Tiistai 12.3.2019 - Member of Tuesday Club
The repair of the SM-1 helicopter’s (HK-1) two rotor blades (No1 and No3) has been going on for about a month. The fractures on the trailing edge of the blades have been repaired. Now the focus is on repairing the damages in the fabric and plywood covering. The damaged fabric covering has had to be dismantled in large areas.
The installation of the new fabric covering was first tested in the small damaged area in the middle of blade No 3. The damaged fabric had been dismantled in an area which was two rib-sections wide and reached up to the plywood-covered area in the leading edge and to the wooden strip on the trailing edge.
The new fabric will not be sewn onto the ribs as it has originally been. The fabric has been sewn on the ribs in such a complicated way that it is not possible to follow a similar procedure in the repair work. The Tuesday Club team considered the situation. If the rotor blade had been damaged during the using period of the helicopter, the wooden and fabric covered rotor blade wouldn’t have been repaired. Most likely a new rotor blade would have been installed. The Team decided that their task was to repair the rotor blades so that they would look intact and the outcome of the repair work would resemble the original blade structure as far as possible.
The patching of the damaged area was started by fastening painter’s tape around the edges of the dismantled area so that the original surface was visible about 1,5 cm at the edges. The original fabric areas were sanded smooth using sandpaper 250. The sanding dust was removed using a cloth moistened with a mixture of Sinol and water.
The area to be repaired was two rib sections wide (25 cm) and reaching from the trailing edge up to the plywood on the leading edge (35 cm). The Team decided to fasten the new cotton fabric covering by its edges using contact adhesive. Small fabric patches can be fastened by using only shrinking dope.
A piece of fabric matching the size of the hole in the rotor blade was cut from cotton fabric, which is used for covering airplanes. Scissors with zigzag blades were used so that the fabric will have a saw-toothed edge, which will fasten more firmly onto the bottom material than a straight-cut fabric edge. The rotor blades of SM-1 helicopter have originally been covered with cotton fabric and that is why the Team didn’t use modern reinforced fabric in the repair work.
The patch of new fabric was first glued onto the existing material at the top edge. The Team used contact adhesive (Bostik) and the adhesive was spread in equal width on the new fabric and on the edge of the repair area. When the adhesive had dried for about ten minutes, the upper edge of the fabric was pressed, pulling the edge at the same time, onto the upper edge of the opening.
Then the sides of the fabric patch were glued. This was done in 10 cm long phases, advancing towards to the trailing edge of the rotor blade. When the edges of the patch, with adhesive, were pressed against the edges of the dismantled area, the premature contact of the surfaces was prevented by using a piece of cardboard between the surfaces. When the work progressed, the piece of cardboard was slowly pulled away.
Working in a similar way as when fastening the upper edge of the fabric, the side edge of the fabric was pulled in both directions when fastening it. This is how the fabric got its preliminary tightness before the actual tightening with shrinking dope. When the new fabric had been glued by its edges all the way up to the wooden strip on the trailing edge, the patch was ready to be tightened.
The tightening of the covering fabric will be started by water treatment where the fabric is sprayed wet a few times and left to dry. Then the actual tightening will be done by applying several layers of nitrocellulose varnish on the fabric. The varnish, i.e. shrinking dope, will give the fabric its final impermeability and tightness.
Photos: Lassi Karivalo
Translation: 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
Maanantai 25.2.2019 - Member of Tuesday Club
A Polish helicopter SM-1 (SM1/600 SZ) is on display in the Finnish Aviation Museum’s Hall II. It has been in use in the Finnish Air Force and it has the registration number of HK-1. The helicopter was made in Poland, based on the principles of the Soviet Mil Mi-1 copter. The Finnish Air Force had four Polish SM-1’s in use during 1961-1967. These helicopters were assembled Finland at the Air Force hangars in Tampere in early 1961. Helicopters HK-1 and HK-2 were modified for training purposes.
The SM-1 has rotor blades which are over 6 meters long and have mainly wooden structure. Each blade has a round metal tube as a spar, surrounded by wooden ribs on the leading and trailing edges. The leading edge of the blade is covered with plywood and the tip of the edge has a narrow metal strip, covering the full length of the blade.
The tip of the blade has plywood covering, otherwise the blade has fabric covering. The upper surface has been painted dark green and the lower side pale blue. The root of blade No1 has the manufacturer’s labelling SM-1, No 1R10012, BLADE No 1, ATTEST No 844, DATE 11.1.1961.
