Greg Gleason's ChartEng utility for Motors

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GregGleason

GregGleason

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These Excel files (*.xlsm format) are designed to import into Excel. It allows for comparative viewing between motors, both in data and graphical terms.

The .eng files you want to import must reside in the same folder that the Excel files.

The two files are just for organizational convenience.

You can copy the file and make it for other motor sizes, vendors, etc. The key is the formatting of the .eng files. They need to be consistent. The 29mm motor spreadsheet has an example .eng file included.

As far as I know, the algorithms are correct, per the information at ThrustCurve.org.

The best part, it's free. My part in paying it forward.

Enjoy.

Greg

View attachment ChartEng18and24Ver22.zip

View attachment ChartEng29Ver22.zip
 
I took a quick look at a couple of the graphs. Everything looks pretty close to the standard way NAR S&T calculates the specs. The only thing I see different is the "percent motor class" calculation. It should be the percent of the difference of the total impulse and not the absolute total impulse. In other words, an F would be what percent it is between 40 and 80 N-secs, not what percent it is of 80 N-secs. So, a 60 N-sec motor would be a 50% F and not a 75% F.

You can compare with the calcs I do within my Thrust Curve Tool program. This is what S&T uses.

-John
 
So the formula for % Impulse Classes is:

% Impulse = (Motor Impulse-Class Minimum)/(Class Maximum-Class Maximum)

For John's example, the F motor impulse is 60 Ns, the F class minimum is 40 Ns, and the F class maximum is 80 Ns.

% Impulse = (60-40)/(80-40) = 20/40 = 50% F

Bob
 
Yikes!

What a rookie mistake. :blush:

Thanks John and Bob.

I'll see if I can get version 2.3 out, soon!

Greg
 
Also, the rated total impulse is the area under the curve from the 5% of peak start-up point to the end of the tail of the burn. It doesn't include the portion from start-up to the 5% point. It shouldn't make a difference unless it's a slow start-up motor. But, this is the way NFPA1125 defines it.

The average thrust is the total impulse between 5% points divided by the burn time (the time between 5% points).

I assume you're doing a linear interpolation between sample points and not just taking the closest sample point to the 5% of peak.

-John
 
jsdemar said:
Also, the rated total impulse is the area under the curve from the 5% of peak start-up point to the end of the tail of the burn. It doesn't include the portion from start-up to the 5% point. It shouldn't make a difference unless it's a slow start-up motor. But, this is the way NFPA1125 defines it.

The average thrust is the total impulse between 5% points divided by the burn time (the time between 5% points).

I assume you're doing a linear interpolation between sample points and not just taking the closest sample point to the 5% of peak.

-John
Click to expand...

John,

Just for clarification:


  • The 5% is 5% of the peak or max thrust of the motor burn
  • The burn time is the time of burn, less the 5% head and tail
  • Total impulse includes the 5% head and tail (total thrust curve)
  • Average thrust is the thrust between the head and tail, divided by burn time

Is this correct?

I checked the algorithm and I am using linear interpolation to get the 5% marks (that was a pain to code). But I don't think I was calculating the average thrust correctly. I took the total thrust and divided it by the burn time, which appears to be not in line with the definitions of NFPA 1125. I will need to address that into the next release.

Greg
 
GregGleason said:
John,

Just for clarification:


  • The 5% is 5% of the peak or max thrust of the motor burn
  • The burn time is the time of burn, less the 5% head and tail
  • Total impulse includes the 5% head and tail (total thrust curve)
  • Average thrust is the thrust between the head and tail, divided by burn time

Is this correct?
Click to expand...

All correct except that the total impulse skips the 5% head area, but includes the tail area.

-John
 
Hi,

jsdemar said:
All correct except that the total impulse skips the 5% head area, but includes the tail area.
Click to expand...

That's contrary to what's reported on ThrustCurve.org:

Based on NFPA 1125:

* The burn time is from 5% of peak thrust, at both the beginning and end of the curve.
* Average thrust is the total impulse during the 5%-defined burn time, divided by the burn time.
* The total impulse is measured over the whole thrust curve (not the 5%-defined burn time).
Click to expand...

This is from the very bottom of https://www.thrustcurve.org/motorstats.shtml

Which one is correct? Does someone have NFPA 1125 available at hand for an authoritative source?

Regards,
Sampo N.
 
Sampo said:
Hi,

That's contrary to what's reported on ThrustCurve.org:

This is from the very bottom of https://www.thrustcurve.org/motorstats.shtml

Which one is correct? Does someone have NFPA 1125 available at hand for an authoritative source?
Click to expand...

The note at the bottom of that thrustcurve.org page was from an email I sent to John Coker a few years ago. For almost all thrust curves, the beginning impulse (before the 5% point) is extremely small and won't make a difference. But if the startup is slow, it's measureable. NFPA says to ignore it, so that's how I've implemented my Thrust Curve Tool software.

Here's what NFPA 1125 says:
7.8.5 Total impulse shall be measured between the point
when the thrust rises to 5 percent of the motor’s peak thrust to
the point of last measurable thrust prior to ejection or blow
through, or, if it is a plugged motor, to the point where all
action has ceased.​

-John
 
Sampo said:
Hi,



That's contrary to what's reported on ThrustCurve.org:



This is from the very bottom of https://www.thrustcurve.org/motorstats.shtml

Which one is correct? Does someone have NFPA 1125 available at hand for an authoritative source?

