WH Super Decathlon #2
I’ve owned a set of Wendell Hostetler’s 30% Super Decathlon drawings for probably over 10 years now and just haven’t had the time to build one for myself. I actually built one of these for a customer back in 2008 (build pictures can be seen under 2008 Projects at the left) but it was only built to a point where the customer was comfortable finishing it. The kit that it was built from was a somewhat botched hand cut kit from a cutter out of New Jersey that had to be re-worked extensively. During that process I had made several changes to the design that will be incorporated into the laser cut short kit that we plan to offer. These changes in no way infer that the Hostetler design is flawed and were purely cosmetic or personal preference in nature.
Please be patient as we work out the details and permissions required that will allow us to offer a line of quality laser cut short kits. In the meantime, follow along with the test build of the Wendell Hostetler 30% Super Decathlon which will showcase the quality that we intend to be a part of any kit that we offer…
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A box of laser cut parts for the Decathlon...many, many parts.
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Some of the larger laser cut parts including the 3/8" aircraft ply firewall and the 1/4" balsa fuse doublers.
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The main fuselage sides cut from 1/8" lite ply and the 3/8" aircraft ply wing joiners.
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The laser also gives us the ability to "engrave" part numbers and helpful directions right on the parts.
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The accuracy of a laser cutter just cant be matched!
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Here we go! 1/4" balsa doublers glued to the 1/8" lite ply main fuselage sides with a thin smear of 30 min. epoxy.
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Preparing the fuse sides with the vertical components of the formers.
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Preparing the former tops for installation later.
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Cutting matched pairs of former cross pieces ahead of time will save time later and ensure a square fuselage.
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One of the modifications to the original design was the addition of tabs and slots to the fuse/fin mounting plate. This addition makes aligning the rear of the fuselage a snap.
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Bringing the sides together over the fuselage top view plan.
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Laying out for the fin mounting rails. Future kits will have these marked out by the laser.
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Fin mounting rails in place.
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Squaring things up with the former cross pieces in place.
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The design does not require the diagonal bracing but I add some as a personal preference, These will ensure that the fuse maintains its shape until formers and sheeting are added later. Some of the bracing is temporary and will be removed after sheeting.
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A few more temp braces to help keep the correct curvature of the forward fuselage.
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Front end pulled together and held in place by the interlocking firewall. The landing gear mounting plate is also epoxied in place at this time,
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Tailwheel mounting plate epoxied in place.
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You can see why the fin mounting rails were put in place earlier...much harder to access at this point.
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Not required by design but i like to add some triangle stock to high stress areas. There is also some behind the firewall.
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Moving on to the tail feathers...the elevators are started by cutting the skins to shape. Cut all four, pin together, and sand the edges to be identical.
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Hard to see here but the trailing edges are tapered with a sanding block to 1 3/4". Leave approx. 1/16" of material on the edge. If you do this step ahead of time, be sure to bevel each piece correctly to end up with a right and left top and bottom skin.
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The elevator ribs were cut from scrap 1/8" sheeting. These parts will be laser cut on future kits.
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Balsa blocking added for hinges and control horns.
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One elevator half completed and ready to join to the leading edge.
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Make sure the elevator centerline is vertical and glue it to the leading edge.
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Second half glued on. I will cut the halves apart after the hinging is complete.
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Horizontal stabilizer construction is pretty straightforward and all stick material except for the laser cut center piece.
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Use a straightedge to ensure the sub leading and trailing edges remain straight.
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1/4" square balsa for the diagonal bracing.
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Sheet one side of the stab before removing it from the plan.
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1/4"x1/2" balsa blocking added at the hinge locations.
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Sheet the remaining side and add the 1/4"x1/2" basswood trailing edge.
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1/2" square balsa leading edge will be shaped later.
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The elevator tips are made by laminating two 1/4" laser cut parts together. This is another departure from the original design which was built up from ribs and sheeting.
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Elevator tip sanded to shape. You can see a small dip in the sheeting that is outlined in pencil. This will be filled and sanded later.
