54mm flying case testbed

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Neutronium95

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Ever since following the Bare Necessities build thread as a teenager, I've been enamored with submin or flying case style rockets. Building something optimized purely for performance really appeals to me, and this year I really want to start actually building some of the designs that have been rattling around in my head.

Before I start going after records that require expensive motors, I wanted to actually learn how to do a lot of the things I'll need for extreme performance rockets in the future. That's where this rocket comes in. It'll be a flying case design, intended to fly on Aerotech 54/1706 motors. A very rough initial sim showed that a K1103 could get close to Mach 3, which will provide a good stepping stone to some of my future flights, which will exceed that speed.

My general plan for this project is to start with building a few different iterations of the nosecone and avbay, until I have something that'll fit the electronics and recovery system into as small of a nosecone as possible. From there, I'll be able to nail down the fin can design in order to keep it nice and stable. In the future, the same nosecone and avbay should transfer over to other motors for higher flights, allowing for K, L, and M record attempts by just swapping out the motor and fin can.

The design of the avbay and recovery system will be pretty similar to my H13 record attempt and my 75mm min diameter rocket. The electronics will be on top of the motor, and packaged as tightly as possible. They'll be in a coupler section, and the nosecone will fit over them. The remaining volume in the nosecone will be full of the parachute and shock cord. I'll be using cable cutter dual deploy, which has worked pretty reliably for me in the past. I'm not entirely certain what the final electronics configuration will be, but I'm currently leaning towards a Featherweight GPS and LL Electronics XLF-6V beacon for tracking, a Blue Raven for primary deployment and data logging, and an EasyMini as a backup.

Step one for this build is to try making a nosecone. I'll be using some techniques borrowed from some of my friends. To keep things simple, I'll be laying up Soller Composites fiberglass sleeves over a 3D printed plug. I'd like to eventually get a plug that could survive going in an oven to cure a higher temperature resin, but printed PLA will be fine for my initial experiments. I pulled the plug off of the printer this evening, and will do the first test layup this weekend.

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Super excited to watch this. I've got a motor sitting for a similar project that's been mixed into my backburner for some time. However, I think it might be time to hop to it here soon!

Braden
 
The first attempt at a nosecone didn't work out that well, but I learned a decent amount.

I used Soller Composites fiberglass sleeves to form the nosecone. I planned on using three layers, but while the first two layers went on fine, the third got stuck partway down, and my attempts to get it all the way on just shifted the lower layers. The maximum diameter with the first two sleeves applied was pretty much the maximum that the sleeve could fit over, and there was 3.5" of straight section at the base of the plug, for a coupler to fit into.

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On the bright side, the prelubricated latex mold release layers worked great to separate the failed part from the plug. In general, with the exception of the sleeve grabbing, the process mostly worked.

I have more sleeve material coming soon, I'm hoping to try again this weekend. I printed a new plug, with a shorter straight section. I'll print a part to glue into the base of the nosecone to form a cylindrical section for the coupler to fit into. I'm going to start playing around with the avbay design this weekend to make sure that this one will actually work on a rocket. I also need to design and print some molds to cast the nosecone tip in.
 
My second attempt at a nosecone is curing now. Still not flight ready, but significantly better than the first attempt.

I tweaked the plug design, with a shorter straight section, a slightly smaller tip diameter, and a small radius on the tip, so that the prelubricated latex release layers wouldn't get cut on the edge when getting stretched over the plug.

I also had more sleeve material on hand. I also realized that what I thought was 2" sleeve, was actually 1.5", which explains all of the issues I had on the first attempt. I only used the larger diameter material for the final layer, and it worked pretty well there, with some minor issues conforming to the tip of the plug. Finally, I remembered to cut the excess off with a knife while it was leathery, instead of with a hacksaw once it was fully cured.

I did run into an issue when I tried to adjust the second layer of sleeve, and ended up making a nasty wrinkle in the first layer that I couldn't work out. Between that, and the tip not quite conforming to the plug, this still isn't good enough to fly, but it's significantly better.

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I think that I'll try again tomorrow. I'm going to try to arrange it so that the outer sleeve is under tension while it cures. The Soller heat shrink tube is also a possibility, but I am a bit concerned about heating up the PLA mandrel too much.

