Brant's Brant - My TRA L3 build of the Rocketry Warehouse BBII

Good Evening TRF. I haven't done a lot of build threads but I wanted to document my L3 build and share it with you.

This build is the Rocketry Warehouse Black Brant II. This is a 6" fiberglass kit that I purchased from RW in June 2015 when they first offered it. I initially planned to scratch build a BBII for my L3 but the initial offering price for this kit from RW was too good to pass up. I was going to start my L3 build in 2015 but I ended up changing jobs and moved all the way across the country from Massachusetts to Oregon that summer and needed some time to get settled in. I took 2016 to get familiar with the club out here (OROC), set a new personal altitude record (20k feet), a personal speed record (Mach 1.9-ish) and started using 75mm motors for the first time.

Now it's time for my Level 3. Clearly, I had no choice but to build a Black Brant for my L3. It just seemed appropriate to build my namesake for this and, unlike some other misguided individuals on this forum, I know how to spell BRANT :neener: (at least when it comes to the rocket and my name)



I started by constructing a proper OpenRocket file.
View attachment Black Brant II-6 inch-RW-BH.ork



Here are the parts laid out. On the right are some additional 6" to 3" centering rings that I purchased so I can build a tracking bay in the nosecone.

I'm starting with the boat-tail, motor tube and motor retainer.


The kit came with 3 centering rings: Two 6" rings and one 5" that fits into the tail. I added one extra 5" ring to beef up the aft end and attached an Aeropack 98mm flanged retainer.


Rings and retainer


I epoxied the two 5" rings together then drilled and tapped holes for the 8-32 screws that hold on the retainer.

For this build I'll be using mostly Rocketpoxy and West Systems Epoxy. Of course all parts are appropriately cleaned and roughed up prior to bonding. I typically use 60-100 grit sandpaper and I also score the surfaces as needed to improve adhesion.

-brant

edit - added BBII pic
edit II - added OR screenshot

Looking forward to following this build, and good luck with the cert. (And, without getting too pedantic about these things... thanks for spelling Brant correctly )

Hey, I'm still convinced that Brandt is the correct spelling.

https://shop.locprecision.com/product.sc?productId=111

They even spell it Brandt

Looking forward to this build, the BB is growing on me. Subbed!

blackbrandt said:

Hey, I'm still convinced that Brandt is the correct spelling.

https://shop.locprecision.com/product.sc?productId=111

They even spell it Brandt

Click to expand...

It's spelled Brandtf. The F is silent.

blackbrandt said:

Hey, I'm still convinced that Brandt is the correct spelling.

https://shop.locprecision.com/product.sc?productId=111

They even spell it Brandt

Click to expand...

Everyone slips up once in a while

mccordmw said:

It's spelled Brandtf. The F is silent.

Click to expand...

The F is always silent - and don't forget the silent K too "Kbrandtf"

Continuing on...

When the completed retainer assembly is dropped into the boat-tail, it sticks through the opening just the right amount - I'll have about an inch of the retainer showing. This should blend nicely into the overall appearance of the rocket when completed.



As I build the boat-tail and add the motor tube, the retainer needs to move freely so it can be centered. I made this little jig from some double-walled corrugated cardboard and a small section of 6" tubing. The hole is big enough to let the retainer fit through but smaller than the boat-tail. This support will allow the weight of the parts to be on the fiberglass boat-tail and not the retainer.

The parts


With the boat-tail and retainer assembly in place


Next I used JB Weld to affix the motor tube to the retainer assembly.

I let this dry overnight.

blackbrandt said:

Hey, I'm still convinced that Brandt is the correct spelling.

https://shop.locprecision.com/product.sc?productId=111

They even spell it Brandt

Click to expand...

Very good - but come on, much as we all love Loc and their great kits, I think typo/spelling isn't always their strongest point: '4" Diamter' for example

Anyway, to clarify this whole debate - a black brant (no 'd') is a breed of goose, indigenous to Western Canada. The BB was originally developed by the Canadian division of the UK Bristol Aeroplane Company, so the name was appropriate, since many UK sounding rockets for civilian use were named after various non raptor birds - Skua, Petrel, Skylark etc. But everyone already knew that, right?

That is going to be a really nice rocket - when do you hope to do your L3 certification?

By the way, are you the guy that helped me set up my RRC3s for the Dragonfly at NXRS?

RocketFeller said:

That is going to be a really nice rocket - when do you hope to do your L3 certification?

By the way, are you the guy that helped me set up my RRC3s for the Dragonfly at NXRS?

Click to expand...

I'm that guy. That was a fun rocket to see fly.

I'm hoping to fly this at one of the early launches at Brothers - the May launch or NXRS.

farsidius said:

I'm that guy. That was a fun rocket to see fly.

