Bell D-188

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.

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.