"Bridges at Toko Ri" PML Bullpuppy

So I found an unbuilt 3" PML Bullpuppy (or is it "Bull Puppy") in my garage from 1997 when I was getting back into rocketry but took a small detour (ha!) to have kids.

Everybody's Bullpup is always white. It's such an iconic scale rocket that I wanted to do something completely different as I embarked on this build. This is my first build thread here though Ive been lurking for eons. So this is what I came up with: I'm a pilot and one of my favorite aviation movies is "The Bridges at Toko Ri" with William Holden and Mickey Rooney (1954). Sure it was before my time (I wasn't even born), but the F-9F Panther jet is one of the most beautiful early jets, so I decided to use them as my inspiration.

Those of you purists will likely balk at my design choice, but I'm just really tired of the white-with-Air Force-marking Bull Pup. I know it's how it really looked, but I wanted something different. So off I embark on building this thing.

Aside from the out-of-the-box design, I will modify the rocket slightly as follows:

1. Fiberglass the internal fillets
2. foam the fin can
3. Added wood bulkhead on the tail/motor mount
4. Slimline Quick-lok motor mount from Giant Leap
5. Bigger 'chute
6. Wood bulkhead and screw eye in nosecone
7. foamed nose cone (based on Rocsim weight calcs)
8. fiberglass inside of piston

Materials:
I'll be using Z-poxy 15 and 30-min epoxy and JB-weld epoxy for everything. Nothing special. Also some 5-minute Devcon from Lowes for a lot of it. I'm not a huge believer in making rockets crazy strong. We'll see how it goes. I will be using FIXIT Epoxy putty from Apogee for all external fillets. I was impressed by the video and I played with some and it seems great. Filler will be green Squadron putty because I love it. Other than that, Rustoleum primers and paints. 2 oz fiberglass cloth with z-poxy resin.

So today is build day #1. Tasks completed:
- Washed all the parts to get mold release off and prep for sanding
- Found my design inspiration from the movie.




Marc C. Lee
Rocket Geek and pilot
BAR.

I'll be watching, I have similar interest for similar reasons. I beg, no plead with you not to use FixIt for your fillets. It won't turn out the way you want and they are heavy. If that is not enough reason, they don't seem to bond very well either so they will crack/split sooner than later. You'd be much better off with just a smear of 30 minute epoxy with a rubber glove. Personally I'd get some filler and add it to some slow set and do the tape method, easy and darn near fool proof.

BTW, my math professor in college flew the F9 in Korea. Also, the Oriskany was tied up in Pensacola for a while when I was there waiting for the OK to be turned into a reef.

I agree with grouch, don't use fixit putty. It's brittle and cracks after s few landings.

Nice!!! op:

Mlee said:

So I found an unbuilt 3" PML Bullpuppy (or is it "Bull Puppy")

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According to PML, it's listed as "Bull Puppy".

Also timing seems uncanny recently...just got my 3" Bull Puppy from the post office today (ordered over a month ago).

BUILD DAY #2 - Photos below

After washing everything I started into the tail cone today.

The Bull Puppy presents a challenge for builders when using a threaded motor mount. The boat-tail tapers down to where it is the same diameter as the motor mount tube. It's designed so the motor tube just adheres to the bottom of the boat-tail and motors are friction-fit. For me I want a better motor retention system- hence the Slimline. The problem is the Slimline motor mount requires at least 3/8" inch of motor mount tube so it can adhere properly. Since the motor mount tube on the Bull Puppy is designed to be flush with the boat-tail, that would be impossible. That leaves one choice: Cut off about 3/8" off the bottom of the boattail. That also means reaming out the inside of the boat-tail so the motor mount tube will slide through the opening.

So I cut off the 3/8" after filling the imperfections in the boat-tail with green squadron putty. I used a precision model/hobby saw that is extremely thin and sharp. It's the "Zona" flush-cutting saw from Micro-Mark hobbies and it worked great. TIP: You can buy a knockoff which is almost as good and works just fine (and is around $3) from Harbor Freight tools.

Once the end was cut off, I reamed the inside diameter with a dremel using a "432" sanding band. It was messy work and you HAVE TO PRESS LIGHTLY because - at high speed- the dremel will go through the plastic like buttah... I kept pushing in the motor mount tube to make sure my diameter was JUST right.

