Mach 1, BT-60 Black Hole EXT

[Eric]

So I'm going to put this build thread in MPR because that's what it was designed for. But it will have a HPR aspect to it.

So I order one of Mach 1 Rocketry's new fiberglass BT-60 kits... And they are pretty sweet. I am basing my comparisons off of my Madcow/RW Rapton and Go-Devil 38.

This fiberglass tubing is lite... It is advertised at .5mm. And you can see right through it.

For a $45ish kit it is very complete.



The BT-60 kits do not come packs as meticulously as the bigger kits I have ordered from Mach 1. They come standard in a bag shipped inside of a box. But these parts are light and they arrived with no damage. And that seems to be pretty standard with other kids of this size.



I believe you can get these kits with a 24mm motor mount. But I opted for the 29 mm. And I also received the option that moves this into a much more exciting rocket. The BT-60 coupler tube is the same diameter as a 38 mm motor mount. So the option to go with 38 mm includes using a stuffer tube that covers the fin slots.

After a day of hard contemplation I decided to go with 38 mm. Only because my end plan is to fly it on an I59 long burn.

So after washing all the components and wiping down with acetone. All the epoxy locations received a rough scuffing. Then the motor stuffer tube was epoxied into place.



I now have only .5mm of fin tab engagement. So the fins went to the band saw and received a trim. After a light evening out on the Belt Sander everything lined up nice.

 

[Andrew_ASC]

So what 38mm MPR loads do you plan on flying before stepping it up to the I59?

 

[swatkat]

Eric will likely just go straight to the I59. If not, I've got a few 38mm G67R's if you want to try one. 38/120 case.

So what 38mm MPR loads do you plan on flying before stepping it up to the I59?

 

[Eric]

So what 38mm MPR loads do you plan on flying before stepping it up to the I59?

G50 or G60. I'm not sure yet. I have a lot of choices to choose from. And I might also adapt down to 29 and fly some hobby line reloads

 

[Andrew_ASC]

Looks like a epic kit with a lot of motor options for the money. Somebody could get an L-1 cert on a kit like that for cheap.

 

[Eric]

Looks like a epic kit with a lot of motor options for the money. Somebody could get an L-1 cert on a kit like that for cheap.

Oh yes, I agree. Keep the 29mm motor tube. Have him add a nice TFR chute to the kit. A tube of 5 minute epoxy, A can of spray paint, then grab an H115DM...

Level 1 for maybe $85, and a rocket that will outlast any cardboard kit.

 

[crossfire]

The H115DM is a fun motor.

 

[Eric]

Continuing with the build.

After all the fin roots were squared up. I scuffed them real good with 60 grit and wiped them and the airframe with acetone. Used the Go-Devil's fin alignment guide, and filled the fin slots with BSI 30.





Really lightweight fiberglass. Finger seen through boby tube and thicker stuffer tube.

I applied some masking tape and propped it so everything was aligned and held still for 2 hours. Then used lined the rear fin set up with the front set.



Then filled the rear fin slots with BSI 30 and clamped each fin in place.



Let it all cure for the night. And I did primer the payload and upper portion of booster tube. Just to start the primer bonding early.

The next morning at work, I re-scuffed the fin joints and wiped with acetone.



Then i masked off one side of the rocket. Did I pretty heavy masking to keep the mess down and cleanup easier.



Next was to mix up some Rocketpoxy and lay some fillets. I did a pretty big fillet for a rocket this size. My thinking was that I removed a lot of my fin engagement material.

The avbay endcaps came together with some Rocketpoxy.




I shaped the fillets with a tongue depressor. Then pulled the tape after 5 minutes. After another 5 minutes of waiting I ran an IPA dipped gloved finger over the fillets. They smoothed out great....

 

[Nytrunner]

what are your projections for the I59 in that thing? 6k?

 

[Eric]

what are your projections for the I59 in that thing? 6k?

If I can keep the weight on track with current estimates. The I59 will take it to 9200' with a speed of 780 ft/sec. Leaving the rail at 75 ft/sec while experiencing 16G's. It Will reach apogee after 22 seconds...

 

[Andrew_ASC]

What electronics are you going to run to get it back and recover it? Since that I59 is plugged.

 

[Eric]

What electronics are you going to run to get it back and recover it? Since that I59 is plugged.

That's a great question. But I had not given it much thought yet. I really wish I could get a generic printed sled. Just flat, with no standoffs, and a tube for one or two all threads.

But I just went out and took a look at what I could do. I do have some balsa that I fiberglassed. Is very light and pretty stiff in small sizes. And might be lighter than the fiberglass sheet that I could cut to whatever size I need. I wish I had thinner fiberglass sheet.

At first I was thinking a TRS to handle tracking and deployment. But the TRS by itself is 31grams. Or I could use the Raven 3 on its power perch that is 19 grams with everything. That setup would be small enough I could put an egg finder Mini on the same side of the sled. And if I tried hard I bet I could fit the stratologger CF on the back. I don't really like the thought of only one deployment channel.



But I'm still kind of undecided on the Avbay construction and components.

And I will have an Eggfinder mini flying with it. And maybe the MW T3 as well

 

[swatkat]

Hmm, if only you knew someone who had a 3D printer and was good at designing....

That's a great question. But I had not given it much thought yet. I really wish I could get a generic printed sled. Just flat, with no standoffs, and a tube for one or two all threads.

But I just went out and took a look at what I could do. I do have some balsa that I fiberglassed. Is very light and pretty stiff in small sizes. And might be lighter than the fiberglass sheet that I could cut to whatever size I need. I wish I had thinner fiberglass sheet.

