4" to 3" 2 stage to 100k

Bean74525

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Over the summer, @Frosty_Burrito and I decided to build a rocket capable of reaching 100k ft. This initially started as a much tamer project, but eventually evolved into a full minimum diameter 2 stage. It can fit a CTI 98 6xl to a CTI 75 6xl and current sims using an N3800 to M840 have it going ~112k and Mach ~3. If we go above our mass budget, we can easily use a larger motor in the booster so that we are still reaching the 100k ft. goal. This isn't meant to be the most optimized build by any means, we just want to get to 100k without compromising on too many things (especially recovery). Before we even attempt the full flight, we will be doing multiple test flights on much smaller motors to make sure everything is working properly.

Here are some pictures of the progress so far:

The fins were cut out of 1/8" G10 on a water jet and then covered with 4 layers of 6K carbon from Soller on each side. One of the big parts of this project is learning to vacuum bag, so we used it as much as possible. Once cured, the fins were cut out then sanded back to shape on a belt sander.

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For beveling, we made a jig with a table saw based on this video. It took some practice to get right, so the sustainer fins turned out much better than the booster fins, but it should still be alright. We'll probably use a router
based jig in the future though this one worked alright in the end.


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The fins were then tacked on with ES6209 and a little CA, and external fillets were done with more ES6209 and colloidal silica.

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Since the fins already have a good amount of carbon added to them, we aren't going crazy with tip to tip. We are adding two additional layers of carbon on each fin and going up to the bevel. The first layer extends roughly one inch past the fillets and is made of 6K carbon from Soller. The second layer extending to the bevel and is made of 3K carbon. Each of these was also vacuum bagged and they came out fairly nicely. When the layup is complete, we intend on coating the bevels as well as the leading and trailing edges of the sustainer fins with JB weld for heat resistance. Our other choice would be to use Cotronics like Jim Jarvis, but that seems a decent bit more expensive and has a short shelf life.
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In terms of the interstage, we are planning on having the sustainer motor stick out the aft end of the rocket and slide into a tube in the transition. After reading the Aeropac 100k report, we assumed we would not be able to use a normal 75mm airframe as the fit was too loose, and this was confirmed once we got the parts in hand. To remedy this, we rolled a short carbon tube directly on a CTI 75mm casing. While there is still a little wiggle, it is a much better fit than a normal airframe, and is much easier to shim with some tape.

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I've reached the image limit for this post, so ill be adding more of our progress in this thread soon.
 

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Frosty_Burrito

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Some other relevant pictures

Transition
1658864170764.png

Sustainer Avionics Bay:
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2 Raven 4 Altimeters
1 RTOM3
1 TeleGPS
1 Featherweight GPS
1 RunCam Split HD
Independent 1S or 2S LiPo batteries for each component. Altimeters are controlled by a screw switch, the GPS units are plugged in during assembly and stay on the whole time.

Booster Avionics Bay:
1658864105208.png 1658864113241.png


2 Easy Mini Altimeters
1 TeleGPS
2 RunCam Split HDs
Batteries and GPS are the same in the booster.

There will also be COMSPEC trackers attached to the shock cords on both stages.
 
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JimJarvis50

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Guys,

Looks like a great project. Two-stagers are fun. I'm looking forward to seeing more details as the project evolves.

Regarding the cotronics, as it turns out, I just ordered a pint. It should show up within a few days. I won't use it all, and if you'd like to share it, I suspect that could be arranged.

Jim
 

Bean74525

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Guys,

Looks like a great project. Two-stagers are fun. I'm looking forward to seeing more details as the project evolves.

Regarding the cotronics, as it turns out, I just ordered a pint. It should show up within a few days. I won't use it all, and if you'd like to share it, I suspect that could be arranged.

Jim
Thanks Jim! We'll probably have to take you up on that offer. Ill send you a PM about it.
 

Frosty_Burrito

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Quick update with some pictures. We're finishing up the last tip-to-tip. Starting this weekend and next week we're going to finish up the transition and assemble the electronics bays.

Results of yesterday's lay ups. Some cleanup will be required in the fillets but overall we're happy with how they came out:

PXL_20220728_133118965.jpg
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Current lay ups in progress:
PXL_20220728_235638654.jpg PXL_20220728_235645619.jpg

We ran into some issues vacuum bagging two different sides of the fins in the same bag, but two fin cans works well.
 

Frosty_Burrito

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The internal tube in the original transition was not installed straight enough and resulted in about a .7 degree deflection angle between the stages. We are worried that this may cause undue stress or induce a spin/corkscrew during the portion of the flight that's they stages are connected. Despite only being about 4 seconds of flight, it's better to be safe than sorry.
Screenshot_20220807-125714.png

We are making a whole new transition and tube. The transition is curing, and the tube will be started shortly.
PXL_20220807_164925247.jpg

Like last time, the shrink tape on the tapered section does not sit nicely and needs to be made of many tiny strips. If anyone knows of a better way to do this, please let me know.

The ebay is also coming along nicely. Some edits need to be made to fit the cameras correctly, but so far there are not any major edits needed.
PXL_20220807_032002203.jpg PXL_20220806_012016802.jpg PXL_20220807_170453179.jpg
It is worth noting that, unlike previous models, the RunCam Split HD requires a BEC stepdown to 5V when running off of a 2s LiPo. It will not turn on otherwise, which I have not found in other models like the Split 3 Micro.
 

Reinhard

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Like last time, the shrink tape on the tapered section does not sit nicely and needs to be made of many tiny strips. If anyone knows of a better way to do this, please let me know.
I've seen electrical shrink tube used for composite tubing. It will conform better to that shape than tape.

