4" Wildman Darkstar Build
This project was the third Wildman Darkstar rocket I built. It features a custom Sticker Shop wrap and was dubbed Neutron Star.
The Darkstar line of rockets is very popular for a lot of reasons. They are easy to build, fly wonderfully, look cool and, usually, have a distinctive whistle during the boost phase.
This project was built as a standard dual deploy rocket with a primary and backup flight computers.
Parts List and components
Initial Build Notes
For this build, I approached things a bit differently. I used a Sticker Shock (https://stickershock23.com/) wrap for this build and this was my first time trying to implement one. I talked to Mark a couple times and he designed a really amazing wrap for this build and it took him a couple weeks to get it done. He highly recommended waiting to install the fins after installing the wrap, so I needed to do things in a bit of reverse order. Following Mark’s guidance and the video he has on his site, I basically got all the various holes and hardware in the booster, payload and switch band done before installing the wrap, then installed the fins. I also built the nosecone to accept electronics.
Started off as normal by dry fitting all parts and sanding down the ends to ensure a tight fit at all junctions. I then labeled all the ends so I can remember which parts had been fitted to other parts.
I also marked out the lines on the couplers for later use:
And marked down the fin lines and rail button lines all the way down the tubes. One note, normally I would not mark the outer surfaces with a Sharpie because the Sharpie lines have a tendency to bleed up through paint, but I am doing a wrap on this rocket, so it is not a problem.
Motor Mount Build
I taped the retainer onto the end of the MMT and taped the tailcone onto that so I could accurately measure out the various spacings on the MMT for the CRs and retainer. A reminder from the 3″ build, if you are going to use one of the Aeropack tailcone retainers, the spacing is much different. Luckily, Wildman included a fairly long MMT with this kit, so there was more room to work with at the forward end of the fin slots (as compared to the 3″ model). I didn’t tack anything in place at this point, I just measured things out and marked the MMT.
The MMT measurements allowed me to get an accurate length for the kevlar bridle. For this build, I used a 1/2″ tubular kevlar rated to 6000 pounds. Pretty straightforward here, measured the length so the bridle would just reach the edge of the booster when done. Cut the kevlar by saturating the cut point with thin CA then used a utility blade to cut it clean when dry. Nice clean cut.
Next up, I measured the thickness of the kevlar to determine how deep the slots on the forward CR should be, measured and marked them on the CR, then ground out the slots with a permagrit file.
Then I tacked the forward CR in place with some CA and set aside to dry
I used the fin slots to mark out the fin lines on the MMT and masked them off with some tape. I also masked off the end of the upper fins slots where the middle CR will go to avoid getting any epoxy in that area. I fed the bridle ends through the slots and epoxied them down with some Aeropoxy 6029 and taped them in place. I epoxy them slightly angled away from the fin slot – I figure it adds a bit of security to have them angled away from the slot in the CR, but also helps ensure they don’t inadvertently interfere with the fin installation later.
I drilled some holes in the rear CR and threaded some scrap kevlar thread in them to allow me to easily insert the CR and pull it back out, which needed to be done a number of times through the build.
Once the bridle epoxy cured, I coated everything with Proline 4500, including filleting the forward CR ring, top and bottom and let it cure overnight before conitnuing.
I tacked on the rear CR with some mounting putty and the retainer with tape so I could epoxy in the MMT and the forward CR. I used Aeropoxy 6209 for this – mixed up a healthy batch and got a good layer in, just forward of the fin slots. I placed the MMT in the body tube to the right depth (checked by inserting the fins), ensuring the fins lines marked on the MMT lined up with the fin slots, and put this aside to cure for the day.
Booster Section Build
I did not inject the internal fillets for both the forward and rear fins this time. I only injected the front fins and then did the rear internal fillets through the aft opening before I fixxed the rear CR in place. I usually forget to grind out the injection holes before putting in the MMT, so this time I made it a point to do it first on the checklist. I find it much easier to use a Dremel to grind the holes when there is no MMT blocking the bit.
Normally, I would not finish the fins prior to installation, but since I am going to wrap the tubes, I want the fins to be painted before installation.
Before I epoxied the kevlar on the MMT, while I had the MMT in booster to mark the fins lines, I also inserted the fins and drew a baseline. Then I drew a line 2mm above that for a fillet. Mark says you can fillet right over the wrap, but I wasn’t so sure I wanted to do that. Normally, I do a 5mm external fillet. I will meet half way here and later trim the wrap 2mm back and have fillet sit half on bare FG and half on the wrap. Should be nice and strong and, hopefully, provide a blend into the wrap.
With the lines on the fins drawn, I masked them off and formed a holder out of some packing foam and then hit them with 3 coats of primer and wet sanded lightly with 400 grit after last coat. Then, 4 total coats of Duplicolor Black Engine paint, 800 grit wet sand between the 3rd and 4th coats. And, finally, 3 coats of Duplicolor Gloss Clear Engine paint.
