Myrsky project goes on Christmas break

Keskiviikko 23.12.2020 - Tuesday Club member

Suomeksi

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Merry Christmas 2020 and New Year 2021! The Tuesday Club Member.

The hammering and tinkling of the Myrsky project have stopped in the restoration space of the Finnish Aviation Museum. It is time to have a break and rest over Christmas. We will be back at work on January 5th.

Because of the coronavirus pandemic this year has been very exceptional for the Tuesday Club. Naturally it has also been exceptional for Finland and for the whole world.

In March we had to terminate all our activities. Since June it has been possible to continue the restoration of VL Myrsky II (MY-14), but with only a handful of club members working at a time. The restoration of the Caudron C.50 aircraft and the reparation of the PZL SM-1SZ helicopter blades have been on a break all the time.

In spite of the small task force, a lot has been accomplished in the Myrsky restoration work. The Myrsky’s wing structures have been completed and now the lower sides of the wings have been painted with undercoat paint. After the Christmas break the undercoat painting will continue on the upper sides of the wings. The Tuesday Club team has worked in close co-operation with the Finnish Aviation Museum and the Finnish Air Force Museum.

I hope sincerely that the coronavirus pandemic will be blocked next year and the whole Tuesday Club team can return to work at the Finnish Aviation Museum. Hopefully in the autumn 2021, at the latest, it will be possible to continue the restoration work on the historically valuable aircraft with the full task force.

We wish you a peaceful Christmas time and a better New Year 2021!

Photo: Lassi Karivalo.

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14, MY-5

Myrsky?s test wing is built to be wing for MY-5

Tiistai 22.12.2020 - Tuesday Club member

Suomeksi

During the corona virus pandemic, the work in the Tuesday Club has concentrated on the restoration of VL Myrsky II (MY-14) and the number of workers has been limited to only a few at a time. The finalisation of the Myrsky-project’s test wing has been on a break. Now both wing halves of the MY-14 are in the undercoat painting phase and carpenters are available for other work. The team decided to continue building the test wing and to get it ready.

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The test wing is the root section, 2.5 meters long, of the Myrsky’s starboard wing, which was built to test and model the construction of the actual wing for the Myrsky. The main emphasis was on testing how the landing gear area is built, and the landing gear installed. Testing was useful because the original drawings were inadequate and inconsistent and several times it was necessary to discuss how to proceed. Sometimes the built section had to be dismantled. Due to the test wing the mistakes were not repeated when the actual Myrsky wing was built.

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The test wing will be useful also in the future. Originally the aim was to place the test wing on display at the museum as an example of a wooden wing structure in a WWII fighter, designed by the State Aircraft Factory. This is why the upper surface of the wing will be partly covered with transparent plexiglass so that the interesting inner structures and equipment can be seen.

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The saying goes that the appetite grows while you are eating, and this is what happened with the test wing. A fuselage frame of Myrsky MY-5, in poor condition, is available for the test assembly of the MY-14 wing. The Tuesday Club team decided to restore this fuselage frame so that it could be placed on display with the test wing assembled on it. Then the museum visitors could see the mixed-structure Myrsky, having a fuselage frame made of steel tube and the wooden root part of the starboard wing. The MY-5 fuselage frame has already been restored, but it has been cut behind the cockpit and is now waiting for the test assembly of the MY-14 wing

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But the appetite kept on growing. The team decided to build a 1.0-meter section of the Myrsky’s port wing to go with the 2.5-meter section of the starboard wing. The port wing section includes the wheel well of the landing gear. Neither of the wing sections is ready but they have been joined with a steel plate and the preliminary wing assembly for the MY-5 can already be seen. We can start talking about the Myrsky MY-5 wing instead of the test wing, because it has already done its task as the test item in the MY-14 restoration.

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And this is not all yet! The Tuesday Club team is dreaming – when the Myrsky MY-14 restoration has been completed – of continuing with the MY-5 fuselage frame and assembling original parts and equipment, which are available, and building the missing vertical and horizontal stabilizers and elevators. The MY-5 would be a great example for the museum visitor of how the mixed-structure Myrsky has been built. How far the MY-5 fighter will eventually be built and assembled remains to be seen in the future.

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The Tuesday Club team will continue with the construction of the Myrsky’s wing sections, 2.5 m on the starboard side and 1.0 m on the port side. The starboard side section structures are almost ready, and the landing gear has once already been assembled on it. Work continues with the leading edge. The leading edge ribs have now been glued on the front spar. The edge strip connecting the ribs to each other has been glued on the tips of the ribs as well as the battens between the ribs.

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The construction of the wheel well on the port wing section is ongoing. The plywood ring on the upper edge of the wheel well was built from narrow plywood strips which were glued into a pack on a mould. The wheel well cover is fastened on this ring. The wheel well cover will be made from aluminium sheet by metal spinning. For the 2,5 m starboard wing the cover has already been made.

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The wheel well walls are also being covered with plywood. The billets for the walls were cut from 1,2 mm plywood sheet. The billets will be fitted into place and finalised. The short wing section on the port side will not have the landing gear as the longer starboard wing section does, the wheel well will remain empty.

Photos: Lassi Karivalo.

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14, MY-5

Undercoat painting of Myrsky?s wing is well under way

Maanantai 14.12.2020 - Tuesday Club member

Suomeksi

Due to the corona virus pandemic only a handful of Tuesday Club members can continue the restoration of VL Myrsky II fighter (MY-14), but some results have been achieved, nevertheless. The undercoat painting of the wing halves is under way at the moment. Before that the edges of the compartments of the wing were covered with protective linen fabric strips. This phase has been described in the previous blog.

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The undercoat painting of the Myrsky’s wings will be done in two phases and with two different kinds of undercoat paint. First the cleaned and ground plywood surface is painted with alkyd paint which contains aluminium flakes. The undercoat paint used in this phase is TEMALAC AB 70 alkyd paint which contains aluminium flakes, and the shade of the paint is RAL 90006, white aluminium. This paint is used to fill the grain structure on the plywood surfaces and to make the plywood surface very smooth. The flake paint is applied on the plywood surfaces twice and after both rounds the surface is honed with sandpaper. The aluminium flake alkyd paint is covered with a layer of slightly darker grey paint, Teknos Oy’s adhesion primer Futura 3, with the shade RAL 7005 Mouse Grey. After this the surfaces of the wing are ready for the final camouflage painting.

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Left photo: Heikki Kaakinen.

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The undercoat painting of the wings was started by painting the compartments for the landing gear, the flap and the aileron. They were painted with the Teknos Oy paint Futura 3. The work was mainly done with a small roller, but the tight spots were painted with a brush. When the compartments had been painted, the lower surfaces of both wings were painted with the Tikkurila Oy TEMALAC AB 70 aluminium flake alkyd paint. The alkyd paint was spread with a dense foam rubber roller. The areas where precision was required were painted with a brush. The possible drippings were wiped with a cloth.

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When the flake paint had dried, the surfaces were honed with Imperial P 150 sandpaper, pressing only with fingertips. This means that a piece of cork or wood was not used with the sandpaper. Fingertips are flexible and a good tool when honing painted surfaces. Before the honing work the sandpaper was torn into four strips and each strip was folded into a pack of four layers. Now the sandpaper was a square with four layers. The honing was done by moving the sandpaper with fingertips in circles on the painted plywood surface. When one of the layers of the sandpaper pack got blocked with honing dust, the next layer was taken into use. When the honing work was ready, the dust was removed from the plywood surface with a vacuum cleaner and by wiping the surface with a damp cloth.

