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crossfire

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Do you know if that is something Wildman sells separately? I can't find it on their website, thanks

(edit: ninja'ed by Tom 😉)
I am sure he would sell you one. Most of time when you buy retainer from WM if your useing his thin wall tubeing one is included.
 

mtnmanak

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Flew it a couple times this weekend at MDRA - all flights perfect. Even with a strong wind, one of the flights almost literally landed back on the pad. Flew it on an Loki H125 and a Loki H130. Great flights. Didn't want to push the altitude this weekend. Winds were 10-15 MPH and this is a light bird.

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mtnmanak

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3" Darkstar Build Begins Here

Kicked off the next build in the series. Quite a few build threads out there on the 3" version in particular, not the least of which is CJ's "bible" and Wayne's detailed thread, both referenced and PDFed earlier in this thread.

I am planning to document each of the builds in the same detail. If nothing else, it highlights any differences between versions and/or updates to the kits since earlier threads were posted.

This build will be similar to the 2.6", main differences being:
- Using the Aeropack Tailcone retainer instead of the normal "flat" Aeropack retainer
- Build the nosecone out using CJ's glueless technique and keep it open for a tracker
- Install a backup altimeter for redundant dual deployment

I had already cleaned and sanded all the tubes earlier (did the 2.6", 3" and 4" tubes at the same time), so first step was to clean up the ends of the tubes. All these red FG tubes from Wildman seem to have the same bump at one end. At least, all the ones I got. Could have been unique to the batch of tubes I got in the kits I ordered. Either way, easy to fix. Match all the ends up that mate to another piece and sand with a sanding block until all pieces fit perfectly. Label all joints so you know which ends match to another piece.

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mtnmanak

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Next, I used the fin slots to mark the couplers before I glue in the MMT

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mtnmanak

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Filed out the notches in the forward centering ring to accommodate the 1/2"-2200# tubular Kevlar bridle. Permagrit file made it an easy and quick process.

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mtnmanak

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Then I measured out the right distances for the tailecone retainer and the front CR. The MMT for this kit is quite short. With the tailcone retainer on, there is less than a 1/4" of the MMT extending past the forward CR in order to get the CR past the end of the fins slot. That will be fine, although some people may not be happy with that, so you may want to factor that into your planning for this kit and get a longer MMT.

Once I had the right positioning for the forward CR, I tacked it on with CA and taped the tailcone retainer in place for the duration of all the fitting that will need to be done.

With the forward CR in place, I measured off the correct length of tubular Kevlar for the bridle. The goal was to ensure the loop ends up just below the lip of the fin can. I used the fins slots to mark the fin lines on the MMT and extended the lines down the whole length of the tube. I used some 18mm Tamiya tape to tape off the fin areas. I used some CA to stiffen up the ends of the tubular Kevlar and cut the ends clean.

I had already sanded all the parts, but I always like to sand again right before I epoxy anything to the FG tubes, so I sanded the areas for the ends of the bridle. Finally, I epoxied the ends of the Kevlar to the MMT, being careful not to get epoxy near the fin lines or down by the middle CR line. I taped the Kevlar in place and will let it cure overnight. For this, I used Aeropoxy 6209.

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mtnmanak

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Epoxy under the bridle cured nicely, coated the whole thing with Proline 4500 and also added fillets to the forward CR with Proline. Setting aside to cure today.

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mtnmanak

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While the Proline is curing, getting a few things done.

First, assemble the nosecone using CJ's glueless method. Doesn't get much easier. Trim an all thread to length, attach it to the metal nosecone tip. Insert coupler and bulkhead. Secure with an eye nut. One change from the kit, I am using a 3" aluminum bulkhead I had on-hand rather than the FG that came with the kit.

Not putting in a tracker now, but plan to at some point down the road.

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mtnmanak

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The Proline on the MMT tube cured and I moved onto sewing the loop at the end of the bridle. Once the loop was sewn, I secured it with some heat shrink tubing.

