Mil MI-8T HS-4 tail boom stabilizer covering began

Keskiviikko 27.9.2023 - Tuesday Club member

Suomeksi

An example of a Mil MI-8T helicopter, used by the Defence Forces and registered as HS-4, is situated in the Karelian Aviation Museum. The tail boom stabilizers’ covering fabric is rotten and partly lacking altogether. Two thirds of the area of the stabilizers is covered with fabric and one third with sheets of aluminium. The aluminium surfaces are still in good condition, apart from a worn-out coat of paint.

Photo by Kimmo Marttinen

In the spring the Karelian Aviation Museum offered the covering work of the stabilizers to Aviation Museum Society’s Tuesday Club. We agreed, because we had earlier covered the tail boom stabilizers of HS-6, which stands at the yard of the Tuulonen shopping centre. We promised to start the work in the autumn.

For the covering a permission from The Finnish Defence Forces Logistics Command (FDFLOGCOM) was needed, because the helicopter is still in their possession. Permission was granted and in such a form, that we could cover the stabilizers with fabric as they originally were, or alternatively with thin aluminium sheet.

We agreed with the Karelian Aviation Museum that the stabilizers would be covered with a weatherwise better thin aluminium sheet, instead of fabric, as we had done with the HS-6 stabilizers last year. At the same time it was decided that after the covering the stabilizers would be painted all round, ergo the upper surfaces greyish green and the undersurfaces light grey, according to HS-4.

The Museum detached the HS-4 tail boom stabilizers in April, after which they were delivered to the Finnish Aviation Museum in Vantaa. At the beginning of the Tuesday Club’s autumn season the removal of the remaining rotten pieces of fabric was started. The last bits were removed with the tip of a knife. In the same manner we scratched off the thick layer of paint on the stabilizer’s steel reinforcements.

Before the grinding of the HS-4 tail boom stabilizers’ faded and dirty aluminium surfaces could be started, the tone of the colour of the stabilizers’ upper and under surfaces was defined. At the Vantaa branch of Pintaväri the light greyish green of the upper surfaces was defined as the Defence Forces camouflage light green paint, code AN 22. With an electronic tone gauge the stabilizer’s faded green coat of paint was defined to be the greenish tone SG010-G9OY. The light grey of the undersurface was defined as S2500-N. We also defined the tones of the stabilizers’ aluminium surface, using the colour maps at the Finnish Aviation Museum. According to them the upper surface green was RAL 6013 Reed Gray. The undersurface light grey is closest to RAL Effect 830-1. According to the camouflage scheme of the Defence Forces for Mi-8 helicopters, the tone of the stabilizer upper surface is Light bronze green, and the undersurface is Light aircraft gray. We’ll take a closer look at this tone-of-paint-puzzle before the actual painting phase of the stabilizers.

The grinding of the faded paint surfaces was done by a random orbital grinding machine, using P180 and P240 grit sanding discs. Our aim wasn’t to grind the faded coats of paint to pure aluminium. It’s sufficient when dirt and loose paint have been removed from the surfaces and the stabilizer steel reinforcements cleaned of rust. When grinding the stabilizer surfaces, darker green adhesive primer appeared. On some uneven parts pure aluminium surface appeared.

There are roundhead rivets on the stabilizer and the stabilizer’s tip, made of glass-fibre reinforced plastic, has been attached with roundhead screws with grooves. When working on the rows of rivets and screws, the random orbital grinding machine wasn’t the best tool. So we used a grinding brush fixed to a power drilling machine to clean the rivet and screw stubs, which was very suitable for the purpose. Both the HS-4 tail boom stabilizers are ready now for the actual covering.

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Matti Liuskallio.

Covering the DO-5 openings for the stabilizers

Torstai 21.9.2023 - Tuesday Club member

Suomeksi

When in June we were preparing the C-47 (DO-5) fuselage, owned by Aviation Museum Society Finland, for display at the Turku Airshow, the working list included covering the DO-5 tail openings for the stabilizers with aluminium plates. The reason for the covering being to prevent rainwater from getting inside the fuselage. At the time we didn’t have time to make the covers to shield the openings. At the beginning of the Tuesday Club’s autumn season we included the covering of the stabilizer openings on our work list.

Photo by Janne Salonen.

At the moment, the DO-5 fuselage is situated by the Turku Airport, next to the Caravelle III or OH-LEA “Bluebird, which is the object of restoration and owned by Aviation Museum Society Finland. That’s why we had to go to Turku to measure the covers for the stabilizer openings. On Monday, September 4th, we headed for Turku.

Photo by Jouko Tarponen.

Measuring the sizes of the openings on the DO-5 and making cardboard templates of them took quite a few hours. Our work was facilitated by the fact that we had at our disposal a high enough worktop, given to us by the Caravelle restoration project, on which we could reach to measure the vertical stabilizer’s opening, which was highest up. Or as a matter of fact, the vertical stabilizer’s attachment point isn’t an opening at all, like the horizontal stabilizers’, but the vertical stabilizer is attached from its lower part to aluminium attachment brackets rising from the fuselage.

We started with the right-hand side horizontal stabilizer opening in the tail. A cardboard template was made by shaping and attaching to the stabilizer opening several numbered cardboard panels, one after the other. Finally we shaped a cardboard template of the curved leading edge of the stabilizer opening. Because we assume that the right- and left-hand side openings are symmetrical, we only made a cardboard template of the right-hand side stabilizer opening.

A cardboard template of the vertical stabilizer’s attachment point wasn’t made, because it isn’t an opening in the fuselage like those of the horizontal stabilizers. At the vertical stabilizer’s attachment point, from the top of the “cut off” tail, seven rectangular 10 cm high solid attachment brackets, made of aluminium, are sticking up stretching 240 cm in distance. The vertical stabilizer is attached to these brackets with screws, and from its hem to the side of the fuselage.

Photo by Reijo Siirtola.

We ended up sheltering the vertical stabilizer’s attachment point with a rainproof case. The case would be pressed on the 10 cm high attachment brackets. The top of the case would be of sturdy plywood, covered with a sheet of aluminium. The sides of the case will be made of sheets of aluminium. They will be attached from their top rim to the edge of the plywood cover, so that the top rim remains under the downward bent edge of the aluminium sheet on top of the case. This will guarantee that the joint becomes watertight. The bottom sides of the case overlap the top of the fuselage by 4 cm. Thus the rainwater running along the case’s sides can’t get inside the fuselage.

To build the case covering the attachment point of the vertical stabilizer, a sketch was made, where all the relevant details to build the case were measured.

Photos by Ismo Matinlauri.

Because the DO-5 tail cone isn’t fixed to the fuselage, the tail cone opening must also be protected from the rain. The opening will be protected with two aluminium sheets, because of the structure of the tail’s cross-section. So we made individual cardboard templates of the top-and lower halves of the fuselage of the DO-5 without the tail cone.

The covering of the DO-5 tail stabilizer openings was started with the case protecting the vertical stabilizer. First the plywood top will be built. It will act as the frame for the case. There was suitable, sturdy plywood in the material storage of the Finnish Aviation Museum. We will have to make the top plate out of two halves, though, because the length of the plate at our disposal isn’t enough to cover the whole 240 cm length. The measures for the vertical stabilizer taken in Turku, were transposed to the plywood plate, which became the case’s top. Next the top plate will be sawn into measure.

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Matti Liuskallio.

Caravelle's autumn season started in the beginning of September

Keskiviikko 6.9.2023 - Ismo Matinlauri

Suomeksi

The restoration work of the Caravelle OH-LEA at Turku airport started efficiently on Monday, September 4th, when there were nine volunteers at work. In the Turku area it rained a lot in August, and it wasn’t possible to do any of the remaining restoration work outside the aircraft. During the summer weekends the Caravelle was open to visitors, and this led to some restrictions to starting the work inside the aircraft.

On the last weekend we had the summer season’s last open doors event and after this it was possible to continue the restoration work from where we had left it in June. The half cloudy weather was ideal for sanding, polishing, and painting the last identification markings.

On the underside of the fuselage there is a small area which needs to be sanded and painted with aluminium colour paint. The last identification markings will be painted on the wings and fuselage. The largest of these is the registration OH-LEA missing on the underside of the wing.

Photos by Lassi Karivalo.

A lot of polishing work is still needed, this is the main item to be completed on the outer surface. Polishing will be continued as long as the weather allows. However, there is so much to be polished that the work will continue next spring.

