A Bat with Two Engines?

   The Savoia Marchetti S.81 bis.
   The picture above the headlines portrays the S. 81 bis, an almost unknown version of the Savoia Marchetti S.81 Pipistrello (Bat), a very important, ubiquitous  Italian bomber that fought in the Ethiopian campaign, in the Spanish Civil War and in all the theaters of the Second World War in which the Regia Aeronautica was engaged (and, later, even with the Luftwaffe).

The S.81 prototype

At or around the end of 1934 and the beginning of 1935, when the production of the Savoia Marchetti S. 73B (Belgium) airliner for SABENA began, the S.73's were advertised as derivatives of the S. 81 Pipistrello bomber which, meanwhile, had reached the flight test stage of its development; but the three-engined S. 73 airliner did not derive from the bomber at all. In fact, as late as September of 1934, the 18 passenger airliner version of the S.81 was still referred to as the S. 73C (Civile, that is, commercial).

Aguelock (in today's Mali), 1937. A Touareg is guarding a Belgian SABENA's S.73 that is being refuelled, before continuing on the "King Albert Route" to Black Africa.  

Actually, without a doubt, the variant of the S.81 that featured the highest number of modifications, with respect to the Pipistrello, was the S.81 bis, which was another of the many Italian attempts to transform a three-engine aircraft into a twin (the most famous one is probably the S.M. 79B). 
The only S.81 bis that was ever built was propelled by two 840 hp (kW 618), V 12, liquid cooled  Isotta Fraschini Asso XI RC, and it featured a windowed bow which housed the station of the bombardier. 
Since the empty weight and the payload had remained basically the same, the airplane suffered from the scarce power of the two engines, which was about 20% lower than the power of its trimotor progenitor; and in fact the S.81 bis was never able to reach an airspeed higher than 185 knots. As a result, the two engine Bat was terminated.

1938. A CSA's S.73 in Prague-Ruzyne

This was the much - edited translation of a couple of paragraphs of an article from the July-August 1978 issue of the Italian aviation magazine "Aerei." The picture of the Touareg came from the book "Dai Wright all'avvento del jet," di Nino Arena, Edizioni Bizzarri, Roma, 1976.

Leonardo Pavese



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