Painting of the Mi-8 helicopter tail boom stabilizers

Tiistai 16.1.2024 - Tuesday Club member

Suomeksi

The restoration of the Karalian Aviation Museum situated Mil Mi-8T (HS-4) tail boom stabilizers has been concluded. It started at the Tuesday Club in the autumn season 2023. The decayed covering fabrics of the stabilizers of aluminium structure were removed and the stabilizers were covered with weatherproof thin aluminium sheets instead of fabric. Because it was decided to paint the stabilizers all round, the worn paint surfaces were ground ready for painting. The priming of the stabilizers has been described in an earlier blog.

The stabilizers of the tail boom will be painted according to the paint scheme used in Mi-8 helicopters in the Defence Forces. The upper surfaces will get a camouflage colour AN 22 green (Light bronze green), which compares to the NCS-shade map NCS S6020-G50Y. The under surface will be light grey (Light aircraft gray), which corresponds to the RAL shade map RAL 7038. As the surface paint the Teknos Futura 15 outside furniture paint was chosen. Corresponding to the aforementioned shades, the grey and green paints were bought at the Pintaväri Vantaa branch.

The painting was started from the upper surfaces with the green Futura. The smooth surfaces were painted with a narrow mohair roller. Uneven surfaces like the rivet studs, the stabilizer stem and the strut were painted with a brush. The first time over gave a fairly good coverage, but to achieve a good surface the stabilizers have to be painted twice over.

After the green paint had dried, the under surfaces were painted once over with the light grey Futura. This paint, too, gave laudable coverage with the first painting. However, the under surfaces were painted a second time over after the paint had dried, to achieve an even and well protecting surface.

We still had to paint the stabilizers’ upper surface for a second time. The painting of the upper surface for the second time was left last, because at the seam of the upper and under surfaces of the stabilizer, the green paint gives a good coverage over the light grey paint. In this context the green and grey border surface of the stabilizer was taped over with painter’s tape. Another option would have been to paint the border area with a roller without masking. However, we ended up with masking, because it produces a neat and tidy straight border between the grey and green paint.

When masking is used in painting, it’s important to take off the masking tapes immediately, before the paint dries. If you leave the tape in place till the paint is dry, when taking the tape off it easily tears dried paint along, and the neat border that was meant to be achieved by masking, will be lost.

The Mil Mi-8T helicopter of the Karelian Aviation Museum has now had its tail boom stabilizers restored and they are ready to be delivered to Lappeenranta.

Photos by Lassi Karivalo.

Translation by Matti Liuskallio.

Priming the HS-4 tail boom stabilizers

Torstai 30.11.2023 - Tuesday Club member

Suomeksi

When both the fabric covered areas of the Mil Mi-8T (HS-4) helicopter tail boom stabilizers had been covered with thin 0,3 mm aluminium offset printing sheet, we could move on to priming these new aluminium surfaces. Obviously, the decayed fabric coverings were renewed with aluminium sheets instead of fabric.

Right hand side photo by Mårten Juslin.

The first phase in priming is to remove grease and dirt from the surface to be painted. KUSTOM-anti grease agent was used to remove the grease. The agent was applied to clean cloth and both stabilizers’ new aluminium surfaces were meticulously wiped with it. The anti-grease operation for other surfaces of the stabilizers will be done in conjunction with the paintwork because their surfaces are already set up for the paintwork.

Photo by Mårten Juslin.

The next step is the graining of the new aluminium surfaces to be adhesion-primed, especially as the HS-4 tail boom stabilizers’ new surfaces are smooth like a mirror.

Photo by Mårten Juslin.

The graining of the new aluminium surfaces was done with a traditional scouring pad. After graining, the graining dust was wiped off the surfaces with a clean cloth. It was noticed that more dirt had accumulated to the cloth used for wiping off the grease and dirt than to the cloth used for wiping off the graining dust. This goes to show, how important part of the priming, the removal of grease and dirt is.

Right hand side photo by Ari Aho.

