Yellowjacket - 3" Blue Tube Rocket

[weboide]

First things first - this is not an upscale of the Estes kit. I just wanted to go with a yellow and black paint scheme, so the name seemed appropriate.

This rocket grew out of a need for a 3" rocket that was both light and durable, with a 54mm MMT. Something that would fly nicely on a wide variety of 54mm loads without the relative hassle of a MD rocket (and the ability to stay under 5k foot waivers at smaller launch sites). I decided to use Blue Tube because I have worked with it before on a 4" Dynastar Snarky upscale I did, as well as having seen several rockets built with it before that. It's stronger than regular LOC tubing or phenolic, no need to glass it like you do to phenolic, and lighter than fiberglass. I also think that in the smaller diameters, it's more than strong enough to withstand the stresses of just about any commercial motor you can find, especially in a "not quite minimum diameter" rocket like this one. I also added an Aeropack tailcone retainer just because I thought it would complement the look of the rocket, and make it just a bit more than a large 3FNC bird. The fins will be 1/8" baltic birch ply with two layers of 4oz glass.

I've attached the rocksim file below, along with a picture of the rocket design. The mass in the rocksim file is still approximate, and it hasn't been adjusted for any needed nose weight yet. Interestingly, according to Rocksim it's not quite 1 caliber stable with 5 and 6 grain 54mm motors, so once I get a true unloaded weight with recovery and such, I'll adjust nose weight as needed. I'm also toying with the idea of sticking a piece of all-thread in the nose to allow for adjustable nose weight, but that may or may not happen depending on how lazy I feel.



View attachment Yellowjacket.rkt

 

[cwbullet]

sounds promising.

 

[weboide]

The fins are completed. I cut out three 1/8" ply rectangles, which wound up being 1/2" shorter than they should have been (measure once, cut once, commence swearing), so the fins have 1/2" less sweep than the rocksim. I updated mine, no issues, so I went with it. Next, I cut out two pieces of glass for each side of each fin, rotating the pieces 45* from each other. I put the glass on with US Composites laminating epoxy, then some peel ply, then put all of them under vacuum at 15" Hg, which is roughly 7.5psi. I just have a venturi generator that plugs into my air compressor, and I can't handle the racket of the compressor running 24/7, so with it running about 50% of the time I got 15" Hg. Then I went upstairs for three hours. I pulled everything out, trimmed up the fins while they were still green, and am overall very happy with how they turned out. No irregularities in the surface, good bonding to the entire flat surface and enough of the bevel to make for a clean edge. The apparent warp in the fin in the second picture is an optical illusion created by my cell phone's camera.

 

[weboide]

Next up is the motor mount assembly. I'm going to go the injected fillet route since it seems the easiest way to get epoxy into the roughly 3/8" clearance between the MMT and BT. I had already JB welded the Aeropac to the MMT a while ago when this project was first conceived (about 6 months ago), so I don't have to worry about doing that this time around. Next up was to locate the centering rings appropriately on the MMT. Due to the small lip on the tailcone retainer, the aft centering ring needs to be inset about 1/16" from the back of the BT. The simplest way to get the aft CR where I wanted it seemed to be to just put the tailcone and the centering ring on and then stick the assembled motor mount into the body tube. So, that's what I did. I then added a couple drops of thin CA to tack it in place, and then removed the MMT assembly. With the aft CR in place, I could now locate the position for the mid CR (which I added to facilitate the injected fillets).

Or so I thought. I then realized I had no idea where on the MMT the fins go. So, off to The Payload Bay to print a fin marking guide! Fin marking guide in hand, I marked the body tube (what? I thought we were doing the MMT?) for the fins and (in a rare moment of forethought) the rail buttons. I then carefully measured three times (lesson learned!) for the location of the fin slots, and slotted the BT.



I next inserted the MMT back into the BT, and spent about 15 minutes fitting each fin to its respective slot, carefully labeling each one so I wouldn't mix them up. Once each fin and slot fit pretty well, I removed the fins and marked the MMT through the slots with a pencil. After withdrawing the MMT, I labeled it (again, forethought!), slid on the mid CR, managed to get all three fins on and held in by the CR by myself, and then tacked the mid CR in place with thin CA.



