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- Dec 20, 2015
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Anybody, anywhere have a simple, perhaps new, method to determine the Center of Pressure. My rockets are sorta large and the string thing won't work. . .and neither will the card board cut out idea.
The biggest problem with cardboard cutout is it vastly overestimates the effect of the body tube and so for most rockets is 'way too conservative (in the sense that it estimates the CP as being much too far forward).@Sooner Boomer you can do cardboard cut out of multiple profiles. ie 0 and 90 degrees, more if you have lots of asymmetric parts Taking the worst case should be sufficiently conservative.
Cardboard cut out is just finding the centroid of the shape. For large birds you can do this mathematically.
Vanilla tubefins work fine in OROpen Rocket if it is not a tube finned or otherwise oddly configured design.
Not saying it's a perfect method by any means. But learning and affording cfd software isn't for everyone. There are things that Barrowman equ's can't handle, and RockSim and OR definitely have their limits. If I was RSO at a launch and someone came in with CFD plots for a highly unique design I'd have hard questions before I let it on the pad about how the work was verified. I've seen way to much GIGO on analysis models to take the word of a pretty plot. The important point I think we're both trying to make is to think about the assumptions the analysis is based on.The biggest problem with cardboard cutout is it vastly overestimates the effect of the body tube and so for most rockets is 'way too conservative (in the sense that it estimates the CP as being much too far forward).
Not saying it's a perfect method by any means. But learning and affording cfd software isn't for everyone. There are things that Barrowman equ's can't handle, and RockSim and OR definitely have their limits. If I was RSO at a launch and someone came in with CFD plots for a highly unique design I'd have hard questions before I let it on the pad about how the work was verified. I've seen way to much GIGO on analysis models to take the word of a pretty plot. The important point I think we're both trying to make is to think about the assumptions the analysis is based on.
That is nice, but a downloadable PDF would be better. I'm not sure I like the fill in the blanks spreadsheet approach. Back in the early 80's I published a blank CP worksheet in my newsletter. In any event, I remember being frustrated, staring at those equations from the Handbook, while in Junior high. My math teachers were unwilling to help me and were only interested in advancing their own agenda. I just needed a little intro to algebra.Back in the day, circa 1995, a Tripoli rocketeer, named Bruce Lee, developed a simplified method to manually calculate Center of Pressure.
His 10-year old son was able to do the computations with ease.
Dave F.
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That is nice, but a downloadable PDF would be better.
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