Big Bird: A copyright lawyer's nightmare

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Dec 27, 2014
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This is the build thread for my Falcon Heavy downscale. In the spirit of Randall Munroe ( I'm naming it Big Bird for now. Technically, heavy is in the 1000 most commonly used words, but Heavy Bird just doesn't have the same ring. Color scheme is likely bright yellow, possibly with googly eyes on the fairing.

Major features are:
54mm body tubes
38mm motor mount in the center core
29mm motor mounts in the side boosters
Boosters eject while the core is under thrust
BP-powered booster ejection charges
Eggtimer Quantum to control booster ejection and parachute deployment with JLCR to limit drift
3-D printed nose cones for the side boosters and the main fairing
First flight at Fire in the Sky Memorial Day weekend (in less than 6 months!)
First flight on 2xF59 WT (1s burn time) and 1xH110WH (2s burn time)

This is a "mostly scale" project. The center core would scale out to about 32.5", but I wasn't about to cut an inch and a half off of the 34" LOC tube purely for scale realism. I also originally intended for the center core to break at the scale staging break, but that got harder than expected due to the booster ejection design. Shapes of the fairings and nose cones are all taken from dimensioned diagrams imported into CAD and then turned into 3-D shapes in Rhino. The trailing edge of the fins match the bottom edge of the landing legs pretty well. I'm also stealing ideas from Cabernut and SpaceEggs. The ejection system is based on an idea from TRF as well, but I don't know who to credit for that.

The plan for construction is to do all of the hard stuff first. For me, that means the booster securing and ejection systems. I know I can do the fins, bulkheads, and electronics work, so that will wait until later.

Photos to follow...
I think you mean that ‘heavy’ is in the ten hundred most commonly used words.

Sent from my iPhone using Rocketry Forum
First stop, upper booster securing and ejection control. A trip down the plumbing aisle at my local Lowe's Depot found a bunch of brass 1/4" pipe that I'm going to use for the upper booster anchor and also to hold the booster ejection charge. The next two photos show the assembled bits. The ejection charge will be in the top leg of the T. I am planning on building the charge into the pipe, then screwing it in to the T during flight prep. The small hole in the top of the elbow is for the ejection charge leads. A nice side effect of brass pipe is that it is non-sparking, so I feel a little safer screwing the live charge into the T. I would have used a cap on the top of the T instead of an elbow, but there wasn't one in the store. When the charge fires, the ejection gases will come out the two sides of the T towards the boosters.

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Next three photos show the T dry fit and then glued in place with epoxy and wood flour. The T blocks the body tube, so the main chute will have to go up in the upper airframe, HED-style.

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This photo shows the guts on the booster side. There is an aluminum tube (also non-sparking, yay!) that is a hair bigger than the brass T, cut off to length. It sockets into a wood block on the far side of the booster so there is a really good connection. The small hole in the end of the wood block is for a piece of 1/8" rod that I used to put the wood block into place. The epoxy in the socket blocks that and seals the end of the aluminum tube. In flight, the aluminum to brass joint will hold the boosters and center core together until the ejection charge fires. The ejection charge can't vent inside the booster tube, so it will push the booster off the brass pipe. What I like about this setup is that the booster and center core are positively held together in case one of the motors misfires.


Here's the setup with epoxy curing. Before gluing, I drilled holes and dry fit everything. Then I mixed epoxy and wood flour and glued the T into place in the center core. For each side booster, I dribbled epoxy/wood flour into the hole for the aluminum tube down to the far side where the wood block would be. Then I put the wood block into place with a piece of 1/8" rod and put the aluminum tube into place through the hole. Finally, I assembled everything together and made sure all of the pieces were flat and square to each other, then left for the epoxy to cure. 1/2" plywood set the distance between the center core and the side boosters, and masking tape held the whole mess together. This procedure let me adjust for any errors in craftsmanship and make sure that everything will stay true and square in flight.

Here are pics of the curing setup and of the finished product without nose cones.

