Weather effects on rocketry (looking for advise)

I have a TARC team in the launching stage of their rocket and we are experiencing inconsistencies in our altitudes from one launch to another, we want to factor in windspeed and weather conditions in to our simulations, any advice would be welcome.

You are correct to want to do these things. Things to run in a sim include wind speed, temperature, humidity, launch rod/rail angle.

What percentage difference are you seeing between flights with same motor?

Mark didn't go far enough with his reply. Unless you're seeing differences that exceed the testing margins for motors you are more likely getting variations in motors. One of the reasons why simulations will only get you in the ballpark and not on the target (to badly mix metaphors.)

Peter Olivola said:

Mark didn't go far enough with his reply. Unless you're seeing differences that exceed the testing margins for motors you are more likely getting variations in motors. One of the reasons why simulations will only get you in the ballpark and not on the target (to badly mix metaphors.)

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Peter, that was the reason for my attempt at a leading question about what variation are they seeing. I was planning on seeing what the answer was to that question, and then use the answer to explain some of it with motor variation.

rocketnana said:

...we want to factor in windspeed and weather conditions in to our simulations, any advice would be welcome.

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Umm, OK. So, what is the issue? Are you using an available simulation software like Rocksim? If so, you can play with weather conditions to your heart's content. If you are deriving equations from scratch as part of the TARC experience, then you need to dig into the associated physics and math.

markkoelsch said:

Peter, that was the reason for my attempt at a leading question about what variation are they seeing. I was planning on seeing what the answer was to that question, and then use the answer to explain some of it with motor variation.

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I should have mentioned we are using open rocket as our simulator, so maybe it is time to purchase something?
I have been trying to help students for a few years with this TARC competition, and it seems we are missing something. Our #1 team have a great design, depending on mass addition our first launches all ranged between 790-961ft, so we were sure we just need ti find the mass sweet spot.


Next launch date same rocket, adjusting for mass we thought we would be spot on, no only 750ft (windy, also chute did not fully deploy), with no changes except a new motor from the same packet, we launched again over 900ft (not so windy, chute did fully deploy). Could the wind or the deploy of chute make that much difference to an altitude reading?I was also hearing ignition could be the answer?

Not familiar with the goal of TARC competition is. Is it payload to a given altitude? Would need more details

That said if it was that windy on the second go I am betting you lost altitude due to weather cocking.

Rain will have a result in lower altitudes. Snow, and you are more likely to lose the rocket (same goes for fog). :wink:

My rockets go really, really low in the rain and snow. Like, really.............really low

Here is more info on the variability allowed in both motors and delays:

"Most rocketeers want predictable total
impulse and delay times. The key test pa-
rameters that address that requirement are
that the standard deviation of the measured
total impulse must be less than 6.7% of the
mean, and measured ejection delays must
not vary more than one second or 20%,
whichever is greater, from the labeled de-
lay. For further test parameter details, see
the NFPA standards listed above."

Complete article here https://www.nar.org/wp-content/uploads/2014/08/ST-Sport-Rocketry-Article-Nov-10.pdf

Variables include temperature, motor variation, delay variation, angle off the launcher, wind speed/direction, and altitude. Will work up allowable variation if you will send me which motor you are using. I would suggest playing with all of the above to see what impact each variable has. Hopefully some combination will explain what you saw.

NAR motors here: https://www.nar.org/standards-and-testing-committee/nar-certified-motors/

More info at thrustcurve.org


Best of luck

You can adjust for windpseed in Open Rocket. It's in the flight simulations.

There isn't a lot to choose between Open Rocket and Rocksim for the job you're doing. Both give you the ability to bake in weather. Your indicated deltas are well within the combination of weather and motor variability. Using Open Rocket you can run optimizations against mass for the variations in weather you're seeing. Using the variability limits in 75Grandville's post should clean up your observation vs. simulation discrepancies, at least within acceptable numbers.

rocketnana said:

I should have mentioned we are using open rocket as our simulator, so maybe it is time to purchase something?
I have been trying to help students for a few years with this TARC competition, and it seems we are missing something. Our #1 team have a great design, depending on mass addition our first launches all ranged between 790-961ft, so we were sure we just need ti find the mass sweet spot.


Next launch date same rocket, adjusting for mass we thought we would be spot on, no only 750ft (windy, also chute did not fully deploy), with no changes except a new motor from the same packet, we launched again over 900ft (not so windy, chute did fully deploy). Could the wind or the deploy of chute make that much difference to an altitude reading?I was also hearing ignition could be the answer?

Click to expand...

Sorry, Mark, I wasn't trying to be critical of your post. As I'm sure you know all too well, the expectation of perfect simulation defeats many efforts.

markkoelsch said:

Peter, that was the reason for my attempt at a leading question about what variation are they seeing. I was planning on seeing what the answer was to that question, and then use the answer to explain some of it with motor variation.

Click to expand...