03/31/2008. The last Boeing Model 15D PW-9D was converted to an experimental aircraft by the installation of a 600 hp Curtiss V-1570 Conqueror engine replacing the original 435 hp Curtiss D-12. Delivered on September 4, 1928, the aircraft was reconverted to a standard PW-9D after testing was successfully completed. View also photo 8071.