Open Rocket Math

[Lt72884]

I am curious to know if a PDF exists of all the equations OR uses to do the calculations of CP, CG, stability, apogee, velocity, thrust, burn out time etc etc.

i want to print it off and keep it as a reference sheet and pass them out to my team.
IE, we would like to do some of our own calculations for altitude based on a specific N-S motor, mass of rocket, CD of rocket etc. Just to have them in our notes, presentations and assignments.

thanks

 

[UhClem]

The documentation includes some of those but there is no closed form equation for apogee, burn out time, etc. Those require numerical simulation which is why you have OpenRocket.

 

[Lt72884]

The documentation includes some of those but there is no closed form equation for apogee, burn out time, etc. Those require numerical simulation which is why you have OpenRocket.

so how does OR numerically get the values for apogee and burn out time?

i will look in the documentation as well for those you speak of.

thanks

 

[Charles_McG]

‘Use the Source, Luke”

I -think- the person credited first on the splash screen published the background development as a thesis paper. If I’m not wrong , you could search for that, too.

 

[Lt72884]

‘Use the Source, Luke”

I -think- the person credited first on the splash screen published the background development as a thesis paper. If I’m not wrong , you could search for that, too.

OHH, yeah, my version of OR does not have a splash screen, it just opens. I will get beta version since i know that has a splash screen because i saw it in a youtube video or something

thanks. ill search this up too

 

[UhClem]

so how does OR numerically get the values for apogee and burn out time?

Trivial for an engineering student. For some value of trivial.

You could always dig up an early version of RASP. The BASIC listing for RASP-93 is in my copy of the Handbook of Model Rocketry. Simple non-graphical interface.

 

[Lt72884]

Trivial for an engineering student. For some value of trivial.

You could always dig up an early version of RASP. The BASIC listing for RASP-93 is in my copy of the Handbook of Model Rocketry. Simple non-graphical interface.

Lol, i feel you on that. Though i did like my numerical methods class.

Ok, ill look at your hand book as well as search for RASP-93 on google and see what comes up. One thing i have had for a while is this PDF

http://www.rocketmime.com/rockets/RocketEquations.pdf
and i have this link as well

https://en.wikiversity.org/wiki/PlanetPhysics/Single_Stage_Rocket_Burnout_Height

 

[JoePfeiffer]

so how does OR numerically get the values for apogee and burn out time?

i will look in the documentation as well for those you speak of.

thanks

The motor thrust is a lookup table driver from test stand data. Burnout time is when the thrust reaches 0.

Flight dynamics use a fourth order Runge-Kutta approximation.

 

[Off Grid Gecko]

I've done spreadsheets using sectional density and a rough approximation to make a table of values.
It's a dynamic equation. If you want to do all the DiffEq to make it work that's on you, but when I'm trying to get rough figures I'll smash out a spreadsheet real quick, put in my coefficients and then let it populate. Takes about an hour or so to get a hacked together spreadsheet working where each line is dependent on the values in the last and set the time increment to .1 or .05s.

I had one a long time ago where I was even calculating the drag based on some old approximation method that I found somewhere on the internet for making 3 or 4 fin designs and running flight calcs in OpenOffice for simple nosecone/body-tube/fins designs and placed the weight inside. It would calculate center of drag as well but it would not use that in the flight projection. Just kind of "assume the rocket is flightworthy" kind of thing.

TBH, OR works just fine and you can extract all the simulated flight data directly from the program, or a graph (people love charts and graphs in presentations more than stacks of paper with tiny numbers on them).

I think there's a program called FAR you might be able to get on discount as a student (not sure) that does all kind of fluid modeling as well and is much more academic in nature. I don't remember the exact name of the program or where you can get it from, but there are advanced modeling tools out ther.

 

[Lt72884]

The motor thrust is a lookup table driver from test stand data. Burnout time is when the thrust reaches 0.

Flight dynamics use a fourth order Runge-Kutta approximation.

ok, that makes sense. i just did a runge-kutta assignment in excell a couple of weeks ago. very interesting math

 

[Lt72884]

I've done spreadsheets using sectional density and a rough approximation to make a table of values.
It's a dynamic equation. If you want to do all the DiffEq to make it work that's on you, but when I'm trying to get rough figures I'll smash out a spreadsheet real quick, put in my coefficients and then let it populate. Takes about an hour or so to get a hacked together spreadsheet working where each line is dependent on the values in the last and set the time increment to .1 or .05s.

