X-Git-Url: https://git.gag.com/?p=web%2Fgag.com;a=blobdiff_plain;f=rockets%2Fairframes%2FMehGaNuke%2Findex.mdwn;h=35445aec0b0d2e45ec0b080bb03a7593fb54202b;hp=1d8052865c3b50003fa638b606438041a8d5c5c6;hb=0f1b79405cb0ec823308f6e8cd39c432dc766be3;hpb=e36f482ef663beab1c0ca1646bbf2b6681433033 diff --git a/rockets/airframes/MehGaNuke/index.mdwn b/rockets/airframes/MehGaNuke/index.mdwn index 1d80528..35445ae 100644 --- a/rockets/airframes/MehGaNuke/index.mdwn +++ b/rockets/airframes/MehGaNuke/index.mdwn @@ -110,9 +110,38 @@ 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. The expected increase +in stability should allowing a reduction in nose weight, increasing safety. +It should also make recovery system loading less arduous on the rail. Of +course, this means the rocket will be closer to the length of an upscaled +Nuke Pro Maxx rather than the original Lil Nuke. + +For main deployment, the ARRD is being 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 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 -[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 @@ -163,17 +192,39 @@ 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!