MadCow 66mm Black Brandt II FG

[snrkl]

Started construction on my first FG kit tonight. I’ve been putting it off for a few weeks - the thought of working with FG and having to worry about the dust was annoying me. But I bit the bullet this evening.

All parts washed and dried yesterday, and I did a dry fit.

MMT assembly was the order of tonight.

Replaced the open eye bolt in the kit with a welded one. FG CRs were too loose to hold with 15min epoxy, so I did first tack with a small amount of 15min epoxy while the CR was supported with a ring of tape that I removed once the epoxy gelled.







While waiting for epoxy to gel on the MMT, I roughed everything up and drilled the holes in the fin slots for infecting fillets.



Last, but not least, as this kit has an open tailcone with nothing to glue to, I’ve opted to glue the motor retainer on now, and the TC will slip over it.


Gave it a good filet of JBWELD...



The stack is laid up to cure - it will be a few days till I can get back to it...

 

[snrkl]

Side note: even though I attached the eye bolt with a good dose of loctite, as I was filleting CR’s, I used some excess epoxy to drown the eyebolt nuts fore and aft.

 

[Wallace]

What/who's retainer is that? Is it plastic?

 

[grouch]

It's not a retainer.

 

[snrkl]

What/who's retainer is that? Is it plastic?

It’s a PML HAMR aluminium retainer: https://m.publicmissiles.com/motor_retainers.aspx

What you can see is the green masking tape I have it wrapped in and the JBWELD I attached it with.

 

[snrkl]

It's not a retainer.

Oh; isn’t it? - what is it then?!



[emoji12]

Unless you’re referring to the 38mm vitamin tube I’m using to keep everything aligned and centred, in which case...

 

[snrkl]

Unwrapped MMT:



Easier to see the retainer now.

MMT in and the TC installed..


Had an “over insertion” of the MMT - it was stiff, then once the second CR goes in, it slides like butter.

This was then compounded by me putting it vertically, but upside down - two large runs where the epoxy that was meant to fillet the CR went for a run!

I didn’t want the assembly resting on the MMT, so I tipped it the other way round assuming the epoxy was more gelled than it was.




Well - that’s a learning point. I now have a better way to keep it the right way up, but not resting on the MMT by clamping the BT to the workbench leg but having something under the MMT to stop it moving downwards.

 

[snrkl]

The CRs will get a good fillet when I inject the fin fillets.

I’ll take a look at the FWD CR once it’s all cured and can always drill, inject and seal if needs be.

 

[DM1975]

It's not a retainer.

I’m hearing that with an Arnold Schwarzenegger type accent. “It’s not a tumor”

 

[snrkl]

Had a terrible “oh dear” moment today.

Dry fitting the fins, and one just WOULDN’t sit flat.

Couldn’t for the life of me figure it out.

Don’t know how, but there was a massive epoxy run over the MMT right under the fin slot.

I have NO idea how it got there...

A few minute later, I managed to break the bond on the drip using a very fine tipped hobby file.

Then it dawned on me.

How did I get that epoxy off?

I hadn’t roughed up the fin tang contact point on the MMT...

Doh...

I’ve done the best I can to rough it up through the slot with a fine flat file that JUST makes it through the 1.8mm fin slot, with a wrap of masking tape to prevent it from enlarging the slot.

Learning points:

1) rough up the whole MMT before you mark it up and glue rings

2) do something differently to prevent epoxy ending up on the MMT where the fins go. Possibly next time, I’ll have to apply the epoxy with the tube vertically or something.

 

[DeepOvertone]

Did you remember to rough it up around the CRs? Did you rough the inside of the BT at the CR mounting points? I have nearly forgotten that step a few times myself.

 

[snrkl]

Did you remember to rough it up around the CRs? Did you rough the inside of the BT at the CR mounting points? I have nearly forgotten that step a few times myself.

THAT, I did remember... I even roughed up the surfaces on the CRs...