With the mid CR in place, the only remaining piece of the MMT to finish is the upper CR and recovery attachment. I decided to do the "loop of 1/2" Kevlar epoxied to the MMT" trick, so I pulled out my 1/2" Kevlar, measured once, thin CA'd the Kevlar where I was going to cut it, and spent the next five minutes cursing and telling myself how I was never going to CA the Kevlar before cutting it again (not that I'd done that before). After finally getting the Kevlar cut, I mocked it up on the MMT, and discovered that it was roughly one foot too short. I tossed the 24" piece of Kevlar in my "random bits of Kevlar" drawer, re-measured (twice!) and cut a 36" piece of Kevlar, cutting before CAing this time. With learning having occurred (again), I mocked up the Kevlar and discovered that it fit beautifully, making a loop that sticks out about 1" beyond the end of the BT. I then epoxied both ends of the Kevlar to the MMT tube with 15 minute epoxy. The astute observer will notice what appear to be popsicle sticks stuck to the ends of the Kevlar - these served as impromptu clamps the make sure that the ends of the Kevlar stayed stuck to the MMT, as well as pressing on the Kevlar to saturate the whole thing with epoxy. The fore CR was then epoxied on, also with 15min epoxy.



Attachment of the recovery harness and centering rings complete, the final step was to fillet the centering rings on to the MMT. The fillets were done with 15min epoxy mixed with chopped carbon fiber, mostly because it was the first additive I found when I opened my "drawer of random things". The rear CR was filleted only where it would not contact the fins.

 

[jus_rockets]

Love the design and cant wait to see finished pics.

 

[weboide]

Thanks! I'm hoping to have it done for a launch on the 11th, so it should be together and ready for paint by Thursday night.

 

[weboide]

Next up was getting the MMT into the BT. This was accomplished by epoxying the MMT into the BT



After that cured, it was time to prep the fin slots for attaching the fins. For each fin, 5/32" holes were drilled 2" from either end of the slot on each side of the slot, then each side was sanded with 80 grit sandpaper to rough it up a bit. Each fin was then tacked into place with 15 minute epoxy, aligned using my finely calibrated Mark 1 Eyeball alignment jig :cyclops:

One fin tacked, holes for epoxy injection



End result of Mark 1 Eyeball alignment jig



After the fins cured, it was injection time. For each set, 30mL of US Composites medium laminating resin was mixed with the ever popular "dime-sized pile" of chopped carbon. Each fin edge received ~12mL after everything was said and done. Naturally, each set required about 2-3 hours to cure before the rocket could be rotated, so this was an activity spaced around doing other things, like work.

Gratuitous mixed epoxy shot

 

[weboide]

At some point during the day while pondering rockets when I should have been working, I realized that I had enough room in the fincan to potentially put a main parachute. I copy and pasted the fincan and nose from the Yellowjacket RockSim file to a new one, tweaked it a bit to better represent the real-world configuration, and started seeing what I'd need to do to the nose to get it to work. Obviously, an electronics bay in the nose would now be required for high flights, and even for low ones when I don't want to walk as far. In the shorter configuration it needs a wide range of nose weight to work with different motors - from ~2 to ~16! oz. It seemed then that some method of changing the nose weight would be in order.

View attachment Yellowjacket Fincan.rkt

I have now decided to build both a standard e-bay for flying the full Yellowjacket, and build the nose so it can house both electronics and adjustable weight. For the standard e-bay, I have a couple LOC 3" e-bay kits laying around, so I grabbed one of those to use. However, since the LOC tubing is slight smaller in OD than Blue Tube, a bit of adjustment to the switch band was in order in the form of a single wrap of 6oz fiberglass.



With that curing, I turned my attention to the nose. A method I have used before when I need adjustable weight and electronics in the same nose is to anchor a piece of all-thread in the nose which runs the full length of the nose, terminating as the attachment point for a wing-nut that holes a bulkplate into the aft end of the nose. Given the success of this method before, I decided to go with what I know and do it again. I first measured and cut a 14" long piece of 1/4-20 all-thread. Too much? Maybe, but it also satisfies the minimum 2oz of nose weight requirement, so I went with it. I scored the inside of the nosecone tip with a sharp bit of metal on a stick to help with epoxy adhesion. Then, I put a nut and washer on the end of the all-thread that would go in the tip of the nose, drilled a hole in the nose, stuck the 1/4-20 all-thread in the nose, and then threaded a piece of smaller all-thread across the nose to hold the nut and washer in position.

