Canadian Level 4 Certification Build - Ultimate Wildman

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rocketgeek101

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Welcome to the build thread for my Ultimate Wildman which I'll be using to attempt my Level 4 with the Canadian Association of Rocketry this summer. :)

And yes, that "4" is not a typo. In Canada HPR certification is broken down into four certification levels (L1 = H; L2 = I; L3 = J, K & L; L4 = M, N & O). Level 4 is equivalent to TRA or NAR Level 3.

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Note: Dimensions are in mm and are accurate for the specific kit I received.

OpenRocket screen shot:
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Without further ado, let the build begin!

The parts:
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After unboxing everything and inspecting each of the components, the first order of business was to clean up the fibreglass parts. I set up the garden hose in the middle of winter to do this while there was a few feet of snow on the ground, as some of the parts were much too large to fit in the basement sink (and there is no way I'd be allowed to rinse off these parts in the shower:angiefavorite:).

The first assembly step was to drill 12 circularly spaced 1/4” holes in the rear centering ring to attach the 98mm AeroPack retainer. An 8-32 PEM nut (McMaster-Carr part no. 95117A444) was installed in each hole by means of a sophisticated installation tool (hammer) to provide a secure threaded metal attachment point for each of the twelve 8-32 hex-screws holding the retainer to the rocket.
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With the installation of the AeroPack done, the rest of the motor mount was then assembled. Throughout this build all of the fibreglass surfaces were prepped for bonding with epoxy by thoroughly scuffing with 60-grit sandpaper. The surfaces were also wiped with a paper towel wetted with isopropyl alcohol to remove any skin oils or other contaminants that may be present on the surface of the parts prior to bonding. A simple water break test was often used to validate a surface as being ready to accept epoxy. I used RocketPoxy for all structural joints. For non-structural joints, Gorilla 5-minute epoxy was occasionally used.

All three CR's were epoxied onto the motor tube. The middle and rear CR's were positioned so that they respectively touch the top and bottom of the the through-the-wall fin tabs. This will essentially result in the thrust of the motor being transferred to the airframe without directly stressing any of the epoxy joints. The shock cord is attached to the booster section by means of two steel lifting eyebolts bolted through the forward CR. The nuts holding the eyebolts in place were coated with epoxy after securely tightening to prevent them from loosening over time.

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In lieu of traditional or injected internal fillets, I decided to use a newer technique that has been gaining popularity. I laser cut thin strips of plywood that were then glued to the motor tube to construct fin pockets:
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To attach the fins, each pocket is filled with about 55 ml of epoxy by injecting through the slot for the fin, after which the fin is inserted. The plywood strips simply serve to keep the epoxy around the base of the fin, and are not intended to be structural. With this method, the “internal fillets” are done at the same time as the initial fin attachment.

The main shock cord is attached to the motor mount with a short 1/2” tubular Kevlar Y-harness. I used a sewing awl to hand-sew loops in the harness directly around the eyebolts on the forward centering ring using 250-pound Kevlar thread.
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As you can tell, my stitching is not the neatest, but these loops sure feel strong. A sewn loop should weaken the cord considerably less than tying a knot would.
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The completed motor mount ready to be installed:
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The motor mount was then installed into the booster airframe. 55 ml of epoxy was placed in the airframe where the forward centering ring will be located, and the motor mount was partially inserted. ~20 ml of epoxy was injected in-between the two forward CR's though the tops of the fin slots and also at the base of the booster airframe where the rear CR will sit. At this point the motor mount was fully moved into position. Also at this time the rear 1515 rail button was installed.