I had one a long time ago where I was even calculating the drag based on some old approximation method that I found somewhere on the internet for making 3 or 4 fin designs and running flight calcs in OpenOffice for simple nosecone/body-tube/fins designs and placed the weight inside. It would calculate center of drag as well but it would not use that in the flight projection. Just kind of "assume the rocket is flightworthy" kind of thing.

TBH, OR works just fine and you can extract all the simulated flight data directly from the program, or a graph (people love charts and graphs in presentations more than stacks of paper with tiny numbers on them).

I think there's a program called FAR you might be able to get on discount as a student (not sure) that does all kind of fluid modeling as well and is much more academic in nature. I don't remember the exact name of the program or where you can get it from, but there are advanced modeling tools out ther.

oh, i know OR works fine. I LOVE IT!! i personally like to do the math by hand to help solidify my understnading of how things work. There is something about doing it yourself at least once before using a software package, that really helps nail in the science of it.

I have found some equations that i might start using in excel to do some basic tests with.

 

[Off Grid Gecko]

oh, i know OR works fine. I LOVE IT!! i personally like to do the math by hand to help solidify my understnading of how things work. There is something about doing it yourself at least once before using a software package, that really helps nail in the science of it.

I have found some equations that i might start using in excel to do some basic tests with.

I'm pretty sure (though not 100% cetain) that OR is "simming" the data through an iterative step interval as well. It's just easy. You have thrust, vel, drag, etc right. That works out to a force acting on the rocket. Follow that force for a given dt, and all of those numbers are going to change. drag depends on altitude and vel, thrust data can be gotten for most motors, velocity changes from the boost, et all.
So unless you just love figuring out partial differential equations, the iterative approach is best. I think most of these modeling softwares iterate because it just becomes to messy of an equation to solve in closed form. Especially when you take into account that thrust curves are plug-n-play data. But even if you model it for a flat thrust curve, there's still a LOT of other pieces to worry about.
Personally I would not attempt to solve it in closed form because it would probably mean simplifying a lot of stuff that the iterative approach let's you modify. With an iterative excell sheet you can always add in motor burn profiles, altitude density maps, account for barometric pressure, etc. At .1s it's going to be as close as you will likely get to reality, but .02-.05s makes a smoother data table.

 

[Lt72884]

I'm pretty sure (though not 100% cetain) that OR is "simming" the data through an iterative step interval as well. It's just easy. You have thrust, vel, drag, etc right. That works out to a force acting on the rocket. Follow that force for a given dt, and all of those numbers are going to change. drag depends on altitude and vel, thrust data can be gotten for most motors, velocity changes from the boost, et all.
So unless you just love figuring out partial differential equations, the iterative approach is best. I think most of these modeling softwares iterate because it just becomes to messy of an equation to solve in closed form. Especially when you take into account that thrust curves are plug-n-play data. But even if you model it for a flat thrust curve, there's still a LOT of other pieces to worry about.
Personally I would not attempt to solve it in closed form because it would probably mean simplifying a lot of stuff that the iterative approach let's you modify. With an iterative excell sheet you can always add in motor burn profiles, altitude density maps, account for barometric pressure, etc. At .1s it's going to be as close as you will likely get to reality, but .02-.05s makes a smoother data table.

So this is where the runge kuta comes into play then? or which iterative excel sheet do you recomend? i know a few methods from my numerical class, but i am not a software engineer at all or even close to it.

 

[Off Grid Gecko]

So this is where the runge kuta comes into play then? or which iterative excel sheet do you recomend? i know a few methods from my numerical class, but i am not a software engineer at all or even close to it.

When I did it I just made an excel spreadsheet and copied the various equation lines down like 400-500 rows to give me enough room to play with it. If you aren't good with excel or OpenOffice Calc then it might not be the best solution I guess. I also have been known to use Godot Game Engine to do some number crunching for me but as you said you aren't a software engineer so that's maybe not the best bet.

Lemme dig up a simple one I made just to play around with some water rocket figures one night. It was late so there's prolly some stuff a little bonkers on here but my numbers were matching what I was seeing on YT vids (those guys are totally doing this wrong, lol).

