Le Rhône

Le Rhône was the name given to a series of popular rotary aircraft engines produced in France by Société des Moteurs Le Rhône and the successor company of Gnome et Rhône. They powered a number of military aircraft types of the First World War. Le Rhône engines were also produced under license worldwide.

Although not powerful (the largest wartime version produced 130 hp), they were dependable rotary engines. The Le Rhône 9 was a development of the Le Rhône 7, a seven-cylinder design. Examples of Le Rhône engines are on public display in aviation museums with several remaining airworthy, powering vintage aircraft types.

Operation
The copper induction tubes had their crankcase ends located in different places on the 80 and 110 hp versions – the 80 hp versions had them entering the crankcase in a location forward of the vertical centerline of each cylinder, while the 110 hp version had them located behind the cylinder's centerline. This resulted in the 80 hp version's intake plumbing being "fully visible" from the front, while the 110 hp version had the lower ends of its intake tubes seemingly "hidden" behind the cylinders.

A complicated slipper bearing system was used in the Le Rhône engine. The master rod was of a split-type, which permitted assembly of the connecting rods. It also employed three concentric grooves, designed to accept slipper bearings from the other cylinders. The other connecting rods used inner-end bronze shoes, which were shaped to fit in the grooves. The master rod was numbered as number one and the shoes of numbers. two, five and eight rode in the outer groove, the shoes of three, six and nine in the middle groove and four and seven in the inner groove. Although this system was complex, the Le Rhône engines worked very well.

The Le Rhône engines used an unconventional valve actuation system, with a single centrally-pivoting rocker arm moving the exhaust valve and the intake valve. When the arm moved down it opened the intake valve and when it moved up it opened the exhaust value. To make this system work a two-way push-pull rod was fitted, instead of the more conventional one-way pushrod. This feature required the cam followers to incorporate a positive action, a function designed in by using a combination of links and levers. This design functioned but it did prevent the incorporation of valve overlap which limits power output. Due to the structural and cooling limitations of the overall engine design the Le Rhône engines produced as much power as they were capable of, regardless.

Production
As well as production by Société des Moteurs Gnome et Rhône, which had bought out Société des Moteurs Le Rhône in 1914, the Le Rhône was produced in Germany (by Motorenfabrik Oberursel), Austria, the United Kingdom (by Daimler), Russian Empire and Sweden.

Le Rhône 80 hp (60 kW) engines were made under license in the United States by Union Switch and Signal of Pennsylvania, and the 110 hp (82 kW) Oberursel UR.II rotary engine used by Germany in World War I, in such famous fighters such as the Fokker Dr.I triplane, was a close copy of the 110 hp 9J version.

Variants
data from : Moteurs de Légende by Gustave Hartmann.
 * Le Rhône Type 7A
 * (1910) 50 hp (37 kW), seven-cylinder rotary engine - twenty built for use on Borel Monoplanes and Sommer Biplanes.


 * Le Rhône Type 7B
 * (1911) 50 hp (37 kW), seven-cylinder rotary engine - Thirty-five prototype engines built.


 * Le Rhône Type 7B2
 * (1912) 60 hp (44.7 kW), seven-cylinder rotary engine - 350 built at Societe Moteurs le Rhône.


 * Le Rhône Type 9C


 * (1916) 80 hp (60 kW), nine-cylinder rotary engine.


 * Le Rhône Type 9J


 * (1913) 110 hp (82 kW), nine-cylinder rotary engine.


 * Le Rhône Type 9Ja


 * (1915) 110 hp (82 kW), nine-cylinder rotary engine.


 * Le Rhône Type 9Jb


 * (1916) 120 hp (89.5 kW), nine-cylinder rotary engine.


 * Le Rhône Type 9Jby


 * (1916) 130 hp (97 kW), nine-cylinder rotary engine.


 * Le Rhône Type 9R
 * (1916) 170 hp (127 kW), nine-cylinder rotary engine.


 * Le Rhône 14D
 * (1912) A two-row rotary, consisting of two seven-cylinder banks rotating round a single two-throw crankshaft.


 * Le Rhône 18E
 * (1917) A two-row rotary, consisting of two nine-cylinder banks rotating round a single two-throw crankshaft.


 * Le Rhône 28E
 * (1918) A four-row rotary, consisting of four seven-cylinder banks rotating round a single four-throw crankshaft.


 * Le Rhône 11F
 * (1913) An 11-cylinder rotary.


 * Le Rhône 9Z
 * (1920) A 9-cylinder rotary.


 * Le Rhône K
 * (1916) A 9-cylinder rotary prototype engine.


 * Le Rhône L
 * (1916) A 9-cylinder rotary prototype engine.


 * Le Rhône M
 * (1917) A 9-cylinder rotary prototype engine.


 * Le Rhône P
 * (1917) A 9-cylinder rotary prototype engine.


 * Le Rhône R
 * (1917) A 9-cylinder rotary prototype engine.

Oberursel copy
Oberursel produced the 110 hp model, supposedly without authorization in Germany. The Oberursel Ur.II was a straight copy of the Le Rhône, but the Le Rhône was preferred over the Oberursel due to the materials used in the French product. However, by July 1918 there was a shortage in Germany of castor oil, a plant-derived lubricant that the rotaries required as it could not be easily dissolved into the fuel, and because it possessed lubrication qualities superior to mineral oils of the day. A new Voltol-based lubricant, derived from mineral oil, was substituted and was blamed for engine failures on rotary-engined German fighters such as the Fokker E.V which used the Oberursel Ur.II. It has been suggested that without proper lubricants, the Le Rhône rotary would have been equally failure-prone.

Applications

 * Airco DH.5
 * Avro 504
 * Bristol M.1
 * Bristol Scout
 * Caudron G.3
 * Caudron G.4
 * Hanriot HD.1
 * Fokker Dr.I
 * La Cierva C-6, autogyro, 1924
 * Macchi M.14
 * Morane-Saulnier N
 * Mosca MB 2 bis
 * Nieuport 11 "Bebe"
 * Nieuport 17
 * Nieuport 27
 * Sopwith Camel
 * Sopwith Pup
 * Standard E-1
 * Texas-Temple prototype
 * Thomas-Morse S-4C