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, I designed and built a complete replacement.
119 To increase stability, the main airframe tube length was extended from
120 the original 4.5 feet to approximately 6 feet. This increased stability
121 allowing a reduction in nose weight, increasing safety. It means the
122 length is more than a strict scaling of the Lil Nuke, but is less than
125 For main deployment, the ARRD was replaced with a
126 [Tender Descender L3](https://tinderrocketry.com/l13-tender-descender-tether),
127 which has the advantage that the release mechanism is orthogonal to the
128 axis of flight. That seems important when the airframe is this heavy and
129 apogee occurs at a non-nominal velocity, as in the first flight.
131 The original build had internal 1x2 ribs and a baffle yielding a "D" shaped
132 main bay with the apogee charge gasses going up the channel without pushing
133 on the main deployment bag. For this rebuild, 3 ribs were run the airframe
134 length between the 12" airframe and a concentric full-length 8" deployment
135 bay, with centering rings on each end. One sector of the rings was
136 vented to allow apogee ejection gasses to flow from the charge cups on the
137 leading edge of the fin can to the nose, bypassing the main chute bay.
139 ## Design / Simulation File
141 * Original [mehganuke.ork](/rockets/airframes/MehGaNuke/mehganuke.ork)
142 * Revised [mehganuke-v2.ork](/rockets/airframes/MehGaNuke/mehganuke-v2.ork)
147 Purchased 12 feet of 12 inch concrete casting tube from White Cap, they cut
148 it for me into pieces approximately 8.5 and 3.5 feet long.
151 Peeled the tubes inside and out, resulting cardboard measures 12" ID,
152 and 12.25" OD. Cut two centering rings from scrap 1/2" OSB to allow use of
153 on-hand 3/4" copper water pipe as an axle during glassing operations. I
154 ended up cutting the longer piece of airframe tubing to ease the glassing
155 process, such that I can "wrap normally".
158 Realized I only have enough glass to do one layer on the coupler. Placed
159 order for a full roll of 60" width 6oz E-glass. Used West Systems 105
160 resin and 209 extra-slow hardener mixed in 3-pump batches to bond one layer
161 of glass and peel-ply to the coupler tube. Took either 15 or 18 pumps total,
162 the cardboard tube is much "thirstier" than the PML phenolic tubing I've
163 glassed for previous projects. Given how much cheaper the concrete casting
164 tube is, this is fine, I'll just need to pay attention to my epoxy stock and
165 order more if needed!
168 Peeled the peel-ply on the coupler. Looks adequate for use as a coupler,
169 but there are several spots where more epoxy would have made me happier. Will
170 compensate when wrapping the airframe tubes. Given how "thirsty" the cardboard
171 is, I think the trick will just be to paint the tube with a thick layer of epoxy
172 before starting to apply the glass, then be generous when wetting each layer.
174 At this point, a lot of time passed, detailed note-taking more or less
175 stopped, and the airframe wasn't completed until early 2018!
180 All the photos and video I've collected associated with this project can
181 be found [here](https://thor.gag.com/index.php?/category/MehGaNuke).
183 Kent Burnett's drone video hightlights reel from Airfest 2018 includes
184 [video of the launch](https://vimeo.com/295459157#t=636s) starting at
191 The first flight of this airframe was at the
192 [Kloudbusters](http://kloudbusters.org/)
193 [Airfest 24](http://kloudbusters.org/airfest/) in Argonia, Kansas, USA,
194 on Saturday, 1 September 2018. The motor was a 6-inch "O" built by James
195 Russell using his well-known "Russell Red" formula. The total launch mass
196 was about 205 pounds on the rail. Due to a slightly larger than optimal
197 nozzle throat, the motor burn at 7.7 seconds was a bit longer than expected,
198 pushing the airframe with an average acceleration of only 2.89 G to a
199 maximum speed of Mach 0.6 on the way to 8068 feet above ground.
201 Weather-cocking due to wind caused the airframe to have a residual speed at
202 apogee of nearly 60 meters per second, so not surprisingly there was zippering
203 of the top of the main airframe tube. It also seems clear that the ARRD
204 failed to retain the deployment bag, as the main chute deployed a few seconds
205 after apogee. We had some difficulty with the ARRD during assembly on the
206 rail, so this wasn't terribly surprising. Recovery was completely safe with
207 the nose descending under 2 5-foot mil-surplus chutes, and the bulk of the
208 airframe descending under a 28-foot mil-surplus chute.
210 The stress at deployment tore the strap off the deployment bag, and the
211 deployment bag was not recovered. After studying the zipper and thinking
212 about the main deployment sequence, several changes will be made before the
215 - The main airframe tube will be replaced with a tube that's a bit longer
216 (for greater stability), and has an internal 7.5-8" diameter tube instead
217 of the flat baffle to ease main chute deployment.
