Different Yak-1 canopies

[-=PHX=-SuperEtendard]

I wonder why there were 2 different canopy variants in the Yak-1. Looks like the early Yaks had this extra glass panel with a rearward angle, similar to how the Bf-109 achieves rear vision while having the turtledeck above the cockpit. This early variant provides better vision than the later one, why was this changed? Lower cost? Easier for mass production?

 

 

[GridiroN]

Wikipedia says the top Yak is an early prototype style Yak. The upper canopy likely complicated production. The Yak was also meant to have leading edge slats but they were ditched for some reason. 

[HBPencil]

Apparently the change in the rare glazing to that patterned on the LaGG-3 from approx batch 49 onwards was caused by a shortage of plexiglas.

Edited November 14, 2016 by HBPencil

[Brano]

It was more about plexiglas quality. Soviets had problems with bent/round shaped plexiglas technology. It used to create microcracks on curved surfaces,which decreased transparency over time. Straight plates where easier to manufacture.Bronyespinka/rear armored plate of the pilot seat also blocked most of the rear view,so it wasnt practical either.