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I'm looking to potentially build an underwater glider, a type of submarine that's slow but can operate on extremely low power draw. However, in order for it to work effectively I've found several sources hinting that the dimensions of the components, especially the wings, are critical to its success.

However, I've found very sparse information about what these dimensions should be! I'm happy to do a bit of trial and error if it comes down to it, but to save some work does anyone have any information on what the critical dimensions should be?

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    $\begingroup$ I don't have any information beyond the trial and error (hence the comment instead of a full answer), however, I would recommend going to your local hobby store and buying two or three different kinds of foam RC airplane/glider wings on the cheap. Weigh them down and drag them through the water in your local pool to get an idea of how they glide, and you can always cut and re-form the foam with a hot knife to perfect how it glides. I'm not familiar with underwater gliders but this seems to be a quick, cheap place to start. Good luck! $\endgroup$ – Chris Nov 2 '12 at 0:53
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There is no right answer.

However, I think I can clarify what you've read so far. You need a buoyancy engine to supply the thrust, wings to direct that thrust, and some ability to change your pitch angle when you change the buoyancy. So, you'll need to balance the strength of your engine with the drag created by your wings. At the same time, your wings need to be big enough to convert vertical forces of buoyancy into horizontal motion. (Generally, the shallower depths you work with, the less power your buoyancy engine will require.)

Existing Gliders

This is a complex problem, and the existing solutions to it vary wildly.

Seaglider

The Seaglider AUV (built at the University of Washington, now owned by iRobot) is shaped to achieve laminar flow. The antenna attaches at the back, allowing the vehicle to communicate while pointing nose-down at the surface. It has no external moving parts; all control is done by shifting weight internally. Seaglider, in pieces
(source: washington.edu)

Spray

The Spray Glider (built at Scripps Institute of Oceanography, now owned by Bluefin) is a more cylindrical shape. The antenna is located in one of the wings, and the vehicle lays on its side on the surface to communicate.
Spray Glider
(source: auvac.org)

Slocum Gliders

Slocum gliders go for a cylindrical shape that's more suited to the pressure housing. They have an electric powered version, but the real magic is in their more modern "thermal glider" -- they take advantage of the fact that pressure increases with depth but temperature decreases with depth to make an engine that requires no (or very little) electrical input. Like Seaglider, the antenna is in the tail. Slocum Glider
(source: rutgers.edu)

Liberdade XRAY

The Liberdade XRAY is shaped like a flying wing and (to my knowledge) is actually the fastest autonomous underwater glider ever made. It's more for naval use than scientific use -- it tracks submarines. Liberdade XRAY

Approaching the problem (from scratch)

If you can't find a hydrodynamics expert to help (which would be the best option), I would suggest starting with your buoyancy engine and working outward.

  1. Figure out how much buoyancy your engine can create
  2. Figure out how much power your engine requires
  3. Decide how large of a battery you'll need -- this will be a significant proportion of total weight
  4. Explore your ability to trim your vehicle (likely by moving the battery fore and aft) and calculate the pitch angles you'll be able to produce
  5. Repeat steps 1-4 as necessary
  6. Make a prototype shape, make its buoyancy half of what the engine can produce (minus a little for safety). Then drag it to the bottom of a pool and see what happens.
  7. Repeat steps 1-6 as necessary
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    $\begingroup$ A few pictures of those other gliders would be cool. $\endgroup$ – Rocketmagnet Nov 9 '12 at 23:51
  • $\begingroup$ Delivered :) Anything else I could add for clarity or depth? $\endgroup$ – Ian Nov 10 '12 at 17:32
  • $\begingroup$ Great pictures. Nice gliders. +1. $\endgroup$ – Rocketmagnet Nov 10 '12 at 19:46

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