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RWS327-Building the Wings
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Ribs complete, Spars built now it is time for the first dry fit of the ribs to the spars. Wow! It really could turn into an airplane.
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I started assembling the first wing Feb 99 and then stared at them on my bench for a year while doing other things.
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The first thing to do was to line all the rear wing spars up and using a carpenters square draw a pencil line at each rib station across all four spars on the side with the web. If the intercostals are correct, the lines will end up to one side of each intercostal. Then match each rear spar with one front spar. Lay the front spar webbing down next to a rear spars and using the square, draw matching lines on the front spars. " |
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Upper Wings |
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To assemble the wings I slid the ribs onto the rear spar, webbing to the rear, being sure to put the shortened ribs at station 0 and 72 (59 3/4 for lower wing) so that they match the doublers.
Now is the time to add the spar doublers to the front of the rear spar where the bolt blocks and over the scarf joints of the rear spar. I didn't do the scarf joints on the front spar until just before adding the nose ribs; this made it so the front spar would lay flat on the table.
I laid the front spar, webbing down, on my table, then set the rib/rear spar assembly on the front spar and lined up the ribs. At this point I stopped to double check everything. Are the spars facing the correct direction? Ribs all the same direction? Did I use upper or lower ribs? Is this a right or left wing? Once satisfied that all was correct and lined up I opened the glue bottle.
One at a time I pushed the front end of a ribs over just enough to apply glue to the matching intercostal, moved the rib back into place and nailed it down using two brass coated nails as specified, making sure that each rib was properly aligned. I used the brad driver shown on the tools page.
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I applied glue to all ribs, but before the glue started to set, I clamped one carpenters square to each of the end ribs to make sure the dried square.
After the glue had set I one by one slide each rib about 3/8" to one side and applied glue to each side of the rear spar where the rib went. Then slide the rib back. Then before the glue starts to set I "eyeballed" from each end to make sure that the tail end of all ribs were aligned on the rear spar and that the wing was straight. I clamped the squares in place again while the glue dried.
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The next step is to glue on the trailing edge. I held the trailing edge pieces next to one of the spars and drew matching marks at each rib location. I applied glue to the tail end of each rib and set the trailing edge piece in place. I used heavy rubber bands at each rib to hold the trailing edge down tight against the ribs while the glue dried. The rubber band is wrapped over the T.E., passed under the gusset and looped around the 5/16 x 3/4 piece you see at the lower left corner.
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Checking the alignment of the T.E. You can see more of the rubber band usage on the wing to the right. (Messy Basement)
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Once the ribs are glued to both spars and the trailing edge I added the 3/4" square antidrag braces.
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A close up before the compression brace was installed. (Next time the compression braces go in first)
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The root brackets are installed and attached to the center section. Now back to the basement to add the compression, trailing edge diagonal braces and the I-strut/flying/landing wire attachments.
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And the compression members.
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Trailing edge diagonal brace.
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Although Roger's method of attaching the I-Struts is simple and can be done by just about anyone, it uses a lot on bolts and brackets. I chose to do mine the way many other planes are done (including "EL Gordo" by David Morrow). This is by using a cross pin that has a tapped hole, anchored in the spar block. I am using 5/8" 6061 drilled and tapped to 1/4-28 thread (AN4 size). Rather than drilling through the spar cap I decided to add a 1/2 birch ply doubler to rear of the front and front of the rear spar. To make sure I drilled the boltholes correctly, I made the cross pins and inserted a bolt (I am using non AN bolt for the design phase). The doublers were match drilled to 5/8" while clamped in place. Then placed the metal part in the hole of the doubler, lined it up correctly and drew a pencil line on each side.
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I then took a backed hobby saw and cut a small groove between the lines. After that I clamped the doubler back in place and drilled a hole with my smallest bit following the grove, I enlarged the hole one bit size at a time until it was 1/4. I used a 1/4" round file to clean up any interference. I extended each hole beyond the pinhole so that bolt threads could protrude beyond the cross pin. In these two pictures you can see the setup when it is ready to be glued. I have found that by raking the plywood surface with the hobby saw it does a very nice job of deglazing the plywood with out making a lot of saw dust. The set ups you see here is for the lower wing, it has two holes, one anchor on top for the I-Strut and one on the bottom for tie-downs. The smaller set up on the right is for the rear spar.