Regards,
Sampo N.
Click to expand...
John D is correct. ThrustCurve.org is wrong.

Goto https://www.nfpa.org and read NFPA 1122, 1125 and 1127 or go to https://nar.org/SandT/docs/ST-MotorTestingManual.pdf and download the S&T Motor Testing Manual which is based on the above Codes.

IRC ThrustCurve also has the incorrect formula for calculating % Class impulse which should be (TI act. - TI class min)/(TI class max -TI class min)

Bob
 
bobkrech said:
John D is correct. ThrustCurve.org is wrong.

Goto https://www.nfpa.org and read NFPA 1122, 1125 and 1127 or go to https://nar.org/SandT/docs/ST-MotorTestingManual.pdf and download the S&T Motor Testing Manual which is based on the above Codes.

IRC ThrustCurve also has the incorrect formula for calculating % Class impulse which should be (TI act. - TI class min)/(TI class max -TI class min)

Bob
Click to expand...

Bob,

Thanks for posting the link to the S&T Motor Testing Manual. A cursory read of that document tells me the fine folks that perform those tasks are a critical link in hobby rocketry. They help to keep it safe, reliable, and credible.

Greg
 
GregGleason said:
Thanks for posting the link to the S&T Motor Testing Manual. A cursory read of that document tells me the fine folks that perform those tasks are a critical link in hobby rocketry. They help to keep it safe, reliable, and credible.
Click to expand...

Yep, S&T and TMT both have very critical jobs. And talking with folks who've done the testing, it might be fun the first time, but it gets tedious, quickly.

Imagine getting 10 distinct motors from a manufacturer. I believe both organizations do three firings of each motor. That means 30 motors to assemble, put on the stand, and clean afterwards.

Bleah.

-Kevin
 
powderburner said:
Greg,

I don't know if you have seen Excel used for 'drawing' these sorts of pix, but here is an old thread with an example of the process

https://www.rocketryforumarchive.com/showthread.php?threadid=2175

PM me if you want a little help figuring it out
Click to expand...

Thank you for the kind offer. Currently I have access to a number of CAD tools so that help my design work. Sometimes I use both Excel and CAD to help with designs, such as running the calculations to come up with a von Karman nose cone design.

Greg

NoseConeSmallVK_Final.jpg
 
Greg, this is a very nice tool. Thanks for making it available to everyone. The comparison charts are very nice. In fact, what originally made me ask about the tool was a comparison chart you posted on the D12 vs E9 thread. In that thread, another member mentioned I might want to consider the Estes E12, so that is one of the engines I was hoping to compare with your tool. I don't see a sheet for that one, and I was wondering if you have one. If not, don't worry, I've seen the curve for the E12. I can do a stare-and-compare. It's just nice to see the curves plotted together on the same chart.

Thanks again for making this tool available!
 
ThirstyBarbarian said:
Greg, this is a very nice tool. Thanks for making it available to everyone. The comparison charts are very nice. In fact, what originally made me ask about the tool was a comparison chart you posted on the D12 vs E9 thread. In that thread, another member mentioned I might want to consider the Estes E12, so that is one of the engines I was hoping to compare with your tool. I don't see a sheet for that one, and I was wondering if you have one. If not, don't worry, I've seen the curve for the E12. I can do a stare-and-compare. It's just nice to see the curves plotted together on the same chart.

Thanks again for making this tool available!
Click to expand...

You are welcome.

You can import the E12 curve. Just have an .eng file with the E12 data in it in the same folder as the Excel file. Then launch the import tool.

Greg

View attachment Estes.E12.eng
 
Great tool Greg. Could you create a how to tab for those of us that aren't very good with Excel on how to import .eng files and how to use the various parts of the tool. I tried to import the Este.E12.eng file but the vendor name says "Not Found" maybe I did something wrong.

Thanks,
 
davdue said:
Great tool Greg. Could you create a how to tab for those of us that aren't very good with Excel on how to import .eng files and how to use the various parts of the tool. I tried to import the Este.E12.eng file but the vendor name says "Not Found" maybe I did something wrong.

Thanks,
Click to expand...

You're welcome.

There was a "bug", that is now fixed.

Also, I added a tab with a "How To" that will walk you through the motor adding process (a great suggestion, BTW).

Unfortunately, the "How To" feature has made the new file size 200KB too large for the forum. :( So I can't upload it here anymore.

Time to figure out "Plan B".

Greg
 
I'm not sure I understand exactly how it is supposed to work. I have the two files in the same folder. I'm assuming that the import function is started by the "Add Motor" button. When I click it is get "Runtime Error 68: Device Unavailable"
 
ThirstyBarbarian said:
I'm not sure I understand exactly how it is supposed to work. I have the two files in the same folder. I'm assuming that the import function is started by the "Add Motor" button. When I click it is get "Runtime Error 68: Device Unavailable"
Click to expand...

Follow the process in the "How To" file, and see if that helps.

Greg
 
Also, if someone could let me know if the 2.5 fix works or not.

One way to tell if you have the latest file is by looking in the "Vendor" tab, you should see an "Estes"/"Estes" row.

Greg
 

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