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

Plywood covering on lower side of Myrsky's port wing is under way

Torstai 12.9.2019 - Member of Tuesday Club

Suomeksi

The covering of the lower side of Myrsky’s (MY-14) starboard wing was finished in early autumn and the work on the port wing could be started. The lower side between the wing spars will be covered with plywood. On the trailing edge side of the rear spar the aileron and flap will be assembled. The leading edge in front of the front spar will be covered later.

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Pieces from 3 mm thick plywood sheet were cut diagonally to cover an area at the tip of the wing. These sheets are placed on the area between the spars to cover the area between 10 ribs, starting at the wingtip. One more sheet of plywood will be needed before the whole lower side of the wing is covered. The edges of the cut sheets were beveled for a lap joint and the lower side was protected against moisture using lacquer tinted red.

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Screws will be used to make sure that the plywood is pressed tightly against the ribs and the supporting battens between the ribs. The holes for the screws were drilled on the plywood sheets. Three screws per batten between the ribs were used. Flathead screws are used and the matching beveling was drilled on the plywood sheets. Before gluing the correct positioning of the plywood sheets was ensured.

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Epoxy glue and Erikeeper Plus glue was used when gluing the plywood sheets into place. 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 place, using a nail at each corner of the sheet so that it will not move during the gluing.

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Then the screws were fastened. A screw was placed into each hole, then a cordless screwdriver was used to fasten them through the plywood into the battens between the ribs. The work was finalized using a manual screwdriver so that the screw heads were about one millimeter below the plywood surface. The indentations on the surface will be covered and coated later.

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The gluing of the plywood sheet edges on the front and rear spar was not secured with screws but using staples. The staples were “shot” on the plywood through small protecting pieces of plywood so that the surface of the plywood is not damaged. The proper fastening of the staples was secured using a hammer. When the glue has dried the protecting pieces of plywood and staples will be removed.

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Finally, a thick strip of plywood was placed on top of the lap joint of the plywood sheets. Clamps were used to secure the strip and a metal weight was placed on top of the strip. Now the lower surface of the port wing had been covered from the wing tip as far as the auxiliary fuel tank / bomb rack. The plywood sheet covering this area is already under work.

Photos: Lassi Karivalo

Translation: Erja Reinikainen.

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

Ducts for Myrsky's oil cooler are built

Lauantai 7.9.2019 - Member of Tuesday Club

Suomeksi

Myrsky’s Pratt & Whitney R-1830 Twin Wasp engine has a barrel-shaped oil cooler, similar to those on the DC-3 Twin Wasp engines. The motor oil is cooled, using air which flows through the cooler. At one end of the cooler there is a horn-shaped duct for supply air and at the other end a horn for exhaust air. Both ducts have a very complicated shape. The cooling supply air intake is at the leading edge of the port wing root. The exhaust air is lead out under the fuselage through an opening in the front fairing at the wing root.

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(Öljynjäähdytin = Oil cooler, poistoilma-aukko = exhaust air vent, ilma-aukko = cooling air intake vent).

The air flow to the oil cooler is controlled using the three parallel dampers inside the supply air duct. When all dampers are closed, they shut off the air flow to the cooler. By adjusting the dampers, the pilot can control the air flow to the oil cooler and the engine oil temperature.

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The Tuesday Club team was surprised to find an oil cooler for a Pratt & Whitney R-1830 Twin Wasp engine on the shelf of the working space in the Finnish Aviation Museum. The museum gave the oil cooler to be installed on the MY-14 engine, which was greatly appreciated. When an oil cooler was available, the work on the supply and exhaust air ducts could be started.

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There are no original oil cooler ducts for Myrsky, so all parts will have to be reproduced. The work was started by building a part of the supply air duct which connects to the left end of the cooler. Myrsky’s original drawings were used to make a horn-shaped wooden last. One end of the last is round in diameter, matching the shape of the barrel-shaped oil cooler. The other end of the last is square is shape, matching the shape of the supply air duct’s other end.

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First a sheet of cardboard was wrapped around the wooden last so that a cardboard pattern can be made and used to cut a suitable piece from 1 mm thick aluminum sheet. The appropriate piece of aluminum sheet was cut, and it was bent around the last with tightening straps. The aluminum sheet was bent to match the duct shape. When the semi-finished duct was unfastened from the last, its edges were fastened to each other with rivets. The final phase was to cut the ends of the duct to the right shape, matching the last, and honed smooth. The first part for the supply air duct was ready.

