Caravelle's radome is repaired and repainted

Keskiviikko 7.12.2022 - Tuesday Club member

Suomeksi

The radome, disassembled from the nose of the Caravelle III (SE-DAF) which is now owned by Aviation Museum Society Finland, is being repaired at the Tuesday Club. Its painted surface has cracked, and it has been also badly damaged in a collision.

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The radome is made of Kevlar and its surface has originally been puttied and painted with matt black paint. The black paint surface has cracked and peeled off in several places. The white putty and the Kevlar surface under it are visible in the damaged areas.

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The cracked paint and the white putty on the radome surface were chiseled off down to the Kevlar surface. This caused grooves and holes on the radome’s surface. The Tuesday Club team decided to fill the grooves and holes with epoxy filler. This material was also a good choice for smoothing and levelling the radome’s damaged area which had been patched with glass fibre fabric.

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Light epoxy filler (Lightweight Epoxy Filler) and hardening agent were purchased from Biltema. Following the product instructions, a portion of filler was mixed. The filler was spread with metal spatulas on the holes on the radome’s surface and on the damaged area, which had been laminated with glass fibre fabric. A thin flexible plywood veneer was also used when spreading the filler, pulling it on the radome’s surface, following its curved shape. The filler followed well the curved shape of the radome. Several portions of filler had to be mixed before all the grooves had been filled and smoothed.

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When the filler had dried, it was sanded, mainly manually. Sanding by hand gives a better touch on the radome’s curved surface than working with a grinder. After sanding the filler treatment was repeated and sanded again to get a smooth surface, matching the radome’s curved shape as accurately as possible.

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After two rounds of filling and sanding, the team decided to paint the surface with a primer. Spray MAX Primer filler was chosen, and it was purchased from the Pintaväri store. This primer fills well the small roughness on the sanded surface and it can be re-sanded and re-painted.

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Two layers of Sprey primer were spread on the sanded radome surface. Before applying the paint, the cover holes of the radome’s fastening bolts were protected. Although the result after the primer paint looked quite good, the smooth mat black paint surface revealed some uneven areas, and we will still have to fill and sand the radome’s surface in some areas before it is completely smooth and ready for the finishing paint.

Photos by Lassi Karivalo.

Translation by Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, Caravelle, Tuesday Club, SE-DAF

The repairing of the Caravelle's right wingtip

Maanantai 21.11.2022 - Tuesday Club member

Suomeksi

The right wingtip of the Caravelle III (SE-DAF), which was acquired from Sweden by Aviation Museum Society Finland and is now in a hall in the Pansio port area in Turku, has been badly damaged at its leading edge. The damage has been caused by some airport vehicle which has hit the Caravelle’s wingtip during the decades when the aircraft stood on the side of the airfield. There is a dent also in the middle of the tip of the left wing. Furthermore, the trailing edge of the horizontal stabilizer tip and the radome at the nose of the aircraft have been damaged in collisions. The wings, the horizontal stabilizer and the radome will be repaired at the Tuesday Club.

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Fortunately, the tips of the Caravelle’s wings and the horizontal stabilizer can be detached. The Aviation Museum Society’s volunteer team in Turku detached the wing tips, the damaged tip of the horizontal stabilizer and the radome to be taken to Vantaa. These parts were brought from Pansio in the boot of a car and on a trailer to Vantaa, to be repaired at the Tuesday Club.

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The leading edge of the right wingtip is broken along a distance of 40 cm. The navigation light and its uniquely shaped lamp shade are broken too. The navigation light shade on the left wing is unbroken. When repairing the right wingtip, the left wing will be used as a model. 

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The navigation light is badly broken. It may be possible to make a new lamp socket for the light bulb, but it will probably be impossible to make the navigation light shade which has a complicated shape. It can hardly be found as a spare part, either. Well, we can surely ask Le Caravelle Club in Sweden, they have restored a former SAS Caravelle.

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The repair of the right wingtip was started by drilling out the rivets which fastened the crumpled aluminium sheets on the wingtip. After this the sheets could be bent open, and we could get a better view of the damaged tip’s structure.

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We tried to mould the damaged aluminium sheets and see if they could be bent into their original shape. However, the duralumin sheets on the wingtip are made of such hard aluminium that they broke when they were bent back into their original shape. We had to admit that the damaged wingtip can’t be repaired by using the original sheets. The wingtip and its supporting structures will have to be rebuilt from new aluminium sheets. Fortunately, we have the unbroken tip of the left wing to use as a model. We dismantled the whole damaged area of the right wingtip.

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We analysed different alternatives for building the right wingtip and concluded that the broken part will be rebuilt from several sheets of aluminium, which are moulded into the shape of the wingtip and riveted together. For this purpose, a wooden last will be made, shaped as the unbroken left wingtip, but its mirror image. Each sheet of aluminium will be bent into shape against this last and then riveted to each other to form the new wingtip. Before riveting, a new supporting structure for the wingtip will have to be built.

