), their transport economy would improve three fold. To do so would require the controller to trim the glider for nose high attitudes during descending glides and nose low attitudes during ascending glides. Present control systems lack sophistication and supporting flight instrumentation necessary for maintaining stable high angle of attack flight attitudes. The present glider shapes are analogous to gliding blimps, and have excessive wetted surface area for the wing loading at which the gliders are flying. Two remedial approaches were studied: increasing the wing loading by increasing the capacity of the buoyancy engine and reducing the wetted surface area. Numerous sets of computations based on higher ratios of net buoyancy volume to total vehicle volume found that it is possible to make underwater gliders perform very close to the transport economy of natural flyers when operating in the present scale regime of birds. In larger scale regimes, these computations found that underwater gliders can equal or better the transport economy of some of the most efficient man-made flyers.