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Another similar supply air duct part was made for the display object, which will be built around the fuselage frame of MY-5. A four-meter long test wing is being built during the restoration process and this test wing will be fastened on the MY-5 fuselage frame. The aim of this partly restored MY-5 is to illustrate what the inside of the Myrsky looks like. The fuselage frame will not be covered, and the test wing will be partly covered using transparent plexiglass.

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While the supply air ducts for the oil cooler were being made, also the work on the control dampers was started. The leader of the Myrsky-project, Mr. Matti Patteri, programmed the shape of the dampers on a laser cutter, using original drawings. The dampers were laser cut at ProLaser Oy and they have been sent to the Tuesday Club and are waiting for further activities.

Photos: Lassi Karivalo except historical photo: The Finnish Avitation Museum's photo archive.

Translation from Finnish to English: Erja Reinikainen.

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

Myrsky activities in July

Tiistai 23.7.2019 - Member of Tuesday Club

Suomeksi

The Tuesday Club members involved in the restoration work of Myrsky (MY-14) don’t want to stay away from the workshop, not even in July! They want to bring the restoration project forward even during the holiday season.

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The team has concentrated on finishing the covering on the starboard wing’s lower side. Now all the inner structures and the equipment inside the wing have been covered with plywood. However, some minor details in the plywood covering are still under work.

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When the lower side of the starboard wing is ready, the work will continue on the port wing. The upper side of the port wing has been already covered between the spars. The work on the port wing includes installing all operation mechanisms of the ailerons and landing gear inside the wing, fastening the trailing edge ribs on the rear spars and covering the flap cavity on the trailing edge with plywood. Simultaneously the covering work can be started on the lower side, in the area between the spars, starting at the wing tip. All this work has been done already on the starboard wing, so the team anticipates the work to progress smoothly.

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The wing has not been the only Myrsky work item in July. The port and starboard horizontal stablilizers have been covered and the plywood covering seams have been buffed out. The vertical and horizontal stabilizers were fastened on an assembly jig in order to install the root fairings on the seams where the stabilizers meet. The original Myrsky tail root fairings can be used, and no reproduction is needed. However, the original tail root fairings have been slightly damaged, so they need to be straightened and repaired before assembly.

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The original duraluminium elevators have also been repaired, because they have some fractures and some parts are missing. The elevators will be installed on the horizontal stabilizer when they have been repaired.

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A wooden last was made to shape the Myrsky’s engine cover, ie. NACA ring. In July the last for the upper half of the NACA ring was sent to the company which will prepare the ring. The upper half consists of three aluminium plate segments welded together. The three parts were shaped against the last, using a lead whip. When the shape was correct, the segments were welded together to form the upper half of the NACA ring. The part came back to the Tuesday Club in mid-July. The upper half of the ring will have to be slightly modified and an opening for the engine air intake will have to be made before the upper half can be fastened on the rest of the NACA ring.

Photos: Lassi Karivalo.

Translation from Finnish to English: Erja Reinikainen.

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

Flap niche on Myrsky's starboard wing

Sunnuntai 23.6.2019 - Member of Tuesday Club

Suomeksi

The assembly of Myrsky’s starboard wing has been going on for a couple of months. The ribs of the trailing edge have been installed up to the trailing edge strip. Also the operating mechanisms for the aileron, flap and landing gear have been installed through the holes in the ribs. At this point the Tuesday Club team could start covering the flap niche with plywood. When the flap is up / closed, it is pressed into this niche in the wing’s trailing edge. There is a notch in the trailing edge ribs, forming the perimeter of the niche.

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The rest of Myrsky’s wing is a wooden structure but the flaps are split flap type plate flaps, made of duraluminium. When the flaps are up / closed and pressed into the niche under the wing, the flap is a part of the wing’s lower surface. When the flap is down / open, it turns down pushed by operation bars and angle gearboxes. The flap doesn’t move down and back as the flaps on modern passenger airplanes do.

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The starboard wing’s flap cavity work was started by covering the front wall, 70 mm high, with 1.2 mm thick plywood. The next phase was the upper side of the niche which is as wide as the flap. Fortunately the starboard wing lay upside down, i.e. the lower side up. Fastening the plywood against the trailing edge ribs was much easier than it would have been if the wing were the right way up.

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The flap niche will be covered with two sheets of plywood, connected in a lap joint. Two pieces of plywood were cut from 1,2 mm thick sheet of plywood, matching the dimensions of the niche. The joining edges of the sheets were beveled for the lap joint. The sheets were placed on the ribs, making sure that they settle properly against the ribs and the sides and can be glued into place.