At first I was thinking a TRS to handle tracking and deployment. But the TRS by itself is 31grams. Or I could use the Raven 3 on its power perch that is 19 grams with everything. That setup would be small enough I could put an egg finder Mini on the same side of the sled. And if I tried hard I bet I could fit the stratologger CF on the back. I don't really like the thought of only one deployment channel.

View attachment 360415

But I'm still kind of undecided on the Avbay construction and components.

And I will have an Eggfinder mini flying with it. And maybe the MW T3 as well

 

[Eric]

So I'm looking for some input and opinions. I am now looking at cutting any excess weight. The kit components weighed in at 12oz. Removing 4 centering rings and 6 fin tabs took the weight to 11oz.

The Rocketpoxy fillets added 19 grams of weight. I sanded them down real smooth removing 4 grams of that weight. First coat of primer went on the fins.



Cutting down on Avbay weight...
Below shows my standard eye bolt securing method. Then I could lighten it up a little bit. Or use a Kevlar Loop and get a real weight savings of 1oz.


I want to use two altimeters for redundancy, since I'm planning on flying plugged motors.

I am having a custom sled printed. It will have a flat area dimension of 40mm x 165mm. With a single #10 allthread channel running the length of the bottom. This will be half the weight of the fiberglass sled I would make.

I went with lighter choices for altimeters. I will use a Raven3 on a power perch. And a Eggtimer Quantum on the other end of the sled. I will connect it directly to the battery. So I will only have one magnetic switch to turn on.





So..... Should I fly this rocket in a traditional dual deploy configuration? Drogue in booster, main in payload?


Or.... Main only with a Chute Release out of the booster tube?

The Chute Release weighs 19 grams.

Going with the Chute Release will allow me to save at least an ounce with removing : drogue, shock cord, nomex/dog barf, and two deployment charges.

Plus, I won't have to cram the Av sled and add the Eggfinder mini there. Or squeeze it or the T3 tracker in the nose. I would like to fly both trackers. I could mount both trackers in a foam wrap in the payload section. Facing there antennas in opposite directions.

The payload and nose will just be secured with tight friction fit.

 

[Andrew_ASC]

Single deploy. Single altimeter. Single tracker. JCLR. Heck; on competition multistages we don’t fly a JCLR because it won’t fit. But that’s a noob opinion. You were crying about weight.

 

[Eric]

Single deploy. Single altimeter. Single tracker. JCLR. Heck; on competition multistages we don’t fly a JCLR because it won’t fit. But that’s a noob opinion. You were crying about weight.

I'm aiming for 10,000' with a plugged motor. You think no redundancy is wise? Adding the Quantum/battery adds 34 grams. The extra tracker/battery adds 39 grams. So its a 2.5 oz penalty for redundancy and flight testing at high altitude.

 

[Andrew_ASC]

Never ever said it was wise. We were aiming higher. One flight last year had Apogee deploy at 11.5k ft. They had a heck of a hike.

 

[Joe Rocket 97]

OK, maybe I missed it but does the stuffer tube come with the kit or does it have to be ordered along with the avionics bay? Plan on ordering one next week

 

[Eric]

Never ever said it was wise. We were aiming higher. One flight last year had Apogee deploy at 11.5k ft. They had a heck of a hike.

That's so great for your team. Sounds like a very successful flight. And thank you for the unwise advice. I'll give it some though. As I continue (crying?) about weight.

 

[Eric]

OK, maybe I missed it but does the stuffer tube come with the kit or does it have to be ordered along with the avionics bay? Plan on ordering one next week

The stuffer tube came with mine as a test. I believe Steve will make your kit with any motor size you want (24,29, or 38). He is "Designer Fly" on TRF. Or Steven Skinner on Facebook. I would message him beforehand and let him know what you want. He usually responds very fast on Facebook

 

[Andrew_ASC]

I think the second altimeter in your case is a good compromise and with Kevlar loop you get a weight savings.

 

[lawndartman]

A jlcr would be OK. If it were me, I would put a long silver streamer it the bird and let it go with that. You have little money in this project, don't over think it. All this extra stuff will not help it a bit. I would fly that, it if I were you....

 

[Eric]

A jlcr would be OK. If it were me, I would put a long silver streamer it the bird and let it go with that. You have little money in this project, don't over think it. All this extra stuff will not help it a bit. I would fly that, it if I were you....

Thanks for the idea. Would the Mylar material from one of those emergency space blankets work? Sized at 2" x 48" ? Or 60" ?

And I agree there is little money in the kit. Just in avionics and motor hardware.

 

[lawndartman]

You want something that will 'twinkel', silver or gold.With a few people around, should be easy to see. Space blanket? Why not! I like that.

 

[Eric]

So after the primer coat baked in the oven for 24 hours. I started sanding it all off. Started with the fillets. The primer filled the low spots really well. I was surprised that even the body tube leveled out a little. You can see the low spots from the filament winding of the tube.

Tomorrow I will put the first coat of flat black. Then determine if it needs another round of sanding.

 

[Eric]

I put 3 light coats of flat black on today. And it turned out pretty smooth.

Can you wet sand a flat finish paint?

I think I want to sand a few areas a little smoother. Then do a couple more light coats. Then decals and clear coat.

 

[swatkat]

Looks great... and while you are at it, my plane needs another coat of wax I better not find any bondo putty around the aft cargo doors either!
Just sent you a photo of the sled in progress, should come in around 27g.

 

[swatkat]

And I've got all the silver mylar you'd ever want, just let me know.

 

[Wallace]

Can't go wrong w/mylar streamer in something that small that's gonna be pushing 10k. As much as you can fit...Eggfinder mini's are great also. Just find the smallest lipo you're comfortable with.

 

[crossfire]

Won't clear coat make it look like a gloss black?