Black Brant II build thread

[cellofellow]

I built an Estes Black Brant II earlier this summer, which since has been sacrificed to the power line gods.

I built it a bit slapdash and want to do better this time.

Today I got out the kit and weighed the parts (seemed like it would be nice to have a baseline). I cut out the fins and the plastic bits. Photo is of it dry-fitted.

My first challenge is the shock cord mount. This kit comes with a standard Estes trifold mount but I want to use something else. I've measured out some kevlar and want to tie that to the motor mount tube and feed it through the centering rings before I glue them up. The centering rings attach to a plastic coupler that sits between the main body tube and a smaller bit of body tube and below that a tail cone. I'm not sure how best to perforate the two fiber centering rings but I feel like I should glue them together and then drill with a pin vise that I have. Anybody have any other ideas?

I also wonder what it would take to make the payload section useable, that is instead of just glueing the plastic eyelet to the bit of coupler that attaches to a bit of nose cone at the top, instead I somehow put a shock cord mount inside the nose cone. I would have off the decorative toothpicks antennae in that case.

 

[K'Tesh]

My suggestion... Use paperclips, bent and cut to fit, to make the antennae. It'll increase the area you have to use for a useful payload.

 

[Bruiser]

Black Brant is one of my favorite sounding rockets. I still haven't built a BB II though. Looking forward to watching your build.

-Bob

 

[bjphoenix]

I built one from an old ragged kit I found in my club's stash. I built mine with 18mm motor mount and put 2 centering rings on the motor mount tube to attach within the body tubes and made a smaller ring to go on the end of the tube to fit just within the tail cone. I also didn't like that short piece of body tube going onto the nose cone so I put the coupler and short piece of tube on the front of the main body tube, and left off the little radio antennae. I had to search the internet to find a clear diagram to show exactly where all of the decals went.

 

[cellofellow]

I built one from an old ragged kit I found in my club's stash. I built mine with 18mm motor mount and put 2 centering rings on the motor mount tube to attach within the body tubes and made a smaller ring to go on the end of the tube to fit just within the tail cone. I also didn't like that short piece of body tube going onto the nose cone so I put the coupler and short piece of tube on the front of the main body tube, and left off the little radio antennae. I had to search the internet to find a clear diagram to show exactly where all of the decals went.

Interesting that you modded it down to 18mm motors. I flew my lost one a few times on 18mm motors with adapters and it never seemed stable. I was just looking at how crazy big CTI 24mm motors get and while I probably shouldn't use a reloadable motor on a rocket with only friction retention I definitely want to keep this thing 24mm.


Speaking of which does anybody have any ideas on adding some retention to this design? Even tape doesn't work very well as there's no throat to tape to with the tapered tail cone and the fins attaching at the base of the cone, leaving friction only, which isn't ideal.

 

[cellofellow]

Getting started on the motor mount and the shock cord. I tried to rearrange the components in the tail section but they only go exactly as the kit designs, I thought maybe one of the centering rings could go between the two plastic pieces but this is not the case.



So the two centering rings are glueing to the motor mount tube and the tail cone, small tail body tube, and plastic coupler are glued up separately. Once the centering rings are dried I will drill for the shock cord.

I glued up the nose & payload section but left off the small plastic bulkhead where the shock cord is supposed to attach. Instead I tied some kevlar to the nose cone directly. I had considered cutting off the bottom portion of the nose cone and attaching the kevlar to the tip of the nose with some epoxy putty, but upon seeing the base of the nose cone I decided to just wing it with the in-built shock cord ring. Hopefully this doesn't result in a lost nose.

 

[bjphoenix]

Interesting that you modded it down to 18mm motors. I flew my lost one a few times on 18mm motors with adapters and it never seemed stable. I was just looking at how crazy big CTI 24mm motors get and while I probably shouldn't use a reloadable motor on a rocket with only friction retention I definitely want to keep this thing 24mm.

