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,
-[A Mediocre Corporation](https://mediocre.com/) and its flagship site
+[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
+"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! A meh-ga nuke!
+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
+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 planned to be on a James Russell research red-flame "O" motor), and
+(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.
+[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 suggests that turning the nose out of solid pine would work
-out just about perfectly.
-
-Because such a heavy nose cone will put significant compression load on the rest
-of the airframe, we'll 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 should
-more than suffice.
-
-The fins will be fabricated from nominal 1/2 inch birch plywood, rounded,
-vacuum-bagged with one layer of carbon fiber for stiffness and one layer of
-fiberglass for surface preservation and strength. They will insert into fin
-grooves cut in the forward and aft fin rings and interlocked with two
-intermediate rings. All fin to ring joints will be augmented with chopped
-fiber and/or glass fabric scraps. Once the fin can is fully assembled, an
-extra layer of fin to fin glass across the airframe will be installed to
-help keep the fin can together during landings.
-
-The airframe will be constructed from 12-inch concrete form tubing with the
-inner and outer layers peeled, wrapped with two layers of 6oz fiberglass. A
-section of airframe tubing wrapped with one glass layer will be slit and
-closed down to form a coupler so the main airframe can be built in two pieces
-to ease transportation and flight prep.
-
-Recovery will involve a 3-foot drogue parachute deployed by blowing the nose
-cone off at apogee, and an ARRD will be used to release a 28-foot main chute
-from a deployment bag. For high flights, a reasonable main deploy height for
-traditional "dual deploy" recovery will be chosen. For lower flights, the
-main will be deployed just long enough after apogee to permit the drogue to
-re-orient the airframe, approximating the "main out at apogee" experience.
-
-A side-access electronics bay will be constructed in the valley between two
-fins near the leading edge of the fins. Electronics will consist of one
-each Altus Metrum [TeleMega](http://altusmetrum.org/TeleMega) and
-[TeleMetrum](http://altusmetrum.org/TeleMetrum) boards. The TeleMega is
-overkill, but I'm curious to see what the airframe rotation rates are like
-in flight, and the gyros will capture that. Each will use a single 850mAh
-LiPo battery, and rotary switches mounted in the airframe for on/off. Two
-charge cups will be mounted on the forward ring of the fin can for apogee
-deployment, and an ARRD will be mounted on the other side of the same ring
-for main deployment.
-
-The main airframe tube will contain ribs and additional structure to carry
-the load induced by the nose cone, and to direct apogee deployment gasses
-around the main parachute deployment bag.
-
-Because the kinetic energy at ground impact even under the large main will
-be fairly high, the ring at the aft end of the airframe will be doubled
-to 1.5 inches thick for extra strength.
-
-The airframe will be set up with 1515-sized rail buttons, and use of
-Terry Lee's launch trailer with 20 foot rail is assumed to ensure stability
-for all flights.
+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
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!
+
projects / web / gag.com / blobdiff