Tiistai 10.12.2019 - Member of Tuesday Club
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.
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.
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.
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.
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.
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.
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.
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.
Torstai 19.9.2019 - Member of Tuesday Club
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.
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.
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.
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.
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.
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.
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.
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
Torstai 12.9.2019 - Member of Tuesday Club
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.
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.
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.
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.
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.
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.
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.
Lauantai 7.9.2019 - Member of Tuesday Club
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.
(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.
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.
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.
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.
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.
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.
Tiistai 23.7.2019 - Member of Tuesday Club
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.
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.
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.
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.
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.
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.
Sunnuntai 23.6.2019 - Member of Tuesday Club
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.
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.
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.
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.
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.
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.
When the glue had dreid a triangular wooden batten was added to support the seam of the front wall and the roof plywood sheets.
Now the niche of the starboard flap had been covered.
Photos: Lassi Karivalo.
Translation from Finnish to English: Erja Reinikainen.
Tiistai 11.6.2019 - Member of Tuesday Club
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.
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.
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.
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.
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.
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.
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.
Torstai 11.4.2019 - Member of Tuesday Club
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.
Now the Myrsky wing restoration and assembly has reached the point where only the ribs on the wings’ trailing edge are missing.
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.
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.
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.
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.
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.
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.
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.
Maanantai 8.4.2019 - Member of Tuesday Club
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
The scarf joint of the two pieces of plywood connecting on the front spar was secured with staples from a stapling gun.
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.
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.
Maanantai 4.3.2019 - Member of Tuesday Club
There are dozens of access, maintenance and operation panels on the wing of Myrsky. The panels are of five different sizes.
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.
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.
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.
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.
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.
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
Keskiviikko 20.2.2019 - Member of Tuesday Club
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.
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.
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.
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.
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.
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.
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
Maanantai 14.1.2019 - Member of Tuesday Club
The VL Myrsky fighter has inside both wings a rack for fastening an auxiliary fuel tank or a bomb. The Tuesday Club team had several original parts of the rack for the Myrsky restoration work. The rack parts were repaired and cleaned and assembled together to form the racks on both wings of the Myrsky and also for the short wing built for test purposes. The rack on the test wing has been already tested.
The racks had been installed on both wings on the Myrsky. The area around the rack had also been preliminarily covered with new plywood so that the rack could be tested. Holes were made into the plywood covering for the rack mounting locator pins and the catch, which the auxiliary fuel tank or the bomb is locked on. Another hole was made for the indication pin, which forwards the information to the pilot when the auxiliary fuel tank or bomb has been released.
The testing of the rack could be done easily as the wings are on the assembly jig with the lower side upwards. For the test procedure the team could use an original Myrsky auxiliary fuel tank - fortunately a bomb wasn’t needed for the testing! The team decided to test the rack on the starboard (right) wing.
The auxiliary fuel tank was lifted upside down on the wing, which was upside down on the assembly jig. The tank was placed above the rack so that the four wooden steering blocks met the mounting locator pins, which penetrated the wing covering. The lock ring on the surface of the auxiliary fuel tank slid through the hole on the wing covering towards the lock catch on the rack.
The team was annoyed to discover that the fuel tank didn’t lock on the rack. When the tank was lifted and the distance of the lock catch from the wing surface was measured, the team noticed that the rack, placed inside wing between two wing ribs, was located about 5 mm too deep. The lock ring of the auxiliary fuel tank didn’t reach the lock catch. Although the rack had been installed according to the measurements on the drawings, this was what the situation was.
The team sighed and continued working, dismantled the rack and installed it again, this time 5mm closer to the surface of the wing. The auxiliary fuel tank was tested again on its place, this time it locked perfectly on the lock catch of the rack.
Photos: Lassi Karivalo
Translation: Erja Reinikainen
Lauantai 8.12.2018 - Member of Tuesday Club
There are several different inspection, maintenance and operation hatches on the wing of VL Myrsky II. There are four hatches for the auxiliary fuel tank racks which also served as bomb racks, two on either side. The hatches are made of 1 mm aluminium sheet. They are round and 17,5 cm in diameter. In the middle of each hatch there is an elongated lock disk, which has a spring and can be pushed open and closed using a finger.
The operation hatches of the auxiliary fuel tank rack have a complicated structure. Fortunately, the Tuesday Club team had a detailed original construction drawing for making the hatches. The drawing has been dated in November 1944, so it is from the time when the Myrsky planes were in production. Also one original auxiliary fuel tank rack hatch had been found. Other original hatches are not available.