Compared to some people I'm a wimp with rockets, I like to keep them in sight. For a BT55 rocket I'm happy with B6-4 motors, a C6-5 will get more altitude than I want most of the time. However I'm starting to build more of my rockets with 24mm mounts and just use C11 motors.

Speaking of which does anybody have any ideas on adding some retention to this design? Even tape doesn't work very well as there's no throat to tape to with the tapered tail cone and the fins attaching at the base of the cone, leaving friction only, which isn't ideal.

Friction fit is almost an artform. When I started with rockets everything was friction fit so I learned how to do it but even then it is a bit fiddly. I put tape on, test the fit, then add a bit more or take off a bit until I get just the right fit. The motor has to come back out without destroying the rocket but otherwise has to be on the verge of being too tight.

I like the Estes Sprint and built a BT55 version with a paper tail cone. I made it friction fit so I wouldn't have to deal with cutting into the paper tailcone. Then I discovered BT60 plastic nose cone and tail cone for the Sprint XL in my parts box. That tail cone has a little fairing on the side for the motor retainer so I built one that way. I think if you wanted to use an engine hook you could cut a small slot in the plastic tail cone and go for it. Put it on the back side of the rocket where the launch lug is and don't worry so much what it looks like.

 

[Back_at_it]

Looking good. One recommendation. I would not trust the stock attachment point on the nosecone. They have been known to break even with the stock rubber shock cord. Since you are using Kevlar, you are removing any shock absorbing properties as Kevlar doesn't really stretch. I would drill a hole in the base of the cone and thread the shock cord around a thicker part of the nosecone base.

 

[cellofellow]

Looking good. One recommendation. I would not trust the stock attachment point on the nosecone. They have been known to break even with the stock rubber shock cord. Since you are using Kevlar, you are removing any shock absorbing properties as Kevlar doesn't really stretch. I would drill a hole in the base of the cone and thread the shock cord around a thicker part of the nosecone base.

Hmmm, yeah that might have been a better move. I'll try and see if I can still do that but at this point it'll be rocket surgery.

 

[bjphoenix]

Here are diagrams showing decal placement.

 

[cellofellow]

Here are diagrams showing decal placement.
View attachment 664782

View attachment 664781

Ooh, thanks. I ended up removing the decals and masking and painting the roll pattern onto my old one. I'm still considering doing that again, but if I get the decals right the first time I shouldn't really need to.

 

[cellofellow]

I think I have a solution for both shock cord mount and motor retention. Apogee Peak of Flight #95 has a page or so on a competition "Lariat Loop" retention technique.

The Lariat Loop​

People that fly in rocketry competitions know all about a special engine restraint method popularized by Apogee Components’ founder Ed LaCroix. In this method, the shock cord is used to secure the motor to the rest of the model. So even if the tape used to hold the motor failed, the motor would not separate from the rest of the rocket. It would remain attached by the shock cord. I’ve never tried this method with high power rockets, so if you have, let me know if it works.

...

How does it work?​

The Lariat Loop works like one of those Chinese finger handcuff toys. The harder you try to pull it out, the stronger it becomes.

Since the cord is tied in a slip knot, if the motor tries to slide out backward, the cord cinches down even tighter. There is enough friction in the system to prevent it from sliding out. It doesn’t look like it would work, but competition modelers swear by the technique.

...

The small diameter of Apogee’s Kevlar® thread and 100 lb test-strength cord makes it possible for you to eliminate the need for an engine clip, while still assuring that upon ejection, the engine cannot separate from the model and disqualify your flight. Apogee has dubbed this clipless engine retention method the “Lariat Loop,” and the following two figures illustrate it’s use. NOTE: Use of a Lariat Loop assumes that the engine protrudes from the model at least 1/4 inch when installed for flight.

