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Kill Bill Build
#11
(09-17-2010, 09:36 AM)Dale Stoyer link Wrote: I also tried this with the V9 free trial with weird results.  Mike said it worked in 9.1 - could it be a difference in the two versions?  (v9 demo vs. 9.1 registered)

Dale

Mike said it handled split fins designs. He didn't say that it worked correctly.  My verison handles split fins also, it just doesn't calculate CP consistently.  The CP should just depend on fin shape not how many segments make that shape.
John Derimiggio
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#12
(09-17-2010, 12:28 AM)Bill Clune link Wrote: We have V.8 here in TCR World HQ and it gets it wrong as well.

Also What did I do? why you wanna kill me?

You ruined Thuma Urmans wedding.
John Derimiggio
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#13
I used the method you said and version 8 did it wrong.
Bill Clune L2 | NAR#88583
MARS Club|SRC|METRA|MDRA - Forever
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#14
I figured out the problem is with the Barrowman's equations themselves.  Since RS uses Barrowman and modifications to Barrowman it's going to be wrong too.

I went back to the original Barrowman equations and played with them.  My conclusion is those equations are only valid if the split fins are far enough apart so they act independently.  If they are close enough so that the lower set is in the slipstream of the upper ones those equations are not going to calculate CP correctly.

I can post the technical details here but it can be complicated,  especially for the real men who fly EX.
John Derimiggio
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#15
Real Men? Hahahahaha.  Ex my &^$^#%.  John, you are correct about RockSim regardless of the version.  PML cheated!  They apparently sim'd the rocket but made it full fins, then just split them, but kept the original equation.  Amazing.  Perhaps that's why Linda's Endeavor keeps heading for the CORN.
Jim Goggins NAR  L3
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#16
(09-17-2010, 12:02 PM)Jim Goggins link Wrote: Real Men? Hahahahaha.  Ex my &^$^#%.  John, you are correct about RockSim regardless of the version.  PML cheated!  They apparently sim'd the rocket but made it full fins, then just split them, but kept the original equation.  Amazing.  Perhaps that's why Linda's Endeavor keeps heading for the CORN.

Its interesting digging into Barrowmans equations (here is the original paper http://www.apogeerockets.com/education/d...report.pdf.

For split fin rockets the Barrowman assumptions will work if they are spaced far enough apart so that they are aerodynamically independent.  Otherwise there is no guidance of far enough they have to be apart to trust the Cp calculation.

But for those simple 3FNC rockets that those EX guys like to fly, the RS calcs should be fine.
John Derimiggio
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#17
(09-17-2010, 12:25 PM)jderimig link Wrote: But for those simple 3FNC rockets that those EX guys like to fly, the RS calcs should be fine.

3F is optional these days...
Dale Stoyer - L3
NAR #91256
TRA #13499
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#18
Please take note, I said V9.1 not V9. Go to apogee, find the upgrade then try it. There is a BIG difference between the two
I just wanna fly ROCKETS!!

Dutch
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#19
Mike,

9.1 has the same problem unless you can prove differently.  The problem is with the Barrowman's equations which Rocksim uses.
John Derimiggio
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#20
So here is rendering of Kill Bill.  Details may change.  It currently is a few inches less than 10 feet long and 5.5" in diameter.  I am trying to go for as a mean look as possible.

The fins will be a composite layup, fiberglass over Divinycell foam.  This will keep the weight down at the rear.  I am shooting for as low a static margin as comfortably safe (like I have done with my last 2 builds). I like my rockets to go where I point them.

[Image: killbill_2_divinycell_3.jpg]
John Derimiggio
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