The drawing on the auxiliary fuel tank rack hatch illustrates well how detailed drawings have been made even of the smallest parts when the Myrsky was designed. The drawing describes in detail the construction of the hatch and its parts, 12 of them in total. 42 rivets are needed when the parts are assembled together.
When the team started making the hatches for the Myrsky wings, billets for all the different hatches were cut from 1 mm aluminium sheet. Some of the hatches are round, some rectangular. A laser cutter was used for cutting the hatches. The exact shape and size of each hatch was programmed for the laser cutter and the data was fed into the cutter using a memory stick. The holes for the rivets were also cut using the laser, several rivets are needed to fasten the parts together. The advantage of the laser cutter is that the outcome is exactly according to the original drawing.
The first task of the team was to make the hatches for the auxiliary fuel tank and bomb racks. Six hatches are needed, two for each side and two for the Myrsky test wing. The first item to be made were the crescent-shaped stiffeners on the inside of the hatch. Twelve billets, slightly larger than the final stiffeners, were cut from 1 mm aluminium sheet. Two holes were cut according to the original drawing for making the stiffener lighter. For pressing the billets into shape, female and male pressing moulds were made. The billets were pressed into shape between the moulds.
The extra “skirt” was cut off.
The following task was to drill rivet holes on the edges of the crescent-shaped plates, so that they could be riveted on the inside of the hatch. The stiffener was clamped tightly on the inside of the hatch plate, exactly on the right place. Then the hatch plate was turned around and the rivet holes for fastening the stiffener, already laser cut on the hatch, were marked using a marker pen.
The holes were drilled along the edge of the stiffener. Soon all 12 stiffeners were ready to be fastened on the hatch plates.
Another Tuesday Club team was working on the lock disks which will be placed in the middle of the auxiliary fuel tank hatch. The parts of the lock disk were riveted together and the lock disk was preliminarily placed into the opening in the middle of the hatch. A lot of work will be needed before the six auxiliary fuel tank hatches are ready, not to mention all the other hatches, which are at the billet stage.
Sunnuntai 11.11.2018 - Member of Tuesday Club
The VL Myrsky II (MY-14) is being restored by the Tuesday Club and its wings are nearly ready in the area between the wing spars. The upper sides of the wings have been covered between the spars, but the lower sides are still without plywood covering. The covering won’t be finished before all the equipment, tubes and wires have been installed inside the wing. However, the covering of the lower side of the wing tip could be partly installed. Here the wing tip part means the rounded end of the wing.
The upper side of the wing tip was covered with a single sheet of plywood, stretching over the whole wing tip area. This was possible because the upper surface of the wing tip is arched only in one direction. The lower side of the wing tip arches significantly upwards towards the tip and also sideways. This is the reason why the lower surface of the wing tip can’t be covered using one sheet of plywood: a large sheet can’t be bent properly into two directions.
The solution was to use narrow strips of plywood which are glued together. These strips of plywood can be bent to match the double arching form of the wing tip.
15 cm wide strips of 1,5 mm plywood were cut to match the length of the wing tip. The strips are be glued together using lap joints, so the edges of the strips were beveled (2 cm of the edge), using a mitre grinding machine. Before gluing, the inner surfaces of the strips were protected using polyurethane varnish, tinted red.
The plywood strips were glued into place one by one, starting in the middle of the wing tip. Heavy weights were placed on the strips after gluing. The plywood strips were clamped tightly on the rib and batten structures of the wing.
The whole lower side of the wing could not yet be covered because the navigation light wiring, etc. has to be installed inside the wing. The covering of the lower side of the wings has been started: three strips of plywood have been glued into place on both wings.
Perjantai 9.11.2018 - Reino Myllymäki
Perspex or acryl or PMMA was found in the beginning of the 1930s. It got a tradename Plexiglas in Germany and Perspex in U.K. These tradenames led to generic name pleksi (in Finnish) or perspex (in English). Nowadays these generic names mean later innovations like polycarbonat (PC), too.
The VL Myrsky II restoration project has a windcreen already glazed with green frames. This item has been shown in several exhibitions. It is a spare part never used in any Myrskys. It might be installed to another aircraft and little changed. Therefore it won't be installed to the MY-14.
The restoration team of the Finnish Air Force Museum used another windscreen for the MY-14. The windscreen has four perspex plates: one arched and three straight plates. The arched plate is original and it was smoothed. The straight plates were disappeared and the team made new ones. The plate edges have rabbets so that the plate will be on the same level with the frame. The rabbets were made by a rabbet cutter.
