L2 Rocksim help

Am new to using Rocksim and am slowly figuring it out, (more like screwing up the files that I am working on! )

Currently working on Madcow Rocketry 5.5" V2 Rocksim file from their website. Have adjusted it to a 75mm motor mount and using an Aerotech K560W in the sim.

So when I launch it in the sim, it shows it unstable, I have tried to adjust the mass of the nosecone, but it does not change its CG and still shows it unstable. How do I add weight to the tip of the rocket and move my CG forward? Also I have ordered a Fruity Chute Iris Ultra 84" standard, but not sure how to change it in the sim to show it, and its weight...

So much to learn...

I can look at it a bit later if you would be so kind as to post the file.


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You have put the mass of the NC into RS. I assume you have checked the box that says something like "use mass overrides" somewhere on that page? Is the mass of the rocket on the summary window going up as you change the number for the NC?

Yeah your mass and/or CG may be "overridden by stage" or some such. Not Sucre how Rocksim works exactly, I use Open Rocket.

Mass override tab.
Go to Measured center of gravity (CG) data.
Then set the CG for the sustainer. It is measured from top of the rocket.

Okay, will be working on the file today when I have time, and see what I can get done.

Here is the V2 rocksim file that I downloaded from Madcow

View attachment V2 L2 Cert.rkt

A couple of quick observations on your file...

First, a 5.5" V2 is a healthy size rocket. Looking at your total weight w/o the motor, it says it only weighs 12 oz. Before adding any other components, it's good to look at each part to see if the calculated mass was manually overridden.

For example, the nose cone calculated mass is 40.2 oz, but it's been manually overridden to 4.1 oz.

Once you have the weight of the various components close to reality, the rocket will be much closer. I have built the same size V2 (LOC, not Madcow). Most people will tell you that you'll need nose weight to ensure stability. Since it has a 75mm motor mount, it may be likely to be tail heavy if you fly it with short, stubby motors.

OK, who created this file? It was one very messed up file. Luckily, I am good with Rocksim

That said, I have fixed it as well as I could with actual correct dimensions, and masses based on calculated densities I have measured. It is attached. It was not the correct diameter, not the correct materials. It was bad. To make it better you would need to measure and weigh each part.

A few thoughts. The Iris 84" is a bit much for this rocket...it will come down pretty slow.

I have never seen any filament would rocket component that is .25" thick.

That At motor is minimal thrust for this. You would be better off with1.5-2 times the thrust to get it moving.

Final thing. The V2 is unstable typically. The real missile had active guidance and a 1 ton warhead in the nose. No active guidance. I think you need about 3 pounds in the nose.

Questions let me know.View attachment V2 L2 Cert.rkt

Thanks for all the help! I am using the new file and adjusting it to my measurements and weights. So far, so good!

8thPaladin said:

Thanks for all the help! I am using the new file and adjusting it to my measurements and weights. So far, so good!

Click to expand...

Sorry if I came off a little cranky. I had been up for quite a while at that point. If you have questions please let me know- I have been using Rocksim since version 3 or 4, and was a beta tester for the last two major versions (8 and 9).


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No problem. The file is great! Now I can work on it and get it ready for its flight. Again, thanks all for the help!