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mtnmanak

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The other thing I got done today was test fitting the fins. As you can see in the picture below, the tabs were originally a little less than 1/4" too long. I thought maybe I was doing something wrong and tried all sorts of refitting and moving things around. Went back and checked Wayco's DS Extreme thread and saw he had the same issue, so understood this was not necessarily uncommon for these kits. A quick trip to the miter saw with a cutoff blade (very, very much suggest you cut these outdoors with a respirator - it produced a huge amount of FG dust, even with two shop vacs running on the saw - or use a wet tile cutter saw) trimmed them to proper length and I cleaned up the edges on my belt sander. After that, they fit perfectly.

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mtnmanak

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Next step is to get the holes "drilled" into the fins slots for the internal fillet epoxy injections. As has been noted in a bunch of other threads, I prefer to sand or grind any holes in FG tubes, when possible, rather than using a drill bit. For the fin slots, it is easy because the slot is already cut. I first used a conical grinding attachment on a dremel to make the first cuts, then expanded the holes with a round grinding attachment. I just check the hole size against the size of the nozzle on the 10ml syringes I plan to use to know when the hole is big enough.

With the slot holes in and the MMT ready, I was ready to epoxy the MMT in place.

I resanded all the lines where the fins will contact the MMT and tacked the rear CR on with some putty, so I could pull it out later.

I placed a good line of epoxy around the inside of the tube just forward of the front fin slots and then installed the MMT so the forward CR was epoxied just at the leading edge of the slot. I will keep the rear CR on until after the forward fins are in. Putting all this aside to cure for the night.

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mtnmanak

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With the forward CR secured and the MMT in place, time to get the forward fins on. Resanded the fins along the tab and fillet areas and then epoxy each fin in with quick cure epoxy. The main structural strength will come from the injected fillets later. We want a good bond with the forward CR in order to ensure a good seal later on during the injection process or the epoxy will leak all over the place. So, make sure to butter up the leading edge of the fin tab as well as the root edge and make sure when you install the fin, it is tight against the forward CR. At this point, I only butter up the root edge to very close to the trailing edge of the tab - I don't want to get too much epoxy there yet because the middle CR needs to butt up against it tightly and we will do that in the next step.

For the forward fins, I used my guillotine fin jig along with a 3d printed jig from Badass Rocketry. Will leave about 15-30 minutes between each fin to ensure they are nice and solid before taking them out of the jig.

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mtnmanak

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Forward fins are all in and cured, next step, epoxy in the 2 middle CRs. First, I used a long thin stick to put a good ring of epoxy around the airframe and MMT just aft of the forward fin tabs. I also ensure I got a good amount of epoxy on the fin tabs themselves to ensure a good seal. Then I used two thin sticks to push the CR in place and butt it up right against the fin tabs. For the other center CR, I put a good ring of epoxy around the tubes at the front of the rear fin slots, then pushed the CR in place until I could just see it at the edge of the fin slots. Once the epoxy was tacky, I took a small amount of laminating epoxy (very low viscosity) and use a syringe to inject a very thin layer on the CR to seal it in place.

When all the epoxy was at the leather stage, I installed the rail buttons. I measured between the fins and drew line down the whole tube and repeated between the next set of fins. I installed both 1010 and 1515 rail buttons. The rear buttons were placed 1 inch from the end of the airframe and the forward buttons were placed 3-1/2" from the from of the tube. I used weld nuts to hold them in place. I tacked the weld nuts in with CA and covered the back of the nut with a circle of tape, then epoxied the nuts in from inside the tube and set the whole things aside to sure for the night.

Tomorrow, need to get the rear fins in place and start injecting the epoxy for the internal fillets.

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mtnmanak

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okay, rail buttons on and all the middle centering rings in place, moving on to the rear fins. As with the forward fins, need to butter up the front of the tab as well as the root edge in order to ensure a good seal with the CR. Rear fins are easy to line up using the medium size guillotine jig - just make sure they are perfectly in line with the forward fins. Using quick cure for the installations, so should be good to move on in a couple hours. Would like to get at least one section injected today so it can cure over night.