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Right photo: Jouni Ripatti.

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Photo: Heikki Kaakinen.

When the lower sides of the wings had been painted twice with the aluminium flake alkyd paint, the painting work on the upper sides of the wings was started. The flake paint was spread with a roller. When both sides of the wing have been painted with the flake paint, they will be ready to be painted with the TEKNOS Oy Futura adhesion primer. On top of this the Myrsky’s green-black camouflage painting will eventually be added.

Photos: Lassi Karivalo, except othervise mentioned.

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

Reinforcing fabrics for plywood seams on Myrsky's wing

Sunnuntai 22.11.2020 - Tuesday Club member

Suomeksi

The C-type wing of the Myrsky-fighter (VL Myrsky II) has plenty of plywood seams which are reinforced with linen fabric strips. The purpose of the fabric is to protect the plywood seams from problems caused by moisture. There are fabric strips e.g. on the edges of the aileron and flap compartments, on the leading edge of the aileron, on the edges of the landing gear wells and on the wing tips. The tips of the horizontal stabilizers have also been reinforced with fabric.

Originally the Myrsky’s wings didn’t have these fabric strips to prevent moisture problems. The aircraft factory started planning these for the wing in late 1944 when the whole Myrsky series had already been built. The reason for this were the problems in the plywood seams, caused by moisture, and due to which some glued plywood seams on the wings had opened. In the same modification the structure of the rear wing spar was changed, and the Myrsky C-wing was created. The first series production aircraft the A-type wing. It was replaced by the B-wing, then the B1-wing and eventually in 1945 by the C-wing. The construction of the VL Myrsky II meant continuous improvements and modifications.

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The structure of the Myrsky’s A-, B- and C-wings differed mainly in the rear spar. In the A-wing the rear spar became thinner at the seam of the aileron and the flap, thinning steeply towards the wing tip. This point proved to be weak and led to the breaking of the wing. This is why the rear spars of the A-wings were reinforced by adding a strengthening piece on the side of the spar – and this is how the B-wing was created. This was not a good solution either. That is why a new rear spar was designed, it thins linearly towards the wing tip. The wing with the new kind of rear spar was called the C-wing and the aim was to replace the Myrsky’s B-wings with the new type. Only about a dozen C-wings were built during 1945 and they were only installed on a couple of Myrskys before the aircraft type was written off. Obviously the MY-5, the MY-41 and the MY-50 were the only ones which had the C-wing.

The MY-14, which is under restoration, had a B-wing. In December 1945 the aircraft got a new wing at the Lentorykmentti 1 (Flight Regiment 1) Depot in Pori. It is not known what kind of wing was installed. Around the same time a C-wing was installed on the MY-5. So it can be speculated whether the MY-14 got a C-wing, too.

The MY-14 will get a C-wing when it is being restored. The steering committee of the Myrsky restoration project decided that building a C-wing for the MY-14 is both justifiable and appropriate. This solution was chosen mainly because the drawings that are available for the restoration work represent the C-wing and, excluding the rear spar, the wing resembles the B-wing. It can be speculated, as shown above, whether the MY-14 had a C-wing in 1945 or not.

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During the autumn the Tuesday Club team has fastened linen fabric strips on the plywood seams of the wing, i.a. the edges of the flap compartment on the port wing. The work was started by cutting the saw-toothed fabric strips for all the edges of the flap compartment from 105 g/m2 linen fabric using ”zig-zag” scissors.

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The fabric strips will be glued on the edges of the compartment with grey Futura 3 undercoat paint, hue RAL 7005, which is the same undercoat paint with which the whole MY-14 wing will be painted. The fabric strips are glued on the clean plywood surface before the plywood covering is painted. This was not the procedure with the fabrics on the leading edge of the aileron. The team was too eager to get the work done and the first layer of undercoat paint had already been applied on the ailerons before the fabric strips were remembered!

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Before gluing, areas matching the width of the fabric strip were drawn on the edges of the flap compartment. Above the plywood edge the paint was applied with a roller and below the edge with a small brush. The layer of paint was the adhesive surface for the fabric. Now the saw-toothed fabric strip could be pressed against the wet paint surface. When the fabric had been smoothed tightly against the painted surface with fingers, a layer of paint was applied on it with a roller and a brush so that the whole fabric strip was covered with paint.

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At the moment the fabric strips have been installed on the edges of the flap and aileron compartments, the edges of the landing gear well and the seams of the wing tip on the port and starboard wings. The strips protect the seams from moisture. The surfaces of the strips will be honed smooth before the wing gets its undercoat paint.

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The both wing halves of the Myrsky MY-14 are practically ready for the undercoat painting of the wings’ plywood surfaces. The plywood surfaces have already been honed smooth. Before applying the first layer of undercoat paint, the plywood surfaces will be washed to remove any grease and oil. A solution containing 50% Sinol and 50% water will be used.

Photos: Lassi Karivalo

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

About wing root fairings on VL Myrsky II

Maanantai 9.11.2020 - Tuesday Club member

Suomeksi

The wing root fairing, which covers the joint of the Myrsky’s wing and fuselage, consists of two sections. The longer rear section of the fairing covers the joint of the fuselage and wing from the trailing edge of the wing up to the level of the front spar. From there the front section of the fairing continues all the way around the leading edge of the wing. The front and rear sections of the wing root fairing are joined together with a butt joint. An aluminium plate has been riveted on the lower surface of the rear section of the fairing and this plate is pushed under the edge of the front section of the fairing. The wing root fairing is fastened on the wing and the fuselage mainly with flange nuts. The front fuselage of the Myrsky is covered with thin aluminium plate.

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The front section of the wing root fairing bends around the leading edge of the wing to the lower surface of the wing, up to the edge of the wheel wells. The fairing also covers the bottom of the front fuselage between the engine stand and the wheel wells. The wing root fairings on the port and starboard side are joined together in the middle of the fuselage. Both fairings can be unfastened separately. The outer edge of the port side fairing borders with the oil cooler air intake. The cooler exhaust opening is located on the starboard wing root fairing on the lower surface of the leading edge.

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Not a single original Myrsky wing root fairing has been preserved for the restoration work. This means they had to be built. The Tuesday Club team decided to make first the front sections of the wing root fairings based on the original drawings. Manufacturing them was a complicated and multi-staged process. The front section of the wing root fairing curves in many directions and it had to be made from three different aluminium plates, which were modified separately and welded together.

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The material for the fairings was 1 mm thick aluminium thin plate, from which the billets for the front sections of the fairings were cut. To shape the fairing sections into the desired shape, a mould of the front fuselage and wing connection was made from battens and plywood. Separate moulds were needed for the port and starboard wing root fairings. The billets of the fairings from aluminium thin plate and the two shaping moulds were delivered to Flanco Oy, where the shaping was done. From there the shaped fairing sections, still attached to the shaping mould, were delivered to GA Telesis Engine Services Oy for welding. From there the welded front sections of the wing root fairings came back to the Tuesday Club.

