# Meh-ga Nuke ## Motivation Years ago, Bdale flew some [Woot](http://woot.com) screaming flying monkey dolls in his [L3 certification airframe](http://gag.com/rockets/airframes/Goblin10/), leading to some seriously amusing [videos](https://www.youtube.com/watch?v=q7C-sqdSo8M). Unfortunately, that airframe was one of many lost in the [Black Forest Fire](http://www.gag.com/blackforestfire.html). At a conference late in 2014, one of the founders of Woot approached Bdale to talk about the possibility of another sponsored rocket project for his new venture, [Mediocre Laboratories](https://mediocre.com/) and its flagship site [meh](http://meh.com). Bdale had already started thinking about building another "big-ass rocket" ... After giving it some serious thought, the goal became building something bigger than anything Bdale had built and flown before, but that would fit in with the "mediocre" theme somehow. Most rocket folks start out flying "three fins and a nose cone", so doing a simple rocket of that style seemed like a good starting point. The coolest such rocket clan Garbee has ever built was undoubtedly [Robert's first high-power airframe](http://gag.com/rockets/airframes/LilNuke/), a [LOC Precision](http://shop.locprecision.com/) [Lil' Nuke](http://shop.locprecision.com/product.sc?productId=114&categoryId=12) kit. So .. how about a stupidly-large upscale of the LOC Lil' Nuke! Bdale's wife Karen suggested the name, since this is definitely a meh-ga nuke! ## Design Details After a bunch of playing around in [OpenRocket](http://openrocket.sourceforge.net/), and considering the limits of the CNC equipment at hand, an airframe diameter of approximately 12 inches was chosen. We can fly high on 6-inch research motors (first flight was on a James Russell research red-flame "O" motor), and fly low and super crowd-pleasing on fast-burning M motors like the [CTI Pro98 M3400WT](http://pro38.com/products/pro98/motor.php) in a suitable adapter. To achieve sufficient stability on an O motor, the nose needs to be pretty heavy. Simulation suggested that turning the nose out of solid pine would work out just about perfectly. And thanks to the fire, Bdale had some large pine logs drying... but trying to turn a nose cone out of one of those was kind of a disaster! So we ended up asking Dan at [Python Rocketry](https://pythonrocketry.com/) for help, and he delivered an outstanding bespoke nose cone for the project! Because such a heavy nose cone would put significant compression load on the rest of the airframe, we took notes from Kevin Trojanowski's large rocket group projects, and decided to build internal structure to carry that load rather than depending on the airframe material itself. Some quick back of the envelope calculations suggest that 3 ribs made of cheap, common 1x2 pine lumber would more than suffice. For the airframe, we acquired a length of 12-inch concrete column form, peeling the inner and outer layers to get rid of the waxy surfaces. The tubes were then wrapped with two layers of 6oz fiberglass using West Systems epoxy and peel-ply fabric to consolidate the fibers and make for a reasonably smooth finish with minimal sanding. A section of airframe tubing was slit and closed down to form a coupler at the front of the fin can, so the main airframe can be separated to ease transportation and flight prep. The fins were fabricated from nominal 1/2 inch birch plywood with rounded edges. They were inserted into fin grooves cut in the forward and aft centering rings and interlocked with two intermediate rings for mechanical strength. All rings were CNC cut from 3/4 inch birch plywood, except the aft ring which was doubled by laminating two pieces of plywood to form a 1.5-inch-thick aft ring more likely to survive the kinetic energy of landing. The epoxy used for all fin to ring joints (and most others in the airframe) was augmented with West Systems 403 Microfibers, yielding very strong yet light joints. Once the fin can was fully assembled, the fins were laminated with with one partial layer of 5.7oz 2x2 twill carbon fiber for stiffness, and one layer of tip to tip 6oz fiberglass for surface preservation and strength. Charge cups for primary and secondary black powder charges mount on the top of the fin can forward ring where they are easy to load before adding the main airframe tube to the stack. This ring also sports an ARRD intended to release the main chute during descent. The main airframe tube has 3 ribs epoxied to the inside of the skin that sit on the fin can forward ring after assembly, and provide a bearing surface for the nose cone once it is installed. In this way, the compressive load from the nose mass carries down through the ribs into the fin can plywood stack, and no significant load is carried by the aiframe tubing itself. The main airframe also has a "baffle" between two of the ribs that causes the gas produced by the black powder charges to flow up past the main parachute to blow off the nose cone. Because the nose ended up