On Tuesday, May 12, 2020 at 7:14:59 AM UTC-7, wrote:
... I DO NOT think it was a perfect kit...there maybe have been defects in the factory assembly of wings (maybe curing rates? maybe molds, I don't exactly know).

I toured the Aviastroitel factory in Moscow in 1999, when the AC-4 was being produced. All the structure was formed in a former Soviet aircraft factory outside Moscow, and then brought to Aviastroitel for finishing, completion and testing. All the structure was of good quality, but required a lot of finishing. So it could just be that a lot of finishing is required and those are the "defects" mentioned. After visiting Schleicher and Schempp-Hirth, the visit to Aviastroitel was fascinating. The Russians do an amazing job with very little.

I have traveled in Eastern Block countries. I was always amazed and how well the Russians lived on so little!
Could be their education level was very high, they are extremely strong people. Interesting place, it has been 20 years but I valued my time getting to know these people. As for the glider, I have no comment.