1. In line with one of the model’s fins, a small hole is drilled through the body tube wall. [Not going to do this.]
2. Pass one end of a 30 inch or longer Kevlar® cord through the hole and out the tail-end of the model.
3. Form a slip-knot (using a half-hitch), in the end of the Kevlar® line running out the tail-end of the model.
4. Now slip the Lariat Loop around the normally exposed end of the motor casing, and cinch the Loop down tight. Enough tape should now be added to the motor’s exterior to allow for a smooth fit of the motor into the model. Remember, pull out the slack that will form in the Kevlar line as you push in the motor.

All I have in terms of Kevlar is 300# so I would probably want to get some 100# instead, otherwise it might be a bit too tight. If I do this I'll set up a static test stand and "fly" the whole rocket on it to ensure that the recovery system ejects and the motor is retained. If the test fails... maybe just glue in a trifold anyway and then rely on friction fit as designed? I won't have the option of falling back to a center-ring mounted shock cord.

It's a bit of an odd design when I consider that the shock cord isn't actually attached to the rocket body at all.

 

[cellofellow]

I tested the Lariat Loop method with the rocket taped together and taped to a launch rod. I think it's a go, but it's a little bit if a faff to set up. I certainly will need a launch checklist for this rocket.

 

[loopy]

Hmmm, yeah that might have been a better move. I'll try and see if I can still do that but at this point it'll be rocket surgery.

If you're using a long enough kevlar lead, you should be fine. Just make sure it's long enough that it wont' snap tight on ejection. The other option could be to cut the cord and put a bulkhead with an eye bolt in the coupler and do it that way.

 

[cellofellow]

I did some rocket surgery today. I drilled out the base of the nose cone and fixed a kevlar line with epoxy putty to the nose.



I'll have to wait 24 hours for that putty to cure to test if it's strong enough, but it's probably fine.

 

[jmasterj]

Not sure I would trust the adhesion to the plastic nose cone, but I guess you'll find out!

You can just epoxy it to the inside of the coupler if you want to go that route, but cutting holes in the nose cone sloped portion of the shoulder works from LPR all the way up to the big plastic HPR nose cones.

 

[cellofellow]

Not sure I would trust the adhesion to the plastic nose cone, but I guess you'll find out!

Yeah I guess I'll find out! I did rough up the plastic with sandpaper and put a little bit of styrene cement on the putty too. Not sure what that will do but maybe at least soften up the plastic to accept the epoxy?

 

[cellofellow]

I don't have any pictures at the moment, but I airfoiled the fins today. They might be a bit too thin but I think it'll all work out. Next step is to paper the fins, which I haven't done before.

I also need to finish glueing up the lower tail section and motor mount. The MMT tube itself is supposed to interface with the plastic coupler but it doesn't touch, so using modeling cement as recommended in the instructions or CA just isn't going to work. I didn't have a suitable epoxy on hand though so I had to go get some.

Given how thin the roots of the fins have become except at the beam I will certainly have to fillet them too. I was planning on it anyway but now it's essential.

 

[cellofellow]

My fin papering seems to have turned out crappy. Using Apogee's method where the paper is soaked through with water-thin CA was very difficult and a lot of the paper hasn't bonded well, but some of if has so I can't just peel it off. My choice of paper, tracing vellum, didn't help either.




Trimming the edges hasn't gone well either. I'm also starting to wonder if papering fins doesn't work on an airfoil because it's not flat, given I sanded these by hand. A test strip on a scrap piece of (flat) balsa worked pretty well.

Anyway, I've got some fresh balsa wood coming in the morning and I'm the meantime I'll see what sandpaper can do to rescue this at least in appearance.

The fins are the last structural bit to finish. With them glued and filleted it could be ready for a test flight sans paint and decals.

 

[cellofellow]

Sidebar: payload bay antennae.



I decided to make the antennae with some hat pins, which are a bit more sturdy than paperclips. They're bonded in with epoxy putty.

But, now that I have them in there, I kinda think now I should have waited until at least I had the tube spirals filled in. Now I've got to fill and sand around them.

Oops.