With the forward CR epoxied in place, this would normally be the point in the build where I epoxy in the forward fins, proceed with the next CRs, then rear fins, etc. But, since I am going to wrap it, I need to jump forward to a bunch of things I would normally do as finishing steps. Mark recommends drilling all holes prior to wrapping the tube and then going back later and cutting the holes out with a hobby knife. So, I needed to plan out and drill all the various vent holes, switch holes, shear pin holes and PEM nut fasteners prior to starting this wrap. Frankly, I should probably be more diligent about doing these steps earlier in the build anyway, so this forced my hand to do some better quality engineering up front.
I laid out the dry assembled tube with the retainer taped in place and all the seams/joints taped tightly:
Measured and marked the vent holes in the booster, switch band and payload bay:
Marked out the holes for the 1010 and 1515 rail buttons:
Measured and marked for the PEM nuts:
Measured and marked for the 2 switch holes:
And measured and marked for the PEM holes on the Nosecone and the shear pins:
Then I drilled everything out and cleaned up the holes with a file. Holes drilled:
- 4 body tube vent holes – 5/32″ each
- 2 Switch band vent holes – 5/32″ each
- 1010 rail button holes – 3/16″, cleaned up with file and test fitted with the weld nuts
- 1515 rail button holes – 1/4″, cleaned up with file and test fitted with the weld nuts
- PEM nut holes in payload bay and Nosecone (using 4-40 PEMs) – 1/4″ each
- 2 switch holes – 1/4″ each
Once all holes were drilled and cleaned up, I installed the PEM nuts in the payload bay and nosecone
Then I drilled and tapped the 2-56 shear pins:
And, once the epoxy on the hardware cured, I assembled everything, put all the screws in and Dremeled witness marks at all appropriate junctions:
Next thing I tackled was the wrap – go over to the “Paint and Finishing” section below to see that
Once the wrap was on, I moved to installing the forward fins. First, I trimmed 2mm of the wrap away from the fin slot to promote better adhesion.
Then, I used a guillotine fin jig and a Badass Rocketry 3D printed fin guide to tack the forward fins in with quick cure epoxy.
With the forward fins all epoxied in at the root, I epoxied in the CR that goes right behind the fins. I used a generous amount of mid-cure epoxy to ensure a good seal for when I inject the internal fillets. Also, I should note that this time when I epoxied the fins in, I paid particular attention to getting a generous amount of epoxy on the forward edge of the fin tab and the beveled edge. I really tried to get a great seal in the fin compartment this time to avoid leaks!
I then moved on to injecting the internal fillets for the forward fins. First step was to make sure everything is sealed. I got leaks on the past two builds, so I spent extra time for this build – I did’t want to leak epoxy on that nice wrap.
I beefed up the fillets on the rearward CR with some quick cure epoxy, just to make sure there aren’t any gaps I missed. Then I went around each fin and sealed the edge with some quick cure epoxy, making sure this time to really concentrate on the beveled ends of the fin tabs to ensure I get some down in the gap. I think this is where I got the leaks last time.
Finally, taped the holes shut on the fin sections I wasn’t filling at the time.
I used West Systems 105 Resin with the 205 “fast” hardener. Switching from Aeropoxy 2032 that I used on the earlier builds. I love the Aeropoxy epoxy, but I have to admit that it takes forever to cure, even if you can keep the heat up. West 205 gets to leather stage in just a few hours, even at room temp, so you should be able to get all the fillets injected in one day instead of two days. Also, switching to West 406 Colloidal Silica from milled FG. I am skeptical that milled FG does much to increase the strength of the epoxy whereas there is evidence (from West Systems literature) that the colloidal silica actually increases the structural strength, so mixing in about 1/2 a teaspoon or so. Also, using some black dye (the stuff that comes with RocketPoxy). Reason for the dye is to be able to better see where the epoxy goes (i.e. – if I get a leak) and so that any epoxy that comes up through the hole matches the black fins/future external fillets.
I leveled out the rocket laterally and longitudinally before injecting the epoxy.
I used a 20ml syringe and injected 10 ml into each side of the fin compartment. That didn’t fill it up, but it was definitely enough to move the rocket around and coat the whole fin tab with a decent layer of epoxy. This time, there were no leaks!
I filled up the injection holes with Aeropoxy 6209 mixed with a copius amount of West 404 High Density filler. I mixed it to beyond peanut butter consistency so it would stay in the hole. I mixed in some black dye to make sure I don’t give myself more problems later with the color.
Next step – getting those rear fins in. This rocket is too long to fit in the guillotine jig for the rear fins, so just using some angle aluminum to ensure the rear fins are lined up with the front fins. I used regular 5 min epoxy to tack the fin root to the MMT.
