This is very important! Ensure you construct a left and right wing! We don't want to end up with two lefts or two rights.... :-)
The wing construction starts off the same way as the stabs. Firstly I cut out a couple of pieces of MDF upon which the wing will be built. Then the wing jig parts are prepared by gluing the parts to be joined together with CA. I used a straight edge to help keep the jig parts straight. The root and tip ribs are at 90 degrees to the trailing edge. Once again, marks were made on the MDF to help align the jig base.
All the ribs and spars need to be removed from their panels. I suggest using a sharp scalpel and steel rule for doing this. If you try to break them out you may damage the part. Some of the spars will need to be joined. Simply line the spar up against a straight edge and hit it with CA. The main spars will be stripped from a suitable piece of 1/4" balsa and will probably have carbon tows laminated to the bottom side of each one.
A dry fit of the ribs and spars is done to make sure all fits well before gluing the doublers onto certain ribs as shown in the drawing. Take care not to run CA into the gap between the ribs and the jig as this will make separation later more difficult than it needs to be.
The wing spars are stripped from 1/4" balsa sheet. For this build I will be adding carbon tow to each spar for extra stiffness. The first job performed on my new CNC router was to mill a 1/8" slot in each spar for the carbon to be laid into. A video of the slots being cut is here.
I laid some 12k carbon tow into the spar slots with laminating epoxy resin. The spars were placed on a flat surface to allow curing. As you can see from the photos below, I grabbed everything I could to weigh the spars down to keep them flat. :-)
There aren't many doublers in the wing, only three on the root rib R1. You'll also need to laminate the two tube socket ply ribs (R5A) together. CA was used to glue the doublers and tube socket ply rib.
The tube socket hole was a little too big for the actual socket. This will be adjusted for future kits. To remedy this issue, some 0.5 oz glass cloth was epoxied around each rib socket hole. See picture below. Of course, you will need to cut the socket to length and glue into position with 30 minute epoxy. The ply socket rib R5A is placed halfway between R5 & R6. You can see from the pictures that I just made a pen mark on the spars and then aligned the glue joint of R5A with these marks. I also made sure that R5A was square to the base board.
The aileron hard point is laminated from four pieces of 1/4" balsa (laser cut). I just placed them into position and hit them with CA. Done!
As per the plan, 1/16" balsa shear webbing is fitted to the front of the main spars and also the rear of the spars behind the socket. The shear webbing is supplied in the kit. CA was used to adhere the shear webs.
The next step is to figure out how the wings will be attached to the fuse. this needs to be decided before actually sheeting the wings.The wing can however be separated from the jig now.
My plan is to use wing adjusters on this model and I would like to have nylon retention bolts at the front and back of the wing. More procrastination required... lol
The wing skins are made with 2.5mm competition balsa. I used 100mm x 915mm (4" x 3') sheets. These sheets are just long enough to do the wing leading edge. Each sheet weighed in at between 16 and 20 grams. The edges of each sheet will need to be trued up. I firstly cut each edge with a scalpel and straight edge. I only take the smallest amount off which is probably around 0.5mm or less. Try to keep the scalpel at 90 degrees to the cutting surface. Then each edge gets a brief sand. I have a 1m piece of aluminium angle with 120 grit sand paper glued to it with contact adhesive. The angle is then clamped over the edge of a flat bench. You'll only need one or two passes to true up the sheet edges. Once true, each sheet should butt up together without gaps.
I start with the trailing and leading edge sheets. Lay them on top of the wing frame and allow about 1/8" of overhang. The leading edge sheet needs a little material removed from the tip. Each time you make a cut, run that edge over the sand paper again. Then tape it together with masking tape. The two sheet can then be placed on a flat surface and the remaining sheets cut to complete the skin.
Once all the sheets are taped together, you can then glue them. Lay the skin joints over the bench edge to open up the joint. Then lay in a bead of Alphatic resin glue. Work it in with your finger and the lay the skin flat on the bench and wipe off the excess with a damp rag. Repeat this process for each joint. Once all joints are glued, lay some wax paper down on the bench and lay the skin down onto it with the masking tape facin up. The grab some weights to keep the skin flat. See picture.... When the glue cures remove all the weights and pull the waxed paper off the skin. Then remove the masking tape over each joint. Your skin is now ready for sanding prior to gluing to the wing frame. Yes, it's easier to sand the skins now before gluing them onto the wing frames. For this job I use a big sanding pad with 400 grit paper on it. It doesn't take much work at all to sand the high spots out of the skins. You want to sand across the grain too.
