In the late 1940s, Republic Aviation designed the awkward-looking XF-91 Thunderceptor for the newly formed U.S. Air Force. It used rockets for an extra boost into combat, but could carry only enough fuel for a 25-minute flight. As did the Luftwaffe before it, the Air Force found solace in the wings of another turbojet—this time the F–l04 Starfighter. Turbojets triumphed because they used oxygen from the air to burn their fuel; rockets had to carry their own supply of liquid oxidizer—a fundamental disadvantage that could not compensate for the higher speed.
The ramjet had better luck. Invented by Frenchman Rene Lorin in 1913, it dispensed with the turbine’s rapidly spinning blades and instead used the force of air rushing in through its carefully shaped intake to compress air for combustion. It could function, therefore, only after being accelerated by another form of propulsion to very high speeds.
In 1948, Stanley Hiller put ramjets at the tips of helicopter rotors for added power, but several problems grounded his prototypes. The ramjets provided only marginal improvement in performance, consumed excessive fuel, and were highly visible at night because of their luminous exhaust. Republic Aviation incorporated the ramjet into another unsuccessful interceptor, the shark-like XF-103, which was designed to fly with both a ramjet and a turbojet, but when the XF-l03 was canceled in l957, the ramjet died with it—at least for piloted aircraft. Several missiles have employed ramjet propulsion systems.
The Anglo-French Concorde is arguably aviation’s most beautiful blunder. How could such a triumph of engineering qualify for a list of wrong turns? It failed in the marketplace. Airlines, other than the state-owned national carriers of the countries that built it, would not buy it because it carried too few passengers and consumed too much fuel. The Concorde was also limited to water routes—its noise and sonic booms made it too annoying to fly over land—a limitation that further weakened its economic viability. Only 14 entered service.
The Soviet Tu-144 was backed by a government that subsidized fuel and ignored noise, sonic booms, and ozone depletion—three concerns that ended the U.S. effort to build a supersonic transport. The Soviet program survived a horrific crash at the 1973 Paris Air Show and proceeded through an initial production run of 10 aircraft. In 1975, after at least two more crashes, the remaining Tu-144s began a weekly mail route between Moscow and Alma Ata (now part of Kazakhstan). Passenger service began later, in 1977. Operations continued for several years, hobbled by delays and cancellations. More troublesome were problems of high drag and fuel consumption.
Unable to find solutions, Soviet officials grounded the Tu-144 in l978 and, in an act of desperation, approached managers of the Concorde for help with problems that varied from metal fatigue to engine inlet design. When it became clear that the aircraft lacked the range to cross the Atlantic and thus compete for profitable routes, it lost all propaganda value and was deactivated. With it went the last hopes of a major role for an SST in civil aviation.
In the years following World War II, the Pentagon pursued three programs to build fighters that, like rockets, could take off vertically: the Ryan X-13 Vertijet, the Lockheed XFV-l, and the Convair XFY-l Pogo. All three flew during the mid-l950s. The Ryan and Convair craft took off vertically, hovered, and landed on their tails, but were hard to control. Lockheed’s entry was never able to take off or land vertically because the engine the Navy provided lacked power for vertical flight.
Unlike other aircraft on this list, the tail sitters had no devoted champions; it became pretty clear pretty fast that the concept was doomed. Fighters had to be capable of carrying extra fuel and heavy weapons, and the tail sitters’ limited engine power was simply not enough.
The military continued to covet craft with the vertical-takeoff-and-landing capability helicopters and the speed of a fighter jet. The British Harrier fighter fought effectively in the Falklands War of 1982 and served as the first operational fighter of this type. The F-35 Joint Strike Fighter will use downward-deflected thrust from a mainengine-driven lift fan to take off, hover, and land with a full array of weapons—enough to make a tail sitter keel over with envy.