I'm hoping to fly this at one of the early launches at Brothers - the May launch or NXRS.

Click to expand...

Thanks again for your help!

I am also looking at attempting L3 this year, although not until fall (probably Fillible's Folly, but maybe Rocketober). Good luck!

Typically, centering rings get to butt-up against something like a fin tab, but this small 5" ring in the boat-tail is all alone; and while there will be other centering rings forward of this one and I know it's mostly just holding the retainer in place, I want it to be secure.

These next steps were all carefully executed since it all had to happen while epoxy was partially cured but still pliable to ensure that the motor tube would set straight and true in the boat-tail.

The motor tube/retainer assembly gets epoxied into the boat-tail

Secured with RocketPoxy. I let this sit about 40 minutes.

While this was setting I cut 12 one inch strips of 6oz fiberglass and mixed up some West Systems epoxy (105 resin + 205 hardener).


I coated the inside of the boat-tail around the 5" ring and the motor tube. Then I laid-up the fiberglass strips between the retainer screws


Once all the strips were applied I brushed them with additional West epoxy until they were evenly coated

Lookin' good! This will create a strong supporting framework for that lonely centering ring

These next steps were done to ensure the motor tube cured straight in the boat-tail. Again, this was all completed while the epoxy in the boat-tail was still curing and pliable:
I slid on a 6" centering ring into the boat-tail and then the body tube coupler. Next, I tacked on the upper centering ring to the motor tube with super glue.


I slid a 6" body tube over the motor tube - this pulled the motor tube straight - and I let the whole thing cure for about 4 hours.

I didn't glue in the coupler or 6" centering rings yet. I know I probably could have set up and epoxied the entire aft section with the body tube at this point, but I really don't like to move too fast. I wanted to make sure everything in the boat-tail set up as expected.

After this was set, I pulled off the body tube, took out the coupler and centering rings and looked it over to make sure it dried as I expected.

I replaced the 6" centering ring into the boat-tail. I applied a fillet of RocketPoxy to the motor tube and then coated the inside edge of the boat-tail with additional epoxy. I slid the boat-tail coupler in place, and let it cure.


Looks pretty good if you ask me

Straight as an arrow.

You'll see a few marks and arrows drawn on the parts I'm assembling. I always dry fit a few times before setting parts with epoxy. I'll make orientation marks where I think parts line up best. I don't like surprises when I building. It's not uncommon to find that some parts fit better when turned one way vs. another.

I just love this rocket. Nice building techniques and attention to detail so far. Looking forward to seeing the progress and ultimately a flawless L3. Do you have your motor choice selected?

BTW language police, you're on the wrong forum, you need to goto www.englishlitelitests.whocares

I'm waiting for a couple more centering rings to arrive in the mail before moving on to the fin can. The rings should have been here Saturday but all the snow and ice has brought Portland to its knees and I haven't received mail or packages since Wednesday (a full week).

The kit only come with two 6" centering rings for the motor tube. One of those fits into the boat-tail the other is meant to be mounted to the top of the tube. I purchased two more from Madcow - one to fit at the top of the boat-tail (and help sandwich in the fin tabs) and the other to double up the top ring for additional strength. I'm still deciding if I want to attach my Kevlar harness to a couple U-bolts on the centering rings, or if I'm going to epoxy it to the side of the motor mount - which is what I do for most of my builds. I see pros and cons for both approaches. I have a few days to think about it.

For kicks - here's the body tube and a fin with the finished boat-tail (and a 1 foot ruler for scale).

That's one big fin!

mpitfield said:

I just love this rocket. Nice building techniques and attention to detail so far. Looking forward to seeing the progress and ultimately a flawless L3. Do you have your motor choice selected?

Click to expand...

I'm planning to fly it on a CTI M2045 Blue. Should send it about 10.5k to 11k ft AGL.
The rocket has a 98mm motor tube. This motor is 75mm. I'll adapt it down - I'm not ready to invest in the next size....yet.

What are you looking at for the final weight flight ready?

Thanks

crossfire said:

What are you looking at for the final weight flight ready?

Thanks

Click to expand...

I estimate the final, ready to fly weight, sans motor will be 31-32 pounds.

farsidius said:

I estimate the final, ready to fly weight, sans motor will be 31-32 pounds.

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Mine came in at 32 lb. Due to field size limits, I've only flown it on mid range L's so far.

Rocketjunkie said:

Mine came in at 32 lb. Due to field size limits, I've only flown it on mid range L's so far.

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Thank you for sharing that. It's a really good feeling when someone can validate an estimate. All the parts came in at 26 lbs. Then I weighed my chute, harnesses, retainer, electronics, hardware and estimated epoxy weight. I knew I'd be close.