While the skins were drying, I took the opportunity to laminate the wing tips. Cut the tips from the 1/4" laser cut sheets. There are four 1/4" tips per wing. Again, Alphatic resin was used along with a coupl of clamps. Once the glue cures, sand the edges flat.
I'm going to run paper tubes in the wings for the aileron extensions. I did a small test piece just to make sure it fitted ok. The tubes will be approximately 40cm long and are wrapped around a 15mm mandrel. I cut the paper 60mm wide and about 42cm long. Then add some double sided tape to one edge and start wrapping it around the mandrel. The paper I used is a bit thicker than normal photocopy paper and has a natural curve to it as it's off a plotter roll. Don't try to roll against this natural curve.. This is one of those jobs where an extra set of hands come in handy... I find taping the ends to the mandrel and using a long ruler helps to wrap the paper and hold things while removing the backing from the double sided tape.
The paper tubes are then inserted into the pre-cut holes in the ribs and glued into position.
The anti-rotation pins are cut from 8mm carbon tube. They are cut to a length of 30mm. To make cutting easier and allow a free hand, I drilled an 8mm hole in a piece of scrap 12mm ply. This was held in a drill press vice and a Dremel cut-off wheel was used to cut the carbon. Simply measure out 30mm plus about 1-2mm for the cut. Once cut, the 12mm ply can be used to sand the carbon tube ends square and to the 30mm length.
I added some 1/4" balsa to the back of the root rib where the anti-rotation pins are mounted. This is just for a bit of extra support once glued. The pins will be glued in after the wings have been skinned. this will make it easier to sand the root rib flush. Each anti-rotation pin hole in the root rib was carefully reamed out to 8mm to suit the carbon pins. Future kits will have 8mm holes laser cut into them. The factory Allure anti-rotation are 10mm so you could also ream the 8mm holes out to 10mm.
The time came to separate the wing frames from the jigs. Use an Exacto knife to cut the root rib tabs and then remove the blade to cut all the balsa rib tabs. A pair of tweezers can help in getting into the hard to reach tabs. I'm quite happy with how the weight of each frame came out at 120 grams and 121 grams. The bottom of each wing frame can now be tidied (sanded) up ready for sheeting.
All the wing skins (4) have been glued together awaiting sanding. The weight of each skin is 58 grams so that means we are at 236 grams without the tips, leading edge and trailing edges. It's probably reasonable to target a weight of 275 to 290 grams ready for covering.
I was originally going to retain the wings with thumb screws and blind nuts at the front and rear of the wing. In the end, I decided to stick with the standard 6mm nylon bolt next to the wing tube. This replicates the factory composite wing method of wing retention. To aid sanding of the root rib, an extra hole was made in the root rib to allow fitment of the nylon retention bolt after the wing is skinned.
You'll need to add a couple of 1/4" balsa gussets to the front of the tip rib. Once the wing tip is fitted, you'll actually sand into this area to shape the tips. The top and bottom of this gusset will need to be sanded a little to allow the skinning to sit down on the tip rib. Some more balsa was added to two of the bottom spars to build them up above the ribs. This has now been sanded down flush with the ribs. This minor issue will be rectified on future kits. The weight of the first frame ready for skinning is 118 grams.
All the skins have now been sanded prior to gluing to the wing frames. The starting weight was 58 grams per skin and after sanding this dropped to 52.5 grams per skin. That puts us at 223 grams for two skins and a wing frame without glue.
Now the fun begins.... Gluing the wing skins to the wing frames. As with the stabs, polyurethane glue was used for this task. This glue gives you a reasonable working time and is activated by moisture. It pays to get everything prepared as much as possible before starting to add glue to the wing frames. You'll also need a cheap foam roller to spread the glue and remove any excess. Excess glue is excess wight.
