Minimum Diameter Rocket Build - 38 mm Carbon Fiber

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Steinerino

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Hi All - New member here. Starting a new project and just made all the plans and initial purchases. Thought I would share with the group for comments and discussion.

Objectives of this project are a number of firsts here for me:
  • Work with carbon fiber - a new rocket material
    • Builds on past rocket builds using plywood/paper (Level 1 certification) and fiberglass (Level 2 certification)
  • Challenge the build process with minimum diameter format
  • Build rocket to use DMS motors with option to grow into RMS motor (I don't use RMS yet)
  • Utilize radio tracking
    • Solve the issue with my lost Level 2 fiberglass rocket
The parts picture is here and attached a pdf of the parts list. Now waiting for the parts to arrive!

Larry


Mongoose Parts.jpeg
 

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Hi All - New member here. Starting a new project and just made all the plans and initial purchases. Thought I would share with the group for comments and discussion.

Objectives of this project are a number of firsts here for me:
  • Work with carbon fiber - a new rocket material
    • Builds on past rocket builds using plywood/paper (Level 1 certification) and fiberglass (Level 2 certification)
  • Challenge the build process with minimum diameter format
  • Build rocket to use DMS motors with option to grow into RMS motor (I don't use RMS yet)
  • Utilize radio tracking
    • Solve the issue with my lost Level 2 fiberglass rocket
The parts picture is here and attached a pdf of the parts list. Now waiting for the parts to arrive!

Larry


View attachment 505534
Hopefully, the nosecone is fiberglass. You can use it for your tracker compartment.
 
Here is a parts list not in the pdf format I attached.

  • Madcow Mongoose
    • Model
    • Carbon fiber body with fiberglass nosecone
  • Nosecone Tracking & Sled:
  • Parachute
  • Electronics Bay
  • Shock Cord/Tether
  • Shock Cord Attachment
    • Madcow 1.6” G12 coupler - cut down section of coupler to glue inside airframe at ~19” from bottom of rocket
    • Then use Kevlar soft link – glue inside the coupler to permanently couple to the shock cord.
      • Cover nylon portion with JB Weld epoxy to protect this attachment
    • Leaving enough room to add AeroPack minimum diameter retainer at a later date
    • Leaves much of internal airframe open for motor ejection charge as well as parachute/shock cord packing
    • In the future, if I move to true dual deployment, I can swap out the large parachute in the sustainer with a drogue pretty easily
  • Initial recovery electronics
  • Electronics Bay
    • No initial electronics, but will build out with the aluminum rods and the Additive Aerospace sled
    • Over time, I do like the simplicity and reliability of the RRC2 that I have used in other rockets
  • Motor Retention
  • Eye Bolts
  • Rail Attachment
  • Epoxy
    • JB Weld
    • Madcow black dye
    • Will not be painting the rocket – let the carbon fiber show thru!
  • Nose Weight –
    • ????Need to determine with Rocsim
 
I have built a number of the exact same model in both 38mm and 54mm. I've only ever used ProLine epoxy fillets to hold the fins on - no tip to tip - and have survived flights to Mach 2.4 (54mm) with no issues. One thing I've learned is to not put the fins so far forward as is typically shown with these rockets. Keeping them closer to the rear improves the stability by keeping the CP farther back (especially with the 54mm version).

I note that your Featherweight sled has two aluminum all-thread pieces that run alongside the antenna. I've done that with a single piece of the same type of all-thread and it definitely affects the radio signal. If you end up using that layout, you'll want to ground test your range and make sure you aren't losing a lot of signal strength and that you'll still be able to track the rocket based on its expected altitude. (As has been mentioned, you'll need to put the tracker in the nosecone, which is fiberglass, and not in the carbon fiber body tube.)

For motor retention, I've always used friction fit plus tape around the end, which works fine, but I realize that some RSOs won't allow friction fit on HPR motors. I've never seen that Apogee video before - that's a pretty clever way to do it. If you use the wire method, you might want to compare the amount of overhang of different motor cases to make sure the length of wire you choose will work with expected motors. (DMS vs. RMS) I'm looking forward to how you decide to handle this and the results.

Creating an anchor for the recovery harness is a bit of a challenge due to the small diameter. I glue a bulkhead above the longest motor I'll fly (which is either the CTI 6XL or the Loki K627 case) supported by a very short section of doubled coupler. (Bulkhead at the bottom, coupler on top.)

WARNING: The edges of the thin carbon fiber tubes are very sharp and can cut through kevlar as the rocket sways back and forth under chute. You must protect the kevlar wherever it comes into contact with a sharp edge. Heat shrink tubing works well, although I would use two layers.

For the 38mm kit, getting the chute packed is a challenge - don't be surprised if you really struggle with that and end up with a smaller chute, or something without a lot of seams. You also need a thin chute protector cut down to size. I think you'll have a real challenge getting a JLCR to work in such a small airframe.