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1" foam nose ribs and 1/8" Plywood nose ribs were made using a plywood template on table mounted router and a 1" straight sided bite with a bearing at the tip.
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This is a close-up of the backside of the template. Note the tips of the nails are group down in diameter so that they can more easily be pressed into the rib material.
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Once the foam ribs are routed to shape holes are cut allow access into the D-cell. I think it doesn't make much difference in weight. I used a can of clams as my guide and the first one was the template for the rest.
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I am using plywood ribs on the ends and foam ribs in between. Here I am cutting slots in which to install the 5/16 x 5/8 member that runs along the nose of each wing. First I cut the slots in the Ply ribs and the stacked them with the ply ribs on the ends and cut the slots.
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In this photo you can see the 1/4" sq. stock used to glue the ribs to the spar.
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Here are the ribs that required special treatment. The top one is as used on the standard Special, I use these at the root and tip. Note: the one at the root is placed on top of a spar doubler so it needs to have 1/8" from the back before gluing on the 1/4" sq glue piece.
The lower one is a foam rib but has 1/16" trimmed off of the circumference and 1.5MM ply glued on, this one went at station 36 and acts as a backup for the butt joint of the nose wrap. (Rubber bands used to hold it until the glue sets)
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My front spars required three doublers, one at each of the hardware mounting points and one at the spar web scarf joint.
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Here I have the root and tip ribs glued and am starting to add the foam ribs. I found that masking tape worked best to hold the ribs in place while the glue sets. Excel and Gorilla do not affect the foam and hold it well.
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Her I knotched ribs and drilled one hole for the flying/landing wire brackets, the second hole gets drilled when the wings are rigged.
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On the nose wrap, I cut it to size (20"), pulled the edges together and wrapped spiral style some nylon twine to hold it so it looked teardrop shaped when viewed from the end. I did this four sheets to each bundle. Then dipped it in the tub, and let it sit for a few days.
When the wing was ready I held the wrap in place and marked where the nose ribs and 5/16 x 5/8 cross stringer fit with a pencil.
Painted the non-glue areas with varnish and let dry.
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To glue the ply on I did it pretty much as the instructions and videos said, except: I spread glue on all unvarnished areas of the ply and on all upper surfaces of the nose ribs and spar. I used the PVC clamps to hold the ply to the spar cap.
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Then flipped it over making sure it was flat on the table (THIS IS THE LAST CHANCE TO NOT HAVE A WARPED WING), and applied glue to the unglued areas and the 5/16 x 5/8 cross piece. You can see glue on the top (now on the bottom) and the areas the have varnish. It's hard to see but the 5th rib in this picture is cut 1/16" smaller and has a 1" strip of 1/16" ply glued to it's face, this spans the joint in the two pieces of nose wrap. (See figure 21 of your plans)
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Note small notch in the bottom corner of each rib, this is foe drainage if water should get into the wing.
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I used the Plumbers twine putting 3-4 wraps of twine between each rib and making sure that the wrap was on the nose over each rib. Note: I ran the twine so that as I pulled the twine it would pull the wrap up and around the nose ribs (If you go the wrong way it make it harder to get the ply tight). I pulled it tight like lacing a shoe, spayed water on the outside surfaces. I kept tightening and spraying until the ply was down very tight. Next I slid 5/16 x 3/4 (that's what was handy) under at the flat part top and bottom.
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I tightened the lacing again and slid them towards the nose until there was good contact in the areas of most curvature. I slid bottom 5/16 x 3/4 first so the slack moved towards the free (top) edge.
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On the ends of the spar where the blocking is I couldn't use C-clamps on the spar caps so I clamped then like this. Staples work well too.
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Once I was satisfied that I had good contact, I put clamps on the remaining (top in picture) spar cap.
I didn't use the twist sticks, which I think are a good idea and had planned to use, because I didn't need them when I got to that point. I also didn't have the problem of the twine cutting into the spars that others have had, I think because I used 3-4 spirals of the twine per rib bay, which meant less pressure on each wrap of twine.
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I used 1/4" pieces to add extra pressure over the ribs to make sure I had good contact.
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String, weights and wax paper to keep the joint tight as possible.
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Wing tip info is below with the bottom wings.
