just another post – most likely moll could help with this one

lets say you had a tumbling cone shape – could i still apply the previous rule of thumb calculation to claculate its rpm based on its original forward speed/ velocity ?

wookiemeister said:

just another post – most likely moll could help with this one

lets say you had a tumbling cone shape – could i still apply the previous rule of thumb calculation to calculate its rpm based on its original forward speed/ velocity ?

OK, let’s think this through.

• Rule of thumb is based on the Strouhal vortex shedding frequency.
• Tumbling tends to be a combination of two separate vibrational modes.
• There are two more phenomena apart from vortex shedding that play a part in generating vibrations. One of the other two can safely be ignored.
• A good reference for these sorts of flows is Clift “Bubbles, Drops and Particles”. I have a photocopy somewhere, but I’m pretty sure it doesn’t extend as far as tumbling cone shapes.
• No doubt the US military did some research on this because their ICBM re-entry vehicles are cone-shaped. The chances of a finding a de-classified copy of that on the web, though, are slim.

I’ll get back to you.

wWhere would cavitation fit in here?

roughbarked said:

wWhere would cavitation fit in here?

Not at all. That’s only where your cone is travelling faster than the speed of sound underwater.
Tumbling cones travel much more slowly than spin-stabilised cones.

A quick question. Is the diameter of the cone base greater than its height? eg. in a re-entering Apollo spacecraft. If the diameter of the cone is greater than the height then it falls base-first with no significant tumbling.

My main suggestion is to try out the quick theoretical approximation above by buying a styrofoam cone from Spotlight, carve to shape if required, drop it off the top of a three storey building, and film the result. That’s how I tested my parachutes.

The diameter of the cone is much less than its length, lets say its length is about 3 times longer than its diameter.

wookiemeister said:

The diameter of the cone is much less than its length, lets say its length is about 3 times longer than its diameter.

The interior of the cone may not be uniform.