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, I designed and built a complete replacement.
+
+To increase stability, the main airframe tube length was extended from
+the original 4.5 feet to approximately 6 feet. This increased stability
+allowing a reduction in nose weight, increasing safety. It means the
+length is more than a strict scaling of the Lil Nuke, but is less than
+the Nuke Pro Maxx.
+
+For main deployment, the ARRD was replaced with a
+[Tender Descender L3](https://tinderrocketry.com/l13-tender-descender-tether),
+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 were 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 was
+vented to allow apogee ejection gasses to flow from the charge cups on the
+leading edge of the fin can to the nose, bypassing the main chute bay.
+
## Design / Simulation File
-[mehganuke.ork](/rockets/airframes/MehGaNuke/mehganuke.ork)
+ * Original [mehganuke.ork](/rockets/airframes/MehGaNuke/mehganuke.ork)
+ * Revised [mehganuke-v2.ork](/rockets/airframes/MehGaNuke/mehganuke-v2.ork)
## Construction Log
## Flight Log
+### First Flight
+
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. Due to a slightly larger
-than optimal nozzle throat, the motor burn was a bit longer and average thrust
-a bit lower than expected... but a side-effect was a 9-10 foot brilliant red
-flame tail that was awesome to see! The rocket hit about Mach 0.6 on the way
-to 8068 feet above ground, and was recovered safely. 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 some modest zippering of the top of
-the airframe. It also seems clear that the ARRD failed to retain the deployment
-bag, as the main chute deployed a few seconds after apogee. The stress at
-deployment tore the strap off the deployment bag, and the deployment bag was not
-recovered. Some minor re-design of the deployment sequence seems indicated
-before future flights. All in all, though, this was an outstanding group
-effort, a lovely flight, and a huge crowd-pleaser!
+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!
+
+### Second Flight
+
+In 2021, the NAR National Sport Launch was held near Alamosa, CO. Doug
+Gerrard planned to be there with his camera-laden launch pad so there was
+the possibility of a highly-documented launch. Since I
+really wanted to fly this project in Colorado and that was a national-scale
+event, plans were made. As a NAR sanctioned event, the motor needed to be
+commercial and not research. Simulations led to the choice of a CTI N3301
+White Thunder which would fit case hardware already on hand. This would
+require fabricating an adapter from the 6" motor mount to the 98mm
+motor, but that seemed easy enough. My thanks to the good folks at
+[Moto-Joe Rocketry](http://moto-joe.com/) for helping me obtain the reload.
+
+Unfortunately, logistics issues prevented flying at the NSL. The second
+flight ended up happening on Sunday, 19 September 2021, at the
+[Tripoli Colorado](https://www.tripolicolorado.org/) Fall Frenzy launch.
+
+In addition to the rebuilt main airframe section and motor adapter, a
+TeleGPS was added to the nose bay. Then, at the last minute, Meh-ga Nuke
+was equipped with two keychain cameras mounted looking up and down.
+
+The rocket was about 145 pounds on the rail of Terry Lee's launch trailer,
+and was flowing with 2 e-matches and a pinch of Pyrodex P in the Tender
+Descender, and apogee charges of 6g primary and "fill the cup"
+secondary. The rocket departed the rail with about 5.5g max acceleration
+on the way to Mach 0.7 and an apogee altitude of 9183 feet. The dual
+deployment process worked as designed, but unfortunately the shround on
+the main tangled, probably due to a hasty repacking of the deployment bag
+during assembly on the rail. Wind pushed the airframe ENE out of the
+optimal landing area and into a "field of rocks", where the higher than
+expected landing velocity of the main airframe and fin can assembly and
+wind drag resulted in cosmetic damage to the fin can and more significant
+damage to the main airframe tube. The nose cone also suffered damage as
+a result of the wind causing the chutes to pull it across rocks.
+
+Both TeleMega boards returned good data logs. The TeleGPS in the nose
+cone wasn't heard during launch and flight (it turns out the unsupported
+antenna wire broke off sometime before landing, perhaps even before
+launch?), but the data recovered from the board shows a clean trace of
+the nose cone's path during flight. Good thing we didn't need the
+GPS to locate and recover the nose cone!
+
+The video from the up-looking camera worked great through apogee, but
+unfortunately the video froze before the main deployed so only audio was
+recorded for the rest of the flight. The down-looking camera video came
+out very well, though! It shows only a couple rotations of the airframe
+during ascent with some great view of the flight line, etc. It also
+captured the nose cone and two 5 foot surplus military parachutes deployed
+at apogee travelling past the main airframe rapidly at apogee. The
+shadow of the nose cone and associated chutes descending independently can
+be seen in the video before landing... and the very violent landing of
+the fin can and main airframe can be clearly seen.
+
+All in all, this second flight was another huge crowd-pleaser and very
+satisfying overall. Particular thanks to Terry Lee for his help
+rebuilding the main airframe and the use of his launch trailer, George
+Barnes IV for his outstanding photos on launch day, and my wife Karen who
+attended the launch with great enthusiasm despite being only a few weeks
+into the recovery from major surgery.
+
+I think the primary lesson learned from this flight is that the design
+of the airframe pretty much guarantees the main airframe tube is going
+to be damaged in each flight. The video proof of what we already
+understood intellectually about the dramatic reversal of direction the
+airframe
+undergoes at apogee when the nose comes off and the drogue chutes deploy
+alone is enough to rip the leading edge of the airframe apart back to the
+first centering ring below the nose shoulder. So, even without landing
+in rocks and being dragged due to high winds by the main chute, we
+probably just need to acknowledge the main airframe is in some ways a
+"single use" design.
projects / web / gag.com / blobdiff