2.6" Wildman Darkstar Build
This project was the first Wildman Darkstar rocket I build. In retrospect, there are some changes I would make to the build process, but mostly this build laid the ground work for all the other Darkstar builds I have done.
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.
The 2.6″ version normally comes with a 38mm mount. It also comes in a 54mm mount version, which I will build in another thread. This project was built as a standard dual deploy rocket with a single flight computer.
Parts List and components
Initial Build Notes
As noted on the Darkstar fron page, you need to check all the ends of the tubes, etc, for smoothness. As these photos show, you will usually find one end of each tube to have a bump. I used a sanding block with 180 grit sandpaper to get this one smooth.
This kit did not come with a switch band, so I ordered an extra one. Some folks don’t use switch bands at all, but I like them. Not only do they give you place to hold the switch (or access an internal one), they provide a rock solid “stop” between any two parts. This ensures things like shear pin holes and PEM nut holes always line up.
Motor Mount Build
I marked out the MMT for all the CRs and retainer. I am using a regular Aeropack 38mm L2 retainer (not aware of a 38mm to 2.6″ tailcone retainer out there, but would have used one if I could find it). My build process is to glue the forward ring on first, then work my way backward, gluing each successive CR to the fins as I go and then use the injection method for internal filleting.
For measuring and marking, though, you need to start with the retainer. It dictates how the entire MMT will be placed and fit. So, I marked the retainer line, then taped the rear CR in place (nothing glued right now). I put on the forward ring and laid the tube out next to the lower body tube to determine best spot for the forward CR and marked that spot. An old Estes BT-60 tube marking guide helped to keep the CR straight for marking. Then I taped the forward CR in place so I could insert the MMT in the fin can and use the fin slots to mark out the fin locations. I clamped the MMT in place to ensure it didn’t move and used a drafting pencil to mark the fin locations. Drafting pencils have really thick lead – great for being able to extend the lead out enough to make markings like this without breaking the lead. Once I had the fin slots marked I took everything off the MMT and used a sharpie to make all the lines clear and label the front and aft ends.
The forward CR needed notches for the Y-Harness. I used 1/4″ wide, 1200# test kevlar for the harness.
I used a center finder tool to mark an exact diameter line across the CR, then laid the kevlar across it to mark the width of the strap. The strap is about 1/16″ thick, so marked the depth. A “fine” grain sanding rod from PermaGrit made short work of filing out the slots.
I taped the retainer and rear CR in place securely – it will need to stay in place throughout the rest of the MMT build as I take the tube in and out of the fin can until it is time to install the middle CRs. I taped off the fin lines to ensure no epoxy gets on them while gluing the y-harness strap in place. Some Tamiya 10mm tape fit perfectly. The 38mm motor tube does not leave a lot of room to glue the straps exactly opposite each other. They will have to be glued very close to the fin lines, so will need to be vigilant on keeping it clean.
I re-measured the position of the forward CR and tacked it in place with CA. I measured out the kevlar to fit so I had about an inch or so loop protruding from the fin can. I am going to sew the loop on the end of the harness, so it should end up almost flush with the end of the fin can. To cut kevlar, I find it easiest to mark the spot, saturate that point with CA, then cut with a knife. Gives you a nice clean cut that won’t fray and you can sand it so it will fit through the slots you made in the forward CR. I laid out the kevlar on the MMT, marked the end point and glued it in place with some Aeropoxy 6209. I am just gluing it in place right now, will completely cover it with Proline 4500 later. Once the glue was tacky, I removed the Tamiya tape so it wouldn’t get glued in place then set the whole assembly in the “hot room” to cure.
The epoxy on the kevlar strap cured well, so moved on to covering the strap with Proline 4500. I reinstalled the Tamiya tape on the fin lines and further covered the area with masking tape. The Proline can get messy. First, I tacked in the top piece of strap above the CR. Then covered that portion of the strap and filleted the outer portion of the CR. Next, I covered the strap with a healthy slathering of Proline. When tacky, I removed the tape and set aside to fully cure.