The installation of the strainght perspex plates was the first stage, then the arched plates will be taken under construction. There were arched perspex plates in the windscreen, canopy and aft glazing. The installation of the gun sight is under construction, too.
During the arrangement of the storage, the Myrsky's weapons were taken to wait the installation. There is two 12,7 mm LKk/42 heavy machine guns of VL Myrsky and six 12,7 mm Breda-SAFAT heavy machine guns of Fiat G.50 in same box in the photo.
Sunnuntai 4.11.2018 - Member of Tuesday Club
The wheel well covers for VL Myrsky II (MY-14) wings have been under construction since spring. Three covers will be made: two for the actual Myrsky and one for the test wing.
The wheel well cover consists of two sheets of aluminium and a supporting frame in between, made of 15mm steel tubes. The aluminium sheet on the inside is slightly smaller than the outer sheet. Rivets are used to attach the aluminium sheets to the supporting structure so that the cover forms a box construction. The wheel well cover is attached to the edge of the wheel well with two hinges. The hinges are fastened on the edge of the steel tube structure of the cover.
During this autumn the wheel well cover for the test wing has been under construction. The assembly of the wheel well cover, and the function of the hinges will be tested on the test wing before making the covers for the actual Myrsky wings.
The steel tube structure was made first, then the hinges were welded on the frame and then the cover structure was assembled into the wheel well hole. The hinges were fastened to the edge of the wheel well to see how the cover fits and functions. Several modifications were needed, and the position of the hinges had to be changed before the assembly team was happy with the result. When the correct position of the hinges on the tube frame had been found, the aluminium plates could be riveted on the frame.
The aluminium plates and the tube structure were clamped together, into a tight package. Holes for the flush rivets were drilled along the edges of the cover so that the drill penetrated both aluminium sheets and the tube construction between them. The holes are about 4cm apart and their edges were bevelled with a drill so that the rivet tops will be at the same level as the aluminium sheet top.
Before riveting the aluminium sheets were sent to be chromed. Chroming forms a thin organic layer on the surface of the aluminium and protects it from oxidation. The chromed surface is an excellent foundation for painting work. The chroming was not done by the Tuesday Club.
When the chroming had been done, riveting could be started. 20mm long flush rivets were used. A pneumatic riveting hammer was used when placing the rivets one by one into the holes on the wheel well cover. No problems occurred during the riveting work and the aluminium sheets and the steel tube frame soon formed a box construction. The cover could be fastened on the edge of the wheel well by installing the hinges. When the cover was closed, it fitted tightly into the wheel well opening.
The next step in the restoration work will be to assemble a spring mechanism into the wheel well under the cover. This mechanism will push the cover open when the landing gear is taken out. A lever will be installed on the inside of the cover to close the cover. When the landing gear is pulled in, the wheel of the gear will push the lever and the wheel well cover closes.
Sunnuntai 28.10.2018 - Member of Tuesday Club
In the restoration work of VL Myrsky II the installation of the navigation lights is under way. When the tip of the wing was built, a gap was left on the front corner of the wing so that the navigation lights could be installed later.
The navigation light on the wingtip consists of a transparent aerodynamically designed plexiglass cover and its frame, made of aluminium, which attaches the cover onto the wing structure. The actual navigation light bulb is inside the cover, surrounded by a small red or green plastic cover.
The plexiglass cover of the navigation light is made in a vacuum moulding machine. The heated 2mm pvc plexiglass plate is pressed on a mould which has the shape of the navigation light cover. When the plexiglass has cooled on the mould, it is cut into shape.
The mould for the navigation light cover was made from wood. Pieces of wood were glued together to form a piece large enough for the moulds of the navigation light covers on both wings. The piece of wood was cut and milled following drawings so that it had the shape of two navigation light covers, back to back. When the desired shape had been reached, the piece was cut into two parts. Now the moulds for the two light covers were ready.
The cover is assembled into the gap at the wingtip using a frame made of aluminium sheet. For the making of the frame a mould is needed, following the shape of the plexiglass cover. The aluminium frame is made of two halves, upper and lower, which are welded together around the mould. Also in this case the mould was made from wood, matching the shape of the navigation light cover.
The upper and lower halves of the aluminium frame were screwed onto the wooden mould and the ends of the two halves met correctly. A piece of copper tube was placed under the ends of the frame halves to protect the mould from excessive heat when welding the parts together. The tube also forms a solid base under the frame edges when the welding is done.
