Barrowman or RockSim?

[speedyweasel]

If you were faced with which method to believe, Barrowman or RockSim, which would you choose?</br></br>I am buying parts for a scratch-built, 2-stage complex rocket right now. The difference between Barrowman and RS on this project is a full 9 inches on a 67-inch rocket. Ridiculous. The difference in nose weight is ten pounds.</br></br>I do have a very blunt interstage joint (6.5"-to-4"), so I wonder if that's what's confusing it.</br></br>Anybody able to help me with this? Which one should I believe?

 

[speedyweasel]

Here's the file. Have at it!</br></br>By the way... this is a Standard Missile 3 (SM-3), one of the cornerstones of the DoD's Aegis BMDS. This is the missile we have tested successfully against several ballistic missile test drones, including the "test firing" right before North Korea tried its little Taepodong-II stunt. I'm no conspiracy theorist, but I can't help wondering if we ever ran that test... it seems like a heck of a coincidence that we just happened to have SM-3-equipped Aegis cruisers in theater at the time of launch, happen to have "test fired" an SM-3 within a few days of the Taepodong failure, and the Taepodong somehow fell apart during the boost phase. </br></br>I'm gonna go put my tinfoil hat back on now.

 

[Stymye]

yep.that gets asked alot



https://www.rocketryforum.com/searc...d=776494&sortby=lastpost&sortorder=descending

 

[teflonrocketry1]

Its just not worth using an old CP estimation method (Barrowman) that was developed for the pre-hand calculator era. For reasons to use the RockSim equations and not the Barrowman equations visit:
https://www.apogeerockets.com/education/downloads/Newsletter105.pdf

Bruce S. Levison, NAR #69055

 

[teflonrocketry1]

SpeedyWeasel,

I went through the RockSim file you posted. The problem between the Barrowman and RockSim equations lies solely with the fins on the sustainer. Look at the simulation with just stage one; the CP difference between the two methods is 10 inches. Since Barrowman equations weren't developed for complex fin shapes I would not use them for this design. Using the RockSim equations allows you to shave 5 pounds off the amount of nose weight required for stable flight.

Bruce S. Levison, NAR #69055