I wasn’t quite satisfied with the amount of epoxy above the forward CR, so before the initial epoxy had fully cured I injected a further 50 ml of epoxy above the forward CR (which I had to do by reaching down from the top of the booster tube) to ultimately create a ~0.8 cm deep epoxy dam above the CR. Probably excessive, but since this joint has the potential to experience significant stress during deployment, I chose to be liberal with the epoxy. The exposed portion of the Kevlar Y-harness was wrapped with masking tape so that if any epoxy got on it (which did happen) it would not reach the Kevlar fibres.
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The nice thing about translucent tubing is it allows you to check your epoxy work to some extent:
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Once the epoxy had cured, I put a fillet of epoxy on the remaining side of the rear CR:
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I also epoxied the switch band to the avionics bay coupler:
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The fin tabs were then sanded and wiped with isopropyl alcohol in preparation for epoxy.
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I 3D printed a jig to ensure proper alignment of the fins.
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One at a time, each fin pocket on the motor mount was filled with 55 ml of epoxy and the fin inserted.
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The fin jig was slid into place to hold the fin in the correct position and the entire assembly was left to cure with the fin oriented vertically. The remaining fins were also fitted in place to help keep the fin jig correctly positioned. This process was done a total of three times to attach each fin.
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Here you can kind of see how the fin pocket effectively guides the epoxy to encapsulate the fin root:
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rocketgeek101: A little armchair quarterbacking here. As my final step in fabricating the 1/2” tubular Kevlar Y-harness, I would have soaked the sewn portion with super thin cyanoacrylate glue. Along with your 250-pound stitches, that would ensure it never comes apart. I use this method frequently with 1" nylon tubing. I admit I've never soaked Kevlar with CA; if someone else on this forum knows that causes something ugly to happen, I'd like to hear about it.
Bob Schultz
 
rocketgeek101: A little armchair quarterbacking here. As my final step in fabricating the 1/2” tubular Kevlar Y-harness, I would have soaked the sewn portion with super thin cyanoacrylate glue. Along with your 250-pound stitches, that would ensure it never comes apart. I use this method frequently with 1" nylon tubing. I admit I've never soaked Kevlar with CA; if someone else on this forum knows that causes something ugly to happen, I'd like to hear about it.
Bob Schultz

The general advice I've read is that Kevlar does not like getting glue on it. When it bends, the glue can create sharp points that will cut away at the fibres potentially leading to failure of the harness after a few flights.
 
. . . . and speaking of stitching, I install folded-back about 18" of a single line of stitches in my nylon tubing shock cords. The energy used to tear out those stitches upon ejection is managed energy that doesn't zipper the body tube or damage the chute. I take the shock cord to my friendly local neighborhood tailor who sews the stitches in using his industrial-grade sewing machine. Takes him just a few seconds, costs me three bucks. And the tailor gets a kick out of knowing that his work is involved with the flying of (what seems to him) a really BIG rocket!
Bob Schultz
 
. . . . and speaking of stitching, I install folded-back about 18" of a single line of stitches in my nylon tubing shock cords. The energy used to tear out those stitches upon ejection is managed energy that doesn't zipper the body tube or damage the chute. I take the shock cord to my friendly local neighborhood tailor who sews the stitches in using his industrial-grade sewing machine. Takes him just a few seconds, costs me three bucks. And the tailor gets a kick out of knowing that his work is involved with the flying of (what seems to him) a really BIG rocket!
Bob Schultz

What strength thread do you use for that? If I understand correctly, the length of the stitching is 18" but because of the way the force is distributed, it will only be applied to one stitch at a time (and thus each stitch will break in succession until the energy is dissipated).
 
Thread strength: just good old-fashioned tailor's clothing thread, whatever he happens to have in his sewing machine when I walk in the door. It can't be monster strong thread, because I want it to break when the time comes to absorb energy. If I carefully placed a microphone, I'll bet I'd hear a ripping sound a whole lot like what happened when I was fourteen and tore out the seam in my swim trunks when I tried to impress that redheaded girl by doing a cannonball off the end of the boat dock.
Bob Schultz
 
Glue on the harness is usually bad.
We stitch ours with a bar-tacker using kevlar thread and then cover the stitching with heavy-duty heat-shrink.
 
The past few weeks have been pretty busy with the end of the winter semester, but today I started laying down the first set of external fillets. This is actually one of my favourite parts of a build.

I started by sanding down the areas where the fillets would go with 60 grit and then wiping with IPA.
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Next I taped off where the fillets will go with green painters tape and mixed up and applied Rocketpoxy to the area. I pulled the epoxy into the shape of the fillet using a 1.5 cm radius tool I made on my 3D printer. Unfortunately I forgot to take any pictures of these steps but I will try to remember to do so on the next set.

