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! Bdale's
31 wife Karen suggested the name, since this is definitely a meh-ga nuke!
35 After a bunch of playing around in
36 [OpenRocket](http://openrocket.sourceforge.net/), and considering the
37 limits of the CNC equipment at hand, an airframe diameter of
38 approximately 12 inches was chosen. We can fly high on 6-inch research motors
39 (first flight was on a James Russell research red-flame "O" motor), and
40 fly low and super crowd-pleasing on fast-burning M motors like the
41 [CTI Pro98 M3400WT](http://pro38.com/products/pro98/motor.php) in a
44 To achieve sufficient stability on an O motor, the nose needs to be pretty
45 heavy. Simulation suggested that turning the nose out of solid pine would work
46 out just about perfectly. And thanks to the fire, Bdale had some large pine
47 logs drying... but trying to turn a nose cone out of one of those was kind of a
48 disaster! So we ended up asking Dan at
49 [Python Rocketry](https://pythonrocketry.com/)
50 for help, and he delivered an outstanding bespoke nose cone for the project!
52 Because such a heavy nose cone would put significant compression load on the
53 rest of the airframe, we took notes from Kevin Trojanowski's large rocket
54 group projects, and decided to build internal structure to carry that load
55 rather than depending on the airframe material itself. Some quick back of
56 the envelope calculations suggest that 3 ribs made of cheap, common 1x2 pine
57 lumber would more than suffice.
59 For the airframe, we acquired a length of 12-inch concrete column form,
60 peeling the inner and outer layers to get rid of the waxy surfaces. The
61 tubes were then wrapped with two layers of 6oz fiberglass using West Systems
62 epoxy and peel-ply fabric to consolidate the fibers and make for a reasonably
63 smooth finish with minimal sanding. A section of airframe tubing was slit and
64 closed down to form a coupler at the front of the fin can, so the main
65 airframe can be separated to ease transportation and flight prep.
67 The fins were fabricated from nominal 1/2 inch birch plywood with rounded
68 edges. They were inserted into fin grooves cut in the forward and aft
69 centering rings and interlocked with two intermediate rings for mechanical
70 strength. All rings were CNC cut from 3/4 inch birch plywood, except the
71 aft ring which was doubled by laminating two pieces of plywood to form a
72 1.5-inch-thick aft ring more likely to survive the kinetic energy of
73 landing. The epoxy used for all fin to ring joints (and most others in the
74 airframe) was augmented with West Systems 403 Microfibers, yielding very
75 strong yet light joints. Once the fin can was fully assembled, the fins
76 were laminated with with one partial layer of 5.7oz 2x2 twill carbon fiber
77 for stiffness, and one layer of tip to tip 6oz fiberglass for surface
78 preservation and strength.
80 Charge cups for primary and secondary black powder charges mount on the
81 top of the fin can forward ring where they are easy to load before adding
82 the main airframe tube to the stack. This ring also sports an ARRD
83 intended to release the main chute during descent. The main airframe tube
84 has 3 ribs epoxied to the inside of the skin that sit on the fin can forward
85 ring after assembly, and provide a bearing surface for the nose cone once it
86 is installed. In this way, the compressive load from the nose mass carries
87 down through the ribs into the fin can plywood stack, and no significant
88 load is carried by the aiframe tubing itself. The main airframe also has
89 a "baffle" between two of the ribs that causes the gas produced by the black
90 powder charges to flow up past the main parachute to blow off the nose cone.
92 Because the nose ended up being really heavy after adding sufficient nose
93 weight to stabilize the airframe on big motors, recovery starts by blowing
94 off the nose at apogee and deploying 2 mil-surplus 5-foot parachutes on
95 a "V" harness. The main chute is a 28-foot man-rated mil-surplus chute in
96 a Giant Leap deployment bag, and the harness is fabricated from lots of REI
97 1-inch climbing strap (in bright purple, of course!) and a number of
98 different size stainless steel quick-links.
100 A side-access electronics bay in the valley between two fins provides
101 space for two removeable "sleds", each holding an Altus Metrum
102 [TeleMega](http://altusmetrum.org/TeleMega). Each TeleMega has a single
103 dedicated 850mAh LiPo battery, and a rotary power switch mounted in the
104 airframe for on/off. Custom dipole antennas were designed and integrated
105 into the construction just inside the airframe skin to maximize telemetry
106 performance, with RG-188 teflon coax and SMA connectors to the flight
109 The airframe is configured with two 1515-sized rail buttons, and is really
110 only considered safe to launch from Terry Lee's launch trailer with 20 feet
111 of very stiff 1515 rail.
