If it had been built, the Bell D-188A project would have been one of the most unorthodox aircraft to fly, and certainly the most unusual in the USAF inventory. In 1955, Bell Aircraft was requested by both the USAF and the USN to develop a VTOL/STOVL supersonic, all-weather fighter-bomber and defence interceptor. The project was highly ambitious and was designed to fulfill a multitude of roles for two different services and, as a result – based on the poor record of other Air Force/Navy aircraft projects – it is highly dubious as to its success. The aircraft was designated the Model 2000, and was offered in two different versions – the D-188 for the US Navy and the D-188A for the USAF. Bell had – rather optimistically – called the Navy version the XF3L-1 and the Air Force version the XF-109, although neither of these was official. On December 5, 1960, Bell publicly showed off the design as the XF-109 – the USAF version, as the USN had lost interest the year earlier, however in the spring of 1961, the USAF canceled the program and no examples were built.
The aircraft was unconventional, and consisted of a long, thin, area ruled fuselage with a large fin and all-moving stabilators in the tail. The single-person cockpit was in the extreme nose and the small-span wing was mounted high on the fuselage. At the ends of each wing were pods that contained two turbojets each. These pods were designed to swivel through an arc of 100 degrees (horizontal to 10 degrees past vertical) to allow for both horizontal and vertical flight. To take off vertically the pods were rotated to direct the engine's thrust downward, while for horizontal flight the pods were rotated back to the horizontal. The pods were capable of directing thrust slightly forward as well for enhanced landing manoeuvres. In addition to the four wing engines, four engines were also mounted in the fuselage – two in the rear directed out of two separate tail ducts, and two directly aft of the cockpit and positioned vertically to aid in VTOL flight, exhausting out of two ventral ducts. The D-188A featured an engine bleed system to assist in VTOL manoeuvering. Bleed air from the fuselage engine compressors would have been directed to a pair of thrusters in the nose and two more in the tail to aid in pitch, roll and yaw.
Armament would have consisted of two 20mm cannon in the fuselage, an internal weapons bay and eight wing hard points for missiles and other ordnance.
As mentioned, the military designations were not official and were speculative on the part of Bell. The Navy’s XF3L-1 was not assigned, but would have been the D-188’s designation had the aircraft been built, as this was the next in the USN series. The USAF XF-109 designation had previously been assigned to a proposed Convair F-106B variant, however, had subsequently been left blank and Bell assumed – if the D-188A had been built – that this would have been assigned to the aircraft. Many reference works refer to the D-188A by its assumed experimental series number, but in fact the XF-109 designator was never assigned.
Townend, David R. Clipped Wings – The History of Aborted Aircraft Projects, Markham, Ontario, AeroFile Publications, 2007, ISBN 978-0-9732020-4-5.