08/31/2014. Remarks by Johan Visschedijk: "The single-seat R-6C was also known as the Q.E.D. (Quod Erat Demonstratum, meaning "That which was to be proven, has been."), and registered NX14307 the sole example was first flown by Lee Gehlbach on August 15, 1934. It was sold to Jacqueline Cochran who raced it unsuccessfully in the 1934 MacRobertson race. Continuing engine problems prevented the aircraft being qualified for a number of races: 1934 Bendix (flown by Lee Gehlbach), 1935 Bendix (pilot Royal Leonard), 1936 Thompson (pilot Leon Atwood), and 1938 Bendix (pilot George Armistead). Subsequently it was briefly owned by aircraft dealer Charles Babb before it was acquired by Francisco Sarabia Tinoco of Ciudad Lerdo, Durango, Mexico, in 1938.

On May 27, 1939, Sarabia flew the aircraft, registered XB-AKM and named Conquistador del Cielo (Conqueror of Heaven) from Mexico City to Washington, D.C., USA, in 10 hr 47 min, beating Amelia Eathart's 1935 record of 14 hr 19 min. Unfortunately, on the return flight Sarabia crashed on take off from Bolling Field, Washington, D.C. Sarabia, not wearing a shoulder harness, sustained head injuries and died. The aircraft was returned to Mexico and after repairs it was put on display in a one-aircraft museum in Sarabia's home town."