Once the fillets were shaped, I made sure everything was level and left it to sit for a bit
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I then removed the tape. Once these have cured for a few hours, I will rotate the rocket and do the next set.
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Pro tip: you can figure out where you need to place the tape by measuring out the radius of your fillet shaping tool:
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Here is a picture of the simple fillet shaping tool I 3D printed. Basically a glorified extra wide plastic popsicle stick.
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Before applying the epoxy I give the area a final wipe with some 99% IPA.
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I then mixed up some Rocketpoxy and poured it on. Each fillet ends up using about 20-25 ml of epoxy.
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Then I used my shaping tool to pull each fillet:
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Once that is done, I removed the tape and made sure the assembly was level before leaving it to cure.
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I did the second set of external fillets this afternoon and the third set this evening. At this point most of the structural work on the booster section is done. I'll be shifting my focus now to working on the upper half of the rocket.
 
Beautiful!
What kind of paint scheme do you have in mind?
What do you intend to name her?
Bob Schultz
Haven't really settled on the paint scheme yet. Currently leaning towards naming her Cosmic Kiss, though that may also change if I think of something I like better.

Here are some of the ideas I've come up with and sketched out. I have a friend who will make me some vinyl decals for this project with her Cricut.

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The past few weeks have been pretty busy with the end of the winter semester, but today I started laying down the first set of external fillets. This is actually one of my favourite parts of a build.

I started by sanding down the areas where the fillets would go with 60 grit and then wiping with IPA.
View attachment 514349

Next I taped off where the fillets will go with green painters tape and mixed up and applied Rocketpoxy to the area. I pulled the epoxy into the shape of the fillet using a 1.5 cm radius tool I made on my 3D printer. Unfortunately I forgot to take any pictures of these steps but I will try to remember to do so on the next set.

Once the fillets were shaped, I made sure everything was level and left it to sit for a bit
View attachment 514350

I then removed the tape. Once these have cured for a few hours, I will rotate the rocket and do the next set.
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I wanted to thank you for showing us how to use the level to ensure the epoxy doesn’t drip over the fin edges. It’s great to learn new tricks at my age!
 
For tracking I'll be using a Featherweight GPS tracker.
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I've been working on designing a mount for the tracker that will be 3D printed. The large conical piece is a base that will be bolted to the inner facing side of the nosecone bulk plate (the nose cone coupler will be attached with some 8-32 screws, permitting access to the inside of the nosecone). The tracker itself is mounted to a sled that is designed to be threaded into the base for easy attachment and removal (this would also make it easy to swap the tracker between rockets). At the moment the main issue I have with the design (which is not a concern for this project) is that it is a bit bulky. In the future I will probably refine the design into a version 2 that is more compact, allowing it to be used in smaller rockets, but for now I will stick with this as I should move onto designing the avionics bay sled :)

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For tracking I'll be using a Featherweight GPS tracker.
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I've been working on designing a mount for the tracker that will be 3D printed. The large conical piece is a base that will be bolted to the inner facing side of the nosecone bulk plate (the nose cone coupler will be attached with some 8-32 screws, permitting access to the inside of the nosecone). The tracker itself is mounted to a sled that is designed to be threaded into the base for easy attachment and removal (this would also make it easy to swap the tracker between rockets). At the moment the main issue I have with the design (which is not a concern for this project) is that it is a bit bulky. In the future I will probably refine the design into a version 2 that is more compact, allowing it to be used in smaller rockets, but for now I will stick with this as I should move onto designing the avionics bay sled :)

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Awesome tracker! Can you please share the stl file when complete?
 
I printed and assembled the tracker mount out of PETG.

Time for some pics!

Fully assembled unit: the fibreglass bulkhead will get epoxied into the nosecone coupler (the coupler will be attached to the nose using screws to make it removable). I added a cover to the design that goes over the tracker sled for a bit of added protection (mostly for during prep; I doubt the cover will do much to offer additional protection during the actual flight). The mount is attached to the bulkhead using three 8-32 machine screws.

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Detail of the sled assembly: the battery cover and Featherweight tracker are attached to the main sled using 4-40x1/4" machine screws.
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