Scratch Building Reload Kit

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NMSU_IREC

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For my college's IREC team, we are starting to build our reload kits/propellant grains. We will be implementing these in a COTS motor casing. We used RPA and our knowledge from our aerospace engineering classes to design a nozzle, and we have a machinist who will machine it out of graphite with a lathe.

A question I have is how we will mount the nozzle to a phenolic case liner. I am looking at J-B ExtremeHeat, but I've seen mixed reviews. I'm wondering if anyone has other recommendations, and possibly other materials for the case liner.

I know the first thing most people on here are going to be concerned about is safety, as this can definitely be dangerous. Luckily, we have a senior NAR and Tripoli Level 3 member in our community who would be able to help us roll the propellant grains. I am also NAR Level 3 certified, so I have a lot of knowledge of high-powered rocketry. Any tips on rolling propellant grains would also greatly be appreciated.

I'll definitely be posting updates on this hopefully insanely cool project. It's very early in the design, but our ultimate goal is to launch in March 2019 on my old L2 rocket. Thank you for all the suggestions. We are brand new at this and realize we have a lot to learn.

Not to worry, They're still working on debugging the new format.

double/triple posts are common.
 
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The discussion you want to start here will probably get moved to the research forum shortly.


Can you explain your mentor's experience with making EX motors? Which COTS motor case are you looking to use, and what size motor is it?


I'm only speaking for myself, but your usage of the word "rolling" when talking about making propellant grains makes me feel like you don't have any experience/exposure to this aspect of rocketry.
 
Our mentor has been actively involved in the rocketry community for well over 30+ years, he has been an L3 member for about 20 years, and he has built dozens of his own experimental solid rocket motors. We will be using a Cesaroni 38 mm 5-grain case.

Yes, you are correct, we have no experience with manufacturing propellant grains, and there isn't much information out there. That is why if we were to do this, we would have a mentor who has done this before, to show us the proper/safe procedure.

Our team does have propulsion design experience, as we are composed of mostly aerospace engineering students. I'm confident that combining our design knowledge with his manufacturing experience that we could build a successful rocket motor.
 
Of all the EX hardware out there, why use CTI? Snap ring cases were made for EX. And voila, the snap rings hold the nozzle and fwd closure in place. CTI HW is not designed for EX use, but if you do, then why wouldn't the screw-in closures that come with the casing work? :confused:
 
Of all the EX hardware out there, why use CTI? Snap ring cases were made for EX. And voila, the snap rings hold the nozzle and fwd closure in place. CTI HW is not designed for EX use, but if you do, then why wouldn't the screw-in closures that come with the casing work? :confused:
CTI 38's have a plastic forward and rear closure that are included with the reload, they would also need to make a rear closure to use it for EX. As you say why would anyone choose smaller diameter CTI for EX when the snap ring cases are do much simpler and better for EX.
 
why would anyone choose smaller diameter CTI for EX when the snap ring cases are do much simpler and better for EX.

I'm going to go with "this is the case we have on hand".

Thinking out loud here- I'm betting existing casting tube/liner supplies are not compatible diameter-wise with CTI- so they'll have to make their own there too.
 
I'm going to go with "this is the case we have on hand".

Thinking out loud here- I'm betting existing casting tube/liner supplies are not compatible diameter-wise with CTI- so they'll have to make their own there too.
I certainly wouldn't know where to get them.
 
Of all the EX hardware out there, why use CTI? Snap ring cases were made for EX. And voila, the snap rings hold the nozzle and fwd closure in place. CTI HW is not designed for EX use, but if you do, then why wouldn't the screw-in closures that come with the casing work? :confused:

I'm going to go with "this is the case we have on hand".

Thinking out loud here- I'm betting existing casting tube/liner supplies are not compatible diameter-wise with CTI- so they'll have to make their own there too.

A set of Loki 38mm-740 snap ring hardware intended for EX is ~$100 including the nozzle, plus a bit for per-launch supplies. I'm going out on a limb here, but it seems crazy not to use that. If nothing else, think of the cost and hassle to get liners the right size if they don't match up perfectly. Plus, if you can't afford $100 plus shipping for the right piece of gear, you probably shouldn't be in EX to begin with. Finally, if your mentor has that much experience, maybe check in with him/her? That is a problem they would have solved before.
 
Finally, if your mentor has that much experience, maybe check in with him/her? That is a problem they would have solved before.

Frankly, I'm a little surprised that their mentor hasn't suggested something else already. While it's certainly possible to do an EX motor with a CTI case, you're going to have to solve several problems that would be non-issues with a Loki or similar case.
 
Moved to research while I review it. Locked for review.
 
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Ok, I have reopened this thread. It is on the right side of the line. Do not cross into the specifics that will get us into trouble. Specifically, read: "Research Rocketry (making your own motors, igniters, etc) is a special topic, the specific details of which are not to be discussed except in an area specifically designated for such topics. This includes propellant and igniter compositions, specific product recommendations, and techniques for processing propellant. Posts on the topic of Research Rocketry containing information not widely available in published materials are limited to the access controlled area."

I will keep a close eye on the thread.
 
Back to the original poster. What is your final goal? Hitting a certain altitude? Making your own motor? Something else?
 
Our ultimate goal, which we believe we could accomplish for our 2020 competition, is to build an EX solid rocket motor to reach 10,000 feet.

However, as we are just starting and have several old L2 rocket bodies and 38 mm casings, we want to start small and then go from there. Our goal for right now is to just successfully launch a J-class rocket motor that we designed and built, and then to slowly scale up from there.
 
So, in summary, what you should be taking away from this is: don't use CTI HW; buy Loki, XPS, Binder Design, some kind of EX hardware. It will cost you more to try to fabricate CTs and liners than to just buy known EX stuff. If you post something in the WANTED forum, you might even find a kind soul who would lend you the hardware set.
 