The work inside the aircraft has also started. The repairs and painting of the flight deck and the toilet area will be the first work items. The floor and the ceiling area in the cabin will follow in the coming weeks.

It was a pleasure to have visitors from the Tuesday Club at Vantaa. Three club members came to Turku to measure the openings on the tail of the DO-5, which is temporarily parked next to the Caravelle. Protecting covers will be made at the Tuesday Club to cover the holes before the autumn storms arrive.

The busy afternoon was spent at work, but there was a moment for lively discussion when the Turku team and the Tuesday Club members had a coffee break together inside the aircraft at “Café Caravelle”. The Tuesday Club is a valuable support and aid for the Turku team when the details of the restoration work are pondered. We are looking forward to making good progress during the autumn.

Photos by Jouko Tarponen except if otherwise mentioned.

Translation by Erja Reinikainen.

Time to test-fit the Myrsky oil cooler

Lauantai 19.8.2023 - Tuesday Club member

In Finnish

Parallel with the fitting of the wing root fairings, the test-fitting of the barrel-shaped oil cooler was commenced. The Myrsky oil cooler is situated in the fuselage centre line, attached to the main spar “forehead”. Air comes to the oil cooler through an air duct from the left-hand wing’s leading edge. Respectively, after going through the oil cooler the air exits from the underside of the right-hand wing.

For the MY-14 fighter restoration we have at our disposal an original Pratt & Whitney R-1830 Twin Wasp engine’s oil cooler, the very engine that powered the Myrsky. We received it from Airveteran Oy. Instead we have had to manufacture all the accessories for the oil cooler, including the ducts for the supply and exhaust air and the dampers adjusting airflow.

The air ducts were made of 1mm thick, easily workable aluminium sheet. The pieces cut off the sheet were shaped in wooden shaping lasts, after which the seams were welded. We also made the dampers or gills that adjust the amount of air going through the oil cooler. The dampers adjusting the amount of supply air are controlled mechanically from the cockpit.

Photos by Heikki Kaakinen.

Normally the oil cooler is permanently attached to the main spar. Because the MY-14 wing is made of two halves and the oil cooler is situated at the junction, the oil cooler must always come off, when and if the Myrsky will be dismantled for transportation to another museum or some other place to be placed on display. That’s why a handy rack with attachment straps was constructed. The oil cooler will be strapped on it and the rack is easily detachable from the wing spar and can also easily be reattached.

Photos by Heikki Kaakinen

The test-fitting of the oil cooler was started by attaching the oil cooler attachment rack on the junction of the wing halves. The oil cooler was tightened to the straps. After that the cooler’s right-hand cooling air exhaust duct was fitted into place. The duct opens to the underside of the right-hand wing’s leading edge.

Photo by Heikki Kaakinen

The gills adjusting the incoming airflow were attached to the other end of the oil cooler. The gills are situated between the oil cooler and the supply air duct. The duct for incoming air is twofold. One end of the duct’s straight part is attached to the supply air damper and the other end to the front end of the L-shaped supply air duct. The opening of the incoming air duct is situated in the right-hand wing’s leading edge. There’s still work to do in fitting the oil cooler parts before every part is settled in its place as planned. A veritable “collection of gadgets” this Myrsky oil cooler system has proved to be.

The pitot-tube, which measures the airspeed of the aircraft and is situated on the left-hand wing, was also test-fitted. The pitot-tube rack has been in place for long in the left-hand wing’s leading edge. We noticed, to our chagrin, that the 300 mm pitot-tube at our disposal was of a wrong length. It should be of the 500 mm long type. This can be seen in the Myrsky blueprints and photos taken of the Myrsky. Might there be a pitot-tube of the right length for us in the collections of the Finnish Air Force Museum?

Along with all other tasks numerous inspection hatches on the wings are being fitted into place. We had to grind the collars of the hatches a bit deeper, so that the hatches would become flush with the wing surface.

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Matti Liuskallio.

The DO-5 fuselage on display at the Turku Airshow

Perjantai 23.6.2023 - Tuesday Club member

The fuselage of the Douglas C-47 A, registered DO-5, owned by Aviation Museum Society Finland was on display at the Turku Airshow as part the Aviation Museum’s stand. The DO-5 fuselage, which was used by the Finnish Air Force for training paratroopers in the 1960’s, was refurbished enough in the Aviation Museum Society’s Tuesday Club for the fuselage to be brought on display to Turku. The Airshow visitors could be allowed inside the fuselage to see how the aircraft was used in training the paratroopers.

Photos by Janne Salonen

Photo my Lassi Karivalo

The DO-5 fuselage was transported from the Aviation Museum’s yard at Vantaa to Turku Airport on the Thursday before the Airshow weekend. The Aviation Museum Society’s stand was situated in the Airshow area close to the mighty Boeing C-17 Globemaster. So there they were in close vicinity, the USA Air Force Air Transport aircraft from the 1930’s and the 1990’s, albeit in different calibre.  

Photos by Lassi Karivalo

The Society had also brought on display the “Snoopy” aircraft donated to the Society and awaiting full restoration. This experimental aircraft from 1969 was constructed by the brothers Ari and Esko Hietanen from Turku.

Photo by Janne Pauni

The DO-5 fuselage drew great interest among the Airshow visitors. On both show days, Saturday and Sunday, people poured into the DO-5 to hear about the history of this individual aircraft and about the refurbishing projects done by the Tuesday Club, including the full-sized photo in the cockpit of the instrument panel of the Kar-Air DC-3 OH-VKB, which is situated in the Aviation Museum.

Photo by Juha Veijalainen

Photo via Jarmo Kaipainen

We told the visitors in particular how the DO-5 was used at Utti as a jump aircraft to train paratroopers and after it was taken off from flying, how the fuselage was utilized on the ground as a dry run platform before the first real jump as a paratrooper. We didn’t keep count how many persons visited the interior of the DO-5, but we estimate that the number is nearer 2000 than one thousand. It was a pleasant incident, when someone visited the aircraft and said that he had jumped from this very aircraft in 1963 on his conscript time, when it still served as a jump aircraft.

Those who visited the aircraft were also very interested in the Aviation Museum Society’s DO-5 project in itself. They thought it was commendable that Aviation Museum Society Finland saved from the scrap yard an aircraft used by the Air Force in the 1960’s, with the cabin still in its original paratrooper training attire. Our project isn’t solely to preserve a C-47 because there are plenty of them still flying in the world, including converted airliner flying “Dak”, the OH-LCH, owned by Airveteran Oy.

In preserving the DO-5 we’ll be able to save for the future generations Air Force history from the 1960’s concerning paratrooper training. We at the Tuesday Club can be proud as Punch for what we have already done to refurbish the fuselage. Without our input the fuselage wouldn’t have been in such a condition that it could have been put on display. There’s still a lot to do with the DO-5, but time will show how far we can go. The positive feedback we received at the Turku Airshow only confirmed how important our idea was, from the point of aviation history, to save the DO-5 used by the Air Force in training paratroopers more than 50 years ago.

We, inside the DO-5 telling the visitors about the history and use of the aircraft, were literally in a hot spot. The scorching weather and the sun blaring from a cloudless sky heated the interior really hot. The temperature must have been nearly +50 degrees Celsius, even though we had installed a few fans to ease our existence. We did survive the hours’ long “sauna” of both airshow days. It must be admitted that cases of mineral water and Coke relieved the situation in preventing dehydration.

The positive attitude of the visitors motivates Aviation Museum Society Finland to carry on with the refurbishing of the DO-5. From the point of view of the Tuesday Club the situation is problematic, because for the time being the DO-5 remains in Turku and our club operates in the Finnish Aviation Museum’s premises in Vantaa in co-operation with the Museum.

Photos by Janne Salonen

After the Airshow the DO-5 fuselage was transported to Turku Airport to the vicinity of the Caravelle III, which was restored as Finnair’s “Bluebird”, and is owned by Aviation Museum Society Finland. There the Old Lady DO-5 can stay by the little younger Old Lady the “Bluebird” on public display.

Photos by Janne Salonen

The former SAS Caravelle (SE-DAF) presently in Finnair colours, outside the actual Airshow area also interested the Airshow visitors very much. So about 1300 people popped in to get acquainted with the Caravelle “Bluebird” on their way from the Airport terminal bus-stop to the gates of the Airshow area. It was well worth getting acquainted with, because the newly painted Finnair “Bluebird is a truly resplendent sight.

