Learning Rocksim - Am I doing this right?

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OC_Rocket_Man

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I have Madcow making me a modified kit - a 5 fin 4" Cowabunga that I am just calling the Artillery Rocket.

I have been playing with Rocksim today and modified the Cowabunga.rkt file to what I believe mine will resemble. Adding mass objects (like a motor retainer, JLCR, nose weight), adding fins, adding a centering ring, shifting the MMT slightly aft to take an Aeropack retainer upsizing the parachute to 36".

Can someone tell me if I'm actually doing any of this correctly? I just downloaded this program a couple hours ago after watching some YouTube tutorials so I am flying blind.

And yes I realize I haven't added engines yet and that actual nose weight values will be dependent upon engines

Thanks!
 

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While I'm not familiar with RocSim, from what you've described, it sounds about right.
 
Looks good. The extra fins will add drag to the aft end helping as well.

Mine has a bay in the nose cone and that added about 5 oz. I have since went back and added 5 oz to the NC shoulder just to be able to fly some bigger motors.

You want it to have a stability around .5 CAL after it has a motor. 4 oz in your nose cone should get you up into J motors for that rocket.
 
While I'm not familiar with RocSim, from what you've described, it sounds about right.

Looks good. The extra fins will add drag to the aft end helping as well.

Mine has a bay in the nose cone and that added about 5 oz. I have since went back and added 5 oz to the NC shoulder just to be able to fly some bigger motors.

You want it to have a stability around .5 CAL after it has a motor. 4 oz in your nose cone should get you up into J motors for that rocket.

Thank you both for your input.

Now I have another question. Using the hypothetical build weight on Rocksim of 41.8oz, when I enter things into Thrustcurve for a 38mm CTI H143 SS it shows a projected altitude of 1535 ft. When I run the Rocksim flight simulation, it shows a projected altitude of 2109 (I had a higher number but changed the launch site elevation to 0.) And they obviously have different delay times. Is this normal to get such a disparity between the two programs?
 
What's the drag coefficient set two in each model?

Until you just typed this, I had no idea.

On Thrustcurve, I didn't set anything. Just plugged in diameter/weight/MMT size/MMT length.

On Rocksim. I just checked the Cd Override tab and it was set to "calculate at simulation time". I unchecked that box and used the "Cd for sustainer stage alone" with the figure 0.65 (which I have no idea where that came from it's just there), reran the launch and now it says 1487 ft.

I know what Cd is, but I'm not even going to pretend to know how to calculate it, or whether to use the override or the simulator numbers.
 
I have RocSim and I like it, but I won't say I am an expert at it. One thing I would recommend is to weigh the actual rocket when it is completed and compare it to the RocSim weight. They might be different. I would also recommend that you find a way to locate the actual c.g. and compare it to RocSim. At times when I did this I found that the real model weight was heavier than the RocSim prediction and that the measured c.g. was also different than the RocSim value. In this situation the correction to RocSim to match the real model is simple. Just make up the model weight difference in RocSim with the added weight option and move the added weight by trial and error until the RocSim c.g. matches the real life c.g.
 
Until you just typed this, I had no idea.

On Thrustcurve, I didn't set anything. Just plugged in diameter/weight/MMT size/MMT length.

On Rocksim. I just checked the Cd Override tab and it was set to "calculate at simulation time". I unchecked that box and used the "Cd for sustainer stage alone" with the figure 0.65 (which I have no idea where that came from it's just there), reran the launch and now it says 1487 ft.

I know what Cd is, but I'm not even going to pretend to know how to calculate it, or whether to use the override or the simulator numbers.

Thrustcurve defaults to 0.6, I think, but you can edit to whatever you want. Put the same value in RS override, set the atmospheric properties to standard sea level, and no wind or turbulence. Make sure identical thrust curves are used by both software. Then, RS and TC should match each other nearly exactly.
 
I can never hit an altitude in Open rocket and have never used Rocksim, so I can't help with all that. I have got to within 10 or so feet but have also missed by 500. A lot may have to do with location or improper sizing of static ports.
 
I can never hit an altitude in Open rocket and have never used Rocksim, so I can't help with all that. I have got to within 10 or so feet but have also missed by 500. A lot may have to do with location or improper sizing of static ports.

Mikey......within 10 ft IS hitting it lol
 
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