With a larger J motor you should be able to hit 15,000' and get close to Mach 2. With the Loki K627, 20,000' and over Mach 2. I really enjoy the challenges of small MD rockets, and the Mongoose is my favorite kit. Good luck and enjoy the build.


Tony
 
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@manixFan -- Thanks for the very thoughtful post. Really helpful. I am experimenting with each new rocket trying very new things -- so I am excited about this challenge. You raise a number of important issues for me to consider.

I am not sure I understand your chute attachment description -- likely me being thick here. Are you suggesting creating and gluing in a bulkhead with an eyebolt for attachment? I was going to use the engine ejection charge to deploy the chute - but if the JLCR does not fit, then I am forced into electronics (and building really small ejection charge wells. And in that case, I need to drill more holes in the aluminum bulkheads I purchased. These would be major changes to the design I had planned. I was hoping to start flying this in a much more simplified way. One option here (if JLCR works) is to glue in the bulkhead with the attachment -- But leave holes for motor ejection to release the chute. My plan was even simpler with kevlar attachments epoxied directly inside a coupler segment with no bulkhead at all.

I am concerned that typical threaded rod would impair GPS transmission. Featherweight notes that there is a lot of loss budget in their products -- so that they track up to 100K. I agree its good to ground test. I found an interesting issue that came up this weekend. The power connector for the featherweight is on the side - so the wire wraps around the sled. When sliding the sled into the nosecone, it could pinch the wires between the fixed nut used to position the sled -- and possibly be damaged in flight (with sudden acceleration and therefore movement of the sled to and from the nut). So I am looking to change the orientation of the connector so it goes off the back of the featherweight - next to the on/off switch. I have an email into Featherweight to check on this. Possibly I am too far in the weeds - but don't like the thought of pinched wires.

Thanks for the tip on the carbon fiber edges being sharp. I do like to over-design and this would be a great area to protect the kevlar shock cord so it lasts a long time.
 
Dang, you're right of course on the mismatch in my post between the bulkhead and motor ejection. I don't use motor ejection for any of my MD HPR rockets, so I completely missed that you need to pass the ejection charge past whatever you use to anchor the parachute. Your method of course will work, although I would test it out on a piece of scrap first to make sure you don't lose too much strength right where the epoxy ends. Kevlar hates hard edges of any kind.

You don't say how high you are going, but even if were are going to 15,000', you'll likely have enough signal strength to get a good fix on your location. But still worth some testing. A good method is to hang the nosecone somewhere high and then see what kind of range you get. I was fortunate enough to have a friend with a drone who suspended my nosecone while he flew away from me and I watched the signal strength. But even putting it on a tall wooden fence post would help, anything to get it up off the ground.

If you are handy with a soldering iron and a vacuum de-solderer or solder wick, flipping the power terminal should not be a problem. You can see below that I have one that has the power routed over the board.

Sounds like you have a really good handle on things, and like I mentioned before, the Mongoose is my favorite all time rocket.


Tony

reversed.jpg
 
Your advice is great - thank you! Appreciate the collaboration. I just ordered these connectors below so I can actually route the wire to go off the back end of the board - right next to the on/off switch. I hope to insert the wires into the block you show -- and then make a 90 degree turn and then glue the female connector to the board. This way the connection is made between the rails and runs under the sled to the battery that is housed on the underside. Hope that this makes sense.

1646772394295.png
 
I’m happy to provide my experience, but of course it’s just a single data point. Always good to check out other ideas as well.

I have used many of those exact same connectors, along with JST types, for power connections. For devices that don’t need a lot of current, those shown work well.

Your plan is fine, I’ve done something nearly identical and used hot melt glue to hold things in place.


Tony
 
I note that your Featherweight sled has two aluminum all-thread pieces that run alongside the antenna. I've done that with a single piece of the same type of all-thread and it definitely affects the radio signal. If you end up using that layout, you'll want to ground test your range and make sure you aren't losing a lot of signal strength and that you'll still be able to track the rocket based on its expected altitude. (As has been mentioned, you'll need to put the tracker in the nosecone, which is fiberglass, and not in the carbon fiber body tube.)

Tony

Tony,

Thanks for bringing this up.

I am working on some electronics sleds right now, and I am planning on setting them up so that the antenna protrudes through the bulkhead so as to be out in the open.

Do you see issue with this?

I may consider converting to a different type antenna (no longer the whip, but the threaded connector) to allow me to relocate the full signal of the antenna out of the bay and put the altimeter exactly where I want it.

Thanks,
Mike
 
Tony,

Thanks for bringing this up.

I am working on some electronics sleds right now, and I am planning on setting them up so that the antenna protrudes through the bulkhead so as to be out in the open.

Do you see issue with this?

I may consider converting to a different type antenna (no longer the whip, but the threaded connector) to allow me to relocate the full signal of the antenna out of the bay and put the altimeter exactly where I want it.