The shaped front sections of the wing root fairings are now waiting for the Myrsky MY-14 wing halves, built by the Tuesday Club, to be joined with a steel plate into a uniform wing. Then the wing will be tested on the fuselage frame of the MY-5. The fuselage frame of the MY-5 has already been sandblasted and painted. At the same time, the front sections of the port and starboard wing root fairings can be tested, whether they need additional shaping before their details can be finished.

Photos: Lassi Karivalo

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

Leading edge of Myrsky's aileron is strengthened with a fabric inset

Tiistai 3.11.2020 - Tuesday Club member

Suomeksi

The plywood covered aileron of Myrsky-fighter (VL Myrsky II) has a reinforcing linen inset on the leading edge. The purpose of this inset is to protect the seam of the leading edge batten and the plywood sheets which are fastened on it. The strip of linen fabric is fastened on the leading edge with paint during the undercoat painting. The leading edge is not uniform, there are two notches in it for the hinges of the aileron. A reinforcing strip of linen fabric will be installed also on the edges of the wheel wells on the wings.

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The MY-14 fighter, under restoration at the Tuesday Club of the Aviation Museum Society, has now the reinforcing strips on the leading edge of its ailerons. However, a small mishap occurred. Both ailerons had already been painted with the first undercoat paint, which is used for smoothing the surface, when the team remembered the reinforcing linen strip. Therefore, the undercoat paint, already honed smooth, had to be removed on the leading edge, over the width of the reinforcing fabric strip. The plywood surface was roughened so that the adhesive surface would be better for fastening the linen fabric on the leading edge with undercoat paint.

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For the ailerons’ leading edge, a strip 15 cm wide was cut from 105 g/m2 linen fabric. A sawtooth pattern was cut on the fabric edges zig-zag scissors to make the adhesive surface of the fabric better than that of a straight edge. On airplane covering fabrics frayed edges were used for this purpose in the 1920s. When the fabric edge was frayed, the warp was unwoven over some centimetres’ distance. The sawtooth practice became common in the 1930s.

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Before assembling the fabric on the leading edge, the aileron was supported to an upright position. Then a good layer of paint was spread on the leading edge, using a small foam rubber roller, over the width of the linen fabric strip. The fabric strip was placed carefully on the leading edge and pressed as tightly as possible against the wet paint.

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When the fabric had fastened on the paint, adhesive undercoat paint was brushed on it. The Tuesday Club team made sure there was a sufficient layer of paint all over the fabric strip and that the sawtooth edge of the fabric had fastened tightly on the leading edge surface.

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Both of Myrsky’s ailerons were treated in the similar manner. When the paint has dried, the painted surface on the fabric will be carefully honed smooth, making sure that the honing will not break the surface of the reinforcing fabric. If needed, an additional layer of paint will be added on the fabric and honed. Finally, the aileron will get the paint finishing with the green-black paint scheme.

Photos: Lassi Karivalo

Translation: Erja Reinikainen

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

Undercoat painting of Myrsky's ailerons and horizontal stabilizer

Torstai 22.10.2020 - Tuesday Club member

Suomeksi

The VL Myrsky II (MY-14) is under restoration in the Tuesday Club and the surface finishing work on its horizontal stabilizer and ailerons has continued. The finishing work will be done in three phases. First the cleaned and ground plywood surface is painted with alkyd paint which contains aluminium flakes, this is repeated with grinding and honing in between. This paint is used to fill the grain structure on the plywood surfaces of the horizontal stabilizer and ailerons, and to make the plywood surface sealed and smooth. The undercoat paint used by the Tuesday Club team was TEMALAC AB 70 alkyd paint which contains aluminium flakes, and the shade of the paint is RAL 90006, white aluminium. The undercoat painting work has been described in an earlier blog.

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The aluminium flake alkyd paint will be covered with another undercoat layer of alkyd paint, which will form the adhesive surface for the actual finishing paint on Myrsky’s horizontal stabilizer and ailerons. The Tuesday Club team used TEKNOS adhesion primer Futura 3, with the shade RAL 7005 Mouse Grey. The Futura 3 adhesion primer is slightly darker than the TEMALAC, so it was easy to see where the new layer of paint had not yet been applied. Two layers of paint were applied on the horizontal stabilizer and ailerons, with grinding and honing between the layers. The painting work was done using a polyester roller. The horizontal stabilizer and ailerons now have their undercoat paint.

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The ailerons are not ready for the finishing paint yet. A strengthening strip of linen fabric needs to be fastened on the ailerons’ leading edge. The strengthening fabric reaches around the leading edge so that it protects the seam of the plywood surfacing and the solid wood leading edge. The strip of linen fabric will be glued on the leading edge using the adhesive primer. Before fastening the fabric on the leading edge, the paint surface on the leading edge has been ground away over the width of the fabric strip.

Photos: Lassi Karivalo

Translation: Erja Reinikainen

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

Tuesday Club activities are suspended until end of the year

Maanantai 19.10.2020 - Tuesday Club member

Suomeksi

Tuesday Club activities have been suspended due to the Covid 19 coronavirus pandemic since March. However, the restoration work on VL Myrsky II (MY-14) has been continued by a small task force, so that the continuation of the project is ensured.

The coronavirus pandemic seemed to subside during the summer, and we thought it would be possible to relaunch Tuesday Club activities in the autumn. Then we would know whether the positive development of the epidemic is permanent and there would not be a second wave. But this is not what happened. The epidemic started to spread again in August and by September it was obvious that the second wave had arrived.

Therefore the Finnish Aviation Museum and the Aviation  Museum Society came to the conclusion that the risk for the Tuesday Club members, many of whom were in the risk group, to catch the virus in the museum’s restoration space would be too high if the activity continued. Therefore, it was decided that the Tuesday Club activities are suspended until the end of the year. This was very disappointing decision for the Club members, but it was the right and understandable thing to do.

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The Finnish Aviation Museum and the Aviation Museum Society decided, nevertheless, that the restoration activities of VL Myrsky II (MY-14) can be continued by the Tuesday Club at the museum, but with restrictions. The aim of these measures is to ensure that the Myrsky restoration project can be completed next year. The restrictions mean that only about half a dozen Club members can be working simultaneously on Myrsky in the restoration space – naturally wearing masks and other protective items also, if needed.

The Finnish Aviation Museum decided to suspend also other activities run by volunteers (such as guided tours) until the end of the year. The justification is to protect the risk group members in the common spaces of the museum. The recommendations, given on 21.9.2020 by the Ministry of Education and Culture and the Finnish institute of health and welfare, say that the risk group members should avoid close contacts during the epidemic, and therefore it is not advisable to take part in public events or gatherings, or activities arranged in public spaces.

Photo: Lassi Karivalo

Translation: Erja Reinikainen

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

About electrical equipment in Myrsky's wing

Maanantai 12.10.2020 - Tuesday Club member

Suomeksi

The VL Myrsky fighter has 24V direct current electrical system. In the wings the equipment that need electricity are the navigation light, in the port wing the heating for the pitot tube (i.e. speed detector), the releasing system of the auxiliary fuel tank or bomb and the release indicator of the auxiliary fuel tank or bomb. These devices are operated from the cockpit with switches. Indirectly electrically operated are also the landing gear and the flaps, located in the wings. These are moved with operation bars, linked to electrical motors located in the fuselage. The ailerons move mechanically when the stick is moved.

