11-01-2007, 12:32 AM
Join Date: Jun 2005
Originally Posted by CPMcGraw
Got one of these in working order today, after picking up a dud yesterday. I wanted to see if I could come up with a better booster that would give some real performance, or at least gain some substantial altitude, compared to the booster you get with the camera. This first version is a throw-together, what-if type of design, and I'm just guessing about the actual weight of the camera. I have not yet weighed the payload to get an accurate value, but I'm guessing no more than 2.5 oz. It really doesn't feel that heavy, maybe just a little more than a hollow plastic NC of the same size.
The camera shoulder loose-fits into a standard ST-13 tube, so that's where I'm starting from. Other variations of this theme are coming, so this is just a beginning baseline.
Diameter: 1.34 (ST-13)
Fin Span: 4.84"
Weight: 3.31 oz (Camera estimated at 2.5 oz)
D12-5......1015'......Dv 26 FPS......48" x 3/16" Rod
Takes about 7.2 seconds to reach apogee, so the 12-18 seconds of record time should be enough to get a flight video.
I really like the booster and your choice of fin design. Looks great!
There is however a limitation that I haven't been able to figure out in RockSim that is throwing your margin of stability out. Margin without engines in RockSim shows 32.28 & I think it's probably closer to 6.43
RockSim is throwing it out somewhere in your Nose Cone Tip, Transition or Fin used for the camera shroud estimation.
To determine this I eliminated those three items from the design file and replaced those items with a single ogive BC-12561 Semroc cone, same as used on the SLS Javelin. I then added a single mass object to the true CG of the Semroc cone at 4.595" to bring the total rocket weight to 3.3085 to match your designs weight and I get a 6.43 margin without engines.
RockSim just doesn't estimate the CG accurately in this case (and I'm not sure why it doesn't).
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