{"id":1137,"date":"2012-02-20T22:21:30","date_gmt":"2012-02-21T04:21:30","guid":{"rendered":"http:\/\/haveblue.org\/?p=1137"},"modified":"2012-02-20T22:21:30","modified_gmt":"2012-02-21T04:21:30","slug":"just-one-word-are-you-listening-composites","status":"publish","type":"post","link":"https:\/\/haveblue.org\/?p=1137","title":{"rendered":"Just one word… Are you listening?… Composites."},"content":{"rendered":"

\t\t\t\t‘Composites’ (which for a very long time I mistakenly equated with ‘carbon fiber’) were always one of those mysterious materials to me – rare, expensive, difficult to work with, but with incredible strength. Something of a real-world parallel to Mithril or Adamantium, if you will. It turns out that there’s nothing really magic about it (though production of carbon fibers is still difficult and expensive) when you consider that the hard fiberglass chairs in a school cafeteria are composite (the fiberglass being the base reinforcing material and the epoxy being the binding matrix).\u00a0 I always wanted to learn more about composite fabrication methods, and lately I’ve been learning more than I perhaps wanted to.<\/p>\n

It started with stumbling across a video<\/a> of some East European F3K competitors having a bit of fun with their DLGs<\/a> (F3K is a class of aeromodeling competition with hand launched RC gliders). I never had any sort of interest in gliders whatsoever – if it didn’t have a motor, what fun could it be? But after watching the video and seeing the incredible capabilities of a 1.5m airframe that you hurl into the air yourself, I was intrigued. I attended a DLG contest in September to learn more about this particular segment of RC flying, and was smitten with the graceful purity of unpowered flight.\u00a0 I now understand what some people see in ballet – I simply had to experience it in a form I could comprehend.\u00a0 After the contest, I decided that I’d like to give it a try myself. Fortunately, Steve Meyer, one of the fellows at the contest (a seasoned competitor who actually qualified for the USA 2011 team) had an old plane that he was willing to sell for a good price and a few weeks later I had my own DLG to try out. Launching it the first few times was equal parts terror and exhilaration, but I started to get the hang of things quickly enough and even managed to catch it a few times (outside square loops on the other hand, well, I’ll give that one a few years). I gained more valuable experience in RC flight during the first half hour with the DLG than I had all summer. I then began to fly it every chance I could get, though the creeping wind and colder weather kept thermals to a minimum. On the last reasonably warm weekend of November, I was flying at the local park, trying to put more power into my launches. When spinning around, my fingers slipped off the launch peg, and I felt more than heard a sickening crack as the plane made a beeline right for the nearest swingset. In retrospect, I had enough time to get my fingers on the sticks and pull up, but was shocked enough that all I could do was watch the impact.<\/p>\n

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Would you believe that this is what it looked like post-impact?\u00a0 Incredibly, airframe damage was pretty minor – a few small creases on the wings, ailerons and horizontal stabilizer.\u00a0 Really a tribute to the sturdy design of Dr. Mark Drela<\/a> and Aradhana Singh Khalsa’s<\/a> beautiful execution of it in kit form (and certainly Steve’s expert assembly of the Light Hawk II).\u00a0 The right aileron servo was completely stripped, but I hoped that it wouldn’t be too horrific to replace and ordered a new Dymond D47 while I surveyed the rest of the damage.<\/p>\n

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This is the worst of it – a crease on the underside of the right wing (with a slightly smaller matching crease on the top surface), and the reflective tape removed to reveal the stripped servo.\u00a0 The servo has been glued in place, so I’ll need to Drem-mill (Drem-mill?\u00a0 Dremel? Get it? Eh?\u00a0 Er, never mind…) it out of the pocket.\u00a0 Fixing the crease itself would probably be easy, but fixing it well<\/em> seems a more daunting task.\u00a0 Steaming small dents out of the wing (which is a high strength blue foam covered in Kevlar) works quite well, I found – just pour boiling water over the dent, and the foam magically reverts to an undamaged state (or use an iron pressed against a wet paper towel on the wing).\u00a0 These creases however, don’t steam out – trust me, I tried.\u00a0 So I’m saving them for later while I get up to speed with the basics of composites.<\/p>\n

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This is the left wingtip, where the launch peg is located.\u00a0 You grasp the peg with your index and middle fingers, whirl around, and release the plane (a left handed pilot would have the launch peg on the right wing).\u00a0 I think the crease in the Kevlar skin just above the peg may be the result of the sickening crack I felt\/heard (honestly, I though the peg itself had snapped off).\u00a0 From what I’ve read, this is caused by swinging your arm downward on release (a natural movement, as it’s how you would throw a baseball).\u00a0 This makes sense, as the buckling happened only on the underside of the wing.\u00a0 My plan is to poke a few small holes into the crease, use a syringe to inject epoxy into the damaged area and clamp it to a flat surface while it cures.<\/p>\n

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For anyone wondering “why is it made out of Kevlar – you expecting to be shot at?\u00a0 Har har!” – this is the reason.\u00a0\u00a0 The nose took the brunt of the impact from what I can tell, and you can see the cracks at the 4 corners of the rear cutout of the pod where the epoxy matrix entirely failed.\u00a0 If this was just carbon fiber or fiberglass, I’d have a lot of pieces and fragments in the photo and would be looking for a whole new plane.\u00a0 Carbon and glass are strong but brittle, while Kevlar is extremely tough and the fibers will remain intact to hold the airframe together even with such damage.\u00a0 The nose is one of the most interesting parts of a DLG, if for nothing else than the sheer density of components.\u00a0 The battery is crammed all the way forward with two small servos behind it (I don’t even want to think of the difficulty in getting the control rods connected), followed by a voltage regulator and low voltage beeper, with the radio receiver bringing up the rear.\u00a0 There’s even a ballast tube further back sized for tungsten weights, but I haven’t even gotten to that point yet.\u00a0 The red cord coming off the side of the nose is the charging plug, which you remove to turn on the electronics (this eliminates a standard power switch, saving precious grams).\u00a0 Custom wing airfoils, specific weave patterns of fabrics, CNC made molds for airframe components – these are standard fare for top competitors, making DLGs truly the F1 cars of the air.<\/p>\n