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The auxiliary fuel tank or bomb is released from the hanger on the wing when the hook-shaped lock/release latch of the hanger is released. The fuel tank or bomb has a bracket for hanging the tank/bomb on the latch. The latch is released electrically using a solenoid. The fuel tank or bomb release indicator functions so that when the tank or the bomb is on the hanger, the indicator’s spring pin is pressed into the indicator. When the tank or the bomb is released, the pin is freed and causes an electrical impulse in the indicator and forwards the information to the signal lamp in the cockpit.

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The electrical cables in the wing are led through ducting tubes inside the wing. Power cables from the fuselage are led into the joint box which is fastened on the wing rib next to the auxiliary fuel tank / bomb hanger. From the box there are separate power cables to the different devices. There are two round hatches on the upper surface of the wing for maintenance work that is needed on the hanger and the joint box.

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The Tuesday Club team is installing the electrical cabling on the port wing. The cables have been pulled through the ducting from the wing root to the joint box. The cables for the navigation light, pitot tube and auxiliary fuel tank / bomb hanger are being installed into the joint box. At the moment the cabling is still loose and crawling through the maintenance hatch on the wing top, but some cables have already been installed to their proper places.

Photos: Lassi Karivalo

Translation: Erja Reinikainen

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

Myrsky's wing root walkway

Lauantai 26.9.2020 - Tuesday Club member

At the wing root of VL Myrsky II, on both sides of the fuselage, on the wing’s plywood covering there is a strengthening strip of plywood. This makes it possible to walk on the wing when doing maintenance work. Very often these strengthened strips, which allow stepping on the wing, are clearly visible from the wing surface or painted black at least. However, this is not the case in the Myrsky, where these plywood strips have the same black and green paint scheme as the upper side of the wing.

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Upper photo: The photo archive of the Finnish Air Force Museum.

On the Myrsky drawings these strengthening plywood strips are called “step plates”. They are fastened on the wing’s plywood covering with glue and screws. The aluminium wing root fairings, which protect the connection of the fuselage and the wing, are fastened onto the fuselage side edge of the step plates with flange nuts and screws.

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The step plates for the Myrsky’s wings are being made at the Tuesday Club. The semi-finished plates were cut from 2 mm thick plywood according to the original drawing. The actual plywood covering of the wing is 4 mm thick at the wing root. The step plates for the port and starboard wing are mirror images. The position of the fastening screws and wing root fairing flange nuts were marked on one of the step plates, following the original drawing. The pencil marks were highlighted with a metal punch. The punch markings will make it easier to drill the holes into their exact positions.

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After this the mirror image step plates were placed accurately on top of each other and fastened with pieces of double-sided tape. In this way the holes for the screws can be drilled simultaneously on both plates and exactly in the same position on the plates. The holes for the fastening screws were drilled with a 3 mm drill bit.

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For the flange nuts on the wing root fairings, holes for the nuts had to be made on the edge of the step plate. These holes must match the shape and size of the flange nut and be slightly oval-shaped because the nut is sunk through the step plate, all the way to the level of the wing surface.

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First three holes were drilled into the plywood with a 3 mm drill bit, these holes help when the oval hole is made into the step plate. The small holes were used when making the holes larger with a column-type drill, using drill bits of two different sizes. The work continued by shaping the holes into their correct size and shape with a chisel and a file.

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The following phase will be to fit the step plates into their places on the top surface of the port and starboard wing and to fasten them with glue and screws. The step plate has already been preliminarily fitted to the root of the starboard wing.

Photos: Except separately otherwise mentioned, Lassi Karivalo.

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

Myrsky MY-5's fuselage frame was taken to sandblasting and painting

Keskiviikko 16.9.2020 - Tuesday Club member

The earlier blogs describe how  the Myrsky MY-5’s rusted fuselage frame will be straightened, sandblasted and painted before it can be used for the wing test assembly of Myrsky MY-14.

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The text in the box: Original paint under the bracket.

The MY-5 fuselage frame has been fastened on a sturdy metal frame, the assembly jig, outside the restoration space at the Finnish Aviation Museum. It has been straightened on the jig and the remaining parts and equipment have been dismantled. Most of these are different band-shaped fastening brackets. The fuselage frame was cut behind the cockpit, so that it became easier to handle and it can be brought into the museum’s restoration space for the test assembly of the MY-14 wing. Later the fuselage frame parts will be welded together so that it will be the whole Myrsky MY-5 fuselage frame.

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The fastening brackets, which were still attached on the MY-5 fuselage frame, are important when the original paint and its tint are being investigated. When the brackets were unfastened, some well-preserved original paint of the fuselage frame was revealed. The painted surface has been protected from rusting, hidden under the brackets.

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The original paint surface was cleaned by grinding it lightly, so that the tint of the paint became even more intensified. On both sides of the cleaned painted area a paint test was made, using two different shades of grey Isotrol paint (linseed oil alkyd paint). This was necessary so that the team could choose the appropriate tint of the undercoat paint for the fuselage frame. The tints of the tested grey paint were RAL 7005 ja RAL 7042.

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On Tuesday, September 15th, the shortened MY-5 fuselage frame was loaded on a trailer, using a stacker. The frame will be taken to Auto- ja Teollisuusmaalaamo Oy, a paint workshop in Vantaa. The Tuesday Club team tried also to fit the rusted engine frame on the trailer, but it wasn’t possible. The engine frame will be transported to the paint workshop later.

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At Auto- ja Teollisuusmaalaamo Oy the fuselage frame will be sandblasted and painted with undercoat paint. When the sandblasting has been done, the clean metal surfaces will be covered with clear varnish, which protects the frame from rusting. The grey Isotrol undercoat paint will be applied on top of the varnish. The MY-5 fuselage frame, with its undercoat paint, will return to the Finnish Aviation Museum in a couple of weeks.

Photos: Lassi Karivalo.

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14, MY-5

City of Vantaa politicians visit Finnish Aviation Museum and learn about aircraft restoration

Maanantai 7.9.2020 - Tuesday Club member

City of Vantaa politicians visited the Finnish Aviation Museum for “practical training” as a part of the Politician’s museum internship campaign, coordinated by the Finnish Museums Association. The politicians who visited the museum were city council member Minna Räsänen (sdp), member of parliament, city council chairman Sari Multala (kok) and member of parliament, city council member Jussi Saramo (vas). Räsänen and Multala were present at the museum, Saramo attended via remote access.

As a part of the “practical training”, the cooperation of the museum and Aviation Museum Society was introduced to the guests. The Tuesday Club volunteers’ work was illustrated in the museum’s restoration space, although the Tuesday Club has officially been terminated because of the corona virus pandemic.

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From left to right: Pia Illikainen, Minna Räsänen ja Matti Patteri.

In the restoration space museum Intendent Matias Laitinen told the guests about the volunteers’ role at the Aviation Museum. Tuesday Club project manager Lassi Karivalo introduced the aircraft restoration activities of the Tuesday Club. The leader of the VL Myrsky II (MY-14) restoration project Matti Patteri introduced the history of domestic aircraft industry and explained how museum aircraft, and more specifically the Myrsky, are restored in practice. The Myrsky project was launched in 2013 and up to now the restoration team has spent about 30 000 working hours. Most of the work has been done by volunteers. The Myrsky restoration also includes cooperation with vocational colleges, e.g. Vantaa Vocational College Varia and Tavastia Vocational College in Hämeenlinna, and naturally work contribution from the Aviation Museum staff. The visitors learned that the main motivating factors for the volunteers’ participation are the sense of community, the good team spirit and the interesting work items.

