Le Rhône
| Company type | Company |
|---|---|
| Industry | Aircraft engines |
| Founded | 1911 in Montreuil, Paris, France |
| Founder | Louis Verdet, Pierre Berthet, Edouard Martin |
| Fate | Acquired by Société des Moteurs Gnome in 1914 to form Gnome et Rhône |
| Headquarters | Montreuil, Paris , France |
| Products | Rotary aircraft engines (Le Rhône series) |
Le Rhône refers to a line of rotary aircraft engines manufactured from 1910 through 1920. Originally marketed by the Société des Moteurs Le Rhône, the company was incorporated into Gnome et Rhône following a 1914 acquisition. During World War I, more than 22,000 nine-cylinder Le Rhône engines were produced, surpassing the sales of the company's other wartime powerplant, the Gnome Monosoupape.
Production licenses for Le Rhône engines were issued to manufacturers in countries including Great Britain, Austria, Italy, Russia, Sweden, and Germany. These power units were installed in prominent WWI aircraft such as the Sopwith Pup, Sopwith Camel, Nieuport 11 "Bebe", and Fokker Dr.1 "Triplane".
Operation
As with all rotary engines, the Le Rhône maintained a stationary crankshaft while the entire rotating assembly—comprising cylinders and crankcase—revolved around it.
In contrast to the Gnome Monosoupape design, Le Rhône engines employed a more traditional configuration featuring a shaft-mounted carburetor and intake and exhaust valves located in the cylinder heads. Fuel was routed through copper tubing from the hollow crankshaft to the cylinders—positioned at the front on the 80 hp 9C variant and at the rear on the 110 hp 9J model. This carburetor arrangement allowed pilots to throttle fuel flow during flight, leading to reduced fuel and oil consumption—a primary reason why Aéronautique Militaire preferred Le Rhône engines over Monosoupape types.
The cylinders incorporated replaceable grey iron liners to enhance durability and were sealed solely by piston rings without employing bronze obturator rings commonly found in Gnome and Clerget engines.
A sophisticated slipper bearing system was utilized, featuring a split master rod with three concentric grooves designed to accommodate slipper bearings from the other connecting rods. The remaining rods contained bronze shoes that fit into these grooves, ensuring even thrust distribution and minimizing stress on the master rod.
A notable characteristic was its valve actuation mechanism: a single centrally pivoting rocker arm controlled both intake and exhaust valves via a two-way push-pull rod instead of separate one-way pushrods. This system used linked cam followers to guarantee positive valve movement, reducing vibration but limiting valve overlap, which consequently restricted maximum power output.
Production
The Le Rhône series originated with a seven-cylinder rotary engine developed by Louis Verdet at Rossel Peugeot. In 1910, Verdet partnered with Pierre Berthet to establish Société des Moteurs d’Aviation Verdet; however, this collaboration was short-lived. By 1911, Verdet joined Edouard Martin and others to found Société des Moteurs Le Rhône based in Montreuil, Paris.
Between 1911 and 1913, Société des Moteurs Le Rhône manufactured seven-cylinder rotary engines that earned endurance awards. The company introduced its first nine-cylinder model—the 80 hp 9C—in 1912, followed by the 110 hp 9J in 1913. These two variants became the most successful within the Le Rhône lineup.
In July 1914, Société des Moteurs Le Rhône was purchased by competitor Société des Moteurs Gnome, creating Gnome et Rhône. Throughout WWI, Gnome et Rhône produced approximately 9,560 units of the 9J and 8,700 of the 9C at its Paris factories located in Kellermann and Gennevilliers. Nearly 45% of these engines were exported during 1915 to countries including Great Britain, Italy, and Russia. Due to their improved fuel efficiency compared to Monosoupape engines from Gnome et Rhône, Le Rhône models were preferred.
The final engine in the series was the 9Z (Z9), a 60 hp rotary that first ran in 1920; production totaled roughly fifty units. Subsequent engines no longer carried the Le Rhône designation.
Manufacturing beyond France
During the First World War, British licensee Peter Hooker was responsible for producing several thousand units of the 9C and 9J engines, with additional manufacturing contributions from W.H. Allen, F.W. Berwick, and Daimler.
Before the war, production of the 9C model took place in Austria at Steyr Werke and in Germany through Mercedes-Benz and Siemens. In 1916, Motorenfabrik Oberursel commenced manufacturing the 9J variant, designated as the UR.II.