I stitched the loop at the end of the Y-harness and reinforced the stitching with heat shrink tubing.(NOTE: In retrospect and future builds, this is the time to add a good swivel. I failed to do so in this build).
Next, I made the holes into the fin slots for the injection of the epoxy for the internal fillets. Instead of drilling, I used a 3/16″ round needle file to make prefect holes in the fins slots. That gave me just enough room to get a small Dremel sanding drum in there. On the lowest speed, the Dremel still cuts easily into the FG, but produces almost no dust (still wear a respirator anytime sanding/filing FG – especially if you are using power tools). In fairly quick fashion, I had two neat holes in the fins slots. You should make your holes sized to fit the syringes you will be using.
Next, I dry fit the MMT again and used an aluminum angle to draw lines down the whole body tube that bisect the fin slots perfectly. These lines are really helpful in lining up a fin jig later. Also, before I get the fins in place, I inserted the upper portion of the AV bay into the fin can and used the fin slots to mark out 3 evenly spaced lines around the coupler to use later for rivet positioning.
Just before I epoxied the MMT in place, I took the tape off that I was using to hold the rear CR in place and tacked it on with some mounting putty. I needed that CR to stay put throughout much of the next few steps, but once the forward CR is glued in, the small diameter tubing makes it difficult to reach in and get tape off the MMT. The putty is good at keeping the CR in place and easy to reach in and remove later.
With that done, I used a long stick to put a generous ring of epoxy right at the end of the fin slots (careful to avoid the fin slots themselves) and inserted the MMT tube until the forward CR was just peeking out from the front of the fin slot. I had already dry fit the fins a number of times and know the slot is about 1/8″ longer than the fins, so the forward CR needs to be about 1/2 showing for things to seal up nicely. Make sure that the fin lines you drew on the MMT line up with the fin slots.
Booster Section Build
Once the MMT was securely in place, I moved on to the forward fins. I used my medium size guillotine fin jig for the forward fins (see Tools and Techniques). I set the fins in with 5-min quick cure epoxy since the main structural bond will come from the epoxy I inject later on. The procedure is to line up the body tube in the jig (the lines I drew down the BT earlier make this very easy), get the guides aligned properly, butter the root edge of the fin and seat it in the slot. Just make sure the fin is securely against the MMT. I allowed each fin to cure for about 20 min before rotating the body and moving on to the next fin.
For the “middle forward” CR, I used a long stick to slather a good bit of quick set epoxy around the body tube and MMT at the rear edge of the forward fins. Main intent is to seal the CR so later when I inject the laminating epoxy, it doesn’t leak every where. The other thing to watch out for is that there is very little space between the MMT and the BT – be careful not to get epoxy on the walls while you slide the stick down because it will be almost impossible to wipe off and then you won’t be able to slide the other CR in. Also, keep all epoxy away from the fin lines drawn on the MMT.
Once you have the epoxy in place for the CR, I use two dowels to push the CR down the tube and get it in place resting on the back of the fins. I am horrible at taking photos that focus in the right spot, so the photos I took of this don’t show down the tube very well.
I moved straight on to the next CR. I used the same stick method again to fillet the back of the “middle forward” CR and to set a line of epoxy for the “middle back” CR right at the forward edge of the rear fins slots. Again, I used the dowels to push that CR in place. This one is tricky because you have to be careful when you get close. If you push it too far, the really isn’t a way to pull it back. So just nudge it until it lines up with the forward end of the fin slots and (for my fit) about half the CR is showing.
Before I got the rear fins on, I installed the rear rail buttons. As I have noted in other threads, I install both 1010 and 1515 rail buttons on any rocket that can handle it. I do this not because this rocket needs a 1515 button, but because it greatly adds to my flexibility at the field. There is often a line for the 1010 pads, but the 3 or so 1515 pads are almost always empty. Not only can I skip the line if I have 1515 buttons on the bird, but the 1515 rails are usually longer, which is nice, and I feel like it is a bit of “community service” to my fellow rocketeers to not take up another 1010 pad slot that someone else could use. Be a good neighbor – install both!