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From left to right: Sari Multala and Matti Patteri.

Due to the corona virus pandemic situation, the museum’s volunteer activity has been terminated since March. In the future the working procedures will have to be reorganized. A large volunteers’ gathering can’t be organized yet, and not for some time – and in the social aspect this is very unfortunate. During the corona virus time the Aviation Museum Society has arranged for its members, and to all who are interested, remote access to presentations about aviation history. The museum has produced videos and audio tours with its partners. However, by now everybody is very eager to get back to work and to meet the volunteer friends at the museum. The aim is to relaunch the Tuesday Club activities in October, at some extent. The corona virus situation in Finland will define whether this is possible or not.

Photos: Mia Kunnaskari.

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

Undercoat painting of MY-14?s horizontal stabilizer

Perjantai 28.8.2020 - Tuesday Club member

Before the painting work, the port and starboard halves of the VL Myrsky II’s (MY-14) horizontal stabilizer were fastened on an assembly jig, made of square steel tube. On the jig the stabilizer can be turned around as needed in the various phases of the surface treatment process.

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The seams of the plywood covering on the horizontal stabilizer had been spackled and ground smooth before starting the undercoat painting work. The plywood surfaces were washed, using a water-Sinol-solution, containing 50% of water and 50% of Sinol. This is a normal procedure for removing grease from the surfaces before painting. After the wash, the surfaces were dried with a heat blower and sanded three times, with 240 abrasive paper.

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Photo: Jouni Ripatti.

The MY-14’s horizontal stabilizer will be painted in several phases. First an undercoat paint is spread on the plywood surface, and the actual paint is applied after this. There will be several layers of both paints. The undercoat paint and the actual surface paint are both alkyd paints, as were the original paints when the Myrsky fighters were being built in the 1940’s at the State Aircraft Factory (VL) in Tampere.

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Right photo: Jouni Ripatti.

The undercoat paint, which is used for the plywood surfaces of the MY-14 under restoration, is TEMALAC AB 70 alkyd paint which contains aluminium flakes. The shade of the paint is RAL 90006, white aluminium. The aluminium flakes will fill the grain structure on the plywood surface, which will make the plywood surface smooth and sealed when it is ground and honed.

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Photo: Heikki Kaakinen.

Now the upper and lower surfaces of the horizontal stabilizer have been painted once with the undercoat paint containing aluminium flakes. For the first layer the paint was made thinner, using Ruiskuohenne 1032, and the paintwork was done with a polyester roller (mini paint roller). The roller produced a very even layer. When the paint had dried, the surfaces were ground smooth for the second layer. The next undercoat paint layer will be done using paint, which is not thinned, and which is slightly darker in colour than the first layer. The darker shade will show clearly which areas have been painted for the second time and which haven’t. If a third layer of undercoat paint is needed, it will be darker than the second one.

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An unexpected break in the painting work appeared, when the darker shade of TEMALAC AB 70 undercoat paint wasn’t available due to holidays. The Tuesday Club team will have to wait for the mixing and delivery of the darker paint before continuing the undercoat painting work on the horizontal stabilizer.

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The MY-14’s horizontal stabilizer will eventually be painted according to the standard paint scheme of the Finnish Air Force in the 1940s: the upper surface will have a green and black pattern and the lower surface will be painted light blue.

Photos (expect otherwise separately mentioned): Lassi Karivalo

Translation: Erja Reinikainen

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

About Myrsky MY-14 oil cooler, wing root fairings, landing gear doors and MY-5 fuselage frame

Maanantai 24.8.2020 - Tuesday Club member

When the VL Myrsky II (MY-14) port wing half covering was being finished in the restoration space of the Finnish Aviation Museum, also other Myrsky-project items were under work.

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Before the Corona virus pandemic interrupted the work, the Tuesday Club team had completed most of the engine’s oil cooler supply and exhaust air duct parts. They have been made from 1 mm thick aluminium plate. Now it was time to start building, according to the original drawing, the airflow control device into the supply air duct. The control device consists of a circular frame, inside which there are three flaps, which move on their axles. The air flow into the oil cooler can be controlled continuously with these flaps. The air flow control is done from the cockpit.

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The parts needed for the air flow control device were cut from 1 mm thick aluminium plate, using a laser cutter, at ProLaser Oy. Holes for the rivets, which are needed in the assembly work, were drilled on the semi-finished control flaps. The parts of the air flow control device were also chromated to prevent corrosion.

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The assembly work of the oil cooler control device was started at the circular frame. When the round frame had reached its final shape, the ends of the axles of the three control flaps were riveted on the frame. There is a slot on the end of the axle, into which the edge of the aluminium flap fits. The three flap plates fitted perfectly on the axle slots. The following phase will be to rivet an aluminium profile on the flaps, which locks the flaps on the axles.

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Some metal work has been needed when making the aluminium fairings, which cover the connecting point of the Myrsky’s fuselage and wing. The work was started on the fairing which covers the wing’s leading edge and the fuselage. The complicated fairing shape consists of three pieces of aluminium plate, which are welded together. The preliminary fairing parts were cut from 1 mm thick aluminium plate. A wooden last was made for shaping the aluminium sheets into the desired shape. Two lasts are needed, one for the starboard wing and the other for the port wing. The preliminary fairing parts were shaped into their final shape at Flanco Oy, using the last. The shaped fairing parts were welded together at GA Telesis Engine Services Oy.

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The work on the landing gear enclosure doors of the test wing has also continued, including the door fastened on the wheel hub and the oleo strut door. The doors had been nearly finished already in March. The remaining aluminium profile stiffeners were riveted on the inner surface of the doors. The doors were now ready to be installed. The bulging parts or the “bumps” on the outside of the oleo strut door have also been welded into place. These bumps are needed for the landing gear retraction fork which is fastened on the oleo. These bumps have also been welded on the preliminary oleo door plates of the actual Myrsky wing’s landing gear. However, the actual wing doors have not been chromated yet and their stiffeners have not been fastened.

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The Myrsky MY-5 fuselage frame, which was brought from Tikkakoski, has also been under work. The parts, which were still fastened to the frame, have been unfastened and now the frame is “clean” for sandblasting. The fuselage frame will be sandblasted at Auto- ja Teollisuusmaalaamo Oy, where it will also be painted grey.

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A pile of different kinds of brackets and parts was dismantled from the MY-5 fuselage frame. Some of the parts had to be unfastened with some violence, using an angle grinder for the work, because the badly rusted fastening bolts couldn’t be opened. The rust will be removed, and the parts will be painted. All the parts will be needed when the MY-5 fuselage frame is restored to be the exhibition fuselage, which illustrates the structure of the Myrsky fighter. The 2,5-meter test wing, built during the Myrsky project for testing the wing construction procedure, will eventually be fastened to the MY-5 fuselage.

