Black Brant II scratch build thread

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Worsaer

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Ok, so I've been here for a number of years and have learned a lot from others' build threads. It's time to do one of my own.
The problem is it takes me a long time to build things - fitting it in between all the other important stuff in life, so this might take a while.

Anyway, I have been accumulating materials for this build for at least a year, and I am finally ready to get started. A few parts are still on the way, but at the rate that I build they'll be here in plenty of time.


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So, to kick it off, here's the 75mm motor mount, 20 inches long, intended to handle a CTI 4GR 75mm, or the AT 54/2800 case.
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I prefer to use carpenter's wood glue to bond the CRs to Blue Tube, following up with epoxy fillets.
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Once the fin can is sealed up there's no opening it back up for repairs, so I decided to play it safe and use high temp JB Weld for the motor mount fillets.
You can also see the backing for the lower rail button mount, and the heavy Kevlar strap for the recovery harness, also bonded to the motor mount with JB Weld.
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Because I'm a belt and suspenders kind of guy, I used two wraps of Kevlar tape with epoxy to help retain the recovery harness.
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That's all for the first post. Next up: Slotting the body tube.
 
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That strap ain't goin' anywhere!!!


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3fnc or4fnc?
It's a 3FNC... Ok, next steps.

First - mark off the slots using masking tape. I use a Dremel tool to hand cut slots, and it's easier on my eyes to follow a tape line than marks on the body tube.
The fin slots are 1/4" x 10".

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Here it is after cutting and cleaning up the slots. After test fitting the fins it took a bit more effort to get a clean fit.
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Now to install the motor mount assy into the 4 inch body tube... I again tape off the slots to prevent epoxy from oozing all over the surface when I slide the mount into the tube.
Once properly aligned, I put a band clamp around the body at the mid-fin CR to pull it in while the glue cures.
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Next step: Attaching the fins
 
Well it looks like your going to use a tailcone retainer and its made of BlueTube. A Phoenix?
 
Hmm. I can't see the first few images from your initial post... Says "Sorry, This person either moved of deleted this image." =/
 
Hmm. I can't see the first few images from your initial post... Says "Sorry, This person either moved of deleted this image." =/

Thanks for the heads-up Lucas. I was cleaning up and broke the links. They probably looked ok from my side because they were cached. They should be working now. If not, please PM me.
 
Well it looks like your going to use a tailcone retainer and its made of BlueTube. A Phoenix?

So far all of my scratch builds have been Blue Tube. I don't have the patience to glass body tubes, and Blue Tube works well for me.
And you're correct, it's a 4" to 75mm Aeropack tailcone retainer. My first time to use one.

But no, not a Phoenix.
 
Time to attach the fins - now it's going be be pretty obvious what it is. (I'll rename the thread soon...)


To this point it's going to seem like I have a fondness for JB Weld, or own stock in their company, because I'm also going to use it to attach the fins to the motor mount tube. In this case I opted to use it only because I want the heat rating for all the MM attachments, and I'm willing to trade off the extended cure time.


So first off, before installing the assembled motor mount into the body tube, I double checked the fit of the three fins.
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I'm using what KenRico called the "double butter" technique to ensure there is adequate adhesive on the root edge of the fin. The first photo is before inserting the fin into the slot. The second is after removing it. You can see how thin the glue is.
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After applying a second bead of adhesive, I inserted the fin and held it in place with my Rube Goldberg High Power Fin Alignment Jig (patent pending).
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Many hours later...... the second fin. (The perspective of this photo is all wrong. It doesn't look like the two of three fins are in the right position - trust me, they are.)
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Next up: Once the three fins have cured, injecting some fillets...
 
Black Brant II? Looks good so far.

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This isn't the most exciting part of a build - here we go nonetheless.



I use West Systems epoxy, and their 404 filler to get the desired consistency.
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Then, after CAREFULLY drilling holes in the airframe so as not to also puncture the motor mount tube (been there, done that), I tape of the joint between the fins and tube to create a nice seal. We don't want the epoxy oozing out all over the place.
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S-l-o-w-l-y, injecting the epoxy, and double checking to ensure the body is level.
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To complete the structure of the fin can, I need to add the permanent extended length coupler. As shown in this photo, it will rest on top of the upper fin CR, and the top MMT CR sits inside the coupler. I purchase full-length couplers and cut them to the desired length.
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So, here's how it looks so far, with the coupler and the Aeropack cone retainer in place.
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Ok, it's time to get out of my comfort zone. This is the first time for me to do fiberglass fin reinforcements. I would NOT describe the following steps as a "how-to", but I learned from the experience, and have a better idea of what I would do next time.


