Yet another build thread for Dragon Rocketry's Fat Boy XL

[Sooner Boomer]

It's my intention to build this and fly it on as big of a 38mm motor as I can reasonably fit. I want to make this a quality build, so I'm not going to be in any hurry. I've built a LOT of Fat Boys since getting back into rocketry over 23 years ago, it's one of my favorite kits.

The Dragon Rocketry Fat Boy XL is a well designed kit with a two-piece 3D printed nosecone, laser cut plywood centering rings and fins, and a smooth 4" cardboard body tube (no spirals to fill!) pre-slotted for fins and marked for rail button alignment. It comes with a 3D printed screw-together motor retainer, nose weight, eye bolt (for recovery harness attachment), and rail buttons. No instructions are provided, but the design is extremely simple and mirrors the original Estes design. I ordered it with the 38mm motor mount.

Unboxing:



Nosecone - the nosecone is 3D printed (it's not quite a pink as it appears in the pictures). It comes in two parts so noseweight can be added. The bulkhead came already glued in, with eyebolt in place. The bulkhead is offset towards the top of the coupler.



Fins and centering rings - laser cut from plywood. The rings fit tight to the motor mount (a good thing). The parts will require some sanding to remove char. A hole is cut for recovery harness eyebolt.


Motor mount and motor retainer - the motor mount is cardboard. It is marked for centering ring location and orientation.

aft end indicated
forward end
motor mount with 38/240 and 38/360 cases


Body tube - pre-cut slots for fins and alignment for rail buttons

 

[Sooner Boomer]

The kit comes with 6 ounces of BBs as nose weight. I'm going to use all of them. Additionally, there are 3 piece rail buttons and retaining screws and eye bolt


The decals (stickers)


That's what comes with the kit. There is no recovery harness or parachute. I'm anticipating needing a 36" chute, but a 45" might be needed. We'll see what the final weight ends up at.

My one concern is that there's no provision for an altimeter. I guess I've become spoiled by how much more reliable, and how much simpler flying is when using one. I don't think it would be major work to add something like an Eggtimer Apogee. Mounted in the nose, both the body tube and the nosecone (bulkhead) would need to be vented. I'm going to build the kit as-provided, with an eye towards getting a replacement nosecone in the future. I've got several Warp9 reloads I'd like to try in this "Boy".

 

[Hobie1dog]

Thanks for all the pictures.

 

[jmasterj]

You could build in a little AV-bay between the motor tube and airframe, between the centering rings. 4" is probably challenging but doable.

 

[StreuB1]

My one concern is that there's no provision for an altimeter.

EggTimer Apogee is perfect for this. Only $15 as well.

 

[KenECoyote]

What about the JL Chute Release?

 

[Sooner Boomer]

The Eggtimer Apogee and JLCR are a perfect combination for this rocket. My concern is that I don't know how strong the 3D printed bulkhead in the nosecone is. Ideally, I would drill an appropriate hole in the center of the bulkhead (or even off-center), and glue in an easy mount. I don't know if the bulkhead would need to be reinforced, possibly with a piece of 1/8" ply. The nosecone and body tube would need to be vented for proper altimeter operation. No hurry. I'd like to have it built in time for our next launch in four weeks. I'd rather have it done right than done fast.

 

[Sooner Boomer]

I sat on the couch last night with a set of calipers and the Fat Boy XL kit. The Apogee can't be installed in the nose cone. The way the bulkhead is positioned, the shoulder in the nosecone (and how deep the coupler is installed), make it such that a hole would need to be drilled in the curved part of the nosecone to get access to the arming screw. Plus, it would sit so far up inside the coupler, it would be difficult to get access to hook the ematch leads up to the posts on the altimeter. What I'm going to do is try to design a compartment that will attach to the inside of the coupler, at the aft end. this should solve all of these problems.

Also - got the centering rings sanded so the motor mount fits through them. Still working on sanding the end of the motor mount so the retainer fits. I think I'll try sanding a bit off of the retainer. Don't think I will shape any profile into the leading edge of the fins; will sand off char and leave them square.