To make that payload bay useable for e.g. an altimeter I have some bulkhead material coming, both that fit the coupler ID and the body tube ID. If I sandwich those together I'll have a nice lid, with a hole that the shock cord can pass through. But once I get it I'm not sure how I'll close it. A clutch grabber on the cord, like a drawstring? Or should I have installed a threaded rod into the nose cone from the beginning? (Which sounds heavy.)

Anyway, turns out I'm learning a lot here.

 

[bjphoenix]

I'm also starting to wonder if papering fins doesn't work on an airfoil because it's not flat

I don't do airfoils because they don't stand up well to handling or landings but airfoils look much better. With just flat fins they are easier to paper because I can clamp a fin and paper between 2 flat pieces of wood. I've wondered how I could do this with airfoiled fins. I think it would require some kind of foam to press the paper against the fin but would just be clamped lightly, one side at a time.

 

[cellofellow]

I don't do airfoils because they don't stand up well to handling or landings but airfoils look much better. With just flat fins they are easier to paper because I can clamp a fin and paper between 2 flat pieces of wood. I've wondered how I could do this with airfoiled fins. I think it would require some kind of foam to press the paper against the fin but would just be clamped lightly, one side at a time.

The instructions have a pretty dramatic airfoil tapering to a point on the leading and the trailing edges, but I really overdid it on these fins, getting down to a paper-thin knife edge which would start to disintegrate. I've got to figure out what the designer of the kit really meant when those instructions were written. I should probably also look more closely at photos of the original rocket.

Or just have them square... but the airfoil does make a difference at very high speeds with the big 24mm reloads (CTI G motors), which I know I probably won't use but I kind of want to. Decisions decisions.

 

[bjphoenix]

Or just have them square... but the airfoil does make a difference at very high speeds with the big 24mm reloads (CTI G motors), which I know I probably won't use but I kind of want to. Decisions decisions.

I round the edges of my fins as a compromise between durability and aerodynamics.
It's a BT-55 rocket, a D12 will probably give it more altitude than you want. Wimpy me- I built mine with an 18mm motor mount.

 

[cellofellow]

I've got new fins cut, papered, tapered, and now tacked to the body tube and ready for fillets.



I used 32# printer paper and 3M 90 spray adhesive for the fin paper, and they're just tacked on with CA for now, I'll be using PC "Super Epoxy" (a thick 15 minute epoxy) for the fillets.

It's coming along.

 

[bjphoenix]

I've got new fins cut, papered, tapered, and now tacked to the body tube and ready for fillets.

That looks great. (Actually looks just like mine did at that stage.)

I have tried different things to seal/smooth the exposed balsa around the fin edges. I had some latex house primer so I tried painting that on. It works well enough but doesn't sand very easily. These days I use thinned Elmers Carpenter Wood Filler. It doesn't paint on as well but it sands real easily. I think thinned Elmers glue or wood glue could be painted on if you didn't have anything else but it doesn't sand very well either.

 

[cellofellow]

I've got the fillets applied and they're curing now. Also glued on the launch lugs but I think that they'll need a light filleting too. There's going to be a lot of sanding to get the fins along side the fillets back to smooth, in other words it got a bit messy.

 

[cellofellow]

It's starting to look like a rocket. I've got wood filler over the spirals and am in progress of sanding it down.

 

[bjphoenix]

It's starting to look like a rocket. I've got wood filler over the spirals and am in progress of sanding it down.

put a few drops of water on the top surface of the filler in your container, mix it up a little bit with a small brush so it's about the consistency of mustard then paint it on the spirals with a small brush. it will reduce the sanding a lot.

 

[cellofellow]

Finally got the filler and primer sanded to a satisfactory level and here's the base white paint job.

 

[cellofellow]

I masked the fins for a checked roll pattern last week and finally got a chance to paint them. I've used an airbrush here which is new for me. We'll see how it turned out in the morning.



I decided against painting the body roll pattern and will instead use the kit-provided decals because one of the stripes has the "C.A.R D.E." word mark on a black background and I really don't have any other way to accomplish that. Let's see if I can have this finished tomorrow or at least this weekend.