Basic Simulation Project to get started with a Solid Propellant Rocket

[Vicknesh]

Hello all, I am very new to the domain of amateur rocketry and I have recently joined a university team to build a model rocket that is to be run using Solid Rocket Motor.

So now I am completely confused on even how to start and I had read through a few of the previous posts and discussions in this forum to help me but I don't think I got what I needed. Plus to get us started and the entire team being very new to this type of thing, almost all of us are quite confused about how to start. So the basic task that we started with was to do a trial design of a Solid Rocket Motor and we had chosen APCP as the propellant. Now the task was to simulate using a program written in any language, the process of what happens during the static test. We were told to simulate the thrust vs time curve, the impulse curve over time, and then the pressure within the combustion chamber with respect to time. I think this was a very basic task to get us started but I have no idea how to start.

So take for example the APCP as the propellant. I read a few basic things about it and then I chose a specific design of the grain. Now how do I choose what is the core diameter and the diameter of the motor? I cannot just choose a random value cause the results will make no sense. Then I looked and went through all the required equations for simulations, but then I came to this iterative problem that I needed to first know the chamber pressure and temperature. Using that I can somehow proceed to the next steps and use the program to iteratively find the next values. But then how do I even know these values to begin with? I don't know where to look for the data. Then for all the equations, I see a lot of variables that are specific to the propellant like the burn rate, and many other parameters. Where do I get these things from? I don't even have a rough guess on what the value should be.
Can someone help me out on this by probably directing me to a place where there is not just theory and equations, but a place where a real-life initial sizing is done for these motors?

I know for a fact that ProPEP3 and a few other software already exist for this but I don't really want to use them cause I want a deeper understanding of what is happening. I played with the software but I don't really have a feel of what or where the results come from.

I would really appreciate any help. I hope you can understand the fact that I am asking for help of a sort such that we are a new university team working on this and we need some very basic steps to even start our journey.

Vicknesh

 

[NTP2]

To get access to the research forum you will need to get your L2 so no help on that front until then. But I appreciate your interest in learning rather than just trying until it works.

 

[Alan15578]

The igniter provides the initial temperature and pressure, so start there, then run your motor sim from there, The initial motor grain and nozzle geometries will come from optimization.

 

[Vicknesh]

Ok I will try to get started that way

 

[cbrarick]

find a mentor. Making rocket motors is not a benign process. Learning the correct methods is not a You-tube type of thing. You only live once, and have come with no spare body parts.

 

[tfish]

The questions you're asking are not..just some very basic steps. Is this truly going to be a model rocket? With like A-C motors? Or high power rocket?
The design of the grain is based on... what you want or need the motor to do. Progressive, regressive, neutral or long burning. The grain lengths cores and nozzle throat are based on the propellant.
It truly is rocket science and not easily learned in a forum like this. Find a mentor that has the time and knowledge to help you abd your team out.

Tony

 

[jqavins]

In addition to what others have said above, It seems like you might need some guidance on the basic process of engineering any complex project. And, when asking for help (which is a good thing to do, so coming here was a very reasonable thing to do) be sure to include all the detail that you can. Sometimes details that seem to you to be incidental or unrelated can be helpful to others who are trying to help you. I've been guilty of failing to do this myself on more than one occasion. I've had specific questions for one small part of a problem, and I wanted people to confine their answers to that specific part, so I didn't provide the context, and that was a mistake.

Step one: define the scope of the project. Are you just out to make a solid rocket motor, or are you also making a rocket to launch with it? Do you have a test stand for the motor, or does the project include building that too? Most armature rockets just go up and come down (on a parachute) and may take some video and altitude measurements; does yours have any other special mission?

Step two: identify the specific requirements. Are you shooting for a minimum altitude? A specific altitude? A minimum, maximum, or specific speed or mission duration? Are you required to use and/or avoid using particular materials? Etc. All that was assuming you're building the rocket, and there can be similar questions even if it's just the motor.

Step three: divide tasks and make sure you have the right team: you said that you're part of a university team, and I don't mean to say you don't have the right people. For a propellant, you need the chemistry, the grain shape, and the grain casting process, at least. You also need a nozzle design, which is a small piece, but critical. You also need a case design; you might buy a commercial case (I'd recommend that) or you might make your own, and then you need to design it as a pressure vessel that can hold the nozzle and anything that you decide to use on the front end. So, you've got chemistry, fluid dynamics, structural, and manufacturing to consider. For the rocket, there are also various pieces; that part is overall easier, but I don't mean it's easy (just that the motor is really hard).

