BroncBuster II (Scion->Leviathan HPR): Finished! Flown (x3)! Tree'd and Free'd!

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Pop lugs, not drugs
Oct 15, 2016
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Huntsville AL
In order to prepare for L2 sometime in the future, I decided to practice construction and deployment techniques on a fleet of modified Pro Series II mid-power rockets. If mistakes occur, I lose a $40 rockets and a month's work instead of a $400 rocket with at least a couple moths work. This Leviathan refit is where I'll practice internal fin fillets, tube slotting, Chute-release use, and an accessible/replaceable shock cord mount. Possibly adjustable nose weight as well if I want to fly motors larger than a small H.

Bronc Buster.jpg10358997_281001962078492_1033519608579021638_o.jpg
The Leviathan is without a doubt my favorite Pro Series II rocket. Simple, stocky, durable, and it flies well built to instructions (in fact too well sometimes). I built the original BroncBuster two years ago and launched it from the middle of a crop irrigation circle on an Estes G80-7T because it was the biggest motor I could get. Perfect boost, high deployment, steady descent. Unfortunately, I had painted it dark green and orange (school colors) and an incoming front blew it into a citrus orchard (which also happens to be dark green and orange). To this day, I know not where it hangeth.

Since the Leviathan was discontinued, I ended up buying the Scion when I read on the forum that its basically just a cheaper Leviathan with a longer unslotted tube (even has the 4th fin). When I received it I cut the rear tube down to the proper length and set out to make a 4-fin slot template using Solidworks drawings. This turned out harder than I thought it would because some printers demonstrate asymmetry along the feed axis on their paper. I went through several template iterations before I got one with the proper geometry.

An aluminum angle (angluminum?) and Xacto made the fin slots go smoothly, and the aft section finally came together for a dry fit. Which naturally means I had to get a complete dry fit picture!

I'm currently in the prime/sand cycle, so posts will likely catch up.
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Random tool tip after reading this...

For 4 fin rockets, making a template can be REALLY easy.

1) Wrap a piece of paper around the rube, and mark where it overlaps.
2) Cut paper to size so it's a single wrap.
3) fold paper in half. Now you have 2 lines 180 degrees apart.
4) Fold in half again. Now you have 4 lines 90 degrees apart.
Good tip indeed. If you look at the tube picture next to the discarded template trashcan, you can see two of the paper creases I used to double check the alignment.

Also, if I can get the drawing and printer settings aligned properly, I can make 3, 5, 6, etc.... templates as well.
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Looking forward to your build. The Leviathan is a great rocket with plenty of possibilities.

For my Scion-to-Leviathan build, I just ordered an extra pre-slotted 10" tube for $5. Now I have a full length extra 3" tube that I might turn into a 1:131 scale Saturn V or something. But then again, saving the $5 and getting some more practice with fin slot cutting isn't a bad idea either.

You can still find some genuine Leviathan kits around here and there, albeit at a premium.
Thanks Caber! I looked for Leviathan's and only found them for $56+ and usually ~$70. And I didn't think to post in he [Wanted] section, nor did I know that a club member has two of them still bagged in his storage. (He's a mad collector of Estes and older model rockets, last I talked to him he had ~815)

Copying from my L1 (4" Madcow Patriot), I added a 3/16 eyebolt to what became the forward centering ring slightly angled for ease of threading. The more I read about Hi-power and performance mid-power, the less I like the trifold paper shock cord mounts.
I took this motor mount as an opportunity to use Titebond II for the first time and attached the forward and middle rings. First I squeezed a bead on the ring positions, slid them into place, and smoothed/added fillets on each side. That shrinkage was astounding. I'd heard about Titebond's volume reduction but geesh.... The next day I roughed the glue corner and added another thin layer. I figure if can get 1/16" fillet thickness of glue on 5/6 ring sides, I'm looking at a failure load of ~3600 lbs for the motor mount to rings (assuming a conservative 3200 psi bond strength). Pretty sure the paper will lose cohesion first.
While those were drying it, was time for tube spirals and elmers wood filler to meet. 16 ft of tube spirals.....

Now for mounting, I didn't want the "shrinkage lines" that are rumored to come with TBII on the inside of the body tube, so I smeared the inside of the aft section with Loctite 5min Heavy Duty. That's been my goto epoxy for mid power (and spaghetti bridges, but that's an entirely different story) and the working time has been just right for getting pieces of this size prepped and stuck in place.

