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Overstable fix?

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SaltyCracker

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I'm helping my son build a LOC Tomahawk and with a G38F installed, Rocksim is showing an overstable margin of 4.
I have to add 9oz. of mass near the forward centering ring to get it down to a margin below 2.5. That doesn't seem smart though.
What should I do?
 

Neutron95

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Just fly it as is. It will be a bit more sensitive to wind, but it's manageable. Just use a longer rail, higher thrust motor, or fly on calm days. I've built a few overstable rockets, and they've all flown fine.
 

rharshberger

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Just fly it as is. It will be a bit more sensitive to wind, but it's manageable. Just use a longer rail, higher thrust motor, or fly on calm days. I've built a few overstable rockets, and they've all flown fine.
+1 fly it as is, a margin of stability of +4 is fine as is, yes it will have a mild weathercocking tendency but not too bad. A Mean Machine has a margin of stability of like +11 to +13 iirc and they weathercock quite a bit, but not enough to be unsafe.
 

n27sb

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What setting are you using in stability in RS. Cardboard cutout can overestimate.

Have you checked the actual CG by balancing the rocket to see if it matches RS.

RS has a tendency to overestimate CG on long skinny rockets.

A margin of 4 is ok on on calm days but if you choose to reduce it you can:

Remove forward weight
Add rear weight
Add heavier motor
Reduce fin size
Add fins forward of the CG
 

SaltyCracker

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Thank you Neutron95 and Rich for sharing your knowledge.

What setting are you using in stability in RS. Cardboard cutout can overestimate.
Have you checked the actual CG by balancing the rocket to see if it matches RS.
RS has a tendency to overestimate CG on long skinny rockets.
A margin of 4 is ok on on calm days but if you choose to reduce it you can:
Remove forward weight
Add rear weight
Add heavier motor
Reduce fin size
Add fins forward of the CG
Valuable indeed. Thank you.
I kept the Rocksim stability calculation.
I have not verified the CG yet because it's not finished and I probably wouldn't have anyway because I would have just trusted Rocksim. I'll keep your warning in mind for now on.
As far as reducing stability by adding weight to the tail end, what would be the recommended max? I don't expect there to be a simple answer to that but any guidance would be helpful.
 

Nytrunner

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I have not verified the CG yet because it's not finished and I probably wouldn't have anyway because I would have just trusted Rocksim. I'll keep your warning in mind for now on.
This is an important step of any simulate/build project. Glue can add more weight in strange places than you think.

For my part, I try and keep the CG-CP distance between 8-15% of rocket length during flight. That takes into account odd cases like long super-rocs and short stubbies where 1 "caliber" just doesn't work anymore
 

SaltyCracker

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This is an important step of any simulate/build project. Glue can add more weight in strange places than you think.

For my part, I try and keep the CG-CP distance between 8-15% of rocket length during flight. That takes into account odd cases like long super-rocs and short stubbies where 1 "caliber" just doesn't work anymore
Lesson learned. I'll do my own CG verification for now on.
 

Jee3300R

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I like my rockets overstable, even with 4+ margin. Sometimes even with 2-3 cal they end up arching downwind, especially with smaller fins.
 
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