Possible to "stall" a sub?

[GoldenRivet]

hows bangkok treating you?

edit: while i agree with you that a lack of speed renders the dive planes useless, i still maintain that they do not "stall like an airplane" as the original post asked.

airplane wings do not stall because of a lack of speed, they stall because of an exceedence of a critical angle of attack, this can occur at 60 knots, 100 knots, 140 knots etc... speed is completely out of the equation.

the original post asked "will a submarin stall like an airplane?" the answe of course is "no"

as i said in my previous posts, though the lack of speed will render the dive planes useless, they are not "stalling" like in an airplane.

[gAiNiAc]

Originally Posted by GoldenRivet

hows bangkok treating you?

edit: while i agree with you that a lack of speed renders the dive planes useless, i still maintain that they do not "stall like an airplane" as the original post asked.

airplane wings do not stall because of a lack of speed, they stall because of an exceedence of a critical angle of attack, this can occur at 60 knots, 100 knots, 140 knots etc... speed is completely out of the equation.

the original post asked "will a submarin stall like an airplane?" the answe of course is "no"

as i said in my previous posts, though the lack of speed will render the dive planes useless, they are not "stalling" like in an airplane.

I haven't been to Bangkok since 1991...........

Anyhow, It's a submarine!

No they don't stall like aeroplanes.

I'd hate to be in one that rolls over though.......

A split-s.... to the abyss.

blub,blub,blub,blub.........

[gAiNiAc]

Originally Posted by bobchase

Those textbook answers about using diving tanks to change depth are not the way a sub really works for most of the mission. Yes, the flooding of the main tanks is done to submerge the boat. Once submerged, the boat is put into a state of almost neutral buoyancy and kept there. This is called 'trimming the boat' and it would happen as soon as the boat is submerged, long before it clears the continental shelf.

Some, perhaps most, ship handlers prefer a slightly negative buoyancy. The negative buoyancy proponents like it because the sub handles much like an airplane when it answers to changes in the helm. The downside is that if main propulsion is lost, then the sub eventually sinks down to crush depth. As it is against the regs for a Navy reactor to actually fail, unless its intentionally done as a crew training drill, skippers usually go with the better handling option.

Some ship handlers actually like a slightly positive buoyancy. The positive buoyancy folks trade off better handling against the 'if all else fails, we can always float to the surface' option.

A truly balanced buoyancy is universally avoided. It's almost impossible to maintain depth with that trim and the faster you go, the harder it becomes.

Large changes in depth are done with a combination of the planes and the speed through the water. Certainly not with flooding or blowing the tanks like is often described in literature. Those last two options cause so much acoustic noise that the enemy would hear it half an ocean away and come over to kill your noisy butt.

Boats with sail mounted planes use the sail planes for a fast rise or fast dive at speed and they also use them for small, completely level, changes in depth. This type of boat's rear planes are only used to adjust the angle of attack (or lack of angle) during a rise or dive. Once they are at the new depth or even along the way, small and very quiet changes are made to the trim tanks with pumps to account for the change in water volume in the main tanks as well as changes in water density.

The boats with bow and stern planes can also do a perfectly level change of depth too but it is much trickier to do it in them. They can, however, make a big change of depth faster.

I think that the word 'stall' is not applicable to a sub because there are no lifting surfaces. However, loss of forward momentum will cause a stall-like event to occur. But don't go looking for a flat spin like a Mig 25 gets into with a sub. You've got minutes to hours to contemplate your demise.

Bob

Yup!

[Puster Bill]

Thanks for all the replies!

After reading them, and giving it some careful thought, I think what is happening is that the increased drag from the dive planes going hard up slows the boat down to the point where the dive planes can't support her.

I should have mentioned that I'm using GWX, which of course means that the deeper you go, the more negatively bouyant you are.

I had forgotten about the Thresher, which was a true hydrodynamic "stall" situation. This isn't exactly the same. It's not like you loose lift because of flow seperation on the diving planes, it just that the extra drag of going hard arise on the planes slows you down enough that you can't go up. And I want to reiterate that this is at slow speeds, 1 to 3 knots at most. You can even see a precursor of it at higher speeds: Try tooling around at, say, 6 knots straight and level. Then order surface. You'll slow down by a knot or so as the plane operators go hard up on the planes. It doesn't matter if you are travelling fast enough, but if you are deep and slow, it could be a problem.

Oh, and in theory it would be possible to "loop" a submarine on dive planes, given enough power and a strong enough hull (because you would need an awful lot of vertical 'room' to do it). A U-boat couldn't, because of lack of power and lack of depth capability, but I would expect an ultra deep diving nuclear boat to be able to do so, especially if it was a "short" boat like a Skipjack class (which isn't to say the Skipjacks *COULD* do it, just that their hull form would be better suited for it than a longer, skinner sub like a 688 boat).

