Bell D - 188A The Bell D - 188A ( unofficial military designations XF - 109 / XF3L ) was a proposed eight - engine Mach 2 - capable vertical take - off and landing ( VTOL ) tiltjet fighter that never proceeded past the mock - up stage . Development . Had it 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 US Air Force inventory . In 1955 , Bell Aircraft was requested by both the USAF and the US Navy 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 cooperative 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 Navy and the D - 188A for the Air Force . Bell had rather optimistically called the Navy version the XF3L - 1 and the Air Force version the XF - 109 , although neither of these designations were official . On 5 December 1960 , Bell publicly showed off the design as the XF - 109 – the Air Force version , as the Navy had lost interest the year earlier , however in the spring of 1961 , the US Air Force canceled the program and no examples were built . Designation . 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 US Navy ' s number series . The Air Force 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 . Design . The aircraft was unconventional , and consisted of a long , thin , area ruled fuselage with a large fin and all - moving stabilator s in the tail . The single seat 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° ( horizontal to 10° 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 maneuvers . 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 operation , exhausting out of two ventral ducts . The D - 188A featured an engine bleed system to assist in vertical lift and maneuvering . 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 movements . 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 .