Two of the three rotor blades of HK-1 have been damaged. It is not known when and how this happened. The Tuesday Club agreed with the Finnish Aviation Museum and the Aviation Museum Association that the rotor blades will be repaired by the Club. The rotor blade No1 was carried from the museum’s Hall II into the restoration space on February 5th, 2019 and the repair work was started.
The trailing edge of the rotor blade consists of the wooden strips on the upper and lower surface, which have been glued together at the edge and to which the ribs are fastened. The trailing edge on blade No1 is fractured in two places. The plywood and fabric covering has some holes, tears and scratches and the paint is badly flaking in some places.
The repair work was started at one of the fractured points on the trailing edge. There the wooden strip on the lower side of the trailing edge has broken into three parts. To have a good view of the damage, the torn fabric covering around the area was dismantled. The broken pieces of the trailing edge were removed, cleaned and fitted together on a table. The team decided to glue the pieces together and replace a small missing piece with epoxy.
The pieces of the trailing edge were glued together against the wooden strip on the upper side of the blade, using clamps. The glue was Erikeeper Plus. When the glue had dried, the clamps were removed, and the team was happy with the result. There were small gaps between the glued pieces and a small piece was missing, so the gaps were filled with epoxy. When the epoxy had dried, the trailing edge was in good condition and the outcome was even better than the team had expected. Finally, the surface of the glued trailing edge was buffed out. Now one of the fractures on the trailing edge had been repaired and it was left to wait for the covering of the damaged area.
There are bruises and cracks in the plywood covering and in some places the ribs under the covering have been damaged. The small cracks in the plywood were repaired using epoxy. When the epoxy had dried, the surface was honed smooth. The team hasn’t yet decided how to repair the larger cracks in the plywood covering.
The small holes in the fabric covering can be repaired using fabric patches. However, in most damaged places the fabric will have to be dismantled as far as the nearest ribs and to the leading and trailing edges. This is necessary in order to have sufficient gluing surface around the edges of the new fabric. The team hasn’t decided whether the new fabric will be glued onto the ribs or sewn on the ribs (as it has originally been). The new fabric will be pulled tight using shrinking dope.
The fabric covering was cut off in the damaged area in the mid-section on the upper surface of the blade. A thin rim of fabric, about 1 cm wide, was left on the edges of the ribs. When the fabric was removed up to the plywood covering on the leading edge, the team noticed something strange. There was a thin layer of paper under the plywood covering on the leading edge, resembling wax paper. There was no paper under the fabric covering and the team didn’t know why it had been installed under the plywood.
The painted surface of the fabric covering on the rotor blade is badly flaking and damaged in large areas. The paint peels off in thin strips. In some places it may be possible to fix the flaking using varnish or paint but in the worst places the flaking and damaged fabric will have to be dismantled and replaced. This is how the place on the upper side at the root of the blade had been repaired.
The SM-1 rotor blade repairs are well on the way.
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
Torstai 24.1.2019 - Member of Tuesday Club
It has been agreed with the Finnish Aviation Museum that the following project for the Aviation Museum Association’s Tuesday Club will be the Caudron C.59. At the moment the airplane is in storage at the Päijänne-Tavastia Aviation Museum in Vesivehmaa. The fabric-covered Caudron C.59 (CA-50) is in poor condition, having been in storage for more than 90 years. Its restoration work is estimated to take a couple of years.
One of the main work items is to repair the damages on the covering of Caudron’s wings, rudder and horizontal stabilizers. One wing has only the supporting frame structure which is so bent that the wing will have to be straightened and covered with new material. The fuselage covering is also badly damaged. The cockpit, engine space and landing gear will need thorough repair and maintenance. In the near future it will be decided in which order the parts of the Caudron C.59 are brought to the Tuesday Club for restoration. The Finnish Air Force Museum has an 8-cylinder V-engine Hispano Suiza 8 Ab, which has been used in Caudrons and other planes. This would be a good addition to the plane under restoration.
The Tuesday Club is prepared to start working on the Caudron C.59 when the surfaces of the Junkers 50 A Junior have been cleaned and the plane moved into the II hall of the Finnish Aviation Museum. The rotor blades of the Aviation Museum’s helicopter SM-1 (Mi-1) will also be repaired first. It may be possible to begin the restoration of the Caudron while the rotor blades are still under repair. Some of Caudron’s parts will be transported from Vesivehmaa to the Tuesday Club before the end of February.