Some extra filleting on front ring edge, and then the tube coupler was also epoxied right in front of it. I should have cut down its length a little, but I wanted to leave plenty of material in the front for later. Fortunately I have long fingers and can still access the eyebolt to poke shock cords through and undo sheepshead knots. Also I discovered that several slits on my epoxy 1:1 applicator allows me to slip out the double plunger, cleanup the pieces, and then refill with the bulk bottles! Future savings abound!
I have a bunch of used 5-minute syringes like that... I never thought of re-using them. Good/easy way to ensure 1:1 mix ratio.:)
I was getting fed up with paying ~4 bucks for .85 oz in the convenient applicator. Now I can get 8 oz for 16 bucks and still have a consistent, low waste mix process.
I really doubted my arm would fit down a 3"x30" tube to get to the eyebolt, so I decided to use removable rivets on the tube coupler. First time I used these was back with my school's IREC team. If they worked on a 30 lb M powered vehicle, they'll be fine for my little F-I fleet. And they can be ordeed in bulk from Walmart and Mcmasterr. In order to fly these on any launch setup, I'm using the included .25" lugs and some 1010 buttons from Doghouse (like everybody says, great service and communication. They arrived 3 days after I placed the order. My apartment didn't give me the package notification, so I emailed Doghouse, and they said "should already be there". They were, just trapped in the apartment mailroom :))

After marking the tube for rivets, lugs, and buttons, I took a trip to borrow my uncle's Dewalt and bit set. I really should have smeared superglue on the sites before drilling, but this is a learning build after all. I also reamed the Doghouse buttons with the next bit size up, so I could use 6-32 weld nuts (brads, t-nuts, whatever you want to call them) for mounting. I ended up dabbing superglue in and around the holes then sanding down the ridges. Then I bent the weld nuts so they'd conform to the tube better and used the Loctite to fix them in place.

With all the rivets and weld nuts installed, I decided to make a spur of the moment parachute shelf. Using the rear centering ring as a template, I cut two rings with wider centers out of a HAZ box. After shoving them into place, I drizzled TBII on the edges to fix it. Definitely the least thought out portion of this build, but hopefully it'll keep the cord and parachute bundle from sliding back and mucking with the CG. I also used TBII to place and align the lugs, then put a small bead of epoxy the next morning when it was cured.
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I did the exact same thing with mine - launch lugs on one side with buttons on the other. Good to have options.
Fin time. Everyone knows that shaping a fin into an airfoil reduces drag, but how much does it in reality? I like the appearance of the airfoils, but really wanted to get an idea of the drag reduction. Just to pretend I was still a mechanical engineer, I used Solidworks to make the square cut fins and the airfoil then set up the Flow Simulation tool to return the resultant forces along the flight axis (at a speed predicted during flight on a G79).

Its nice to see a concept illustrated by data once in awhile. The velocity plot at the reference cross sections shows a drop in velocity on the square leading edge, and the larger drop at the blunt trailing edge could easily indicate turbulence and vortex formation (both contributing to drag).
Looking at the foiled fin, there is a smooth velocity transition as the flow accelerates over the fin. An elliptical edge is optimum for minimum flow separation in subsonic flight and the tapered back end joins the flows with a much smaller drop in velocity.
Looking at the the force outputs, there's a 70% reduction in drag. Multiply that by the 4 fins of the leviathan and you have nontrivial performance improvement.
Foil difference.png

Simulations and flow models are cool, but back to reality. I really need to get a power sander, because using a hand block with 60 grit got real old real fast. The upside is that I think the practice is improving my consistency. Loctite Heavy Duty makes an appearance again to Fix the fins in place, and I used TBII on the tab to motor mount and root to body tube fillets. Then I used the loctite again on the inner body tube fillets. And some super glue on the much thinner trailing edge just for stiffness' sake.
and to think that one can reap much of the benefits by simply rounding the leading & trailing edges...
A Dremel and sanding drum used carefully, or with the sanding attachment, makes quick work of the leading/trailing edges on those ply fins. Finish with a block just to even it all up. I've only hand sanded ply fin edges once....used the Dremel on every one since.
and to think that one can reap much of the benefits by simply rounding the leading & trailing edges...