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Vertical stab is built using the same processes as the horizontal.
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Framework completed and ready for sheeting.
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One side sheeted. I have added 1/4" square blocking at the edges of the sheeting cutouts...not required but my preference.
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Don't forget the hinge blocks! I almost did on this one.
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Sheeting completed, basswood trailing edge added, and balsa leading edge added.
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Here is the fin nestled down between the mounting rails added earlier.
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The main cabin supports have to be routed out to accept the 1/8" steel wire. This is easily accomplished with a rotary tool.
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Another view of the routing.
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Marking for the angled cuts on F16 and F17. Lay these parts out carefully as they will determine the wing alignment.
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All 4 rails in place one last time to check alignment. There are laser marked lines on the fuse sides that mark their position.
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Getting ready to bend the cabin wires using F2 and F3 as a reference.
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DO NOT bend the wires exactly as they appear on F2 and F3 since they are angled back. You must use the fuselage side view to determine the true length of the upper legs.
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Test fitting once again but with the wires in place.
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Checking the fit of the wire against F13.
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For added security, I bent the ends of the wires 90 deg. so they could be drilled through F16 and F17.
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Here you can see the wire sticking through a 1/8" hole drilled in the cabin supports. The excess will be cut off flush.
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I made up the 1/8"x1/2" alum bar strut mount while waiting on the cabin support epoxy to cure. This strut mount method is different than what is shown on the plans.
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Forward cabin support epoxied in place. Fill the routed area with epoxy and glue the wire to the support all the way to the top as well.
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Test fitting the rear cabin support and checking alignment again with F13, F14, and F15s in place.
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Rear cabin support ready to be epoxied in place.
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Temporary former F4 top in place to help set the curvature of the F15 rails.
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1/8" basswood glued across the two F15s. The temporary F4 top will remain in place for a while.
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1/8"x3/8" balsa stringers added so they can be used to align the fuse top formers.
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Front and rear top formers in place.
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Use a stringer in the center slot to align and position the center former.
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All of the 1/8"x1/2" balsa stringers in place.
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Strut mounting bar bolted in place with (3) 4-40 SHCS and nylon locknuts.
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Follow the guidelines printed on the fuse sides and glue on the remaining 1/8"x3/8" balsa forward stringers.
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Left side stringers glued in place. Notice that the bottom ones taper from 3/8" to 3/16" and that the bottom stringer is 3/16".
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If you wish to build a functioning door it can be cut out at this time. Glue the stringers to the right side of the fuse as you did the left side.
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Laying out the holes to be drilled for the U-bolts. These bolts are actually part of 1/16" wire rope clamps.
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U-bolts in place capturing the cabin wires.
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Rear view of the U-bolts and nuts. I will either use a liberal amount of locktite on these nuts or most likely replace them with nylon locknuts.
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Placing and aligning the bottom front formers.
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Bottom rear formers glued in place.
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Bottom front 1/8"x1/2" balsa stringers.
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All bottom stringers glued in place.
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I glued some 1/4" sq. balsa to former F8 top to help align the vertical fin.
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Former F8 glued in place. F5 - F7 tops are also in place at this time.
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3 of the top rear stringers glued in place.
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Another view of the top rear stringers.
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The outer 2 top rear stringers are a little tricky in this area. Wet the balsa to prevent it from cracking as you curve it in place.
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All the stringers set and ready to start sheeting. I set the tail feathers in place just to check it out.
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Left side sheeting started aligning it with the uppermost stringer.
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Forward top sheeting glued to the side sheeting prior to wetting/fitting.
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I made a copy of the cabin window area so I could make up sheeting for this area.
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I'll start with this and cut the windows out later.
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Glued in place and windows marked out.
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Left side window cutouts. I decided to run this sheeting to the top of F15 instead of trying to fit it to the shape of the wing. The reasoning will be clearer once the wing center section is built.
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Right front top sheeting completed.
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Right side cabin area sheeting applied.
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1/4"x3/8" basswood cross member added at F4 above the windows. When the epoxy cures I will remove the lower cross brace.