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When everything was ready, the plywood sheet towards the wingtip was glued first and then the sheet towards the wing root. Two-component epoxy glue with cellulose fibre was used. The glue was spread with a brush on the ribs, on the battens between the ribs, trailing edge batten and the front and end battens of the flap niche.

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When the glue had been spread, the plywood sheets were pressed against the ribs and locked into place with aa couple of nails. Then heavy weights were placed on top of the sheets to press the glued surfaces together.

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When the glue had dreid a triangular wooden batten was added to support the seam of the front wall and the roof plywood sheets.

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Now the niche of the starboard flap had been covered.

Photos: Lassi Karivalo.

Translation from Finnish to English: Erja Reinikainen.

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

Lover side of Myrsky's starboard wing is covered

Tiistai 11.6.2019 - Member of Tuesday Club

Suomeksi

The Tuesday Club continues its work during the summer. The work concentrates on the covering of the starboard wing’s lower side between the wing spars. The wing tip has already been covered and one sheet of plywood towards the root of the wing. The covering work continued by gluing a third sheet of plywood in place. The covering of the whole lower side of the wing is possible when all the equipment and operation mechanisms inside the wing have been installed (such as the fastening and rejecting mechanisms of the auxiliary fuel tank). The upper side of the wing has already been covered earlier.

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The original Myrsky wing plywood sheet had been cut from plywood board at a 45-degree angle, i.e. diagonally compared to the veneer layers. In ordinary thin plywood the bending strength and stiffness depend on the direction of the surface veneer, whereas diagonally cut plywood is equally stiff in both directions. However, cutting plywood sheets diagonally wastes material compared to cutting in the direction of the veneers. The restoration team decided to cut the plywood sheets diagonally for the Myrsky (MY-14), as they had originally been.

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The work on the third sheet of plywood on the lower side of Myrsky’s starboard wing was started by placing a 3mm thick sheet of plywood on the wing area to be covered. The required piece was marked so that it can be cut diagonally. When the piece had been cut, its lower side was protected against moisture using lacquer tinted red. The areas to be glued were not lacquered.

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Some finalizing work was needed before gluing the plywood. The supporting battens between the wing spars were honed exactly into the same level so that there won’t be any dents or bumps in the plywood surface. Holes were drilled into the plywood so that the gluing can be secured with screws on the supporting battens on the wing surface.

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When all the preparations had been made, glue was spread on the front and rear spars, on the ribs and on the battens between the ribs. Epoxy glue with additional cellulose fibers was used on the spars and Erikeeper Plus wood glue on the ribs and battens.

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The sheet of plywood was lifted above the wing and pressed against the glue. The correct position was checked and then the plywood sheet was secured in place, using a nail at the corner of the sheet. The screws were added to fasten the plywood sheet on the battens between the ribs. A cordless screwdriver was used, but the work was finalized using a manual screwdriver.

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Cargo straps and strips of wood were used to press the plywood against the glued surfaces. Also clamps and metal weights were used to make sure that the edges of the plywood sheet press tightly against the glued surfaces. Now the third sheet of plywood on the starboard wing had been installed.

Photos: Lassi Karivalo.

Translation from Finnish to English: Erja Reinikainen.

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

Assembly of Myrsky's wing ribs on trailing edge

Torstai 11.4.2019 - Member of Tuesday Club

Suomeksi

The preparation of ribs for Myrsky’s wings was started in the very beginning of the Myrsky restoration project in 2016. At the time ribs were made for the mid-wing section (between the wing spars) and for the leading and trailing edges.

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Now the Myrsky wing restoration and assembly has reached the point where only the ribs on the wings’ trailing edge are missing.

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Both wings have 12 ribs on the trailing edge between the root of the wing and the aileron gap. Each rib has a notch for the flap on the lower side of the trailing edge. There are also holes in the ribs for the operating mechanisms of the ailerons and landing gear.

For the installation of the trailing edge ribs the wing was placed upside down. This way it is easier to install the operation mechanisms for the ailerons and landing gear through the holes in the ribs. Furthermore, it is easier to make sure that the flap fits into the notch in the ribs.

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As preliminary work the bearing block, operation bars and angle gear box for the flaps and ailerons have been installed. Also the operation mechanism for the landing gear, which penetrates the ribs, had been tested in its place.

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The most important preparatory work item was to build the assembly jig from steel tubes. It is necessary to use the jig to be able to place the ribs on the trailing edge in the right position. They must be exactly on the same level with each other and with the rear spar and the batten on the trailing edge.