I removed a good 1/32 of material all around the inside. I then evened it out with 80-grit dry sandpaper. I needed the roughness of the 80-grit to allow good adhesion of the motor mount tube.

Once the boat-tail was ready, I inserted the tube for a final dry fit and it was snug. I made a pencil mark around the diameter of the motor mount tube so I would know where to put the epoxy. I smeared only the motor mount tube with 15-minute Z-Poxy right along my line marking. If I had also put it on the boat-tail, it would have smeared on the motor mount tube and make installing the retainer later too difficult. The end (the last 3/8") needed to stay clean and pristine. So epoxy (lots of it so it would run into the gap between the boat-tail and motor mount tube( was applied liberally onto the motor mount tube. I then slid the tube into the boat tail so 3/8 protruded beyond the end. The fit was just right.

NOTE: The kit comes with a temporary centering ring so the motor mount tube stays centered. Use it! Works great. Just slides on, then off when epoxy cures.

After waiting for a couple of hours for the epoxy to cure, I mixed up a small batch of JB Weld, smeared it on the protruding motor mount tube and slid the Slimline motor retainer onto the tube. I cleaned the excess off immediately with a wet finger and used the extra to fill in the gab between the boat-tail and the retainer. Wiped off excess with alcohol.

Boat-tail with seams filled-in with Squadron putty. Measured 3/8" and cut off with flush saw by hand. very easy


Showing my progress with the flush knife. Then sanded the bottom so it was smooth and even with no plastic shards.


Temporary centering sleeve used to keep motor mount centered while drying




Motor retainer installed and dry.

Looking good so far!

BUILD DAY #3

Today we mount the fins into the boat-tail. First up was sanding the G1- fiberglass fins to a good, aerodynamic shape. I did this by hand (man that was a lot of fins) and they came out great. Used a standard airfoil profile.

Tacked the fins onto the motor mount tube with 15-min epoxy and smoothed the excess. Taped them down to keep them perpendicular. Roughed up the root area of each fin- both at the motor mount tube part, and the part that juts out of the boat-tail. These areas will have epoxy fillets and need to be roughed up with 80-grit.

Left all four fins to dry. Then cut fiberglass rectangles from the 2 oz. cloth the full length of each fin root. These will go only on the inside fillets for strength. The Bull Puppy has weak fins so I intend to strengthen mine as much as possible. The process is messy and difficult because there is hardly any room between the inside of the boat-tail and the motor mount tube. used long, thin tweezers to place the fiberglass then cover it with resin and hardener using a regular hobby brush.


last step: wet-sanding the fins with 600-grit to make them baby-bottom smooth


Tacking the fins on with 15-min epoxy and using thin masking tape to hold each fin in the correct position


Holding in place and taping


My uber-cheezy rocket holder jig. But it worked.


All fins mounted. Not much room to place fiberglass fillets


Cutting fiberglass strips for the fillets on the inside of the boat-tail


Placing fillets with tweezers. Then covering with Z-Poxy 15-min. Light and strong


Final, dry fiberglass fillets after a few hours. Each strip extends about 1/2" inch onto both the fin root and the motor mount tube.

Next up, we'll urethane-foam fill the boat tail then add external fillets.

Mlee said:

The Bull Puppy presents a challenge for builders when using a threaded motor mount. The boat-tail tapers down to where it is the same diameter as the motor mount tube. It's designed so the motor tube just adheres to the bottom of the boat-tail and motors are friction-fit. For me I want a better motor retention system- hence the Slimline. The problem is the Slimline motor mount requires at least 3/8" inch of motor mount tube so it can adhere properly. Since the motor mount tube on the Bull Puppy is designed to be flush with the boat-tail, that would be impossible. That leaves one choice: Cut off about 3/8" off the bottom of the boattail. That also means reaming out the inside of the boat-tail so the motor mount tube will slide through the opening.

Click to expand...

