Rsiming the Estes Echostar

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Well-Known Member
Jan 25, 2004
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I built an Rsim model of the Estes Echostar and was wondering which CP calculation formula best suits this model, I would have thought the cardboard cutout method because of all the fins some of which are a little odd shaped, but according to this method the CP looks way to far forward than what I would think of as normal, Rsim and Barrowman methods seem to be way farther back than normal, I've attached a screenshot, what method would you think works for this rocket?
hmmm, the rocksim file from EMRR for Echostar - which I would trust because I've used it and it simmed close to what we got for real - shows 7 calibers (overstable) for Barrowman & Rocksim, and 4 calibers for cutout. want to re-check your rocksim file? I know there are limits to the cutout model's accuracy.

it's a payload model, are you flying a payload? add it to the sim, that would change the CG.

anyways you should always do a swing test.
Without motors mine sims out at 7.75 and 8 calibers over stable for barrowman and rsim, this isnt the EMRR model, I drew this model up myself, took all the measurements, this way I know all of the information is correct because I put it there, I've had Rsim models drafted by other people that were WAY off on some of the measurements. I'm not flying a payload so I didnt add it to the Rsim model
If you add a shock cord and pack it and the parachute all the way down to the top of the sustainer's motor mount tube there are only about 5 calibers of stability for this design with C6 motors in the sustainer and booster. I get around 8.72 calibers of stability (RockSim) for the design without motors.

This simulation file may not be that accurate. Are there more centering rings inside the sustainer? The EMRR file only indicates one CR and a bulkhead, is that correct? Do you know the true weights of the polystyrene nose cone and tranisition?

Bruce S. Levison, NAR #69055