Translation by Matti Liuskallio.

Tuesday Club's DO-5 work completed

Keskiviikko 21.6.2023 - Tuesday Club member

The hard work of the Tuesday Club members was instrumental in getting the fuselage of the type C-47A DO-5, owned by Aviation Museum Society Finland, into sufficient shape for putting it ready for showing before the Turku Airshow. It was touch and go because the last tasks weren’t finished until two days before the fuselage of DO-5 was transported from the yard of the Finnish Aviation Museum to Turku Airport on June 15th, 2023.

The last significant project was to install new plexiglass panes for the cockpit. The Air Force DO-5 hasn’t had original panes in the cockpit for decades. Part of the windows lacked panes altogether, resulting rainwater and snowstorms ruining the cockpit badly, whilst the fuselage lay forgotten for decades in the Utti forests.

Because the original cockpit panes and the large sliding panes on both sides of the cockpit weren’t available, we ended up with acquiring plexiglass panes for the window openings. On top of that we decided to attach the plexiglass panes to their frames with a mixture of glue and sealant mass. In this way the windows become watertight, preventing water to seep into the fuselage. This also meant that the big sliding panes on both sides of the DO-5 cockpit couldn’t be slid open anymore.

To acquire new 5mm polycarbonate plexiglass panes we made a template out of thin plywood for each of the window openings. For the windscreens we had already in the autumn acquired from ETRA plexiglass panes ready cut to form. Cold weather and the oncoming winter, however, put paid to carrying on with the installing of the windowpanes. We fastened then the plexiglass panes and the temporary panes in the other windows with plastic tape from their edges to wait for the warmer temperatures of the spring, when we could continue with the cockpit windows.

Photos by Lauri Veijalainen

Other tasks to refurbish the DO-5 fuselage in the spring delayed attaching the new plexiglass panes, so that we didn’t get to it until May 2023. Then the plexiglass panes for the large sliding windows on the sides of the cockpit were acquired.

Photos by Lauri Veijalainen

Each plexiglass pane was squeezed into its frame and a thin rubber strip was installed under the lower edge of the pane in order to get the pane at the right elevation in its groove. After that the edges of the panes were taped either by masking tape or with plastic tape so that there remained a suitable zone for the glue and sealant mass. The tape is to protect the rest of the surface of the pane from the sealant mass to spread and that the seam of the sealant mass will be clean.

Photo by Lauri Veijalainen

After the taping, the glue and sealant mass was squeezed out along the seam of the pane and the frame. After that the mass was formed even with a plastic forming spatula. As mass we used black Soudaseal and Würth glue and sealant mass. When the seaming was ready, we extracted the protective tapes along the pane edges and the protective film on the panes. The seaming of each pane turned out to be very neat.

Photo by Lauri Veijalainen

There are also small sliding windows in the cockpit that can be opened. For them we received original framed panes from Airveteran Oy. Installing them proved to be a bit problematic. Both the sliding window frames lacked a locking screw from the bottom, with which the window was pressed with its rubber seal tightly against the frame to make it watertight. On top of that, both the frames of the sliding windows we received were both for the right-hand side. Luckily the right- and left-hand side pane differ from each other little enough, so we pushed the right-hand side pane deep and tightly enough into the grooves of the left-hand side frame. There it can remain for the time being, until we’ll find a suitable pane for it.

We noticed that along the windscreen and cockpit side window frames there were empty screw holes. What for, we wondered? To stop water from leaking into the fuselage, we blocked the holes by screwing groove-headed sheet metal aluminium screws into each of them.

Photos by Lauri Veijalainen

Photo by Janne Salonen

With the windows we had accomplished all the agreed tasks to refurbish the DO-5, so for our part the fuselage was ready to be transported to Turku Airport and to be on show there at the Airshow on June 17th -18th. The DO-5 fuselage left for Turku on Thursday June 15th.

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Matti Liuskallio.

Making the lower part of C-47 (DO-5) nose cone

Lauantai 3.6.2023 - Tuesday Club member

Suomeksi

In an earlier blog I told that we were lent the lower half of a DC-3 (OH-VKC) nose cone to make the missing lower half of the DO-5 nose cone out of fibre glass. The DO-5 operated at its time in the Finnish Air Force as a jump aircraft for paratroopers. Aviation Museum Society managed to buy the DO-5, which was heading for scrap yard. Unfortunately the middle section of the wing is missing.

We needed the lower part of the nose cone on loan to make an outer surface fibreglass mould. With the help of the mould we’ll make the missing lower half out of fibreglass. Why do we make the lower half out of fibreglass and not of sheet aluminium? Simply because making the lower half out of aluminium is much more challenging and, on the other hand, because the fibreglass lower half of the nose cone fills its place well in the nose of the non-flying DO-5.

The lower half of the OH-VKC nose cone we loaned, and the DO-5 nose cone upper half are of the same DC-3 family, but they have been manufactured in different times and places. Because of this we still wanted to test, whether the OH-VKC lower half and the DO-5 upper half are a match. They weren’t an exact match, but close enough for us to use the loaned lower half of the nose cone to make a fibreglass mould.

The first phase in making the fibreglass mould was to stiffen the lower part of the OH-VKC nose cone so that it wouldn’t distort when under work. This was because the lower half, made of thin aluminium sheet, detached from the nose of the OH-VKC is “sloppy” and won’t retain its form. A wooden cross stiffener was made between the opposite corners of the lower half. Then curved stiffeners in the form of the lower half edges were sawn out of 20 mm thick film plywood, which were attached to the edges of the lower half of the nose cone. The stiffeners were fastened by utilizing the existing attachment screw holes in the edges. Now the nose cone lower part will stay in form when handled.

Photos by Reijo Siirtola

Before making the fibreglass mould the bottom surface of the nose cone had to be cleaned into aluminium from the paint and filler covering it. The mottled history of the OH-VKC could be seen in the many layers of paint on the nose cone. An attempt to remove the layers of paint using a grinder failed because the sanding discs got choked instantly. Next a paint removing agent and scraping the paint off was tried. Suitable for our purposes proved to be Solmaster MP EKO Maalinpoisto (paint remover). Plenty of Solmaster was applied onto a restricted area of the aluminium surface and the area was covered with fabric to prevent evaporation. When the substance had worked a while, the paint could be scraped off with a wooden spatula. The wooden spatula worked well, and it doesn’t damage the aluminium surface of the lower half. Because the surface remained sticky, the final cleaning was done with thinner and xylene. In this way, phase by phase, the nose cone lower half’s surface was cleaned. Finally the surface was buffed with a nylon slip disc (Mirka nylon 60x30x6m).

Photo by Reijo Siirtola

Before layers of fibreglass fabrics, impregnated in polyester resin, could be applied on the surface of the lower half of the nose cone, the surface had to be carefully sealed. The sealing is important, because the sealer prevents the resin impregnated fibreglass mat from sticking on the aluminium surface below. Five layers of Miracle Gloss 8 sealer by Kevra Oy were rubbed on the lower half’s surface. Three first layers were rubbed on the cone surface with an interval of an hour, then a 12 hour pause, and finally the last two layers again with an interval of an hour.

After 24 hours the lamination could be started. As lamination mat Biltema woven fibreglass fabric 30-512 was used, and as resin Biltema Polyester resin 36-0780”. The Polyester resin was chosen because its price was a shy quarter of the corresponding epoxy resin, and it won’t stick easily on the sealed surface of the mould.

Photo by Reijo Siirtola.

Before the real lamination with fibreglass fabric, a test lamination with a small piece of fibreglass fabric was made. A piece of fibreglass fabric was impregnated with polyester resin while the piece of fabric was spread on cardboard. When the white colour of the fabric changed into transparent, it was turned over and polyester resin was applied on the other side, too. The cardboard from a cardboard box is an excellent base for this purpose. It’s strong enough to withstand the fibreglass mat to be impregnated with polyester resin and the resin won’t absorb into the cardboard to any significant degree. The piece of fibreglass fabric, impregnated with polyester resin, was “squeezed” tightly with a roller onto the surface of the lower half of the nose cone. The fabric stuck on well, and what was most important, after drying the fabric came off the next day without damage. So the sealing was a success.