Very likely. When I get out of work, I'll run a model with simple rounded edges and we shall see! :cool:
Ever since I was a kid I've been asking "but why does it work?", so the investigation will likely never end.

A Dremel and sanding drum used carefully, or with the sanding attachment, makes quick work of the leading/trailing edges on those ply fins. Finish with a block just to even it all up. I've only hand sanded ply fin edges once....used the Dremel on every one since.

10 more Pro Series II fins to sand into shape, so I will need to get SOMEthing. I had Secret Santa, holiday travel, and a Chute release to buy, so I figured giving manual sanding a try once wouldn't hurt (much). With the dremel, my only worry is uniformity, or accidentally carving round divots in a thinned trailing edge. I'm still really attached to the idea of a belt sander though. It's coverage allows the whole edge (or at least large portions of a really long edge) to be in contact at a time. Plus, I'm used to shaping with them (back when I had a university machine shop full of fun things to use).
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It's not hard to get an even edge....the more you do it the better you get. Use a light touch and many passes....or use the sanding guide attachment if you have it. I use the Dremel to rough out 95% of the edge, then finish up by hand.
I recently started using my palm sander for ply fins. The one with the pointed edge. Sands flat and easily controllable for contours. I tried to sand by hand again but my shoulder and elbow weren't having it.
I tried a palm sander with the pointed edge when I was working the 1/4" fins on my L1 (early march?). I remember being extremely disappointed with the material removal rate and went to the floor mounted belt sander. Got all four nicely matching within 20 minutes (and that was going slow).

Its possible that they only had smaller grit pads available for that hand sander. If I were to get a palm sander (sheet or orbital), I'd try and stick with 60 for the shaping, then just hand smooth them with 220->500.

I'll need a high removal rate for the 4" Phoenix I want to get when the four PSIIs are done. What's the Phoenix have? ~6 ft of swept leading edge? Not gonna hand sand that into shape.
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So I created an fantastic finishing and painting plan last week.
Staggered the components, so I had few days just waiting for paint to dry.
It went like this:

Tue 11/26FinsChute shelfPrime
--pull tape
--pull tapemask/blue
Sun 12/4--pull tapemask/green--pull tape
Monmask/blue--pull tape
Tue--pull tape
Wed mask/green
Thurs --pull tape

And this is what has happened to it (lets see how it lasts):

Tue 11/26FinsChute shelfPrime
Thurs Grumble about spirals not being totally filled. Go to club meeting. Go to Hobby Lobby to buy Taser launch set as White elephant gift.
FriGo to company End of Year recog. Banquet (and white elephant). Search forum for how to fill primed spirals with Spot and Glazing putty
SatSleep in. Do dishes. Fiddle with Solidworks flow simulator (Fins!). Go buy Titebond Q&T, Bondo S&G putty, and Loctite HD bottles. Pick up Secret Santa package from uncle (end up staying for dinner).
Sun 12/4Install rear ring. Search for lost motor retainer (I apparently stuck it in the Partizon bag when cleaning up). Apply TBQ&T fillets (seems to work pretty well).
Apply putty to stubborn spiral.Since I have the putty, fill in mold seam while I'm there.
Make Dinner and food for week ahead
MonPost about messed up painting schedule
Sand/primeSand/prime (again)
Wedsand/orange'--pull tape'--pull tape
Thurs'--pull tapemask/green
Frimask/blue'--pull tape'--pull tape
Sat'--pull tape Deliberate endlessly
Sun 12/11mask/green about nose weight

Just some pics of the process, and No Rivets Left Behind!
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The rains are stopping and humidity has dropped, so I may be able to stay on schedule for a short time! (and my Chute-release should be getting here by the weekend)
The aft has been primed twice, the tube was wetsanded and has the first color on, and the nose is in day two of drying.
I retrieved the pressure distribution from my flow simulation and am using that to guide the color scheme.
IMG_20161207_182029031.jpgPressure distrib.pngBroncbuster II.jpg

Those are the colors of UTRGV where I graduated.
They have the colors, mascot, and logo "trademarked for the athletic department only" so our rocket club couldn't even call themselves the Rocket Launchers at UTRGV (they denied the org constitution until "at UTRGV" was removed this year). Way to build school spirit eh? We went on to place 7th out of ~43 last year in the Basic category: 10 lb payload to 10k feet. (including above MIT and Embry Riddle).
Since I am no longer affiliated with the school, I can freely use any combination of three colors I want. Even if they happen to coincide with a certain institution...
(Being 2m +/- 5mm, I'm always stuck in the back of photos)

The, logo/color/mascot stinginess is why I'm slightly irked I graduated from "UTRGV". It was formed as a merger between Univ. of Texas Pan American (my school: Go Broncs!) and another last year. I took a year off (total, not sequential) to do internships, so I missed graduation as a Bronc by one semester (!) and had to walk as a "Vaquero".