Only the top fin is epoxied in this photo – the other two fins are taped in to allow the Badass rocket jig to help keep things straight.
With the rear fins in and bonded to the MMT, I began working on the internal fillets for the rear fins, I used Aeropoxy 6209 with enough colloidal silica to make it into a very thick paste. This is probably one of the most fun activities in HPR – glooping epoxy into a fin can for internal fillets!
The black dye in this case is merely to make it easier for me to see where I have put the epoxy. If I don’t dye it, it is really difficult for me to see the translucent epoxy way down in the tube and I can’t be sure I coated all the necessary surfaces. The black dye makes it foolproof.
First, I taped off the ends to avoid getting epoxy where the rear CR and retainer will go.
Then, I generously coated the fin section, leaving about 1/2″ at the end of the fin un-epoxied to avoid interfering with the rear CR.
With the internal fillets done and cured, I moved on to the external fillets. I used Proline 4500 for this. Usually I use RocketPoxy for external fillets, but I was looking for that inky black Proline delivers to blend in with the wrap.
I cut the wrap back 2mm earlier in the thread and want a little bit of overlap with the fillet, so measuring out 3mm from the fin to tape off the fillet area. Once the mask was in place, I applied the Proline and smoothed with a gloved finger. Then I removed the tape in about 10 minutes, hoping the edge of the Proline will settle just a bit. I did’t want to mess with it too much, concerned about messing up that nice wrap. Worse case is that there is a bit of a square edge on the fillet that stands proud of the wrap/fin. Nothing I can’t live with and not worth screwing up the wrap or paint on the fin. Came out good enough for me.
With the external fillets done, the next few steps were all done at once:
– Installed the weld nuts for the rear rail buttons. Tacked them in with CA and held them tight by screwing in the rail button while the CA dried.
– Placed a tape-round on the back of the weld nut to protect the threads from the epoxy
– Had the Proline out from the external fillets, so mixed up a largish batch and put a generous amount around the MMT, body tube and rear edge of the fins for the rear CR. Also, coated the back of the weld nuts while I was spreading epoxy around
– Installed the rear CR tight against the rear of the fins
– Used the rest of the Proline to spread an even coat on the rear CR
– Finally, mixed up a batch of JB Weld and epoxied the retainer in place. Placed an Aerotech 54mm 2800 case in the MMT tube to keep the retainer centered and weighted down while the JBW is curing.
– Set the whole assembly aside to cure overnight.
All epoxy cured nicely – I test fit the tailcone retainer over the motor case, no issues. Also epoxied in the upper rail button weld nuts.
Fair warning for anyone else that gets this kit – Like I did in the 3″ Darkstar build, I did get an extended coupler tube. The kit comes with an 8″ coupler tube for the e-bay and I replaced it with a 10″ coupler I got from Wildman. Mainly, this was becuase I wanted to use one of the printed Additive Engineering sleds and the switch mounts are on one end of the sled. My experience in the past is that to get the switch ports away from the end of the tube, you need to push the sled to one side or the other and a longer tube helps keep the switch band fairly centered. In this case, my measurements indicated that a 10″ tube would put the switch band almost center using the not-quite-5″ long dual altimeter 98mm sled. So, if you use the same components and wonder why your switch band ends up considerable off-center, that is why.
The components for this build will be:
– Redundant MW RRC3 altimeters
– 98mm Dual Altimeter Additive Engineering 3D printed sled
– Shurter rotary switches
– Wildman aluminum bulkheads
– 1 foot long 1/4″-20 all thread
Started off fitting the switches in place. As usual with these printed sleds, the terminals are quite close to the bed of the sled, so I like to solder the wires on at a 90 degree angle. Getting pretty used to doing these now and can knock them out pretty quickly. I added the heat shrink tubing and installed the switches once everything cooled. One aspect I would note if you solder the wires on at an “extreme” angle is that it makes it more difficult to slip the locking nut back over the wires and onto the switch. You could solder the wires on while the switch is in place on the sled, but I am not good enough or dexterous enough with my soldering to make that work well, so I estimate how wide I can make the angle before I solder the wires by test fitting the nut over the wires. It isn’t perfect, but I can usually carefully bend things around a bit to manipulate the nut on if I get too wide. Learned that lessen the first time I tried this method a while back and I ended up having to desolder and try again.
The switch has 4 posts, I cut away the two outer posts.
I used 22 AWG wire for this build with high temp silicon coating.
The sled comes with some small nylon standoffs – perfect size for keeping the RRC3 components off the deck. I lined them up and used the screws that came with the sled to anchor the two altimeters on. Trimmed the switch wires, got the battery terminals in place and installed ferrules on all wires. Screwed them into the altimeter and that portion was complete.
Note: I usually screw the battery covers on backwards when there is no battery in the compartment. Reason is twofold – I don’t want to lose the covers or screws and it ensures I know I didn’t inadvertently leave a battery in the compartment when storing/shipping the rocket.
