Beginner rocksim question. How much should parts weigh?

[blackwing94]

I fairly new to model rockets and brand new to Rocksim. Grandkids got me into model rockets over Christmas. Now I’m… (sigh) hooked.


I’m working on my first modification project. I have two Estes Super Neon XL kits and I’m mixing the parts. The stock Neon uses an 18 inch BT-60 tube and an 11.25 inch BT-60 tube. I’m combining the longer 18 inch BT-60 tubes from each kit to make one Super Neon with a 29mm motor mount (from Apogee). I’m combining the two smaller 11.25 inch tubes from the kits with the stock 24mm motor to make a Not-quite-as-Super Neon.


When I opened the kits, I weighed all the parts. Then I built the rockets in rocksim. I noticed most of the calculated weights for the parts in rocksim were different from the weights I obtained. For example, the 11.25 inch BT-60 tube in rocksim comes in at .9249 oz. The tube I weighed came in at .582 oz. Should I over ride all the rocksim weights, or use the rocksim values. I'm concerned where my CG will "actually" end up. Or am I doing something wrong (the most likely choice)? Thanks.

 

[Titan II]

Use the correct weights (what you weigh). I usually just finish the rocket, check the weight and CG, then put this data in Rocksim.

 

[markkoelsch]

Did you use the correct manaufacturer's tube? There will of course be some variation is density hence weights. Also check when you select a part from the data base that it has the correct material. There are some errors in the database.

Also, use your weights. I would buy a reasonable scale. Something likely accurate to a gram is sufficient. Enter these weight as a mass over ride, but also need to change the center of gravity then.

If building remember that by default no rocket has glue or paint as a discrete part. So, generally I try to enter glue mass where I can ( easier with epoxy as I weight it to mix it) and keep track of fillet weights and such. Enter these into the sim. Then you will be close on Cg weight of paint is another thing.

 

[KenRico]

Use the correct weights (what you weigh). I usually just finish the rocket, check the weight and CG, then put this data in Rocksim.

I do this too..mainly to confirm the Center of Pressure location and a stability verification.

It has been easier for me to download a .rkt from a forum post or rocketreviews.com and update it with my sizes and weights as measured. Then I reweigh and balance and override .

Have been using Thrustcurve.org for an overall performance estimate and best delay times for motor deploy.

Kenny

 

[blackwing94]

Thank you for the advice. I'll use my weights.
I'm using a digital scale that measures to .01 gram. I'm weighing the parts as they come out of the Estes kit bag. I wanted to build the simulation from scratch and as a first exercise in rocksim, but I did review other examples of Super Neon rocksim files before I started. As parts come together I'll weigh again (and again) to get a feel for how much weight glue, primer, and paint add.

 

[cls]

Definitely use your weights, on as many separate pieces as you can. Much better than just overriding the total weight.

Also, when you get to bigger rockets, add mass items for the glue used for joints, filets, caviar ballast, etc.

All that makes a difference. You can get your sim to within a few percent of actual.

Enjoy!

 

[Woody's Workshop]

First you have to make sure your scale is calibrated correctly to get the accurate weight.
Most new electronic scales when turned on will go through a calibration cycle.
If you are using an old triple beam type scale, you will brass weights to properly calibrate the scale.