Well, what do you know! When I download this file into Rocksim it shows this rocket is much more stable than in OR. The stock file shows the cal at .99 in RS and .012 on OR. How can this be? Dave Barber with Loc says that there must be something wrong with the file in OR as the Rocket should NOT need 2lbs of nose weight to fly it on an L. Now I’m having to try to learn RS on my thirty day trial after being used to OR. So far I haven’t figured out how to make the rocket match my exact build on RS but I’ll keep playing with it. Any ideas on what could be going on with the discrepancies between OR and RS?ARGH, I did the whole thing above with the motor in! Might have totally screwed up the numbers. Let's double-check it using hack #2, which is definitely easier although it has its own downsides.
1) Make a note of stage measurements: mass 230 oz, CG 50". Now disable the overrides on the stage:
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First observation: Is 69 oz difference between original model weight and actual measured mass really correct? When you measured for the override did you do it *without* the motor?
2) Let's assume it's all correct, even though it sounds doubtful to me. We have 69 oz difference to make up between model and actual. So we'll add a 69 oz mass object and adjust its position until the CG matches the 50" original measurement. It doesn't matter which component we add the mass object to; I'll add it to the top of the Fore Recovery Airframe Section. I get its final position at 29.5" from top of the parent component.
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3) Now you can add your noseweight and adjust. Because the total rocket mass has not been overridden, it will factor in the added mass appropriately. This time, I achieve the same 1.02 stability margin with...
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35 oz! Well whaddya know, I guess I didn't screw up hack #1 in the previous post. 35 oz vs. 37 oz might be accounted for just because I positioned the weight slightly differently.
Bottom line: you're gonna need 2+ pounds of weight in the nose to fly that configuration.
Been a while since I've used RS but I do recall you had a choice of 3 different methods of calculating the CP. Barrowman, RocSim and a third I can't recall. There was also an option as to which one (or combination of them) were displayed. I remember on a couple of designs the difference in location was, I felt, significant. Not sure if this is still an option but it's a good place to start.I wonder why the difference?
On RS it is set to Barrowman equation as well so we should be talking apples to apples as far as I know.OR uses straight-up Barrowman equations which are the most conservative for CP. Rocksim offers the same Barrowman as well as their own method, which is the most liberal. RASAeroII offers their modified Barrowman which fall in the middle. Pick your poison.
In my experience, OR is far too pessimistic. I wasted a lot of time stressing over OR's CP predictions and added nose weight where it wasn't needed on a few of my builds. I stopped using it and now stick with RS and RAII.
Thanks for the file! It opened fine. I did notice that when you entered mass on some of your components you left the CG location as "0". You need to give a proper CG location for the component or RS will set the component's full mass at the Forward End ("0" End) of the component. So you rocket's overall CG will be incorrect.Here is it. Let me know if it doesn't work for you for some reason.
I would start off "simple" so that you can get the feel for RS. Weigh the body tubes, 75mm motor tube, coupler & stiffy tube, centering rings, etc. All the items that have simple shapes. Then just set their CG location at their midpoint. For example, your 75mm motor tube is 23" long - so set its mass at 13.5" from the front of that tube. Your coupler is 11" long - so set it's CG at 5.5". And the CG for the 1/4" thick rings is 1/8" (0.125"). You can also do this for the fins, but finding the CG of a fin is a little tricky but doable.Ok. Thanks for that tip. This file I sent you is from Jason with Loc and that is the stock file. I haven’t done anything to it. So I should weigh the avbay, main section and booster separately and then with a string balance and find the CG of those and input each one into RS? Is there anything else that I should weigh and correct? Is it not good enough to just balance the final built Rocket all put together and input the CG of that isn’t RS? I have not done that into RS yet as I am still learning this program. Thanks for the help.