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The assembly work was started on the right / starboard wing. When the assembly jig was in place, the ribs could be placed one by one between the rear spar and the rear tube of the jig. At this phase the ribs were only preliminarily fastened.

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When all the ribs on the trailing edge had been placed in a neat row between the rear spar and the rear tube of the jig, the operation mechanisms of the flap, aileron and landing gear were pushed through the holes in the ribs. At first glimpse the several operation bars and mechanisms are a jumble, but each bar and tube has a purpose and has its own route through the ribs.

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It was also tested how the flap settles into the notch in the ribs. The original aluminum flap pressed nicely into the notch and it also opened as expected.

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The ribs will be glued onto the rear spar when the trailing edge batten which joins the tips of the ribs is ready and has been assembled into the jig.

Translated from Finnish to English by Erja Reinikainen.

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

Myrsky horizontal stabilizer is covered with plywood

Maanantai 8.4.2019 - Member of Tuesday Club

Suomeksi

The rebuilding of the Myrsky (MY-14) horizontal stabilizer is a good example how the restoring work progresses in phases. The phasing of restoring work is due to the prioritization of the various restoration projects. The rebuilding of Myrsky’s horizontal stabilizer has been going on whenever there has been a break in other Myrsky work, e.g. building the wings.

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The frames of the horizontal stabilizer halves were finished already at the end of 2016 and then a 12-month break in the work followed. In 2018 the work was continued, and the halves of the horizontal stabilizer were covered with 1,5 mm plywood between the front and rear spars. Before the plywood covering was installed, the inner structures of the horizontal stabilizer halves and the inside surfaces of the plywood were varnished with polyurethane varnish, tinted red.

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In the beginning of this year the covering of the leading and trailing edges of the horizontal stabilizer was started. The work was started at the trailing edge, where the hinge brackets for the elevator had been fastened. The trailing edge of the horizontal stabilizer is concave in shape to match the elevator’s leading edge which is hemispheric.

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The covering of the trailing edge was started by carving the rectangular wooden battens on the upper and lower edge pointed, so that the trailing edge is curved inwards. As the work progressed, the shape of the trailing edge was checked regularly using a gauge to make sure that the concave shape is correct.

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When the battens on the upper and lower edges had been carved, the halves of the horizontal stabilizer were fastened on an assembly jig, trailing edge upwards.

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The covering work was started by cutting a thin strip of 1,5 mm plywood, matching the length of the trailing edge. Before the strip could be fastened, several supporting pieces of plywood (shaped to match the shape of the trailing edge) were glued on the trailing edge, using Casco Outdoor wood glue.

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Then the plywood strip could be glued on the trailing edge. Epoxy glue was spread on the upper and lower surface of the trailing edge, on the end pieces and on the supporting plywood pieces. The plywood strip was forced against the concave trailing edge using a thick round wooden pole. The pole was fastened on the horizontal stabilizer using cargo straps. When the glue had dried the straps were removed and the additional skirts of the plywood were cut off. Both halves of the horizontal stabilizer were covered in a similar way. The halves were turned around in the assembly jig and the work on the leading edges could be started.

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Pieces of 1,5 mm plywood were cut for the leading edge on both stabilizer halves. On the leading edge the covering piece of plywood stretches around the edge from front spar to front spar. The piece of plywood had to be shaped like a trough to match the profile of the leading edge.

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First the plywood was moistened with water. Then the damp plywood was pressed tightly around the leading edge of the horizontal stabilizer and fastened using supporting battens and cargo straps. In a couple of days the plywood had dried and the straps could be removed. The Tuesday Club team was pleased to see that the plywood now had the correct trough shape and matched the shape the leading edge. An alternative work method would have been to use hot steam to moisten the plywood and then fasten it on a mold.

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Before gluing the plywood, it was test assembled around the leading edge. The team wanted to make sure that the plywood trough pressed tightly on the tip batten and on the leading edge ribs and reached on both sides as far as the front spar. The plywood covering of the mid-section of the horizontal stabilizer had been glued in an earlier work phase on the front spar. The leading edge covering meets this mid-section plywood with a scarf joint.

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When the leading edge plywood covering was in place, the epoxy glue was mixed and cellulose fibre was added as binder. The glue was spread with a brush on the leading edge batten, ribs and the edge of the mid-section plywood on the front spar. The trough shaped plywood covering was pressed against the leading edge and fastened tightly using supporting battens and cargo straps.

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The scarf joint of the two pieces of plywood connecting on the front spar was secured with staples from a stapling gun.

