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How Ramjets Work

Ramjets, Ahead of Their Time?

Whoever said that you have to walk before you can run never met Frenchman René Lorin. He saw the possibilities of ram-pressure propulsion as early as 1913, when pilots were still flying glorified wooden kites. Aware of the design's uselessness at subsonic speeds, he instead designed a ramjet-assisted flying bomb. The French military waved him off. Hungarian engineer Albert Fono, another ramjet pioneer, pursued a similar idea in 1915 and received a comparable reception from the Austro-Hungarian Army [sources: Gyorgy; Heiser and Pratt; Wolko].

Ramjets designs enjoyed a short vogue between world wars. Soviet engineers made early strides in rocket-based ramjets (see next section), but interest burned out before 1940. The German occupation interrupted French engineer René Leduc's early work, but his persistence and secrecy paid off on April 21, 1949, when his Lorin-inspired 010 model made its first powered flight of a ramjet aircraft. Carried aloft atop a Languedoc 161 airliner, it flew for 12 minutes and reached 450 mph (724 kph) at half power [sources: Siddiqi; Ward; Wolko; Yust et al.].

And, for a while, that was that. Despite Leduc's success, lack of funds ended official support for his research in 1957 [sources: Siddiqi; Ward; Wolko; Yust et al.]. The ramjet was beginning to look like an invention with no application. Meanwhile, World War II had ushered in the first generation of operational turbojets: the British Gloster Meteor, the German Messerschmitt Me 262 and the American Lockheed F-80 Shooting Star [sources: Encyclopaedia Britannica; Encyclopaedia Britannica; Encyclopaedia Britannica; National Museum of the USAF; van Pelt].

As the war ended and the Cold War heated up, it became clear that turbojets and turbofans presented more practical subsonic and low-supersonic solutions than ramjets. Thereafter, most U.S. and Soviet work in ramjets focused on building intercontinental missiles. In 1950, American engineer William H. Avery and the Johns Hopkins University Applied Physics Laboratory produced Talos, the U.S. Navy's first ramjet missile. Future generations would refine and streamline the design, introducing hybrid ramrockets capable of achieving high supersonic speeds (Mach 3-5) (see next section) [sources: Hoffman; Kossiakoff; Ward].

Despite intriguing designs like the Hiller XHOE-1 Hornet helicopter, the proposed Republic XF-103 bomber interceptor and the short-lived Lockheed D-21B unmanned reconnaissance drone, ramjet aircraft languished until the 1964 debut of the Lockheed SR-71 Blackbird. The fastest manned aircraft until its retirement in 1989, the Mach 3+ Blackbird also used a hybrid engine, sometimes called a turboramjet [sources: National Museum of the USAF; Smithsonian; Ward].

We'll dive into the SR-71 and other ramjet hybrids and subtypes in the next section.