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mtnmanak

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While the fins are curing, going to build out the electronics. Using an Adeng 75mm sled from Wildman. Seems to be nice with a good selection of pre-drilled holes. For this build, I am using a Stratologger CF as the main altimeter with a Raven backup. The sled is too narrow to fit both side-by-side, I thought about using the NC for a HED backup, but I would like to save that for a tracker. Luckily, the two altimeters are very small and they fit nicely in a top-bottom config. By using a modified Featherweight "Power Perch" with the included LiPo, it also means the Raven is self contained and will use a magnetic switch, so no need to install a second battery or switch. Nice.

After test fitting the two altimeters in various places and configs on the sled, the best organization seems to be to have the Raven on "top" (the side with the switch bridge) and the Stratologger on the "bottom" (side with the 9V battery compartment).

Installing the Stratolooger was the easy part. There were already a set of pre-drilled holes that lined up with the St.CF mounting holes, so I screwed some 4-40 mounting posts in and secured the altimeter with 4-40 screws. I then soldered wires onto a Shurter rotary switch (note, they need to be soldered on perpendicular to the switch cylinder, or they won't fit on the sled). Routed the wires cleanly to the switch and installed the wires using ferrules. Also, measured out the required length of wires needed from the battery mount and installed the battery wires to the altimeter, also with ferrules.

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mtnmanak

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The Raven was a little bit more difficult to install. A couple issues came up.

First, the whole Power Perch assembly would not fit on the sled, so I am only using the battery retention pieces and the port "dongle" that plugs into the ports of the Raven that also provides the magnetic switch and receptacle for the LiPo battery.

Then, I also realized nothing really sat flat on the sled. All the various parts needed to be off the surface, so I used 4-40 posts. This required me to drill some extra holes for the post. No big deal.

Next problem came when I realized that, by using the posts, the Raven itself was slightly raised compared to the port connector, so if I just screwed the Raven to the mounting posts, it would be flexed since one end would be higher. Fixed that issue with some washers between the Raven and the 4-40 mounting post.

Next problem was that, by raising the whole assembly using the mounting posts, the LiPo would be hanging in mid-air. Luckily, the distance between the battery and the sled was exactly 1/4", so I cut piece of plywood to fit under it. I epoxied the shim onto the sled and the battery sat perfectly flat.

Finally, the screw provided with the power perch to mount the rotating battery retainer arm was too short to use in this config, so I used a longer screw I had on hand.

When complete, the whole assembly sits nicely and is very secure. Added bonus, the position of the battery snugs it right up to the coupler tube when installed, so the tube should hold it in from a side-to-side perspective and the retainer arm should keep it secure longitudinally and vertically. As noted earlier, this whole thing is self contained - no switch or battery wires to run to it. Just run the wires to the terminals on the bulkhead and we should be good.

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mtnmanak

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Last thing for today, got the bulkhead terminals in place.

First, used a wire wrap tool to wrap the terminals with 24 gauge wire and then soldered the wire on.

Drilled the holes in the bulkheads and had to file them a bit to fit the solder connection points. Then fed the wires through the holes and epoxied the terminals in place with quick cure epoxy. They epoxy also serves to seal the holes from any ejection charge gasses.

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mtnmanak

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I installed the charge wells - using the small charge wells from Rocket Junkies. Used the included hardware and also sealed the bottoms of the wells with some Fabri-tac.

I secured forged eye bolts in each bulkhead with 1/4" nuts/washers and Loctite red.

When I first started measuring everything out, I noticed the kit comes with a short coupler for the AV bay. It is about 6 inches long. As the photos below show, the sled fits in it, but if I want to use the switch as it sits on the sled, the switch would be about an inch from the end of the coupler. Simple solution was to get a longer coupler. I bought one from Wildman and they got it out to me within a couple days. This one is 9" long and has enough space to accommodate the sled and switch position.

