Salmson Z-9

The Societe des Moteurs Salmson began development of aircraft engines in 1908 and started producing engines in 1913. No other water-cooled radial designs can boast such a long list of achievements. Salmson also built in-line and barrel engines, but the most famous Salmson engines are the water and air-cooled radials. The Z-9 model was widely used during World War 1.



Salmson Z-9 Early Later
Type water-cooled 9-cylinder radial water-cooled 9-cylinder radial
Bore 125 mm (4.92”) 125 mm (4.92”)
Stroke 165 mm (6.50”) 170 mm (6.69”)
Displacement 1,112 cu in 1,146 cu in
Power 230 hp @ 1,500 rpm 250 hp @ 1,550 rpm
Weight ? 473 lbs


Later Salmson Z-9s had a compression ratio of 5.4:1, a specific fuel consumption of 0.490 lb/hp/hr and a specific oil consumption of 0.077 lb/hp/hr.

Cylinders were constructed of steel with welded-on sheet-steel water jackets. They were captured by the two halves of the crankcase via two flanges at their base. Slightly inclined valves were actuated via rocker arms, pushrods and tappets running on three intake and three exhaust cams running in the same direction as engine rotation at one-quarter engine speed. Aluminum pistons were fitted with four compression rings and one oil ring. Intake valves opened at TDC and closed at 55 degrees ABDC. Exhaust valves opened at 65 degrees BBDC and closed at TDC.

Two nine-cylinder magnetos supplied dual ignition. Carburetion was via either Claudel or Zenith duplex carburetors. Oil was circulated by two oscillating-plunger pumps.

The two-piece crankshaft ran on ball-bearings and was joined via a short taper on the rear end of the crankpin, held to the rear crankcheek via a pin and nut. Several thousand of the later Z-9 models were produced during 1917 and 1918.

Not only was the Salmson Z-9 noteworthy as a water-cooled radial, but it also among the last production engines to successfully replace the usual master/articulated connecting rods with a true-motion Canton-Unne mechanism.

The idea of a water-cooled radial seems strange today, but such engines were quite common in the early days of aviation. The first US aircraft engine, the Balzer-Manly that powered Samuel Pierpont Langley’s ill-fated Aerodrome, was a water-cooled 5-cylinder radial. By 1939, others had been built by Albatross, Anzani, Clement-Bayard, Fiat, Garuffa, Rumpler and Salmson. During the Second World War, Wright Aeronautical tested a 42-cylinder liquid-cooled radial, Lycoming tested a 7,755 cu in, 36-cylinder liquid-cooled radial, and BMW built a 28-cylinder liquid-cooled radial.



The Canton-Unne mechanism was conceived by Georges Henri Marius Canton and Pierre Georges Unne, who filed their first patent application in France on December 15, 1908. Please refer to the diagram of the Canton-Unne mechanism. On the left is a transverse section of a representative radial engine. At the upper right is a detail of the Canton-Unne mechanism, a transverse section of which appears at the lower right. Each connecting rod (8) is attached to a single spool (9), which rotates on the crankpin (10) of the crankshaft (6). A gear (14), fixed to the spool (9), engages intermediate pinions (15), which also engage another gear (17) that is fixed to the crankcase (3). Gears 14 and 17 have the same number of teeth. Intermediate pinions (15) rotate on a shaft (16) that is fixed in place via an arm (18) that is an integral part of the crankshaft. As the intermediate pinions (15) “walk” around the gear fixed to the crankcase (17), they cause the spool (9) to rotate at the same angular velocity as the crankshaft, thereby eliminating the need for a master rod. A counterweight (19) balances the rotating and reciprocating masses attached to the crankshaft. While there have been many attempts to replace the master/articulated connecting rod scheme, none seem to have been worth the effort, although people continue to try.