Wow...great looking kit and superb job on the build thus far. Only problem I see is that....now I want one!:wink:

Well done; keep up the good work!

-Eric-

farsidius said:

I'm planning to fly it on a CTI M2045 Blue.

Click to expand...

Do you have one?

ECayemberg said:

Wow...great looking kit and superb job on the build thus far. Only problem I see is that....now I want one!:wink:

Well done; keep up the good work!

-Eric-

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Thanks! The BBII is a great rocket. Every size or kit I've built has always been a superb flier. However; those large, swept-back fins can sometimes be problematic for landing on the larger scale versions. I've learned to reinforce the root of the fin at the boat-tail.

watermelonman said:

Do you have one?

Click to expand...

I do have one. I picked up one early last year. I didn't want to be stuck in a bind with the uncertainty of supply issues.

-brant

farsidius said:

I do have one. I picked up one early last year. I didn't want to be stuck in a bind with the uncertainty of supply issues.

Click to expand...

Nice. I have been trying to get my hands on one for some time. Let me know if you happen to change your mind, I have lots to trade!

watermelonman said:

Nice. I have been trying to get my hands on one for some time. Let me know if you happen to change your mind, I have lots to trade!

Click to expand...

I'll keep that in mind, but I wouldn't hold my breath if I were you. :eyepop:

Ok, I got in my extra centering rings last week. Who would have thought it would take a week and a half to get something in the mail from the state next door? Interestingly, though not surprisingly, I still have packages being held by UPS and FedEx that are going on two-weeks. They're really milking this bad weather delay excuse even though roads have been completely cleared since last Tuesday. And to add insult to injury, an item I ordered just two (business) days ago was delivered this morning.

Enough crabbing, on with the build....

I spent the weekend doing more thinking than building but I did get a lot of prep work done. I sanded and roughed up my motor tube and centering rings. I epoxied two centering rings together - this will be used at the top of the motor tube where I'll make my harness attachment. I also glued in a centering ring at the top of the boat-tail assembly




Roughing up the motor-tube with a 60-grit drum on my Dremel. When working with large surface areas I typically start out with the Dremel to rough up the surface and then go over it by hand with coarse sandpaper to even out the roughed-up surface. Sheesh, that lighting really makes that vein in my head stand out - it really isn't that pronounced (at least I hope not).

So, it's update time. You probably thought I went on vacation or something.

A little bit of story time before I post more pictures:

I spent some time contemplating my recovery harness needs and techniques. I'm notorious for overbuilding my harnesses (I've been known to put a 1" Kevlar Y-harness in a 10-15 lb rocket just because I know it will outlast the rocket. I also typically just epoxy my harnesses directly to the motor tube. I'll admit that like many of us on here, I build many of my rockets by looking at what others have done and copying it because it worked for them. Occasionally I'll work out the math for my ground testing of charges and I even did the math for shear pins once, even though I already knew how many I was going to use because I was following someone's build. I'm not sure why I don't work out more on my own. I like figuring out things - I do discovery and troubleshooting for a living. I think it's fun. Anyways, enough confession time.

Talking with my TAPs about my harness needs, we decided that I should use a different attachment method for my harness - something that would allow for inspection as well as easy replacement, if needed.

For the harness, I'm going to use a little common sense. Almost three-quarters of failures in rocketry occur during recovery. This is certainly one area of the build where you can take a little time and work through it. One of my TAPs shared what he called the 50G standard: "Deployment is often the highest G load a rocket sees during flight. It always seems slow because it is far away but recovery events can be really violent especially if the flight is less than nominal. The accelerometer data often shows spikes of 30 or 40 G's when the parachutes come out, hence a little safety margin and I come up with my 50G standard. If the rocket weighs 30lbs then 30lbs X 50 G's=1500lbs. So every component including the weakest link (knot, bulkhead, threaded fastener etc.) in the recovery harness has to equal or exceed that tensile strength. This is reasonable design with out being over designed".

This rule isn't just anecdotal. Last week I spent some more time scouring the forums for information on determining appropriate strength needed for different components. I came across this thread from a few years ago: https://www.rocketryforum.com/showthread.php?36628-Calculating-recovery-system-loads. I think it explains very well the maximum force you would expect to experience (excluding catastrophic issues). I copied a snippet here:

"If you are flying drogueless, sooner or latter you'll get a flight where the upper section will lead the fin can down and the main will open well below the fin can. The fin can will fall past an almost stopped main chute and hit the end of the two shock cords. Calculate the force the fin can, with an empty motor case, will develop when it free falls the distance of both your shock cords. This should be the maximum force you should ever see on your recovery system, excluding deployments at high speeds which are going to be failure modes, much less predictable, and probably not something you can or want to design for".