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Bottom sheeting soaked before fitting/gluing.
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Previous piece glued in place. Some of the Decathlons curves are challenging for 1/8" balsa to navigate.
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Cutting a slot in the bottom sheeting to fit around the strut mount bar.
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Part of the bottom sheeting in place.
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Sheeting sanded to an angle to get a good glue bond with the bottom sheeting.
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Rear corner sheeting is tapered to transition into the flat bottom.
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Bottom front sheeting shown completed.
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Continuing on with the bottom rear sheeting.
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I used crossgrain sheeting to finish off the bottom rear.
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All the sheeting sanded to the proper angles.
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The rear of the sheeting where it transitions to flat. I will have to add small tapered pieces on the bottom stringers to give the covering somewhere to adhere to.
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Rear side stringers added. Saving these for last allowed me to use up any pieces that were cut from other stringers since they can be spliced anywhere.
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Hard to see in this photo but I have doubled the thickness of the sheeting around the windows to stiffen this area up a little, I've also added a 1/8"x1/4" balsa stick to the bottom of the rear window to give something for the "glass" to mount against.
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I cut about 1/16" off of all sides of the cabin door except the top. Later i will add sheeting on the sides to get a good fit to the fuse. It will be much easier to sand the added sheeting than all of the materials that make up the door.
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Building up the door to be the same thickness as the fuse side.
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Medium Robart hinge points will be used for the door hinges.
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I didnt add blocking for the door hinges figuring that they would pass through the 1/8" plywood side and be secure enough. Turns out that the hinges have to be angled such that they just barely make it to the ply. I will remedy that situation by retrofitting some hinge blocking.
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First block fit in place.
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Blocking sanded flush and the hinge location laid out again.
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The door is ready to drill for the hinges...again.
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Oops...forgot that was there.
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Blocking cut to fit around the cabin support.
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Much better now.
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Looks like a working door to me.
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Getting the window sheeting ready.
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The top half of the door/window is framed up out of 1/8"x3/8" balsa sticks.
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The upper half is a little fragile until you can take it off and reinforce all of the glue joints.
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Window cutout completed and doubled on the inside like the rest.
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Finished door/window.
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Works good for now but I will do a final sanding/fitting later.
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Rollin out the wing plan!
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The 4 main wing spars have to be spliced to get all the way out to the tip. Use a kerf joint and make sure you get a good fit.
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Spar splice glued together along a straightedge.
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I used 48" long basswood for the spars which meant that i only had to add about 1 1/2".
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Having the sheer webs laser cut makes building the wing go quickly. I was able to square up the first rib and then glue in webs/ribs all the way down the line without having to square up each piece.
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From rolling out the plan to here in about 15 minutes.
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1/4" balsa trailing edge added at the aileron opening.
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W3A and some laser cut gussets added.
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Between the spars is filled solid with basswood at the strut mount locations.
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Tip rib W6 is larger than all the rest so that it doesn't need to be cap stripped. Here I am making a W6A to catch the leading edge sheeting. Future kits will have these parts laser cut.
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W6A glued in place as well as the top spars.
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Time to work on the wing joiner boxes.
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Use the 3/8" plywood joiners to make sure you have a good fit inside the box. Be sure to pull them out before the epoxy cures just in case some epoxy oozed into the box.
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I used some epoxy/milled fiberglass to make a fillet between the plywood joiner box and the ribs it fits up against.
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Front joiner box is constructed just like the rear. Be sure to use the correct plywood joiner (F13/F14) as they are different sizes.
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Splicing the 1/4" balsa sub leading edge.
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Sub leading edge glued in place flush with the tops of the ribs. you can also see the balsa infill on top of the spar that will be sanded to match the ribs.
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Sand the sub leading edge to follow the contour of the ribs.
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The tops of the joiner boxes have to be fiberglassed prior to sheeting the wing center section. I chose to tack the cloth in place with thin CA and then brush thinned epoxy over it.
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Here is another personal preference departure from the original design. I like to have some sheeting at the trailing edge to stiffen it up and to give more surface gluing area for the tapered trailing edge.
