12/15/2017. Remarks by Johan Visschedijk: "The Blériot SPAD S.61 was a single-bay staggered biplane with fabric-covered metal wings and a wooden monocoque fuselage, it was powered by a Lorraine-Dietrich LO 12Ew twelve-cylinder W-type engine of 450 hp, and the prototype was first flown on November 6, 1923. Production orders were placed on behalf of both Poland (250) and Romania (100), for the S.61-2, which appeared in 1925 carrying an armament of two synchronized 0.303 in (7.7 mm) MAC (Vickers) machineguns. A further thirty S.61-2s were built under license in Poland from 1927 by CWL (Centralne Warsztaty Lotnicze) and its successor PZL (Pailstwowe Zaklady Lotnicze).
Variants that progressed no further than the prototype stage included the S.61-3 which reverted to the metal wing structure of the original S.61-1 (the production S.61-2 having a wooden wing), and had four 0.303 in (7.7 mm) Dame machineguns and increased fuel tankage. First flown on May 9, 1925, it was intended to participate in the 1925 fighter trials. Re-engined with a 480 hp Lorraine-Dietrich LO 12Ee, it flew on June 6, 1925 as the S.61-4. Three examples of the S.61-5 were built, powered by the 450 hp Hispano-Suiza HS 12Gb engine. The first of these was flown on May 13, 1925, and one was supplied to Turkey. The second S.61-5 flew on September 9, 1927 as the S.61-8 after being re-engined with a 500 hp HS 12Hb engine, and the final fighter derivative was the S.61ses built for Polish evaluation. This differed from earlier models in being a sesquiplane with a swept upper wing. The S.61ses was flown on May 1, 1926, but proved to have inferior characteristics to those of the standard S.61-2.