 

[Hobie1dog]

I'm starting to get infatuated with Fat Boy rockets.

 

[KenECoyote]

I sat on the couch last night with a set of calipers and the Fat Boy XL kit. The Apogee can't be installed in the nose cone. The way the bulkhead is positioned, the shoulder in the nosecone (and how deep the coupler is installed), make it such that a hole would need to be drilled in the curved part of the nosecone to get access to the arming screw. Plus, it would sit so far up inside the coupler, it would be difficult to get access to hook the ematch leads up to the posts on the altimeter. What I'm going to do is try to design a compartment that will attach to the inside of the coupler, at the aft end. this should solve all of these problems.

Also - got the centering rings sanded so the motor mount fits through them. Still working on sanding the end of the motor mount so the retainer fits. I think I'll try sanding a bit off of the retainer. Don't think I will shape any profile into the leading edge of the fins; will sand off char and leave them square.

How about using the nose coupler as a recessed bay? Flip the eyelet around, add a bulkhead cap that recesses in, anchor eyelet in the nose tip, main chute in the nose, use tape or shear pin to keep nose on?

It's doable, but imo a LOT of work, so that's why I'd just use a JLCR.

 

[DragonRocketry]

How about using the nose coupler as a recessed bay? Flip the eyelet around, add a bulkhead cap that recesses in, anchor eyelet in the nose tip, main chute in the nose, use tape or shear pin to keep nose on?

It's doable, but imo a LOT of work, so that's why I'd just use a JLCR.

The only problem with that is there will be very little room for recovery items. This is why the bulkhead is up inside the coupler. Also will limited you to smaller 38mm motors.

 

[KenECoyote]

The only problem with that is there will be very little room for recovery items. This is why the bulkhead is up inside the coupler. Also will limited you to smaller 38mm motors.

Yup, that's why I mentioned recessed rear bulkhead. The drogue chute fits into the rear of the coupler and the drogue chute (or just skip and save for longer motor) would go partly into the coupler. The altimeter bay can be just an inch section of the top of the coupler.

Note that I haven't built mine yet, so just brainstorming right now.

 

[Sooner Boomer]

Found a cardboard tube of correct size (I think it was a core to a roll of something). I cut it to length, colored it with a marker, drilled a hole for the arming screw switch, and soaked it inside/out with Dollar Store CA. The glue toughened the tube up a lot. Waiting for the drill to charge, and I will put some vent holes in the tube. Then the Easy Mount gets glued on, and finally, the tube gets glued to the inside of the coupler. I cut the tube so the end of the altimeter sits about 1/4" below the lip of the coupler. I'll probably cover the ends of the ematch terminals with tape before flight. I left the tube long, so that it contacts the bulkhead. It doesn't need to be this long, but I was worried something migh hang up between the tube and the bulkhead.

 

[Sooner Boomer]

Got the BBs glued into the nose. Glued and filleted altimeter tuben into nosecone coupler. Glued and filleted top centering ring to motor mount, then tacked it into the body tube with CA. Thinking ahead - when the garage warms up a bit, I'm going to primer and sand the fins before I glue them in. Except for the fin tabs. I don't think I'll use any/much external fin fillets. It gives a cleaner, more angular look, and it makes it easier to mask for painting. I want to use high build sandable primer for the nose. It's going to be next month before I can get a can. No hurries.

 

[Sooner Boomer]

Installed aft rail button. The supplied rail buttons didn't come with nuts. They come with a 1/2" #8 machine screw with an Allen drive button head. The rail "button" is made of three pieces, a white nylon tube, and two black washers. When in place and tightened properly, it forms a rigid unit. The button will not swell on overtightening. I drilled a hole in the body tube, and soaked it in thin CA. When that was set, I put a 1/2" #8 screw with a washer through the hole, and slid another washer on from the inside. I dabbed a bit of Super Lube on the threads, then put a nut on the screw and tightened it down. I mixed up a batch of epoxy and coated the nut and washer on the inside of the body tube with a generous amount, then put it aside to set.