In Sweden, AB Thulinverken produced the 9C and 11F engines under the names Thulin A and Thulin G, respectively. Meanwhile, in the United States, the Union Switch and Signal Company completed 1,057 units of the 9C by the end of hostilities.
Italy’s Gnome et Rhône continued engine production until a Turin-based consortium acquired the company in 1915, after which licensed manufacturing persisted. Additionally, assembly operations were carried out at Gnome et Rhône’s Moscow facility until it was taken over during the 1917 Russian Revolution.
Engine Variants
Le Rhône engines predominantly featured two main cylinder dimensions throughout most of their production. Early models dating from 1910, including the widely utilized 9C, had a bore and stroke measuring 105 x 140 mm and were manufactured in configurations ranging from seven to eighteen cylinders. The subsequent 9J series introduced in 1913 employed nine cylinders with increased dimensions of 112 x 170 mm, while the 9R and 18R versions were slightly larger at 115 x 170 mm.
Production Models
- Le Rhône 7A
- (1910) 50 hp seven-cylinder rotary engine — twenty units produced for Borel Monoplanes and Sommer Biplanes.
- Le Rhône 7B
- (1911) 50 hp seven-cylinder rotary engine with an 8.48-litre displacement — thirty prototype units completed.
- Le Rhône 7B2
- (1912) 60 hp seven-cylinder rotary engine — Société Moteurs le Rhône manufactured 350 examples.
- Le Rhône Type 9C
- (1912) 80 hp nine-cylinder rotary engine displacing 10.9 litres. Known as the Rhône 80 Horsepower, over 10,000 units were built by Gnome et Rhône and licensees worldwide, extensively utilized in French and international aircraft.
- Le Rhône 11F
- (1913) 100 hp eleven-cylinder rotary engine — fifty units produced.
- Le Rhône 14D
- (1913) 120 hp two-row rotary engine with a displacement of 19.96 litres, featuring two seven-cylinder rows on a single crankshaft. This model was not accepted by French military officials.
- Le Rhône 18E
- (1913) 160 hp two-row rotary with a total volume of 21.8 litres consisting of two nine-cylinder rows on one crankshaft. It was not homologated until 1917 and differs from a later prototype bearing the same designation.
- Le Rhône Type 9J
- (1913) 110 hp nine-cylinder rotary engine also referred to as the Rhône 110 Horsepower. Approximately 12,000 units were produced by Gnome et Rhône and foreign licensees.
- Le Rhône 9R
- (1916) 170-180 hp nine-cylinder rotary featuring dual spark plugs per cylinder. Two hundred fifty units were manufactured under British license.
- Le Rhône M
- (1917) Limited production run of nine-cylinder rotary engines.
- Le Rhône 9Z
- (1920) 60 hp nine-cylinder rotary equipped with dual spark plugs per cylinder; bore and stroke measured at 84 x 106 mm. Fifty units completed.
Prototype Engines
- Le Rhône K
- (1916) Nine-cylinder rotary prototype model.
- Le Rhône L
- (1916) Nine-cylinder rotary prototype variant.
- Le Rhône P
- (1917) Nine-cylinder rotary prototype incorporating three valves per cylinder (two intake valves and one exhaust valve).
- Le Rhône 18E
- (1917) Prototype two-row rotary delivering 340 hp, created by combining two rows of the 9R on a single crankshaft.
- Le Rhône 28E
- (1918) Prototype four-row rotary generating 320 hp, configured with four seven-cylinder rows (115 x 140 mm bore and stroke) mounted on a four-throw crankshaft.
Foreign Variants
- Thulin A
- A Swedish-produced licensed version of the Le Rhône 9C, manufactured by AB Thulinverken
- Thulin G
- A licensed Swedish variant of the Le Rhône 11F, constructed by AB Thulinverken
- Oberursel UR.II
- A German-licensed reproduction of the Le Rhône 9J, produced by Motorenfabrik Oberursel
- Oberursel UR.III
- A German-licensed version of the Le Rhône 11F, built by Motorenfabrik Oberursel
Le Rhône Engines in Operation Today
Original Le Rhône powerplants continue to be utilized by enthusiasts of World War I aircraft replicas. One prominent example is housed at the Pioneer Flight Museum in Kingsbury, Texas, where it powers a replica Fokker Dr.I. This particular engine formerly equipped an original Thomas Morse Scout, which is currently undergoing restoration with intentions to fit another Le Rhône 80 hp engine. Several additional Dr.I replicas and restored Thomas Morse Scouts featuring authentic Le Rhône engines remain active within the United States.