The Caudron C.59 was used for the advanced training of pilots and 3 planes were bought in 1923 from France for the Finnish Air Force. Two of the planes were destroyed in a crash. The Caudron C.59 which is at Vesivehmaa has the identification number CA-50. It did its last flight on October 1st 1929 and was put into storage.
The Caudron C.59 resembles the Caudron C.60, used by the Finnish Air Force (it had 64 Caudron C.60’s). Due to the Hispano Suiza 8 Ab V-engine the front fuselage of the Caudron C.59 is slightly narrower than the thick nose of the Caudron C.60 with its rotating Clerget 9 star engine. Most likely the Caudron C.59 CA-50 in Finland is the only remaining individual of this plane type in the world. The Caudron C.60 (CA-84), restored by the Tuesday Club, is on display in the Finnish Aviation Museum.
Photos: Lassi Karivalo except when separately otherwise mentioned
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
Torstai 27.12.2018 - Member of Tuesday Club
The Tuesday Club team worked hard before Christmas to finish the I.V.L. K.1 Kurki restoration work so that the plane could be placed on display at the Finnish Aviation Museum before Christmas.
The fuselage of Kurki was in the Middle hall of the Aviation Museum, where the other parts were assembled as soon as the painting work of the new plywood surfaces on the tail parts and wings had been completed. The first parts to be assembled on the fuselage were the elevator and the horizontal stabilizer. The assembly work went well, and the control cables could be installed.
Kurki’s large wings had been partly covered with new plywood and the painting work on the new areas on the right / starboard wing were completed first. The assembly work of the starboard wing could be started in the beginning of December. The wing was lifted to the correct assembly height using a stacker. The lifting was secured with a cargo strap around the wing, attached on a beam in the ceiling. The cargo strap also prevented the Kurki from falling over when it had only the starboard wing assembled.
The lifting of the wing went well and the fastening elements on the root of the wing were pushed into the holes in the fuselage. The wing was easily locked in place. The assembly of the three wing struts was far more difficult. Four of the six wing struts had been made by the Tuesday Club team, because only two original parts were available. The team had no information on the actual shape of the fasteners at the ends of those struts and had improvised. This was why the strut fasteners had to be slightly modified during the assembly work to make them fit on the fasteners on the fuselage and on the wing. Finally, the fasteners slid into position and could be locked.
The painting of the port wing had been completed and the assembly work could be started on December 11th. The assembly procedure followed the procedure with the other wing, everything went smoothly until the wing struts were installed. Again, the fasteners on the wing struts had to be modified to make them fit. The wing was fastened in place and the wing struts fastened. Now both wings had been assembled and the securing cargo line could be removed. The ailerons were assembled on the wings and finally Kurki was a real airplane, for the first time in 91 years. When the test flights were finished in the autumn in 1927 the Kurki was dismantled and the parts were stored.
The Kurki can’t be described as smooth and beautiful! No wonder that it was nicknamed at the time as “Järvinen’s box”, according to its designer Asser Järvinen, the manager of the Airplane Factory. However, the Kurki is impressive with its huge wings. The Tuesday Club wish they had the proper Siemens-Halske 12 engine for the Kurki so that the plane would look like a real flying airplane. Unfortunately, there is not a single SH 12 engine available in Finland for the Kurki.
The remaining task was to turn Kurki around in the Middle hall of the museum, into its final display position. Maneuvering the plane was fairly easy, the Kurki rested on its skis and tail wheel on pallets with wheels. The problem was that the final assembly work had taken place under the main ceiling beam in the middle of the hall and now the wingtips of the Kurki nearly touched the walls of the hall. The plane was inched into a diagonal position in the hall, but that was a close call: there was a marginal of 5 cm between the wingtip and the wall.
When the Tuesday Club was working on the assembly, the Aviation Museum Society had been making preparations for the Kurki exhibition, including information posters. The posters describe the history of Kurki and also the restoration work at the Tuesday Club. There is also information about the design and construction of Kurki and about the history of the Air Force Airplane Factory, which operated in the Viapori sea fortress in the 1920’s.