I decided to use yellow glue to glue in the top centering ring. It's tight, and it's easier/cleaner when I have to use my finger to smooth out a joint. I'll build up a nice fillet over the next week. I'll probably use epoxy for everything else.

I got two coats of primer on the fins. They'll sit for a few days before I sand them and apply more (if needed). Now waiting...

 

[DragonRocketry]

I drill into the centering ring and tap it with a 8/32 tap. I then soak the threaded area with thin CA. This makes nice threads to thread the screw into.

 

[Sooner Boomer]

Checked on the primered fins. They looked like they had cured enough. I used a random orbit sander to smooth all the sides. and brought them into the house. I added more yellow glue to the fillet on the top centering ring. I need to dig out some thick CA tomorrow. I'll use it to make glue dams on the inside of the body tube at the fin joint, and along the motor mount fin joint. This helps keep the epoxy fillets in place. I *may* glue the fins in tomorrow, if it's warm enough. I try to let epoxy cure in the garage so it doesn't stink the house up. Can't (won't) spray paint in the garage unless it's 70 or warmer. Forecast is for wet and rainy through the rest of the week. It will probably be next week before I can buy paint, anyway. Need more Bondo for the nosecone, too.

 

[Sooner Boomer]

Got fins in place and glued down with CA. I use this along the seams so the epoxy I'm going to use for the internal fillets doesn't leak through any gaps. Sanded nosecone with 220 using random orbit sander. It's too cold, wet, rainy, to do any painting or more glue work. Project may have to sit for a few days until weather improves.

When sanding the nosecone, I noticed how transparent the plastic is. I glued the nosecone and shoulder together using Gorilla brand epoxy. It's black (although not metal-filled like JB Weld). I can see the dark band of glue through the nosecone.

 

[Sooner Boomer]

Back at it after a break. I should be able to get everything finished over the next few days; the weather has warmed up!. I'm still applying Bondo and primer, and still sanding on the nosecone. That's going to take a while. Fillets are next (internal only). I think I've decided what/how I want to paint it. At first, I wanted to go with the original Fat Boy paint scheme. I built a "stock" FB with a 29mm motor mount and traditional paint about 20 years ago. I decided to go for something a bit more challenging this time It starts with a couple of base coats of black. Then light, alternating, coats of Rust Oleum Iridescent and Dupli Color Jade Green Metallic. This should look *amazing* in the sunlight. The biggest problem is going to be even, consistant application. Drips and runs are going to kill it. This will be a sloooow process.

 

[KenECoyote]

Back at it after a break. I should be able to get everything finished over the next few days; the weather has warmed up!. I'm still applying Bondo and primer, and still sanding on the nosecone. That's going to take a while. Fillets are next (internal only). I think I've decided what/how I want to paint it. At first, I wanted to go with the original Fat Boy paint scheme. I built a "stock" FB with a 29mm motor mount and traditional paint about 20 years ago. I decided to go for something a bit more challenging this time It starts with a couple of base coats of black. Then light, alternating, coats of Rust Oleum Iridescent and Dupli Color Jade Green Metallic. This should look *amazing* in the sunlight. The biggest problem is going to be even, consistant application. Drips and runs are going to kill it. This will be a sloooow process.

That sounds like a great plan and I can't wait to see it!

I'm actually doing a hybrid of what you've mentioned for my FB XLite... it'll be the original FB scheme, but I'll try an anodized red with it. However, that requires a base of black and chrome and sure enough the gloss black Rusto is giving me major headaches (drips, splatters, crinkling, orange peel, etc.).

When one can of gloss black splattered, I tried another can, but it then wrinkled badly , so I quickly switched back and it actually got the wrinkles down!

I took a gamble and tried a can of semi-gloss black over all of the mess (it was that or filler primer again) and it's actually looking better now. I will try wet sanding when it dries.

