The Polikarpov I-16’s chubby fuselage contains, of course, room for the pilot in the cockpit area, situated over the wings.
In order to keep the plane speedy, the cut-out for the flyer’s head and shoulders was kept fairly small. The plane’s instrument panel is nestled some 8.5 inches forward of the front lip of the cockpit. The location makes it hard for a flyer to see the instruments in the deep, dark recesses of the aircraft interior.
The solution was a pair of the Perspex “portholes” that help illuminate the cockpit with light from above.