To begin, I put down some small fillets on the fins.

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Next, I thought I would try using fiberglass 'tape', since it has a selvage and is less prone to unraveling. I ultimately used two layers of tape, 1.5 inch and 3 inch, laying it down on my pre-marked lines.

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This is my first time to use peel ply. I did the first fins without it so I'd have something to compare to, and I was really impressed with the outcome using peel ply.
However, here was one of my important lessons learned. I should have used a single piece of peel ply across both fins, instead of two separate pieces.
The gap between the two pieces resulted in an uneven surface that I need to fill.

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The result wasn't pretty, but it will be strong, and I'll do better next time.
 
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It's funny. Snow Ranch is closer, but schedule conflicts result in me flying at TCC a couple of times a year instead. The new SARG field is only about 45 minutes away, but my bigger stuff isn't allowed (yet). I need to look at April Snow Ranch dates - I might be able to make a launch before things dry out too much.

I also might make it to Dairy Aire on Sunday, 5/18 if all goes well... This bird won't be ready, but I have a couple of others waiting for their first flights.
 
We've had two launches at Snow Ranch this month already. I don't think they have another scheduled.
 
Good build thread. Love rocket. Do you know what your going to fly it on and expected altitude?
 
Good build thread. Love rocket. Do you know what your going to fly it on and expected altitude?

For the first flight I'll likely fly it on a K550, to roughly 6,500'. The sims show this as staying below the transonic range. If she flies as planned, I'm planning a more 'interesting' flight of a K1050W, which sims out to a little over 10,000', and 1100 fps.
 
Time to work on the nose cone.

A couple of days ago I received my Black Brant nose cone from ScotGlas. It seems to be well made, and is surprisingly light.
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The shoulder is relatively thin, and doesn't fit Blue tube very well. As I have done on other projects, I opted to cut off the shoulder, and use a custom Blue Tube coupler.
Since I will also be including a 54mm tube in the nose cone for a tracking bay, there will be centering rings as marked on the outside of the nose cone.
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following closely. I was planning a similar build but hadn't decided on a 54 or 75 mmt yet. I think this settles it 75 it is
 
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following closely. I was planning a similar build but hadn't decided on a 54 or 75 mmt yet. I think this settles it 75 it is

Yeah, I tend to build them with a motor mount one size larger than I think I'll need. If I don't, invariably I wish I did!
Most of the time I will likely fly this adapted down to 54mm, but I like the look of the 75mm tail cone, and it will allow me to push the limits later if I want to.
 
Ok, more not so interesting detail on the nose cone tracker bay.

The nose cone will have 3 centering rings, and a bulk plate with a stainless steel eye bolt.


First, here's the forward centering ring. For this one I used some kevlar 'fluff'.
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In this photo you can see the mid centering ring just forward of the Blue Tube coupler.
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For the aft centering ring, it has three T-nuts, to which the bulkhead will be fastened, for accessing the inside of the tracker bay.
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As I said before, I'm a belts, suspenders, and duct tape kind of guy. Having had T-nuts come loose inside a sealed airframe before, I use more than just some glue on the backside,
I used a scrap of fiberglass cloth to keep them in place.
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Here are the parts for the bulkhead. It's drilled with three matching holes.
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I've been watching this one for some time. I didn't really get how big it was until I saw the water bottles behind the nosecone in one of the photos above. This is going to be an impressive presence out on the flightline.

:pop:
 
Can you outline your nosecone coupler install method a bit? I have a Scotglas Black Brant cone in my basement that needs some TLC. This includes a new shoulder, as the existing one is a bit flexible for my taste.

Is the ID of the "extension" of the cone (the straight area where your coupler is) the appropriate dimension for a coupler?
 
Can you outline your nosecone coupler install method a bit? I have a Scotglas Black Brant cone in my basement that needs some TLC. This includes a new shoulder, as the existing one is a bit flexible for my taste.

Is the ID of the "extension" of the cone (the straight area where your coupler is) the appropriate dimension for a coupler?

The shoulder of my Scotglas nose cone was also a bit thin for my tastes. Additionally, it was too tight a fit for my BlueTube body tube. Having experienced something similar with another manufacturer's nose cone, I simply cut off the shoulder right at the base of the nose cone. There was a small overlap of fiberglass/epoxy where the two were joined that I simply sanded down. (I measured the inside diameter of the nose cone before doing this, and found the Blue Tube coupler would be a good fit.)

Due to the rough texture of the inside of the nose cone, I only sanded it lightly to remove big burrs, then used some West Systems epoxy with some filler to get good adherence. It works great, and also give you a much more substantial tube for shear pins, etc.

I hope this makes sense.
 
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