Open Rocket warning - Stage began to tumble under thrust

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billdz

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While running a simulation on Open Rocket, I got the warning message "Stage began to tumble under thrust". Ran the simulation again and the warning went away, got the green check. Ran the simulation several times, sometimes I get the warning, sometimes I get the green check, even though no change in parameters at all.

What does this warning message meaning and why would it appear sometimes but not always on the same simulation?

Thanks for any info,
B
 

T-Rex

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Probably marginally stable. Add some nose weight and see if it changes....
 

dhbarr

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Other issues can be: not enough fin, rod too short, wind too high, multistage config incorrect
 

billdz

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But if the parameters are exactly the same, why would the result change?
 

dhbarr

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But if the parameters are exactly the same, why would the result change?
Because it is not a simplistic if-x-then-y solver.

It's a series of interrelated best estimate multi-dimensional sub-trans-super-sonic compressible/non-compressible flow thingy, and several of those subprocesses need randomness to arrive at any useful conclusions.

And if one or more design bits are marginal, sometimes you're on the right side of the RNG and sometimes you're not.
 

markkoelsch

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Your design is playing it to close to instability. Add some fin, add some nose weight, or make it longer.
 

Buckeye

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The result should not change unless some randomness is enabled in the simulation. Or, there is poor coding where conditions are not properly reset.
 

dhbarr

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The result should not change unless some randomness is enabled in the simulation. Or, there is poor coding where conditions are not properly reset.
Swirling air in an atmosphere, yeah that's pretty variable. Would be contributory to the randomness, I'd think :)
 

billdz

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Yes, I see if you click on Run Stimulation several times on just about any rocket and any configuration, there will be slight variations every time, the apogee changes by a few meters, speed changes a bit, etc. So my rocket must be on the very edge of stability.
 

Buckeye

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Yes, I see if you click on Run Stimulation several times on just about any rocket and any configuration, there will be slight variations every time, the apogee changes by a few meters, speed changes a bit, etc. So my rocket must be on the very edge of stability.
Maybe so, but the computer should return the same answer every time. No slight changes, but exactly the same every time you hit run. Mine do. I turn off all wind. There is some purposeful randomness coded in your sim. I suspect wind is where it is happening.
 

billdz

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That seems to be it, I turned off the wind and now the sims stay the same.
 

dhbarr

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So, just to be clear: instead of adjusting away from the possibly marginal condition, we've taped over the check engine light.
 

Buckeye

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Nope. Just verifying where the variation occurs to answer the OP'S question.
 
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