Repairs on Kurki's port wing are almost completed

Suomeksi

The damaged and partly rotten wings of I.V.L.K.1 Kurki are being repaired by the Finnish Aviation Society’s Tuesday Club. The repair work is at the phase where the starboard wing is ready and its new covering is being painted. At the end of January the port wing was brought to the workshop from the Päijät-Häme aviation museum storage in Vesivehmaa. Now the repairs on the port wing have been almost completed.

The rotten plywood covering of the Kurki’s port wing had to be dismantled around the national swastika emblem on both sides of the wing, several square meters in total. Before the dismantled areas could be covered with new plywood, the damaged inner structures of the wing had to be repaired and partly renewed. These repairs were finished in mid-April. The preparations for the new covering included also building wooden bridge structures under the seams where the new plywood covering meets the old. When this had been completed, the installation of the new covering could be started.

The lower surface of the wing was covered first and the work was started at the small dismantled areas between the leading edge and the front spar. New 1.2 mm thick plywood was used, matching the original covering material. After this the large area was covered, extending across the whole width of the lower surface of the wing. There a different approach had to be taken – the original installation of the Kurki covering from 1927 couldn’t be followed.

The Kurki wing is very wide (225 cm) and it has been originally covered with a single board of plywood which is as wide as the wing. Such large boards were not available and a different method had to be used when installing new covering on the lower side of the wing. The existing plywood boards were 150x150 cm. Therefore the wing had to be covered using two sheets of plywood with a butt joint on the rear spar.

Two pieces were cut from the plywood board, one to cover the area between the rear spar and trailing edge and the other to cover the area between the rear spar and leading edge. The pieces were modified to fit in their places. Special attention was paid to the edges meeting at the butt joint: the seam on the rear spar must be tight.

When the plywood pieces had been correctly positioned, supporting battens were fastened on their lower surface, following the original construction where the battens support the covering between the ribs. The supporting battens keep the plywood from bending inwards due to aerodynamic reasons when the plane is in the air. The lower surface of the plywood was protected against humidity using Le Tonkinois varnish.

Casco Outdoor wood glue was used when gluing the new plywood sheets on the ribs, wing spars and leading and trailing edges.

The gluing was ensured according to the original procedure, using 10 mm long nails and 3x12 mm brass screws, following the pattern where after three nails a screw is fastened into the plywood.

Now the large dismantled area on the lower side of Kurki’s wing had been covered with new plywood and the work could proceed to the upper side of the wing. At this phase the wing was turned over.

On the upper side of the wing less damaged covering had been dismantled than on the lower side. The largest area was around the national emblem, between the rear spar and the trailing edge, extending the width of five ribs. Some old covering had also been removed between the front spar and the leading edge, between two or three ribs.

Two sheets were cut from the 1.2 mm thick plywood board, matching the dismantled area between the rear spar and trailing edge. One of the sheets covers the area between three ribs on the left side of the area, the other the area between four ribs on the right.

The plywood sheets were positioned in their places and the supporting battens were installed as described above. The surfaces were protected with varnish. An elongated opening was made for the aileron wire lead-in and the aluminium plate collar, dismantled from the original covering, was installed.

The sheets covering the dismantled area will be fastened on their upper edge to the edge of the original plywood, using a butt joint at the rear spar. The lower edge the plywood will be fastened on the batten of the trailing edge. Along the length of the wing the new plywood sheets will be fastened to each other and the adjoining old plywood, using lap joints. This method was chosen because the original plywood covering of the Kurki wing have been fastened at the ribs using lap joints so that the edges of the plywood sheets overlap a couple of centimeters. The plywood covering has been started from the tip of the wing.

The plywood sheets on the upper surface of the wing will have to be modified a little before they are ready to be glued in place. The restoration work was left at this point  before when a summer break started in the Kurki project. The autumn season of the Tuesday Club will begin on August 14th and the work goes on.

Photos: Lassi Karivalo.