As a primer or adhesive primer we chose the handy spray paint (Car System Prefill Spray Miranol) and its tone (RAL 7005). Light grey is in this case a good tone for the adhesive primer, because the stabilizers’ undersurfaces will be painted light grey (Light aircraft grey).

Photo by Mårten Juslin.

The stabilizers that were ready for priming, were taken to the painting tent at the yard of the Finnish Aviation Museum. There the primer was misted on the stabilizers’ surfaces as a thin, but engulfing veil. The stabilizers are now ready for the paintwork.

Photos by Lassi Karivalo except if otherwise separately mentioned.

Translation by Matti Liuskallio.

Mil Mi-8T (HS-4) helicopter tail boom stabilizers' covering with thin aluminium sheet

Sunnuntai 29.10.2023 - Tuesday Club member

Suomeksi

The tail boom stabilizers’ covering of the Mil Mi-8T helicopter, situated in the Karelian Aviation Museum, has started briskly. As was told in an earlier blog about the HS-4, the stabilizers will be covered with a thin aluminium sheet, instead of covering fabric. This is because the aluminium sheet stands much better to weather. And we must remember that HS-4 stands outdoor at the Museum yard most of the time and it’s not airworthy anymore.

The covering of the stabilizers got really started after they had been stripped off tattered and rotten fabric and the faded aluminium surfaces were ground and waiting for painting after covering.

We decided to start the covering from the underside of the right-hand stabilizer. The covering will be done with 0,3 mm thick aluminium offset-printing sheets that were donated to us. Because one printing sheet isn’t enough to cover the whole area, both sides of the elevator will be covered with two aluminium sheets, joined to each other with edge joints.

We drew the area to be covered from the stabilizer stem and tip onto cardboard and cut the cardboard with a cutter to serve as models for the stem and tip aluminium covering sheets. Then we put the cardboard models on the aluminium sheets and attached them to the sheet with tape. This way the cardboard models stuck to the sheet when the aluminium sheets were cut to form with a cutter.

The edge joint of the stem and tip sheets is made on the centre rib of the stabilizer. Therefore a 5 cm wide aluminium support strip was riveted on the rib. The edge joint of the aluminium sheets will be placed in the middle of the support strip and the sheets will be riveted into the strip at the edges. Now the covering sheets could be placed on the stabilizer to their final form. The edges were formed, however, in such a way that the sheets are equally wide at the joint and their top edge joins tightly with the edge of the steel reinforcement on the surface of the stabilizer.

When the underside sheets had been shaped into place, the riveting was commenced from the tip sheet. The sheets will be riveted to the stabilizer at their outer edges with 3,2 x 6,0 mm blind rivets or pop rivets. First the places of the rivets were marked with a pen at three cm intervals at the edges of the sheets. Then the marks for drilling the rivet holes were snapped with a spike. The drilling took place with a 3,2 mm bit.

After the holes on one side were done, the pop rivets were riveted in place one after the other. The rivet was tightened with rivet pliers through the covering sheet into the structure of the stabilizer. After the stabilizer tip sheet had been riveted at its edges to the stabilizer underside, the stabilizer stem covering sheet was riveted to its place.

Because the aluminium sheets were only riveted at their outer sides, the contact surface of the rib and aluminium sheet was seamed with silicone. That way the aluminium sheet glues itself to the rib and won’t resonate in strong winds.

After the undersurface of the right-hand stabilizer was covered, the upper surface covering could be continued in similar manner. The procedure will be the same, when covering the left-hand stabilizer of the HS-4 tail boom with thin 0,3 mm thick aluminium sheet. When both stabilizers have been covered with aluminium sheets, it’ll be time to move on to the painting phase of the stabilizers, and that, as Kipling put it, is a different story.

Photos by Lassi Karivalo.

Translation by Matti Liuskallio.

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

Keskiviikko 27.9.2023 - Tuesday Club member

Suomeksi

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

Photo by Kimmo Marttinen

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

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

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

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

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

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

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

Photos by Lassi Karivalo except if otherwise mentioned.

Translation by Matti Liuskallio.