Step four: make a plan. Who on the team will do each piece, relating to step three. Some people may have more than one piece of the whole, some pieces may use more than one person. Everybody takes part in everything is a recipe for chaos and failure. Make a schedule, and make it achievable. Take into account that some things have to be done sequentially. For example, a preliminary rocket design can be done based on the intended, expected, hoped for motor performance, then the rocket design can only be finalized after the motor performance is known. Etc.

Step five: start the design. Believe it or not, designing a rocket - unless it's a very small, light, simple one - should start with selecting the motor. You look at the performance requirements and a WAG at the rocket's weight, then figure out what motor you need. Then you do the detailed rocket design around that motor. That's when using commercial motors with known performance and you're able to pick from a list. In your case it's more complicated because you'll have to pick what motor you want based on the oversimplified rocket design, then in parallel you do a somewhat detailed design based with the motor you're trying to make while you try to make it, then you make the fully detailed rocket design around the motor you end up with. That's just an example of how some things in the project can be done simultaneously while others must be done sequentially, so make sure you've got a schedule (back in Step four) that makes sense.

Remember that you'll have to make and test several motors before that part is done, so build that into the schedule, build all the rocket design iterations into the schedule, and build rocket construction into the schedule For the construction part, include the iterative design changes that will surely be needed as you find challenges you didn't anticipate.

This is not everything! This is a general approach to you rocket project (and, in a way, to any complex engineering project) and there are hundreds of elements I've left out.

 

[cls]

Books. You're in college, you are already reading lots of books. There are books about rocket motors. Your library may have these already. One of the important books about rocket motors is George Sutton, Rocket Propulsion Elements. Any edition. That book has equations which will tell you what code to write off your simulator. You probably ought to get a chemistry book, too.

 

[rocket_troy]

Hello all, I am very new to the domain of amateur rocketry and I have recently joined a university team to build a model rocket that is to be run using Solid Rocket Motor.

So now I am completely confused on even how to start and I had read through a few of the previous posts and discussions in this forum to help me but I don't think I got what I needed. Plus to get us started and the entire team being very new to this type of thing, almost all of us are quite confused about how to start. So the basic task that we started with was to do a trial design of a Solid Rocket Motor and we had chosen APCP as the propellant. Now the task was to simulate using a program written in any language, the process of what happens during the static test. We were told to simulate the thrust vs time curve, the impulse curve over time, and then the pressure within the combustion chamber with respect to time. I think this was a very basic task to get us started but I have no idea how to start.

So take for example the APCP as the propellant. I read a few basic things about it and then I chose a specific design of the grain. Now how do I choose what is the core diameter and the diameter of the motor? I cannot just choose a random value cause the results will make no sense. Then I looked and went through all the required equations for simulations, but then I came to this iterative problem that I needed to first know the chamber pressure and temperature. Using that I can somehow proceed to the next steps and use the program to iteratively find the next values. But then how do I even know these values to begin with? I don't know where to look for the data. Then for all the equations, I see a lot of variables that are specific to the propellant like the burn rate, and many other parameters. Where do I get these things from? I don't even have a rough guess on what the value should be.
Can someone help me out on this by probably directing me to a place where there is not just theory and equations, but a place where a real-life initial sizing is done for these motors?

I know for a fact that ProPEP3 and a few other software already exist for this but I don't really want to use them cause I want a deeper understanding of what is happening. I played with the software but I don't really have a feel of what or where the results come from.

I would really appreciate any help. I hope you can understand the fact that I am asking for help of a sort such that we are a new university team working on this and we need some very basic steps to even start our journey.

Vicknesh

You really need to mix and cast some propellant and evaluate the burn rate either by motor tests or by burning strands in a pressurized environment. There are some nominal values for internal ballistic parameters "a" & "n" out there for some propellants, however the processing of the propellant and QC of the casting and inhibitation can have a significant influence on those values.

TP

 

[jqavins]

You really need to mix and cast some propellant and evaluate the burn rate either by motor tests or by burning strands in a pressurized environment. There are some nominal values for internal ballistic parameters "a" & "n" out there for some propellants, however the processing of the propellant and QC of the casting and inhibitation can have a significant influence on those values.

TP

As can the QC of the ingredients.

 

[terryg]

Note that you are responding to a thread from Oct. of 23.....

 

[cls]

Note that you are responding to a thread from Oct. of 23.....

Oops

> Last seen Oct 20, 2023

 

[cbrarick]

old thread but bad advice.