 

[Sooner Boomer]

One thing that might help is recoat time. You've got a window when the paint can cure, outgas, as a single layer. This window is usually from about 15 to 30 minutes after the last coat, or wait 24-48 hours (mfgr's spec) after. If you spray in the "forbidden" window, the layers may dry at different rates. This causes them to shrink at different rates. Bad things happen then. I painted an aluminum guitar effects box, badly. The next day, the finish had all sorts of cracks in it. I decided to go with it. I waited two days, then smeared gold paint into the cracks. It kinda looked like lightning.

 

[Sooner Boomer]

Working on fillets. May do paint tomorrow. Don't know if I have enough black for the base coat. The black lump to the right-hand side is where the nut for the rail button is epoxied to the inside of the body tube, just above where the centering ring goes.

 

[Sooner Boomer]

Got the aft centering ring glued on to hide all that ugly epoxy fillet mess. I epoxied the motor retainer on. I put two "coats" of thin CA on, to wick into the joint, the cardboard of the body tube, and the wood of the centering ring. When that had set, I made a fillet out of baking soda and dripped on more CA. The white powder is baking soda. You can also see the screws in the mounts for the rail buttons (for painting), and the vent holes for the body. No external fillets this time...

 

[Sooner Boomer]

I got unusually ambitious tonight, and painted the rocket. Both the fins and the nosecone had been puttied and primered before assembly. I sprayed two coats of Duplicolor primer, two coats of black base paint. I decided to go wild, and painted a mist coat of green, followed by two coats of Iridescence, and a final light coat of green. It was hard to stop messing with it, and it was hard not to get heavy-handed, to just lightly mist the paint on. Sitting in the garage, it looks like I got close. Tomorrow in the sun will tell! Pics in the daylight!

 

[Sooner Boomer]

Not much sun out, at least it's stopped raining. Here's what I've got. I think it turned out very well. I think the same thing could be done in blue. They already make a product in red.

 

[Sooner Boomer]

I've been getting the name wrong on the green paint. It's DupliColor Deep Jewel Green Met, part # BFM0327. The Rust-Oleum is Colorshift Iridescent, part # 384335.

 

[Sooner Boomer]

Still waiting for sunshine to take some pics that show off the paint. Speaking of paint - I have no real idea why I thought the sparkly green would look good. I hadn't thought much about the rest of the build. Turns out this was exactly the right color to go with the light green vinyl letters.

Got it all put together except for the motor. The completed rocket with parachute, harness, altimeter, and everything (5.5 oz BBs in nose) weighs 2 lb 8 oz. I plan on bringing it down on a 45" chute opening with a JLCR at 500'.

 

[KenECoyote]

I've been getting the name wrong on the green paint. It's DupliColor Deep Jewel Green Met, part # BFM0327. The Rust-Oleum is Colorshift Iridescent, part # 384335.

Very cool! I have that colorshift paint as well, but haven't tried it yet.

I tried the one that turns purple blue on a Mean Machine and loved it, but on the second flight it got treed and then got a bit wrecked pulling it from a tree (will fly again one day).

 

[Sooner Boomer]

No more waiting. We had a nice sunny day, today. Here it is in all its sparkly glory!



It should go up on an I180 on Saturday!

 

[Sooner Boomer]

Very cool! I have that colorshift paint as well, but haven't tried it yet.

I tried the one that turns purple blue on a Mean Machine and loved it, but on the second flight it got treed and then got a bit wrecked pulling it from a tree (will fly again one day).

I got started playing with color changing/shifting paint about 20 some-odd years ago. I found a kit for DupliColor "Mirage" purple-green paint (the kit was a can each of black base coat, color coat, and clear). I named the rocket the "Octiron" after Terry Pratchett's description of the color of magic. I tried to core sample the runway a year or two back, requiring a repaint. The new color is color-shifting, but doesn't have the rich purple the original had.