... aparently spreadsheet format isn't acceptable,, let's try screenshot

 

[Off Grid Gecko]

When I did it I just made an excel spreadsheet and copied the various equation lines down like 400-500 rows to give me enough room to play with it. If you aren't good with excel or OpenOffice Calc then it might not be the best solution I guess. I also have been known to use Godot Game Engine to do some number crunching for me but as you said you aren't a software engineer so that's maybe not the best bet.

Lemme dig up a simple one I made just to play around with some water rocket figures one night. It was late so there's prolly some stuff a little bonkers on here but my numbers were matching what I was seeing on YT vids (those guys are totally doing this wrong, lol).

... aparently spreadsheet format isn't acceptable,, let's try screenshot

Maybe make friends with someone studying finance or office stuff at your school

 

[smstachwick]

Stability specifically can be pretty simple. Rocket CP can be calculated using a set of algebraic formulas conceived by James Barrowman, called the Barrowman method. It calculates the locations and relative strengths of aerodynamic forces acting on the rocket’s nose, fins, and conical transitions at subsonic speeds and low angles of attack. The equations are accessible enough to plug in measurements of your rocket’s basic dimensions and simplify/compute mostly by hand. Depending on how you measure or compute your fin mid-chord line value, you may have as little as one square root calculation to make and the rest is doable without even a calculator.

My thread on learning Barrowman’s method is here:

Thread 'Barrowman method tutorial'
https://www.rocketryforum.com/threads/barrowman-method-tutorial.171556/

The equations can be found here:

http://www.rocketmime.com/rockets/Barrowman.html

 

[SolarYellow]

I am curious to know if a PDF exists of all the equations OR uses to do the calculations of CP, CG, stability, apogee, velocity, thrust, burn out time etc etc.

i want to print it off and keep it as a reference sheet and pass them out to my team.
IE, we would like to do some of our own calculations for altitude based on a specific N-S motor, mass of rocket, CD of rocket etc. Just to have them in our notes, presentations and assignments.

thanks

Didn't see anyone mention it yet. Yes, there is a white paper which I believe details the basis for all the calculations. It's easily findable. I'm intentionally not providing a link because you have multiple threads asking about very, very basic things that you'd easily and quickly find the answers to if you actually went and searched rather than starting a thread asking people to spoon feed them to you.

 

[Lt72884]

Didn't see anyone mention it yet. Yes, there is a white paper which I believe details the basis for all the calculations. It's easily findable. I'm intentionally not providing a link because you have multiple threads asking about very, very basic things that you'd easily and quickly find the answers to if you actually went and searched rather than starting a thread asking people to spoon feed them to you.

, does this white paper have a name? or is it just white paper open rocket which is really vague.
edit: i have found about 5 different white papers from 5 different people when searching for whitepaper open rocket calculations. whats the specific one you are thinking of?

tahnks

 

[krislhull]

By you stating "asking people to spoon feed you" pretty much invalidated everyone who actually answered my questions. You basically insulted them for helping me out

so moving on, does this white paper have a name? or is it just white paper open rocket which is really vague.

Uh, you might want to rethink what you just said. He did not insult anyone who has helped you out at all. Have you tried using the search function of the forum to see if you can find answers that way? The people on this forum are extremely open, but we also are asked the same questions multiple times on a very regular basis. When one of the previous posters above mentioned that you can search for the mentioned thesis paper, did you actually spend some time searching? I actually found a link to said white paper in less than 30 seconds of searching on this forum.

 

[Lt72884]

Uh, you might want to rethink what you just said. He did not insult anyone who has helped you out at all. Have you tried using the search function of the forum to see if you can find answers that way? The people on this forum are extremely open, but we also are asked the same questions multiple times on a very regular basis. When one of the previous posters above mentioned that you can search for the mentioned thesis paper, did you actually spend some time searching? I actually found a link to said white paper in less than 30 seconds of searching on this forum.

i know your asked alot of questions over and over, and yes, i have searched for alot of stuff that i have not even asked. I have about 13 tabs open from this forum, from exporting fin templates, scaling for pdf printing, etc etc.