With the new coupler in hand, I laid out the proper distances for the sled on the rails and secured it in place with some 1/4" nuts which were secured with some Loctite blue.

With the sled in place, I could determine the length of wire needed to us between the altimeters and the aft bulkhead and install the 3M mini snap connectors I use. Finished sled config is below.

Next, with the sled inside, I marked the position of the switch on the outside of the coupler tube and used that to determine the positioning of the switch band. I drew the lines for the switch band and sanded the coupler and the inside of the switch band. I epoxied the switch band in place, using the payload bay tube to ensure the switch band was not crooked.

All other 1/4"nuts were secured with Loctite red.
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jbrracer

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Looking good man!

what did you use bond wise for injection internal fillets and where did you pick up the terminal blocks for the lids?
 

mtnmanak

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Looking good man!

what did you use bond wise for injection internal fillets and where did you pick up the terminal blocks for the lids?
For the 2.6" Darkstar I used Aeropoxy 2032 with 3660 hardener and milled FG. For this 3" bird I am planning to use the same.

I got the small terminal blocks from Missile Works: https://www.missileworks.com/store/#!/2-Point-Bulkhead-Terminal-Block/p/24591229/category=5760489

I like these for the small diameter builds. When I build the 4" and larger versions, I am planning to use the larger, more traditional terminal blocks.
 

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The fin epoxy is cured, so let's get to injecting some epoxy.

First, I used some quick cure to get a generous amount of epoxy around the aft end of the airframe and the ends of the rear fins and seated the rear CR in place. Once that epoxy was leathery, I added a generous layer to fillet the end of the tube over the rear CR, being careful not to get any on the area where the retainer will go.

I then put a very small fillet of quick cure around the base of each fin to help seal them and keep the injection epoxy from leaking out. I taped all the seams and leveled the bird out on my stand.

I mixed up about 30 ml of Aeropoxy 2032/3660, added some milled FG and some fluorescent yellow dye. I am planning to paint this rocket yellow, so may as well go with yellow in the epoxy. I injected the first section of the fin can and put it aside to cure over night.

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mtnmanak

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I ended up having a leak overnight. Turned out that I overlooked the extent of the gap the the taper on the leading edge of the forward fins and the trailing edge of the rear fins. Not difficult to fix, will seal up those gaps and continue with the injections. Since it takes a good 24 hours or so for this epoxy to cure well, it will be a couple days before I can move on to the external fillets.

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David_Stack

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I find these builds by yourself, CJ, etc. inspirational!

Disclaimer, I've never built nor even seen one of these kits in the flesh but I'm curious: if you had left the fin tabs closer to full length back in post #72, would that have lessened the issue you experienced with the injected epoxy leaking out at the body tube / fin slots?

If the external fillets are going to extend up the exposed surface of the fins anyway, was it really necessary to remove some of the fin tab to bring the bevelled portion of the fins closer to flush with the body tube?
 

mtnmanak

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I find these builds by yourself, CJ, etc. inspirational!

Disclaimer, I've never built nor even seen one of these kits in the flesh but I'm curious: if you had left the fin tabs closer to full length back in post #72, would that have lessened the issue you experienced with the injected epoxy leaking out at the body tube / fin slots?

If the external fillets are going to extend up the exposed surface of the fins anyway, was it really necessary to remove some of the fin tab to bring the bevelled portion of the fins closer to flush with the body tube?
Great question and very fair point.

For the question about the impact of the fins being above the body tube, in all likelihood, the portion that was proud of the body tube probably would not have caused any issues for most flights. You are right that I could have most likely built up a bit of a "ramp" with the external fillet and been fine. There are a few reasons I chose to correct the issue:
- In theory, the 1/4" sticking above the body tube could increase turbulence along the fins. Not much of an issue at sub-sonic flight speeds, but I do plan to fly this rocket above Mach 1, so any opportunity to keep the fins streamlined is a good one. In the same category, I chose to install both 1010 and 1515 rail buttons, but they are removeable. I will make a field call as to which I will use per launch and remove the unused ones for each flight to decrease turbulence along the tube.
- I have built a lot of rockets (not as many as a LOT of people on this forum, but definitely a couple hundred over the past 40 years) and part of me just can't let a small thing like that go. Call it OCD. I figure, if I am going to pay $200 for a kit, I am going to take the time to get it right.
- At the end of the day, it was an easy fix. 10 minutes with a chop saw and belt sander and Bob's your uncle.