You really need to mix and cast some propellant and evaluate the burn rate either by motor tests or by burning strands in a pressurized environment.

most ex people don't do strand burning, and if you're not set up for it, this can be dangerous. this is also very old school way of characterizing motors.
You can static burn with pressure and thrust to get the data you need.
Besides, most ex people are not developing new formulas, just using what's out there. there's no shame in this, either

So, unless you know what you're doing and have the proper equipment, PLEASE DON'T STRAND BURN it's not safe unless you meet those criteria. It's not a You-tube learned behavior with cobbled together equipment.

 

[rocket_troy]

old thread but bad advice.

most ex people don't do strand burning, and if you're not set up for it, this can be dangerous. this is also very old school way of characterizing motors.
You can static burn with pressure and thrust to get the data you need.
Besides, most ex people are not developing new formulas, just using what's out there. there's no shame in this, either

So, unless you know what you're doing and have the proper equipment, PLEASE DON'T STRAND BURN it's not safe unless you meet those criteria. It's not a You-tube learned behavior with cobbled together equipment.

Well, it depends. Some highly metalised composite propellant either needs to be strand burned or fired in rather large test motors because of the issue of choking up small throats with oxide slag which can not only provide erroneous internal ballistic values (for scaling up) but also can often produce structural failures of overstressed retention. I've done strand tests, as have past acquaintances quite safely.
Yes most people do motor characterization because it's easier and requires less support equipment and most amateur compositions can accommodate it. Note I suggested test motors *or* strand testing.

TP (who has tested/characterized/flown over 1000 solid motors over the decades)

 

[John Kemker]

In addition to what others have said above, It seems like you might need some guidance on the basic process of engineering any complex project. And, when asking for help (which is a good thing to do, so coming here was a very reasonable thing to do) be sure to include all the detail that you can. Sometimes details that seem to you to be incidental or unrelated can be helpful to others who are trying to help you. I've been guilty of failing to do this myself on more than one occasion. I've had specific questions for one small part of a problem, and I wanted people to confine their answers to that specific part, so I didn't provide the context, and that was a mistake.

Step one: define the scope of the project. Are you just out to make a solid rocket motor, or are you also making a rocket to launch with it? Do you have a test stand for the motor, or does the project include building that too? Most armature rockets just go up and come down (on a parachute) and may take some video and altitude measurements; does yours have any other special mission?

Step two: identify the specific requirements. Are you shooting for a minimum altitude? A specific altitude? A minimum, maximum, or specific speed or mission duration? Are you required to use and/or avoid using particular materials? Etc. All that was assuming you're building the rocket, and there can be similar questions even if it's just the motor.

Step three: divide tasks and make sure you have the right team: you said that you're part of a university team, and I don't mean to say you don't have the right people. For a propellant, you need the chemistry, the grain shape, and the grain casting process, at least. You also need a nozzle design, which is a small piece, but critical. You also need a case design; you might buy a commercial case (I'd recommend that) or you might make your own, and then you need to design it as a pressure vessel that can hold the nozzle and anything that you decide to use on the front end. So, you've got chemistry, fluid dynamics, structural, and manufacturing to consider. For the rocket, there are also various pieces; that part is overall easier, but I don't mean it's easy (just that the motor is really hard).

Step four: make a plan. Who on the team will do each piece, relating to step three. Some people may have more than one piece of the whole, some pieces may use more than one person. Everybody takes part in everything is a recipe for chaos and failure. Make a schedule, and make it achievable. Take into account that some things have to be done sequentially. For example, a preliminary rocket design can be done based on the intended, expected, hoped for motor performance, then the rocket design can only be finalized after the motor performance is known. Etc.

Step five: start the design. Believe it or not, designing a rocket - unless it's a very small, light, simple one - should start with selecting the motor. You look at the performance requirements and a WAG at the rocket's weight, then figure out what motor you need. Then you do the detailed rocket design around that motor. That's when using commercial motors with known performance and you're able to pick from a list. In your case it's more complicated because you'll have to pick what motor you want based on the oversimplified rocket design, then in parallel you do a somewhat detailed design based with the motor you're trying to make while you try to make it, then you make the fully detailed rocket design around the motor you end up with. That's just an example of how some things in the project can be done simultaneously while others must be done sequentially, so make sure you've got a schedule (back in Step four) that makes sense.

Remember that you'll have to make and test several motors before that part is done, so build that into the schedule, build all the rocket design iterations into the schedule, and build rocket construction into the schedule For the construction part, include the iterative design changes that will surely be needed as you find challenges you didn't anticipate.

This is not everything! This is a general approach to you rocket project (and, in a way, to any complex engineering project) and there are hundreds of elements I've left out.

Listen to Joe. He knows whereof he speaks. Great advice for you, there.