Photo by Reijo Siirtola

Now we could start to laminate the whole of the surface of the lower half with fibreglass fabric. For that purpose three pieces covering the lower half surface were cut out of the fibreglass fabric. First the surface of the lower half of the nose cone was completely covered with polyester resin. After that the first piece of lamination fabric was impregnated with resin and it was laminated on the surface of the lower half of the nose cone. Three layers of fabric were laminated. Finally on top of the layers thick ropes were laminated with polyester resin, which after drying would form a supporting structure keeping the mould in form.

Photos by Reijo Siirtola

The next day the fibreglass mould could be detached. The detaching succeeded with ease, and no traces were left on the aluminium surface – thanks to the excellent sealer. Extra bits out of the edges of the mould were cut off. Slight unevenness was noticed on the inner surface of the detached mould. The uneven patches were sanded, and the surface was spackled with Biltema’s fibreglass filler (36-0137) and buffed. Thus the fibreglass mould had been finished for the lamination of the lower half of the nose cone.

Photo by Reijo Siirtola

The lamination of the lower half of the nose cone began with the sealing of the inner surface of the fibreglass mould. After sealing the lamination was started, but this time with fibreglass mat. The reason for this was that with using of fibreglass fabric some unevenness seemed to remain, which necessitated extra buffing. With the fibreglass mat, which was pressed out of short glass fibres, the fibres criss-cross with each other. That gives a very smooth surface when laminated with a roller. Due to the structure of the mat it has also a good tensile strength in every direction.

Photo by Reijo Siirtola

A piece covering the inner surface of the mould was cut. Polyester resin was first applied to the surface of the sealed fibreglass mould. After that the polyester resin impregnated pieces of fibreglass mats were laminated with a roll, one after the other, onto the inner surface of the mould. After the fibreglass had dried out the laminate was detached from the inner surface of the mould. It could be seen that the surface of the lower half of the fibreglass cone was remarkably smooth, nearly ready for painting.

Photos by Reijo Siirtola

Because the fibreglass lower half of the nose cone wouldn’t hold its form without support, new supports cut out of thick plywood were installed. Thus it was secured that that the new fibreglass lower half of the nose cone stays in form when fitted on to the nose of the DO-5. The surface of the fibreglass lower half was spackled and sanded and primed with grey primer. When the lower half of the OH-VKC nose cone and the fibreglass lower half were put side by side, they looked identical, as was planned.

Photo by Juha Veijalainen

The new lower half of the nose cone was ready to be fitted onto the nose of the DO-5. During the fitting it will be seen how much we’ll have to work on its edges, so that we’ll be able to get it settle the way we want, against the upper half of the nose cone. To fit the lower half of the nose cone onto the DO-5 nose, we removed a sheet metal covering plate, which had protected the “cut off” nose. Behind it all sorts of rubbish, accumulated in the nose during the decades, was revealed and had to be cleaned off.

After cleaning we installed the upper half of the DO-5 nose cone in place and started fitting the fibreglass lower half in place. When fitting the lower half we noticed that the lower half was just within the tolerances, as we had hoped it would be. Naturally the edges of the lower half and the plywood supports inside had to be modified a few times so that the lower half of the nose cone was settled in the way we hoped, against the fuselage and the upper half.

The fibreglass lower half of the nose cone was ready waiting for the finishing coat of paint. At this stage it was painted grey and is allowed to stand out from the original upper half of the cone. If the DO-5 aluminium fuselage is to be polished at some stage, the fibreglass lower half of the nose cone will be painted with a paint that will emulate the aluminium surface.

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Matti Liuskallio.

Caravelle towbar restored

Lauantai 27.5.2023 - Tuesday Club member

Suomeksi

The original towbar for Caravelle III (SE-DAF), acquired from Sweden by Aviation Museum Society, was brought along. It was used by SAS. The towbar was abandoned by SAS along with the termination of the Caravelle fleet’s career. The towbar had lain decades at Arlanda Airport along SE-DAF.

The towbar was taken under restoration at the Tuesday Club in the autumn of 2022, in a similar fashion as the derelict Super Caravelle towbar was restored, used by Finnair. The SAS towbar is of the first version made by the Sud Aviation industries. For its part the Super Caravelle towbar used by Finnair is of the third and last version. The differences between these towbars are minimal and concern mainly the wheel rack of the towbar.

Along with the spring all the parts of the towbar were refurbished and painted. The last job before assembling the towbar was to repair the wheel rack to working order. When the towbar wheel rack was dismantled in the autumn season, it was noticed that the rim of the other wheel was so far gone that it was unusable. The other wheel’s rim was sound enough to be usable with a bit of welding. A new tyre and inner tube were bought for it and one of the bearings, which had broken when the wheel was dislocated from the axle of the wheel rack. When the rim had received its blue colour, the inner tube and the tyre were fitted in place.

To replace the unusable wheel, we managed, after a spot of searching, to find a wheel with an inner tube looking like the original wheel, and fitting the towbar’s 25 mm axle. A majority of the “wheelbarrow” wheels on sale were made for a 20 mm axle. When the rim of the new wheel had also been painted blue you could hardly tell them apart. The wheels were attached on to the wheel rack’s axles, after which the test assembling of the towbar could be commenced.

The test assembling will be necessary, because the towbar will be transported in parts to the Turku Airport area, where it will be assembled on show next to the ex SAS Caravelle SE-DAF, now being restored as the Finnair “Bluebird”. By test assembling it will be ensured that the assembling in Turku will take place without surprises.

The towbar test assembly was started by setting against each other the flanges of the halves of the towbar. We had to do some thinking, because the guiding pins for the flanges of the towbar halves didn’t line up with their holes so that the lifting handles are in the same line. We established that the towbar halves must have been 180 degrees out of line of each other already when they came to Finland.

This we hadn’t noticed when dismantling the towbar, because the towbar lacked the lifting handles, which would have indicated the position. If they had been there, we would have noticed that one handle was beneath the towbar, the other one above. So our conclusion is that the towbar was wrongly assembled at Arlanda. An indication of this is that in the photos we took before the dismantling of the towbar, the metal support of the towbar which should touch the ground is sticking to the skies.

To solve the problem of test assembling we sawed off the guiding pins and pressed the flanges of both the bar halves against each other so that the lifting handles were above the towbar and lined up properly with each other. After this the flanges were locked to each other with two locking collars around them. The collars were tightened fast by their brackets with bolts. This way the towbar halves had been connected.

Now it was time to attach the wheel rack to the towbar. The wheel rack was attached to the towbar by its attachment collars. The rack wasn’t attached in the middle of the towbar, but some way on the pull loop end side of the centre of gravity. Thus the aircraft towhead end, which connects with the nose gear, weighs down and leans on the ground by its support. Finally we attached the manufacturer’s plaque on the side of the towbar. The towbar is still lacking the Caravelle logo, which will be painted on its side before it will be ready to be delivered to Turku.

The derelict towbar underwent a complete transformation at the hands of the Tuesday Club. It changed from the rusty and partly damaged towbar into a renewed one, resembling the towbars used by the Finnair Caravelle fleet. It received the same appearance as the Finnair Super Caravelle towbar we restored a year ago.

Photos by Lassi Karivalo

Translation by Matti Liuskallio

DO-5 cabin to get new window panes

Tiistai 9.5.2023 - Tuesday Club member

Suomeksi

The windowpanes in the cabin of the DC-3 (C-47) – aircraft, owned by Aviation Museum Society, have gone opaque or non-transparent during the decades of storing in the woods. It has been decided to renew the panes. We’ll have time at the Tuesday Club to renew at least the port side panes before the Turku Airshow. The DO-5 fuselage will be on display at the Aviation Museum stand. The DO-5 panes will be renewed using UV-shielded polycarbonate plexiglass. It’s a lasting and easily workable material.

On both sides of the ”DAK’s” passenger cabin there are seven windows. The windowpanes are 47,7 x 34,9 cm in size. Their thickness is 5 mm. The panes have been fastened with 20 3,8 mm thick and 18 mm long roundhead grooved screws. The holes for the screws are situated in each window according to standard, at the same place. Between the frame and the pane there’s a 2 mm thick rubber seal. The seal has a speciality that it has holed rubber studs for each 11 mm hole. The studs press themselves into the screw holes so that the screws go through the rubber studs. The rubber studs prevent the screws being in direct contact with the plexiglass and operate as vibration dampers. The screws have been tightened against the plexi glass surface with nuts and washers, or instead of the washers with a supportive metal batten.

