Do submarines still has to bend inwards when turning?

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For example, when we turn in a bike, we have to bend slightly inward for the centripetal force. However, considering there’s no concept of “ground” underwater, do submarines still have to bend inwards? If yes, is it for the same reason as bikes?

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Anonymous 0 Comments

My previous answer was removed, so I will copy and paste rather than linking, it was written by a redditor when this question was asked a while ago.

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Submarines (usually) do not have any roll control, only pitch (bow/fairwater and stern planes) and yaw (rudder). Submarines do roll during maneuvers, but it is an unintended and often undesirable consequence. When a submarine turns/yaws, usually the submarine initially rolls outboard because the center of buoyancy is above the center of gravity. The same is generally true for surface ships; they roll in the opposite direction of a turn.

When a submarine yaws, the sail and hull have a non-zero angle of attack relative to the oncoming water. Thus they begin to produce lift. The sail is above the hull, thus the lift it produces rolls the submarine. Often the roll is into the turn, so the submarine transitions from a roll outboard of the turn to quickly inboard of the turn. This phenomenon is often called “snap-roll.” (Due to the complicated vortical flows over the sail and hull, sometimes the roll due to the sail and hull is in the opposite direction; it’s a complicated phenomenon, especially with hulls that are not perfectly axisymmetric.)

Snap-roll is undesirable because the submarine is leaning into the turn and the rudders are now partially acting to dive the submarine. You could imagine that if the roll was 45 degrees (an extreme case), the rudders are now 50% turning the submarine and 50% diving it. Since snap-roll usually occurs at high speed, this sudden dive is not a welcome maneuvering characteristic.

There are many ways to reduce or eliminate this problem. The first idea was to blunt the trailing edge of the sail so that it would produce less lift. This was tried on the *Nautilus*, but resulted in vortex shedding and extreme vibration. The next solution was to install a “dorsal rudder,” a flap in the trailing edge of the sail, again to reduce lift in a turn. This was tried twice on the *Albacore*, but it did not work especially well and resulted in significant forces being applied to the sail structure.

One solution that did work was to adjust the areas and positions of the control surfaces and stabilizing fins at the stern to counteract the lift produced by the sail. Other submarines have stern planes that can operate independently, allowing enough roll control to counteract snap-roll. So some submarines do have roll control, but it is only to make sure the submarine rolls as little as possible.

Anonymous 0 Comments

On the assumption that you mean “lean in” by “bend”, then a submarine doesn’t have to. They can just turn flat, like a car, by turning the rudders at the back.

Bikes have only one way to apply continuous force, their tire contact patch. You have to tilt this to get your normal force from the ground to push you around the turn. This is roughly analagous to why airplanes roll to turn (they’re using lift, not ground normal force, but they still have to tilt it). You can turn an airplane with just rudder but it’s ugly.

Submarines, on the other hand, aren’t going particularly fast and can generate *huge* control forces because water is dense. So they can just turn with their rudder and call it good. In principle, they have all the controls needed to do a rolled turn, like an airplane, but they don’t need to.

Anonymous 0 Comments

The bike is tilted toward the center of the turn in order to generate force from the ground to push the bike into actually turning.

A sub (any boat, actually) cannot do this because there’s no solid connection between it and the ground. Instead, it uses rudders and it’s own shape to skid sideways, which generates the necessary reaction force from the water, to push the boat into the turn.

A car in a drifting or sliding turn is doing a similar thing.

Anonymous 0 Comments

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Anonymous 0 Comments

You only have to bend on bikes

A) your contact area to the ground is very shallow, so even a bit of centripetal force will have your resulting g vector point outside the contact area, causing you to fall over. If you’re not **on** the ground, or have a wider contact area (like a car), the centripetal force can’t throw you of balance (as easily)

B) Bikes have a really high center of gravity, which greatly exacerbates the effects in A)

Neither of those applies to subs.

Anonymous 0 Comments

No, submarines do not bend due to extreme structural rigidity and positive internal pressure.

If you are talking about leaning into a turn so as not to fall over due to centrifugal force then the answer is also no. Submarines have no localized points of contact to the ground which would act as pivot points of lateral forces.