[web/gag.com] / rockets / airframes / MehGaNuke / index.mdwn

# 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.

### Revisions for Version 2 ###

Because the main airframe zippered somewhat on the first flight, and the
ARRD released at apogee, rather than just repairing the existing airframe
tube, we're going to build a replacement.

To increase stability, the main airframe tube length will be extended from
the original 4.5 feet to approximately 8 feet.  This will increase stability,
allowing a reduction in nose weight.  It should also make recovery system
loading less arduous on the rail.  This means the rocket will be closer
to the length of an upscaled Nuke Pro Maxx instead of the original Lil Nuke.

For main deployment, the ARRD is being replaced with a Tender Descender L3,
which has the advantage that the release mechanism is orthogonal to the 
axis of flight.  That seems important when the airframe is this heavy and
apogee occurs at a non-nominal velocity, as in the first flight.

The original build had internal 1x2 ribs and a baffle yielding a "D" shaped 
main bay with the apogee charge gasses going up the channel without pushing
on the main deployment bag.  For this rebuild, 3 ribs will run the airframe
length between the 12" airframe and a concentric full-length 8" deployment
bay, with centering rings on each end.  One sector of the rings will be
vented to allow apogee ejection gasses to flow from the charge cups on the
leading edge of the fin can to push the nose off without push up on the 
main in its deployment bag.

## Design / Simulation File

Original [mehganuke.ork](/rockets/airframes/MehGaNuke/mehganuke.ork)
Revised [mehganuke-v2.ork](/rockets/airframes/MehGaNuke/mehganuke-v2.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 by itself 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!