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Splicing the top leading edge sheeting.
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Top leading edge sheeting glued in place.
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Center sheeting almost completed. At this point it is safe to remove the wing from the building board.
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Now that's what i call a cap strip! 1/8"x3/8"x16" long balsa. All of the rib tops can be cap stripped at this time.
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1/2" balsa hinge blocks added.
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Bottom trailing edge sheeting applied and sanded square with the ribs. This is a good shot showing the extra gluing area for the tapered trailing edge that i mentioned earlier.
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The balsa trailing edge glued in place.
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3/32" plywood rib doublers and servo hatch rails epoxied in place. This servo mounting method is different than what is shown on the original drawings.
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3/4" paper tube for routing servo wiring. I wrapped the paper tightly around a 1/2" dowel and slid the dowel into the wing. When i released the paper it uncoiled tight to the 3/4" hole in the ribs. I then wrapped a piece of packing tape around the tube between each rib and spot glued it in place with some thin CA.
At this point I have 34 hours of total build time in this project and should have no problem having it framed up for display at a local RC flea market coming up in 4 weeks. After building hand cut and/or die crunched kits for the better part of 32 years, I can’t say enough about the speed and ease with which a laser cut kit goes together. Combined with CAD drawn parts and plans, the laser cut parts fit together perfectly…the first time…with no sanding required. The charring on the wood edges can mostly be removed with a few light strokes of 120 grit sandpaper (the thicker plywoods require a bit more elbow grease) if you so choose but it has no effect on the ability of glues to soak into the wood for a good bond.
The left wing construction continues below and then picks up with the center section construction. I did not take any pictures of the right wing panel construction as it is simply a mirror image of the left. the important thing is that you remember to build one right and one left panel.
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Bottom sheeting and cap strips started.
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Attach the servo hatch cover prior to fitting the cap strips.
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Cap strips fitted and glued around the servo hatch cover.
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The trailing edge can be sanded to shape after the cap stripping is completed.
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Sand the leading edge sheeting flush to the sub-leading edge.
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Leading edge glued in place.
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Leading edge is rough sanded to shape.
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Gathering up the parts to build the aileron.
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Aileron ribs glued to the bottom sheeting. Notice the cutout for the plywood control horn that will be added later.
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Blocking added for the aileron hinges.
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Top sheeting glued on and everything sanded flush to the front of the ribs,
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Plywood control horn glued in place.
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1/2" balsa leading edge glued in place.
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3/8"x1" trailing edge before shaping.
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Trailing edge after shaping.
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End cap glued on each end of the aileron. This is a personal preference item that is not shown on the plans.
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Aileron taped in place for now.
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Some basswood blocking for the jury strut mount.
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Jury strut mount blocking is 3/4" thick total.
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Taping up the tail feathers to get ready for display.
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Prepping to build the wing center section.
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Plug in both wing panels to ensure proper alignment of the plywood joiners.
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When satisfied with the alignment, glue the center section ribs to the plywood joiners.
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Sub-leading edge glued in place. A little wax paper will prevent gluing the outer panel tight.
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All ribs glued in place with a temporary brace to keep the trailing edge aligned.
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Center section is now off the fuselage and clamped tight to one wing panel in preparation for sheeting.
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Bottom trailing edge sheeting glued in place.
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Bottom sheeting cutout for access to the U-bolt nuts.
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Balsa filler on top of the plywood joiner sanded to match the rib contour.
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Working forward with the top sheeting.
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More balsa filler on the front joiner.
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Top sheeting finished and sanded flush with the ribs.
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Bottom sheeting installed and leading edge glued on and rough shaped.
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Finished center section bolted to the fuselage.
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Everything together for the first time.
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Only the wingtips need installed yet. For size comparison, the workbench is a 32"x80" door slab.
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Aluminum gear drilled for mounting bolts.
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Gear bolted in place.
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Completed fuselage ready to go to sale.
The Decathlon took 63 hours to frame to this point. There is still some work to do before covering but that will be up to its new owner as they fit the motor and electronics.
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