MadCow 66mm Black Brandt II FG

I forgot to post the ratios I used for the cake icing texture mix:

105: 7.5g
206: 1.5g
Microbaloons: 2.2g

So a 5:1:1.4 ratio.

Sanded and recoated

And sanded and recoated

Microbaloons are very dangerous if inhaled. They are itty bitty glass spheres that play havoc on your lungs. Please be careful with that crap.

grouch said:

Microbaloons are very dangerous if inhaled. They are itty bitty glass spheres that play havoc on your lungs. Please be careful with that crap.

Click to expand...

Waaaaaaay ahead of you:

And again

I’m happy enough so far with the finish on the microbalooned epoxy they I’m laying a filler coat on the fin fillets:






Why do I always feel like this step is ruining all the ones that came before it?! [emoji12]

NOTE TO SELF: DO NOT FORGET THE RAIL BUTTONS BEFORE PRIMING!!

snrkl said:

I’m happy enough so far with the finish on the microbalooned epoxy they I’m laying a filler coat on the fin fillets:

Click to expand...

Does that stuff sand easily?

As soon as you have some disposable income, look into getting a small kit of Proline 4500 from Wildman. The first time you do fillets with it, you'll wonder where it's been all of your life! Seriously, it's that easy. Mix, fill, shape while curing, pull tape, allow to cure......no sanding necessary unless you want to put a top coat of paint on it. That's why everyone uses it on their colored fiberglass tubes and black plate fins.

timbucktoo said:

Does that stuff sand easily?

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Pretty easily. Easier than straight west system and not as easy as CWF... I’d say 30-40% easier than straight epoxy.

And smoothed with an isopropyl covered tool (but not pressed like a fillet would normally be - just enough to reduce the amount of sanding needed...

After 80 grit and 240 grit sanding with a 38mm tube under the paper..









About an hour of sanding all up.

The waviness is deceiving - the white epoxy over the cleat makes it look terrible. All of these fillets, you can’t even detect a change when running your finger across or along them...

There are a few small imperfections, I’m likely going to use either filler/primer or CWF and sand then thin CA soak the CWF.

So the last two days has been all about rail buttons. I need them fitted before I prime (despite the fact I’ll be taking them off again when I do actually start laying paint.

Let me say this: rail buttons are a pain in the 4r$e... and I’ll explain why.

The ones that come from AusRocketry don’t have a tee nut and fit an m4 screw. The button is flat on top and bottom and the hole is the same all the way through.



The ones from MadCow that came with this rocket are set up for a countersunk screw and came with a self tapping wood screw that is miles too long for the application.


The ones from apogee components are my favourite, but ONLY if you don’t lose the screw.
View attachment 367404

They come with a tee nut and a countersunk screw and the body of the tee nut actually fits inside the ID of the button. Did I mention, DON’T lose the screw? I’ve found it impossible to figure out what the screw is. It has an OD of 3.4mm and a thread count of 0.8, and I haven’t been able to find them anywhere local.

So back to the rocket:

The upper button is going to be in prime laundry snagging location so there I want to use the apogee button backed by a tee nut with a drizzle of smooth epoxy to make it snagless...

But: there was no room in the fin can for a tee nut without getting in the way of the tail cone, so there I have to drill and tap. (Never done that before, but I’m all about the learning...)

But I can’t use the apogee one on the fin can as I can’t tap it without the right tap, and again, the only taps at the hardware store are metric. I even scrounged through a box of old imperial taps they were throwing out to no avail.

No worries I said: I’ll get me an m4 countersunk screw...

Well... no. Not one single hardware or electronics store or place that was open on the weekend stocks m4 countersunk screws.

So no matching apogee button at the aft end.

Practiced my drilling and tapping in some scrap ply that I soaked the hole with thin CA before tapping. It worked a treat.

So I drilled and taped the FG, opting to go through the BT in the middle of the TC shoulder (more material) and put the decidedly different AusRocketry button on the rocket’s aft end.

(This aggravates my sense of balance and neatness, but I’ll have to find a way to live with it.)

The MadCow buttons: I have ZERO idea who would put a forward rail button into FG tuning with a coarse thread self tapping wood screw. By my calculation, even if I trimmed the screw, you’d only have 1/2 a thread engaged with the FG. And when (not “if”) it failed, I’m sure it you’ll make a lovely mess of the hole on its way out.


As it stands, they’re all in now.


Rather than trying to get epoxy on the back of the tee nut using a syringe on a long stick, I opted instead to drill the BT vent hole exactly opposite the rail button.

I used my heat shrink tube on the end of a syringe trick, combined with my “mix the epoxy in the syringe” trick to drip the epoxy directly on top of the tee nut.



Interestingly, the iPhone 8 camera can take a picture through a 3mm hole and focus on the opposite end of a 66mm BT quite nicely. This was an amazing view of my handiwork:

1x optical zoom



2x optical zoom

The apogee button - I forgot to add it and forgot you can’t add pics after a post is posted...

I finally found a way to run 3d properly in OR to let me skin this beast... I ran up an Ubuntu 18.04 virtual desktop and installed openJDK 8 (THIS is something I will now try on my mac, as it worked FLAWLESSLY on ubuntu)...

Now I can finally see what this beast is going to look like:

Primer reveals all..

Just priming the tail end for now as most of this will be sanded off.