I drilled the holes for the weld nuts and tacked them in place with CA. I screwed the rail button on to ensure the weld nut was tight. While the screw was in, I placed tape over the weld nut on the back to protect the threads from epoxy, then coated the whole weld nut with quick set epoxy. This allows you to still remove the rail button and seals it against the injection epoxy later.
Now that the middle CRs are in and the rail buttons are on, I pulled out the larger guillotine jig and aligned the rear fins to the front fins. Same method as the front fins – tack the fins in with quick set epoxy on the root edge.
Once the rear fins were set, I epoxied the rear CR in place and put a healthy layer of epoxy over it, being careful not to get any on the area where the retainer will be glued. Also, I used a toothpick to put a thin line of epoxy in the fillets of the fins to form a nice seal for when I inject the laminating epoxy.
I got all the seams taped up and used Aeropxy 2032 with some milled FG mixed in for the injection fillets. I used about 1/2 tsp of FG. I mixed up the epoxy by volume then put a couple drops of black dye (the kind you get with RocketPoxy) in to make it easier to see the flow of the epoxy once I inject it. I leveled off the fins and injected the epoxy. I took about 5ml per hole, with a little more for the front holes, little less for the back holes. I let this sit level in the “hot room” till it gelled (about 4-5 hours) then repeated.
The internal fillet epoxy settled nicely, so I moved on to the external fillets. There were a few spots where the epoxy I used to seal the edges got a little wider spread than I wanted, so I sanded all the fillet areas down again. I used RocketPoxy with the black dye for the fillets. I used the 1/2″ PVC pipe to mark out the areas to tape. RocketPoxy is not viscous enough when you first mix it to stay nicely the way you shape it (it will flow out too much), so I mix the RocketPoxy first, then mark out and tape the section I am going to fillet. By the time I have my pencil lines drawn and gotten the tape down, the RocketPoxy is just starting to stiffen up. The timing works out (at room temperature) so that, by the time I gloop it on and smooth out the fillets, it is gelled enough to pull off the tape and clean up any errant drips. Then I set it aside in the hot room. I gave each section a couple hours and then went on to next one.
Once the fillets cured, I sanded them smooth.
I started by drilling the holes in the end caps. I used 8-32 threaded rod for this build (fits in the MW RRC2 sled) and 1-5/8″ eye bolts, which also has an 8-32 thread, so all the holes can be the same diameter (11/64″).
I made sure the sled fit on the rails then tacked the nuts onto what will be the front bulkhead using some blue Loctite. I used a Shurter rotary switch for this (sled is built for it). The RRC2L I am using doesn’t have explicit switch ports, so the instructions tell you to wire the switch between the positive terminal on the battery wire. So I soldered a 22 gauge wire to one terminal on the switch, fed all the lines where they are supposed to go on the sled and soldered the positive lead from the battery connector to the other terminal on the switch. I installed the RRC2L onto the sled, trimmed the wires to fit and installed ferrules on the ends of the wires. Tested it and it is good to go.
After messing around with placement of the sled in the AV bay, I determined the switch band needs to be bit aft, not centered. This is to get the switch under the band. I could trim the eye bolt screw, but not worried about the switch band being aft. Once I determined the switch band placement, I marked it and sanded the spot a little more, then epoxied the switch band on. I determined best hole placement for the switch hole, then drilled a small hole. There was some tear out (as usual). Use a round diamond file to clean out the hole. I reinforced the hole with CA then filed. Added some more CA and drilled out a bigger hole to accommodate the screwdriver I will need to fit through there to turn the switch. Some more filing and I ended up with a pretty clean hole in the right place.