Next up is trying to pack a Blue Raven and Featherweight GPS along with their requisite batteries and switches into the smallest possible volume. Once I have a good estimate of how much the whole nose section with avionics and recovery system will weigh, then I can finalize the fin size and shape and get started on the fin can. I'm not sure whether I'll just get a piece of commercial fiberglass tube and CNC cut fins or if I'll try rolling a tube and cutting my own fins. I also need to start CADing up the tower parts for cutting by Send Cut Send.
 
just a thought... to avoid wrinkles, apply the layers one at a time. Wait for the first layer to become leathery before applying the next one.

Maybe.
 
Telescope the layers into each other, and apply as if it were one sleeve? Make the straight section have a very slight draft angle? Apply the sleeve dry, and wet out afterwards? That gives lots of time to get it right.
 
Laid up nosecone number 3 this afternoon, and it went well, and could probably be flown. Not sure if I'll use it or if I'll make one with a more heat tolerant resin for flights close to Mach 3, and operations in the Mojave desert in July.

The 2" sleeves went on much more easily than the 1.5" sleeves. I was easily able to adjust things without forming wrinkles in lower layers. I cut the final sleeve longer than the first two and put some hooks through it to cure it under tension, and that seemed to work well for getting the material to conform to the nosecone tip.
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I just started playing around with the dimensions, but it's looking like I should have a decent amount of room in the nosecone base to fit the electronics. I'm planning on a Blue Raven and Featherweight GPS, and if I can find the room I'll put in an EasyMini for redundant deployment.
 
Here's a comparison between all three of the nosecones. The third one came out great, I did forget to cut it off a little bit below the tip of the plug to make removal easier. I had to make an additional cut with the hacksaw, but once I did that a few quick knocks on the patio freed it. I'm very satisfied with the construction method, but I'm npt certain about the materials. I don't know how much I trust the West Systems epoxy at Mach 3. Or just lying in the sun in July in the Mojave.

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I had initially hoped to be able to pack the electronics tightly enough so that I could reuse the same avbay design in a 38mm submin, but I doubt I'll be able to manage that. Just running a piece of threaded rod into the forward closure makes all of the structural work easy, but it's also bulky and just kind of annoying to work around when going for maximum packing density.

I also took a look at aluminum tubes for the tower. i was initially hoping to build an adjustable tower for this project, but I don't know if I'll have the time for it. A single size tower with 3D printed end plates worked pretty well for my last min diameter project.
 
As laminating resins go, West Systems is about the worst choice here. It has a rather low Tg (Glass Transition Temperature) that cannot be improved by heat treating. It's intended to soften, so when wood boat hulls get hot it can move with the wood a little (my theory anyway; it was designed for glassing wooden boats). West is good for prototyping being readily available.

The problem with any of the internal mold methods are threefold:

1) You are achieving accuracy on the inside of the part, but you are requiring accuracy on the outside (accuracy matters more for high speed flights or it won't fly straight - aerodynamic forces are roughly a function of the square of the speed times the atmospheric pressure at whatever altitude you are checking. Heating is cube of the speed)

2) You achieve a better finish on the inside, but have lots of finishing work to do on the outside.

3) Lack of compression on the layup during curing results in a so-so fiber to resin ratio, so the resultant parts are a little weak for their weight.

Good progress, but not a way I'd recommend! Good luck!

Gerald
 
As laminating resins go, West Systems is about the worst choice here. It has a rather low Tg (Glass Transition Temperature) that cannot be improved by heat treating. It's intended to soften, so when wood boat hulls get hot it can move with the wood a little (my theory anyway; it was designed for glassing wooden boats). West is good for prototyping being readily available.
I'm in full agreement about the epoxy. I'm not quite sure what I'm going to choose for the flight parts, and for my other upcoming projects yet. My main restriction is that I want to keep using my 3D printed tooling, since it's easy to make. So I need something that will cure at room temperature, can be demolded, and then post cured to the final Tg without distorting during the post cure.

1) You are achieving accuracy on the inside of the part, but you are requiring accuracy on the outside (accuracy matters more for high speed flights or it won't fly straight - aerodynamic forces are roughly a function of the square of the speed times the atmospheric pressure at whatever altitude you are checking. Heating is cube of the speed)

2) You achieve a better finish on the inside, but have lots of finishing work to do on the outside.

3) Lack of compression on the layup during curing results in a so-so fiber to resin ratio, so the resultant parts are a little weak for their weight.

I did settle on this technique after talking to Mike Passeretti at FAR a few weeks ago. It's been pretty well tested on several high performance flights.

I'm not too concerned with getting a perfectly accurate outer mold line to be quite honest. As long as it's symmetrical, I'll be happy. I've played around with nosecone shapes in sims and not seen massive changes. If it diverges from the intended shape because the wall thickness is a bit thicker at the tip I won't be worried.

