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, they were dependable rotary engines. The Le Rhône 9 was a development of the Le Rhône 7, a seven-cylinder design. Examples of nine-cylinder Le Rhône rotary engines are on public display in aviation museums with several remaining airworthy, powering vintage aircraft types.

Operation

In most respects the Le Rhône engines were typical rotary engines, so that the crankshaft remained stationary in operation, with the entire crankcase and its attached cylinders rotating around it as a unit.
The copper induction tubes had their crankcase ends located in different places on the versions; the 80 hp versions had them entering the crankcase in a location forward of the vertical center-line of each cylinder, while the 110 hp version had them located behind the cylinder's center-line. 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 valve. 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 prevented valve overlap and so limited power output, but as the engine structure and cooling arrangements would not have been adequate at a higher power output, this should not be considered a significant design fault.

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, Austria, the United Kingdom, Russian Empire and Sweden.
le Rhône engines were made under license in the United States by Union Switch and Signal of Pennsylvania, and the 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 le Rhône 9J version.

Variants

Data from :
;Le Rhône Type 7A
;Le Rhône Type 7B
;Le Rhône Type 7B2
;Le Rhône Type 7Z
;Le Rhône Type 9C
;Le Rhône Type 9J
;Le Rhône Type 9Ja
;Le Rhône Type 9Jb
;Le Rhône Type 9Jby
;Le Rhône Type 9R
;Le Rhône 9Z
;Le Rhône 11F
;Le Rhône 14D
;Le Rhône 18E
;Le Rhône 18E
;Le Rhône 28E
;Le Rhône K
;Le Rhône L
;Le Rhône M
;Le Rhône P
;Le Rhône R
;Oberursel Ur.II
;Oberursel Ur.III

Oberursel copy

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 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.
A reproduction of the Oberursel has been manufactured by The Vintage Aviator Company in New Zealand in very limited numbers by reverse engineering an original Oberursal engine, presumably for their own project aircraft. The engine has been test-run and is described at http://thevintageaviator.co.nz/projects/oberursel-engine/oberursel-ur-ii-rotary-engine-build-history.

Le Rhônes still flying today

Several enthusiasts are using original Le Rhône engines for World War I replica aircraft today. A flying example can be seen at the Pioneer Flight Museum, Kingsbury Texas in a replica Fokker Dr 1. pioneerflightmuseum.org The engine had previously been flown in an original Thomas Morse Scout, which is now under restoration with another Le Rhône 80 hp engine planned for that flying aircraft. There are other reproductions of Dr 1's flying original Le Rhône engines, as well as the restored Thomas Morse Scouts in the United States.

Applications