How did I miss your post yesterday? (Maybe forum gremlins.) I started on my Bull Puppy last night and there is a separate yellow sheet inserted in the instructions which note that if you're using a motor retainer such as the HAMR (PML's glue on retainer): "the motor tube MUST protrude beyond the aft centering ring by 3/8"....ignore the kit instructions and make the required adjustment...However, it is always prudent to check the CP/CG relationship on any rocket before flight."

Well, this bit of updated info looks like it may have been added more recently; however I didn't see this until last night and I think your method works well and makes the retainer more streamlined, so I like what you did (nice work!). Still, this should be helpful for others who have this kit and may be following. I'm using an Aeropack, so I extended the tube as the note mentioned (I was actually already doing this before I saw the note...do enough of these and you already know a lot of kits require your own modification).

Great looking rocket! I did my L1 with a PML Bull Puppy. I wouldn't worry about the purists, almost all of the models already have the canards shifted aft from the real thing. I actually think the models look way better.

I also did my L1 with my Bull Pup, great rocket. Sadly I just lost mine this past LDRS34 on the Friday. I was told yesterday that they found the remains, which fell from 4900' and apparently my fins and canards are still attached. But it is zippered right back to the top CR and not likely repairable, we will see.

So I will be watching your build thread with interest as I may build another but differently this time. I do like your preferred colour scheme based on the Panther. There is at least one other rocketeer that stepped out of the box with the colour scheme https://www.rocketryforum.com/showthread.php?106383-Bullpup-12D-finished

I would also agree with what others said and don't use fix-it epoxy, it is too brittle for those big fins and will not adhere as well to the QT as other epoxies. I scuffed up the QT around the fillet areas on the fins and faux canards with 80grit, then used red baron 30 min flex-cure epoxy mixed with micro-balloons. It worked very well and my fillets turned out great and were flexible enough for this big rear fins which will flex on landing.

My rocket loaded was just under 5lbs and I used a 36" Classic Elliptical Fruity Chute, which brought it down around 15'/s, I also used the GLR slimline retainer but flush. I do like how you recessed yours.

Thanks for your comments. That's interesting that they're now including an addendum to the instructions. Mine was an old version. I should add that extending the tube does make a difference in the CG though it's not much (according to my free 30-day copy of Rocsim, LOL).

to explain better what I did, instead of extending the motor mount tube, I reduced the length of the boat tail and reamed the inside enough that the Slimline retainer would fit slightly INSIDE the boat tail. In other words, I epoxied the Slimline to the motor mount tube and then slid the WHOLE thing into the boat tail from the top. I put epoxy on the Slimline retainer before I slid it in. So the boat tail is epoxied to the inside of the boat tail, and the motor mount tube is epoxied to the slimline retainer.

by doing that I kept the length of the motor mount tube the same and the recessed slimline is a better look. I could have also just stuck the tube out further and epoxied the retainer to the tube so it butted against the boat tail. Would have been easier in retrospect. But I like how this looks.

I agree with you...I initially didn't really care, but I just put the retainer on to see and then removed and just put the cap on and it looks much better with the retainer body recessed as you did.

KenECoyote said:

I agree with you...I initially didn't really care, but I just put the retainer on to see and then removed and just put the cap on and it looks much better with the retainer body recessed as you did.

Click to expand...

cant wait a it to see yours! Are you doing anything special.

Nothing special...wanted a bigger Bullpup for quite a while and finally got it. I earlier debated a different color scheme and my searches didn't find much...I was almost going to do it all red, but I have a lot of red rockets. Your color scheme idea is great! I was thinking similar for a different rocket I have on long-delay pre-order (think WWII sci-fi dogfighter rocket).

As a reference, here is the GLR slimline retainer butted up against the boat-tail. This pic was taken to show a wrinkle issue I had on the base/clear, so the retainer was tapped up prior to the repair work.

View attachment 266742

That actually looks great. Also, huge compliments on your fillets and finish work. Not easy to do as you know.

marc

Here's some pics of the retainer end I was working on...following the PML instructions to extend the motor tube by 3/8" and with an Aero Pack...reminds me of Mario Bros, so I may consider filling in the gap by extending the boattail. (sorry for the big pics):


And here it is without the Aero Pack body and just the Retaining ring (simulates a recessed body):

BUILD DAYS 4 & 5

First, I know you guys all said not to use Apogee's Fix-it Putty. But I have to try for myself so I know how it is. The videos make it look easy, and I loved how you could shape and smooth it with water. It is heavy and I noticed after curing it does seem brittle. But these are for external fillets so strength is not as important. So I did try the putty and I did like how easy it was to work it. I didnt like the weight. I also loved how easily it sands. I don't know, the jury is still out.