I am considering making a female mold to press the plug with layup into. That will add a significant amount of complexity that I'm not sure I'll really need. Heat shrink tape is another possibility, but that also has possible concerns with the 3D printed plug.

The better finish is a good point, but the outside is significantly easier to clean up, and I care about having a nice consistent internal surface for the coupler to interface with.

Finally, I only really care about getting a good enough fiber to resin ratio. From the sims I've run, the designs I'm working on aren't too sensitive to mass. If the nosecone is a bit heavier than some ideal layup, I'm not that concerned. If it's weaker, then I can just make it a bit thicker.
 
I'm in full agreement about the epoxy. I'm not quite sure what I'm going to choose for the flight parts, and for my other upcoming projects yet. My main restriction is that I want to keep using my 3D printed tooling, since it's easy to make. So I need something that will cure at room temperature, can be demolded, and then post cured to the final Tg without distorting during the post cure.
System 3000 cures at room temperature and can then be post-cured in an oven off the tooling.
 
I've made a bit more progress in the last few days. I finally got around to casting a tip onto the good nosecone. I used a 3D printed two part mold, and filled it with rocketpoxy, then jammed the fiberglass nosecone in. It worked pretty well, the mold release failed in a few spots, but with a bit of persuasion, the mold came off. A bit of sanding cleaned it up, and it came out pretty good. The only real blemish is a few spots where the frayed ends of the kevlar shock cord anchor are poking through. I might try fixing that by embedding the ends of the kevlar into a small blob of epoxy beforehand on future nosecones. Or by going to a more traditional aluminum tip on larger builds.

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I'm hoping to make a lot of progress this weekend. I have a mold for the contoured coupler printing right now, and would like to get to the point of having a complete version of all of the parts above the motor by the end of the weekend. Having those weights will allow me to finally get started on the fin can. I'm not entirely certain whether or not this will be the flight nosecone, or if I'll make another with the Fibreglast resin that I ordered. In all honesty, I'm more concerned about it possibly distorting in a hot car than failing due to thermal problems in flight. The high temp resin is more needed for my BALLS project...
 
In all honesty, I'm more concerned about it possibly distorting in a hot car than failing due to thermal problems in flight. The high temp resin is more needed for my BALLS project...

Worst case, travel with cooler.. LOL
 
This project keeps on getting delayed. Now that I'm back from spending a week hanging out with friends at LDRS I can get back to this. I'm hoping to launch at the August 5th FAR launch. This was supposed to be a pathfinder for my BALLS project, but I'll probably have to start building that before this one flies.

I got some of that Fibreglast System 3000 resin recommended by @eggplant earlier. I laid up a nosecone, nosecone coupler, and a fin can tube with it. I haven't done the post cure on those parts yet. The tube has a bit of black residue because I wrapped it in electrical tape to get a bit of compression. I tried staggering the sleeves at one end to get a smooth taper in thickness down to a single sleeve thickness at the front end of the fin can. That worked out pretty well.
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I've been kind of unsatisfied with every fin jig I've used or seen to date, but last week I came up with this design, and I'm pretty satisfied with it. Two 3D printed parts, eight pieces of Aluminum bar, and a bunch of clamps, and I have a jig that will constrain the fins in every way I need. I need to figure out how to make parametric parts in Onshape, but once I do I plan on releasing design files for a few different versions of this design.

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The fin can tube needs some more work before I'm ready to bond the fins on, but I might be able to get to that point tomorrow. I also just played around with things, and it looks like I'll have a decent amount of room for avionics, and once my wire whip antenna Featherweight GPS arrives, I'll have even more. I also might do a layer of carbon tip to tip on the fins. I don't think that they'll need it, but it can't hurt, and I'd like to practice the process, especially the vacuum bagging before doing a more complicated layup on my BALLS project.
 
That rocket design is truly impressive, showcasing a perfect blend of innovation and aesthetics. I'm eagerly looking forward to witnessing its maiden flight, sure to be a mesmerizing spectacle!

In addition, the fiberglass mold technique employed in the rocket's test constructions looks exceptionally well-executed, showing precision and craftsmanship, making the rocket's future flight even more captivating to anticipate. Ill make sure to be there when it launches!
 
In addition, the fiberglass mold technique employed in the rocket's test constructions looks exceptionally well-executed, showing precision and craftsmanship, making the rocket's future flight even more captivating to anticipate. Ill make sure to be there when it launches!
Hope you'll be at BALLS then...