The Kurki exhibition was opened on December 18th. The plane is on display in the Middle hall of the Finnish Aviation Museum, at least until the end of January but probably longer. The exhibition is definitely worth a visit: Kurki is one of the most extraordinary products of the Air Force Airplane Factory.
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.
Maanantai 26.11.2018 - Member of Tuesday Club
The I.V.L. K.1 Kurki was built in 1927 in the Air Force airplane factory at the Viapori sea fortress. The restoration of the Kurki prototype has reached its final phases in the Tuesday Club. One of the last, but not least tasks was to find and install the lost venturi tube on Kurki’s wing strut. The venturi tube is used for indicating the plane’s speed and it is based on the changes in air flow velocity.
The venturi tube has been fastened on the forward wing strut on the right / starboard wing – this can be seen on old photographs of Kurki. On the original wing strut the fastening point of the venturi tube can be seen and also some fastener clips for the air tube leading from the venturi tube to the cockpit.
An old but damaged venturi tube was found at the Finnish Air Force Museum, resembling the old one on the Kurki photograph. The Tuesday Club was pleased of the find, although the stem of the venturi tube had disappeared. Also the round plate at the end of the stem had disappeared, the plate is necessary for fastening the venturi tube on the wing strut. The old venturi tube from the 1920’s is made of cast siluminium, an alloy of zink and aluminium.
The motto of the Tuesday Club says: what is missing, we will make. So without further discussion the club members started making the missing venturi tube stem and fastening plate. The first task was to drill a hole on the venturi tube at the point where the original stem had broken. New nut thread was made for fastening the new stem. The new 15 cm long stem was cut from round aluminium pole, 5,5 mm in diameter. Screw thread was made on both ends of the stem so that it can be fastened on the venturi tube and on the fastening plate.
The fastening plate was made by cutting a piece from 4 mm thick aluminium plate and grinding it round. Holes for fastening screws were made and a hole was drilled in the middle, with nut thread for fastening the venturi tube stem. The sides of the wing strut are slightly curved, the fastening plate of the venturi tube has to be similarly curved. A model of the wing strut was made from stiff steel plate and this was used when hammering the fastening plate into the right curved shape.
Finally the parts of the venturi tube were ready to be fastened to one another. First the stem was screwed into the hole in the venturi tube. Then the fastening plate was screwed onto the other end of the stem so that the end of the stem penetrated the plate and was about 2mm out on the other side. The venturi tube was firmly fastened on a vise by its stem and the end of the stem was hammered flat on the underside of the fastening plate. Now the stem was tightly fastened and locked onto the fastening plate. The final phase was to stamp the year 2018 on the underside of the fastening plate so that the new plate and tube stem can be seen to be different from the original parts of the venturi tube. The venturi tube had now been repaired and was ready to be fastened.
The venturi tube was preliminarily attached on the front wing strut of Kurki’s starboard wing. The tube won’t be fastened before the collar-shaped support made of aluminium plate has been installed around the wing strut. This supporting collar under the venturi tube can be seen on old photographs of Kurki. The covering plywood on the wing strut is only 1,2mm thick so the venturi tube fastening plate and its screws need the additional support of the collar.
Photos: Lassi Karivalo.
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.
Torstai 18.10.2018 - Member of Tuesday Club
The Finnish Aviation Museum is planning to move into new premises located in the former Finnair cargo terminal, close to the T1 terminal of Helsinki-Vantaa airport. For the future relocation of the collection, the Finnish Aviation Museum gave instructions to the Tuesday Club to begin the registration and packing of collection items so that the parts will remain in control and proper order during the move. The first target were the parts dismantled from Valmet Tuuli III, which is being repainted at the Tavastia Vocational College in Hämeenlinna. Some dismantled parts have been waiting for its return on the shelves of the restoration space, marked with plywood identification tags.
It has been agreed that Tuuli III itself will stay in Hämeenlinna during the museum’s relocation and it will be brought back for further restoration after a couple of years. The dismantled Tuuli III parts are being used to test the registration and packing procedure developed for moving the aircraft parts of the Aviation Museum.
The Finnish Aviation Museum (Antti Laukkanen and Matias Laitinen) developed a multivariate Excel-table, into which all the labelled aircraft parts or part groups are carefully registered. After registration the parts will be packed, numbered and stored on traversers to wait for the relocation.