I used a dowel rod, with some double sided foam tape and pieces of 80grit sandpaper...

 

[snrkl]

I’m working up the effort to get the belt sander out and clamp it inverted to do the fins, so Focus shifts to the nosecone.

On a j400 Smokey Sam, this is going >5500ft, so this bird needs to fly with my EFMini.

That means a nosecone AV bay.

Following the same design as my L1 and (hopefully) soon to be L2 birds (Portal and Deadpool) I’m using two CRs and a bulk plate, with a 40mm BT for the nose bay.

I quite like the m6 gnurled finger screws with captive washer I found online so this means m6 tee nuts.

This is HARD to fit on a 66mm - 38mm CR, as the tee nuts are 3-4mm wider than the CR...

A dremel grinding stone and some sanding later and the drilled and Tee-nutted CRs are fit into the NC

First the one that has a Kevlar loop for NC retention. Normally this goes behind the shoulder step in the NC, but this FG NC has no shoulder step internally. So we rough it up well and epoxy like our lives depend on it:



As I’m eternally afraid of epoxy making Kevlar brittle, I’ve refined my approach to use heat shrink tube for areas where epoxy and Kevlar meet - this keep the epoxy out of the Kevlar and helps it retain its youthful “pre marriage” figure...



3mm braided Kevlar used here..

Then we turn to the aft NC CR. This one has the three tee nuts that have been ground down to fit the inside profile of the FG NC:




You’ll also note the semicircle sanded into the ring to allow the NC retention Kevlar to pass through. The bulkhead has the same hole.

Nuts are temporarily backed with masking tape so the epoxy flood won’t run into the nuts, but can flow all around them.

The second CR is in and curing now. A photo to follow once I can turn it upside down.. (not making THAT mistake again!

 

[snrkl]

The AFT NC CR


The gnurled bolts with captive washers


The bulk plate fitted (but not screwed down fully as the epoxy is still tacky...)


Once the epoxy is cured, I’ll screw it down and sand the bulk plate to make sure it fits smoothly into the BT when the NC goes on.

 

[Estesbasher]

snrkl Get your self some of the additives for you epoxy to thicken it up. This will help on the run you had with your motor tube. I use the west systems 406 colloidal silica and the phenolic microballons also.https://www.uscomposites.com/fillers.html
https://www.uscomposites.com/westfillers.html

 

[snrkl]

snrkl Get your self some of the additives for you epoxy to thicken it up. This will help on the run you had with your motor tube. I use the west systems 406 colloidal silica and the phenolic microballons also.https://www.uscomposites.com/fillers.html

Good call... It’s on my list of things to start experimenting with.

For what it’s worth, we’ve had some seriously hot weather (35°C outside, 40°C in the garage, so the epoxy has been much runnier on this build than I’ve had previously...)

 

[Nytrunner]

Nice work so far. The "1st fg kit" and epoxy runs are giving me flashbacks to the airframe team building our IREC rocket.

So will this be your L2 or do you have another in the works for that?

 

[snrkl]

Lol - the B.B. would significantly breach the ceiling at our launch site on a motor big enough to L2 on. We only have 5000ft, a J400 sims to ~5900ft from memory.

My Deadpool is planned to fly my L2 this weekend.

I have one last Deadpool shake down flight planned on an I236, then it flies on a J400 Smokey Sam for my L2 attempt. (As part of an 8 way J400 drag race, no less! [emoji12])

 

[Nytrunner]

Oh that's right.

Wait a sec, what's this "test-flight" business?

 

[farsidius]

Thanks for sharing your build here - always nice to see another BB coming together. I have one of these sitting in my build pile. I might get to it this winter. It will be my sixth BBII. The BBII is a great flier and good showpiece. The biggest problem with these kits (especially in these large sizes) is the lack of a fin tab through the boat-tail. Make sure to add some significant reinforcement to the fin/boat-tail junction. These huge sweptback fins take a lot of abuse when landing and if not reinforced your filets will crack or your fins will separate from the boat-tail when landing. Even so, still one of my favorite rockets.

