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rtuinila
03-09-2014, 12:31 PM
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

bernomatic
03-09-2014, 01:31 PM
First thing I would check is your wind speed settings. Next maybe rod length.

mikemech
03-09-2014, 04:39 PM
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.

rtuinila
03-09-2014, 07:19 PM
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.

mikemech
03-09-2014, 11:09 PM
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.

rtuinila
03-10-2014, 08:24 AM
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.

Rich Holmes
03-10-2014, 09:57 AM
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.

mikemech
03-10-2014, 10:34 AM
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.

rtuinila
03-10-2014, 08:57 PM
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!

Jerry Irvine
03-10-2014, 09:04 PM
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

Bill
03-11-2014, 12:15 AM
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).


Saturn 1B, Jerry, not Saturn V.


Bill