Help making sugar rocket (and maybe BP) motor calculations

[JMan]

Hi all. (This might be a post for chemistry, let me know). I know I haven't posted in a while but thats due to university. However, for one of my university final projects I am making an amature rocket motor calculator that is able to take into account fuel types (different sugars and possibly BP) and take various inputs such as basic grain dimensions or performance parameters and give you the other. It will then store all of the motors you make as a list and allow you to look back and potentially help optimize previous rockets.

 

That being said, the calculations are not important to my grade, what is important is how error ridden, user friendly, and well the code deals with numbers. So I would like some help with the best way to do basic calculations on a sugar rocket. I was thinking that there is two main ways to measure a rocket motor: dimensions and performance parameters. Dimensions being nozzle (yes or no) nozzle diameter, core diameter, grain diameter, grain length, and fuel type. Performance parameters being take off TTW, total impulse, and fuel type (maybe specific impulse too). (this could be much more detailed, and might need to be much more detailed but this is why I come here to ask)

 

A third and not very hard input would be importing data from a thrust stand (which I do not need much help with if I find out the other calculations).

 

(Just a side note I might not include the ends of the grain, only the cores, as burnable surfaces. That will change depending on how much time I have because it requires using calculus and related rates unless I use very small sample points which I would not like to do)

 

For Dimensions I plan on finding the surface area of the core and the web thickness to determine the takeoff TTW, burn time, and impulse. Maybe specific impulse and pressure will probably be needed anyways. (How would one actually calculate these, I know it has to do with fuel density and exhaust density)

 

For performance parameters I plan on matching the takeoff TTW which will find the core diameter and grain length and then the total impulse will help me find the web thickness. (again what calculations would get me to this?)

 

And a side note, I'll definitely be posting this after I get my grade (don't want plagiarism bots to flag me although I want you guys to get it asap)

[Ferret]

Have you heard of Burnsim?

 

http://burnsim.com/

[JMan]

I have not ferrit. Thank you very much, I'll check it out however I doubt my program will go into that much detail. I'm sure I'll be able to use most (if any) of the calculations I find in there.

 

Update, didn't have much time on it yet but I've already ran into errors with user handeling, coding, and ambiguity. Don't get me wrong it seems wonderful and accurate but I'm making this code for people like me: small backyard amature rocketeers not incredibly involved individules or groups. The code is very much black boxed so finding calculations is hard but it did point me to PROPEP and TCLogger so I'm looking into them.

 

EDIT: I was pointed to this, mildly helpful as it was what I was assuming but good to be reaffirmed.

 

http://aeroconsystems.com/tips/Sugar%20Propellant%20Motor%20Design.pdf

Edited March 24, 2019 by JMan

[stix]

So what programming application will you be using - a Database?

 

FWIW, I built something along similar lines for my own experimental purposes. It's a bit complicated, but it did take the drudgery out of doing manual calculations:

 

MAIN SCREEN:

 

FUEL LOADING & GRAIN CONFIGURATION SCREEN:

 

 

Also, as you have suggested you can work some details back the other way from test stand data:

 

 

These are two separate applications. It would be nice to have it all together in the one app. In the database app (the first 2 images) there is probably too much information and a lot of it not required to be shown. I left it there so I could double-check that the math was correct using a hand calculator.

 

Hope this is of some use.

 

Cheers.

[JMan]

The programming language itself is MATLAB, expandable/editable data bases (as excell files). And yes that is a lot of data but Id like to know how you actually got those numbers. What equations did you end up using to go from dimensions to thrust? Kn is pretty easy. And are you assuming burntime is standard or does the user input that?

[Arthur]

All of the maths is reasonably simple, the formulae are well enough known, it may be hard to prove what is your own original work as many unis use pretty good plagiarism bots.

Showing that you have done literature and web research, pushed the science forward, and coded that would possibly be original enough -ask your tutor or assessor before you go too far.

[JMan]

Although I apprecieate your concern Arthur, I have no worries about this. I understand I may still be flagged due to hits such as saying the language and its purpose and espicaly if someone does tell me a calculation I can use and I put it in. However:

 

1st My grade is not dependent on how well I calculate this, rather how I handle data bases and minuplate variables and functions

 

2nd My teacher knows me well. Shes seen my code before and has confirmed what I said previsouly and that I can get help as long as I put where I got help from (aka this board)

 

3rd I am able to show proof that none of what I have discussed is out of conduct with my schools policy.

 

But I do understand your concern and I will defiantly ask my prof before I continue on this board just to double check.

[Arthur]

It's almost impossible to find a truly new topic of study, do lots of web and literature research first then see where you can push the science forward. List your research results with proper references and state clearly what is your own original work. Your mark should depend on your original work.

[starxplor]

The programming language itself is MATLAB, expandable/editable data bases (as excell files). And yes that is a lot of data but Id like to know how you actually got those numbers. What equations did you end up using to go from dimensions to thrust? Kn is pretty easy. And are you assuming burntime is standard or does the user input that?

 

Ahh, Matlab... brings back memories of uni... literally 20 years ago now!!!

 

I wish I had been so in to pyro back then to include it in my school projects.

 

Good luck with this project!

[stix]

The programming language itself is MATLAB, expandable/editable data bases (as excell files). And yes that is a lot of data but Id like to know how you actually got those numbers. What equations did you end up using to go from dimensions to thrust? Kn is pretty easy. And are you assuming burntime is standard or does the user input that?

 

I didn't use equations to go from dimensions to thrust. The image showing the thrust performance graph was an actual test using a test stand. I think burnsim (as suggested) can give you that sort of detail, but there are a lot of things you need to know first.

 

The burn-time was determined via testing 3 motors using the same grain configuration, nozzle and fuel type then getting an average.

 

The purpose of what I did was to have a simple database record of previous tests and then be in a position to compare, evaluate and decide what to do next. Also the built in calculations makes it much easier.

 

Cheers.