IL2 Sturmovik.  It was the most produced ground attack plane . It went from a single seat craft to a 2 seater out of need,also the wing was redesigned. And in its final version the retractable main gear was changed from semi retracted to fully flush(IL 10).With over 40,000 produced from WW2 to Korea it ranks in the top 3 of all time production. It was known as Swartz Todd(Black Death) by the german soldiers and tank crew that faced it. 

1 - crew of 2

2 - tandem cockpits

3 - fixed tail wheel

4 - slab like tailplane mounted high on the vertical stab.