For the leaks, I don't think it would have changed my oversight. It wasn't the length of the tabs that caused the leak issue. If you look at posts #74 and #76, you can see that they tapered the fins all the way down into the tab, almost to the root edge. So, it would not have mattered, the taper would have still been there all the way down. It was just my oversight not to see the gap left by the tapered edge.

I should have been more clear on the leak. The ends of the fins were epoxied securely to the CRs, but the end of the fin slot is rounded and the taper of the fin makes a gap in the fin slot/fin taper, so the epoxy leaked out at the end and ran down the tube and down the fins that were below the section I had injected. When I inject the epoxy it is room temperature, but I put the rocket in a "hot room", about 100 degrees F, to cure. So, when I put the rocket in their last night, I didn't see anything leaking out, but when it got warm, the epoxy spilled out the end gaps.

Easy fix, just seal the gaps at the tapered ends with some more quick cure. I already injected the second section and watched it closely all morning, no more leaks.
 

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With the internal fillets injected, getting the external fillets on today. Using RocketPoxy with a little yellow dye. For each fin, I like to mix up the Rocketpoxy first (about 20g for this size rocket) and then resand the area, draw my lines, tape it off, etc. In the time it takes to do all that, the RocketPoxy has just about the right amount of time to gel a little bit to the right consistency.

So, simple procedure:
- Mix 20g of RocketPoxy
- Sand the fillet area on tube and fins
- Mark off the edges of the fillet using a 1/2" piece of PVC (for this rocket, that turns out to be about 5mm)
- Extend the line along the whole fin section
- Tape off the lines
- Apply to epoxy
- Smooth out the fillet
- Give it about 10 min and pull the tape
- Smooth down the edges a bit with an alcohol dipped finger tip, while the epoxy is still flexible
- Put aside to cure

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mtnmanak

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Merry Christmas everyone! 🎄

Got the finishing touches done on the build over that past couple days.

Used the very convenient holes on the Badass Fin Jig to mark out the placement for the screws for the ebay/payload bay coupling, the shear pins for the nose cone and the vent holes in the switch band. I also used a diamond wheel on a dremel to cut the witness marks between the switch band/payload bay and the payload bay/nosecone.

I am using the Lumadyne PEM nuts again this build. This time I am using the 4-40 size, as opposed to the 2-56 size I used for the 2.6" DS. I had a lot of trouble with the 2-56 nuts, but the 4-40 ones are bigger and the tube is bigger, so this time they went in with no issues. The hole for the PEM nuts is 1/4". Everyone knows how much tear out is an issue with these FG tubes when you drill into them. I am a big believer in using files to get clean holes. I recently got some diamond hole saws in small sizes and decided to try one out for this build. Since they essentially grind/file out a hole rather than drilling it, I was hoping it would cause less tear out. I taped the inside of the tube as normal and used the 1/4" / 6.5mm saw on my drill press. It turned out pretty well. As long as you go slowly, I got very little tear out. I am not sure how well this would work using a hand drill, the hole saw wanted to skip around on the surface of the tube, but with a drill press, it was easy to keep it on track.

With the holes drilled, I put a little epoxy around the lip of each side of the PEM nuts and set the screw in place while it cured to ensure everything stayed tight and in line. Repeated for the other two holed.

Drilled the pilot holes for the shear pins on the NC and threaded with a 2-56 tap.

I also spent some time sanding the external fin fillets to get them smooth.

This rocket build is functionally done. Primer coats, color coats and clear coats over the next couple days. Decals and motor retainer next week once the paint cures.

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