We started to renew the panes on the port side of the fuselage. At first we detached the pane from the window nearest to the door. One of the detachers was outside the fuselage and held the grooved screw in place with a screwdriver and the other one inside of the fuselage unwound the nut with care. The nuts had inch thread, so they were original. We detached all 20 nuts relatively easily and the screws were detached. The pane’s original rubber seal with studs appeared still to be in good condition, so it could be fitted back with the new pane. The empty window opening was covered from the outside with a plastic sheet fastened with duct tape. The detached rusty screws were cleaned, and their heads painted with anti corrosion paint.

When we continued detaching the panes, it was observed that that the screws of the remaining six windows had millimetre threads and were of various sizes, as if picked out of a junk box. Thus the screws aren’t original and fitted in the ”U.S of A”. Furthermore, the panes were without the rubber seals and attached only with less than ten screws instead of twenty. Because of this the window frames had empty screw holes for water to leak between the frame and the pane and to the cabin. Part of the panes were also thinner than the original ones. So it’s evident that DO-5 hasn’t flown with these panes assembled. The panes have most probably been fitted to the DO-5 cabin at Utti, when the fuselage was transformed into a ground training platform for paratroopers, or after the writing-off of the fuselage and abandoning it into the woods.

We decided to replace all the panes we had detached with 5 mm. thick plexi glass (as was the case in the original), 20 attachment screws and rubber seals. This means that we will have to buy seven panes of plexi glass, new attachment screws and some rubber mat for making the seals. Rubber seals with studs like the originals we are, however, unable to make.

We bought the seven polycarbonate plexi glass panes sawn into measurements at ETRA. Because only one pane was original with original rubber seals, the 11 mm screw holes responding to the rubber studs will only be drilled to that. All the other six panes will be drilled holes for only 5 mm thick attachment screws, because these panes will be fitted with a 2 mm thick smooth rubber seal.

We made a drilling frame out of a sturdy plate and battens, to drill the 20 screw holes into the panes in exactly the right spots. The drilling began into the plexiglass pane for the original window. The new plexiglass pane, still covered with a protective film, was placed under the drilling frame. On top of that was placed the original pane, which had 20 holes of 11mm in diametre for the rubber studs and attachment screws, which was meant as a drilling template. The panes were locked into the drilling frame with clamps.

To drill the holes precisely in the middle of the holes in the template pane, we lathed out of brass a drilling guide, which fits snugly into the 11 mm. hole. In the middle of the guide a hole was drilled for the 5 mm drill bit. The guide was placed into the 11 mm hole in the old pane, which was on top of the new plexi glass pane and through the guide a 5 mm preliminary hole was drilled into the pane under it. Thus a 5 mm hole was drilled into all the 20 holes. After this an 11mm bit was changed in the column drilling machine, and the template pane was removed from top of the new pane. The 11 mm bit was centred on the first 5 mm hole, and it was enlarged to 11 mm. Thus all the 20 holes were enlarged. After the drilling was done, the size of the holes was tested by fitting the rubber seal with studs from the original window to the new pane. The rubber studs fitted perfectly into the drilled holes.

The six other panes were made in a different way, because they will be fitted with a smooth 2mm thick rubber seal. Into these panes 20 holes were drilled with a 5 mm bit. This means that the panes’ screw holes will lack the vibration damping effect given by the studs, but on the other hand this DO-5 fuselage will never again fly, apart from a little shaking when moved about.

When all the holes had been drilled to the new panes, it was time to make the rubber seals. A metre of 1,4 m wide rubber mat was bought from ETRA. Because the panes measure 47,7 x 34,9 cm. there’s enough material for eight seals, enough for a couple of extra ones. A funny thing happened when buying the mat; the shop assistant asked: ”would you like the smelly mat or the one without smell”? The brand without smell turned out to be double the price. To save Aviation Museum Society’s funds we bought the “smelly” brand. By Jove it did smell revolting, but soon the smell evaporated.

To cut the seals from the rubber mat for the six new plexiglass panes, a template out of plywood, exactly like the seal, was made. With the aid of the template the necessary six rectangular shaped rubber seals were cut. Now the seals lacked only the holes for the pane’s 20 attachment screws.

The screw holes were marked in each seal by using one new plexi glass pane as a template, into which 20 screw holes 5 mm in diametre had been drilled. The plexi glass pane with the screw holes was lined precisely on the rubber seal. A mark was made with a pen through each hole. After that the holes for the screws were made in the seal by using a leather piercer. This procedure was repeated on all the six seals.

We still had to find as many as possible new screws with a low round head and groove, resembling the original ones, with nuts and washers, to attach to the windows. You can’t find them in modern ironmongers’ anymore. Luckily the screws we were after could be found at Uudenmaan Pultti in Järvenpää. They were 4 mm thick and 20 mm long. With millimetre threads but being almost a match to the original 3,8 mm thick and 18 mm long screws. The heads of these new screws were painted in silvery grey, so that they wouldn’t stand out gleaming on the side of the DO-5 fuselage. Now everything is ready for the new panes to be installed to the port side windows of the DO-5 cabin.

Photos by Lassi Karivalo

Translation by Matti Liuskallio.

The lower half of DO-5 nose cone on loan to fabricate a new one

Sunnuntai 23.4.2023 - Tuesday Club member

Suomeksi

The fuselage of the Air Force C-47 (DO-5), which had been used for paratrooper training and is currently owned by Aviation Museum Society, is lacking the nose cone. The reason being that only the upper half of the cone survived and a lower half doesn’t exist in Finland for our purposes. Probably such an item could be found abroad for a load of money, but that form of action isn’t for us.

Left hand photo via Laskuvarjojääkärikilta.

After pondering various possibilities to build the lower half of the nose cone at the Tuesday Club, we ended up in building the lower half out of fibreglass. The fibreglass lower half of the nose cone wouldn’t by all means be like the original, made of aluminium sheet, but resembles the original one, however. It would certainly be better than no nose cone at all. Now we have to find on loan an original “Dak” nose cone lower half, so that we could make a fibreglass mould with the help of the original lower half. Based on it we would make the fibreglass lower half of the nose cone. When installed, it would be painted in aluminium finish and simultaneously the upper half would be cleaned and polished.

The solution to acquiring an original lower half was found when the owner of the front fuselage of the ex Kar-Air DC-3 (OH-VKC), situated in Finland, promised to borrow us the lower half of the nose cone. So a group of DO-5 project members travelled en situ to dislocate the nose cone. For the most part we managed easily to detach the screws holding the lower half in the fuselage. We were helped by the preparatory work done by the owner of the OH-VKC front fuselage. A few screws had to be loosened by drilling.

In spite of the awkward working postures and the loose talking typical to us, the lower half of the nose cone was detached from the nose of OH-VKC in a couple of hours and the journey to the Finnish Aviation Museum began.

At the museum we fitted the lower half of the nose cone on loan and the DO-5 upper half together. They did match perfectly well, even though DO-5 is of the Douglas type C-47 or transport aircraft and OH-VKC is an original passenger aircraft. We established the lower half of the nose cone on loan to be perfectly suitable for making a fibreglass mould. Before we get that far, the lower surface of the lower half on loan has to be ground clean of dirt as well as the paint and filler on its surface.

Our aim is that the complete nose cone will be in place in the DO-5 fuselage, when it will be on show at the Aviation Museum Society’s stand at the Turku Airshow on June 17th -18th.

Photos by Lassi Karivalo except if otherwise mentioned

Translation by Matti Liuskallio.

The DC-3 (DO-5) fuselage refurbished for display

Lauantai 8.4.2023 - Tuesday Club member

Suomeksi

Aviation Museum Society Finland will bring to its stand at the Turku Airshow on Jun.17th – 18th the fuselage of the DC-3 aircraft it owns. To be precise, it’s the fuselage of a Douglas C-47 A- 80-DL aircraft. It was completed at Long Beach in 1944.

Photo via Jarmo Kaipainen.

This “Dakota” designated DO-5 last served in the Finnish Air Force as a flying trainer for paratroopers and finally its fuselage was used as a ground training platform for paratroopers. After rotting away for decades in the Utti forest it was donated to Aviation Museum Society Finland. With the fuselage came the tail assembly and the outer wing panels. The fuselage is without the centre wing section. Unfortunately it has disappeared somewhere during the passing years.

Photo by Juha Ritari

Aviation Museum Society restores the fuselage for display purposes. This work is presently undergoing at the Tuesday Club. Lots of work is still ahead, before the fuselage is back at its DO-5 era operational appearance. As may easily be guessed, tens of years outdoors with leaking cockpit windows has played havoc, but we aren’t downhearted as the saying goes. Yes, and the fuselage has already been used as a stage prop for the recent Finnish films “Pertsa ja Kilu” and “ Sisu”.