Once the fillets were done and dried (that took quite a long time), it was time to foam the fin can. PML recommended this so that's why Im doing it. I used the 2-part urethane expanding foam I bought from Apogee as well. It worked great! I did lighten it a bit by adding a few drops of water. I did the fin can in 3 pours, each one about 1/4 of an ounce of each part (A and B). 3 did the job well, especially with the water drops. It was just the right density and very light but strong. Some of the last pour expanded beyond the lip of the tail so I had to trim that down with my saw knife and it was good.

Last today was adding reinforced rings to the upper motor mount. PML's design is weak in the tail cone mating area. It only adheres to the QT tube with the outside diameter of a single wood ring. Instead I sandwiched a G-10 ring I bought from PML with a second wood bulkhead ring. The combination of the original ring plus the other 2 created a much larger area for the epoxy to adhere to. I scuffed both the motor tube and the insode diameter of the rings so they would adhere better. The final assembly is strong, though a bit heavy. It is apparent this rocket will lean toward the heavy side, like most Americans :_)


The epoxy putty/clay was easy to work with and very easy to smooth out. This is just the first pass.


All four fins completed. Just sanding and cleanup. They feel good.


Mixing the 2-part urethane foam from Apogee. I added 3 drops of water to this size pour (about 1/2 ounce)


The completed set of 3 separate pours, allowing each to dry before the next (about 15 minutes)


My made-up sandwich of 3 rings; a G10 fiberglass ring epoxied in between 2 wood rings. Note that I did NOT mount the shock cord to the motor tube. I will connect it with a D-ring later.


The completed tail cone assembly, It is ready to mate with the Quantum Tube body.


Another view of the completed tail assembly. The shock cord will be attached to the top wood ring with a D-ring. The rings are not yet epoxied to the boat tail. I need to drill the D-ring holes and attach it first.

Marc

KenECoyote said:

Here's some pics of the retainer end I was working on...following the PML instructions to extend the motor tube by 3/8" and with an Aero Pack...reminds me of Mario Bros, so I may consider filling in the gap by extending the boattail. (sorry for the big pics):

And here it is without the Aero Pack body and just the Retaining ring (simulates a recessed body):

Click to expand...

I cut just enough of the boattail off so that the Aeropack retainer body fits inside and the ring butts up flush against the boattail when screwed on. Don't have to cut much off.

Mlee said:

The final assembly is strong, though a bit heavy. It is apparent this rocket will lean toward the heavy side, like most Americans :_)

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And stubborn too.

Mlee said:

The final assembly is strong, though a bit heavy. It is apparent this rocket will lean toward the heavy side...

Click to expand...

No kidding! Mine is already has a lead bottom and I'm not even finished with the internal and external fillets yet. How much does your fin can weigh when all done? I would think it's significant given the epoxy, extra CR and even foam.

rcktnut said:

I cut just enough of the boattail off so that the Aeropack retainer body fits inside and the ring butts up flush against the boattail when screwed on. Don't have to cut much off.

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Yup, that's basically what MLee did...in my case I was building at the same time (didn't see his thread update) and I followed the PML instructions to extend the motor tube by 3/8", so right now it's glued in there, hence if I want it to look more streamlined, I'll have to fill in the gap myself. I'll try it as is and see if it bothers me and is worth the work of filling in.

...or maybe I'll just get another kit, build it with recessed retainer and paint it silver with red stars to match Marc's theme here.

grouch said:

And stubborn too.

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Yeah, I know. But at least now I can say I Used it myself and it's just too heavy. I like to KNOW that I've tried something and it doesn't work. At least this way I can join the others here who learned the hard way.

BUILD DAY 6

Today was all about the piston, piston attach strap, and shock cord.