Outside view because my cell phone will NOT focus on the tip of the inside of the nosecone.



30mL of epoxy was then mixed and dumped on top of the whole thing, which was then dunked in a cup of water to cure while I ran to the store to pick up dinner necesseties.

 

[weboide]

After various and sundry bits sitting and curing, I could finally stick everything together and get an idea what the whole stack will look like. This is the result:



I am happy with how this design appears to be translating to reality so far After ogling the full rocket for a while, it was time to get back to work. First up was everyone's favorite, the external fillets. In order to both cover the holes from injecting the internals, as well as add a good bit of strength, I went with 0.5" radius fillets (also, the first dowel piece I found was 1" diameter). Things were measured and tape was laid down, and then more of my favorite US Composites epoxy got mixed with silica and slathered into the joints. After much swearing and gnashing of teeth, the results weren't too bad:



While those cured, I turned my attention back to the nose cone. The first (next?) step was to add an artificial shoulder for the bulkplate to rest against. I dug up an extra 3" stiffy tube I had, chopped off 0.75", slit it to fit, and epoxied it into the nose cone at the top of the shoulder.



Then, while that cured, I attacked a 3" bulkplate with various sanding devices until it fit nicely inside the shoulder of the nosecone. That took long enough that the epoxy on the nosecone had cured, so I drilled for a U-bolt and then test-fit the bulkplate. It fit beautifully.



What I really like about this setup is that the cardboard bit epoxied into the shoulder is not actually load-bearing, it just serves as something for the bulkplate to seal against. The full load of the nosecone is on the center all-thread, which is firmly attached to the tip of the nosecone. At this point, the epoxy on the fillets had cured enough to remove the tape, resulting in 98% perfect fillets. The other 2% will be taken care of with more sanding and swearing.



At this point, all that remains are the "fiddly bits", which I've discovered usually take much longer than you think they will. Barring anything terribly horrible happening, I should be able to get the av bay(s) wired and together, along with the rail buttons installed, by the end of the day tomorrow, leaving me Friday to paint and Saturday for it to "cure" for a launch Sunday.

 

[weboide]

Well, Yellowjacket is complete and ready for flight. Being honest, the paint kinda looks like crap up close due to several factors, including static-y plastic drop cloths. Part of the upper body tube has an "interesting" texture, but it looks good from 10ft so it's good enough for me. I'll be flying it tomorrow on an H399WT (using both a 54-38 and 38-29 Aeropack adapter ), with a possible follow-up flight on a Gorilla J167WC long burn to ~7k feet if the weather permits. Electronics are a Raven II, firing some x-mas light bulb ejection charges at 0.75g for the apogee charge and 0.85g for the main.

 

[weboide]

First flight success! Although there was 2" of snow on the ground, intrepid rocketeers launched anyway. The first flight of the Yellowjackt on a CTI H399WT was flawless. After loading up the motor with a comical arrangement of Aeropack adapters, there was a slight hiccup arming the raven as Yours Truly forgot where he oriented the magnetic switch, resulting in chanting and magnet waving until the altimeter started beeping. The boost was arrow straight with no apparent roll, with a slight "burp" from the H399 just before burnout. Apogee was ~1550 AGL, just about what I expected given the temperature. The main deployed beautifully and the rocket came to a gentle landing about 400 ft from the pads. I've attached the raven data file, and may or may not have pictures later.

View attachment Yellowjacket H399 11 NOV 12.FIPa

 

[MasonH]

Looking good!

 

[86mustang408w]

Any updates? I'm trying to figure out what all I need to scratch build my first rocket. I'm kinda lost on parts I've never built a MPR or HPR. They always have been LPR's that I have scratch built. Keep up the good work, ill be watching.

 

[Rex R]

building mpr & hpr birds is pretty much like building lpr, the parts are the same just bigger/stronger(as needed). about the only difference is that once you move up to Hpr most clubs 'require' rail buttons since large (3/8" and up) rods are harder to come by. for a super bertha I would shop at semroc and use Bt80 size components, either a 24mm mount or a 29mm would work well.
rex