If you want to use tape, you can probably experiment with multiple starts. This will result in uneven density (multiple layers some parts, less on others), but it should cover everything if done right.

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Reinhard
 

alexzogh

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There is supposed to be a tiny gap between the shrink tape wraps to allow for the epoxy to be squeezed out.

Below is a video I made on a filament winder, and I finished it with shrink tape.



You then just sand down the tiny ridges in the gap between the tape wraps.

BTW - looks like it's going to be a really good flyer. great job.
 

Zertyme

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There is supposed to be a tiny gap between the shrink tape wraps to allow for the epoxy to be squeezed out.

Below is a video I made on a filament winder, and I finished it with shrink tape.



You then just sand down the tiny ridges in the gap between the tape wraps.

BTW - looks like it's going to be a really good flyer. great job.


Shrink tape is usually wrapped with at least a 50% overlap. This overlap is increase or decreased if you need more or less compaction: the epoxy will squeeze out between the layers of shrink tape.
 

Frosty_Burrito

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Here is the new tube and the new transition.

Some surface blemishes in the transition, mostly because of the shrink tape. However, some epoxy wiped on and a healthy amount of sanding should clean it up. The CF tube came out beautiful. It's thin, light, and the 11 inches I am using weighs about 120 grams. In the future I am going to try shrink tubing instead of tape, which may work for the complicated contours. The shrink tape worked beautiful on the tube.

PXL_20220809_002544653.jpg PXL_20220809_002537456.jpg


I had trouble removing the tube from the 75mm casing I used as a mandrel despite mold release and a layer of mylar. There was no internal epoxy leakage and the mylar was perfectly smooth. Likely the issues were related to a release agent that wasn't particularly slick, and increased friction due to the shrink tape which we did not use last time. Ultimately, I was able to remove the motor casing/mandrel without any damage. There was a good bit of percussive mold release and ice.

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Frosty_Burrito

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To solve the transition angle issue, we are going to be using the coupler as the primary connection point. Like a normal motor tube, the transition Tube will be epoxied into the coupler by two centering rings. A third centering ring will be sunk into the transition tapered section. Then, the coupler-tube assembly will be inserted into the transition and secured with laminating epoxy. Hopefully this will keep the tube centered and aligned correctly.
 

JimJarvis50

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The pictures show I have done reducing transitions. The fill is just laminating epoxy with West 410. It's like wood, and just sands to shape.

Jim
 

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alexzogh

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Shrink tape is usually wrapped with at least a 50% overlap. This overlap is increase or decreased if you need more or less compaction: the epoxy will squeeze out between the layers of shrink tape.

hmm.... maybe it depends upon the heat shrink tape you use. I use Dunston hi-shrink. They have a handy calculator that helps determine what your overlap should be based upon your winding tension, length of part, and width.


Given the winding tension I use, anything over a 10% overlap risks crushing the underlying cardboard mandrel during heat cure - actually happened to me, which is when the company recommended I reduce or eliminate my overlap given the winding tension, and pointed me to the calculator
 

Frosty_Burrito

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Today I finished the electronics bay wiring for the sustainer and booster. I also attached the centering rings for the ISC tube.PXL_20220812_190748022.jpg PXL_20220812_190754891.jpg PXL_20220810_175125163.jpg PXL_20220810_175133153.jpg PXL_20220812_210705757.jpg PXL_20220812_210707574.jpg
The centering ring jigs may stick even though I tried to wipe all the epoxy off. If they do, I can just crack and cut and sand them away. Of all the centering rings I've installed I think these are the most important ones, so I'm trying to keep them as square as possible.
 

rocketace

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2 Raven 4 Altimeters
1 RTOM3
1 TeleGPS
1 Featherweight GPS
1 RunCam Split HD
Independent 1S or 2S LiPo batteries for each component. Altimeters are controlled by a screw switch, the GPS units are plugged in during assembly and stay on the whole time.

Are you using any switches for the RTOM3 or RunCams?
 

Bean74525

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At this point, the structure and electronics are mostly complete. We've installed motor retention in both stages, unfortunately i don't have great pictures. The booster has a standard aeropack minimum diameter retainer, but the sustainer is a bit different. Since we cant use the standard aft closure on the casing, the thrust is transferred through a coupler at the top of the casing. The motor is then held in by a threaded rod on the bottom bulkhead of the
sustainer ebay.
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Recovery wise, the sustainer is going to have a Rocketman 1ft pro-x drogue and a 48" iris ultra from Fruity Chutes. We're going to be using nylon tube charges for the apogee events and cable cutters from Half Cat Rocketry to open the main. From initial test fits, all of this is going to be difficult to get into the nosecone, so we may need to add a small section of airframe if we can't get it to fit.

Over the next month or two the rocket is going to get painted and then we'll hopefully fly it for the first time at MDRA this winter once they go back to Higgs. Motor choice hasn't been finalized yet, but we'll hopefully send it above 10k.
 

waltr

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I'd like to see this fly. Since I just got my L1 I am planning on joining MDRA next year and make it down for a few launches at Higgs farm. Hope you get to fly it then also.
 

Chad

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How are you planning to do sustainer ignition? head-end? In my two stage design i have the sustainer electronics mounted in the nosecone but then the sustainer ignition wires have to be broken on chute deployment. I have a deans connector that seems to be ok with being jerked apart by the ejection charge but it's not my favorite part of the design.
 

Bean74525

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We aren't planning on messing with head end just yet. The current plan is to run flat speaker wire to the aft end of the motor for the separation charge and air start. We were originally planning on having some sort of wire disconnect, but didn't really like the idea of it so we switched to doing all of the recovery out of the nosecone.
 
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