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  #1  
Old 03-09-2014, 12:31 PM
rtuinila rtuinila is offline
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Default Problems with stability in RockSim

Hi Folks!

I just downloaded the RockSim file for the Apogee 1/70 Saturn V. When I tried to run a simulation using one of the engines already listed in the simulations tab, the rocket went unstable right off the launch rod. Has anyone else tried to run a simulation of this beast and had the same thing happen to them? I'm sure it is some parameter I haven't set up correctly.

Thanks!

Roy
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Old 03-09-2014, 01:31 PM
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First thing I would check is your wind speed settings. Next maybe rod length.
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  #3  
Old 03-09-2014, 04:39 PM
mikemech mikemech is offline
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Quote:
Originally Posted by bernomatic
First thing I would check is your wind speed settings. Next maybe rod length.

+1
If you're set up for smaller rockets (Alpha, Big Bertha) your rod may be too thin or too short for an SV.
(edit) My better 2/3 laughed hysterically. I'm leaving it.
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Old 03-09-2014, 07:19 PM
rtuinila rtuinila is offline
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Thanks, I've tried setting the wind setting to "no wind" and the launch rod to 72 inches with no effect on the simulation. I even tried Mass Override and set the cg to 8 inches from the nose instead of the original 28.000 inches. Still no joy.
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  #5  
Old 03-09-2014, 11:09 PM
mikemech mikemech is offline
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Quote:
Originally Posted by rtuinila
one of the engines already listed in the simulations tab,


Is this a simulation that had been run before you opened RockSim? If so, what were the results of that sim? Compare the details of that sim with yours. Look for differences. The Apogee .rkt file shows a problem with H120-6 and G80-4 motors. Look at the details on those, also.
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  #6  
Old 03-10-2014, 08:24 AM
rtuinila rtuinila is offline
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Yes, when I opened the simulations tab I saw the G80-4 engine listed. When I tried to run a simulation with that engine, the rocket went unstable.
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  #7  
Old 03-10-2014, 09:57 AM
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Rich Holmes Rich Holmes is offline
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I don't use RockSim, but I imported the RS file into OpenRocket and stuck in a G80-4; the flight profile looked fine. But OR doesn't support pods, which are used in the RS model for the conical pieces around the base, so those were omitted. I'd guess these don't have a huge effect on stability but you might try deleting them in RS and seeing what difference it makes.
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  #8  
Old 03-10-2014, 10:34 AM
mikemech mikemech is offline
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The three motors listed in the supplied sims are not in the database. The rod length in sims 0 and 1 is 1.22mm. Trying to run a sim with other motors (in the database) gives all zeros in the data columns, as if the igniter misfired. Time to call/e-mail Apogee.
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  #9  
Old 03-10-2014, 08:57 PM
rtuinila rtuinila is offline
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I emailed Apogee and they sent me an updated RockSim file that is stable! If your file has the escape tower on the Command Module it won't work.

Thanks everybody!
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  #10  
Old 03-10-2014, 09:04 PM
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Jerry Irvine Jerry Irvine is offline
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Put clear fins with no net spin ala Centuri. Use longer burning motors of 1.5-2.5 seconds. Short delay and huge chute(s).

Jerry
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