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,^ait 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.^a

Production orders were placed on behalf of both Poland (250) and Romania (100), for the S.61², which appeared in 1925 carrying an armament of two synchronized 0.303 in (7.7 mm) MAC (Vickers) machine guns. A further thirty S.61²s were built under license in Poland from 1927 by^aCWL (Centralne Warsztaty Lotnicze) and its successor PZL (Pailstwowe Zaklady Lotnicze).^a

Variants that progressed no further than the prototype stage included the S.61³ which reverted to the metal wing structure of the original S.61¹ (the production S.61² having a wooden wing), and had four 0.303 in (7.7 mm) Dame machine guns and increased fuel tankage.^aFirst 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.61⁴.

Three examples of the S.61⁵ were built, powered by the 450 hp Hispano-Suiza 12Gb engine. The first of these was flown on May 13, 1925, and one was supplied to Turkey. The second S.61⁵ flew on September 9, 1927 as the S.61⁸ after being re-engined with a 500 hp HS 12Hb engine, and the final fighter derivative was the S.61⁶ built for Polish evaluation. This differed from earlier models in being a sesquiplane with a swept upper wing. The S.61⁶ was flown on May 1, 1926, but proved to have inferior characteristics to those of the standard S.61².

(For convenience the sub-version designations are often written as S.61/1 to S.61/8 or as S.61-1 to S.61-8.)"