Before that, the MY-5 fuselage frame will be used for test assembling and fitting the Myrsky MY-14 wings. In the fitting phase the MY-5 fuselage frame will be lowered on the MY-14 wing, built by the Tuesday Club team. The wing will be locked onto the fuselage with the four wing attachment brackets or bolsters. The wing parts will be fastened with steel plates and the whole wing can be test fitted in about a month’s time.

Photos: Lassi Karivalo.

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14, MY-5

MY-14´s port wing half is covered with plywood

Sunnuntai 9.8.2020 - Tuesday Club member

The work on VL Myrsky II (MY-14) is continuing at the Tuesday Club, but not at full speed yet, though. Work is being done e.g. on the plywood covering of the starboard wing leading edge and trailing edge, and the sides of the flap cavity. The engine area is also under construction: the air supply duct is being fitted into the opening in the NACA-ring, the cowling under the engine is being built and the gills controlling the air flow through the air duct on the oil cooler are being installed. However, the main emphasis is in getting the port wing plywood covering to the same situation with the starboard wing. The work is almost ready.

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The leading edge of the port wing is now almost covered with plywood. The strips of plywood covering the leading edge were first soaked in water so that they could be bent around the tapering leading edge. When the plywood had dried into shape, it was glued on the leading edge. The seams of the plywood were spackled and honed smooth. Only small areas around the pitot-tube and at the wing tips have not been covered.

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Right photo: Heikki Kaakinen.

The trailing edge area on the upper surface of the wing, between the rear spar and the trailing edge, has also been covered with plywood. First the plywood sheets of the trailing edge area were cut into the accurate size, then covered with protective varnish on the inside and then fitted into place. When the plywood sheets had settled into their places and their bevelled edges met correctly, the sheets were glued into place. Before the inner parts of the wing were permanently covered from sight, the Tuesday Club members who were involved in the work, wrote their names on the inside of the wing as a greeting for the future generations.

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Left photo: Heikki Kaakinen.

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The gluing of the plywood sheets on the upper surface of the trailing edge was secured by fastening pieces of plywood on the wing ribs and the connecting battens with a staple gun. The permanent gluing of the plywood on the trailing edge batten was ensured by fastening a long row of clamps on the edge. When the glue had dried, the clamps and the stapled pieces of plywood were removed. The marks of the staples that were left on the plywood surface and the seams of the plywood sheets were spackled and honed smooth.

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It was a difficult task to fasten a 10-centimeter strip of plywood onto the upper edge of the flap cavity on the port wing. A similar, but narrower strip, has already been fastened on the lower edge of the flap cavity. These strips will form an aerodynamic compartment to the front of the flap space. The leading edge of the flap will sink into this space.

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Photos: Heikki Kaakinen.

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The port wing covering work had now reached the phase where the starboard wing already was. The surface work, i.e. smoothing and honing which are needed before the painting of the plywood surfaces, can now be started. Some painting has already been done: the open inner areas on the top surfaces of the wing roots on both wings have been painted with grey alkyd paint. These open areas at the wing root will not be covered with plywood, because the areas will be left under the Myrsky fuselage when it is lowered on the wings.

Photos (expect if separately otherwise mentioned): Lassi Karivalo

Translation: Erja Reinikainen

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14

About the fuselage frame of VL Myrsky MY-5

Tiistai 4.8.2020 - Tuesday Club member

When the restoration project of VL Myrsky was launched, three damaged Myrsky fuselage frames were available at the Finnish Air Force Museum in Tikkakoski. The rear section has been violently cut away from all three fuselage frames. The least damaged fuselage frame of MY-14 was chosen for the restoration project. This is how the project became the restoration project of the VL Myrsky MY-14 fighter. The MY-14 fuselage rear section, which has been cut off, has disappeared and therefore the rear section of MY-9 was chosen to be connected to the MY-14 fuselage frame. Also a fourth Myrsky fuselage frame (MY-10) exists, in a private collection, and there have been negotiations about purchasing it for the Myrsky project.

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The MY-14 fuselage with its engine and control equipment is mainly restored at the Finnish Air Force Museum in Tikkakoski. The main task of the Aviation Museum Society’s Tuesday Club is to build in Vantaa in co-operation with the Finnish Aviation Museum the other parts of the fighter, such as the wings with all their equipment, the parts of the tail and to build the parts for the nose, e.g. the front engine cowling, NACA-ring and the engine cowlings on the sides.

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Photo: Jorma Laakkonen.

The restoration project started in 2013 and the development of the project has been followed all the time on homepages of the Aviation Museum Society and Myrsky Project, and also in yearly journals. In Tikkakoski the restoration of MY-14 fuselage is already quite far. In Vantaa the Tuesday Club has prepared the tail parts and the wings to the point where their surfaces can be honed smooth and painted. The aim is that the restored – but static – MY-14 can be placed on display during the year 2021.

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The second best Myrsky fuselage from Tikkakoski, i.e. MY-5, was also taken into the restoration project with its separate rear fuselage and engine mounting. The MY-5 fuselage frame has its own important role in the Myrsky restoration project. Some useful parts have been dismantled from the fuselage frame and repaired in Tikkakoski for the needs of the MY-14 fuselage frame restoration. On the other hand, the fuselage frame of the MY-5 will be used by the Tuesday Club for the fitting of Myrsky’s wings. The wing positioning and fastening will be tested on the fuselage frame by the Tuesday Club before the wings are sent to Tikkakoski to be installed on the fuselage of MY-14.

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Additionally, an even bigger role has been planned for the MY-5 fuselage frame. It will be used to build a demo-fuselage of the Myrsky-fighter to illustrate the metal and wood structure of the aircraft. The 2.5-meter piece of the starboard test wing and the 1-meter piece of the port test wing will be fastened on the fuselage frame. Before building the actual wings, the test wings have been built to test the methods how to build the complicated root of the wing with the landing gear and how to lock the wing halves to each other with steel plates.

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The rear fuselage of MY-5, brought from Tikkakoski to Vantaa to the Finnish Aviation Museum, has already been used in the Myrsky-project. The badly rusted rear fuselage frame was straightened in a jig, specially made for the purpose, and sandblasted and painted, using grey alkyd paint. After this the rear fuselage has been used by the Tuesday Club to fit and support the horizontal and vertical stabilizers when they are being built.

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The fuselage frame and engine mounting of MY-5 were brought from Tikkakoski to the Finnish Aviation Museum in Vantaa on July 21st, 2020. The MY-5 fuselage was transported by the Myrsky-project’s PR-man, on his holiday trip to Ostrobothnia. On Friday 10.7 on his way there he took the trailer and “some Myrsky items” to Tikkakoski. On Tuesday 14.7 a group of Tuesday Club members travelled to Tikkakoski and moved, with some assistance from the Air Force Museum, the MY-5 fuselage frame and engine mounting on the trailer to wait for the transportation. The unusual load travelled successfully to the Finnish Aviation Museum on 21.7. Fortunately, the traffic was rather quiet and it wasn’t raining.

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When the fuselage frame was outside the museum, the cargo straps were unfastened. Then the MY-5 fuselage was lifted from the trailer with a forklift and placed on the ground to wait for cleaning and repair. The badly rusted and partly bent and damaged fuselage frame will be straightened and cleaned by sandblasting, straightened and repaired, and then painted grey. Behind the cockpit some frame pipes have been bent and some are even missing.

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Left photo: Heikki Kaakinen.