To secure the Ebay to the payload bay, I used these little PEM like nuts from LumaDyne. They have a coating on them that makes the epoxy adhere better. I used the 2-56 size for this rocket.
I used a piece paper to draw a circle around the payload bay tube about half way up the shoulder of the AV bay tube. I inserted the AV bay, lined up the witness marks and taped it securely. One nice thing about these red tubes is that they are very translucent. By holding it up to the light, you can see where the lines I drew on the AV bay coupler earlier intersect with the circle I drew on the payload bay tube. 3 evenly spaced marks.
The LumaDyne nut calls for a 5/32″ drill bit. That was a hair too small, so I filed the holes a bit to get the nuts to fit perfectly, then glued them in with 5-min epoxy. Once I got everything lined up, it was easy to screw in the 2-56 screw and secure the av bay to the payload bay.
I am used the smaller, through the bulkhead kind of terminal blocks for this narrow diameter tube. I have never been quite sure how you are “supposed” to install these, but this is the way I have always done it and it has worked well so far.
I use a wire wrap tool to wrap some 20 AWG wire on the terminals. Then, I solder it on. Then, I install heat shrink tube around the solder joints. I drill holes in the bulkhead to fit the solder joints, pull the wires through, test for continuity before gluing the terminal block down, then use some quick cure epoxy to anchor the terminal block. Whatever epoxy I have left, I put on the other side to further seal the holes.
With all the electronics and connections complete, I did one final test with all components and everything checked out.
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.
The way the bulkhead is as it comes in the kit, it sits as a cap at the end of the nosecone. For this smaller rocket, I don’t plan to use the nosecone for any electronics, so I wasn’t concerned about gluing the bulkhead in place, but it is not very secure if it is attached as an end cap. I sanded the outer diameter down a bit so it would fit snugly in the shoulder. I also like this arrangement because it makes it easier later to get the broken shear pins out.
Once I fitted the bulkhead in, I made a line with a metallic Sharpie. You can get the metallics in blue, gold, silver, red, etc. These are great for writing on black surfaces.
I put a generous line of quick cure epoxy around the line, inserted the bulkhead, let it cure for about 10 min, then sealed the whole thing up with Proline 4500.
Odds and Ends
I drilled the vent holes in the sustainer tube and the payload tube. The holes are 1/8″ and positioned in the middle of the tubes. I am not putting another vent hole in the AV Bay. For a 2.6″ diameter bird, I think the 1/4″ switch hole in the AV Bay will suffice.
This is noted in the Tools and Techniwues section, but it is good to repeat the tip – if you put a piece of PVC pipe in the tube when you drill a hole, it very much helps to prevent tear out on the inside. Also, it is a good idea to back the inside with tape. In this case, the tube is too small for me to reach down and get tape inside, so I just relied on the PVC pipe. Small amount of tear out, but good for a vent hole.
I also drilled the holes for the shear pins and tapped them for 2-56 pins. I put the holes a 1/2″ up on the shoulder of the nosecone, which leaves them below the bulkhead for ease of removal. I used 2 shear pins for this build.
After the inital coats of paint, I installed the Aeropack 38mm retainer. I re-scuffed the end of the MMT and put a healthy ring of JB Weld around the tube and twisted the retainer on. I used a 38mm case to ensure the retainer remains centered (the Aeropack retainers are slightly loose on the Wildman thin walled tubes) and set it aside to cure for the rest of the day.
Painting and finishing
I started out with 3 coats of primer (wet sanded with 400 grit) and 4 coats of Dupli-Color Black Gloss (wet sanded with 800 grit between the 2nd and 3rd coats). The lacquer dries pretty quickly, but I still gave it a couple days before I put the Stickershock decals on.
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
The inititial flights were conducted on 12 & 13 December 2020 at MDRA Higgs Farm. That weekend it flew on a Loki H125 and a Loki H130 and they were great flights. The rocket has been flown many times since then.