2002 IHLGF Debrief

and

 My First Time to the Rodeo...

by Jay Decker, 7/7/02

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2002 IHLGF Debrief

Greg Norsworthy’s 2002 IHLGF debriefing contained few bits of information that I found useful when considering my next DLG planes:
  • The “revolution” is over. DLG design now appears to be progressing on an "evolutionary" pace.

  • Out of the 70 some odd competitors at the 2002 IHLGF, 10 to 15 guys had huge launches and they were generally the pilots that made it to the fly-offs.

  • There appears to be two diverging DLG design philosophies: 1) design the wing with more area and a little higher total flying weight, e.g., the Encore, or 2) design the wing with a higher aspect ratio and keep the total flying weight less than 9 oz, e.g., the SuperGee. At this point it appears to me that the jury is still out, but Joe Wurts seems to favor planes with the greater wing area design approach, e.g., the Encore.

  • 4-servo wings, flapperon wings, polyhedral wings with flaps and even plain old polyhedral wings all seem to be competitive – yes, it’s still the magician and not the magic in “the wand” (or, how much “the wand” costs).

  • There is an apparent move toward Kevlar wings because Kevlar wings are more durable than fiberglass wings.

My First Time to the Rodeo...

Hmm… Kevlar wings are more durable than fiberglass (FG) wings. I don’t want to build six FG wings, like I did last year, to make through this flying season. So, I decided that I give Kevlar wings ago, cut some AG-12/13/14 Spyder foam wing cores for a new polyhedral DLG and started building my first Kevlar DLG wing. Here’s what I learned during my first time to the Rodeo, the Kevlar wing skin vacuum bagging rodeo that is, and hopefully this might be of some help to you if decide to try bagging a Kevlar DLG wing…

  1. The best single source of how to information on Kevlar DLG wing construction is Chris Kaiser’s Kahu construction article at the Charles River Radio Controllers Web Site (http://www.charlesriverrc.org/articles/kahudlg/chriskaiser_kahudlg.htm). Chris’s article is also an excellent general DLG construction reference. Two other good sources of information, but that require that you sift through message postings to find good information, are the Yahoo! SALglider group at http://groups.yahoo.com/group/SALglider/ and the Yahoo! Allegro-Lite group at http://groups.yahoo.com/group/Allegro-Lite/.

  2. It took about 3 feet of 1 oz Kevlar for the wing skins, that’s 3 feet at $13 per foot, so cut carefully (my foam and FG UpLink wings, cost less than $5 in materials). Chris Kaiser’s technique for accurately cutting Kevlar for wing skins works great.

  3. When compared to bagging a FG DLG wing, it took me an additional three or four hours of prep time before I was ready to bag. Every minute of prep time was worth it after I started mixing resin.

After bagging my first Kevlar wing, I have a new appreciation for why the new crop of Kevlar DLG's on the market cost $300 to $400. Admittedly my shop is not setup for production, but I'd have to charge at  least $500 or more for a Kevlar SuperGee so that I at least made minimum wage.

  1. Cutting the Mylar carriers: 1) cut the top and bottom carriers to extend beyond the TE a ¼ inch, 2) cut the top carrier to extend beyond the LE ¼ inch, 3) cut the bottom carrier 1/16” short of the LE, and 4) cut the top and bottom carrier about an 1/8 inch short of the curved tips and about 1/8 inch beyond the root.

  2. Make sure that you mark the perimeter of the Kevlar pieces on outside of the Mylar carriers. Accurate placement is much more important with Kevlar than FG to minimize time spent finishing after bagging.

  3. Handle 1 oz Kevlar very carefully, it is easy to create runs in the loosely woven yarns. I unrolled the Kevlar onto a clean table, carefully smoothed the fabric and applied wax paper that was coated with a light “mist” application of 3M77 to the Kevlar. I then marked the outlines onto the waxed paper and cut the Kevlar (a variation of Chris Kaiser’s technique).

  4. To get an easily finished Kevlar LE use 1 inch wide strips of ¾ oz FG placed on the LE of Mylar carrier as shown in the figure below. The 1.7 oz Kevlar LE strip was 1 inch wide and was applied to the LE in one continuous piece with 3M77 spray adhesive. After bagging, the LE flash was trimmed with a knife, rough sanded with a Perma-Grit sander, coated with epoxy, blotted off, allowed to cure and wet sanded with 600 to an acceptably smooth finish.

  1. Trim the LE and TE as soon as the resin curing allows you to remove the wing panels from the carriers. Kevlar is much easier to cut when the resin is still a little green. Change or sharpen your blades often, Kevlar dulls an edge very quickly.

  2. I installed CF spar caps and “weblets” per Mark Drela’s SuperGee design. Sanding the channels into the foam core was easy and quick and spar caps do not create bumps in the skins. The “weblets” were also easy to install and I’m looking forward to not having any delamination wing failures in the future.

  3. Put indexing marks on the Mylar Carriers, cores and core beds. I didn’t and found that I had a hard time getting the cores in carriers and carriers on the beds where I wanted them. With FG wings the alignment of the cores in the carriers is not that critical, but the alignment is more critical with Kevlar wings.

  4. After placing the cores on the bottom carrier, apply a very small bead of epoxy and cab-o-sil at the TE of core so that the top and bottom skins do not separate at the TE after the TE is trimmed.

  5. Use slow set epoxy hardener. I didn’t and ended up with a heavy wing (4.5 oz) because I was rushed by setting resin. Next time I’ll use the MGS H287 hardener, which has a 4-hour working life.

 

Kevlar leading edge

Left wing tip. Note the 3 oz bidirectional weave CF patch for the throwing peg.

AG-12/13/14 polyhedral wing halves trimmed, leading edges finished and ready to be glued together.

 
 
 
Photos by Jay Decker, email address:

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