Tango

The oval panel had been on Moscow built planes only. The reason is different way to seal integral fuel tanks. In Moscow the wing was first assembled, then they applied sealing agent throught this oval hole and then the hole was covered by the oval panel. In Gorkiy the sealing agent was applied during assembly of the wing, so the oval hole was not necessary.

Yes, that's right. And I understand that's the reason for this enlightment. MiG-21 is one of the most considerable fighters in the history and I believe the differences among variants should be explained Be frank - how many modelers out of the UK know difference between Lightning F.3 and F.3A?