Horizontal Tail Surface Framework (1927)

The bare tubular steel framework of the Spirit of St. Louis horizontal tail surface resting against a brick wall. — Horizontal Tail Surface Framework (1927) · Donald A. Hall Estate Collection

A photograph revealing a critical, life-saving engineering decision. As confirmed in a 1967 AIAA interview, Donald A. Hall Sr. designed these horizontal tail surfaces to be slightly unstable. This calculated compromise in the 1927 design forced the aircraft to constantly wander, forcing the exhausted Charles Lindbergh to actively fly the plane and stay awake during the grueling transatlantic crossing.