Archive of the Yahoo! Groups mailing list for the Bug hand-launch glider 2002-2018

From: "Chris Lewis" <christopherlewis@...>
Date: Saturday, May 31, 2003 12:25 PM
Subject: Re: Help with rib production?
John - I'm not a great carver either. Your glass form should work but may take more effort to make and if you have a fit problem where the pod won't slip off of the mold (don't ask) you'll have to start all over, whereas a little more filing, sanding and bondo will save your first wood mold. Here's how I did it: From the home center store purchase the following: 1/2" x 4" x 24" Poplar (fairly hard, smooth grain, easy to work, no grain marks in pod.) Take a rasp and rough-in the approximate LE shape in one edge of the 1/2" Poplar. Move to finer files and then sand paper until the shape is pretty good. It does not need to be exact. Cut two sections 3" long with the appropriate dihedral angle and glue together with wood glue. Set aside to dry. Cut the 1" x 2" in half to make a 2"x 2"x12". Glue these halves together with wood glue and set aside. Draw an approximate shape of your pod. About 3-4" from the LE and about 1-1/2" behind the LE. Make the shape taper to fit your battery diameter at the nose to about 1-1/2" wide at the LE. From the LE back you need to transition to where the tail boom exits in a shape that will allow you to still slide the pod off the mold. A gentle taper, not too rounded. You'll know if you get this wrong when you have to cut the pod off of the mold. :( Once the "wing" portion has dried, I sand off the "V" on the lower side of the dihedral joint to make a nice flat surface to accept the pod portion. Place your pod plan side view on the side of your 2"x2" w/o the seam. You can use the seam that runs fore and aft to make sure that your right and left halves are the same distance from the center line. No matter how much you file or sand away, that seam will always show center in the right/left orientation. Rasp, file and sand the basic shape paying attention to how you'll merge the pod piece and the wing piece. The pod tends to angle down about 5-15% from horizontal. Many of our wives have referred to pods as "penis things". That should give you the idea. Once you're are done carving, glue the pod to the wing and set aside. Once this is dry you'll need some body filler (bondo) to make nice round fillets where the pod meets the wing on the underside of the wing and where the top of the pod transitions to the LE. The PETG will not go into sharp corners and we've found that relying on the natural stretch of the hot PETG to approximate those fillets leads to crappy results. Sand this very smooth and let the bondo cure completely. Drill a hole chordwise into the stubbed TE of your mold and glue in a metal rod (or two) that can be clamped in your vise. I have a hobby vise that clamps to the countertop next to the stove. I clamp the rod in the vise so that the nose is pointing straight up. Heat your PETG, pull the pod, let cool, remove, trim, sand trimmed edges, drill mounting holes, go flying! (refer to the Lil' Bugger photos in the LN group to see how mine is trimmed) Print off Bruce Kimball's pod photos in the LN group as a guide. Bruce makes wind tunnel models for Boeing and is a master craftsman. Note that the LN boom exits through the wing and not under the wing like the Bug, so you'll have to make an allowance for the boom to exit that doesn't show in Bruces photos. Hope that helps. Believe it or not, the form is the easy part. Pulling nice smooth pods that are not too thick or not too thin is the challenge. I still feel that I could do much better. If all else fails, call Scobie at Liftworx.com and ask him to sell you a Seeker pod. Also - Be sure to extend your spars to the wing tip for strength. I made my first wing per plan and had to go back and reinforce it. It just couldn't take the tip launch stress. My Lil' Bugger is on it's second full season and it spent hours being crashed by my 11 and 14 year olds. It has never needed more of a repair than something I could perform at the field and go right back to flying. I'm proud to say that crowds have gathered to figure out what my boys were crashing and then just tossing back into the air. You'd think it was a foamie! Chris in Seattle --- In BugHLG@yahoogroups.com, "John Gospodarek" < John.Gospodarek@i...> wrote: > Chris, > Thanks for the reply. Very nice explanation! I have seen several on > the LN Group and yours is very complete. I have the petg and have a > good idea of how to pull the pod. My problem is how to make the > mold. Do you make two half molds from the root rib template and glue > them together? I am not a good carver and am not sure how to get the > angle correct and a good fit, if I don't do it that way. I have even > considered making a foam mold first and doing a FG lay-up over it. > The mold is the stopping point for me. > > John > > > --- In BugHLG@yahoogroups.com, "Chris Lewis" < christopherlewis@e...> > wrote: > > John - Sorry to hear that you didn't have folks come through for > pod > > material. Next time send me a PM and I'm more than happy to help > if I > > happen to have surplus material on hand. My first couple of pieces > > came through the mail, but I burned through them quickly while > > learning. It's just as well that you have a quantity since pod > > pulling is as much art as science. > > > > The pod is one piece of .060 PETG heated over a stove burner and > > pulled over a form. I use a piece about 6.5" x 6.5 to 8" and use a > > couple of spruce sticks 1/4"x1/2"x7" along with a couple > of "binder > > clips" on each side to hold the plastic while heating. The key is > to > > heat slowly until the PETG is droopy, but not until large bubbles > > start to form. Heat thouroughly from edge to edge by moving across > > the burner. I have a pod mold very similar to the one shown in > Bruce > > Kimball's folder on the Little Nipper group. It has a carved, > sanded > > and faired poplar fuse shaped to my liking and about 3" of wing > shape > > attached to each side at the correct dihedral angle and LE shape. > It > > has a 1/4" steel rod drilled into the TE side so that I can mount > the > > form in a vise that is clamped right next to the stove. Once the > > plastic is floppy - Use gloves! you'll immediately want to > > pull it over the pod form and use your gloved hands to make sure > it > > gets into the corners where the fuse and wing stubs meet. It takes > > work and practice. Pull to fast and the PETG gets too thin. Too > slow > > and it cools and doesn't cover the pod mold. Be patient! Practice, > > Practice, Practice... > > > > Re-read my instructions and step 9 indicates the measure, mark and > > drill method for the intermediate rib spar holes. This extra > wingspan > > is crucial to gaining more float time. I don't use pins. I just > glue > > as I go with thin CA using a capillary tube to restrict glue > > application. Goes fast, works great. > > > > Keep in mind that going to the plastic pod means a total redesign > of > > the airplane. The servos must be recessed in the wing, a boom > mount > > must be fabricated, bolt anchors for the pod/boom mount must be > added > > to the wing, servo linkages changed, pod form built and a pod > pulled. > > Glassing the balsa pod, going to a cruciform tail (supergee > style), > > WPU for tail finishes and extending the wing are simpler mod's if > you > > are just looking to move up from the standard bug. It you like to > > tinker, go nuts. The Bug is an amazing platform to start from or > fine > > just as it is. > > > > After talking with Dick Barker of DLG fame, I might try making > this > > pod in two pieces using Vac-bag method and FG. But I've got a full > > sized Uplink to scratch build first. > > > > Hope that helps. > > > > Chris in Seattle