In early 1942 the U.S. Navy’s Bureau of Aeronautics (BuAer) was planning the replacements for the Curtiss SB2C Helldiver dive bomber and the Grumman TBM Avenger torpedo bomber. The aircraft was to carry the torpedo in an internal bomb bay. By late 1943 it became obvious that the proposed VBT design like the Douglas SB2D had drastically increased in size and weight. Therefore the U.S. Navy was initiating a smaller dive bomber design. The BuAer recognized the engineering workload for the major wartime programs and therefore assigned the design to companies without a major wartime production. BuAer selected Fleetwings at Bristol, Pennsylvania (USA), which was acquired by Henry J. Kaiser in 1943.
The XBK dive bomber program was initiated in February 1944 with a contract for two prototypes. To keep the airplane size down it was decided that all stores would be carried externally. A radar could be carried underneath the left wing. The dive brakes were of the lower and upper picket fence type at the inboard wing trailing edge. The horizontal tail was mounted on the tail fin above the fuselage. This feature should also avoid buffeting when the dive brakes were open. Unusual was the placement of the engine exhausts almost aft of the cockpit. It was hoped that this feature would significantly decrease drag.
The XBTK-1 in flight, 1945.
XBTK-1 with leading edge slats.
A mockup inspection without engine was already in April 1944. The engine was installed in May 1944 and the completion of the first prototype was scheduled for November 1944. To speed up later production the U.S. Navy even constructed a new airfield at the Fleetwing plant. In early 1945 BuAer requested that the plane would be able to carry a torpedo. The weapon was fitted to a new centreline station and the designation was changed to BTK. The first XBTK-1 was finally completed in March 1945, making its first flight in May.
The flight testing revealed an inadequate engine cooling and a major fuselage vibration. These problems were corrected up to July 1945, and the R-2800-22W engine, which was already out of production, was replaced by the -34W. The flight testing continued at the U.S. Navy Naval Air Test Center at Naval Air Station Patuxent River, Maryland (USA), in August 1945. After the end of the Second World War the U.S. Navy cut orders to ten planes. The major redesign the NATC recommended was the use of a standard engine exhaust, as the cockpit temperature was very high and cockpit egress and access after an engine shutdown was extremely difficult. Also a new propeller should be installed. The plane was transported back to Fleetwings where redesign began. The second production aircraft first flew in March 1946 and featured built-in leading edge slots which greatly increased the stall performance of the aircraft. However, by early 1946 procurement of new planes was drastically cut down and the BTK found its role already filled by the Douglas AD Skyraider and Martin AM Mauler. In May 1946 it was decided to delay corrections of the design and complete five airframes already in production. Although a promising design, the U.S. Navy finally terminated the contract on 3 September 1946, as there was no need for the aircraft anymore. The five prototypes were scrapped.