Open Rocket CP calculation with tube fins

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kjkcolorado

kjkcolorado

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This question goes out to anyone who knows how OR calculates the Center of Pressure with a rocket using tube fins. I'm planning a 3" tube fin rocket for my next build and am very happy to see OR supporting tub fin designs. However, I would like for the design to include tube fins that are tapered both fore and aft as opposed to straight 90 degrees cuts on both ends of the tube fins. Think of the same side profile as a Madcow DX3 fin, but with a tube. Unless I am missing something, I don't believe this type of tube fin design is supported by OR. Here's the question. If I were to input tube fins with square ends that equal the surface area of the actual tapered tube fins, would the simulated CP/stability calculation be accurate? Essentially I would be trying to represent the 'effective tube length' in OR.
 
I would suggest buying Rocksim as it is built in.

If not, then I might suggest working on some math creating an approximation of the length and surface area of the ring fins.
 
You're right that OR doesn't support this yet. We are using the computation outlined in the old Apogee news letter where a single tube fin is approximated by 3 regular fins. You could try this directly by using the right planform flat fin and duplicate the correct number of times.

Kevin
 
kruland said:
You're right that OR doesn't support this yet. We are using the computation outlined in the old Apogee news letter where a single tube fin is approximated by 3 regular fins. You could try this directly by using the right planform flat fin and duplicate the correct number of times.

Kevin[/QUOTE

OK. First, full disclosure. I just had to look up what 'planform' meant. The definition I see is that it is the shape of a wing viewed from above. I'm not clear how to interpret that for a rocket fin. I started thinking it may equate to a side view of the rocket fin, but with 6 tube fins would that mean putting 18 'traditional' fins of my desired profile in OR? That just doesn't sound right? Can you give me a few more specifics on how I would simulate my situation?
Click to expand...
 
markkoelsch said:
I would suggest buying Rocksim as it is built in.

If not, then I might suggest working on some math creating an approximation of the length and surface area of the ring fins.
Click to expand...

I hate to spend the money on Rocksim with as good as OR is for pretty much everything else I want to do with rocketry right now. I have already calculated the length of tube with straight cut ends that has the same surface area of the tapered tube fins I desire. I guess that is the bottom line question..... will that be an adequate substitution for my situation?
 

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