I drilled all the holes in the aluminum bulkheads for the charge wells, terminal blocks and wiring.
I used Rocket Junkies 3g charge wells for this build. They require a 3/16″ hole and a bit of epoxy.
I used simple 2 wire terminal blocks, 4-40 screws with nylon nuts and bit of epoxy to secure them in place.
I ran the wiring (22 AWG silicone coated) through holes on the bulkheads and filled the holes with some FabriTac. Put ferrules on the both ends and installed into the appropriate ports on the altimeters. I used simple color codes: white wires for the nose/main parachute ports and yellow for the aft/drogue ports.
I installed the forged eye-bolts and all the nuts got a drop of Loctite.
Finally, I installed a couple quick-connects to the wires leading to the aft bulkhead and then used heat shrink tubing to keep all the routing neat and tidy.
I did continuity testing on all electronics and a vacuum test.
Originally, I just used centrifuge vials filled with black powder for the ejection charges. Later, I went back and added charge wells. I found that end caps for copper tubing fit perfectly on the bulkheads. The vials/glove finger method works fine, but I find the setup using charge wells so much easier.
Odds and Ends
Painting and finishing
I tackled the payload bay wrap first. This was my first full wrap from StickerShock, so headed in with a bit of trepidation. The wraps aren’t cheap. They look amazing, though! And while Mark was designing this wrap for me, he told me that he can only print a piece up to 52″ long and this is a 67″ long total tube length that needs to be covered, so it was going to have to be done in a minimum of two sections. The booster and switch band was one section and the payload bay was in the second section, but the payload bay is less than half the 52″ length, so Mark filled the extra space with a second payload bay wrap (no extra charge) which gives me a wrap to practice with. I am glad for this and glad I started with the smaller section first, I learned a few lessons.
Following the steps in Marks video tutorial, I lightly sanded the tube and thoroughly cleaned it with alcohol.
Then, using one of the lines I drew earlier down the whole length of the rocket, I lined up the wrap and put a tape “hinge” on one side:
I wrapped it around to make sure it was square to the tube – first time “Go”!
I peeled the backing off and began smoothing it out from the middle about an inch or two at the time. Mark says this stuff is easy to peel on and off and reposition – he is right, great stuff to work with and the wrapping turned out to be pretty easy.
I got a couple small bubbles, but easy to press out with your hand, no problem:
Once the wrap was on, I heated it up, as per Mark’s instructions. It really shrinks onto the tube very well! It definitely tightens up nicely around the ends and any holes/slots.
And here is where I messed up. The PEM nuts left the wrap in a little tent around them:
I heated it up, thinking the wrap would shrink around the nut. Instead, all that air had nowhere to go, so it completely bubbled up and deformed. I tried to “patch” it, but it is a bit of a mess.
It doesn’t look too bad, so I am going to leave it and save the extra payload wrap in case I ding this one up at a launch.
For the correct way to handle this situation, trim around the inner circle BEFORE you heat it up, the air can escape and the wrap shrinks nicely to the edge of the washer:
Once it cooled, I trimmed the holes, checked to make sure the shear pins still fit, and trimmed the ends. Came out pretty darn good!
You really need at least two people to do the bigger wraps, so I got some help and wrapped the long booster tube. I didn’t get any pictures of the process, our hands were kind of full, but took one of the fin slots after trimming. The whole thing came out incredibly – Mark really made an awesome wrap for this “Neutron Star”!
I sprayed the nosecone with one coat of primer and sanded it down to find the low spots. These nosecones from Wildman can be a little “fuzzy” with FG threads and also have some grooves in the weave. So, sanded off the fuzzies and filled in the grooves with some bondo. Then sprayed it again with 4 coats of Duplicolor engine primer and wet sanded down to 800 grit.
With 3 coats of Duplicolor Engine Black Gloss:
And, finally, with 4 coats of Duplicolor Engine Clear Gloss:
The charges for the ground testing were calculated using the calculator at Insane Rocketry’s site: https://www.insanerocketry.com/blackpowder.html.
The calulation for the drogue charge was 3g of FFFFg black powder. That charge turned out to be good and was used for the primary charge in the cert flight. The backup charge was 4g of FFFFg.
The charge for the main charge was calculated to be 4g of FFFFg. This turned out to be a bit weak, so the primary charge used for the cert flight was 4.5g of FFFFg and a 5.5g backup charge.
Pictures & Flight Videos
Once everything was complete, I coated the entire rocket with a couple more coats of clear gloss and the result was amazing!
The initial flights were conducted on 20 & 21 February 2021 at MDRA Higgs Farm. That weekend it flew on a Loki J-474, an AT K-400 and an AT L-1090 and they were great flights. The rocket has been flown many times since then.