Before we start, make sure all the skins and frames are free of balsa dust. Give them a vacuum and or a blow off with compressed air. The jig that belonged to the first frame was clamped down to the bench. Then the lower skin was placed on top of the jig. A couple of small lengths of masking tape on the trailing edge were used to hold the skin in position. Now we can start applying glue to the bottom side of the first frame. First do the main spars and then the TE/Aileron spars. Use the roller to evenly spread the glue and sop up any excess. The start applying the glue to each rib. I did two or three and then used the roller. Repeat until all ribs are done. Remember to wipe up any runs or excess. I ran one more bead of glue over both main spars and then gave it a quick roll to spread the bead. Before placing the wing frame onto the lower skin, give the skin a misting of water. I used one of those cheap selecta spray things. You don't need much just a misting. Then carefully place the wing frame onto the lower skin glue side down of course. You'll need to make sure the frame aligns with the jig. The top side of the frame can now have polyurethane glue applied to it in the same manner as the bottom side. Once all the top of the frame is glued, mist some more water onto the top skin. The side to be glued of course! The top skin can now be placed down onto the frame. Once again, masking tape was used to help keep the skin in position. The top jig can now be carefully placed on top. Take care to get everything aligned right. An extra set of hands helps with this step. You can now apply some weight to the top of the structure. I placed some off-cut MDF on first and then some old brake rotors I had laying around in the workshop. You could also use bricks. The polyurethane glue will foam up and fill any voids. If excess squeezes out the root or tip just wipe it up with a rag. The wing will need to stay in the jig for four or five hours until the glue goes off.
Im quite happy with how the weights came out. The frames weighed 118 grams each and the skins 52.5 grams each. After skinning the weights were 240 grams and 241 grams. This means a little under 20 grams of glue per wing panel.
Well, the wings have now had the skins trimmed back flush with the ribs and have also been capped. A big gallery of pictures is below.
The weight after sanding the sheeting flush to the ribs was 233 grams. Trailing edges were stripped from 1/4" contest balsa sheet and the leading edge was cut from 1/2" contest balsa sheet. Both the TE and LE were glued onto the wing with Alphatic resin and held in place with masking tape. Once the glue had cured, the LE/TE was sanded flush with the root and tip ribs.
Next step was to attach the wing tips. Before doing so, I marked a centre line on the tip rib extending over the LE and TE. This will be used to help line up the tip block. Alphatic resin was applied to the tip rib and then the tip block centre line was lined up with the marks on the TE/LE. Everything was held in place with dress pins and the trusty masking tape.
The weight at this point is now 267 grams.
Before sanding down the trailing edges, I run a strip of masking tape parallel to the part being sanded. This stops me from sanding into the wing skin. Once flush with the tape, you can then remove the tape. This will leave a small amount of material to be removed during final sanding. This process is repeated for the tips and leading edge. To aid shaping the leading edges, a centre line is marked along the full length of the leading edge.
With the LE/TE and tips all sanded, the weight is now 258/257 grams. All that is left to do now is cut the ailerons out of the wing panel and fit the aileron capping then final sanding. A target weight of 270 grams ready for covering is looking very achievable.
Before cutting the ailerons from the wing panel, we first need to mark out where the cuts are to be made. This can be done by using the jig base as a guide to mark the trailing edges and a light behind the panel to identify the capping slot. With the wing panel on the jig base, make a pen mark on the trailing edge where the aileron root and tip ribs are. You want the mark to be halfway between the aileron root/tip ribs and the adjacent rib. It's pretty obvious where the cut needs to be. Then put a strong light behind the wing panel so you can mark the inboard cutting points. Again, try to make these marks halfway between the ribs and capping slot. Then it's just a matter of joining the dots. Note, the lines from the TE forward should be 90 degrees to the TE. Repeat top and bottom as we will cut from both sides.
To separate the ailerons I used a scalpel and a razor saw. Firstly, with the aid of a steel rule, cut along the previously marked line the length of the aileron. You'll be cutting through some ribs so there will be a few bumps along the way. Repeat for the other side of the panel. Then use a fine toothed razor saw to cut cross grain at the root and tip of the ailerons. Repeat from the other side of the panel. There is a spar that runs the length of the aileron mid chord and this will need to be cut with the saw.
If the above sounds a bit confusing, have a look at the pictures in the gallery below. They probably explain things better than I can.
