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French Ramjet Experiment, the Amazing LEDUC O.21
Raul Colon
Telephone / Fax 787-748-7312
PO Box 29754
Rio Piedras, Puerto Rico 00929

French engineer pioneer Rene Leducís fascination with aircraft propulsion started early in his life. But it was not until his late thirties that Leduc commenced a series of test designed to evaluate the ability of a ramjet engine to propel an aircraft thru the air. Known technically as aero-thermodynamic-duct, the ramjet engine did not posses any major rotating mechanism. It relays on air being force into the main intake. The intake is designed to deprive the air of its kinetic energy and replace it with massive amounts of pressure. From the intake, the air goes thru a diverging duct to the combustion chamber where burning fuel is added to it. The resulted expanded gases are then exhausted producing vast amounts of thrust.

Leducís first attempt at producing a workable ramjet system in 1935 was deem as a success by French aviation authorities. When the practical engine was turn-on, it produces a sustainable 0.039kN or 9lb of thrust for three minutes. An impressive achievement on those pioneer days. He continued experimenting with ramjet designs into the late 1930s, but by this time, the clouds of war had settle over France. He did not perform any research during the German occupation. Once France was once again on its feet, Leduc vigorous continued his research, culminating with the construction of the O.10 aircraft in 1946. The O.10 was mainly a test bed plane, intended to collected data on the performance of an airframe fitted with a ramjet engine. Between 1946 and early 1948, the O.10 made several flights. All as a glider. The O.10 was propelled to the air in the back of a Languedoc commercial airliner. When the Languedoc achieved the desire attitude, the O.10 would be release to glide down to earth. The goal of gliding test flights was the collection of data in regard to the aerodynamics forces influencing the airframe and engine. Then in 1949, the O.10 engine was powered on for the first time during a test flight. It reached 422mph during a brief twelfth minute flight. Two sub sequential test flights failed to produce an increase in speed. However, on the third test flight, the O.10 reached the impressive mark of 500mph.

Two more prototypes aircrafts were design by Leduc. The O.16 and 17. Each achieves a better speed result and confirmed the designer concept with actual flying experience. Although impressive, these aircrafts were not ground breaking platforms. That would be the job of the next O model; the amazing O.21. The O.21 incorporated some characteristics from earlier O. versions, but at its core it was a completely new design. Leduc called for the O.21 to have an operational service ceiling of 65,600ft with a climb rate of 656ft/sec at sea level and up to 131ft/sec at 29,500ft. Because the aircraft was a second generation test system, operational range was not establish; but engineers calculated that the O.21ís ramjet could operated for approximately fifteen minutes after initial ignition. The O.21 had a wing span of 38ft. The fuselage was 41ft in length with a height of 9ft. The whole wing area cover 239sq ft. Its maximum take-off weight was a respectable 13,200lb. The installed power plant was a Leducís ramjet augmented by one Turbomeca Artouste auxiliary turbojet. The Artouste turbojet was to provide the O.21 with the require thrust to accelerate the aircraft to an assigned speed in order to ignite the ramjet engine. This allowed the O.21 to take-off under its own power. After the ramjet was ignited, the O.21 could reach speeds in excess of 620mph.

The O.21 airframe was basically a ďflying engineĒ configuration. It was made of six concentric stainless steel skins, which were joined by perforated burner crowns. The ramjet engine was located at the end of the cockpit and was to be the center of the airframe. The cockpit was conical in shape and could be jettison in case of an emergency. The pilot sat in a semi-reclined seat. At the rear of the seat were the radio equipment, oxygen supply system, the cockpit parachute, and the aircraft avionic systems. A retractable, tandem undercarriage was assemble for the O.21. Additional, two fairings on each wingtip housed the retractable outrigger wheels. Although the aircraft did carry any offensive system, conditions provide the engineers the possibility of mounting cannon systems on them.

On a clear morning on May 16, 1953; the O.21 took to the air in its maiden flight. It performed as advertise. French military officials were impress with the promise of a Mach 2-capable interceptor that can shoot down enemy bombers in short notice, thus government funds were made available immediately for continue research. After the O.21 program had run its course, Leducís introduced the O.22 aircraft. Although the O.22 broke the Mach 1 barrier, doing it on October 1956, and showed much promise; it was not a revolutionary aircraft as the O.21 was. In fact, it was powered by a conventional turbojet engine. In the end, advances in conventional aircraft and engine technology and a stall on the research and development of ramjet engines; led the French government to terminated funding for the program in the fall of 1958. The O. program did produced valuable data, especially on engine/airframe aerodynamic behavior. Much of the research collected on the O.21 and 22 programs were to find its way into Franceís front-line interceptor platforms of the 1960s and 70s.

French Aviation in the Twenty Century, Edt Bill Russell, Martin Press 1991
2 Concept Aircraft: Prototypes, X-Planes, and Experimental Aircrafts, Edt Jim Winchester, Thunder Bay Press 2005
3 Ramjet, The Evolution: 1914-1960, John Connelly, (Paper) 1965