Some additional work is still required before the navigation light cover mould is ready: it needs a supporting structure before it can be attached to the vacuum moulding machine. The mould for the aluminium frame is ready and the halves can be welded together to form the frame.
Lauantai 9.6.2018 - Member of Tuesday Club
In the beginning of this year the Tuesday Club of the Aviation Museum Society has been working on the Myrsky project and the main emphasis has been in assembling the left wing of Myrsky MY-14. The test wing has also been under construction and some metal parts have been made too. The left wing has been assembled in a steel framed assembly jig where the wing spars have been firmly fastened. The area between the wing spars was built in the jig and the areas of the leading and trailing edge will be built later.
In the beginning of May the left wing was at the phase where the area between the wing spars was nearly ready and its upper surface covered with plywood. At this point the wing didn’t need the support of the jig anymore and could be unfastened. A lifting support was built from steel tubes for both ends of the wing before unfastening and moving it from the jig. The supports were necessary because the wing is too heavy to be moved manually.
Photo: Jorma Laakkonen.
When the wing had been unfastened from the jig, it was lifted by the supports at the ends of the wing using a forklift and a manual lift and moved on a wooden working platform. The wing was also turned upside down so that the covering of the lower wing surface can be started.
Photos: Jorma Laakkonen.
The covering of the wing was started by building the supporting battens for the plywood covering. This means fastening the lines of lengthwise battens between the wing ribs. The plywood covering is glued on these battens and secured by screws.
The construction of the battens was started by gluing plywood rests on the upper edge of each rib. The battens will be installed on these rests and the ends will be glued on the ribs. The battens were glued one by one as “bridges” between the ribs. By the end of May the installation of the battens had been completed and the actual covering of the area between the wing spars could be started.
The aim is to have the covering ready before the left wing will be placed on display in the VL Myrsky-project exhibition at the Finnish Air Force 100th Anniversary Airshow. Also the test wing built by the Tuesday Club will be on display there.
When the left wing was unfastened from the jig, it can be used for assembling the right wing of Myrsky. Now the Tuesday Club team had reached the point where both wings of Myrsky can be built and assembled simultaneously and side by side in the restoration room of the Finnish Aviation Museum.
The construction of the right wing in the jig will follow the same procedure as for the left wing. The wing will be built in the jig until the area between the wing spars is ready and the leading and trailing edges will be built later.
The wing spars of the right wing were fastened on the jig and the ribs were installed between the spars. The ribs had been ready and waiting for some time for the wing assembly to begin. The ribs were easily installed and the wing construction began to take shape. The metal brackets for the landing gear system were fastened on the wing spars and ribs and the fuel and air pipes of the auxiliary fuel tank were pushed into place through the holes in the ribs.
When the fuselage with engine, the left half of wing and the test wing are on the show in the Finnish Air Force 100th Anniversary Airshow on June 16th and 17th 2018, there is on the show the biggest Myrsky assembly since 1965. See you there!
Photos (execept when separately mentioned): Lassi Karivalo.
Maanantai 2.4.2018 - Member of Tuesday Club
The Aviation Museum Society is arranging a fund raising campaign for the VL Myrsky restoration project, the campaign began in December 2017 and it ends at the end of November 2018. Five new money collection boxes are needed for the campaign. The Tuesday Club was given the task to make the partly transparent money boxes.
First the model of the money box was designed at the Tuesday Club. The starting point was the existing collection box which is in the lobby of the Aviation Museum. Also the suitable existing materials in the museum material storage had to be taken into account, e.g. old melamine surfaced shelves and thick transparent Perspex sheets.
The collection box was designed to have its sides, bottom and back wall made of 20 mm thick melamine surfaced chip board and its top and front wall of thick plexi. The box is cubicle in shape and its dimensions are 30x30x30 cm. The dimensions were determined by the existing Perspex sheet which was 30 cm wide. The back wall of the box consists of two parts and the upper and lower parts are joined together with a hinge. The lower part of the back wall is used as a hatch to empty the donated cash from the box.
The team decided to build first one test box. Pieces were sawn to measure from the old melamine covered shelves to form the bottom, sides and back wall. Then the bottom and sides were assembled together. After minor adjustments the parts were attached using Erikeeper Plus glue and screws. Then the back wall was cut in two parts to make the hatch. The upper and lower parts of the back wall were connected to each other using a piano hinge. The upper part was attached between the sides of the box using glue and screws. A lock was installed on the openable lower part of the back wall and a hole for the locking beak was made into the bottom plate of the box.
