Which J350W do I select in RS and OR ?

Both RockSim and OpenRocket have 2 entries in their databases for the AT J350W. One is 700 Ns total impulse and the other is 650 Ns (noted as a 0.5" core in RS). Which motor is the current one on the market? I would assume that it is the 700 Ns since that is the total impulse listed in the AT catalog. ThrustCurve.org lists the J350W as 670 Ns total impulse - which splits the difference. When was the motor changed from the "old" core to the current?

For a while after fire at Aerotech's Las Vegas location they had their propellant cast at a location in Texas. Because of the higher humidity there the mechanical properties of the propellant wasn't as good as expected which resulted in a number of failures in the J350. Aerotech increased the core to 1/2" at that time to correct that problem.

So far as I can tell they never changed back.

https://web.archive.org/web/20021129002121/https://www.aerotech-rocketry.com/

I always used the 700Ns. The instructions say 700 Ns. the propellant weight is at 375 grams. Cert documents say 361 grams propellant. Doesn't mean I'm using the correct one though. Eeny Meeny Miny Moe.......................................

dshmel said:

Both RockSim and OpenRocket have 2 entries in their databases for the AT J350W. One is 700 Ns total impulse and the other is 650 Ns (noted as a 0.5" core in RS). Which motor is the current one on the market? I would assume that it is the 700 Ns since that is the total impulse listed in the AT catalog. ThrustCurve.org lists the J350W as 670 Ns total impulse - which splits the difference. When was the motor changed from the "old" core to the current?

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Bingo. Herein lies the biggest challenge when using simulators - the proliferation of motor files from a multitude of sources. Which one is correct?

Thrustcurve gives two data files for your J350W - one Rocksim format (650 Ns) and one RASP format (670 Ns) - which doesn't really clarify the matter. This is not a huge difference, but why does the mere file format affect the performance characteristics? Some RASP vs. Rocksim files of the same motor are much more extreme in their differences, resulting in up to 20% simulation discrepancies. John mentioned that he prefers Thrustcurve to be crowd-sourced, allowing the multiple entries and various formats. It is up to you to decide which one is appropriate for your application. Don't blame the software, it is only as good as the data you fed to it.

I believe the RASAero guys take the time to parse out duplicates, fix quality, and give the best possible motor in their database. This is a Herculean task, for sure. I once obliterated the RASAero motor database and replaced it with RASP files I got from the Aerotech webpage, thinking this was "more official." Turns out the RASAero files were more correct.

In the future, I want to put a bandwidth around my simulations using the standard deviations of the multiple motor files and/or the standard deviations from the test firing of multiple samples in the cert data.