5 Years ago, Bdale flew some [Woot](http://woot.com) screaming flying monkey dolls
6 in his [L3 certification airframe](http://gag.com/rockets/airframes/Goblin10/),
7 leading to some seriously amusing [videos](https://www.youtube.com/watch?v=q7C-sqdSo8M).
9 Unfortunately, that airframe was one of many lost in the
10 [Black Forest Fire](http://www.gag.com/blackforestfire.html).
12 At a conference late in 2014, one of the founders of Woot approached Bdale to talk
13 about the possibility of another sponsored rocket project for his new venture,
14 [Mediocre Laboratories](https://mediocre.com/) and its flagship site
15 [meh](http://meh.com).
17 Bdale had already started thinking about building another "big-ass rocket" ...
19 After giving it some serious thought, the goal became building something bigger
20 than anything Bdale had built and flown before, but that would fit in with the
21 "mediocre" theme somehow. Most rocket folks start out flying "three fins
22 and a nose cone", so doing a simple rocket of that style seemed like a
23 good starting point. The coolest such rocket clan Garbee has ever built
25 [Robert's first high-power airframe](http://gag.com/rockets/airframes/LilNuke/),
26 a [LOC Precision](http://shop.locprecision.com/)
27 [Lil' Nuke](http://shop.locprecision.com/product.sc?productId=114&categoryId=12)
30 So .. how about a stupidly-large upscale of the LOC Lil' Nuke! A meh-ga nuke!
34 After a bunch of playing around in [OpenRocket](http://openrocket.sourceforge.net/),
35 and considering the limits of the CNC equipment at hand, an airframe diameter of
36 approximately 12 inches was chosen. We can fly high on 6-inch research motors
37 (first flight planned to be on a James Russell research red-flame "O" motor), and
38 fly low and super crowd-pleasing on fast-burning M motors like the
39 [CTI Pro98 M3400WT](http://pro38.com/products/pro98/motor.php) in a suitable adapter.
41 To achieve sufficient stability on an O motor, the nose needs to be pretty
42 heavy. Simulation suggested that turning the nose out of solid pine would work
43 out just about perfectly. And thanks to the fire, Bdale had some large pine
44 logs drying... but trying to turn a nose cone out of one of those was kind of a
45 disaster! So we ended up asking Dan at
46 [Python Rocketry](https://pythonrocketry.com/)
47 for help, and he delivered an outstanding nose cone for the project!
49 Because such a heavy nose cone would put significant compression load on the
50 rest of the airframe, we took notes from Kevin Trojanowski's large rocket
51 group projects, and decided to build internal structure to carry that load
52 rather than depending on the airframe material itself. Some quick back of
53 the envelope calculations suggest that 3 ribs made of cheap, common 1x2 pine
54 lumber would more than suffice.
56 For the airframe, we acquired a length of 12-inch concrete column form,
57 peeling the inner and outer layers to get rid of the waxy surfaces. The
58 tubes were then wrapped with two layers of 6oz fiberglass using West Systems
59 epoxy and peel-ply fabric to consolidate the fibers and make for a reasonably
60 smooth finish with minimal sanding. A section of airframe tubing was slit and
61 closed down to form a coupler at the front of the fin can, so the main
62 airframe can be separated to ease transportation and flight prep.
64 The fins were fabricated from nominal 1/2 inch birch plywood with rounded
65 edges. They were inserted into fin grooves cut in the forward and aft
66 centering rings and interlocked with two intermediate rings for mechanical
67 strength. All rings were CNC cut from 3/4 inch birch plywood, except the
68 aft ring which was doubled by laminating two pieces of plywood to form a
69 1.5-inch-thick aft ring more likely to survive the kinetic energy of
70 landing. The epoxy used for all fin to ring joints (and most others in the
71 airframe) was augmented with West Systems 403 Microfibers, yielding very
72 strong yet light joints. Once the fin can was fully assembled, the fins
73 were laminated with laminated with one partial layer of 5.7oz 2x2 twill
74 carbon fiber for stiffness, and one layer of tip to tip 6oz fiberglass for
75 surface preservation and strength.
77 Charge cups for primary and secondary black powder charges mount on the
78 top of the fin can forward ring where they are easy to load before adding
79 the main airframe tube to the stack. This ring also sports an ARRD
80 intended to release the main chute during descent. The main airframe tube
81 has 3 ribs epoxied to the inside of the skin that sit on the fin can forward
82 ring after assembly, and provide a bearing surface for the nose cone once it
83 is installed. In this way, the compressive load from the nose mass carries
84 down through the ribs into the fin can plywood stack, and no significant
85 load is carried by the aiframe tubing itself. The main airframe also has
86 a "baffle" between two of the ribs that causes the gas produced by the black
87 powder charges to flow up past the main parachute to blow off the nose cone.
