Ring fins in Rocksim?

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Well-Known Member
May 10, 2009
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So, the ring vs. tube discussion on Andrew's tube fin thread is very interesting to me because I'm in the process of designing a ring fin 2-stage in Rocksim. I can't figure out how to add a ring fin that goes around the outside of my three standard fins. That is, the inner diameter of the ring fin is equal to the diameter of my three fins mounted to the BT. What I've done is added a "pod" to one of my fins so at least it looks good from the side. Problem is, it doesn't sim worth a crap. :D

Does anyone know how to add a ring fin in Rocksim?
I'm pretty sure that you can add a ring fin (called a ringtail fin in RockSim lingo) by selecting it as an option when you click the "Fins..." button in the "Add new components" button menu on the upper right side of the design screen. There are a number of RockSim designs featuring ring fins posted on EMRR. Take a look at how it is done in more recent files, such as those for the Estes Solar Flare, the Red River Rocketry Red Star and the Starlight Rockets Hyperon.

Ring tails have another meaning for me, though.

Thanks Mark. I figured it out after looking for ringtail. Didn't even see the option - duh! :)
Next question...

How do you gap stage in Rocksim? Or maybe a better question is will it handle a two-stage rocket with a D booster and A-C sustainer? I triple checked my design, and it seems robust and workable. When I try to run a simulation, the sustainer does not light. I can't "virtually" drill holes in the tubes and there is a 3.5" gap between the motors. Does Rocksim allow such a non-standard configuration or should I just wing it and hope for the best?
  • Check to see that you have the motor tube in each stage actually designated in RockSim as a motor tube.
  • Make sure that you load a motor into each stage.
  • Make sure that the motor loaded into the booster stage is designated as having a "0" delay.
  • Make sure that the "0" delay motor is indeed the one that is in the booster stage.
You don't have to do anything special in RockSim to simulate gap staging. As long as you load a motor into each stage, and the motor in the booster has a "0" delay, the program will simulate the staging just fine when you run the flight sim. You can even simulate motor combinations that you would never try in real life. Try loading a D12-0 in the booster stage, and a MicromaxxII in the sustainer! It doesn't matter that you haven't specified a motor mount adapter for the MMX; RockSim load the motor into the sustainer's motor tube as if an adapter was there. It will dutifully run a simulation with this combination, including having it stage and firing the MicromaxxII. Try it!

Mark II had several good hints. Here are some more
* On the Rocket Design Attributes page, make sure that Number of Stages is set to Two Stage Rocket.
* Make sure that the booster motor goes in the Booster section on the Components tree.

These seem like they should be obvious, but they are easy to overlook in the newer versions of RockSim.
Thanks guys. Believe it or not, all the things you suggested were double checked, so I went back and looked at the flight again and sure enough, I had separation. It's just that the booster trajectory was such that it did not apprear to fall off. Instead it stayed in the same relative location to the sustainer. I had to slow the playback speed to notice that it did in fact light the sustainer.

Then I went and adjusted the flight track colors and put a bigger motor in the sustainer. Works like a champ now! :)

Thanks again!

The 'Flight Profile' will actually show the booster dropping off? Interesting..Then again I have never played around with a multi-stage rocket in RockSim!:rolleyes:
It follows the sustainer in the same trajectory, but booster apogee is lower so it trails off and falls separately - just like the real thing. ;)
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Did you try that D12 to MicromaxxII combination yet? :D

No. It will only let me use 18mm motors unless I put an adapter in it. I spose I could do that...