The assembly jig, which was made from square steel pipe for the straightening of MY-14’s fuselage frame, was re-assembled and modified for the MY-5 work. The jig was fastened on the four brackets by the cockpit on the MY-5 fuselage. These brackets are used for fastening the wings with four fastening bolsters on the wings.

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Photo: Heikki Kaakinen.

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The MY-5 fuselage frame, now fastened on the assembly jig, will be measured carefully and straightened. The places of some parts or their fastening brackets will be defined and photographed before they are dismantled for cleaning. Also the rusty engine mounting, brought from Tikkakoski, will be cleaned by sandblasting and painted.

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When the fuselage frame has been cleaned and painted, the rear fuselage frame (which has already been restored earlier) will be welded to it. Then the MY-5 fuselage frame will be ready to serve as the fitting frame or assembly jig for the MY-14 wings, and later as the basis of the Myrsky demo fuselage. The MY-5 demo fuselage will be restored so that the structures remain visible in the way they were left visible when building the short test wings. The restoration of this demo fuselage is not the main priority at the moment, the work will be started when the restoration of the MY-14 has been completed.

Photos (except if separately otherwise mentioned): Lassi Karivalo

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoration, VL Myrsky, MY-14, MY-5

Stiffeners are fastened on Myrsky?s wheel and oleo compartment doors

Tiistai 14.4.2020 - Member of Tuesday Club

Suomeksi

The VL Myrsky (MY-14) is being restored and its parts around the wheel well, including the outer door of the wheel well, the door of the oleo compartment and the door stiffeners were sent to be chromated. When they came back from the chromating process, it was time to fasten the stiffeners on the doors. Chromate bathing means that the aluminum plate is treated with acid solutions containing chromates and a thin inorganic film is formed on the surface of the aluminum with the components of the surfacing bath liquid. This surfacing protects the aluminum plate from oxidization. In the chromate process the Myrsky’s landing gear doors and their parts got a beautiful golden hue on the surface.

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First the stiffening battens were fastened on the landing gear oleo compartment door. The battens have top hat profile. This means that the square batten is open at the bottom and it has sleeves bent to the sides. The sleeves have holes for riveting the stiffening batten on the edges of the door.

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The holes for the rivets had already been drilled earlier on the oleo compartment door and on the stiffening battens. The rivet holes on the edges of the door had also been beveled for flat head rivets. The stiffening battens were riveted on the lower side of the door. The work was started by fastening the battens into place with a couple of pins which were pushed through the rivet holes. Before riveting the battens the oleo compartment door was assembled into place and the team made sure that it fitted properly in its place also with the stiffening battens.

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Then the battens were riveted on to the inner side of the door, rivet by rivet, using the riveting gun. The riveting gun is faster and more practical than using a hammer for the riveting work. When all the stiffening battens had been fastened on the oleo compartment door, the work on the stiffeners for the door on the wheel hub was started.

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The oval stiffening plate on the outside of the outer door of the wheel well was fastened on the wheel hub with four machine screws. Then the places for the rivet holes were marked on the edges of the stiffening plate. The oval plate is fastened on the door with rivets. A prick was used for marking the location of the holes. A temporary screw was fastened to both ends of the oval plate so that the stiffening plate could be pressed tightly on the slightly convex door. The screws keep the stiffening plate in its place on the door while the rivet holes are being drilled.

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The holes were drilled using a vertical drill and beveled with a beveling drill bit. Then the stiffening plate was riveted on the door, from the inside of the door, using a riveting gun.

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Then the box shaped stiffeners were preliminarily placed on the inner side of the outer wheel well door. There are stiffeners on both sides of the door and one at the bottom edge. The stiffeners are riveted by their outer edge on the supporting frame around the inner edge of the door, made of square steel tube, and by their hems on  the door. The supporting frame of steel tube was not chromated but painted with grey Isotrol paint to prevent it from rust.

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The riveting of the box-shaped stiffeners was not started before the Tuesday Club activities were terminated due to the Corona virus pandemic. The stiffeners were riveted on the oleo door but the stiffeners on the outer door of the wheel well are still under work. The landing gear of the test wing will have to wait until the work continues after the virus epidemic is over.

Photos: Lassi Karivalo

Translation: Erja Reinikainen

Kommentoi kirjoitusta. Avainsanat: aviation history, restoring, old aircraft, VL Myrsky II, MY-14

Wheel well and oleo doors for Myrsky are made

Tiistai 7.4.2020 - Member of Tuesday Club

Suomeksi

Retractable landing gear was common already in WW2 fighters and VL Myrsky is not an exception. At the root of Myrsky’s wing there is an enclosure for pulling in the landing gear. The enclosure consists of a wheel well for the wheel and a compartment for the oleo (the shock strut of the landing gear). One half of the wheel well opening is covered by the inner door, made of aluminum plates, also called “daisy cutters”. The door is fastened on the inner edge of the wheel well with hinges. This door is opened automatically by a spring lever when the landing gear is taken out and it is closed by the wheel when the landing gear is taken in.

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The other half of the wheel well is covered by the outer door, which is made of aluminum plate and fastened on the wheel hub, it is a pair for the “daisy cutter”. The oleo enclosure door is made of aluminum plate as well and it is fastened angel on the oleo. These two doors on the landing gear are overlapping at a distance of about 20 cm and they slide against each other when the landing gear oleo is flexing. The wheel is fastened by its axle on the “piston rod” which moves inside the oleo. The landing gear can’t have one solid door fastened on the wheel and oleo because this would disturb the vertical flexing movement of the wheel.

The Tuesday Club team made first the inner doors for MY-14 wheel wells on the test wing and the actual wings. Then the construction of the outer doors and the oleo doors was started. The team decided to make the doors for the test wing first.

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A laser cutter was used when cutting the semi-finished shape of the oleo door from 1.5 mm aluminum plate according to Myrsky’s original drawing. At the same time a hole was cut into the plate where the retraction mechanism fork connects to the oleo. Holes were drilled along the edges of the door where stiffening battens will be riveted.

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A small canopy is needed to cover the hole where the retraction mechanism fork connects to the oleo. A metal mould was made first and the canopy was pressed against it from aluminum plate. The canopies were made for the test wing and for the actual wings. The canopy was welded onto the edges of the hole on the door. After this the pre-cut door was fitted into place into the oleo opening and fastened on the temporary plywood brackets on the oleo. Eventually the door will be riveted on the brackets which are welded onto the oleo.

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The semi-finished shape of the outer wheel well door was also cut from 1.5 mm aluminum plate with a laser cutter. The door is fastened on the wheel hub with four 6 mm flat head machine screws. The holes on the door for the screws have to be exactly in the right position to meet the threaded holes on the wheel hub. The positioning was done by placing a positioning plate with sharp-pointed markers on the wheel hub. A marker was also placed in the middle of the hub. Then the door was positioned carefully into the wheel well and the plate surface was tapped against the marker points. Now there were clear marks on the lower side of the plate for drilling the holes for the screws. The marker marks were strengthened with a spike before making the holes with a vertical drilling machine.

