X-Git-Url: https://git.gag.com/?p=web%2Fgag.com;a=blobdiff_plain;f=rockets%2Fairframes%2FMehGaNuke%2Findex.mdwn;h=d79cb381879a73c2c7351cfd51dbb1d46c6fa07d;hp=129c34733f4487521f1ed4f23eee20ea8ab5dc5c;hb=b60145e545f2b6b36d7a88591a3f961adf14ccfc;hpb=96b64e92205c407c3d01166e51aa9c7b9e14c60a diff --git a/rockets/airframes/MehGaNuke/index.mdwn b/rockets/airframes/MehGaNuke/index.mdwn index 129c347..d79cb38 100644 --- a/rockets/airframes/MehGaNuke/index.mdwn +++ b/rockets/airframes/MehGaNuke/index.mdwn @@ -11,86 +11,104 @@ Unfortunately, that airframe was one of many lost in the 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 @@ -125,3 +143,60 @@ 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! +