The ordinary subarine design has two hulls. The outermost hull is a shell designed to hold water OR air; the inner hull is the "pressure hull" that resists the pressure of the deeps. For the sub to sink, the space between the two hulls is allowed to flood with water; for the sub to rise, the space is filled with air. Usually this space is known as the "ballast tank".
Most fish have a bladder that serves as a ballast tank. I think I once read somewhere that sharks don't, and so must swim or sink. Well, it has been proposed in years past that subs be built without ballast tanks like sharks, and they would simply swim all the time, using stubby wings for lift. They would also be slimmer and thus faster, because they wouldn't have the added bulking diameter of being surrounded by the outer hull (and the pressure hull could be more massive and stronger, not needing to be lifted by the ballast tanks).
In spite of those advantages, though, They haven't been built because of safety issues; if the power fails the sub sinks, probably permanently (settles in sticky sucking muck at bottom of sea, and crew has little chance of rescue even if hull is tough enough to take the pressure).
HOWEVER! Why DO the ballast tanks have to be surrounded by steel? That outer shell is really only tough enough to stay attached to the pressure hull, and little more, because even when filled with air, pressure inside the tank always matches the water pressure. There is no stress on the outer hull from pressure, that is. Ballast tanks could just as easily be inflatable balloons, somewhat blimp-shaped for hydrodynamic reasons. And like blimps, cables would attach them to the sub so they could lift the sub. Being inflatable means they could be stowed in a small space onboard the sub, which again means the sub could have that slimmer profile, go faster using stubby wings for depth-level control, and have those stronger more massive hulls. Got more mass to lift out of the sticky muck? Just stow more-volumous blimps! When supplied with enough air, they expand to the size needed to ensure the sub can rise to the surface.
About the only real problem I can see is that if the sub dangles below the blimp or blimps, then actually reaching the surface could be problematic. The blimps won't necessarily rise into the air, after all, unless lots of helium was pressurized and stored on the sub (wasting space). I think a reasonable solution is to put two blimps UNDER the sub, but also arranging them at the sides. Then they lift from below, and the sub can broach the surface. Having the blimps also beside the sub prevents roll-over, of course, just like ordinary ballast tanks (which actually don't entirely surround an ordinary sub).-- Vernon, Jul 11 2005 Deep Flight http://www.deepflight.com/subs/dfa.htm [Shz, Jul 11 2005] Turkey Sub http://www.co.mohav...C/images/turkey.jpgNot clear if it came from Blimpies. And that looks like white meat, not wings. [DrCurry, Jul 12 2005] Spray UAV http://spray.ucsd.edu/Doesn't take people. Yet. Unless they're very small and can hold their breath for ten hours. [moomintroll, Jul 12 2005] Ah. Thought you were referring to over-stuffed sandwiches.-- DrCurry, Jul 11 2005 [Vernon], don't put the blimps under the sub - what happens if it capsizes?
Edit: isn't there some autonomous underwater drone that uses a system like this to control it's depth? some torpedo-shaped thing that crosses oceans on its own.-- moomintroll, Jul 11 2005 //more-volumous blimps// Plus for that phrase.
You'd need to get all the air out of the blimp prior to diving. A rigid container offers the ability to completely exchange air for water, thus avoiding potentially damaging deformations at depth. That said, it is an interesting idea. Even as a one-time use emergency lift.-- crater, Jul 11 2005 Big [+] . . . I wonder if vectored propulsion would work better than wings, though.-- contracts, Jul 11 2005 [DrCurry], sorry, I didn't pay close enough attention to the category where this Idea was being posted (fixed).
[moomintroll], the cross section of an ordinary sub is somewhat like: o U where the o is the pressure hull inside the U (the outer hull), and the U is wider than the o. It cannot capsize because air on either side-of-the-pressure-hull must be forced deeper into the water. I was trying to describe blimps that partially surround the sub in somewhat the same way, which then would also resist capsizing.
[crater], the pumps that push air into a blimp-shaped bag can also suck air out. This is how they CAN be completely deflated and stowed, while beginning forward wing-supported motion.
[contracts], vectored propulsion would probably be fine for some subs, but not for all. Military subs need to be as quiet as possible, so they only have one propulsion axle.
[Shz], thanks for the link. I did say that the idea for "flying" underwater had been around for years. What safety mechanism is Deep Flight using if power fails?-- Vernon, Jul 11 2005 She can float, just not very well. It has little ballast tanjks; much smaller than a normal sub's. it also has an inflatable emergency surfacing system. sorry about the typing, bnroke my hand at work today.-- Madcat, Jul 12 2005 Forgive me if I'm wrong; I was under the impression that "flying" subs were built to be naturally buoyant, and that the "wings" exerted a downwards force to hold them at depth. This would be safer than them requiring lift to stay afloat.
[edit] had a look at Shz's link; as [Madcat] says, they have slight net buoyancy while the wings exert negative lift to descend.-- david_scothern, Jul 12 2005 Madcat, you broke your hand at work? Tell us how, please, in great detail. Seriously, you deserve a croissant.
//You'd need to get all the air out of the blimp . . . avoiding potentially damaging deformations at depth. // I'm not sure what you mean there, [crater], but I can see some problems with having the bags completely empty--wicked creases and squished fabric layers. I'd put a little water in the folded blimp bag, if this sub is going very far down.-- baconbrain, Jul 12 2005 [Madcat], thanks, and take care...
[UnaBubba], you can't be serious. "light enough to fly"??? UNDERWATER?!?! A 747 doesn't seem to have much problem, in thin air! Perhaps it was my "stubby wings" phrase. I meant the wings would only be stubby when compared to aircraft wings. OK?
[david scothern], thanks for the reminder; I do think I had read about that years ago, too. Still, those naturally buoyant things CAN'T be strong enough for extreme depths, so I do have a tiny piece of originality here somewhere...perhaps in making the inflatable ballast tanks part of the normal submarine operation, instead of for emergencies only.-- Vernon, Jul 12 2005 I teach sailing to little bast... no... children at work. Anyway after class yesterday I was moving a boat on a trailer. We were hooking the trailer up to a truck and the tow hitch slipped. It, and my hand, both smashed into the ground. I didn't need any pins or anything, but I got a bunch of splints on my fingers.
The good news is the left hand is fine so I can work today! At least that's what my boss said. Off to teach the little bastards!-- Madcat, Jul 12 2005 [Vernon], their "Deep Flight I" is good for 3000 feet down. They are working on Deep Flight II with a target maximum operating depth of 37,000 feet or seven miles.-- david_scothern, Jul 12 2005 random, halfbakery