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mtnmanak

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Opening up a space where we can talk about using the tools on Thrustcurve and allow John to have a single place to get feedback.
 

mtnmanak

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Will start it off with a topic from another thread - requesting to have motor case size added to results to better choose motors for the hardware you have.

Could be tackled from a filter standpoint at the end of the process or a selection standpoint at the beginning of the process.

Also, could be an opportunity to have an option that would export all available linked data to the excel/sheet when you export.
 

mikec

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Will start it off with a topic from another thread - requesting to have motor case size added to results to better choose motors for the hardware you have.
If you use spacers, that would complicate this, obviously. That was my motive for requesting the capability of asking for only favorite motors (already added), but that's not quite the same thing -- I use that for the reloads I have, not the cases I have.
 

JohnCoker

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Obviously, filtering motors before the sims are run makes it faster, but the filters beforehand make it less obvious what you're missing since those motors never show up at all.
 

mtnmanak

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I would actually like more info similar to this in the spreadsheet export, then I can filter on all sorts of criteria
 

JohnCoker

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OK, I added three columns to the XLS and CSV download:
  1. motor type
  2. propellant
  3. case
 

mtnmanak

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OK, I added three columns to the XLS and CSV download:
  1. motor type
  2. propellant
  3. case
Awesome! I am building out charts for new rockets I plan to fly at the next MDRA launch - excellent timing, thanks!
 

JohnCoker

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what happened to the existing rockets archive?
Do you mean the list at the bottom of the guide page?

That got so long that it made the page slow to load, so I only show the most recent 10 and there is a search form to find more rockets. (Nothing has been deleted.)
 

JohnCoker

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Another column in the output file that would be useful is "Descent Weight" in order to more easily choose parachutes across the spectrum of motors.
Good idea; I've added a recovery weight column (second to last).
 

mtnmanak

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Good idea; I've added a recovery weight column (second to last).
John - you rock! great add to the spreadsheet.

At the risk of asking for too much, one more add and my workflow in TC would be complete - multiple rail lengths. This is something I always wished I could do in Rocksim as well.

Generally, I find the rails at most launches (out here on the East Coast anyway) are either 6 feet or 8 feet. Rarely, you may see a 10 foot rail and that is usually in the out-cell for Level 3 motors.

So, I have been running the sim twice - once with a 6 foot rail guide and then again with an 8 foot rail guide. Then I cut and paste the 6 foot velocities into the sheet with the 8 foot velocities in a separate column next to the 8 foot velocities. Then, I delete the motors that are slow off the 8 foot guide (you know if it is slow off the longer rail, it won't work on the shorter rail either). Then I use conditional formatting to color code the motors that are slow off the 6 foot rail.

At the field there are almost always more short rails than long ones, so it is good to know which rail length you need at a glance.

If there was a way to run the sim with 2 rail lengths and have the exported sheet note which rails were good, that would cut the above workflow down by about 75%.

For example, here is the spreadsheet I would use at the field for my Widman 4" Darkstar (note, I have not re-created it using the recovery weight column you just added):
 

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Buckeye

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At the risk of asking for too much, one more add and my workflow in TC would be complete - multiple rail lengths.
I agree with this. I constantly monkey with rail length on marginal motors. Instead of multiple rail lengths, print out the rod length required to achieve minimum velocity (currently hardcoded at 50 ft/s, but would be nice to make this a user setting).

I think I just described what RockSim does.
 

mtnmanak

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I flew a rocket this past weekend at MDRA and I saw some discrepancies in the Thrustcurve data when using a larger motor.

The rocket is a Wildman Darkstar 4" DD. Data for the rocket in TC is:

Diameter: 4"
Dry Weight: 5675g
Cd: 0.6

I flew the rocket this weekend on a Loki J-474, an Aerotech K-400 and an Aerotech L-1090.

For the J-474 and the K-400, the sims in TC and Rocksim were very close. The flight data from the altimeters was also very close to the sims.

For the L-1090, however, there was a great variance in the two sims.

TC simmed the bird out at an altitude of 7,432 feet reaching a velocity of 581 MPH
RS simmed it out reaching an altitude of 9475 feet reaching a velocity of 688 MPH

Actual flight data was 9400 feet reaching a velocity of 708 MPH.

Considering the two smaller motors were almost dead on in TC, is there an issue using larger motors? That is a large discrepancy. I used the RS data for the launch and it was well within the ceiling limits, but an over 2,000 foot discrepancy would have been a big issue at a different field if I had used the TC data.

The Rocksim file is attached.

Is there something in TC I need to change to get an accurate sim for the larger motor?
 

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JohnCoker

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Is there something in TC I need to change to get an accurate sim for the larger motor?
The simulator in ThrustCurve.org is very basic; it's just to get an idea of which motors will work for a rocket. I would trust a real simulator such as RockSim or OpenRocket if accuracy really matters.

Note that I do not intend to compete with the real simulators. The goal for the ThrustCurve.org motor guide is minimal inputs and quick simulations across many motors.
 

Buckeye

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Considering the two smaller motors were almost dead on in TC, is there an issue using larger motors? That is a large discrepancy.
The higher, faster, longer the rocket flight, the more the assumptions in TC break down. Things like constant CD, constant air density, etc. As John said, it is quick simulation. Consider that TC runs hundreds of simulations in a fraction of a second. Rocksim is solving more complicated equations and takes longer.