The fuselage of the DO-5 will be brought on display to the Turku Airshow into the Aviation Museum Society’s stand, even though it won’t be in the display condition we aim it to be. It will still be interesting to see the configuration the DO-5 was used in training the paratroopers, because the cabin is still in the condition it was used in para training with the canvas benches along the walls and the parachute opening straps hanging on the running wire.

At this moment the fuselage is at the Aviation Museum’s yard to be restored by the Tuesday Club. Restoration work has been going on both in the cockpit and in the cabin. In the cockpit both the pilots’ seats have been detached and dismantled into parts. They are at a sorry state and partly rusted. We aim to get them restored by the summer. A real challenge are the back plates and the seat buckets which are both made of pressed cardboard. They have all gone mushy because of the rainwater leaking into the cockpit. A probable alternative is to make the back plates and the seat buckets from aluminium sheets.

The door between the cockpit and the cabin has been restored. Presently we have started to renew the cabin windowpanes, which have become opaque. The opaque panes will be replaced with clear polycarbonate ones. One of the panes has already been detached. We hope to get at least the seven panes by the cabin exit door changed into transparent ones by the Turku Airshow.

The cockpit is lacking the instrument panel and instruments. As a first aid measure we aim to install a real and full sized “Dakota” instrument panel into the cockpit copied on an aluminium sheet. The instrument panel was photographed from the Karhumäki Airways OH-VKB DC-3A-aircraft.

And that’s not nearly all. There’s no nose cone on the DO-5 front end. We do have the upper half of the nose cone, but the lower half is missing. There isn’t one in Finland for us to get our hands on. The meaning is to make the missing lower part from glass fibre. To make the glass fibre mould we can borrow an original lower half of a CD-3 nose cone. If the work proceeds as planned, the DO-5 nose doesn’t have the cut off look at the Turku Airshow but has the original “Dakota” nose form.

Sooner or later the DO-5 fuselage, which has now become covered with dirty grey patina, will be polished to pristine condition.

As the good reader will notice, nearly all that I wrote about isn’t ready yet. Let this blog be more of an inducement to go to the Turku Airshow on June 17th -18th and to visit the Aviation Museum Society’s stand and the DO-5 fuselage, the Hawk experience centre, the OH-XEA “Snoopy” light aircraft and also the Aviation Museum Society’s  OH-LEA “sinilintu-bluebird”  Caravelle – jet airliner resplendent in Finnair colours, which will be assembled by the airport passenger terminal.

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Matti Liuskallio.

Covering the Caudron elevator got under way

Perjantai 3.3.2023 - Tuesday Club member

Suomeksi

The Caudron C.59 advanced trainer’s starboard elevator, which had been completely stripped of the covering fabric, had already been waiting for a few years to be covered.

On the ribs, strips of linen fabric had already been tied, onto which the covering fabric will be sewn. The Caudron’s port elevator 1920’s original fabric covering was still in such good condition that it wasn’t seen necessary to be renewed, patching a few holes was sufficient enough.

For the covering fabric was chosen the 165 g/m2 linen fabric called “Kesäyö (summer night)”, bought at Eurokangas. This same fabric was used to covering the elevators and rudder of the VL Myrsky II (MY-14), which is under restoration, although the tightening of the fabric with nitro cellulose lacquer posed its own problems.

Photo by Jukka Köresaar.

The covering was started by cutting a piece of fabric that completely covered the whole of the elevator. The fabric was glued with nitro cellulose lacquer to the leading edge or the hinge side of the elevator. After this the fabric on one side of the elevator was stretched towards the trailing edge and the edge of the fabric was preliminarily attached with sturdy T-headed pins to the steel wire acting as the trailing edge. The extra fabric was cut off.

Photos by Heikki Kaakinen.

The stretched fabric was sprayed wet with boiled water. The meaning of this was the pre- tightening or pre-shrinking of the fabric. The fabric turned translucent when wet. After the fabric had dried, its edge was sewn with linen thread to the trailing edge steel wire. The proper tightening of the covering fabric is done with nitro cellulose lacquer, when the fabric covering of the elevator tightens and resembles a drum skin.

Next, the fabric on the other side of the elevator was stretched and pre-tightened in a similar manner. After pre-tightening the edge of the fabric was folded over the steel wire acting as trailing edge, over the already sewn seam of the fabric covering the other side and was sewn on the wire. The lapel of a few centimetres going over the trailing edge wire was tacked to the covering fabric beneath. A protecting strip of fabric over the stitches of the trailing edge wire will be glued over the stitches with tightening lacquer.

Photo by Jukka Köresaar.

Before the covering fabric was sewn on the strips attached to the ribs, the covering fabric’s lateral lapels were glued to both ends of the elevator. The elevator’s end is a wooden batten 4 centimetres wide. The covering fabric was glued on the end batten with tightening lacquer. The end batten will also be wholly covered with a protective strip of linen fabric.

Photos by Jukka Köresaar.

When covering an aircraft’s wings or control surfaces with fabric, the covering fabric is sewn into the underlying fabric strips on the ribs. When sewing the elevator covering fabric into the Caudron elevator’s underlying strips, which were on the ribs, a curved needle was used.

It could be deftly slid through the covering fabric and the underlying strip. The sewing was done by oblique tacking, in which we used the same form of tacking as was used in the elevator’s original dismantled covering. The original model for oblique tacking came to light when dismantling the elevator’s covering and it was documented for future re-covering of the elevator.

When the covering fabric had been sewn into the ribs, the tightening of the fabric could be commenced with nitro cellulose lacquer. We used the NC-SPEED nitro cellulose lacquer. The tightening varnishing of the fabric is done by stages. The varnishing is usually started with nitro cellulose lacquer thinned to 25 %, from which we move on to 50% and 75% lacquer and after that to unthinned 100% lacquer. It usually takes five to seven layers of varnishing before the fabric is tight enough. As thinner we used the Ohenne 8 (thinner 8). Furthermore, the tightening lacquer is dyed red with iron oxide. The dyeing is done to see clearly when varnishing the covering fabric, which parts of the fabric have or haven’t already been varnished.

The Caudron C.59 elevator’s new covering fabric was varnished first with 25% nitro cellulose lacquer. It was applied with a paintbrush. After the lacquer had dried, the surface of the fabric was sanded with a Super Fine sanding pad. By sanding the fuzz sticking out of the surface of the fabric was removed. With the 25% lacquer the fabric tightened only slightly. In the next phase the fabric will be varnished with 50% NC-SPEED nitro cellulose lacquer and as the fabric tightens, with ever stronger lacquer up to unthinned NC-SPEED lacquer.

Simultaneously with the varnishing, the protective strips for the seams, leading edge, trailing edge

and the end battens were being made. The strips were made of the same “Kesäyö” linen fabric, which was used to cover the elevator. The fabric was cut into 5cm wide strips. The edges were fringed. It means that the warp was unfurled from the edges about 5 mm.  Fringing of the edges of the protective strips enhances the gluing of the strips on the seams of the covering fabric.

Fringing of the covering fabric edges was typical in the covering of aircraft in the 1920’s. Later it was changed into a saw-toothed pattern in the edges of protective strips, which was made by using ”zig-zag-scissors”.

Photos by Lassi Karivalo except if otherwise separately mentioned.

Translation by Matti Liuskallio.

The restoration of the Caravelle III towbar is progressing

Keskiviikko 1.3.2023 - Tuesday Club member

Suomeksi

During Tuesday Club’s autumn season the Caravelle III towbar restoration work reached the point where the majority of the towbar parts had been painted with Isotrol primer, which prevents rusting. Half of them were painted with dark grey Isotrol and the other half with pale grey. We could see that the paint made the corrosion marks on the towbar surface clearly visible.

Photos by Juha Veijalainen.

We made a test where a small area of the towbar was painted with Teknos adhesive primer to see whether it would cover the corrosion. It did, indeed, but the corrosion marks were still visible. The next step would have been to spackle the whole towbar to make the corrosion marks disappear. However, we decided not to. We shall let the corrosion spots show and prove that the Caravelle III towbar has been rusting under the open sky for fifty years at Arlanda airport.

