Open Rocket : Ring Fin Simulation

[chejay]

Has anyone found a way to "make" OR simulate a singular, axial ring fin?

[tbzep]

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EDIT: :chuckle: :chuckle: :chuckle: I didn't notice the "Open Rocket" or "simulation" part of the thread title! I blame it on Obama, Trump, and global warming! Oh, well. I'll leave the post in case somebody wants a large tube or ring "in the wild". :chuckle: :chuckle: :chuckle: :o
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The easiest way is to use a piece of BT-101. If you need one to be larger in diameter, cut the ring and insert another section. Use the tube material to brace it underneath.

This is where I made a section of large diameter tube out of BT-101, but you can easily make any size ring using the same technique.

https://i7.photobucket.com/albums/y283/tbzep/Rockets/Build%20Projects/tbzep%20projects/Saturn%201B/tailring3.jpg

[tbzep]

You can see the whole section I inserted on this long tube.

http://i7.photobucket.com/albums/y283/tbzep/Rockets/Build%20Projects/tbzep%20projects/Saturn%201B/maintube.jpg

[astronwolf]

Has anyone found a way to "make" OR simulate a singular, axial ring fin?
No. It can simulate tube fins, a la Groove Tube.

You might be able to "trick" the program into designing a rocket with a ring fin, like the Astron Sprite. But the simulation will not treat the ring fin as a fin.

[Doug Sams]

Has anyone found a way to "make" OR simulate a singular, axial ring fin?Here's what I would do. You have 3 (?) stubby fins already which hold the ring in place. Enter those into the simulation. Then add 3 more rectangular fins, interspersed between the others, each the same height as the ring fin, and equal in span to its diameter.

It's a rough approximation, but simulation already includes lots of approximations anyway :)


HTH.

Doug


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[DavidQ]

Has anyone found a way to "make" OR simulate a singular, axial ring fin?
I have two methods. One for appearance, and one for "stability".

For appearance, I use the "inner tube" as the ring, and oversize it so that it looks like an outer tube. That lets me model the shapes and appearances. But, it doesn't compute the stability, since OpenRocket ignores outer tubes for that.


For stability, I take out the inner tubes that look like ring fins, and replace them with an OpenRocket ring fin of the same size as the axial ring fin. Their fins are not axial, but are attached to the outside of the rocket. By selecting only 1 fin, OpenRocket can do a best guess at the center of pressure calculation. The center of mass should still be the same, ignoring that it would be off-axis.

I attached a simple rocket to illustrate this. One is the ring fin in an axial position, by using an inner tube. The other is the ring fin in a tangent position, using a single tube fin. There is no engine or mount or chute, because my rockets usually don't need them to fly straight and true. Magic!

[teflonrocketry1]

If you use the geometric equivalence technique for ring fin simulations I came up with about 18 years ago (I used it with RockSim but it should also work for OpenRocket) : https://www.apogeerockets.com/education/downloads/Newsletter27.pdf
You get almost the same result as with the single offset tube fin approximation; Cp = 11.76 in for my technique versus 12.167 in using the offset tube fin, see attachments.