The Tuesday Club has been working on the registration and packing for two days and the experiences gained on the Excel-table have been positive. The registration sheet and the packing procedure are efficient, and the instructions are clear. It took the team two Tuesdays to classify and register a couple of dozen parts or part groups. However, some time was needed to learn to use the Excel-tool. An immense task is ahead when the thousands or tens of thousands of items in the Aviation Museum’s collections will be registered, numbered and packed for the move.
Tiistai 9.10.2018 - Member of Tuesday Club
The restoration work of I.V.L.K.1 Kurki has been almost completed at the Tuesday Club. The painting work of the partly replaced plywood areas on Kurki’s wings and of the new and repaired plywood surfaces on its wing struts remains to be completed. On both wings several square meters of rotten plywood had to be dismantled, mainly around the national emblems. Now the new covering areas are painted using a method similar to the original one.
First the new plywood areas had to be buffed out to remove the “lint” on the surfaces. The plywood surface was moistened using a spray bottle and dried using a heater fan, to make the “lint” stand upright. Then the surface was buffed out using 320 sand paper.
This procedure was repeated several times so that the plywood surface became very smooth. Chemical wood was used to putty the seams between the new and the original plywood sheets, then the seams were honed. Finally, the plywood surfaces were vacuumed and cleaned with a damp cloth, dipped in a solution containing 50 % Sinol and 50 % water.
Some expert advice for the Kurki wing painting was provided by the surface finishing teacher of the Tavastia Vocational College. A brief painting course took place at the Finnish Aviation Museum and the wings of Kurki were used as an example when discussing the treatment of new plywood surfaces and the painting work itself.
One of the key issues in successful painting is to keep dust away from the painting room and the surfaces which are being painted. After the wings had been vacuumed, they were covered using a thin film of plastic, which was cut open at the areas to be painted. On the edges of the painting areas the plastic film was taped tightly onto the surfaces.
The plywood surfaces of Kurki had originally been painted by first applying clear varnish on the clean plywood. On top of that a varnish tinted with silver bronze colour pigment was applied, and finally a layer of clear varnish added on top. A similar method is being used in the restoration work. Instead of clear varnish a corresponding modern material is used: La Tonkinois -lacquer, which is a mixture of varnish and Japan tree oil.
Before the Le Tonkinois-lacquer can be applied on the surface, the amount needed has to be filtered, in order to remove possible “bits and nuggets” in the lacquer. Then a clear base layer of Le Tonkinois was applied on the new and clean plywood surfaces on the Kurki wings and wing struts. A narrow and thin foam rubber roller was used, because fluffy mohair rollers aren’t suitable. When the lacquer had been applied using the roller, the surface was smoothed with a paint brush using long, parallel and light strokes.
When the lacquer had dried, the surface was buffed out with INDASA Fine and Super Fine buffing pads, vacuumed and wiped using the sinol/water-solution. When the plywood surface had dried, a new layer of lacquer was applied. This procedure was repeated so many times that the clear base lacquer layer was so smooth that the tinted layer of Le Tonkinois could be added.
Now the Le Tonkinois lacquer tinted with silver bronze could be applied on top of the clear and smooth base layer. A similar method was used to add the tinted paint layer as described above.
Photo: Jouni Ripatti.
To reach a good result, it is important that the foam rubber roller is moved only in one direction, not back and forth as usually when painting with a roller. After several layers of tinted lacquer and honing the surface between painting the layers, a very smooth silver bronze surface was ready. It had almost a metal shine. Finally, a top layer of clear Le Tonkinois lacquer will be added.
The Tuesday Club has established “a painting factory” in the Mid-hall of the Finnish Aviation Museum. The aim is to finish the painting of the new plywood surfaces on Kurki’s wings and wing struts before the end of October.
Photos: Lassi Karivalo except if separately mentioned.
Tiistai 17.7.2018 - Member of Tuesday Club
The damaged and partly rotten wings of I.V.L.K.1 Kurki are being repaired by the Finnish Aviation Society’s Tuesday Club. The repair work is at the phase where the starboard wing is ready and its new covering is being painted. At the end of January the port wing was brought to the workshop from the Päijät-Häme aviation museum storage in Vesivehmaa. Now the repairs on the port wing have been almost completed.
