Design and Development
American Airlines asked Convair to design an aircraft for coast-to-coast flights, able to fly nonstop New York to Los Angeles against the wind. They wanted somewhat larger passenger capacity than the 880, which was the smallest of the first-generation U.S. jet airliners. The 990 entered production in 1961.
One change from 880 was the large anti-shock bodies on the upper wings to increase their critical Mach and reduce transonic drag. This allowed the heavier 990 to go slightly faster than the 880, cruising at about Mach 0.91, making it the fastest subsonic passenger jet ever built. Only the supersonic Concorde and Tu-144 have ever carried commercial passengers at a faster speed. Originally, there were plans to use the bulges as fuel tanks, but during test flights the extra weight caused the tanks to vibrate excessively. Instead, the inner set of bumps also served a secondary role as fuel dump for the fuel tanks in the fuselage.
The engines were also changed to the uprated General Electric CJ-805-23s, which were unique in that they used a fan stage at the rear of the engines, compared to the fan stage at the front of the engine as found in the Pratt & Whitney JT3D that powered the 990's competitors. The engine was a simplified, non afterburning civilian version of the J79, used in military fighters. Like the J79, the CJ805 was smoky.
Like the 880, 990s were later modified with a dorsal "raceway" added to the top of fuselage to hold wiring for additional instrumentation.
Read more about this topic: Convair 990 Coronado
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