The Slingsby King Kite
Part V: Tricky Ailerons, Wing Sheeting and Fuselage Fairing
This is the fifth part of a six part series. Readers may want to the review previous parts before proceeding with this article.
In the drawing, the aileron seemed to consist of two parts, of which nothing could be found in the photos of the real thing. I therefore decided not to divide it in two parts. Another problem was that the aileron was enclosed on both sides. I therefore chose the same hinges as the horizontal stabilizer; thus the aileron remained removable, as with the horizontal stabilizer.
After cutting off the aileron from the wing, I realized how long and narrow it was — 115cm long and 4.5cm wide. Unfortunately the airfoil choice did not help either as the aileron was only 6–7mm thick. I became convinced that I had to control the aileron in two places and luckily was able to find a place for an extra servo in the wing.
The balsa ribs in the aileron were very thin and fragile so I replaced them all with 2mm solid spruce, took out one, replaced it with spruce, went on to the next, so I kept the dimensions correct.
I wanted to make a plywood D-section for the nose of the aileron. With boiling water I bent U profiles of 0.6 plywood around a 6mm tube and let them dry. I slid the aileron skeleton into this profile and clamped it between a board and a batten. With tape on all surfaces to prevent it all getting glued up. I also built in some twisting. I set it upright and dripped thin cyano between the rib skeleton and the plywood U profile. Now it became much firmer. The trailing edge (TE) is also a sandwich from 0.6mm plywood and balsa. Then I cut and sanded the U profile and the TE into shape. After adding the capstrips and some more sanding, the aileron was roughly finished.
After finishing the second aileron, I went on with the flaps. These were much shorter (56cm) than the ailerons and completely sheeted. They were even thinner than the ailerons, less than 6mm thick so I liked to sheet them in one go.
I took a strip of 9cm wide, 0.6mm plywood, and bent it around a 6mm round rod, whilst pouring it over with boiling water. See also the video Bending 0.6mm Ply Across the Grain (linked in Resources below) for additional information in this regard. Then I clamped and let it dry.
I fitted the skeleton (consisting of spar and ribs) into the folded plywood and now I could mark, cut and sand the plywood. The bottom of the structure was covered with PVA and clamped with a 10x10mm batten and strips of 4mm ply. After the glue had dried I could fold the plywood ‘open’ and drilled holes 1mm from the inside pilot so that the openings at the hinges and rudderhorn could be made later. The top of the ribs were smeared with glue and the whole thing was clamped together. With a Dremel I made openings for the hinges and after some adjustments it fitted neatly into the wing.
I intended to keep the operation of the ailerons and flaps simple; this time not with pull-pull wires, as with the Gull. The pull-pull cables in the wings are complicated and there is a bit more friction which is not good for the centring. I thought to make a pull-push rod on the bottom and a dummy control on the top. Unfortunately I couldn’t figure out how the flaps were operated, so I also chose a pull-push rod on the bottom.
Based on what I saw on a photo I estimated the size of the rudderhorns. I came up with very small horns, I drew them twice too big (by hand). And again I found my friend Adri Brand willing to CNC quite a few. Afterwards the size seemed quite fitting.
The dummy control at the top of the wing was made from 0.8mm steel wire, with a non-functional clip. This rod could move freely in a plastic tube glued to a rib. I made the functioning pull-push rod from an M2 threaded rod with quick links. To remove the aileron — to put the Diacov on — I disconnected the quicklinks, unlocked the hinge pins and then could detach the aileron, dummy rods and all. The flaps only had pull-push rod at the bottom, I made these from 1mm steel wire with a guide tube against bending. After some soldering I could now checked the operating of flaps and ailerons and they worked nicely.
The wings roughly finished, I could now make the fairing. The original had a gap between wing and fuselage of about 10cm; just big enough to mount the wings. After assembly a strip of plywood went over it and I wanted to make it similar.
In the fairing, the grain of the plywood had to run the length of the wing and thus be bent transversely to the grain. Again, see the video linked below for more information on the bending procedure.
After bending the plywood was left to dry, shortened at one side (some length was needed for bending) and then cut off pieces. I started with the TE, narrow pieces, bevelled with a Proxxon power file, with which those tiny pieces can be subtly shaped. They are glued to the end rib and fuselage with thick cyano. Where the curvature in the end rib decreases, I could also take longer pieces. With something long and round I could press the pieces in place while the cyano sets. Sometimes it went wrong and I had to take out a piece. The gap to the wing would be covered by a detachable plywood thing so I had to do the sheeting of the wing first.
I always find it difficult to sheet the D-section of the wing with ply. I enjoyed gluing by semi-dried PVA and heating with a foil iron, but was unable to bend the plywood sharply enough with water and a hot foil iron. This was also due to the profile’s sharp nose. An additional problem being the panels having to be skewed to keep the seam parallel to the longitudinal axis. For that reason I tried to pre-bend the panels, as with the aileron, with boiling water and then let them dry. Afterwards they could be made to fit and be sanded a bevel on it. To prevent cramped fingers I made an attachment: a thin aluminium profile fastened to the worktop with a G-clamp and covered with sandpaper for anti-slip.
I smeared both surfaces to be glued with PVA. The glue had to be spread out still. After drying I put such a panel in its place, it could still be adjusted and then heated with a foil iron to set the glue. The bend in the gull wing was also succeeded with two narrow panels and so it began looking like a wing!
Because the wings are completely sheeted, there are a lot of panels, glued with the same technique, dried PVA and fixed with a foil iron. I had doubts about how that could be stuck to the balsa ribs and thought I should apply twice as much PVA on them. Now the wing was still ‘open’ I could apply some extra glue, but once the top was on, that would no longer be possible.
The completely covered wing now looked robust. Next, I had to shorten the rear of the ply for the ailerons and flaps. I had already shortened the lower ply before applying the upper one, by drilling a few 1mm pilot holes flush with the hinge pins and cutting the plywood along those holes.
Of course, there was still some sanding to be done. The ailerons and flaps remained removable just like the stabiliser. A quick try out to see if everything worked properly, which luckily it did.
The wings were now ready and weighed 936g and 942g respectively.
The connection of the wing to the fuselage was going to be different from what I was used to. The gap between fuselage and wing was covered with a curved strip of plywood. The wing itself is secured with a nylon M3 bolt in plywood lips to the fuselage and wing.
To cover the gap, I made a piece of balsa plywood sandwich for it, which could be slid over the wing from the front, secured with a magnet and a piece of clear tape for safety. Suddenly it looked like a glider! To finish it, the ply was stained with bister, a water based, organic brown colour. Then two layers of dope with some Porienvuller (see Resources) and one layer boat varnish were applied and the ailerons and tailplanes sheeted with Diacov (see Resources).
Next month I wrap up the construction and then it’s on to the fun part — flying! See you next time and thanks for reading.
©2022 Vincent de Bode
Resources
- Bending 0.6mm Ply Across the Grain — YouTube video: “How to bend 0.6 aircraft ply at right angles with the grain, in this case for making the fuselage/wing fairing of a scale vintage glider…”
- Porienvuller — Product page from the Hobma Modelbouw website, a hobby supplier based in the Netherlands.
- Diacov — Product page from the Sarik Hobbies website, based in the UK: “Extra-lightweight iron-on polyester fabric! DIACOV 1000 is ideal for covering scale model aircraft, from…with high tear resistance and temperature stability…”
All images by the author. Read the next article in this issue, return to the previous article in this issue or go to the table of contents. A PDF version of this article, or the entire issue, is available upon request.
