Why The Martin XB-68 Bσmber Never Got Off The Drawing Board
Progress is moving forward rapidly on the Northrop Grumman B-21 “Raider,” the heavy bσmber currently under the development of the United States Air Force as part of the Long-Range Strike Bσmber program. Since the Second World ധąɾ, there have been a number of bσmbers that didn’t get nearly as far – and some never made it off the drawing board. Among the concepts was the XB-68, which was developed in response to a United States Air Force request for the supersonic tactical bσmber to satisfy the WS-302A requirement.
The design of the bσmber began at the Glenn L. Martin Company in 1952 and was revised two years later.
The original design concept of the XB-68 had roughly 45 degrees of wing sweep, which was later changed to a less swept, trapezoidal wing. It was intended to be operated at supersonic speeds at medium and high altitudes.
The finalized design has been compared to the Lockheed F-104, and the XB-68 was to have been primarily of steel construction, with the crew of a pilot-radio operator and navigator-bσmbardier defense systems operator in a pressurized compartment to be cooled by filtered bleed-air from the engines, and a refrigeration unit for evaporative cooling at high Mach numbers.
According to one source, the planned power plant would have been two Pratt & Whitney J75 (JT4B-21) axial-flow turbojets of 27,500 lbf (122,000 N) static sea-level thrust each with an afterburner, providing a maximum speed of 1380 knots at 54,700 feet altitude at maximum power and a combat speed of 1333 knots at 42,200 feet altitude at maximum power. Combat range was planned for 1,250 statute miles (1086 nautical miles or 2011 kilometers) with 3700 lb (1680 kg) payload at 526 knots (974 km/h) average in 4.15 hours.
However, the design almost out of the gate ran into serious difficulties over the inertial guidance bσmbing and navigation system, which, had the bσmber been approved for production, would have pushed deployment back to at least 1963.
It was largely rendered moot when Air Force Headquarters canceled the project in 1957 citing stringent budget limitations and higher priorities on other ωɛλρσɳ systems.
The Air Force reportedly recognized that the medium tactical bσmber design was still years away, plans were carried forward instead to continue the use of an Air Force version of the Navy’s Douglas A3D, which subsequently received the designation B-66. Two XB-68 prototypes and one static test model were canceled and none were built.
Interestingly, despite never going beyond the design stage, Mongram Models actually produced a scale model version of the Martin XB-68 – along with other aircraft that never advanced to the prototype stage. It was likely based on the sole mockup that was produced before the program was canceled in the late 1950s.