Historical coatings mystery solved!

flown in the UK. Work to restore Russian fighter and trainer aircraft opened up a need for specialised engine coatings and restoration specialists Russian Radials to contact Indestructible Paint to explore the possibility of finding modern-day equivalents for the protective coatings originally used.

As a specialist coating manufacturer dealing in the manufacture of coatings for engines, airframe and defence, marine and general industrial use, Indestructible Paint manufactures high performance surface coatings engineered to meet ever-increasing performance requirements as well as small quantities of specialised products for distribution worldwide.

Through translating original Russian documentation for radial aircraft engines, the specifications of the coatings could be established in order for a modern equivalent to be identified and provided by the coatings specialist.

Russian Radials' work to strip and rebuild Russian aircraft engines from original US designs dating back to the 1910s and 1920s, in addition to the inspect and rebuild procedures, meant more precise fitting and finishing details could only be found in the original Russian manuals, which had to be painstakingly translated.

In addition to what could be translated, some of the restoration processes required investigation skills. Most recently the dismantling of a Yak-11 engine revealed an unknown translucent brown coating and a graphite layer, the composition of which was only detailed in a very basic production and application process outlined in the accompanying manual. It was from this combination of investigation and translation that Indestructible Paint was then able to find a suitable replacement.

This latest project involved the restoration of 1950s engine components that used wartime technology dating back to the 1940s. Two components in particular required coatings: the engine casing and the piston skirts. In both cases, the original protective layer was removed to inspect the components for cracks by dye penetrant inspection. Although the original Russian engine overhaul manual gave explicit procedures for the replacement of the piston coatings, as it was 50 years old, many of the coating formulations could not be reproduced using materials available today.

Coatings rock hard!

The first coating needed was a layer of varnish on the interior surfaces of three of the main engine casings, a coating for which no instruction was provided. Indestructible provided a Rock hard stoving varnish 576-450-002 to provide the same protective attributes. The second was a graphite coating to each piston skirt for the purposes of friction reduction. While instructions on how to manufacture this coating were given in the translated manuals, it was not possible to replicate the exact elements required. Graphite dry film lubricant IP9136-R2 was provided by Indestructible as a modern day alternative to the original Russian specified material.

First flown in 1945, the Yak-11 was an advanced dual trainer, which entered series production in 1947. The coatings provided by Indestructible were successfully applied to the engine and will be used in aircraft that still fly within the UK today. These cases are part of Indestructible's growing portfolio in the restoration and preservation of historical aircraft. The engine restored in this case is the ASh-21, a single row, seven-cylinder, single-speed supercharged, fuel injected radial engine developing a maximum of 750hp.

Indestructible Paint has developed a name for investing in the restoration of historical aircraft, having previously provided coatings to replicate the original colours of a WWII Tucano, a Supermarine Spitfire and a Tiger Moth.

www.indestructible.co.uk