89 Because the nose ended up being really heavy after adding sufficient nose
90 weight to stabilize the airframe on big motors, recovery starts by blowing
91 off the nose at apogee and deploying 2 mil-surplus 5-foot parachutes on
92 a "V" harness. The main chute is a 28-foot man-rated mil-surplus chute in
93 a Giant Leap deployment bag, and the harness is fabricated from lots of REI
94 1-inch climbing strap (in bright purple, of course!) and a number of
95 different size stainless steel quick-links.
97 A side-access electronics bay in the valley between two fins provides
98 space for two removeable "sleds", each holding an Altus Metrum
99 [TeleMega](http://altusmetrum.org/TeleMega). Each TeleMega has a single
100 dedicated 850mAh LiPo battery, and a rotary power switch mounted in the
101 airframe for on/off. Custom dipole antennas were designed and integrated
102 into the construction just inside the airframe skin to maximize telemetry
103 performance, with RG-188 teflon coax and SMA connectors to the flight
106 The airframe is configured with two 1515-sized rail buttons, and is really
107 only considered safe to launch from Terry Lee's launch trailer with 20 feet
108 of very stiff 1515 rail.
110 ## Design / Simulation File
112 [mehganuke.ork](/rockets/airframes/MehGaNuke/mehganuke.ork)
117 Purchased 12 feet of 12 inch concrete casting tube from White Cap, they cut
118 it for me into pieces approximately 8.5 and 3.5 feet long.
121 Peeled the tubes inside and out, resulting cardboard measures 12" ID,
122 and 12.25" OD. Cut two centering rings from scrap 1/2" OSB to allow use of
123 on-hand 3/4" copper water pipe as an axle during glassing operations. I
124 ended up cutting the longer piece of airframe tubing to ease the glassing
125 process, such that I can "wrap normally".
128 Realized I only have enough glass to do one layer on the coupler. Placed
129 order for a full roll of 60" width 6oz E-glass. Used West Systems 105
130 resin and 209 extra-slow hardener mixed in 3-pump batches to bond one layer
131 of glass and peel-ply to the coupler tube. Took either 15 or 18 pumps total,
132 the cardboard tube is much "thirstier" than the PML phenolic tubing I've
133 glassed for previous projects. Given how much cheaper the concrete casting
134 tube is, this is fine, I'll just need to pay attention to my epoxy stock and
135 order more if needed!
138 Peeled the peel-ply on the coupler. Looks adequate for use as a coupler,
139 but there are several spots where more epoxy would have made me happier. Will
140 compensate when wrapping the airframe tubes. Given how "thirsty" the cardboard
141 is, I think the trick will just be to paint the tube with a thick layer of epoxy
142 before starting to apply the glass, then be generous when wetting each layer.
144 At this point, a lot of time passed, and the airframe wasn't completed until
150 All the photos and video I've collected associated with this project can
151 be found [here](https://thor.gag.com/index.php?/category/MehGaNuke).
155 The first flight of this airframe was at the [Kloudbusters](http://kloudbusters.org/)
156 [Airfest 24](http://kloudbusters.org/airfest/) in Argonia, Kansas, USA,
157 on Saturday, 1 September 2018. The motor was a 6-inch "O" built by James
158 Russell using his well-known "Russell Red" formula. Due to a slightly larger
159 than optimal nozzle throat, the motor burn was a bit longer and average thrust
160 a bit lower than expected... but a side-effect was a 9-10 foot brilliant red
161 flame tail that was awesome to see! The rocket hit about Mach 0.6 on the way
162 to 8068 feet above ground, and was recovered safely. Weather-cocking due to
163 wind caused the airframe to have a residual speed at apogee of nearly 60 meters
164 per second, so not surprisingly there was some modest zippering of the top of
165 the airframe. It also seems clear that the ARRD failed to retain the deployment
166 bag, as the main chute deployed a few seconds after apogee. The stress at
167 deployment tore the strap off the deployment bag, and the deployment bag was not
168 recovered. Some minor re-design of the deployment sequence seems indicated
169 before future flights. All in all, though, this was an outstanding group effort,
170 a lovely flight, and a huge crowd-pleaser!
projects / web / gag.com / blob