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We started to build the wooden last by gluing together some pieces of plank to make a piece of wood, larger than the wingtip. This piece of wood will be gradually shaped by sawing, carving, planing, and grinding to match the shape of the wingtip’s leading edge. To make the piece of wood exactly match the shape of the wingtip, profile jigs, made of plywood and shaped as the unbroken wingtip, will be used. When the shaping progresses, the profile jigs will be used for testing where the wooden last still needs to be shaped.

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When the glue had dried, we could start shaping the chunk of wood into the wooden last. First the curved side profile of the wingtip was drawn on the piece of wood. A band saw was used for sawing along the drawn line and almost one half of the piece of wood was cut off. Then the shaping continued with a hand milling machine and a plane. When the shaping work is continued, the shape of the last will be checked with the profile jigs. There is still a lot of work ahead before the wooden blank matches the shape of the wingtip’s leading edge and can be used as a last for moulding the aluminium sheets for the broken wing.

Photos by Lassi Karivalo

Translation by Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, Caravelle, Tuesday Club, SE-DAF

The repair of the Caravelle III (SE-DAF) radome has been started

Lauantai 12.11.2022 - Tuesday Club member

Suomeksi

The Caravelle III, owned and brought from Sweden by Aviation Museum Society Finland, is stored in a hall in Pansio port area near Turku. There it is being restored before placing it on display at Turku airport. In Turku the local volunteer team is working on the restoration, which started with cleaning the aircraft’s surfaces before painting. The Tuesday Club has been given the task to repair the damages which have been caused on the aircraft during its long storage period. There is damage on e.g. the right wing-tip, the left tip of the horizontal stabilizer and the radome on the aircraft’s nose. We just can’t help wondering which airport vehicle at Arlanda has managed to bump into the Caravelle so many times.

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Annoyingly, the damage caused by the collision on the radome happens to be right on one of the hatches which cover the fastening bolts of the radome. The radome, made of glass fibre, has bent inwards at an area of about 20x15 cm. The collision has also broken the edge ring of the radome and damaged the rim of the bulkhead on the aircraft’s nose, under the radome. There is also damage on the aircraft’s nose under the bulkhead edge, the metal edge of the nose is bent, and the aluminium covering is creased. The painted surface of the glass fibre radome is also badly flaking.

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The Turku team disassembled the damaged tips of the right wing and the left horizontal stabilizer and the nose bulkhead, with its radar and radome. We fetched the bulkhead and the tips of the wing and horizontal stabilizer from Pansio to be repaired at the Finnish Aviation Museum in Vantaa. The repair of the radome and the wing tip are well under way, the tip of the stabilizer will be repaired later.

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Before repairing the radome, it had to be disassembled from the nose bulkhead. The radome is fastened on the bulkhead rim with three fastening bolts and three guide pins. The bolts can be seen when the hatches on the radome, one above each bolt, are opened.

First the hatches above the two unbroken fastening bolts were opened. Under each hatch a supporting frame could be seen, it is fastened on the radome glass fibre and on the radome’s metal edge. There is a crown-headed fastening bolt in the middle of the frame. The two bolts on the edge could be easily opened and unfastened from the threaded sleeve on the metal rim of the bulkhead. Fortunately also the bolt under the damaged hatch could be opened and after this the radome could be lifted from the bulkhead. We could now see that the radar space under the radome was empty. The radar had been disassembled at some point during the Caravelle’s storing period, but obviously before the radome was damaged.

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When the radome had been disassembled, we could see the damage on the bulkhead’s metal rim, under the radome’s edge. The bulkhead rim is badly bent inwards and broken. It must be repaired before the radome can be assembled back into its place after repair.

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Photo: Reijo Siirtola

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As a preparatory task before repairing the glass fibre radome, the damaged metal frame of the fastening bolt was disassembled. The metal frame has been tightly riveted on the damaged edge of the radome, we didn’t even try to unfasten it in other ways than just by cutting through the radome’s metal edge on either side of the bolt’s frame. The broken area of the radome could now be removed together with the bolt frame.

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Photo: Reijo Siirtola.

The repair plan is to first build a replacing piece for the removed section of the radome’s metal edge. The broken metal frame for the bolt can’t be used any more, so we came up with a solution where a bridge between the radome’s cut edges will be made from strong plywood. The third radome bolt can be fastened on the threaded sleeve on the bulkhead’s rim through the plywood bridge. A metal collar for the bolt will be inserted on the hole on the plywood. This repaired joint of the third bolt will not be as strong as the original, but it will be quite ok for the radome of a non-flying display aircraft. From outside the difference won’t be seen.

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Photo: Reijo Siirtola.

When the radome’s cut edge has been repaired in the way described above, a sufficient number of glass fibre fabric layers will be laminated with epoxy resin on the collision hole on the radome. The laminated area will be ground to match the level of the dome’s original surface. A hole for the bolt hatch will be made into the laminated surface.

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We started to build the piece missing from the radome’s metal edge. A piece of strong plywood was cut, imitating the shape of the missing edge piece. The piece of plywood was glued with epoxy glue as a bridge between the ends of the metal edge. There is still some work needed before the bridge is ready. After that we will laminate the hole in the radome. The edges of the damaged area in the glass fibre dome have already been ground thin for the laminating work.

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, Caravelle, Tuesday Club, SE-DAF