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## Homework Statement

How can I calculate the drag of different missile/torpedo shapes in water? I have five different shapes, similar cylinders with different "noses" One is a long cylinder with a flat nose, another is a cylinder of the same diameter with a hemisphere nose. Third and fourth are short and long cone-shaped noses, and the fifth is a large hemisphere (twice the diameter of the cylinder, sort of a mushroom shape). They all have identical surface area (were designed that way) and are powered by identical electric motors. But they move through water at different speeds, presumably because of their different shapes or "streamlining."

We're talking about low speeds here, these are models of approx. 14-18 inches long propelled by a small 3 volt electric motor.

Is there a formula for calculating the drag or drag coefficient of these different shapes? Is there a rule of thumb (I have heard 90 %) for the amount of drag caused by the torpedos' frontal area/cross section vs. the amount of drag caused by laminar/surface friction?

Thanks, any help is appreciated!