new user trouble with rocksim mass object

After browsing and searching the RTF threads, I've come to ask this question. I'll apologize before and after if there's a rich trove of rocksim user Q&A out there somewhere. Please point me to it.

I am rocksim modeling a 2 x 18 mm cluster modification to an Estes Curvilinear kit. Everything seems to be progressing ok, then I notice that creating a mass object in the nosecone is not being recognized for the purpose of calculated CG, stability margin, or total weight. The M symbol shows up on the diagram and the object is in the rocket component tree. However, the weight, CG, etc. remains unchanged.

I'm trying to use the Rocksim 9 trial version.

Any advice or tips would be appreciated. The rocket, when two 18mm motors are installed, is clearly marginally stable - at best - without adding nose weight. Thanks for your help.

--Tooniner

View attachment estes_curvilinear_cluster.rkt

Sounds like you need to uncheck an override somewhere.
At least, that is what it sounds like.


Matt

Your mass override is turned on. If you need very accurate weights use a gram scale if you have one. The material weights in Rocksim sometimes are not accurate with the actual part due to parts thickness.

how much weight have you assigned to the mass object?

Yep mass override is on in your file. The green arrows in the photo below show where to change it

Slickwilly said:

Your mass override is turned on. If you need very accurate weights use a gram scale if you have one. The material weights in Rocksim sometimes are not accurate with the actual part due to parts thickness.

Click to expand...

Thanks, Bill. I guess that means that it's much better to work on modeling in Rocksim BEFORE construction. This initial attempt at using the software was an afterthought to get help comparing computed CP with estimated. I know I need to add nose weight to achieve a caliber of stability, and thought I'd try getting some help via software.

I guess I could weight the parts from another kit. I teach middle school and want a small field flyer that features a cluster.

And... thanks, David.

Do we think that RS will properly handle the external tube feature? when calculating drag and CP? Admission: I could not figure out how to add the body tube ring (fin can feature) as an "external body tube" so I added it as an internal tube, and sized it to fit around the body tube per the Estes design. Since it's modeled as an internal structure perhaps it is only included for CG and not CP calculations.

Answered my own question: No, RS cannot do the CP calculations correctly if you add a body tube ring using the internal component method. However, it can if you add it using the ringtail button. When I added the Curvilinear kit's draggy feature as a ringtail, the CP moved rearward as you would expect. I'm feeling better about the CP data now and RS seems to say that there's about .80 or more of stability margin without any nose weight.

Tomorrow, I'll swing test it and weigh the finished product to set any necessary override for simulation purposes. Once I have better weight data, I'll upload the rkt file.

Ran out of time to use the balance at work today... Did get a string test done. While I did just read a couple threads about reasons string tests could yield false positives, including one that referred to an interesting old bulletin (by Apogee?), I am convinced The RS weights must be pdf by a lotthat the test works for this rocket. I'm also convinced that this rocket fails the test and it's, in fact, unstable at this point.

Even when thrown by an experienced string tester, on an exceedingly long string, the rocket quickly flips and flies backwards.

I've got to get some accurate weights!