The rotten plywood covering of the Kurki’s port wing had to be dismantled around the national swastika emblem on both sides of the wing, several square meters in total. Before the dismantled areas could be covered with new plywood, the damaged inner structures of the wing had to be repaired and partly renewed. These repairs were finished in mid-April. The preparations for the new covering included also building wooden bridge structures under the seams where the new plywood covering meets the old. When this had been completed, the installation of the new covering could be started.
The lower surface of the wing was covered first and the work was started at the small dismantled areas between the leading edge and the front spar. New 1.2 mm thick plywood was used, matching the original covering material. After this the large area was covered, extending across the whole width of the lower surface of the wing. There a different approach had to be taken – the original installation of the Kurki covering from 1927 couldn’t be followed.
The Kurki wing is very wide (225 cm) and it has been originally covered with a single board of plywood which is as wide as the wing. Such large boards were not available and a different method had to be used when installing new covering on the lower side of the wing. The existing plywood boards were 150x150 cm. Therefore the wing had to be covered using two sheets of plywood with a butt joint on the rear spar.
Two pieces were cut from the plywood board, one to cover the area between the rear spar and trailing edge and the other to cover the area between the rear spar and leading edge. The pieces were modified to fit in their places. Special attention was paid to the edges meeting at the butt joint: the seam on the rear spar must be tight.
When the plywood pieces had been correctly positioned, supporting battens were fastened on their lower surface, following the original construction where the battens support the covering between the ribs. The supporting battens keep the plywood from bending inwards due to aerodynamic reasons when the plane is in the air. The lower surface of the plywood was protected against humidity using Le Tonkinois varnish.
Casco Outdoor wood glue was used when gluing the new plywood sheets on the ribs, wing spars and leading and trailing edges.
On the upper side of the wing less damaged covering had been dismantled than on the lower side. The largest area was around the national emblem, between the rear spar and the trailing edge, extending the width of five ribs. Some old covering had also been removed between the front spar and the leading edge, between two or three ribs.
Two sheets were cut from the 1.2 mm thick plywood board, matching the dismantled area between the rear spar and trailing edge. One of the sheets covers the area between three ribs on the left side of the area, the other the area between four ribs on the right.
The plywood sheets were positioned in their places and the supporting battens were installed as described above. The surfaces were protected with varnish. An elongated opening was made for the aileron wire lead-in and the aluminium plate collar, dismantled from the original covering, was installed.
The sheets covering the dismantled area will be fastened on their upper edge to the edge of the original plywood, using a butt joint at the rear spar. The lower edge the plywood will be fastened on the batten of the trailing edge. Along the length of the wing the new plywood sheets will be fastened to each other and the adjoining old plywood, using lap joints. This method was chosen because the original plywood covering of the Kurki wing have been fastened at the ribs using lap joints so that the edges of the plywood sheets overlap a couple of centimeters. The plywood covering has been started from the tip of the wing.
The plywood sheets on the upper surface of the wing will have to be modified a little before they are ready to be glued in place. The restoration work was left at this point before when a summer break started in the Kurki project. The autumn season of the Tuesday Club will begin on August 14th and the work goes on.
Photos: Lassi Karivalo.
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 28.5.2018 - Member of Tuesday Club
The covering of I.V.L.K.1 Kurki’s left wing with new plywood is going on at the Tuesday Club. The rotten plywood on the lower side of the wing was dismantled and has already been replaced by new plywood covering and now the dismantled areas on the upper surface of the wing are being covered.
The aluminium plate access hatches for the aileron wire pulleys and aluminium plate collar for the aileron wire lead-in are located in the dismantled area on the lower surface of the wing, at the swastika emblem. The wire pulleys inside the wing are attached to the sides of the rear spar.
The Tuesday Club team wanted to keep the access hatches and the wire lead-in collar as they were and move them from the rotten plywood on the new plywood covering. For this procedure the location of the hatches and the collar were measured when the rotten plywood was still attached. The measurements were documented to a drawn scheme which will be used for placing the hatches and the collar in their correct places on the new plywood.
The sliding access hatches had been fastened to the plywood using copper rivets. The aileron wire lead-in collar had been fastened with screws to the supporting batten under the plywood. The collar was easy to dismantle by removing the screws. The access hatches were unfastened by drilling out the rivets without damaging the hatches.
The unfastened hatches and aluminium collar still had their original paint in reasonable condition and the team decided not to remove the paint. The surfaces were just cleaned carefully. The hatches and the wire lead-in collar will not be repainted when the national swastika emblem will be painted on the new plywood covering.