With the ailerons now successfully separated from both wing panels, we can now set about cleaning up the ailerons in preparation for capping. A Dremel with a drum sander bit was used to firstly clean up the exposed ribs on the aileron LE. You only need to sand them down to within about 0.5mm of the LE. Then I used a razor plane to cut down the sheeting to within about 0.5mm of the LE. A foot long sanding bar with 120 grit paper was then used to sand everything flush to the LE. To make sure things are flat, a final sand was done with the sanding bar clamped to a flat surface. See picture in the gallery below.
The capping is 1/4" contest balsa. Laser cut parts are included in the kit which must be glued together first. Alternatively, you could cut your own capping from sheet stock. You'll want approximately 2mm of overhang all round the aileron to allow for shaping later. The capping is glued on with Alphatic resin and held in place with several pieces of masking tape. Make sure you wipe off any excess glue to make sanding easier later.
The next task is to prepare the aileron cut-outs in the wing panels for capping. I used a large Dremel sanding drum to sand the ends of each rib protrusion almost flush with the spar. This makes planing down the skins much easier and reduces the chances of CA lumps getting under the sanding bar and making a mess of your nice work. The overhanging skins were sanded almost flush with the spar and flush to the ribs at each end of the aileron cut-out. A small 1" wide sanding bar was used for this. Look at the pictures below to understand what I'm talking about here. The skins can then be trimmed with a razor plane along the length of the spar. You won't be able to get the plane right into the corners hence the previous step. I took the skins down to within approximately 1mm of the spars. The balance was then sanded flush with the spars using a long sanding block. We're now ready for some capping! The capping was cut from 1/4" contest balsa sheet. You want a couple of mm overhang all round the capping. Alphatic resin was once again used to glue the capping and things were held in place with numerous strips of masking tape. Wipe any excess glue off with a damp paper towel. The masking tape will round the edges of the capping a little which is one of the reasons for having a couple of mm of overhang. Once the glue is all dry, sanding of the capping can begin. I used some masking tape on the skins to protect them whilst sanding the capping. Sand with 120 grit on a small sanding bar first. You want to sand down to the masking tape. Remove the masking tape and finish sanding with 400 grit flush to the skin. Now sit back and admire your work and try not to choke on the balsa dust!
The ends of each aileron were sanded flush with the ribs in preparation for capping.
The aileron ends need to be capped with 2.5mm contest balsa. I used some of the waste material from which the ribs etc were pulled from. Simply cut the balsa a few mm bigger than each aileron end all round. They'll be trimmed flush after the glue cures. Alphatic resin was used and dress makers pins held it all in position. As you can see from the photos, I cut the balsa into rectangles. The TE/LE sides were sanded first and then a razor plane was used to trim the rest to within a mm of the aileron surface. The trusty masking tape prevents marring the surface with the coarse paper and final sand with a block. Done! We now have about a 1mm gap either end of the aileron once fitted back to the wing.
The aileron leading edges can now be bevelled. The first thing to do is mark them out so you know where to sand back to. A good friend told me a little trick about how to do this so the gap closes evenly with aileron movement. First measure the width of the aileron leading edge at one end. Divide this figure by two. While you're at it, mark the centre on the LE. Now that you know the dimension for half the LE, divide this figure by three. Then take this figure and mark it top and bottom back from the aileron LE. Repeat this for the other end of the aileron. Naturally, the root measurement will be bigger than the tip. Then it's just a matter of joining your marks with a straight edge. A long sanding block can then be used to shape the aileron leading edge. Take your time here to get it right. The ailerons are now pretty much finished. The hinging and control horn fitment will be done after covering.
Both ailerons are now bevelled and the servo holes are cut.
I had a minor issue cutting the first servo hole... During construction the jigs were used to hold /store the wings. Somehow the wings must have moved between the jigs and got turned upside down. Using the jig as a reference, I worked out where to cut the first hole. Unfortunately, the hole was cut on the top side of the wing! #%*^+! Not to worry, I simply said a few choice words tidied up the hole and then glued in some balsa and sanded it flush. You almost wouldn't know now...
Moral of the story... Make sure your wings are the right way up when figuring out where to open up the servo holes!
The weight of each wing came in at 264/265 grams prior to covering which is below target weight of 270 grams. MKS servos will be used throughout this model. The wings will be fitted out with BLS950's which is a standard sized brushless servo.