I just posted this in another thread, thought I'd elaborate a bit here for posterity.
DISCLAIMER: I have no idea if this is common knowledge. If so I apologize.
The standard practice to get most accurate flight sim data from OR or Rocksim is to measure mass and CG of the completed rocket, and then apply those numbers as overrides. There is a problem with this approach, though: once you apply the overrides, further changes to the rocket are ignored with respect to mass and CG. Why do we care? Well, maybe you just finished construction of your rocket and you need to figure out how much nose weight to add for stability. You want to come up with an answer based on the actual constructed rocket, but then if you apply the whole-rocket overrides then you will not see the affects of the nose weight.
Here's an easy solution.
I kind of like doing things this way all the time (at least, when I remember) because this leaves the sim ready for any future tweaks.
Enjoy!
Addendum: as pointed out below by @Buckeye, neither this method *nor* using the whole-rocket override provides accurate moment of inertia data. If that is important to you then you'll need to use a different approach.
DISCLAIMER: I have no idea if this is common knowledge. If so I apologize.
The standard practice to get most accurate flight sim data from OR or Rocksim is to measure mass and CG of the completed rocket, and then apply those numbers as overrides. There is a problem with this approach, though: once you apply the overrides, further changes to the rocket are ignored with respect to mass and CG. Why do we care? Well, maybe you just finished construction of your rocket and you need to figure out how much nose weight to add for stability. You want to come up with an answer based on the actual constructed rocket, but then if you apply the whole-rocket overrides then you will not see the affects of the nose weight.
Here's an easy solution.
- Measure the mass of the rocket and CG before nose weight is added.
- Subtract the total rocket mass indicated in the sim. Usually your result will be positive, because actual builds are heavier than the sim. If this is not the case, or if the difference is very small, then make your sim lighter by overriding the mass of a significant component (the airframe is a good choice generally) to zero. Then subtract again, and you should get a bigger, positive number.
- Add a new mass object equal to the difference you just measured.
- Adjust the position of the mass object until the CG matches the value you measured in step 1.
I kind of like doing things this way all the time (at least, when I remember) because this leaves the sim ready for any future tweaks.
Enjoy!
Addendum: as pointed out below by @Buckeye, neither this method *nor* using the whole-rocket override provides accurate moment of inertia data. If that is important to you then you'll need to use a different approach.
Last edited: