So I have been sitting on this thread since May, because I was feeling lazy about typing it up.I am an Engineering student, and at my university participate in the Experimental Rocketry Club. With the experience gained in this group, I have decided to get my own High Power Rocketry Certifications. As such, I have built and flown my level one cert. The certification levels go by the size of the motor. Level one, for instance includes H and I motors, for reference; the kits you probably launched at your neighbors cat when you were little had between an A, and C motor. Each letter, doubles the total impulse of the motor, with an H motor having between 160.01–320 Ns (36.01-71.9 lbs). On my particular rocket, the first launch was flown on a single use H550 motor (with a burn time of .6 s). This short burning, high thrust motor was chosen because the rocket was actually designed for my level 2 certification, with allows J, K, or L motors; and as such the mass of the rocket requires a higher thrust. With my H550, the thrust:weight ratio was ~7:1, well with in the margin of safety. Okay enough of the rocket science for now....I decided I wanted to built from scratch instead of a kit, and that I wanted to base my design off of the Sidewinder Missile. Luckily, someone had acquired some diagrams and schematics of the real sidewinder missiles through FOIA requests, and I was able to scale off of them. The original Sidewinder AIM-9 has a diameter of ~5", while mine is ~3.25". I modeled the entire rocket based on these schematics in Solidworks, and made my modifications; including my motor mount, nose structure, and couplers while maintaining the external dimensions and styling of the real sidewinder. Unfortunately, one of the reasons I have been putting off this thread; is that I had a hard drive fail that housed all of my cad modeling and rocksim files, otherwise I would share them. I do have rev1 of my models, but they are based on a 2.6" diameter instead of the 3.25" my project evolved to. Here are my reference files, as well as the only surviving (although outdated render). If anyone does want the outdated cad models, I'd be happy to share.Reference SchematicsOld RenderThe last two bits of reference material focus on the nose design. The nosecone has to be tethered onto the body of the rocket, and parachute. This means you need a very strong hardpoint to mount the tether on. The way I did it, is similar to another member of the rocketry club. Attached here is a render of the internal structure I used (on a different rocket design). The nosecone is filled with foam, covered in fiberglass/epoxy. It contains .25" allthread epoxied into the nose insert (at the tip), and clamps against the bulkhead, which also helps reinforce the coupler. The bulkhead has a ubolt for the tether, and so the entire nose cone would have to fail in order for the tether to give. Also, to get the exact geometry of the nose, I was lucky enough to have a friend- well mentor that has a real nose from a sidewinder missile I was able to handle and get measurements from.Nose ReferencesThe body tubes for the rocket are rolled on a mandrel. The mandrel is a mailing tube with an appropriate diameter, 3" which will become the ID for the final body tubes. Mylar is then wrapped around the mandrel, so that the fiberglass will not stick to it. I used 6oz plain weave Fiberglass cloth from Raka Inc, with US Composites 635 epoxy resin, with a 3:1 ratio (medium set time). Each body tube has 6 full wraps of the fiberglass. It is applied by wetting out the fiberglass across the length, then rotating slightly and repeating the process. I use Bondo scrapers to spread it out. If the fiberglass/epoxy is shiny, you are using too much epoxy. Lastly, a space heater is used to help the epoxy set. You really want your temp between 70-80 degrees frankenstein for the epoxy work. If your shop is too cold, you can construct a 'kiln' with a heater, fan, and several cardboard boxes that encase the mandrel. I have some reference notes + videos of other rocketry club members doing this on another rocket, if anyone is interested I'm sure I can upload somewhere for you. The process is easy, but stressful.The body tubes are slid off the mandrel while still slightly flexible, but no longer tacky, and allowed to finish setting while standing on end. Once they are hard, the mylar is easily removed, since the epoxy will not stick to it. Next, sand the body tubes to get rid of the excess epoxy and fabric texture. PLEASE WEAR A PROPER RESPIRATOR, AND SEALED GOGGLES. Do it outside if possible. You literally are creating glass/epoxy dust. Save what dust you can, it can be used later as an excellent epoxy filler, just don't mistake it for another white powder. As shown in my pictures, two 40" body tubes, combined weigh just over 2 lb- demonstrating the benefit over a traditional phenolic body tube.The couplers used to connect segments of body tube, are in fact themselves constructed of body tube. They are cut so they are 2x the diameter long, and then cut lengthwise. They are then squeezed in, and inserted half way into the end of a body tube. They are epoxied together, and the OD of the exposed coupler is sanded smooth. Use the filler epoxy + fiberglass dust as needed. You really want 1OD to 1.5OD coupler length extending out past the body tube.For shits and giggles, I made a 6 ply sample of fiberglass/epoxy, and did a tensile test on it. While this really is not the proper test for a composite, it was still interesting to see the yield and