But Broncbuster II will live on! (if I get it painted....)
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Someone named 'John Bean' just sent me this neat little Christmas ornament.
It even lights up! Too bad I don't have a christmas tree. Maybe I can find something Else around here to hang it on...something pointy.
Wrap it around something soft, round and nyloney.....

I'm not in the habit of wearing stockings, so I'll have to find something else..

Meanwhile, north AL has gotten kinda chilly, so I've been trying to take advantage of brief opportunities to paint.

The nose is done and I'll be leaving it alone to cure.
I've got the tube masked in preparation for the green coat tomorrow noonish when the temperature won't be 8 below freezing, and it'll be done.
The aft got another prime/sand round, so it's delayed, and still has 3 colors to go.
Tube's green and done, Aft's orange and I'll wait a couple days before masking for the blue. A couple blue specs got on the nose, so I tried to do some touching up. I am regretting that because now there's a tape line in the orange. I may just have to smooth it down a little hope to even it out with the clear coat after awhile.
I received my vinyl lettering from I'm aware a lot of people here use Stickershock, but for lettering, I love Sign Spec. There's a set on my suburban's rear-side windows that have been there for 4 years with zero lift or fading. Good color and effects selection too. They don't have full body specific rocket wraps, but for what I do, they rock. Also, send them a pic of where you used their decals, and you get a 10% discount For Life (!!).

With that intro, I'm going to hold off on the decal shot until the painting is finished. I jumped the gun in applying them and don't want to spoil the reveal. So here's some weighing and process pics. I'm at ~1#:1oz currently.
I forgot how long masking flames takes, but looking at the finished product is worth it.
Thanks for mentioning I just checked their website for an idea I've had in my mind for lettering and they can do exactly what I was thinking of!

Looking forward to seeing your finished product.
Glad you can use their services Tango!
I've pulled the tape from the blue flame accents on the aft section. Now I'll let it cure another day and try to get it masked and painted tomorrow evening. There's a launch scheduled for saturday near Birmingham, but the rain may have other plans.

(I'm trying to upload a shot of the vinyl on my truck, but its refusing to finish importing the photos...)
Here we go!

That font's called "Batman Forever"



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What software is that? Something available freeware or at a low cost?

What software is that? Something available freeware or at a low cost?

Its the Flow Simulation addon to the SolidWorks CAD program. I'm afraid I don't know how much Solidworks costs, but I know its one of the higher end CAD packages.
I obtained my copy while on my old school's rocket team.
That's how to request a quote

If you know a university student, you might be able to snag a license for $150.

and depending on your view of digital software sharing, there other places to find it.

The thing about CFD (computational fluid dynamics) is that its highly specialized engineering niche, and very time consuming to develop and refine. The open source packages I've looked at (best descriptive my uncle could apply)
Last coat has been masked and is curing.
I should really look into some of that masking paper instead of tap striping. I'm fine with the results I get with the tape strips since I've been doing it for a couple years, but there's always room for learning.

and Photos working again!

Maybe I'll get to launch tomorrow! Unless the Birmingham club is under rain again.
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Launch this morning was canceled due to rain, so I got to spend time making mashed potatos for a Christmas party and unmasking BBII.

I think it came out well. My only regret is the tape line in the middle of the orange nose from when I retouched a couple spots.
The orange launch lugs and rivets stand out exactly the way I wanted them too against the dark green.

The last attached picture shows harness trailing out. Nothing fancy there without the Chute release installed. Sheepshead knotted to the forward Centering ring's eyebolt, and tied to the molded nosecone loop for now. When Upsale CNC gets my nose ring and bulkhead done, I'll chop the molded loop off and install the variable weight fixture.

Until then, I'm on a break from rockets for the holidays while I drive to visit old home and friends in southern Texas.
Thanks for reading!



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