The team was pleased about the way the test box looked and “mass production” to build the other four boxes could be started. The bottoms, sides and back walls for all four collection boxes were sawn from the existing shelves. The frames of the four boxes with the openable hatches were built following the model.
As old melamine covered shelves had been used to build the boxes, the sides of the chip boards had to be covered to make them look nice. White covering strip was used for the sides, it was glued into place using the heat of a flat iron. Before the plexi pieces were installed to form the front wall and the top, a piece of carpeting was glued on the bottom of the box as padding.
The front walls and roofs for all five collection boxes were sawn from 30 cm wide and 7 mm thick Perspex sheets. The sawn edges of the plates were buffed out.
The transparent parts were fitted into place in each box. A rectangular opening was milled in the middle of the roof sheets, this would be used for dropping cash into the box. The transparent surfaces were thoroughly cleaned before assembling the plexis on the boxes using screws.
To prevent the stealing of a donation box, 4 mm thick plastic covered steel wire was purchased for each box. Each box also needed two wire rope grips for the loops at each end of the wire. The loops were needed for the padlock. An eye hook was attached on the back edge of the bottom plate and the wire was threaded through. The aim is to attach the money box to a nearby structure and lock it in place using the wire and the padlock.
The work was concluded by attaching stickers on both sides of each box, introducing the Myrsky project and the permit for the fund raising campaign.
The money collection boxes of the VL Myrsky restoration project are now ready. When you see such a box, made by the Tuesday Club, you have a good opportunity, even a responsibility, to drop some money into the box and support the VL Myrsky II restoration project.
Sunnuntai 25.3.2018 - Member of Tuesday Club
The test wing in the VL Myrsky II restoration project has progressed to the phase where the construction of the mainwheel inner door (“the angel wing”) has been started. In the original VL Myrsky drawings this part has been named “hatch” but the word “door” has been used in this translation. The inner door covers about half of the wheel well. The other half is covered by the mainwheel door, which is attached to the landing gear leg and covers half of the wheel.
The opening and closing mechanism of the mainwheel door operates like this: when the landing gear is pulled into the mainwheel well inside the wing, on its way in the wheel pushes a lever on the mainwheel door which closes the door. The outer edge of the mainwheel door fairing presses against the inner door fairing, shutting it firmly. When the landing gear is taken out, the inner door linkage mechanism pushes the door automatically open using spring load.
The mainwheel inner door in Myrsky has box construction. It consists of two aluminium fairings with a supporting metal frame in between. The inner door fairing is 2 mm thick aluminium plate on the outside and 1mm thick aluminium plate on the inside. The outer measurements of the inner fairing are 440x660 mm and those of the outer fairing 485x700 mm, so the inner fairing is smaller than the outer. This means that the outer fairing forms a flange at the edge of the fairing.
Some hinge mechanisms of daisy cutters have been survived but the doors not. Therefore the doors have to be manufactures as new production.
There is metal frame between the inner and outer fairing of the mainwheel inner door. It runs along the edge of the inner fairing. The aluminium fairings are attached to the frame by riveting. Originally the Myrsky mainwheel inner door had an open U-shaped aluminium frame structure, on which the fairings were separately riveted. A different structure was chosen in the Myrsky restoration project. The supporting frame between the fairings is made of 15x15mm rectangular steel tube. The outer and inner fairing are attached to the frame with rows of rivets penetrating the frame. Rows of holes are drilled into the supporting frame for the rivets.
The test wing in the Myrsky project is a wing half, couple of meters long, and it has only one mainwheel well. Therefore only one mainwheel inner door is needed for the test wing. The Tuesday Club team decided, however, to build three doors: one for the test wing and two for the actual Myrsky (which naturally has two mainwheel wells).
The work was started by laser-cutting the fairings according to their accurate measurements: the three outer fairings from 2 mm plate and the three inner fairings from 1 mm plate.
Then the supporting frame structures were made. Pieces matching the inner fairing measurements were cut from 15x15 mm rectangular steel tube. Three sets of pieces were cut, one set of pieces for each “daisy cutter”. Some of the tubes had to be bent to match the curving edges of the inner fairing.
The frame pieces were placed along the edge of the inner fairing of the mainwheel inner door and attached to it using small clamps. Then the work continued in the “welding space”, i.e. a sea container outside the Finnish Aviation Museum where the pieces were welded together to form the frame along the edge of the inner fairing. A similar procedure was used to weld the two other frames.
Now the mainwheel inner door supporting frames and inner and outer fairings were ready. The next phase will be to rivet the fairings onto the frame.