The towbar will be painted to the same paint scheme we used for the Finnair Super Caravelle towbar when it was restored last year. Just to refresh your memory, the towbar now under restoration was brought from Sweden together with the Sud Aviation Caravelle III (SE-DAF), which was acquired by Aviation Museum Society Finland. This towbar has been used by SAS, but we will restore it to Finnair colours. After restoration the towbar will be placed on display at Turku airport together with the Caravelle III, which will be restored to the Finnair 1963 paint scheme as OH-LEA “Sinilintu” (Bluebird).

The main colour on the towbar is the Finnair blue, with 50 cm of the towbar’s pull loop end and 73 cm of the aircraft towhead end painted yellow. The blue paint is Unica outdoor furniture paint NSC S 6030-B and the blue paint Unica outdoor furniture paint RAL 1023.

Photos by Juha Veijalainen.

The top coat painting was started from the smaller parts of the towbar. The towbar wheel rack with its fastening flange was the first part to be painted blue. The paint was applied with brushes. After the first layer we noticed that the covering wasn’t sufficient yet. The surfaces were sanded manually with sandpaper and painted with another layer of blue paint. The result was fairly good. We don’t think the wheel rack needs to be painted a third time.

The bar section of the towbar had been dismantled into two parts. The painting with finishing paint was started with the yellow paint. It was soon noticed that already the first layer of yellow paint covered well the bar which had been painted with pale grey Isotrol primer. However, the yellow paint didn’t cover so well the other half of the bar which had been painted with dark grey Isotrol. It would have been better if both halves of the bar had been painted with the pale grey primer. Well, this means only that we will have to apply several yellow layers on the half which was painted with the dark grey. At this point two layers of yellow paint have been applied.

In addition to painting, also other restoration work has been done. Both ends of the towbar lack the rectangular handlebars made of round metal rods. The Super Caravelle towbar we restored earlier has similar handlebars. We unfastened one of them to use it as a model when building the missing handlebars for the Caravelle III towbar. This Caravelle III towbar is the first version of the towbars manufactured by Sud Aviation, its model number is S.09.107 and the Super Caravelle towbar we restored last year is the factory’s last and third towbar version with model number S.09.107 2.

First we started making the fastening plates for the handlebars, using the Super Caravelle towbar handle as a model. There is a fastener plate welded to both ends of the handlebar. There is a 10 mm hole in the plate for a bolt, which fastens the handle on the towbar.

We found a suitable piece of 4 mm thick and 10 cm wide flat bar iron in the metal storage of the Finnish Aviation Museum’s hot work container. Rust was sanded off the flat bar iron and then four 8 cm pieces were cut from it with an angle grinder. The shape of the Super Caravelle towbar handle fastener was drawn on all of them. The extra material was cut off and their corners and edges were shaped round using an emery and an abrasive band. The fastener plates are now ready to be welded on the handlebar, but the holes for the bolts are missing. The following phase will be to make the actual handles for the handlebars.

On the surface of the Caravelle III towbar there are the remains of the broken handlebar fastening bolts. The bolts were drilled out, first using an 8 mm drill bit. Then a hole was made for a M10 bolt using a larger drill bit. A thread was made into the hole for a 10 mm hexagon head bolt, using a threading tap. The bolt holes are now ready for fastening the handlebars on the towbar.

Translation by Erja Reinikainen.

Photos by Lassi Karivalo except if othewise separately mentioned.

Detaching the MiG-21BIS fighter's pilot seat

Torstai 2.2.2023 - Tuesday Club member

Suomeksi

In conjunction with the scrapping of the Mig 21 BIS fighter, the cockpit section was received by the Aviation Museum Society – and now it has been prepared at the Tuesday club to become an MiG 21 BIS cockpit simulator. The external equipment of the cockpit have already been detached, but the dismantling of the cockpit interior gadgets and wiring to make way for the simulator mechanisms, is still under work.

Photo by Pentti Kuusisto

The dismantling of the cockpit section interior equipment has been hindered by the pilot’s KM-1 ejection seat, which is still in place. To dislocate the seat we received from the Karelian Wing Guild a special tool and a bar, with which the seat locking could be freed and subsequently lift the seat out of the cockpit. A retired Mig 21 BIS ejection seat mechanic from the Karelian Wing Guild paid us a visit and gave us instructions how to detach the seat.

After the start of the Tuesday Club’s spring season we turned our attention to the seat. Armed with the instructions and tools we had received from the Karelian Wing Guild together with the MiG 21 BIS manual, which we fetched from the archives of the Finnish Aviation Museum, we started to detach the seat.

With the aid of the unlocking tool we managed to disconnect the locking under the seat. To lift the seat from its place, the metal bar used to unlock the seat was attached to it with cargo straps. Then the Museum forklift was driven by the cockpit, so that the forks raised to the upper position reached over the cockpit and the bar attached to the seat.

Photo by Juha Veijalainen.

The bar was tied to the forks with straps, after which the seat could be hoisted out of the cockpit, hanging from the forks. It was a close shave whether the forks could be lifted high enough, because the restoration workshop ceiling beam was just above the cockpit and there was only centimetres of extra space. However, we managed to swing the seat over the cockpit side with a bit of manual help, and lowering the forks settled the seat onto a wooden pallet on the restoration workshop floor. Thus the MiG- cockpit was freed of the seat and we gained plenty of space to carry on with dismantling the wiring and gadgets to make way for the simulator equipment.

Photos by Juha Veijalainen.

Because there was no further restoration or maintenance work planned for the seat at this stage, it was attached with straps to the pallet and taken to storage into the container at the Museum yard used for DC-3 (DO-5) parts.

Translation by Matti Liuskallio.

Photos by Antti Laukkanen except if otherwise mentioned.

Changing the patches on lower wings of the Caudron to a modern patching material

Maanantai 26.12.2022 - Tuesday Club member

The patching of the holes on the lower wings of the Caudron C.59 CA-50), the advanced trainer from the 1920’s, was finished in 2021. More than a hundred holes of various sizes could be found on both wings. To patch the holes on the lower wings we had used first cotton and then linen fabric.  We had sewn together the tattered edges of big holes before gluing the patches on them. The patches had been fringed on their edges in the manner of the 1920’s, and they were glued on the holes using nitrocellulose lacquer, i.e. the tightening lacquer for the covering fabric.

In the autumn of 2022 we started the changing of the fabric patches on the lower wings with the Finnish Aviation Museum’s staff supervising the work. The reason for this was that the larger patches of fabric, and especially the linen patches, hadn’t properly tightened. There were also problems with those patches, where the edges of the holes had been sewn together. In these places the stitches had remained lumpy under the patches in a disturbing manner, probably because the fabric hadn’t tightened enough on the stitches. Patches on the wings have to be smooth at least for aerodynamic reasons.

The Museum decided to have the inadequately tightened linen patches and the fabric patches containing stitches to be changed to a new material. As the new material the modern heat-tightening Oratex- material, resembling the 1920s style, was chosen. Patches made of thin Oratex-material, painted in the patinated greyish green hue, produced inconspicuous and at the same time aerodynamically extremely smooth patches, compared with the fabric ones made with tightening lacquer.

To replace the patching material the fabric patches were loosened using thinner for nitro cellulose lacquer (Thinner 8). The patch was surrounded with aluminium tape, so that the thinner wouldn’t damage the 1920s covering fabric. After this a thoroughly Thinner 8 soaked fabric, which was covered with a sheet of plastic foil, was placed on the patch. The foil was taped tightly on the edges to keep the fabric wet and to prevent the thinner from evaporating. After a few hours “the package” was opened and the cotton or linen patch, glued with nitro cellulose lacquer, could be neatly detached. After this the edges of the holes without a patch were cut clean. Patches, with tattered edges sewn together, were cut completely open. Holes with tattered edges will not be sewn anew.

Now the patching of the cleaned holes could be started with Oratex-material. For each hole a larger round or rectangular piece was now cut out of the Oratex-material. After that the patch was glued and tightened on the hole by heating the patch with an iron, which was pre-heated to a suitable temperature, using a protective paper. The heating melts the glue from the underside of the patching material, fastening the patch to its place and tightening the fabric smooth.

This modern material is really handy to use and the patches turned out to be very smooth and tidy. There’s also the extra bonus of not having to protect oneself against the toxic fumes of the nitrocellulose lacquer. The appearance of Ortex- patches differs, however, from the traditional fabric patches with fringed edges from the 1920s. The work will continue in the spring season of 2023.

Photos by Lassi Karivalo.

