Filler ring and supporting ring of Myrsky?s NACA-ring
Maanantai 25.10.2021 - Tuesday Club member
The NACA-ring of the VL Myrsky II is complicated to build. Fortunately the most difficult phases of work have already been completed at the Tuesday Club when building the ring for the Myrsky MY-14 engine, which is under restoration. When the NACA-ring and its parts have been chromated and the fastener consoles, among others, have been fastened on the inner surface of the ring, the NACA-ring can be test assembled on the Pratt & Whitney R-1830 engine, which is available at the Finnish Aviation Museum.
It is rather fortunate that this engine is on display at the Aviation Museum and there is no need to travel for the test assembly all the way to Tikkakoski, where the Pratt & Whitney engine has already been assembled on the MY-14 fuselage, under restoration at the Finnish Air Force Museum. The engine, which is available at the Finnish Aviation Museum, has been on a DC-3 but it suits well for the test assembling of the Myrsky’s NACA-ring.
The Tuesday Club team has been working lately on the filler batten ring (täyterengas), which will be fastened on the edge of the NACA-ring (NACA-rengas), as well as the supporting ring (moottorin suojuksen kannatinkehä) for the engine fairing. The supporting ring is fastened on the filler ring and its edge extends 30 mm outside the NACA-ring’s edge. The supporting ring forms a base outside the NACA-ring’s hem for the edge of the engine fairing. The supporting ring is covered with leather (nahkapehmuste) to absorb the resonance between two aluminium surfaces, which is caused by the engine.
First the filler ring, a 40 mm wide ring cut from 2,5 mm thick aluminium sheet, was fastened on the edge of the NACA-ring. The filler ring was shaped to match the curvature of the NACA-ring’s edge and preliminarily fastened on it with clamps. Then the filler ring was fastened with small bolts. When the ring was firmly in place, the bolts were replaced with flathead machine screws so that the surface of the filler ring is smooth when the supporting ring is assembled on it. Eventually both the filler ring and the supporting ring will be riveted on the NACA-ring.
85 mm wide strips were cut from 1,5 mm thick aluminium plate for constructing the supporting ring. One edge of each strip was bent to form a small gutter. Then the strips were shaped against the filler ring to match the curved shape of the NACA-ring. In the shaping process the supporting ring is also pressed tightly against the filler ring surface. When this had been achieved, holes were drilled through the supporting ring and the filler ring, and the supporting ring was fastened on the filler ring using small bolts.
The filler ring and supporting ring had to be made also where the machine gun barrels penetrate the NACA-ring. This was not easy because the machine gun barrels form “bumps” on the edge of the NACA-ring. This means that the filler ring and the supporting ring had to be shaped to match the gun barrel “bumps”. Several rounds of modifications had to be made before the filler ring and the supporting ring fitted nicely into place at the barrel “bumps”. During the modification process it had to be checked that the edge of the supporting ring extended exactly 30 mm outside the hem of the NACA-ring.
When the supporting ring had been preliminarily fastened, a line of holes was drilled through the ring and the filler ring under it for the future riveting work. Crosshead bolts were placed temporarily into the rivet holes. Now it could also be checked how the air intake duct of the air horn fits against the supporting ring between the machine gun barrels.
Photos: Lassi Karivalo
Translation: Erja Reinikainen