Gnome et Rhône

Gnome

In 1895 the 26-year-old French engineer Louis Seguin bought a license for the Gnom gas engine from the German firm Motorenfabrik Oberursel. Sold under the French translation, the Gnome was a single-cylinder stationary engine of about 4 hp (3 kW) that ran on kerosene (known in the UK and South Africa as paraffin) intended to be used in industrial applications. The Gnome used a unique valve system with only one rod-operated exhaust valve, and a "hidden" intake valve located on the piston head.

On 6 June 1905 Louis Seguin and his brother Laurent formed the Société Des Moteurs Gnome (the Gnome Motor Company) to produce automobile engines. They soon started development of one of the first purpose-designed aircraft engines, combining several Gnome cylinders into a rotary engine. The design emerged in the spring of 1909 as the 7-cylinder rotary Gnome Omega, delivering 50 hp (37 kW) from 75 kg. More than 1,700 of these engines would be built in France, along with license-built models in Germany, Sweden, Britain, the United States, and Russia. The Gnome powered Henry Farman's Farman III aircraft, which set world records for distance and endurance; the first aircraft to break 100 km/h; and in 1910 the Fabre Hydravion, the first seaplane ever to fly. It helped France become the leading country in aviation at the time. Léon Lemartin and Jules Védrines were two young engineers who participated in the design, development, and implementation of the Omega, and in the milieu of the pioneering days of flight they both went on to become successful pilots.

All of the Gnomes were known for their unique solutions to getting fuel to the top of the piston without using piping. Early models used two valves, one in the cylinder head and a second embedded in the piston itself, counterweighted to open at the end of the stroke. Without any springs or pushrods, the valve would pop open on the downstroke, allowing fuel to be drawn into the cylinder from the crankcase area. Unfortunately this design was very difficult to service, requiring the cylinder to be disassembled. To improve reliability and maintenance, later models used the Monosoupape (single-valve) system instead, using a single exhaust valve at the top of the cylinder and using a series of ports to allow the fuel mixture into the top of the cylinder when the piston had moved down in the cylinder past the ports.

The basic Gnome design was then delivered in a series of larger engines. The Gnome Lambda of 1911 was a larger 80 hp (60 kW) version of the Omega, followed by the 9-cylinder 100 hp (75 kW) Gnome Delta in 1914 (also called the Gnome Monosoupape as it used that type of engine design for the first time). Gnome also tried a 14-cylinder two-row version, the Double Lambda of 160 hp (120 kW), but this saw little use, even though it was copied by Oberursel as the U.III in Germany, and used in a few early Fokker fighter designs without success. To deliver more power with the advent of high-power inline engines late in the war, a completely new nine-cylinder Monosoupape design was delivered in 1918 as the Type-N, delivering 160 hp. This design saw use on the little-known but excellent Nieuport 28.

Le Rhône

Another French engineer, Louis Verdet, designed his own small rotary engine in 1910 which did not see much use. In 1912 he delivered a larger 7-cylinder design, the 7C, which developed 70 hp from 90 kg. This proved much more popular and he formed Société des Moteurs Le Rhône later that year. He soon followed the 7C with the larger Le Rhône 9C, a nine-cylinder design delivering 80 hp (60 kW). Compared to the Gnome's, the Le Rhône was considerably more "conventional", using copper intake manifold pipes to bring the fuel to the top of each engine cylinder, along with intake and exhaust valves. Like Gnome, the Le Rhône designs were widely licensed, in this case the 110 hp Le Rhone 9J was produced in Germany by Oberursel as their Ur.II model as designated by IdFlieg, and in the United States; the Union Switch & Signal Company of Swissvale, PA was reported to have produced some 10,000 units - it was also built in Austria, Britain and Sweden.

Gnome et Rhône

After several years of fierce competition, Gnome and Le Rhône began negotiating a merger in 1914, and on 12 January 1915 Gnome bought out Le Rhône to form Société des Moteurs Gnome et Rhône.

Developments of the 9C became their primary product, improving in power to about 97 kW (130 hp) in the 1917 Le Rhône 9Jby, and 130 kW (170 hp) in the related but less commonly used 9R. The ultimate development was the 250 kW (340 hp) double row Le Rhône 18E of 1917 based on 9R components, however like all multi-row rotaries, it suffered from unresolvable cooling problems and was never used operationally.

The Gnome rotaries started becoming less common on front line aircraft after 1916 as power advances failed to keep pace with either liquid-cooled V-8 engines, or even the more advanced conventionally valved rotaries, such as the 104 kW (139 hp) Clerget 9Bf, and they peaked with the 120 kW (160 hp) Monosoupape 9N, however they remained popular for training aircraft.