RockSim question

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Well-Known Member
Jan 17, 2009
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Using V8 right now (will be upgrading soon)

The design I'm working on has cut body tubes.

The Primary tube is a BT-50, running through a pair of BT-80's. In order for anything to work right, I had to set up the BT-80's as inside tubes. Makes the end view look lousy with the fins, but the CP and CV balance out ok.

The ends of the BT-80 are cut on an angle on each end of the two tubes, down 3 inches (I don't know the exact angle). Similar to a Pemberton King Kraken, but with the same angle on each end.

I need to know how to either depict this in Rocksim, or what allowance to use for it. If I leave the tubes as is, the CP, CV and stability margin are all good. My concern is how much would I lose due to the cuts, and how it would affect the balance points.

Thanks all!
I'm still using v8, too. (Have you had your v8 today? :D ) For my FSI Viking clones (which all have parallel bevel-cut tube fins) I just used the total length of the tube, from the tip of the top bevel to the tip of the bottom bevel. (IOW, as if the tube fins were square-cut.) I made sure that the bottom of the tube fins in my RockSim file were at the same distance from the aft end of the airframe as the bottom tips of the beveled fins in the real thing. And the tops of the RockSim tube fins were at the same location as the upper tips of the beveled tube fins on the model. Yes, the real model with beveled tube fins will probably fly a little bit differently vs. the simulated model with square-cut tube fins, but I don't think that the difference will be all that significant. RockSim already needs a bit of tweaking (at least up through v8) to get it to correctly factor in the effect of tube fins, despite the fact that you can add them easily to the design. So also factoring a bevel into the calculation seems like too much work for something that is only an approximation arrived at via a work-around to begin with. I don't know if v9 fixed the tube-fin calculation.

Yeah, that's basically the same thing I did. I figure any affect would be minor. I'm hoping to get this prototype started in about a month. I have parts I need to order yet.

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