In this particular example, what is likely throwing off your TC calculation is the constant CD of 0.6. That drag is way too high, for way too long, and reducing the altitude by a lot.
 

mtnmanak

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The higher, faster, longer the rocket flight, the more the assumptions in TC break down. Things like constant CD, constant air density, etc. As John said, it is quick simulation. Consider that TC runs hundreds of simulations in a fraction of a second. Rocksim is solving more complicated equations and takes longer.

In this particular example, what is likely throwing off your TC calculation is the constant CD of 0.6. That drag is way too high, for way too long, and reducing the altitude by a lot.
I looked a little closer at the TC results and an interesting thing became apparent. The Loki motors at similar impulse levels were much closer to Rocksim than the AT motors. For example, the Loki L-1400 and L-1040 motors were within a 1000 feet of Rocksim results, but the AT motor discrepancies widened as the impulse increased. Not sure how to interpret those results, but it doesn't seem like Cd is the main discrepancy if one motor manufacturer's results are close but another manufacturer is off by as much as 30%.
 

Buckeye

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I looked a little closer at the TC results and an interesting thing became apparent. The Loki motors at similar impulse levels were much closer to Rocksim than the AT motors. For example, the Loki L-1400 and L-1040 motors were within a 1000 feet of Rocksim results, but the AT motor discrepancies widened as the impulse increased. Not sure how to interpret those results, but it doesn't seem like Cd is the main discrepancy if one motor manufacturer's results are close but another manufacturer is off by as much as 30%.
Yes, I forgot to mention that motor files are usually the biggest culprit. Are TC and RS using the exact same thrust vs. time points?
 

JohnCoker

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Yes, I forgot to mention that motor files are usually the biggest culprit. Are TC and RS using the exact same thrust vs. time points?
Another good point. TC uses the latest data it has in the DB and RockSim and OpenRocket use whatever you most recently downloaded (or what they came packaged with).
 

emckee

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Does TC have the capability to overlay thrust curves from different motors? If not, this is something that I'd be very interested in seeing!

If it does already, can someone point me in the direction of how to do it? :)

-e
 

JohnCoker

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If it does already, can someone point me in the direction of how to do it? :)
Yes it does. Most of the times when you have a table of results, it will have a final column that is a check mark. You can select all with the check in the header or individual motors with the checks in the row. Below the table will be a "Compare" link.

For example, here is a comparison of all CTI M motors with Classic propellant. I got this by going to search, entering those three criteria and executing the search. Then in the resulting table I clicked the checkbox in the header and then the Compare link below the table.
 

heada

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I noticed that the new Aerotech/Quest 18mm motors, which are designed to fit into the 18mmx70mm standard Estes motor mount and be direct replacements for standard Estes 18mm motors have the length listed as 81mm and not 70mm. I assume that is due to the ejection well which sits proud of the forward end of the motor and it's listed that way on the motor cert. I was going to ask if it was possible to have them listed as 70mm so it'll show up in the same group as standard 18mm motors but I'm conflicted about it since the ejection well is proud of the forward end of the case and there could be issues in some mounts/configurations.

What say you? Since it is designed to fit in 18mmx70mm, should it be in the same group as 18mmx70mm or should it be listed as it's true 18mmx81mm? This came about when searching for a motor to match a Big Bertha that was 4.9oz dry and I knew a C18W should work but I didn't see it until I made the max motor length 90mm.
 

JohnCoker

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What say you? Since it is designed to fit in 18mmx70mm, should it be in the same group as 18mmx70mm or should it be listed as it's true 18mmx81mm? This came about when searching for a motor to match a Big Bertha that was 4.9oz dry and I knew a C18W should work but I didn't see it until I made the max motor length 90mm.
Yes, I think there is a problem. The certification documents give the overall length, which isn't actually very useful. There are three possible lengths:
  • overall length
  • inserted length (not including nozzle or thrust ring)
  • length at nominal diameter (not including nozzle, thrust ring or forward well)
This is even worse because motors without a thrust ring actually must fit exactly in the MMT, while those with just need an MMT that's "long enough." Rockets that use a motor hook only work with motors that are Estes compatible (70mm at nominal diameter).

I'm not sure what the right fixes are actually, but open to suggestions.
 

heada

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I would think both options 1 and 3. Option 1 because that is the certified data point and there are use cases when you need to know the true length. Option 3 because that is the most often used data point.
 

Buckeye

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I noticed that the options for Temperature, Base Altitude, and Stable Velocity only appear sporadically. If I select a rocket via My Rockets on the right hand column, they usually appear. If I select a rocket via My Stuff > Rockets in the top menu bar, then those options usually do not appear.
 

JohnCoker

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I noticed that the options for Temperature, Base Altitude, and Stable Velocity only appear sporadically. If I select a rocket via My Rockets on the right hand column, they usually appear. If I select a rocket via My Stuff > Rockets in the top menu bar, then those options usually do not appear.
Ah, you're right that path (My Stuff | Rockets) doesn't have the options. There an extra form for the motor guide here, which is how it got out of sync. (There were some other options missing too, because I forgot about this path.) I've replaced this with just a link so it'll always direct you to the regular form now.
 
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