Translation by Matti Liuskallio.

Washing the MiG-21BIS cockpit entity rear bulkhead and covering of the air ducts

Torstai 22.12.2022 - Tuesday Club member

Suomeksi

Preparations to transform the cockpit entity of the MiG-21BIS (MG-111), owned by Aviation Museum Society Finland, into an experience simulator have been going on at the Tuesday Club during the whole autumn season. Clearing the cockpit interior of instruments and wires to make way for the simulator equipment is still going on. Along with that we have concentrated on the work with the external surfaces of the cockpit entity. Later the term simulator will be used instead of cockpit entity in this blog.

The simulator rear bulkhead has been cleared of all the wires and gadgets. After that the bulkhead was cleaned with Tikkurila Oy paint cleansing liquid, prior to the actual painting of the bulkhead. For the cleansing the simulator was pushed out of the Finnish Aviation Museum’s restoration workshop into the yard. Paint cleansing liquid was sprayed with spraying bottles onto the bulkhead and the surface was brushed clean. After that the cleansed surfaces were rinsed thoroughly with water using the museum restoration workshop’s fire hose.

The MiG-21BIS simulator rear bulkhead will be painted to the shade of the faded green exterior surface. This way it will visually match the simulator’s original faded green colour. The front bulkhead will be painted with the same colour. To obtain the colour we went to the Vantaa branch of Pintaväri, carrying one fairing with a faded surface. The shade of green was defined from the fairing (NCS S5010G5OY) and accordingly Teknos Ltd KIRJO paint was mixed for painting the rear and front bulkheads.

However, we decided to postpone the painting of the cleansed rear bulkhead until the air duct openings in the rear bulkhead had been covered. Closing the rear and front bulkhead air ducts is primarily a safety issue. The ducts are large enough for a museum visiting small child and also a bigger one to crawl inside the duct. In the simulator’s front bulkhead there’s also the opening of the nose wheel well.

We decided to cover the air ducts with sturdy transparent plexi glass plates. This way one can see inside the duct. The assembly of the plexi glass covers will be done so that the pieces aren’t easily detachable, so that the museum visitors wouldn’t be tempted to take them off, but in such a way that they could be easily removed if necessary.

We started to make the plexi glass covers with the left air duct opening in the rear bulkhead. With this opening it can be tested how to cut, shape, and implant the plexiglass cover into the duct opening. Only after this plexiglass cover has been fitted into the air duct opening, will we start making the right air duct plexiglass lid.

In the Finnish Aviation Museum’s material container we found suitable 5 mm thick polycarbonate plexiglass. It can be easily sawed and shaped and is not prone to crack when worked on.

A piece of plexiglass was placed on the opening of the air duct and the shape of the duct was drawn on it. After that the plexiglass was sawed with a band saw along the drawing line to its preliminary shape. By fitting the piece of plexiglass on the opening it was moulded phase by phase to the shape of the air duct rim. The aim was to achieve a shape where the plexiglass sits suitably tightly inside the rim of the duct. Eventually the plexiglass was shaped so that it fitted into the duct opening.

We used the left lid as a template for the right air duct, albeit as a mirror image. We assumed that the ducts would be identical. After having cut the plexiglass for the right air duct and tried it on the opening, we found out that the ducts weren’t fully identical – oh well, “big country, big tolerances”. After some additional shaping the plexiglass it fitted snugly to the inside rim of the duct. Now both the lids of the simulator rear bulkhead were ready to be fastened.

To fasten the plexiglass lids we decided to use L-shape holders. One end of the holder would be fastened to the plexiglass cover, the other to the rim of the air duct. For making the holders, strips of aluminium were cut off to suitable pieces and bent into L-shape. Fastening the plexiglass covers will take place after the Tuesday Club’s Christmas break.

Along with the rear bulkhead plexiglass covers, work went on with covering the front bulkhead landing gear well. Unlike the engine air intake ducts, the cover to the landing gear opening will be made out of laminated wood. First we made a template the shape of the landing gear opening out of easily workable insulation board. According the insulation board template, the cover of the landing gear opening was sawed out of 15 mm thick laminated wood. The shaping of the cover to its final form and fastening it into place is postponed to the Tuesday Club’s spring season.

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.

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.

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.

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.

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.

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.

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.

Dismantling the MG-111 cockpit interior for the simulator

Maanantai 5.12.2022 - Tuesday Club member

Suomeksi

Work on the MiG-21BIS MG-111 cockpit to transform it into an experience simulator continues at the Tuesday Club. When the MG-111 was scrapped, Aviation Museum Society Finland received a part of the fuselage, containing the cockpit, to be modified to an experience simulator. To achieve that, most of the equipment of the cockpit entity will be dismantled. In their place the simulator equipment will be installed, but part of the original equipment and parts will also be reinstalled.

Most of the wiring and equipment from the space in front of the cockpit, as well as the wiring from the bulkhead behind the cockpit, were already dismantled at the yard of the Aviation Museum. After this the cockpit part was taken to the restoration workshop of the Aviation Museum, to dismantle the equipment and wiring within the cockpit.

First the space in front of the cockpit and the rear bulkhead were stripped off the last wires and equipment racks and holders there. So both spaces are now empty. The empty front space will at its time house the simulator equipment of the MiG-21BIS cockpit simulator. The rear bulkhead will be tidied and painted and the large openings of the engine air intake channels that are visible there will be covered with plexiglass.

Photo: Juha Veijalainen.

For emptying the cockpit of its equipment, we wanted to detach the pilot’s seat because removing the seat would provide space for working in the cockpit, both during the removing the equipment and installing the simulator equipment. Before we set to removing the seat, we detached the cockpit canopy.

Photo: Ari Aho.

To remove the seat, we received expert guidance and the necessary lifting lever from the former MiG-21BIS mechanics at Rissala. Detaching the seat didn’t, however, succeed because we couldn’t find the release catch under the MG-111 seat, where it normally is. It is possible that the release catch wasn’t reinstalled when the seat was removed when the MG-111 was struck off charge and reinstalled after the detonation charges belonging to the ejection seat had been removed. Well, we’ll try again to remove the seat in December, when we’ll hopefully get a mechanic from Rissala to come and visit and ponder about the thing with us.

Photo: Juha Klemettinen.

Although we couldn’t detach the pilot’s seat, we started to dismantle the interior of the cockpit according to Juha Klemettinen’s advice to transform the cockpit of MiG-21BIS MG-111 into a simulator. Juha removed the instrument panels and other switchboards himself. Our task was to dismantle, as advised by Juha, the space behind the instrument panel of the radar screen and the numerous wires criss-crossing there. How on earth could there be so much wiring!!

We started the work on the cockpit first by removing the radar and then turning our attention to the wires. It wasn’t so much about single wires, but bunches of wires inside a skin. Some of them could be disconnected from their connectors and removed. Disconnecting the wires from their connectors was awkward, because the connectors were either hidden on unobtainable. It came to mind that our Russian colleagues hadn’t paid a thought to easing the work of mechanics when  positioning the wires.

At the end there was no other option left but to cut the wires.  Juha gave us permission to do that. Cutting the thick wires was no mean feat, because the thick bundles containing many wires were very tough nuts to cut.

Someone had the bright idea to acquire a pair of Fiskars garden secateurs (branch cutters) to cut the thick bundles of wire. If the Fiskars secateurs cut 20-30 mm thick branches easily, they should cut through the Russian wires. So we bought a pair of Fiskars branch cutters and they worked very well in cutting the wire bundles. The box containing cut off wires began to fill with wires of various length removed from the cockpit. We still have our work cut out for us before the space behind the instrument panel has been completely emptied.

Simultaneously, as we worked inside the cockpit, we dismantled the multi-pin connecting plugs that ran through the bulkhead between the cockpit and the space in front of it. The shackles that fastened the plugs to the bulkhead could be turned open. After that the plugs were pushed through the bulkhead, to the cockpit, to be drawn out from there. It wasn’t possible to push them into the cockpit very much, because the thick wires didn’t yield. It will probably be possible to remove the plugs with their wires, after a sufficient amount of wires have been removed from the cockpit. In good time the wires from the simulator mechanism will be drawn through the openings in the bulkhead between the cockpit and the space in front of it, where the simulator equipment will be installed.

Photos: Lassi Karivalo except if otherwise separately mentioned.

Translation by Matti Liuskallio.

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.

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.

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. 

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Photo: Reijo Siirtola

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.

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.

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.

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.