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So as a new driver with a broken F1 car, it seemed prudent to start small on the repairs.\u00a0 The vertical stabilizer and rudder (light blue) were unscathed, but the tailplane (in yellow-brown Kevlar) sustained a very slight crease just to its left of the centerline.\u00a0 It was in good company – Steve had pointed out the damage on the right side and had explained to me how he fixed it with a little scrap of lightweight fiberglass cloth and CA (CA is short for short for cyanoacrylate, better known as ‘superglue’ for those who don’t frequent hobby shops or RCG<\/a>).\u00a0 I steamed out the crease as much as I could, and then applied a small rectangular patch of fiberglass cloth wetted with foam safe CA (regular CA will partially dissolve polystyrene foam, so you have to be a bit careful with adhesive choices).<\/p>\n

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I used a hex wrench set as a weight to keep the stabilizer flat as the CA cured (a piece of kitchen plastic wrap keeps it from bonding to the cutting mat).<\/p>\n

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The fix turned out quite well, and I had to position this shot just so in order to glint the light off of the repaired area.\u00a0 The ever-so-slight delamination of the Kevlar from the foam core is no more, and the tailplane is ready for action.\u00a0 Still, the rest of the airframe remains.\u00a0 I decided that getting up to speed with epoxy and fiberglass would be worthwhile before diving into more involved repairs.<\/p>\n

One aircraft I’m preparing for the upcoming flying season is a Diamond 2500<\/a>, which is a giant (at least as far as I’m used to) 2.5m powered sailplane. I chose it because my 2m Radian<\/a> has gotten a bit boring, and because I wanted a good platform for FPV<\/a> flying. The Diamond 2500 has a generous amount of room in the fuselage for extra gear, and I’m thinking of making a replacement canopy\/cover that has the camera and associated equipment attached (so I can easily swap back and forth between camera ship and sport flyer). So the first thing I tried was to just make a rough copy of the existing canopy.<\/p>\n

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I started with a piece of plastic wrap taped over the canopy (it easily peels away from cured epoxy) and then draped a piece of 1.4oz (the weight for a square yard of material) fiberglass cloth over the canopy and carefully wetted it out with laminating epoxy by using an acid brush.\u00a0 Once that layer was done, I thought I’d be adventurous and put down a strip of Kevlar tape (which is just the name for a ribbon of woven material – there’s no adhesive involved), which I also wetted out.\u00a0 Finally, I added one more piece of 1.4oz fiberglass and wetted that out, then covered the whole thing with another piece of plastic wrap (hoping that it would help squish down the layers).\u00a0 Well, I now see the value in vacuum bagging, as the Kevlar strip has air inclusions all along it (you can see that it’s only partially wetted out in the center).\u00a0 I was trying not to overdo the resin (very dry layups are the norm when building DLG gliders – every gram counts), but without bagging, there’s no good way to eliminate the trapped air without simply adding more epoxy.<\/p>\n

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Once I peeled off all the plastic wrap and trimmed the edges, it didn’t look that awful for a first attempt.\u00a0 Rather floppy, though – a little less rigid than if it were made from blister pack plastic.\u00a0 Still, I had absolutely zero concept previously of how a completed part would feel, so now I know that more layers are needed to get the rigidity I need for the part (and that skipping the Kevlar tape is a good idea).<\/p>\n

Now that I have some bits of fiberglass, carbon fiber and Kevlar, I realize how useful these can be in simple household repairs.\u00a0 Superglue and epoxy by themselves rarely hold up as well as hoped, but adding a bit of reinforcement can do wonders.\u00a0 On a replacement rearview mirror I purchased for my truck, the plastic tip was broken off in the package.\u00a0 I figured a superglue-only repair would likely fail in short order, so I used a few small pieces of Kevlar and carbon fiber tow sandwiched between patches of fiberglass to act as reinforcement.\u00a0 Dousing them all with CA and letting it cure provided a reasonably stout repair that has held up just fine for several months (and will probably outlast the truck itself).<\/p>\n

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Ugly, but far more expedient than getting a replacement (and being on the backside of the part, nobody will see it anyhow).\t\t<\/p>\n","protected":false},"excerpt":{"rendered":"

‘Composites’ (which for a very long time I mistakenly equated with ‘carbon fiber’) were always one of those mysterious materials to me – rare, expensive, difficult to work with, but with incredible strength. Something of a real-world parallel to Mithril or Adamantium, if you will. It turns out that there’s nothing really magic about it […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[6],"tags":[],"class_list":["post-1137","post","type-post","status-publish","format-standard","hentry","category-rc-aircraft"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/posts\/1137","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/haveblue.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1137"}],"version-history":[{"count":0,"href":"https:\/\/haveblue.org\/index.php?rest_route=\/wp\/v2\/posts\/1137\/revisions"}],"wp:attachment":[{"href":"https:\/\/haveblue.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1137"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/haveblue.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1137"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/haveblue.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1137"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}