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After a couple of days the cargo straps were removed. The team members knocked on the leading edge plywood to make sure that it had been properly fastened on the leading edge batten and the ribs. The staples securing the scarf joint on the front spar could be removed.

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When the seams of the scarf joint had been ground smooth, the work was ready. Both halves of the horizontal stabilizer were covered in a similar way.

Photos: Lassi Karivalo

Translation from Finnish to English: Erja Reinikainen.

1 kommentti . Avainsanat: aviation history, restoring, old aircraft, VL Myrsky II, MY-14

Making access panel latches for Myrsky's wings

Maanantai 4.3.2019 - Member of Tuesday Club

Suomeksi

There are dozens of access, maintenance and operation panels on the wing of Myrsky. The panels are of five different sizes.

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The restoration project team has some original Myrsky wing access panels, but majority of the panels will have to be made. There is a latch in the middle of each access panel to open and close the panel. The “seesaw type” latch has a hinge in the middle and the latch is opened and closed by pushing it with a finger.

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Because each access panel on the wing has one or two latches, more than 70 latches are needed on the two wings of the Myrsky and on the test wing. The restoration team decided to make all the identical latches in a serial process.

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The frame of the latch is made of two aluminum plates which are riveted together. The access, maintenance and operation panels had been cut from 1 mm aluminum plate, using a laser cutter. This work method was used also to cut the latch frames. Holes for the rivets were also made. The rivets are 2,5x3,5 mm aluminum rivets with countersunk heads. Folds were made on the plate on the inside of the latch, the folds are needed for the hinge and the locking wire.

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The first phase in the making of the latch frame was to make the holes for the rivets on the outer plate of the latch so that the head of the rivet will be on the level of the plate surface.  The holes were made with a special drill piece on a vertical drilling machine.

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The frame of the latch was made by riveting the inner and outer plates together. A powerful manual riveting tool was used. The inner and outer plates were put on the riveting table with the inner surface on top. Rivets were placed into the holes and then the rivets were pushed into place using the riveting tool.

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Each latch frame has six rivets so the tool had to be used several times before the required number of latch frames were ready for further processing.

Photos: Lassi Karivalo

Translation: Erja Reinikainen

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

Leading edge of Myrsky wing is assembled

Keskiviikko 20.2.2019 - Member of Tuesday Club

Suomeksi

The Tuesday Club team has been working on the restoration of VL Myrsky’s wings. The work has progressed to the phase when the ribs on the leading edge of the wing can be installed. Previously the ribs have been prepared for the assembly and the tube for the electrical cable of the navigation light has been fastened on the front spar.

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The ribs for the leading edge of Myrsky’s wings were made about a year ago. Triangular wooden battens were fastened on the root of each rib so that they can be glued onto the front spar. This arrangement makes the gluing surface wider on the rib root. Before gluing the ribs into place their sides were protected against humidity using polyurethane varnish, tinted red.

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The aluminum tube for the electrical cable of the navigation light on the wingtip was installed before the ribs were installed. The aluminum tube was fastened in the middle of the front spar side facing the leading edge. Aluminum clips were used for fastening the tube on the spar. A notch for the tube had to be carved on the root of each rib before the ribs could be glued onto the front spar.

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It is important that all the ribs are glued onto the front spar so that their tips are fully in line. If they are not, this will cause problems when covering the leading edge with plywood. A long metal bubble level was the perfect tool for making sure that the rib tips are in line.

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The level showed that the ribs had slightly different lengths, a couple of millimeters. To compensate the error, thin strips of plywood were glued on the root of the shorter ribs. Several ribs had to be modified to make them slightly longer so that the tips met the level. When all the rib tips were in the correct position, a thin connecting wooden batten (8x8 mm) was pushed through the hole at the tip of each rib. When the batten was in place, the ribs were glued onto the front spar and secured into place with clamps.

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When the glue had dried, the installation of the supporting battens between the ribs could be started. The battens are installed on the ribs on the upper and lower side of the wing, covering the full length of the wing. Strips of plywood were glued on both sides of each rib, at the lower edge. Then the supporting battens were glued onto the strips.

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The battens on the upper side of the ribs will be installed when the wing has been turned around. Another supporting batten was added on the front side of the batten which penetrates the tips of the ribs. Now the tip batten became thicker and the front edge of the batten is at the level of the rib tip. The ribs were installed in a similar way on the leading edge of Myrsky’s both wings.

Photos: Lassi Karivalo

Translation: Erja Reinikainen

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

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