The Super Chug´s landing gear attachment frames are repaired

Suomeksi

Repair work on the damaged PIK-21 Super Chug (OH-XTM) continues in the Tuesday Club at the Puusepäntie workshop. One of the areas being repaired is the damaged double fuselage frame, located between the cockpit and the firewall. These frames are the front and rear attachment frames for the landing gear, to the lower ends of which the undercarriage is attached. Furthermore, the frames ensure that the nose of the aircraft keeps its shape. The rudder pedals are also attached to the bottom rail of the front attachment frame for the undercarriage. For the rudder pedal cables there is an opening in the lower part of the rear frame.

In the crash of the OH-XTM in August 2024, the undercarriage collapsed and folded under the fuselage, severely damaging the lower section of the aircraft’s nose. At the same time, the lower halves of both undercarriage attachment frames were broken, all the way up to the mid-point of the frames. The upper parts of the frames remained intact. The rudder pedals were still attached on the broken lower sections of the undercarriage frame pair.

When considering how to repair the fuselage frame pair, we decided that it was not necessary to rebuild the entire pair. This way, we avoid having to dismantle and rebuild the intact upper parts of the frames, and the entire area between the cockpit and the firewall. The undercarriage attachment frames will be repaired by reconstructing the destroyed lower parts and joining them to the upper parts that have remained undamaged. We can proceed in this way because we are not making OH-XTM airworthy but rather restoring it to become an exhibition piece.

To join the new reconstructed lower sections of the double frames to the intact upper parts, the stubs of the frames were trimmed to equal length. On each side of the frame stubs the 2 mm thick plywood on the sides, supporting the frame, was removed for about five centimetres in preparation for the upcoming new joint.

Fortunately we have access to the original Super Chug drawings, made by Kai Mellén, which provide precise details of the frame structure and the materials required for their construction. Moreover, our work is made easier by the fact that the frame drawings are at a 1:1 scale, allowing us to build the damaged lower section of the frame and check its shape directly on top of the drawing when the work is under way.

To obtain the material needed for the construction, pine strips measuring 12x12 mm and 12x40 mm were sawn according to the material list specified in the drawings. The wood for sawing was obtained from the Myrsky restoration project, so it is dense-grained and of so-called aircraft quality. We also have at our disposal some 2 mm thick aircraft plywood, also left over from the Myrsky project, to be glued on both sides of the new fuselage frame piece for support.

We began constructing the lower parts of both attachment frames simultaneously. We made all the necessary components for building the frames. Once all the parts were ready, they were glued together to form the lower half of each fuselage frame. We used Casco Outdoor wood glue for the work. The glued lower sections of the frames were then sanded with a disc sander. An opening, as shown in the drawings, was made in the rear frame’s bottom rail to allow the rudder pedal cables to pass through.

Both lower sections of the frames were made slightly too long at the top. This gave us some leeway for making the joints, ensuring that the new undercarriage attachment frames would match the drawings exactly in size. We placed each lower section we had built on top of their respective drawings. They matched their drawings well. The following step will be to join the newly constructed lower sections of the undercarriage attachment frames to the original undamaged upper parts.

Photos: Lassi Karivalo

Translation to English: Erja Reinikainen