"i actually found a link to said whitepaper in less..." i found 5 white papers on different calculations from 5 different people on google, so which one is it that im looking for? im not familiar with ANY of the authors of OR like you guys are, so the white paper from so and so, is that an actual author or developer of OR?? thats what i dont know. Searching for a white paper is easy as hell, its knowing WHICH one is the correct one, that is the question.

 

[Lt72884]

When I did it I just made an excel spreadsheet and copied the various equation lines down like 400-500 rows to give me enough room to play with it. If you aren't good with excel or OpenOffice Calc then it might not be the best solution I guess. I also have been known to use Godot Game Engine to do some number crunching for me but as you said you aren't a software engineer so that's maybe not the best bet.

Lemme dig up a simple one I made just to play around with some water rocket figures one night. It was late so there's prolly some stuff a little bonkers on here but my numbers were matching what I was seeing on YT vids (those guys are totally doing this wrong, lol).

... aparently spreadsheet format isn't acceptable,, let's try screenshot

I like this. im gonna download this and just mess around with it. thanks for posting this. It helps me see how it all works

 

[Lt72884]

Stability specifically can be pretty simple. Rocket CP can be calculated using a set of algebraic formulas conceived by James Barrowman, called the Barrowman method. It calculates the locations and relative strengths of aerodynamic forces acting on the rocket’s nose, fins, and conical transitions at subsonic speeds and low angles of attack. The equations are accessible enough to plug in measurements of your rocket’s basic dimensions and simplify/compute mostly by hand. Depending on how you measure or compute your fin mid-chord line value, you may have as little as one square root calculation to make and the rest is doable without even a calculator.

My thread on learning Barrowman’s method is here:

Thread 'Barrowman method tutorial'
https://www.rocketryforum.com/threads/barrowman-method-tutorial.171556/

The equations can be found here:

http://www.rocketmime.com/rockets/Barrowman.html

Now this is awesome. I would have NEVER guessed to search for this person i have never heard of. Thanks for the link

 

[Lt72884]

about 7 years ago in my statics class, i THINK we went over some of these equations, they look kind of familiar.

 

[Lt72884]

Ok, doing a search on the forums did not yield any results i was looking for. I searched for the following:

open rocket math whitepaper
open rocket equations whitepaper
open rocket whitepaper
open rocket equations
equations used for open rocket

the first 3 only yielded one result.. my thread
the other 2 yielded results but nothing of what im looking for. Some white papers from nasa, a thread labeled mcdonalds, and a ton of other threads about a V2,

i do not need the link, just a name of one of the authors for said white paper please.

i do have the barrowman equations now from someone's suggestion and i do have the book by stein.

thanks

 

[Charles_McG]

Ok, doing a search on the forums did not yield any results i was looking for. I searched for the following:

open rocket math whitepaper
open rocket equations whitepaper
open rocket whitepaper
open rocket equations
equations used for open rocket

the first 3 only yielded one result.. my thread
the other 2 yielded results but nothing of what im looking for. Some white papers from nasa, a thread labeled mcdonalds, and a ton of other threads about a V2,

i do not need the link, just a name of one of the authors for said white paper please.

i do have the barrowman equations now from someone's suggestion and i do have the book by stein.

thanks

https://lmgtfy.app/?q=openrocket+thesis

 

[kalsow]

How about going to the OpenRocket web site?? https://openrocket.info/documentation.html

 

[Lt72884]

https://lmgtfy.app/?q=openrocket+thesis

So its a thesis, not a white paper? that would have been nice to know from the beginning since that changes the search results

when using google to search openrocket thesis i find a paper from Helsinki. I will see if this is the one you are all talking about. When i google open rocekt whitepaper, this pdf from helsinki does not show up.

thanks
EDIT: Post number 4 states to search for a THESIS paper. I even replied to said post. I take 100% accountability for forgetting about that post. Thanks for pointing this out Charles

 

[tsmith1315]

Perhaps look for the developer, not the program.

 

[Charles_McG]

And don’t put a space between open and rocket.

 

[Charles_McG]

‘Use the Source, Luke”

I -think- the person credited first on the splash screen published the background development as a thesis paper. If I’m not wrong , you could search for that, too.

Look - post number 4.

But the above documentation link, which is in the Help:About screen of OpenRocket is the same paper.

My wife and sons aren’t very good at online searches, either.