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The door fastened on the wheel hub has an oval-shaped stiffening plate on the outside. It was cut from aluminum plate. The stiffening plate is fastened on the door with the four machine screws which fasten the door on the wheel hub. Holes were made on the oval stiffening plate and the edges were beveled. The stiffening plate will also be riveted on the door by its edges. The outer wheel well door was fastened on the wheel hub with the oval stiffening plate attached. Now the test wing landing gear had both doors in place for the first time. They are well visible when the landing gear of the test wing is taken out.

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There will be stiffeners and supporting battens on the inner surface of the outer door in the wheel well. A supporting frame made of rectangular steel tube will be fastened on the edge of the door. The lower part of the door will have box construction strengtheners made of aluminum plate.

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Pre-cut strengtheners for the inner surface of the wheel well door were cut from aluminum plate with the laser. They were modified to be fitted and fastened into place. Also the stiffeners for the oleo door are now ready.

The stiffeners will not be riveted on the doors before the half ready doors and the stiffeners have been chromated. The chromate treatment will prevent the aluminum plate from oxidizing and it will be done by an outside supplier.

Photos: Lassi Karivalo

Translation: Erja Reinikainen

Kommentoi kirjoitusta. Avainsanat: aviation history, restoring, old aircraft, VL Myrsky II, MY-14

Experimenting dry plywood covering for leading edge on Myrsky's starboard wing

Tiistai 10.12.2019 - Member of Tuesday Club

Suomeksi

The restoration work of VL Myrsky II (MY-14) has progressed well during the autumn and the plywood covering on the starboard wing has been completed, excluding the leading edge. The plywood work on the leading edge has had to wait that the work on the port wing, which is being built alongside, reaches the point where the trailing edge is under construction. This is when the two wings under construction in the restoration space of the Finnish Aviation Museum change places. The wings will be moved from their first work platform on to the other platform. This is necessary in order to have enough working space around the wing to complete the port wing’s trailing edge and the starboard wing’s leading edge.

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The leading edge of Myrsky’s wing consists of plywood ribs and supporting battens between the ribs. The leading edge is covered with 1,5 mm thick plywood. One sheet of plywood covers the surface of four rib-gaps. Four joining plywood sheets are needed to cover the whole leading edge, which is about five meters long. The plywood sheets are joined on a rib, using a scarf joint.

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The challenge in the plywood covering of the leading edge is to bend the plywood sheet around the tapering leading edge. If the profile of the leading edge is very pointed, bending the dry plywood sheet around the edge will cause tears and cracks on the outer surface of the plywood. To prevent the plywood from cracking, the sheet is usually moistened or sometimes the wet plywood is fastened on a last, which models the leading edge. The plywood sheet will dry on the last and form a trough, which can be installed on the leading edge.

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The Tuesday Club team wanted, however, to make an experiment and bend the dry thin 1.5 mm plywood sheet on the leading edge. The leading edge profile on Myrsky’s wing is not very pointed. For the experiment steel bands were made from 1 mm thick steel plate, they were cut 10 mm wide. The bands are used for pressing the plywood sheet evenly against the leading edge ribs. A steel band was made for each rib on the leading edge, corresponding the length of the leading edge profile. The bands were placed on each rib.

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A tightening clamp was made at the upper end of each band, with a wing nut for tightening the band against the plywood. At the tightening clamp the ends of the band are bent to an angle of 90 degrees for the wing nut joint. The lower end of the band is fastened with a screw on the front spar on the lower side of the wing. The upper end of the band (with the tightening clamp) is fastened on the upper side of the wing on the wing spar.

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The dry bending of the plywood covering was experimented without any gluing along the distance of four rib-gaps. The bands were fastened on their places on the five ribs, with the tightening clamps still open. A piece of plywood was cut from the 1.5 mm thick plywood sheet, matching the area of the four rib-gaps. The edges of the plywood sheet were bevelled so that the adjacent sheet can be joined with a scarf joint.

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When the preparations for the experiment had been made, the plywood sheet was fitted, lower edge first, between the leading edge ribs and the tightening bands so that it reached the front spar on the lower side of the wing. Then the plywood sheet was pressed against the ribs, using the bands. When the sheet was in place, the clamps were tightened with the wing nuts. Now the plywood sheet was tightly pressed against the ribs.

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The Tuesday Club team was annoyed when a crack in the plywood veneer sheet was noticed at the tip of the leading edge. This means that the experiment failed: dry plywood can’t be used when covering the leading edge on Myrsky’s wing. The 1,5 mm thick plywood sheet has to be moistened on its outer surface before it is pressed and tightened with clamps against the leading edge ribs.

Photos: Lassi Karivalo

Translation: Erja Reinikainen.

Kommentoi kirjoitusta. Avainsanat: aviation history, restoring, old aircraft, VL Myrsky II, MY-14

Plywood covering on the lower surface of Myrsky's port wing is ready

Torstai 19.9.2019 - Member of Tuesday Club

Suomeksi

The covering of the lower surface of Myrsky’s (VL Myrsky, MY-14) port wing has been finished in the area between the wing spars. Three sheets of plywood have been installed, starting from the wingtip, and the area around the landing gear is ready as well. As the upper surface has earlier been covered with plywood, the following work phase will be the construction of the flap space on the trailing edge. Also, the leading edge in front of the front spar will be covered.

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Pieces from 3 mm thick plywood sheet were cut diagonally to cover the remaining area of the wing. Several holes, large and small, were drilled into the plywood sheet which covers the area around the auxiliary fuel tank / bomb rack. The holes are needed for the equipment on the rack and as operation hatches. The small plywood sheets were shaped to match the shapes of the landing gear and wheel wells.

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When the lower surface of the wing will be covered, as it was on the original Myrsky, the plywood will cover the structures of the wing and the equipment inside the wing (such as the auxiliary fuel tank / bomb rack and the operation mechanisms for the ailerons and landing gear). In a way it is a pity that the complicated wing structure and the interesting mechanisms will disappear from sight and the future museum visitors won’t be able to see them. Fortunately, the Myrsky’s test wing (a 2,5m long piece of the wing) has been built during the project and will be partly covered with transparent plexiglass. On the test wing the structures inside the wing, the landing gear, bomb rack and other equipment can be seen.

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When the last sheets of plywood had been cut into shape and tested in place, the inner surfaces were painted using polyurethane lacquer tinted red. Then the edges of the plywood sheets were beveled for the lap joints.

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The plywood sheet in the bomb rack area was fastened first. Before gluing, the holes for the screws were drilled on the plywood sheets. Screws will be used to secure the glue joints. Flathead screws are used and the matching beveling was drilled on the plywood sheets. Then the glue was spread.

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Epoxy glue was used when gluing the plywood sheets on the wing spars. Erikeeper Plus wood glue was used on the battens between the ribs. The sheet of plywood was pressed against the glued surfaces. The plywood sheet was secured in the right position, using a nail at each corner of the sheet.

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When the screws had been fastened on the joints, the gluing on the front and rear spars was secured using 10 mm nails. Finally, a thick strip of plywood was placed on top of the lap joint of the plywood sheets.

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When this sheet of plywood had been fastened, a couple of smaller plywood pieces were glued into place in the landing gear area. Now the lower surface of Myrsky’s port wing had been covered in the area between the spars. The wing looks like a wing now!

Photos: Lassi Karivalo

Translation: Erja Reinikainen

Kommentoi kirjoitusta. Avainsanat: aviation history, restoring, old aircraft, VL Myrsky II, MY-14

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