being really heavy after adding sufficient nose weight to stabilize the airframe on big motors, recovery starts by blowing off the nose at apogee and deploying 2 mil-surplus 5-foot parachutes on a "V" harness. The main chute is a 28-foot man-rated mil-surplus chute in a Giant Leap deployment bag, and the harness is fabricated from lots of REI 1-inch climbing strap (in bright purple, of course!) and a number of different size stainless steel quick-links. A side-access electronics bay in the valley between two fins provides space for two removeable "sleds", each holding an Altus Metrum [TeleMega](http://altusmetrum.org/TeleMega). Each TeleMega has a single dedicated 850mAh LiPo battery, and a rotary power switch mounted in the airframe for on/off. Custom dipole antennas were designed and integrated into the construction just inside the airframe skin to maximize telemetry performance, with RG-188 teflon coax and SMA connectors to the flight computers. The airframe is configured with two 1515-sized rail buttons, and is really only considered safe to launch from Terry Lee's launch trailer with 20 feet of very stiff 1515 rail. ## Design / Simulation File [mehganuke.ork](/rockets/airframes/MehGaNuke/mehganuke.ork) ## Construction Log 2014.04.16 Purchased 12 feet of 12 inch concrete casting tube from White Cap, they cut it for me into pieces approximately 8.5 and 3.5 feet long. 2014.04.18 Peeled the tubes inside and out, resulting cardboard measures 12" ID, and 12.25" OD. Cut two centering rings from scrap 1/2" OSB to allow use of on-hand 3/4" copper water pipe as an axle during glassing operations. I ended up cutting the longer piece of airframe tubing to ease the glassing process, such that I can "wrap normally". 2014.04.19 Realized I only have enough glass to do one layer on the coupler. Placed order for a full roll of 60" width 6oz E-glass. Used West Systems 105 resin and 209 extra-slow hardener mixed in 3-pump batches to bond one layer of glass and peel-ply to the coupler tube. Took either 15 or 18 pumps total, the cardboard tube is much "thirstier" than the PML phenolic tubing I've glassed for previous projects. Given how much cheaper the concrete casting tube is, this is fine, I'll just need to pay attention to my epoxy stock and order more if needed! 2014.04.20 Peeled the peel-ply on the coupler. Looks adequate for use as a coupler, but there are several spots where more epoxy would have made me happier. Will compensate when wrapping the airframe tubes. Given how "thirsty" the cardboard is, I think the trick will just be to paint the tube with a thick layer of epoxy before starting to apply the glass, then be generous when wetting each layer. At this point, a lot of time passed, detailed note-taking more or less stopped, and the airframe wasn't completed until early 2018! ## Photos All the photos and video I've collected associated with this project can be found [here](https://thor.gag.com/index.php?/category/MehGaNuke). Kent Burnett's drone video hightlights reel from Airfest 2018 includes [video of the launch](https://vimeo.com/295459157#t=636s) starting at about 10:36 in. ## Flight Log The first flight of this airframe was at the [Kloudbusters](http://kloudbusters.org/) [Airfest 24](http://kloudbusters.org/airfest/) in Argonia, Kansas, USA, on Saturday, 1 September 2018. The motor was a 6-inch "O" built by James Russell using his well-known "Russell Red" formula. The total launch mass was about 205 pounds on the rail. Due to a slightly larger than optimal nozzle throat, the motor burn at 7.7 seconds was a bit longer than expected, pushing the airframe with an average acceleration of only 2.89 G to a maximum speed of Mach 0.6 on the way to 8068 feet above ground. Weather-cocking due to wind caused the airframe to have a residual speed at apogee of nearly 60 meters per second, so not surprisingly there was zippering of the top of the main airframe tube. It also seems clear that the ARRD failed to retain the deployment bag, as the main chute deployed a few seconds after apogee. We had some difficulty with the ARRD during assembly on the rail, so this wasn't terribly surprising. Recovery was completely safe with the nose descending under 2 5-foot mil-surplus chutes, and the bulk of the airframe descending under a 28-foot mil-surplus chute. The stress at deployment tore the strap off the deployment bag, and the deployment bag was not recovered. After studying the zipper and thinking about the main deployment sequence, several changes will be made before the next flight: - 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. - Switch from the ARRD to the largest [Tender Descender](http://www.tinderrocketry.com/l13-tender-descender-tether) for main deployment - 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. These changes should reduce the chance of another zipper, and reduce the amount of strap we need to stuff into the bay. All in all, this first flight was an outstanding group effort, a lovely flight, and a huge crowd-pleaser!