Manned Underwater Glider?

Discussion in 'Boat Design' started by crasch, Feb 3, 2015.

  1. crasch
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    crasch Junior Member

  2. RHough
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    RHough Retro Dude

    No

    It would be huge. Look at the thickness of airplane wings. If you want to be able to stand up inside the wing would be very large. Your living space would be limited to the areas you can stand and walk about in.

    Flying wings for air travel don't work for the same reasons.
     
  3. tom28571
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    tom28571 Senior Member

    Don't know why anyone would want to do this but these gliders don't need to be all wing. A central body with wings will work fine and most of the are built this way. A surface sailboat is much more effective way to travel.
     
  4. crasch
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    crasch Junior Member

    Thanks, y'all!
     
  5. tspeer
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    tspeer Senior Member

    There may not be any pure gliders, lacking a means of propulsion other than buoyancy, but there are powered winged underwater craft that are manned. Not exactly live-aboards, though.

    DeepFlight makes several models - Richard Branson has one.

    [​IMG]

    An underwater glider needs to be nearly neutrally buoyant, and to be able to vary its buoyancy. For example, a bellows-type swim bladder can be compressed to make the craft heavier than water so it glides down, and then expanded to make it lighter than water so it glides up. You could use the same sort of ballast tanks as in a submarine. But there's no free lunch - the energy required to change the buoyancy equals the energy expended by hydrodynamic drag as it glides.

    The DeepFlight approach, which uses a positively buoyant submarine that has propulsion and wings to drive it down, is a better way to go for a manned craft. If the power fails, it will glide to the surface.
     
  6. crasch
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    crasch Junior Member

    Thank you, Tom!
     
  7. Clarkey
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    Clarkey Junior Member

    I hesitate to type this post since I am way out-qualified here but I don't quite understand how the energy required to change the ballast state relates to the hydrodynamic drag during gliding? Surely the same amount of energy would be required simply to move vertically in the water column?
     
  8. tspeer
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    tspeer Senior Member

    You're right, it is the same. But the point of a glider is to travel horizontally as well as to move vertically.

    What changes is the distance that the glider can go for the same energy. If the glider has low drag, then it can have a flat glide angle and cover more distance.

    It may seem like a glider can get free propulsion. For example, if you compress the swim bladder to make it descend, and then expand the swim bladder to make it ascend, the glider can travel a considerable distance by the time it gets back to the surface. Now compare that to a boat that had to motor the same distance along the surface. You might think that since the swim bladder returned to it's original state at the end, no net energy had been expended, but the glider had covered distance that would have required the expenditure of fuel by the surface boat, and therefore got something for nothing.
     

  9. Clarkey
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    Clarkey Junior Member

    Thanks - not something for nothing but an elegant and fascinating concept nonetheless, much like sailplanes themselves.
     
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