Covering work of Myrsky ailerons
Sunnuntai 29.10.2017 - Member of Tuesday Club
The aileron frames of VL Myrsky II (MY-14) had been finished in the Tuesday Club by the beginning of September. The ailerons were built according to the original Myrsky drawings. A pair of photographs proves this: an original photo of a Myrsky aileron from the State Aircraft Factory and a photo taken of the aileron made by the Tuesday Club. However, the Tuesday Club used modern Casco Outdoor wood glue.
The ailerons of an airplane often have fabric covering even if the plane itself has duraluminium or plywood covering. On the plywood-covered Myrsky the ailerons were also plywood-covered. According to the original drawings the ailerons had 2,5 mm plywood covering in the area between the aileron spar and the aileron’s leading edge but 1,5 mm plywood in other areas. At the aileron’s leading edge the front edge of the plywood covering reached about 3 cm over the wooden leading edge strip. The seam of the 2,5 mm and 1,5 mm plywood plates was located on top of the aileron spar.
When the aileron covering was discussed at the Tuesday Club, the decision was to use a structure different from the one on the original drawings. The 2,5 mm plywood would be difficult to bend into the curving shape of the aileron’s leading edge so instead of the original material thickness, 1,0 mm plywood - which is easier to bend - would be used first to cover the area between the aileron spar and the wooden leading edge. Then the whole aileron would be covered with 1,5 mm plywood.
Using this method there would be no need to bend the thick plywood at the aileron’s leading edge and also the plywood seam on top of the aileron spar would be avoided. The original material thicknesses (2,5 mm and 1,5 mm) in the different areas of the aileron would be reached as the result of combining the two plywood layers. The Tuesday Club wondered why the Myrsky designer had originally chosen a more complicated and structurally weaker method to cover the aileron.
The right wing aileron was covered first. A piece of 1,0 mm plywood was cut to measure, matching the area between the aileron spar and the aileron’s leading edge covering the whole length of the aileron. Some milling work was required before the piece could be fitted to its place. Then the plywood covering was glued into place. Two-component epoxy glue was used with some cellulose fiber added. The glue was spread on the surfaces of the aileron spar, the ribs of the leading edge and the leading edge batten and the plywood covering was pressed on them.
A compressed air stapler was used to make sure that the plywood covering fixed tightly onto the aileron structure. To avoid the staples to drive too deep into the covering plywood, small additional pieces of plywood were placed between the staples and covering. When the glue had dried the staples and the protecting pieces of plywood were removed. Then the front edge of the plywood on top of the aileron’s leading edge and the rear edge on top of the aileron bar were ground thin and slightly slanting.
Now the covering the whole upper surface of the aileron with 1,5 mm plywood could be started. The decision was to use two pieces of plywood and to place the seam in the middle of the aileron. In front of the aileron spar the plywood is attached to the 1,0 mm plywood which was already in place. In other areas of the aileron the thicker plywood would be glued onto the aileron spar, ribs and the trailing edge batten.
First a cardboard pattern was made, matching the area of the aileron. Two pieces from the 1,5 mm plywood were cut based on the pattern. The plywood pieces were milled and fitted into place for gluing. The covering plywood piece closer to the wing root was glued into place first and after that the piece toward the wing tip.
When gluing, the plywood pieces were first attached to the aileron spar using a couple of nails to keep the pieces in the correct position. Then epoxy glue was spread on the plywood which had already been installed and on the spar and the 1,5 mm plywood was pressed tightly against them. Staples along the edges of the plywood and the spar ensured that the plywood was tightly attached.
The work continued to fix the rear part of the plywood onto the aileron structures. Epoxy glue was spread on the ribs and on the trailing edge batten and the plywood was pressed against them. A heavy steel plate was placed on the plywood as weight and clamps were used to press the read edge of the plywood against the trailing edge batten.
When the glue had dried the clamps and staples were removed. Finally the front edge of the plywood on top of the aileron’s leading edge was ground slightly slanting to match the curved shape of the leading edge.
Now the upper side of the right wing aileron had been covered and the following phase will be to cover the lower surface of the aileron. Before that the inside of the upper surface and the inner structures of the aileron have to be protected with varnish. The lower side of the aileron will be covered using a similar method as was used on the upper surface. When the right wing aileron has been covered, the work on the left wing aileron will be started.