failure behavior. During the yielding, you can see it delaminate, and fibers break on the stress-strain graph. The maximum stress is pretty impressive, at over 30 ksi.Body Tube ConstructionTensile TestTensile Test Video (large file size)Next the motor mount is epoxied into the bottom body tube. The mount is composed of several off the shelf components, because they require precision I cant replicate in my low budget shop. They were procured from LOC Precision, however there are plenty of sites you can get this stuff from. The mount tube has EXACTLY a 54mm inner diameter, allowing me to expand to larger motors later. It has several metal hooks epoxied in to hold the motor, when the ejection charge goes off. The 54mm tube is centered in the body tube using several wooden rings. For the level 1 flight, I also made a 54mm > 38mm motor adapter, so I can fly my smaller H motor in this rocket. This component of the rocket is fairly straightforward so I didn't take any pictures of the process.Motor MountThe nose cone is perhaps the most tedious part of the design. In order to make mine, I had to first restore my antique wood lathe, seen here. Anyways, the cad models are used to create a template for a jig. These jig pieces are cut from plywood and assembled, to help in turning the foam core for the nose cone. Pro tip, use carpet tape to keep boards together while cutting on a bandsaw, the stuff is incredible. The adhesive it leaves behind can be removed with acetone. Anyways, the column of foam is made from squares of insulation foam board glued together with 3M 74 spray adhesive, you can use other adhesives, just make sure it doesnt ruin your foam first. This column is then roughed out on the lathe, and then the jig is used in conjunction with some dowels covered in sandpaper to bring it down to the final profile. This foam insert is then attached to the end of a body tube section, and triangles of fiberglass sheet are epoxied down to it. It is sanded, and epoxy+fiberglass dust are used to help fill in low spots. This process is repeated repeatedly, until you are frustrated enough to just cover it with paint.Nose Cone ConstructionAll 8 fins are cut from .25" birch plywood. Like the jig earlier, they are taped together with carpet tape so that I could machine them to be identical to each other. This process is identical to the jig earlier, so I neglected to document it. Once they are cut and sanded, I cut slots through the body tubes to mount them through the walls. I'm sure a dremel would work, but I have a very fun tool I seldom get to use, a Stryker Cast cutter; which did a fantastic job. Anyways, they are epoxied in with 5 minute epoxy, and additional epoxy + fiberglass dust is added on the joint on the outside of the body tube where the fins are inserted. A bondo scraper is used to give them a nice contour (fillet).Fin ProcessFINALLY all is sanded, and painted. I went with the traditional military paint job of black and gray, with a blue for the name. I named it Cerastes, which is species name of the sidewinder rattlesnake- it is painted on the rocket in place of the model designation on the real rocket livery. After the paint job was applied, I visited a museum and took some detailed pics of all the decals on a real sidewinder. I replicated them to the best of my ability, however I have yet to get them made into vinyls. I will add them before my level 2 flight.Paint!Previously I had run simulations in Rocksim to verify my design. my CG is 36" from the nozzle, with the CP 5" behind it- with the rocket being just over 6' in total length, allowing for stable flight. The last preflight test was a ground test of my ejection, to ensure I am using enough black powder for my charge, and that my parachute harness will work. The harness components were all purchased from LOC Precision. The harness includes some nylon webbing to connect the body to the nose, a flame retardant blanket to protect the chute from the black powder, and the parachute. My initial test failed, with the body tube blowing out where a fin meets the tube. After investigating, I sanded my couplers a bit to allow for more play, reduced the number of sheer pins (nylon screws holding nose to body), and reduced my ejection charge a bit. Subsequent ground tests were successful and the rocket was finally ready for launch. I also have video of the failed ground test, but I promise you arent missing anything, its pretty boring as far as catastrophic failures go.Successful Ground Test VideoThe delay for the parachute was set way too long. I intended for ejection at apogee, however it nearly reached the ground before it deployed. Luckily, the increased speed did not prevent ejection. The apogee was quite low, because as mentioned several times this rocket is really designed for much more powerful motors. My simulations for my level two flight predict apogee at ~5300'.LEVEL 1 CERTIFICATION FLIGHT VideoWhen I went to recover the rocket, I found it dangling ~30' up in a tree. Luckily, another member at the launch had a tool (intended to flip breakers on power lines) and I was able to yank it down. Despite the unarrested 30' fall from the tree, the rocket was recovered undamaged, though needing a fresh coat of paint before I apply my decals for level 2! Thanks for reading if you got this far! Sorry for the long post, I wanted to detail it as an archive of my project.Fucking treePS, I realize my shop was a mess. I was working on 5 projects at the time... plus I'm a bit of a pig. via /r/DIY http://ift.tt/2BloBpJ
