I entered the info into Rocksim 9 for my Delta X rocket that had 4 strap-ons. However, I wasn't able to eject the strap-ons during the simulation. Evidently, there's a trick I don't know for how to do this. Anyway, the mass of the engines in the strap-ons seemed to bring the CG back more than the CP. I added additional weight to the Delta X to bring the CG forward and I don't want to add a bunch of extra weight to the Delta II. Richard > Subject: [roc-chat] Re: Stability of a rocket with strap-on boosters > From: allen.farrington@xxxxxx > Date: Wed, 10 Aug 2011 11:33:33 -0700 > To: roc-chat@xxxxxxxxxxxxx > > Rocksim 9 has tools built-in to model strap-on boosters. If you have Rocksim > 7 or 8, there are ways to trick it into simulating them. > > Allen > -------------------------------------------------------------------- > Allen H. Farrington > 818-653-2284 > web: http://www.allenfarrington.org > > On Aug 10, 2011, at 11:29 AM, Kurt Gugisberg wrote: > > > Richard, > > > > The strap-ons will add some drag stability (base drag) as well as an area > > equivalent to fins or a larger airframe area. Knowing just how to factor > > that in is the tricky part. I think you can fudge it into rocsim somehow. > > > > Kurt > > -----Original Message----- > > From: Richard Dierking > > Sent: Aug 10, 2011 10:34 AM > > To: roc-chat@xxxxxxxxxxxxx > > Subject: [roc-chat] Stability of a rocket with strap-on boosters > > > > I'm considering the size and shape of the 3 fins for my Delta II 7925-10L. > > It's a 4" core transition to 5" on top with 9 strap-ons, each approximately > > 1.5" dia (BT-60 tube). total height is 65". I don't want it to be a > > high-velocity rocket and I'll be using a J135 for the core, six F-30's > > strap-ons 0.5 sec after launch, shed those, then airstart three G's > > strap-ons then shed the last three strap-ons. > > > > For the 3 fins, I'm using 3/16" thick abrasion resistant polycarbonate that > > by my estimate has a stiffness similar to 1/8" birch. The fins are > > through-the-wall and fiberglassed to the 54mm engine mount. I'm thinking > > to configure the fins as clipped deltas to avoid busting a tip during > > landing. Since the rocket has 9 strap-ons, seems to me this would add > > stability during launch (like tube fins). Am I wrong thinking this? I > > would like to keep the fins on the small size. > > > > Please advise and thank you, > > Richard Dierking > > > > -- ROC-Chat mailing list roc-chat@xxxxxxxxxxxxx > > //www.freelists.org/list/roc-chat > > > -- > ROC-Chat mailing list > roc-chat@xxxxxxxxxxxxx > //www.freelists.org/list/roc-chat >