 

[snrkl]

Thanks for sharing your build here - always nice to see another BB coming together. I have one of these sitting in my build pile. I might get to it this winter. It will be my sixth BBII. The BBII is a great flier and good showpiece. The biggest problem with these kits (especially in these large sizes) is the lack of a fin tab through the boat-tail. Make sure to add some significant reinforcement to the fin/boat-tail junction. These huge sweptback fins take a lot of abuse when landing and if not reinforced your filets will crack or your fins will separate from the boat-tail when landing. Even so, still one of my favorite rockets.

The kit came with 3x 1”x6” pieces of glass cloth for just this purpose. You cut them into 6x 1”x3” pieces for the TC/fin interface before filleting.

 

[snrkl]

Oh that's right.

Wait a sec, what's this "test-flight" business?

Uhh.. the whole point of the deadpool rocket was as a “learn to do dual deployment”...

Plus, it means I get to fly it twice on Sunday instead of once... [emoji12]

 

[farsidius]

The kit came with 3x 1”x6” pieces of glass cloth for just this purpose. You cut them into 6x 1”x3” pieces for the TC/fin interface before filleting.

Yes, but one layer doesn't make much difference in these larger kits. Build up a few layers of fiberglass or use some Kevlar strips. I use 4" Kevlar strips and then a layer of FG to smooth it out.

Your build is looking good!

 

[snrkl]

Full BT and fin sand down with 80 grit and a clean with acetone.

Then, onto tacking the fins into place.

Fin 1:

 

[snrkl]

Two

 

[snrkl]

Three


I’ve tried to ensure a slightly better than “tacked” adhesion for the fins to the tailcone.



Over this, there’s is a small strip of FG to go between the fin and TC, followed by fillets.

I discovered today that west system 406 isn’t sold in Australia. Initial research of the local Ausrocketry forum seemed to show 413 as the best available alternative.

Sourced some 413 today at the local boat repair shop. Also grabbed some 105 and a bottle of 205 and 206 to use moving forward (I’ve been using BSI 30min of late)

I’m planning on injecting the 206 slow for the internal fillets, and using some 413 filler for drip free fillets.

I plan to have some play/practice tomorrow to familiarise myself with it all before I use it in anger.

 

[snrkl]

Internal fillets started - injecting is a little more difficult than I imagined; perhaps my holes aren’t big enough.

I thought about using the West System but I decided to go with what I know, and I know this epoxy will run ([emoji33]) internally... [emoji12]



Starting to look like a rocket now...

 

[Bat-mite]

Looking good, man. Nothing like a good, solid FG rocket.

 

[snrkl]

Recovery chain all set up while I wait for epoxy to set.

There’s a 1.5m loop of 3mm Kevlar in the tube from the eyebolt.

Then 3m of tubular nylon.
9”x9” nomex around the very thin nylon chute that came with the kit (no spill hole)
JLCR in there too.



Using my colour coded heat shrink wrap system I developed for Deadpool to make things easier. (Green at the nose, yellow for fwd of eBay, red for aft of eBay and black for the fincan) no ebay in this one, so it’s just green and yellow..

Using leaders with spinners on the chute. Heat shrink keeps the Kevlar out of the spinning bits.
(ignore the yellow - I ran out of green 10m5m heat shrink)

Using alpine butterfly knot for chute attachment - man I love this knot.

 

[snrkl]

Prepping the glass cloth.

Cut into 6x 16cm pieces (learned the tape trick here - thanks all for that!)


Did a “dry run” and glad I did - hard to keep the cloth aligned on the fin line. Decided some black lines would make it easier:


Surface rough and ready (well, roughed, sanded and wiped with acetone)


Wet down the area with an overlap.
Laid the cloth, then wet down the top


And just like that, I’ve laid my first ever fibreglass thing!