The Kurki wing is 225 cm wide and it has been originally covered with a plywood board 1,2 mm thick which is as wide as the wing. The Tuesday Club team has 1,2 mm thick plywood boards which are 150x150 cm so the dismantled wing area will be covered using two plywood boards with a seam on the rear spar. This means that the access hatches, which are located on either side of the rear spar, will be fastened on two different boards: one hatch to the plywood area towards the trailing edge and the other to the plywood area towards the leading edge.
The plywood sheet towards the trailing edge was cut to measure from the 1,2 mm thick plywood board and preliminarily installed in its place. Then the location of the hatch and the aileron wire lead-in collar were marked on the plywood using the drawn scheme. Holes were cut in the plywood according to the drawing. The sizes of the holes were compared to the ones on the dismantled rotten plywood. Finally the access hatch and the aluminium collar could be fastened onto the new plywood covering.
The sliding cover of the access hatch was unfastened and the cover frame was fitted into the hole made for it. Holes were drilled in the plywood at the places where the frame had the rivet holes. Aluminium rivets were used instead of copper ones. A protecting ring was placed on each rivet before hammering the rivets one at a time against an anvil, until the rivet was at the level of the plywood surface.
When all the rivets had been hammered in and the cover frame had been fastened by its corners, the sliding hatch cover could be pushed in place. The aluminium collar for the aileron wire lead-in was fastened in its place using screws.
Now the new plywood covering between the rear spar and the trailing edge had the original access hatch and the aileron wire lead-in collar in their correct places. The plywood sheet was fastened on the ribs using Casco Outdoor glue and rows of nails and screws. The access hatch for the other aileron wire pulley were installed in a similar technique to the new plywood between the rear spar and the leading edge and the plywood was fastened on the wing.
Photos: Lassi Karivalo.
Lauantai 12.5.2018 - Member of Tuesday Club
The Finnish Aviation Museum Society’s Tuesday Club project to restore the Valmet Vihuri II (VH-25) front fuselage has taken almost twenty years. Now the restored part with front and rear cockpits is ready and on display in Hall I at the Finnish Aviation Museum.
The restored Vihuri front fuselage is based on the front cockpit and the engine mounting of VH-25 which were found in a scrapyard in Helsinki in the 1970’s and purchased to the Finnish Aviation Museum. The cockpit had some equipment and wind screen and the engine mounting had some fairing plate remaining. The restoration project started in the late 1990’s but was interrupted for a while and started again with full speed in the early 2000’s.
The front fuselage found in the scrapyard had only the front cockpit so the rear cockpit with its pilot’s seat had to be built following the original Vihuri drawings. Cockpit equipment and instruments found in the collections of the Finnish Aviation Museum and the Finnish Air Force Museum have been installed in the cockpits. The Tuesday Club team is grateful for the assistance of both museums for supplying the material. The Tuesday Club team built several new items for the cockpit, including the luggage compartment, map holder and flare gun with its launching tube.
The front fuselage of Valmet Vihuri II with its cockpits and its equipment is now in the Finnish Aviation Museum, on display for the visitors. The only remaining whole Vihuri (VH-18) I s in the Finnish Air Force Museum. However, the front part of VH-25 in the Aviation Museum offers the visitors something that the VH-18 in the Air Force Museum doesn’t.
The restored front fuselage of VH-25 is mainly covered with transparent plexi, not aluminium plate. Therefore the museum visitor can clearly see what equipment and instruments the Vihuri has.
The cockpit and display lighting is on, as well as the lights in the sight. Above the front seat there is a mirror for having a good view of the sight and its light cross.
The cockpit equipment and instruments in Vihuri are interesting because they originate from earlier plane types used in the Finnish Air Force. When the Vihuri’s were originally built, parts were installed from dismantled Air Force planes. For example the stick in the front cockpit of the Vihuri, the magneto selection switch, the red cockpit light and parts of the oxygen supply system (the regulator, the flow and pressure indicators and valve) come from Messerschmitt Bf 109.
The oxygen bottles of Vihuri are probably from Junkers Ju 88. The rudder pedals in the front cockpit are from VL Myrsky.
The instruments in the instrument panel come from several different planes. The manual pump of the pressurized oil system is from Bristol Blenheim. Unfortunately there is no Bristol Mercury motor available in Finland, so the restored VH-25 has no motor. As you can see, recycling of equipment and instruments has been a key issue in the building of Vihuri.
