For the spanish type 5 un 1937 I decided to paint interior in A-14 as say KL
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The second plane is a type 10 in 1938 in China.
The interior AII blue as we can see in the I-16 Type 5 preserved at Chkalov Museum, have been repeinted after june of 1940.
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I propose that if after 40, interior color is the same that the downside part of the plane (AII blue) it could have been the same thing before 1940.
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Do you agree with that choise ?
Maslov (most likely based on technical manuals) says that: "
in the beginning interior was painted with gray oil paint. After February 1939, in order to improve moisture resistance, fuselage interior was primed with yellow ALG-2 primer and then painted with AE-9."
From this we may conclude that interiors were primarily painted to prevent wood rotting - that is why they used oil paints, not nitro paints (AII paints were never used to protect wood...). In the beginning they used cheaper A-14 and from Feb 1939, better quality and more expensive light gray AE-9 & ALG-2 primer.
HTH,
KL