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 ### Revisions for Version 2 ###
115 Because the main airframe zippered somewhat on the first flight, and the
116 ARRD released at apogee, rather than just repairing the existing airframe
117 tube, we're going to build a replacement.
119 To increase stability, the main airframe tube length will be extended from
120 the original 4.5 feet to approximately 8 feet. The expected increase
121 in stability should allowing a reduction in nose weight, increasing
122 safety. It should also make recovery system loading less arduous on the
124 course, this means the rocket will be closer to the length of an upscaled
125 Nuke Pro Maxx rather than the original Lil Nuke.
127 For main deployment, the ARRD is being replaced with a
128 [Tender Descender L3](https://tinderrocketry.com/l13-tender-descender-tether),
129 which has the advantage that the release mechanism is orthogonal to the
130 axis of flight. That seems important when the airframe is this heavy and
131 apogee occurs at a non-nominal velocity, as in the first flight.
133 The original build had internal 1x2 ribs and a baffle yielding a "D" shaped
134 main bay with the apogee charge gasses going up the channel without pushing
135 on the main deployment bag. For this rebuild, 3 ribs will run the airframe
136 length between the 12" airframe and a concentric full-length 8" deployment
137 bay, with centering rings on each end. One sector of the rings will be
138 vented to allow apogee ejection gasses to flow from the charge cups on the
139 leading edge of the fin can to push the nose off without push up on the
140 main in its deployment bag.
142 ## Design / Simulation File
144 Original [mehganuke.ork](/rockets/airframes/MehGaNuke/mehganuke.ork)
145 Revised [mehganuke-v2.ork](/rockets/airframes/MehGaNuke/mehganuke-v2.ork)
150 Purchased 12 feet of 12 inch concrete casting tube from White Cap, they cut
151 it for me into pieces approximately 8.5 and 3.5 feet long.
154 Peeled the tubes inside and out, resulting cardboard measures 12" ID,
155 and 12.25" OD. Cut two centering rings from scrap 1/2" OSB to allow use of
156 on-hand 3/4" copper water pipe as an axle during glassing operations. I
157 ended up cutting the longer piece of airframe tubing to ease the glassing
158 process, such that I can "wrap normally".
161 Realized I only have enough glass to do one layer on the coupler. Placed
162 order for a full roll of 60" width 6oz E-glass. Used West Systems 105
163 resin and 209 extra-slow hardener mixed in 3-pump batches to bond one layer
164 of glass and peel-ply to the coupler tube. Took either 15 or 18 pumps total,
165 the cardboard tube is much "thirstier" than the PML phenolic tubing I've
166 glassed for previous projects. Given how much cheaper the concrete casting
167 tube is, this is fine, I'll just need to pay attention to my epoxy stock and
168 order more if needed!
171 Peeled the peel-ply on the coupler. Looks adequate for use as a coupler,
172 but there are several spots where more epoxy would have made me happier. Will
173 compensate when wrapping the airframe tubes. Given how "thirsty" the cardboard
174 is, I think the trick will just be to paint the tube with a thick layer of epoxy
175 before starting to apply the glass, then be generous when wetting each layer.
177 At this point, a lot of time passed, detailed note-taking more or less
178 stopped, and the airframe wasn't completed until early 2018!
183 All the photos and video I've collected associated with this project can
184 be found [here](https://thor.gag.com/index.php?/category/MehGaNuke).
186 Kent Burnett's drone video hightlights reel from Airfest 2018 includes
187 [video of the launch](https://vimeo.com/295459157#t=636s) starting at
192 The first flight of this airframe was at the
193 [Kloudbusters](http://kloudbusters.org/)
194 [Airfest 24](http://kloudbusters.org/airfest/) in Argonia, Kansas, USA,
195 on Saturday, 1 September 2018. The motor was a 6-inch "O" built by James
196 Russell using his well-known "Russell Red" formula. The total launch mass
197 was about 205 pounds on the rail. Due to a slightly larger than optimal
198 nozzle throat, the motor burn at 7.7 seconds was a bit longer than expected,
199 pushing the airframe with an average acceleration of only 2.89 G to a
200 maximum speed of Mach 0.6 on the way to 8068 feet above ground.
202 Weather-cocking due to wind caused the airframe to have a residual speed at
203 apogee of nearly 60 meters per second, so not surprisingly there was zippering
204 of the top of the main airframe tube. It also seems clear that the ARRD
205 failed to retain the deployment bag, as the main chute deployed a few seconds
206 after apogee. We had some difficulty with the ARRD during assembly on the
207 rail, so this wasn't terribly surprising. Recovery was completely safe with
208 the nose descending under 2 5-foot mil-surplus chutes, and the bulk of the
209 airframe descending under a 28-foot mil-surplus chute.
211 The stress at deployment tore the strap off the deployment bag, and the
212 deployment bag was not recovered. After studying the zipper and thinking
213 about the main deployment sequence, several changes will be made before the
216 - The main airframe tube will be replaced with a tube that's a bit longer
217 (for greater stability), and has an internal 7.5-8" diameter tube instead
218 of the flat baffle to ease main chute deployment.
220 - Switch from the ARRD to the largest [Tender Descender](http://www.tinderrocketry.com/l13-tender-descender-tether) for main deployment.
222 - Add a TeleGPS to the nose assembly so it can be tracked independently, and let
223 it come down by itself under the 2 existing 5-foot chutes. Add a third 5-foot
224 chute to be a dedicated pilot for the 28-foot main chute.
226 These changes should reduce the chance of another zipper, and reduce the amount
227 of strap we need to stuff into the bay.
229 All in all, this first flight was an outstanding group effort, a lovely
230 flight, and a huge crowd-pleaser!