I decided to reinforce the D-ring attach point with a strip of fiberglass cloth. I did that on both sides of the bulkhead. Then I epoxied the bulkhead containing the D-ring and attach strap to the piston body with 15-min epoxy. It doesn't have to be pretty because nobody will ever see it, so I didnt make it very cosmetically nice.

Lastly, rather than glue the retaining strap to the motor mount tube, I decided to attach it to the 3-ply centering "sandwich" I made yesterday. So, on the shock cord, I threw it on my wife's sewing machine and stitched on a reatiner ring which will connect to an eye ring that I'll attach to the centering rings tomorrow. Yeah, I know how to sew. Don't judge.


D-ring and retainer strap epoxied to the bulkhead with a strip of fiberglass cloth on each side to reinforce it.


Retainer strap attached to back of bulkhead. Nobody will see it so cosmetic appeal is not important.


Strap and bulkhead epoxied to piston body


Finished assembly of the entire piston


Sewing the shock cord D-ring into the cord. Heavy duty thread and needle used on my wife's sewing machine.



D-ring sewed onto the end of the shock cord


The completed and sewed shock cord and D-ring

BUILD DAY 7 & 8

First I sanded the outside of the QT body tube with 400 grit. Then I attached all 4 upper fins after I hand-shaped them into an airfoil profile. These were put on with 15-min Z-poxy and fillets were the same stuff (the FIXIT putty was just too heavy).

Next up was epoxying the centering ring "sandwich" to the fin can. I had to first drill a 1/4" hole to accomodate a screw eye for the shock cord attach point. Unfortunately my hardware store was out of D-rings so I used the smallest eye-bolt I could find.

Then I mated the whole fin can assembly to the QT body tube which I had sanded on the inside with 80 grit to scuff it up for adhesion. After several hours of curing I sanded of the excess epoxy from the mating joint on the fin can and filled it with lightweight filler. In retrospect I should have used Squadron putty; I like it so much better.

Last up was washing the nose cone, inside and out, then adding 1 oz of lead weight (per RocSim) in a glop of 5-minute DevCon epoxy. I then filled the nose code with foam to come up t the 2 oz weight required by RocSim for the nosecone (total weight).


Sanding the Quantum tube with 400, then 600 grit in anticipation of primer.


Attaching the upper fins and adding fillets. Just epoxy fillets.



Epoxied the upper fins on after hand-sanding into an airfoil shape and smoothing with 600 grit. Note that all surfaces are wet-sanded down to 600 grit prior to priming.


Centering ring "sandwich" with eye bolt installed. This is where the piston attach strap with connect to


The fin can finally mated to the body tube. I used 15-min Z-poxy in generous amounts inside the tube. and roughed it up inside with 80-grit


The fin can/tail assembly mated to the body tube. It's ready for sanding and 1 coat of primer, then filling all imperfections with Squadron green putty


After 1 coat of primer, 1 pass of 400 and 600-grit, and more filler at the fin can mating line. Note I have the motor retainer well masked.

Looking good for sure.

Nice Build. I've got an AGM Pit Bill, which appears to be almost the same rocket except the font fins. I appreciate you taking the time to document the build, I've really been to chicken to build it, seeing you build yours will give me the motivation to get mine going. I really like what you did with the motor retainer, I'll have to give that a try.

I'm looking forward to seeing your finished product.

Thanks
Joe

KenECoyote said:

According to PML, it's listed as "Bull Puppy".

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Correction...seems it can be either way. The main webpage for the kit listing is "Bull Puppy", but the spec and motor sheets lists it as "Bullpuppy". Cover of the instruction manual doesn't help to clear things up either. lol

Wow, great progress Marc! Looking fantastic!

I just finished doing epoxy fillets for my Bullpuppy last night. I haven't done this before and was a bit leery (especially because I was using 6-minute epoxy since I didn't have 30min), but they came out great. Hope you don't mind if I share my fillets.





Also I did a prelim weigh-in with the kit parts and a motor case and mine will be in the 40+ oz. range with a motor. I wonder how PML came up with the 32oz. figure. Also now I'm thinking I'll paint mine in a shiny chrome finish...only trick is finding the right clear/protective coat. I have a great chrome paint, but finger prints show up on it like mad.