Life keeps happening and this keeps getting delayed, so it's getting promoted from a testbed for my BALLS project to my BALLS project. I'm thinking about getting a bigger motor to fly there after the K1103. Maybe an L1000 if I can swing the price.
 
I finally got the fins cut out and beveled. I used a different router bit this time, as I had problems with my old one when beveling the fins for my BALLS rocket last year. I think that I'll be going back to my old bit, since while I didn't have any delamination, the bevels are really rough, and will need some hand sanding to clean up.

I'll clean them up and start tacking them this evening. Or tomorrow.

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I've been making progress slowly. The fin can is all assembled and filleted, I'd like to do some more finishing work on it, but I'm in a time crunch and it's flyable so that'll have to wait for after BALLS. I also cast a nosecone tip onto the nosecone that I made with the high temp resin. The only major thing left to get this flyable is to design and print the avbay. Currently I'm planning on a Blue Raven and a Featherweight GPS. I'm leaning towards keeping things simple and just going with main at apogee for the first flight, since recovery is so nice at Black Rock. If it fits in easily I might do a cable cutter, and I'm planning on using one for future flights.
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For your nosecone layers, there's usually a minimum and maximum recommended diameter for the different sleeves. I think you're in the range where the inner layers could be stretched wide, but maybe the outer layer could be the next size up, stretched long? Also have wondered about boiling one in a pressure cooker, but I'm a weirdo like that.
 
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For your nosecone layers, there's usually a minimum and maximum recommended diameter for the different sleeves. I think you're in the range where the inner layerscould be stretched wide, but maybe the outer layer could be the next size up, stretched long? Also have wondered about boiling one in a pressure cooker, but I'm a weirdo like that.
I have made a 38mm NC using a very similar method, actually 3, only the 3rd one was up to snuff. However I didn't end up flying it because of this exact reason. Maybe I was being a little over caution, wondering if you are seeing the same thing. Also did you add anything to the cast tip? I always worry that the epoxy is going to shatter because it is much more brittle than lets say aluminum. Looking great, thanks for sharing!
 
Things are coming together nicely. The nose cone has already been cleaned up since this picture was taken. The plywood ring fits around the base of the forward closure, and braces the base of the nosecone, to give it significantly more resistance to bending loads. It's just one ring that's cut in half, and then secured with several wraps of 6mm masking tape until the coupler fits snugly on it.


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And here's a look at the electronics and nosecone coupler setup. I drilled a hole in a 5/16 coupling nut to make a compact eyebolt*. I tried shortening the nut a bit, but the hacksaw wasn't doing so well so I threw in the towel. With this the rocket is about 90% complete. I just need to do some small things like drilling vent and shear pin holes, along with rigging the parachute. Since the shock cord is cast into the nosecone tip, I erred on making it extra long, so that will probably get shortened if I need more space in the nose for the recovery system.

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All in all the rocket is quite rough, I absolutely do not have the time or energy to get a good finish on it, but it should fly fine in a few days. If all goes well I'll pretty it up, and then maybe fly on a bigger motor. It also looks like a K2050 might be enough to meet one of my clubs standing challenges of breaking 2000mph, without breaking the 18,000 foot waiver. I might do that flight at Holtville Havoc in November.

*It is really annoying that Aerotech chose to use 5/16" threads on the 54mm threaded bulkhead. It's complete overkill for anything you'd want to do with the hardware, and at least in my experience 5/16" hardware is a lot less common that 1/4". If I suddenly realize I need an eyebolt, there are half a dozen 1/4" ones lying around or on rockets that I could steal, while a 5/16 would probably be a McMaster Carr order.
 
This rocket flew today, on a K1103. It went to 13,355 feet and just barely over Mach 3, according to the Blue Raven.

SinceI was having trouble fitting the recovery system into the nosecone, abd I was at BALLS, I decided to deploy the main at apogee, and trust my tracker.

The apogee was significantly lower than the 18,000 feet I saw in the sim, due to the top quarter inch of the fin can softening and rolling over.

Other than the reduced apogee, the flight was perfect. The boost was crazy fast ajd arrow straight. It took forever to land, abd went three miles downrange, but the Featherweight GPS took me right to it.

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That muffin top on the fin can is an interesting effect.

I've seen it before but never on a rocket -- the muffin top I am most familiar with is the one just above my own belt ;)

Kidding aside, sounds like a great flight.

Congrats @Neutronium95 !

Following for more when you're ready.

Thanks

-- kjh
 
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