113 ## Design / Simulation File
115 [mehganuke.ork](/rockets/airframes/MehGaNuke/mehganuke.ork)
120 Purchased 12 feet of 12 inch concrete casting tube from White Cap, they cut
121 it for me into pieces approximately 8.5 and 3.5 feet long.
124 Peeled the tubes inside and out, resulting cardboard measures 12" ID,
125 and 12.25" OD. Cut two centering rings from scrap 1/2" OSB to allow use of
126 on-hand 3/4" copper water pipe as an axle during glassing operations. I
127 ended up cutting the longer piece of airframe tubing to ease the glassing
128 process, such that I can "wrap normally".
131 Realized I only have enough glass to do one layer on the coupler. Placed
132 order for a full roll of 60" width 6oz E-glass. Used West Systems 105
133 resin and 209 extra-slow hardener mixed in 3-pump batches to bond one layer
134 of glass and peel-ply to the coupler tube. Took either 15 or 18 pumps total,
135 the cardboard tube is much "thirstier" than the PML phenolic tubing I've
136 glassed for previous projects. Given how much cheaper the concrete casting
137 tube is, this is fine, I'll just need to pay attention to my epoxy stock and
138 order more if needed!
141 Peeled the peel-ply on the coupler. Looks adequate for use as a coupler,
142 but there are several spots where more epoxy would have made me happier. Will
143 compensate when wrapping the airframe tubes. Given how "thirsty" the cardboard
144 is, I think the trick will just be to paint the tube with a thick layer of epoxy
145 before starting to apply the glass, then be generous when wetting each layer.
147 At this point, a lot of time passed, detailed note-taking more or less
148 stopped, and the airframe wasn't completed until early 2018!
153 All the photos and video I've collected associated with this project can
154 be found [here](https://thor.gag.com/index.php?/category/MehGaNuke).
156 Kent Burnett's drone video hightlights reel from Airfest 2018 includes
157 [video of the launch](https://vimeo.com/295459157#t=636s) starting at
162 The first flight of this airframe was at the
163 [Kloudbusters](http://kloudbusters.org/)
164 [Airfest 24](http://kloudbusters.org/airfest/) in Argonia, Kansas, USA,
165 on Saturday, 1 September 2018. The motor was a 6-inch "O" built by James
166 Russell using his well-known "Russell Red" formula. The total launch mass
167 was about 205 pounds on the rail. Due to a slightly larger than optimal
168 nozzle throat, the motor burn at 7.7 seconds was a bit longer than expected,
169 pushing the airframe with an average acceleration of only 2.89 G to a
170 maximum speed of Mach 0.6 on the way to 8068 feet above ground.
172 Weather-cocking due to wind caused the airframe to have a residual speed at
173 apogee of nearly 60 meters per second, so not surprisingly there was zippering
174 of the top of the main airframe tube. It also seems clear that the ARRD
175 failed to retain the deployment bag, as the main chute deployed a few seconds
176 after apogee. We had some difficulty with the ARRD during assembly on the
177 rail, so this wasn't terribly surprising. Recovery was completely safe with
178 the nose descending under 2 5-foot mil-surplus chutes, and the bulk of the
179 airframe descending under a 28-foot mil-surplus chute.
181 The stress at deployment tore the strap off the deployment bag, and the
182 deployment bag was not recovered. After studying the zipper and thinking
183 about the main deployment sequence, several changes will be made before the
186 - The main airframe tube will be replaced with a tube that's a bit longer (for greater stability), and has an internal 7.5-8" diameter tube instead of the flat baffle to ease main chute deployment.
188 - Switch from the ARRD to the largest [Tender Descender](http://www.tinderrocketry.com/l13-tender-descender-tether) for main deployment
190 - Add a TeleGPS to the nose assembly so it can be tracked independently, and let it come down under the 2 existing 5-foot chutes. Add a third 5-foot chute to be a dedicated pilot for the 28-foot main chute.
192 These changes should reduce the chance of another zipper, and reduce the amount
193 of strap we need to stuff into the bay.
195 All in all, this first flight was an outstanding group effort, a lovely
196 flight, and a huge crowd-pleaser!
projects / web / gag.com / blob