Welcome to the Finnish Aviation Museum to see the front fuselage of Valmet Vihuri II, restored by the Tuesday Club.
Photos: Lassi Karivalo.
Torstai 19.4.2018 - Member of Tuesday Club
The Finnish Aviation Museum has donated the models of BEA Hawk, Folland Gnat, Saab Draken and MiG-21BIS to the Aviation Museum Society’s Hawk Experience Center. The large wooden models were found in the storage room of the museum. The models need some repairs which will be completed in the Tuesday Club before the Hawk Experience Center season 2018 begins in May. The repairs of the BAE Systems Hawk Mk.51 model have already been described in an earlier blog.
After the Hawk model the next target was the Folland Gnat F.1 model. This model wasn’t badly damaged but the cockpit canopy was missing. In addition to some minor repairs the canopy had to be made.
To make the new canopy, first a wooden model of the canopy had to be made. The cockpit was emptied by removing the pilot’s seat and the instrument panel. This was necessary in order to be able to fit the wooden canopy model, made of balsa, in its place in the cockpit. At the same time the measurements were taken of the line where the canopy meets the edge of the cockpit: a metal frame will be fitted on the sides and at the rear end of the canopy.
A piece of balsa was carved slowly to match the shape of the canopy and the correct size by fitting it into the cockpit every now and then. Photographs and 3d-drawings of the Gnat were used to define the shape of the canopy. The wooden model began to take shape when it was gradually and carefully carved and buffed out and regularly fitted into the cockpit. Now the model for the canopy was ready.
Photos: Jorma Laakso.
Before making the actual canopy, the metal frame for the edge of the canopy was made. The wooden model was used to dimension the frame. The location of the frame was marked on the model in red lines. The image of the frame was drawn on a 0.3 mm thick brass sheet and cut off. The thin strips of brass sheet were honed to match the shape of the frame on the lower edge and the rear section of the cockpit and fitted on the balsa model. When the metal parts seemed to fit nicely into place they were soldered together. Now the metal frames were ready to be installed on the actual canopy.
Photos: Jorma Laakso.
The windscreen arc in front of the canopy was made of 0.8 mm thick plywood, laminating four layers of plywood on top of each other. The laminated arc was milled and buffed out into shape. Then a windscreen made of transparent plastic sheet was attached, using a friction-type connection.
Photo: Jorma Laakso.
The making of the actual canopy was started, using the balsa model and a mould. A heated plastic sheet is pressed against the opening in the mould, using the balsa model for pressing. The mould was made from 4 mm plywood with an opening matching the shape and dimensions of the outer edges of the cockpit.
Photo: Jorma Laakso.
A piece of 10x10 cm was cut from a 0.5 mm thick GAG-PET sheet. The sheet of plastic was attached by its edges on top the opening in the plywood mould. The sheet of plastic was heated using a hot air blower. When the surface of the plastic was soft enough, the sheet was pressed evenly into the opening in the mould using the balsa model. The stoppers on the sides of the balsa model prevented the model from pressing the sheet of plastic too deep into the mould.
Photo: Jorma Laakso.
It took about one minute for the plastic sheet to cool down, then the balsa model was removed. A bulge had formed under the mould, shaped like the balsa model. This was the rough form of the canopy. The GAG-PET sheet was removed from the mould and the bulge, i.e. the preformed canopy was cut off.
Photos: Jorma Laakso & Lassi Karivalo.
Now the metal frames (at rear end and lower sides of the canopy) and the windscreen arc could be attached to the canopy. The canopy was placed on the balsa model where the red markings showed the exact place of the frame. When the metal strips had been placed exactly on the marked lines, they were glued in place using UHU POR contact glue. Now the extra plastic material below the frame could be cut off. When the canopy was placed on top of the cockpit to test how it fitted, the result looked good. UHU POR contact glue was used to glue the windscreen arc to the canopy. Then the canopy frame and the windscreen arc were painted dark green.
The last phase of work was to attach the new canopy on the Gnat model. The canopy was placed on the edges of the cockpit and attached with Plastic Padding. When the seam had dried it was honed smooth and painted dark green. The Folland Gnat F.1 model had a new canopy and is now ready to be placed on display in the Hawk Experience Center.
Photos: Unless separately mentioned, Lassi Karivalo.