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Next stop, bottom latches.
Don't worry. There's no copyright issue.

Look out for the trademark police, though. :)
Because big and bird are so commonly used already and you aren’t making anything remotely like the more reknown big bird, nor are you making any money from using the phrase, there isn’t likely going to be any trademark issue either.
OK, folks, here's the bottom latches about 80% done. The intention for the bottom latches is that the center core will have a downward-opening hook that captures a pin attached to the boosters. Between the latch body and the pin, the bottom latches will constrain all movement except the booster falling behind the center core and rotating away from the center core. Once the forward ejection charge fires, the booster will be free to fall away as soon as the aluminum tube on the booster clears the brass tube on the core.

But you wanted to see pictures. Here's the current state of play, with booster nose cones, the lower half of the core payload fairing, and everything assembled. The upper half of the fairing is still to come.


Here's a couple of shots of the finished lower latches. Each latch piece is a 1/2" x 1.5" piece of 1/8" plywood with some carbon fiber sheet laminated on each side. The sheet probably isn't necessary, but I thought it might make the latches more durable, especially the one on the center core. The sheet itself was surplus from a test piece the TARC team I work with made for fin stock. I had to bevel the latch pieces on the booster to fit the small epoxy fillet on the center core. The aft corner of each latch is also rounded where it needs to rotate past the matching body tube during ejection.

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Here's how it went together, all with 5-minute epoxy. First, I marked where the latches would go on the core and glued those into place. Then I fit up the latches for the side boosters. I glued the two on the top first, then flipped it over to glue the remainder. Parchment paper on the center core keeps the epoxy from sticking stuff that shouldn't be stuck. The two small pieces of plywood on top of the latches keep the latches from lifting up when the parchment paper tries to unfold. The two long pieces of plywood have been used throughout the build to keep the boosters square to the center core and keep the distances all the same and repeatable. Masking tape keeps everything in place.

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Next stop, finish the bottom latches. I'm not sure if I want to ground test the ejection before or after I build the motor mounts and fins. Less chance of damage from an energetic ejection if I do it before, but maybe the test isn't realistic that way. Tell me what you think and why.
Nice work, sir! Are the nose cones 3D printed?

Thank you! Yes, the nose cones are 3-D printed. They're pretty decently to scale, at least as far as can be done with drawings from the Internet. I'll have some closer pictures later on, but I'm pretty pleased with how well they came out. I make 3-D printed stuff heavy so that it lasts well. The nose cones all have a 1/4" wall and 50% infill.
Wowzers! Those are some stout nose cones!

I own a 3D printing, design, and consulting business. It's fun to see the things that folks come up with to print. Now that my daughter and I are into the rocketry hobby, I'm sure we'll be printing some rocket parts as well.

I'm enjoying your build, keep up the good work!

If I have a heavy enough nose cone, I won't have stability problems when I go to a 5-grain motor in the center core and 3-grains in the pods! :dark: OK, I'm almost certainly not going to do that, but it's fun to think about. Plus, I've seen too many 3-D printed parts come apart with rough handling.
Progress is being made! More pictures below, plus a few .stl files for my nose cone parts. The center core fairing is a hair shorter than true scale because the 3-D printer I was borrowing time on was a tiny bit too short. It was easier to shorten the fairing than make a third piece.

A couple more pictures of how the aft end latches fit together with the pins through the tabs on the side boosters and the hook on the center core. It holds together really nicely.

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This is the center core motor mount. I used a 1/8" stainless steel wire leader to get the end of the shock cord out past the brass piping. There's enough rough epoxy fillet material in there that it could snag a recovery harness and make a mess of it.


And here's a full stack.


View attachment Core Lower.stl View attachment Core Upper.stl View attachment Booster.stl

Next stop, motor mounts and fins.
Thanks everyone for the kind words. The fins went on next. Installation of the motor mount was pretty typical. Mix up some epoxy, spread it in the body tube just shy of the end of the fin slots, push the motor mount in until the aft face of the forward centering ring is at the top of the fin slots, put aft centering in loose for alignment.

