Mach1 BT60 Alien Interceptor

This is my first high power and dual deploy capable rocket. It should do well on hobby line reloads and any H or I site permitting. Please jump in if you see something dangerous or questionable. I'm on TRF to learn and participate in the community. Thanks!

Good wash down and dry fit. There was a wonky fin which I tried multiple techniques to correct/flatten/true to no avail. Ultimately requested a replacement which Steve quickly provided.

The parts dry fit perfectly and needed no adjustments. Weighed all of them separate for simulation edits. Made a fin tapering jig and tapered the leading and trailing fin edges. Sanded all attachment regions with 60 grit aluminum oxide.

Good dry fit. Plan of action - motor mount. Upgraded shock cord to 1000# because I like burly things and the mass of the completed project seemed a bit more than what the little 300# could withstand. It adds a bit more mass but I figured I don't want to be trying to replace a worn shock cord at the motor mount.

After washing parts with acetone (then only handling with clean gloves and not touching my face etc...) weighed equal parts rocketpoxy and attached foreward centering ring and shock cord to the motor tube. (will attach aft centering ring once aft t-nut is in place and internal fin fillets completed). Planned and drilled holes for rail buttons. Made conformal t-nuts for M4 screws and epoxied to the inner body tube.

Roughed up the surfaces for the bond and made a little jig for the t-nut cementing so the screw would remain perpendicular. Put a small amount of wax in to guard the threads and a small dot of masking tape on the inside. Delivered the nut into position on a long dowel with a magnet. Epoxied the foreward t-nut. It seems unlikely to snag any recovery device, but did epoxy over it to be sure.

Scored the regions of fin contact and roughened all surfaces inside for internal fillets etc. Ensured all parts wiped with acetone. Epoxied foreward centering ring and aft rail button t-nut. Used aft centering ring for proper alignment of motor tube.

Started in on the fin attachment. Made a fin alignment jig from 2x6 lumber I had lying around. After confirming proper alignment in the jig. Would put some rocketpoxy on the motor tube then load up the slot and the fin root. Slide it straight down and clamp into place until cured (24 hours). I work just for a little bit at a time when I'm able so the slow build is why I'm uploading these all at once.

Drilled 3 small holes near each fin slot and injected internal fillets quickly using a curved-tip syringe. They didn't look pretty but I think the internal fillets will do their job preventing fin extraction or wobble.

Looks like your on the right track! APPROVE!

External fillets. I love the fondant ball set I got thanks to this forum!

Looks awesome! That will be a high flier even on hobbylines!

Learned to solder small stuff with a practice kit, then built an Eggtimer Classic. Tested the completed project - it works! Invested in some nerdy magnification, lipo's and a charger, the cost is adding up but I can't stop now!

Initial rough simulations. I'd like to fly the H115DM for a level 1 certification attempt. I had/have concerns about over stability. I posted the question and other than Wallace, the folks responding weren't as concerned as I was with 4.4cal.

Assembled a Quark as a backup computer - started building the E-bay. I found I really enjoy putting these tiny things together - the Quark wasn't very difficult and it definitely went together faster than the classic.

Nice build! I may have missed it, but how long have you been at this build?

DRAGON64 said:

Nice build! I may have missed it, but how long have you been at this build?

Click to expand...

I started around Thanksgiving... just a little at a time...

Awesome build on one of my favorite airframes. Can’t wait to see how it performs for you.

The BT-60 is on my build pile, so the timing of your build thread is spot on. You're doing an awesome job. I'll have to work to match your standards. Can't wait to hear how the maiden flight goes. Thanks and keep posting pictures. I'm learning a lot.

So there was a struggle figuring out how to secure the batteries with the limited space in this e-bay... I settled on securing them with some nylon binding tape folded to three layers and screwed on the ends. The nylon secured them quite nicely and while they can be removed laterally it does take some effort and laterally in the coupler they're not going anywhere as they butt up against the tube. Melted the nylon holes by heating a sewing needle - perfect for the #6 screws. Shortened the power cabling and JST connectors to simplify the wiring and minimize real estate on the sled.

The completed battery "harness".

Shortening the ground side, couldn't fit another euro style connector - so used the innards and some heat shrink. Wrapped from fanned out stripped ends and soldered to ensure all 4 wires contacting (using just one battery for the Eggtimer Classic which has wired power to the deployment channels).

Completed the forward deployment lead connectors. There's not enough room on the bulkhead so I opted for the connections being on the sled inside.

So now the post is caught up to today - I powered up the Classic and had a drogue channel error :{ grr... I'll have to sort this out before I get any further. I'm hoping it is as simple as a bad Christmas light. I hope all the rocking around (despite working on leather padding) didn't screw up the board somewhere. In hindsight I should have sorted everything out then removed the boards from the sleds during the other work so it wouldn't be damaged. It's tough though - to work out the layout and wiring without the board in place. My next dual deploy will be a 4" rocket, maybe that would've been a better first build experience!

Wow, that seems like a pretty heavy build, I'm sure you've weighed all the parts to get the open rocket #'s. My very similar BT-60 kit (Speed Demon) comes in 26 Oz with that motor loaded, with a 3.2 Oz sled and DD electronics added. That gives somewhere near 3300 feet. I'd also recommend a shakedown flight on perhaps the G64 (mine were on G67Rs which are similar in total impulse) to gauge the open rocket simulation results. G67 on mine FWIW was 2200 feet, simmed to 2250. But if your H is taking you that high, that's a pretty big delta.

Didn't realize you might have an FG nosecone instead of plastic looking at the drawing... that would account for the weight delta. 4.4 Cal is fine.

The nose cone is LOC plastic - around 100g without the featherweight tracker, sled and bulk heads. It is pretty heavy I guess. I don't think I went overboard with epoxy - but maybe it's just all the little stuff adding up. In the screen-shot posted I have pretty heavy parachutes and kevlar etc... I think when I make my parachutes they'll come in a lot lighter. I'm excited to get a package from Paragear today.. I got some vectran for lines, zero porosity ripstop for the panels and a couple of small maillon rapides (they're the burliest for the size).

Very solid build! Well done.

Agreed with Normzilla, looks awesome. Sturdy and well thought out!

Completed the electronics sled. The Classic worked, thankfully I just had a loose solder at the tester bulb.

I have some doubts about the strength of the single 8-32 rod holding up to the deployment forces so I sent the Kevlar cord all the way through the e-bay versus tying off a loop to each bulkhead. Is this being overly cautious?