Thanks,
Mike
Mike,

I’m not an antenna expert by any means, but I have been using trackers for nearly 20 years. I’m not exactly sure I am visualizing how you are planning to handle the antenna, but if it is surrounded by an aluminum bulkhead that may be an issue, even it the antenna is above the bulkhead. Is it a Featherweight unit? One of the great things about that unit is you can easily measure the signal strength to see how various configurations affect the potential range.

Regarding whip antennas, I’ve only used those with RDF trackers, mostly taped to the shock cord. Even coiled you should still get decent range from most RDF trackers. I’ve even used them in carbon fiber rockets where I don’t really get much of a signal until ejection when the antenna clears the airframe. A bit stressful during boost but also a relief when the signal strength jumps at deployment.

Not sure if any of this is helpful, but hopefully I’m not too far off track.


Tony
 
Completed most of the nosecone tracker assembly today. Here are pictures of how it all came together. I epoxied aluminum rails with nuts to stop the sled (used loctite to freeze them in place). Needed to chill the assembly in ice water as it got really hot and worried it would melt the sled). I also removed the female power adapter on the Featherweight tracker and moved a different connector off the back end of the board so the wiring would not be pinched by the sled against the forward stop nut. Thankfully there is enough space for this all to fit as you can see in the pictures.NoseconeAssembly1.jpegNoseconeAssembly2.jpegNoseconeAssembly3.jpegNoseconeAssembly4.jpeg
 
Sanded bevels on the fins with 180 grit sandpaper. I don't have electrical tools, so I marked the distances and used a sanding block to get relatively even tapers. The carbon fiber was really receptive to sanding - more so than fiberglass - this was a relatively easy process and just took some patience to monitor as I went. I want to make sure the root edge is well attached before fillets, so sanded and then spent time scoring the fin root edges as well as body tube -- trying to give maximum surface area for bonding.

Recently I have been watching Badass build videos for inspiration -- and loved their build guides. So purchased two of these to ensure alignment and to help with drawing lines to follow for fin placement. I liked their videos so much, bought another minimum diameter rocket from them - so I can try my hand at RMS motors and use their cool nosecone ebay. Will be a fun comparison with this rocket and I can stay with 38 mm motors.

Then, on the theme of strong bonds, I used J-B Weld for the first time as my epoxy. This was much thicker than I expected but delighted that its grey color matches carbon fiber well. I 'buttered up' the root edge and then placed along the prepped areas identified by the marking lines - then sliding the build guides into place. Looks like a great initial bond - and one to build on with solid fillets. Will finish fin attachment this weekend and then think about fillets -- where I will have to place the retention wire mentioned above (Apogee method of engine retainer so I can use DMS motors).
 
Adding files in another format
 

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I searched online for similar discussions -- and I selected 1.75" from the back end of the motor tube to the back end of the fins. Was hard to see in the Rocsim file how far they are up - - likely I don't know how to use the software well enough. It also appears very consistent with the Mongoose product photos.
 
Go to Rocket design components
Click finset
Go to the general tab
It tells exactly where the fins are located.
 
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@Titan II -- Thank you. Can see it now and edit for my model.
One recommendation you may want to consider is “painting” your rocket with several coats of epoxy. If you Google Jim Jarvis and carbon fiber, he has some excellent papers with photos on how to do it. It protects the carbon fiber during Mach flight and brings out the beauty of CF.
 
Got back to my build. I used thick superglue to tack in the wire engine retainer. In a few places, it was a bit 'high' and might show through the fillet. So I purchased larger dowels to make a larger fillet. This was good from a strength perspective as well - because I do not plan on tip-to-tip fiberglass. So I also purchased Rocketpoxy as this would be a bit thinner than the J-B Weld. I added milled fiberglass for strength and used dye to make it black (first time use of epoxy dye). I also had sanded the area for adhesion and wiped clean with alcohol.

Well the result is pictured here. I was hoping for picture perfect fillet - and this was pretty good but not perfect. I do believe that these are super strong -- with J-B Weld as the 'tacking' and then this glass infused fillet. They should not be going anywhere.

Now onto the rest of the fillets that should be easier now that I have practice and there is no engine retainer wire.
 

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Working on a minimum diameter kit myself. May I ask why place so far from the base of the motor tube? I’ve noticed that a lot of folks do that. Seems to me like pushing the CP forward isn’t ideal. I vaguely remember seeing that a lot of folks leave the space there for retention with tape, but Im not sure.
 
Yes tape retention area. Also landing on MMT is better than landing on a fin.
To the OP, be aware the CF will also block your signal to your alt if it has a WiFi switch.
 
Realized I did not upload how this worked out. Ran into challenges with the ebay. Used the Mach1 sled with a featherweight magnetic switch.
 

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Added an Apogee brand 18 inch parachute along with a Mach1 streamer to complete the build (along w Rocketman Kevlar shock cords). The first flight flight on an I175 SW went to 4756. But the main did not come out (yes I had ground tested). I believe the issue was that separation required to push the payload tube off w the nosecone and the chute was stuck inside. I have modified it to separate the nosecone only for its next flight.

The featherweight tracker in the nosecone worked perfectly.
 
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