219 - Switch from the ARRD to the largest [Tender Descender](http://www.tinderrocketry.com/l13-tender-descender-tether) for main deployment.
221 - Add a TeleGPS to the nose assembly so it can be tracked independently, and let
222 it come down by itself under the 2 existing 5-foot chutes. Add a third 5-foot
223 chute to be a dedicated pilot for the 28-foot main chute.
225 These changes should reduce the chance of another zipper, and reduce the amount
226 of strap we need to stuff into the bay.
228 All in all, this first flight was an outstanding group effort, a lovely
229 flight, and a huge crowd-pleaser!
233 In 2021, the NAR National Sport Launch was held near Alamosa, CO. Doug
234 Gerrard planned to be there with his camera-laden launch pad so there was
235 the possibility of a highly-documented launch. Since I
236 really wanted to fly this project in Colorado and that was a national-scale
237 event, plans were made. As a NAR sanctioned event, the motor needed to be
238 commercial and not research. Simulations led to the choice of a CTI N3301
239 White Thunder which would fit case hardware already on hand. This would
240 require fabricating an adapter from the 6" motor mount to the 98mm
241 motor, but that seemed easy enough. My thanks to the good folks at
242 [Moto-Joe Rocketry](http://moto-joe.com/) for helping me obtain the reload.
244 Unfortunately, logistics issues prevented flying at the NSL. The second
245 flight ended up happening on Sunday, 19 September 2021, at the
246 [Tripoli Colorado](https://www.tripolicolorado.org/) Fall Frenzy launch.
248 In addition to the rebuilt main airframe section and motor adapter, a
249 TeleGPS was added to the nose bay. Then, at the last minute, Meh-ga Nuke
250 was equipped with two keychain cameras mounted looking up and down.
252 The rocket was about 145 pounds on the rail of Terry Lee's launch trailer,
253 and was flowing with 2 e-matches and a pinch of Pyrodex P in the Tender
254 Descender, and apogee charges of 6g primary and "fill the cup"
255 secondary. The rocket departed the rail with about 5.5g max acceleration
256 on the way to Mach 0.7 and an apogee altitude of 9183 feet. The dual
257 deployment process worked as designed, but unfortunately the shround on
258 the main tangled, probably due to a hasty repacking of the deployment bag
259 during assembly on the rail. Wind pushed the airframe ENE out of the
260 optimal landing area and into a "field of rocks", where the higher than
261 expected landing velocity of the main airframe and fin can assembly and
262 wind drag resulted in cosmetic damage to the fin can and more significant
263 damage to the main airframe tube. The nose cone also suffered damage as
264 a result of the wind causing the chutes to pull it across rocks.
266 Both TeleMega boards returned good data logs. The TeleGPS in the nose
267 cone wasn't heard during launch and flight (it turns out the unsupported
268 antenna wire broke off sometime before landing, perhaps even before
269 launch?), but the data recovered from the board shows a clean trace of
270 the nose cone's path during flight. Good thing we didn't need the
271 GPS to locate and recover the nose cone!
273 The video from the up-looking camera worked great through apogee, but
274 unfortunately the video froze before the main deployed so only audio was
275 recorded for the rest of the flight. The down-looking camera video came
276 out very well, though! It shows only a couple rotations of the airframe
277 during ascent with some great view of the flight line, etc. It also
278 captured the nose cone and two 5 foot surplus military parachutes deployed
279 at apogee travelling past the main airframe rapidly at apogee. The
280 shadow of the nose cone and associated chutes descending independently can
281 be seen in the video before landing... and the very violent landing of
282 the fin can and main airframe can be clearly seen.
284 All in all, this second flight was another huge crowd-pleaser and very
285 satisfying overall. Particular thanks to Terry Lee for his help
286 rebuilding the main airframe and the use of his launch trailer, George
287 Barnes IV for his outstanding photos on launch day, and my wife Karen who
288 attended the launch with great enthusiasm despite being only a few weeks
289 into the recovery from major surgery.
291 I think the primary lesson learned from this flight is that the design
292 of the airframe pretty much guarantees the main airframe tube is going
293 to be damaged in each flight. The video proof of what we already
294 understood intellectually about the dramatic reversal of direction the
296 undergoes at apogee when the nose comes off and the drogue chutes deploy
297 alone is enough to rip the leading edge of the airframe apart back to the
298 first centering ring below the nose shoulder. So, even without landing
299 in rocks and being dragged due to high winds by the main chute, we
300 probably just need to acknowledge the main airframe is in some ways a