True enough, but numbers, and math, can be complex, part real and part imaginary.
Barrowman method tutorial
- Thread starter smstachwick
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I think I got it!
OR calculation:
My result:
I wasn’t sure how rounding early in the equations would affect the final outcome so I worked with everything on the highest precision available on my iPhone calculator, 16 digits. I’m 99.99999999999999% sure that was overkill, but it worked! And it only took 4 pages of work, plus some change.
Thanks to everyone who was patient enough to provide resources and explain it to me like I’m five. I learned quite a lot and made substantial gains in confidence.
OR calculation:
My result:
I wasn’t sure how rounding early in the equations would affect the final outcome so I worked with everything on the highest precision available on my iPhone calculator, 16 digits. I’m 99.99999999999999% sure that was overkill, but it worked! And it only took 4 pages of work, plus some change.
Thanks to everyone who was patient enough to provide resources and explain it to me like I’m five. I learned quite a lot and made substantial gains in confidence.
Statistics don't lie, but statisticians sometimes do. It's the human element.
Citizen Baslim
Wife: No, you're burning money vertically.
lakeroadster
When in doubt... build hell-for-stout!
Excellent! Thanks for posting this.
In Open Rocket I replicated the (3) rocket examples shown in the Centuri Technical Information Report #33 you posted.
These can be used as verification for the software, to ensure it is accurately calculating CP.
I decided to revisit this with a more complex rocket, with a conical transition and two tube diameters. I went at it with only with pencil and paper, using a calculator only to double-check myself and only proceeding once I’d calculated the correct answer manually. I ended up learning to pull square roots through long division especially for this project, so that was a challenging learning experience.
I’m glad I did, though. I’m starting work with a new client pretty soon who’s having trouble keeping control of his temper in his math classes. Confirming that I can learn a new skill in a dense subject matter puts my mind at ease regarding my own performance on the case, and this kind of math may end up being a good exercise for us to work on skills in collaboration, seeking guidance, recognizing the need to take a break for a bit, tolerating failure gracefully, etc.
Rocketry and aerospace stuff is right up his alley too, so that might be helpful.
I’m glad I did, though. I’m starting work with a new client pretty soon who’s having trouble keeping control of his temper in his math classes. Confirming that I can learn a new skill in a dense subject matter puts my mind at ease regarding my own performance on the case, and this kind of math may end up being a good exercise for us to work on skills in collaboration, seeking guidance, recognizing the need to take a break for a bit, tolerating failure gracefully, etc.
Rocketry and aerospace stuff is right up his alley too, so that might be helpful.
Last edited:
Bruce Lee's simplified technique allowed his 10-year old son to do the Barrowman equations easily ( see attached )
Dave F.
Attachments
lakeroadster
When in doubt... build hell-for-stout!
Any idea when this was written? Reminds me of the forms we used to design pressure vessels back in the early 1980's.
1995, I think . . .
I might have to try this.
It may have already been mentioned but there are some excel files online where all you do is fill in the blanks and it will do the calculations for you using the classic Barrowman equations.
Our old club president, an Aerospace Engineer from a prestigious East Coast University, loved getting out the pencil and paper to do his Barrowmans. Then an oddroc scum, Liberal Arts, Political Science/History major shows up with this abomination claiming he "Mindsimed" it!
The horror!
DO THE MATH!
The horror!
DO THE MATH!
I was wondering if you would show up here
In truth, I think I’ve got the basic equations down. The more complex design I ran spit out a CP at 482.75mm, against 484 in OpenRocket. I suspect that that’s within the range of rounding errors, especially since I was just dropping the third digit beyond the decimal instead of truly rounding.
I’d be very interested in trying Bruce Lee’s version and digging up a spreadsheet, that sounds like it’d be more tolerable than doing 9 pages of math.
lakeroadster
When in doubt... build hell-for-stout!
I'm really surprised Bruce wasn't doing these in Excel by then?
That's great! I am going to use your "Range of rounding error" statement next time the old President is around. And saying: "I love Bruce's Lee's marshal arts methods" would probably help as well. Pad assignments, here I come! YIPPEE!I was wondering if you would show up here
In truth, I think I’ve got the basic equations down. The more complex design I ran spit out a CP at 482.75mm, against 484 in OpenRocket. I suspect that that’s within the range of rounding errors, especially since I was just dropping the third digit beyond the decimal instead of truly rounding.
I’d be very interested in trying Bruce Lee’s version and digging up a spreadsheet, that sounds like it’d be more tolerable than doing 9 pages of math.
But really, it would take a bribe of buying him a beer off of Michael Jackson's THE BEER HUNTER' S favorite list to get an assignment on the far far away pads.
Do the math and show your work, or start drinking heavily?
Singing: "Let's go down to the Delta House!"
Bulto will never give up!
Just to double-check my theory that the discrepancy was the result of a rounding error, I went through the calculations again, just with an additional decimal point in of precision. The result: 482.575mm, just slightly farther from where OR calculated it.
Puzzled, I pulled up the Component Analysis and found that all of my subtotals matched, aside from my Coefficient for the fin set [variable (CN)F]. I came up with 5.761, OR displayed 5.85 I double-checked my math, I didn't see mistakes anywhere. It added up as best as I could tell. Then I noticed the Mach number slider was set to Mach 0.3, as is default. Just on a hunch, I reset it to 0, in keeping with assumption of low Mach number that's fundamental to the equation. BAM! (CN)F immediately recalculated to 5.76 and CP recalculated to 482mm, matching my result.
Time for me to move onto something else then, I think. Maybe take a lesson from Mr. Lee....
Puzzled, I pulled up the Component Analysis and found that all of my subtotals matched, aside from my Coefficient for the fin set [variable (CN)F]. I came up with 5.761, OR displayed 5.85 I double-checked my math, I didn't see mistakes anywhere. It added up as best as I could tell. Then I noticed the Mach number slider was set to Mach 0.3, as is default. Just on a hunch, I reset it to 0, in keeping with assumption of low Mach number that's fundamental to the equation. BAM! (CN)F immediately recalculated to 5.76 and CP recalculated to 482mm, matching my result.
Time for me to move onto something else then, I think. Maybe take a lesson from Mr. Lee....
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