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Gnome et Rhône was a major French aircraft engine manufacturer.

Between 1914 and 1918 they produced 25,000 of their 9-cylinder Delta and Le Rhône 110 hp (81 kW) rotary designs, while another 75,000 were produced by various licensees, powering the majority of aircraft in the first half of the war on both sides of the conflict. In the post-war era they started a new design series originally based on the Bristol Jupiter, but evolving into the excellent 1,000 hp-class (750 kW) Gnome-Rhône 14K Mistral Major radial, which was likewise licensed and used around the world during World War II. They were nationalized as a part of Snecma in 1949, but the brand lived on for a time as the manufacturer of Gnome et Rhône motorcycles and Gnome et Rhône bicycles.

Gnome et Rhône is a familiar name in vintage aviation circles. But few people know that the French company also built motorcycles, from 1920 until the early 1950s. This lovely machine is one of around 3,000 manufactured under license from the British firm ABC Motorcycles—a company closely aligned with Sopwith, another aircraft manufacturer. In those days, aviation and motorcycling were commonly linked, and this particular connection was brokered by a pilot: André Barthélémy, the official Parisian distributor of ABC. Barthélémy was a talented engineer, and fixed numerous mechanical problems with the powerful yet fragile ABC. He increased capacity to 500cc, refined the carburetion and rocker arm system, and added an oil cooler.

(The original engine had a tendency to overheat: its nickname was “glow worm” because at night the cylinders would turn red.) The gearbox was unchanged, retaining the ABC-style hand-shifter with an ‘H’ gate, as you’d find in a car.

One of the most famous aero engine manufacturers of WWI, Gnome et Rhône introduced its first motorcycle in 1919, building the Granville Bradshaw-designed ABC under licence. Previously rivals, the two firms had joined forces in 1914 and then in January 1915 Gnome took over Le Rhône, forming Société des Moteurs Gnome et Rhône. The diversification into motorcycle production had been prompted by the sudden decline in the demand for the company’s aeronautical products after WWI. Proprietary engines were used at first and then in 1923 the firm introduced single-cylinder power units of its own manufacture, pioneering the use of unitary construction for engine/gearbox. In the 1930s a range of BMW-influenced transverse flat-twins with pressed-steel frames was produced. Like their German counterparts, the larger Gnome-Rhône twins found favour as military workhorses, many of the shaft-driven AX sidevalve models being adapted for sidecar use, in which role they featured shaft drive to the sidecar wheel and a four-speeds-and-reverse gearbox, as well as the usual complement of military equipment. There were singles too, of course, which featured pressed-steel frames like the larger twins.

In 1938, Gnome et Rhône took over the celebrated car-maker, Voisin. Gabriel Voisin was perhaps France’s greatest aviation pioneer. In 1907 he built the first practical aeroplane capable of leaving the ground under its own power, and his Aéroplanes-Voisin company was the first mass producer of aircraft in the world. But the end of WWI brought a halt to Voisin’s aviation ventures and after experimenting with motorised bicycles and a light two-seater economy car, he decided to produce an automobile that would be unrivalled for prestige, comfort and speed. The resulting Knight sleeve valve-engined 4.0-litre Voisin M1 appeared in 1919. It was one of the first truly modern cars to be delivered after the Armistice.

Voisin continued to build motor cars of distinction throughout the 1920s, including a number of record-breaking competition models, but the economic downturn of the early 1930s had a disastrous effect on sales. Gabriel Voisin eventually lost control to his financiers and his factory was sold to Gnome et Rhône. When the French Government nationalised the country’s aero-engine makers in 1945, forming Société Nationale d’Étude et de Construction de Moteurs d’Aviation (SNECMA), Gnome et Rhône and Avions-Voisin were absorbed into the new conglomerate. Following the reorganisation, Gnome et Rhône found itself a subsidiary of Société des Aéroplanes Voisin and both names would appear on the company’s motorcycles after WW2.

Gnome et Rhône’s post-war R-series was powered by a single-cylinder two-stroke engine built in unit with a three-speed gearbox, the first R and R1 models displacing 100cc. The 125cc R4’s simple, piston-ported engine produced 6bhp, which was good enough for a top speed of 85km/h (53mph). Despite their relatively small size and modest specification, these little two-strokes demonstrated surprising durability and speed. Their heroic exploits – reported in the French motorcycling press in 1949 – included three students riding R3s from Paris to New Delhi (a distance of approximately 18,000 kilometres) and Gustave Bernard’s dash from Paris to Madrid in 23 hours 15 minutes on an R4. The following year the intrepid Bernard completed the Paris-Bordeaux-Paris round trip in 18 hours 4 minutes while carrying a passenger, his R4 on that occasion being badged as a ‘Voisin Gnome & Rhone’.

Early history and World War I

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 cylinder 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 to take the world records for distance and endurance, as well as powering the first aircraft to break 100 km/h, as well as the first seaplane ever to fly in 1910, powering France to 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 it was also very difficult to service, requiring the cylinder to be disassembled. In order 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 cylinder when the piston dropped far enough.

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, whose Le Rhone engine copies received a "Ur." prefix), in the United States, the Union Switch & Signal Company of Swissvale, Pa. was reported to have produced some 10,000 units, as well as Austria, Britain and Sweden.

Gnome et Rhône

After several years of fierce competition, Gnome and Le Rhône finally decided to merge. Negotiations started in 1914, and on 12 January 1915 Gnome bought out Le Rhône to form Société des Moteurs Gnome et Rhône. Developments of the 9C continued to be their primary product, improving in power to about 110 hp (80 kW) in the Le Rhône 9J by the end of the war. The 9-series was the primary engine for most early-war designs both in French and British service as well as in Germany where, perhaps somewhat ironically, Oberursel had taken out a license just before the war.