[Letum]

It would not be a true loop because the balast would prevent the U-boat going
upside down. It would flip back on to conning tower up 2/3 of the way up.

[GoldenRivet]

what if the u-boat were placed on a treadmill that was going in the opposite direction at the same speed?

[Bronzewing]

It is possible to stall a submarine. The Experimental aircraft carrying submarine M2 was lost that way. Due to the large size of the M class pumping out the ballast took almost 15 minutes. To deploy the aircraft faster, they would wait till they had it beginning to surface, then they'd prop it up with the hydroplanes artificially so they could open the aircraft hangar before they'd completely finished pumping out the ballast. On the day of the accident it is believed the stern planes failed, causing it to stall and sink stern first flooding the open hangar and sinking the boat with the loss of all hands.

[Puster Bill]

Originally Posted by GoldenRivet

what if the u-boat were placed on a treadmill that was going in the opposite direction at the same speed?

If a U-boat were travelling at the speed of light*, and it turned it's running lights on, what would happen?

*Surfaced, of course, because it would be ridiculous for one to go that fast submerged.

[Buddahaid]

This is not a stall, but high speed, high angle surfacing was/is highly risky. When the boat breaks the surface at too high of an angle, it can slide back on it tail in an uncontrolled dive. The ballast tanks are open to the sea on the bottom, the high pressure air bubble equalizes to atmosphereic pressure, and as it slides back at that high angle, sea water will fill the tanks upto what the angle will allow. This creates a now heavy boat that may reach crush depth before the crew can recover control.

Buddahaid

[PingPilot]

Okay, great conversation here, but lets look at the original question.

"Can a submarine stall?"

Not in the TRUE sense, if it is of convensional design.

What can stall, however, is the control surfaces, providing they have enough travel.

Because I've never piloted a traditional sub, I don't know, but would suspect they do.

Could you feel the shudder in the controls? Likely not, as they're probably fly by

wire. Could you feel the shudder in the sub? I doubt it, but I bet it would create

some noise for the enemy to detect you.

Tom.

[thornnnn]

Normally the submarine has a surface weight and a submerged weight. there is a superstructure on the submarine (almost everything you see above water) inside this superstructure are some ballast tanks ..some in front some in back. When submerged these tanks are flooded by opening holes in the top that let the air out. the valves are then closed for submerged operation. the submarine has stern planes and fair-water planes in the tower. the stern planes are the main depth control devices. to dive the stern planes actually go up.. or lift.. (raising the back of the submarine and pointing the HUGE plane of the submarine downward) The whole sub then acts like a wing slicing thru the water. the submarine DRIVES to a given depth.. then internal tanks are flooded or pumped out to make it neutral bouyancy. there are also tanks to make it trimmed (level). the fair-water planes are used to assist in up and down maintain depth but have no where near the effect of the stern planes. to surface the sub would simply drive to the surface.. pumping tanks or initating a normal MBT blow. Emergency blows are reserved for just that.. emergencys. Last thing you want to do is sink a surface ship cus you came up underneath it. Would a sub stall? not normally.. because normally they are neutral bouancy for any given ordered depth. In a situation where the sub was heavy due to flooding or had just drove up heavy, then yeah you could stall.. If there was no flooding.. you might drive tot he surface heavy.. and if you stalled there i cant see slipping back down much more than where you started.. because at some point your pumping of tanks would make you light. If you lost power you would still have your batteries. The only time i got scared was deep dives with a big bell. and of course any unexpected flooding or collision alarms going off. flooding .. loss of propulsion.. and backsliding to certain crush.. is not the way i want to go. THat was always a scary thought. Subs are made out of steel. like steel you can only bend them back and forth so many times till the metal fatigues and fails. This is all taken into account for the life expectancy of the sub.. and the operational constraints/limitations placed on them. I did not like going to the edges. I'd rather NOT have to trust the guys that built these things unless i really had to in a wartime situation. Frankly i lost my faith in us industry when the challenger blew up. That's when i realized we were not infallible. and a submarine is infinitely more complex than a space shuttle. The subs drive(fly) thru water much like an airplane does with the main differences. being a submarine is massive and has much more inertia than a plane. sub has a trim tank system and depth control tanks to enable a variable weight to the sub along with the Main Ballast Tanks (MBT's) everything on the sub is slower to act.. and slower to stop once it starts moving. Plane has tail flaps and wing flaps .. much as a sub has fairwater planes and stern planes. At the end of a watch i could detect the motion of the minute hand on a clock from having stared so intently at the needles for x hours. bottom line is a sub will stall like a blimp .. more than it would like an airplane. but if the blimp did not have enough buoyancy .. it would start its inevitable decline once it lost propulsion. but not like an airplane. unless of course the blimp popped.. and lost all it's buoyancy at once.

[Jimbuna]

Nice detail but this thread is over seven years old.