Using this site which is referenced in the thread https://hyperphysics.phy-astr.gsu.edu/hbase/flobi.html, I calculated the force of my falling rocket from the "stationary" main parachute:
Rocket: 30 lbs = 13.6 kg
15.25 m (50 ft) of recovery harness (height that it's falling from the main)
=17.3 m/s at impact (impact being the point where the harnesses are fully extended from the main)
=2032.5 Joules, convert to foot-pounds of force (1 ft-lb = 1.3 Joules) = 1499 ft-lbs force

Seems like the 50G standard is well thought out. Of course, the longer your recovery harness, the higher the force will be. Also, the parachute isn't entirely stationary, but we can pretend it is for this calculation.

With this in mind, I've selected to use the following in my recovery system:
2 x 3/8" U-bolts (1300 lbs each)
3/8" tubular Kevlar (3600 lb rating)
Sewn loops, no knots (knots reduce the breaking strength of Kevlar)
5/16" quick-links (2400 lbs)

I'm also sewing my own loops into the Kevlar. I'm using 200 lb. Kevlar thread which is probably overkill (it's certainly much heavier than the thread used on any of the commercial Kevlar harnesses I've purchased) but I'll be sewing by hand and this will make me feel good .

-brant

I already mentioned that that I had doubled the top centering ring in case I decided to anchor my harness to it.

I drilled out two sets of 3/8" holes for the U-bolts


Sewing my Y-harness. I'm a good little tailor. It doesn't look big but I would tow my car with this thing. Kevlar isn't that difficult to sew. The trick is keeping a steady tension and using a blunt needle that doesn't break the or snag the fibers.


Harness is attached directly to the U-bolts. U-bolt nuts are secured with the impossible-to-break-free-unless-you-have-an-impact-wrench red Loctite. You can also see that I secured the ends of my harness with some heavy duty shrink tubing


On smaller rockets I've built, I'll usually tack the fins on with superglue then epoxy on the upper centering ring. After the centering ring is set I'll remove the fins and get the motor tube assembly ready to go into the body tube. The fins on this kit are just too big to go that route, so I cut out three placeholders for the fins from heavy corrugate and used those to hold up the centering ring while I secured it. I really liked this approach - it was easy and fast. I don't think I'll do the fin tacking thing anymore.

One last reinforcement of the centering ring:

When using U-bolts, I worry that the stress of the recovery might snap the fiberglass ring. I've never actually heard of this happening (maybe I've missed a thread?), but it still bothers me. As added reinforcement to the ring, I cut out these 1" wide beams that I'm adding as horizontal supports. I saw this idea years ago (don't recall where exactly) and it should provide significantly more strength than increasing the thickness of the ring.

A little prep work on the body tube. I've sanded around the fin tab slots and drilled out some holes for injecting the internal fillets. Also drilled out are some holes for the launch rail buttons


I'm using t-nuts with an added washer to secure the buttons. Some JB weld to sandwich the t-nut and washer together. Why the washer? To give me more threads for the rail button screw. If you look closely, you can see that I ground down the t-nut so it would rest flush with the outside surface of the body tube. Without the washer I would only have half as many threads for the button screw.


Here's the nut in place at the aft end of the tube secured with JB Weld. Then from the outside. Of course, I quickly removed this nut after taking the picture because I wouldn't be able to slide in the motor tube with it there knucklehead!


Continuing on now using the upper button hole, I cut a couple strips of fiberglass (about 1" x 2") and used West Systems epoxy to overlay the nut. This will provide additional strength to the nut and give us a nice smooth bump that nothing will catch on.


For securing the aft button nut (again), I slid the motor tube in half way and then secured the nut in place with JB Weld and then overlaid it with fiberglass like I did the forward nut. Lots of room to work in these tubes.

Using a stick, I applied a ring of epoxy to inside of the body tube just at the top of the fin slots and also to the boat-tail coupler. Heave-Ho! And the two parts get mated together for all time.

"When using U-bolts, I worry that the stress of the recovery might snap the fiberglass ring. I've never actually heard of this happening (maybe I've missed a thread?), but it still bothers me. As added reinforcement to the ring, I cut out these 1" wide beams that I'm adding as horizontal supports. I saw this idea years ago (don't recall where exactly) and it should provide significantly more strength than increasing the thickness of the ring."

I recall centering ring failure being a listed culprit of failed flights in a recent Sport rocketry magazine. IIRC, the offending ring was plywood and there was no backing plate on the U-bolt, but it could happen to fiberglass. I think you made a wise choice.