Fins are 3/16" Lexan. I was originally planning on using 1/8", but that felt a little too flexible to me. Stability should be OK since the fins are pretty enormous. The finished fins look like this:


The holes in the fin root will be filled with filled epoxy to lock the fin root into place. I also scuffed up the fin tabs a little with a rasp to give a better mechanical bond. The covering plastic will stay on until the rocket is done. Incidentally, the dust from cutting Lexan with a sabersaw is incredibly electrostatic. It sticks to damn near everything, especially the cut stock.

Final assembly of the fins looked like this:


I filled the fin slots from the outside with epoxy thickened with wood flour, my go-to adhesive. I hacked together a fin alignment jig out of a piece of the plywood previously seen aligning the boosters to the core and a small piece of aluminum angle I use for marking fin slots. I didn't get quite enough wood flour in the epoxy, so it didn't stay in place quite as well as I'd have liked. Everything feels solid though. I will add some external fillets with some clear 5-minute epoxy. Here's the nearly-complete fin can, plus a bonus full stack. I had planned to put 2 fins on each booster, but now I'm not sure given how big the main body fins are. Will have to think about that a little.

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One question about the booster deploy mechanics. Since there is a radius that the brass tube will follow when it slides out of the aluminum tube in the booster. I assume that radius is large enough that it doesn't get stuck when the deployment charge fires?
One question about the booster deploy mechanics. Since there is a radius that the brass tube will follow when it slides out of the aluminum tube in the booster. I assume that radius is large enough that it doesn't get stuck when the deployment charge fires?

The outer aluminum tube had enough clearance that the booster deployed cleanly without hitting the brass. The other side took a little bit of sculpting with a Dremel and cutoff wheel. I'll build up a masking tape friction fit for each launch. That's probably the fiddliest bit of the whole launch process.

This is fantastic! Any updates on the build/test progress?

We are still on track for launch in less than 6 months. :) Actually, the to do list is getting shorter every day. I just painted the nose cones and did the ejection charge testing. I discovered that there's quite a bit of BP blowby from the ejection tube mechanism that hits the center core body tube. I have to armor that up a little bit because one side actually stripped off the top layer of the tube. Once I get that figured out and the rail button standoffs glued on, it'll be ready for paint. Electronics are basically ready to go, although I need to update sims and do final motor selection. I had hoped to do a test flight with a pair of F motors in the side boosters and the center core empty to test ejection and liftoff, but I won't have time before launching Memorial Day weekend.
Progress report at T-12 days:
Nose cones and center core upper stage* are finished and ready to fly.
Center core armor (+5 against ejection charges!) is glued on.
Side boosters are primed. I ran out of white primer, so one side is white and one side is black. It's a lot like that one old Trek episode with the people with black and white faces.
Center core lower stage is just waiting for rail button extensions to be ready for paint.
Parts are weighed; total dry weight is just shy of 2000g.
Sims are updated and revised. Altitude of 2166' predicted for H110/F59, and 2750' for I175/F59. That's well within visual range.
Speed off the rail is fine for the H110 alone. The H59s would be similar, so there's minimal risk from lighting only either the center core or the side boosters. If only one side booster lights, it's going to be ugly no matter what.

I think I'm going to drop the JLCR. I am not 100% convinced about the chute ejection working (chute is above the stage break and has to get past a coupler) and landing hard is going to be far worse on the booster than a bit of drift. We are lucky to have an enormous field.

* The center core isn't really 2 stage, but it's an easy way to think about the break

I am moving on to altimeter programming for the side booster separation. I'd like to not eject the side boosters if they are not lit and therefore will not On a nominal H110/F59 flight, the rocket will be at 200' altitude and 300 ft/s at booster separation (1.25s). If only the center core lights, the rocket will be at 100' and 157 ft/s when the separation event would be commanded. Unless the field has other suggestions, I think I'll put a 200 ft/s speed lockout on the booster ejection.

Pictures to follow when I have a little more paint on in a couple of days. I will finish everything off this weekend for flight in a week and a half.

