The Avia 51 commercial airplane (Czechoslovakian) : a cantilever high-wing monoplane
This is a 1934 NACA aircraft circular, issued in the United States, describing the Czechoslovakian Avia S1 three-engine cantilever high-wing commercial airplane for aeronautical engineers and researchers. Its photographs show the aircraft's engine, fuselage framework, wing spar and wing structure in factory workshops, plus line drawings of the plan and side views.
