Boeing F-9

The following is an extensive catalogue of the variants and specific unique elements of each variant and/or design stage of the Boeing B-17 Flying Fortress heavy bomber. For a broader article on the history of the B-17, see B-17 Flying Fortress.

The Boeing 299 was the original bomber design made by Boeing to fulfill a request by the United States Army Air Corps for a bomber capable of carrying 2,000 lb (907 kg) of bombs 2,000 mi (3,218 km) at 200 mph (322 km/h). In 1935, the Boeing 299 competed with several entries by other companies at an evaluation at Wright Field near Dayton, Ohio, USA.

On its flight from Seattle)Washington to Wright Field for the competition, the 299 set a nonstop speed record of 252 mph (406 km/h). Though it crashed to its destruction on takeoff during a demonstration, the crash was due to flight-crew error, not from any flaw in the airplane. Subsequent implementation of a mandatory checklist by the flight crew prior to take-off ensured avoidance of the flight crew error. Despite the crash (and more important, its much higher cost per unit), Air Corps leaders were impressed by the 299. Boeing was awarded with a development contract. The aircraft has since been referred to as the XB-17 but the designation is not contemporary or official.

Though still enthusiastic about the Boeing design, the Army Air Corps decided to cut its order for service test YB-17s from 65 to 13 after the crash of the original Model 299. On November 20, 1936, the Army Air Corps changed the source of funding from normal funding to "F-1" procurement, and redesignated the plane Y1B-17 before it even flew.

Unlike its predecessor, which had used Pratt & Whitney R-1690 Hornet radial engines, the Y1B-17 used the Wright R-1820 Cyclone that would become standard on the B-17. Several changes were made in the armament and the crew was reduced from seven to six. Most changes were minor: the most notable was switching from double-wishbone to single-arm landing gear.

On December 7, 1936, five days after the first flight of the Y1B-17, the brakes on the aircraft fused during landing, and it nosed over. Though damage was minimal, the cumulative impact of this event and the crash of the Model 299 triggered a Congressional investigation. After the crash the Army Air Corps was put in notice: another crash would mean the end of the program.

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