One extra side note. I mentioned a 5-grain core and 3-grain outboards way up in the post. Current sims show a J290/H163 would top out at 4000' and Mach 0.77. Weirdly, I don't see any reason I couldn't do that. I'll step up in that direction before going whole hog, though.
T-6 days and counting, all systems go for launch.

The rocket is now flyable, though not fully painted. The remaining paint will be done in the next day or two. The only other work to be done is to pre-lead a few wires to make field prep easier. Launch will be sometime between Saturday afternoon and Sunday evening at Fire in the Sky, Mansfield, WA.


Details of the rail standoffs and the ejection charge armor:
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That looks fantastic! Can you elaborate on the "armor" plating you added to the center section? What drove you to add that armor?
That looks fantastic! Can you elaborate on the "armor" plating you added to the center section? What drove you to add that armor?

I really want the side boosters to separate decisively and definitely not leave one hanging, so the separation charge is fairly aggressive. When I did the separation ground test, the charge gases blew back against the center core. It looks like there was enough leakage below the aluminum tube that the hot gas vented against the center core tube before the booster fully separated. On one side, that gas leakage blew the glassine layer off of the center core tube. On the other booster, it just left a scorch mark. Since I want this to fly several times, I figured I probably need to protect the sides of the rocket a little better. Hence sheet metal armor. The armor fits tight to the brass tube on the center core, and the aluminum tube is cut back a little on the bottom to get a proper fit.
Big Bird launched for its first and final time on Saturday afternoon. My older kid asked me if it was a good idea to name it after a flightless bird. Remember the saying that a good flight is when your rocket works, a bad flight is when your rocket doesn't work, and a great flight is when someone else's rocket doesn't work? This was a great flight for many people.

Big Bird majestically rose slowly off of the pad on the two side boosters (now believed to be one F36 Smoky Sam and one F59 White Thunder), pitched down to near horizontal away from the crowd, and then the main came up to pressure. It made it a few hundred yards before hitting the ground among scrub and grass. I ran out with a small fire crew to check up on the situation. We found the remains by seeing a small could of smoke. After putting out a spot fire, the remains were brought back to camp.

Major lessons learned:
1. Don't use different propellants for clusters if you want them all to light on the pad (vs. airstart). The center core White took a while to light up.
2. Don't trust Sharpie markings on the outside of the reload. Both the F36 and F59 were surplus motors that had been intended for flight for our TARC team. They had been taken out of the package and labeled, but the SS was mislabeled. I believe the propellants look pretty similar, but the SS has a noticeably larger core in the grain. If I had looked at the grain, I would have seen that.

On the plus side, all three casings, the Eggtimer Quantum, the center core and one side parachute, the center core nose cone, and one side booster nose cone were recovered safely. The remaining side booster nose cone was destroyed by fire, not impact.

Pictures and video to follow.
I downloaded data from the Quantum this week and got my pictures together. This is the sad tale of the Flight of the Big Bird...

First of all, the Quantum worked perfectly. The velocity lockout at side booster ejection worked. The minimum velocity was set for 200 ft/s at 1.5s flight time (booster ejection). A nominal flight would have been 300-400 ft/s, and off-nominal with only the center core would have been ~150 ft/s. The boosters did not deploy, although it probably would have been better for them if they had.

I took video, but it's about a second long before the phone went down so I could watch the damage. We're going to go with screen captures to narrate.

Happy times before launch. Everything looks good.

Liftoff! Note one smoky side booster and one white. Cue sinking feeling...

We've got 90 degrees of roll and a little yaw now.

Definitely not vertical. We are near booster burnout.

Center core has lit. This does not look good.

Nearly horizontal. Definitely not good.

Final altitude about 200 feet. Flight time ~5 seconds.

This will buff out, right?

Thanks to everyone here for their kind comments and support, the people who came out to check for fire, and especially the LCO for requesting a fire check. It would have gotten really ugly really fast if we hadn't been so close when we saw smoke.