Yes absolutely, I definitely plan on using the Loki hardware now. I now also realize to post this on the research part, which I will apply for access. Thank you all for your help!
 
A pleasure. You can ask specific questions about formulae and chemicals in the Research forum.
 
If you post something in the WANTED forum, you might even find a kind soul who would lend you the hardware set.

I'd do this if they were local, and I had reasonable faith that they wouldn't turn my case into a crumpled tin can.


To the OP- I would suggest starting with a smaller case from Scott, and then get a larger one for your full run. You can reuse several components like the forward closure, snap rings, nozzle washer. Mostly just need a longer case and nozzle.
 
If you post something in the WANTED forum, you might even find a kind soul who would lend you the hardware set.

I'd do this if they were local, and I had reasonable faith that they wouldn't turn my case into a crumpled tin can.


To the OP- I would suggest starting with a smaller case from Scott, and then get a larger one for your full run. You can reuse several components like the forward closure, snap rings, nozzle washer. Mostly just need a longer case and nozzle.

https://binderdesign.com/store/page11.html
 
Also general EX advice- I have a rocket or two that are small "beater" type rockets with 38mm motor mounts. I put in a nose cone av bay with a cheap altimeter (like an eggtimer quark), so it pops the chute at apogee. That way I can test 38-2 grain motors fairly cheaply, and you don't have to risk your L2 rocket until you have a more proven formula.

(this coming from the guy that blew up his L2 rocket on an EX motor about 5 months ago :))
 
This is a bit tangential to the OP's question, but how much ground testing would you expect to do for an EX propellant before going to flight? In 38 or 54mm, would you cast enough grains for several flights in a single mixing operation? Would you ground test before flight the second time you mix a new formula? The 4th time?

I can take this down if it's too much thread drift.
 
This is a bit tangential to the OP's question, but how much ground testing would you expect to do for an EX propellant before going to flight? In 38 or 54mm, would you cast enough grains for several flights in a single mixing operation? Would you ground test before flight the second time you mix a new formula? The 4th time?

I can answer this from what I do:
1 - I don't usually ground test, mostly due to lack of a location to do it in. If I had a site where I could test nearby my house, I'd probably be doing tests 3-4 times a week.
2- I always cast more than enough for a ground test (at least 8-10 grains in 38 for example). That way I can junk a grain if it doesn't look good. More importantly though, as the size of a batch goes up, minor variances in measuring the materials matters less. if i'm off by 1g on a 100g batch, that's a lot worse than 1g on a 1500g batch.
3- I usually move up a diameter after testing several times in the previous size- usually by moving up in length as well.

The critical point for me is making it repeatable. If you're still needing to test after the 4th mix of a formula, that means your process isn't repeatable enough and has too many uncontrolled variables.

I've had 2 EX catos in 3 years- both of which were the first attempt of a new formula at the time. It sucks, but I use those as a learning experience, in that it was an error on my side that wasn't accounted for.
 
I ground test any new propellant. I have to dust off my test stand for the first use in 2 years. I have a number of motors in storage. I will probably retest them before I use them on the field.
 
Yes, we are looking into ground testing. The only problem for right now is commercial test stands available are ~$1000, including load cells, pressure transducers, a data acquisition module, etc. We want a test stand capable of withstanding around 1,500 lb-f of thrust, as we would like to be able to test N and O class motors in the future. At this size, would you recommend building our own test stand or buying one? I'm looking at this one from Aerocon: https://aeroconsystems.com/cart/mot...ntal/vertical-test-stand-to-1500-lb-f-thrust/
 
I think buying/building a test stand for N+O motors without having made a single EX motor is probably not the best way to go. Personally I'd recommend first working on a formula, and when you have something you think will work, do some basic "stick the motor in the ground" testing. Then worry about characterizing the propellant etc.
 
I think buying/building a test stand for N+O motors without having made a single EX motor is probably not the best way to go. Personally I'd recommend first working on a formula, and when you have something you think will work, do some basic "stick the motor in the ground" testing. Then worry about characterizing the propellant etc.

Having witnessed DJS’s ‘woosh-BANG’ flights, there is much to be said for really basic ‘burn or bang’ testing before in depth characterization.

That said, you’re engineering students, yes? I suggest a little research into National Instruments Fieldpoint setups. The Strain Gauge modules are rare, but everything is eBay-able. And if you build your own bridge, you could just use regular analog-in modules. A controller backplane (opposed to a network backplane) will enable data collection into the kHz. Analog in and relay modules would let you do simple igniter tests and firing. P and T are possible, but I think require more advanced closures. Labview is easy- same as the LEGO Mindstorm. Basically C without pointers, with a UI that looks like circuit diagrams.

But it’s good advice to learn to burn, rather than go bang, first. Unless you split your team and multitask.
 
I think that nearly every computer made these days has an analog to digital converter capable of 100khz sampling rates...it is called a sound card :)
Rex
 
I think that nearly every computer made these days has an analog to digital converter capable of 100khz sampling rates...it is called a sound card :)
Rex

I think the issue is more getting the right force gauge and building the apparatus to support the motor on a test burn.

However, I think this is putting the cart before the horse..would rather see details (in the research section) on how they are planning to make their motors, and what experience their mentor has.
 
However, I think this is putting the cart before the horse..would rather see details (in the research section) on how they are planning to make their motors, and what experience their mentor has.

Quite right. But one last bit - I retract my Fieldpoint suggestion. It's sturdy - but dog slow. ~1Hz. The next gen (cDAQ) is faster (500Hz at 24bit and 16 channels) - but no long eBay scrounge build-able.
 
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