By Museo Storico dei Motori e dei Meccanismi
Museo Storico dei Motori e dei Meccanismi - Sistema Museale dell'Università degli Studi di Palermo
The counter-rotary engine
The aircraft engine Siemens & Halske Sh.IIIa (1917-1918) represents the last development of the rotary engines widely used for aeroplanes during the early period of the aviation history, from 1908 to 1918.
The development
During the First World War many companies, among which Siemens & Halske, a division of Siemens Company, was involved in the production of engines for the Luftstreitkräfte, the German Military Air Force. To satisfy the growing need for aircraft perfomance, in the autumn of 1916 Siemens & Halske developed an innovative 11-cylinder radial engine, the Sh.III, designed by Franz Dinslage. Unlike its contemporary airplane engines, the Sh.III featured an original counter-rotary system.
Sh.IIIa - posterior viewOriginal Source: http://www.museomotori.unipa.it
Rear view of the Siemens & Halske Sh.IIIa.
The "counter-rotary" system
In the counter-rotary engine the internal parts, such as the crankshaft and the connecting rods, rotated clockwise while the cylinders and the crankcase rotated counter-clockwise driving the propeller. This particular arrangement allowed a reduction in the propeller's speed within its best efficiency range, increasing the power output by means of a higher combustion cycle frequency.
Sh.IIIa - "Bi-rotary" system technical drawingOriginal Source: http://www.museomotori.unipa.it
Longitudinal section of the engine Sh.IIIa.
Sh.IIIa - byrotary system schemeOriginal Source: http://www.museomotori.unipa.it
“Counter-rotary” system of the engine Sh.IIIa.
The Sh.IIIa version
The Sh.III was also produced between 1917 and 1918 in two versions. The latter, named Sh.IIIa, features a higher compression ratio and an increased maximum power output of 240 hp at 1000 rpm at sea level. During the war, the Sh.IIIa was produced in about 2000 copies by Siemens & Halske and Rhemag at Mannheim, under licence.
The Sh.IIIa performances
Despite some drawbacks, the Sh.IIIa was a technically advanced engine for its time, with remarkable performances in terms of maximum power output and power-to-mass ratio (about 1 hp/kg). In September 1918, a fighter Siemens-Schuckert D.IV, equipped with the engine Sh.IIIa, set a remarkable record, reaching an altitude of 8100 meters in 36 minutes.
The
end of the Great War
After the First World War, according to Versailles' Treaty, almost the entire German aviation arsenal was destroyed. So, nowadays, only very few Siemsens & Halske Sh.III engines remain.
Aircraft Pfalz D.VIIIOriginal Source: http://www.museomotori.unipa.it
A fighter Pfalz D.VIII equipped with the Sh.IIIa engine, in the last year of the Great War.
The restoration work
The Sh.IIIa is part of a batch of German-manufactured engines originally purchased in 1925 by University of Palermo for didactic and research purposes. In 2010 the engine undergone a full restoration work.
Sh. IIIa - restoration detailOriginal Source: http://www.museomotori.unipa.it
A detail of the Sh.IIIa before its restoration.
Sh.IIIa - detail (3)Original Source: http://www.museomotori.unipa.it
The Sh.IIIa was manufactured in the Siemens factory in Berlin as reported in the original production plate.
Sh.IIIa - cylinderOriginal Source: http://www.museomotori.unipa.it
One of the eleven cylinders of the Sh.IIIa during the restoration work.
Sh.IIIa - components and cylindersOriginal Source: http://www.museomotori.unipa.it
Various components of the valve timing system during the restoration work.
All rights reserved
© Property of the Museo Storico dei Motori e dei Meccanismi - Sistema Museale di Ateneo - University of Palermo (Italy).
Curators: Giuseppe Genchi and Giuseppe Bellomo
Revisor: Giuseppe Genchi
Main collaborators: Maria A. Algeri, Claudia Lo Re, Valerio Spena, Maria C. Esposito.