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Top Wing center section |
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Started Saturday, 20 Jan 2001
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Here is the front Spar for the upper wing center section. It is Douglas Fir (D.F.), Spar caps are 1 3/4 x 3/4, blocks are 3/4 7-ply plywood. The rear spar is 3 1/2 X 3/4 D.F. They will be covered on both side with 1/8 Birch Ply. |
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One of the 1/8 play webs glued on, the cavity is varnished and the non-glued areas of the second web is varnished and ready to be glued. The rear spar is solid Douglas Fir with 1/8 ply skins. Sept 15 2001
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After gluing, the ends of both spars are trimmed to a 5-degree bevel. The front spar is 35" and the rear is 32". This picture shows a close view of the front upper center section spar joint. The OSB blocks are stapled in place to help maintain the 5-degree angle and will be removed later.
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A view showing both front and rear spar to rib joints.
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Lower Wings |
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I build the lower wings the same way and time as the upper wings and then did the necesary steps to finish the flapperons.
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This shows the locations of each of the different ribs I used in my lower wings. Note station 84 does not have the radius cut of the plywood in the aileron area.
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Here you can see the extra aileron rib at station 83.5. Note the non-glued 1/4 spacer between the ribs; it also worked as a place on which to hook the rubber band.
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My flapperon hinges are also a modification. The tip hinge is a 1/4-28 x 1 1/2" with the head cut off and ground to a bullet tip. |
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The next step was to take a 3/16 fender washer and drill it with a number 3 bit and tap it with a 1/4-28 tap, and screw it onto the bolt until it seats against the unthreaded part of the bolt. This assembly is then inserted into the 1/4" hinge hole in the tip end of the flapperon and a 1/4" washer and nylock nut added. A piece of UHMW (Ultra High Molecular Weight Polyethylene is light weight, has a high tensile strength and is as simple to machine as wood. UHMW is self-lubricating, shatter resistant, and abrasion resistant as well. White Color.) will be bolted between the flapperon and the wing to add additional bearing surface.
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The center hinge is also a 1/4-28 x 1 1/4 (AN4-8) with a tapped fender washer screwed on until reaching the unthreaded part of the bolt. In this photo the nut has not been tightened. |
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The hinge strap is slotted and a piece of UHMW bolted to it increase bearing surface and lubrication.
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The root hinge has a bolt on plate that has a 3/8" square rod pressed in and welded to a hole in a 1/8 plate. The plate is bolted to the root end of the flapperon. The square rod extends through a UHMW bearing and into a socket inside of a torque tube inside the fuselage. The 1/4" bolt you see was use to align everything for drilling mounting holes. This photo is before the pivot hole was enlarged to fit the 3/8" rod and before lightening holes were drilled |
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When I made the wing tip bows I planned for the shape that I liked and would work with the spar tips as build. I held the wing tip bow in place and marked the trailing edge, spar ends and the part of the nose stringer that extended beyond the tip rib, so the could be cut to the correct length and angle.
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The stringer tip was cut to act as a gusset.
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The front spar tip was cut 8 7/8" at the short side of the angle.
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The rear spar tip was cut 7 7/8" at the short side of the angle.
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I did some modifications to the tip ends of each spar to get the wing tip shape that I wanted - more like a Pitts. This is the finished product
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The tip bow is 3/4 tall and needs to be cut top and bottom to taper at the trailing edge.
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Cutting the trailing edge of the aileron loose, two cutts here to give a gap.
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What it looked like after timming.
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Trailing edge of tip with gusset added.
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Marking a 45 degree line to follow when cutting the aileron loose.
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Cutting the aileron loose with an Exacto saw. Note: the root and tip hinges are installed, but the center hinge is facing the wrng directions.
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The cut for the root rib, the tip was the same.(The bolts and screws are temporary)
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The aileron is cut free at last and it moves up and down -- Wow! is this fun.
(Oh well, I guess you had to be there)
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Cutting a knotch for the "1/4 x 3/4 with a 45 degree bevel cut fabric attach stringers" to fit into.
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Gluing the fabric attach stringers to the rear of cut ribs, I used the trusty plumber's twine to hold these securely in place.
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I added 1/16th x 3/4 ply cap strips to the top and bottom of each rib.
Reasons: Ties the ribs to the front spar
More glueing area
Strengthens ribs in all directions
Replaces the "patch gussets" that help hold the fabric attach stringers in place
Roger said it was OK to do.
8 Jan 2002
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