Figure it will save some paint and time if the first 3-4 primer coats are focussing on the areas that need work.





Quite a bit of priming and sanding to come.

Round two:

Nosecone




Fincan




And reprimed

Another round of sanding... getting close.

Materials experiment today: thinned CWF with some isopropyl alcohol in the goal of having it dry quicker.

Seems to have worked - the CWF was dry in 30mins instead of the usual 2hrs.

So more wet sanding, a little alcohol fuelled CWF on a seam that seems to have appeared on the edge of the fibreglass fillet where the sanding exposed the fibres and left thread divots.

Some light sanding and it’s ready for re-filler priming tomorrow morning first thing.






As you can see from the pics, I’m now only sanding back primer where there’s low spots that need to be sanded back to...

I’m really hoping that’s the final fill prime for the fins and I can prime the rest. I guess I see tomorrow morning once I can filler prime it.

Once the priming and sanding is done, then starts the rusto 2x prime and final paint, which will be a flat black with gloss red highlights.

I’ve considered doing gloss black but I find the gloss black just turns into high shine in the sunshine and makes things look “not black” which won’t work for this rocket.

Perhaps if I was @Nathan and had a metallic finish car paint with 2pack #awesomesauce gloss it would be ok, but I’m going to go the flat black and see how it looks. Worst case I can recoated in gloss.

Looking good. I've never tried CWF on fiberglass. Bondo putty might be a better choice, if you can stand the smell.

What I do as a final step in a situation like that to get the fillets perfectly smooth and even is to apply a thin coat of 30 minute Bob Smith epoxy over the fillets. It starts out pretty thin and nicely fills any minor imperfections, and leaves a smoother surface than Bondo putty.

Nathan said:

Looking good. I've never tried CWF on fiberglass. Bondo putty might be a better choice, if you can stand the smell.

What I do as a final step in a situation like that to get the fillets perfectly smooth and even is to apply a thin coat of 30 minute Bob Smith epoxy over the fillets. It starts out pretty thin and nicely fills any minor imperfections, and leaves a smoother surface than Bondo putty.

Click to expand...

I’ve been thinking about another epoxy layer. My biggest concern is how to dam the epoxy and not mess the fillets up.

As for the CWF, I’ve used CWF to fill mould seams on plastic nose cones before - once the CWF is sanded and VERY dry, I wick it with a little bit if thin CA to harden and ensure adhesion. Was planning on this step this morning.

I’ve also though of Bondo. I’ll see how these tiny divots do with the CWF/CA mix and go from there. The CWF certainly didn’t want to lay on the FG, that’s for sure!

Nathan said:

Looking good. I've never tried CWF on fiberglass. Bondo putty might be a better choice, if you can stand the smell.

What I do as a final step in a situation like that to get the fillets perfectly smooth and even is to apply a thin coat of 30 minute Bob Smith epoxy over the fillets. It starts out pretty thin and nicely fills any minor imperfections, and leaves a smoother surface than Bondo putty.

Click to expand...

Out of interest @Nathan, how do you lay the epoxy in thinly? Brush? Squeegee with your fillet pull tool? Other?

snrkl said:

Out of interest @Nathan, how do you lay the epoxy in thinly? Brush? Squeegee with your fillet pull tool? Other?

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I carefully drizzle it on with a dowel and then slowly squeegee it with my finger dipped in isopropyl alcohol. I never use any other tools on fillets (except sandpaper).

There’s a few little pin holes that I just can’t get to fill, so that’s where I’m calling it.






They aren’t @Nathan level but I’m calling the fillet special treatment phase of this build DONE... I’ll try his extra thin finger squeegeed 30min epoxy trick next time.

Once the airframe is dry from its most recent water rinse pose sanding, I’ll be priming the whole thing and sanding the whole bird this time.

Getting closer...

All primed.




And coloured





And a package arrived from AusRocketry today:



The skulls are white on white, so you won’t see them until they are removed from the backing paper.

Figuring out motors for the weekend.

Maiden flight is looking like a CTI 276-H152 bluestreak to about 3000’.

Following that I’ll have a CTI 486-I287 Smokey Sam to about 4700’..
(Launch ceiling is 5000’)

Still need to do final weigh in and CG check, then I’ll update the sims and advise accordingly.

I’m imagining that the fillets might have added a little more rear weight - I’ve tried to accomodate with 19mm radius fillets in OR with an “epoxy” material at 1.61g/cm3

I’m regretting the contrast between the flat black paint and the black decals.

I ordered two complete sets, so the plan is after it flies this weekend, I’ve got the Christmas break to remove the upper two decals and I’ll blend the flat black on the bottom into a gloss black at the top, and relay new decals so that the glossy decals don’t look so out of place.

I considered just getting the white bits cut out but the effort required to map the vinyl cutter paths was too much for me to be bothered.

Anyway, without further ado: Punisher, a 66mm MadCow Black Brant II in fibreglass / psychotic vigilante super hero.

Updated sims for tomorrows two planned flights:

Maiden on an H153-BS to 2700ft
Second Flight on an i287-SS to 4500ft...

I also swapped out the default 30" chute for a 48" PML durachute with a vent hole.. It was a little larger, and had to upgrade from a 22cm Nomex to a 30cm one..



(Datapoints graphed so that when I look at this in my online flight log on a phone in the field, I have a chance of being able to read the chart!)