RE: Skyshark
The engine was the Allison XT40-A-2, rated at 5100 eshp and 830 lb of residual thrust. The engine had two Model 501 (XT-38-A) gas turbines mounted side-by-side and connected to a common reduction gearbox. The gearbox drove a set of co-axial propeller shafts that turned a pair of three-bladed -14-foot diameter contrarotating propellers. The two power sections could drive both propellers independently when the other section was declutched. In cruise, one of the T38s could be shut down to increase range and endurance. The engine was mounted in mid-fuselage below the pilot, and was fed by a pair of intakes, one on each side of the lower part of the nose between the wing leading edge and the contrarotating propellers. There were large exhausts on the lower rear fuselage, one on each side, just behind the wing trailing edge.
The first XA2D-1 made its maiden flight on March 26, 1950. Almost immediately, severe engine vibration problems appeared. These would have to be overcome if the aircraft were ever to be suitable for Navy service.
The Korean War gave a new urgency to Navy carrier-based aircraft needs. Despite the fact that Skyshark program had encountered some severe developmental problems, further examples were ordered. On June 30, 1950, ten production A2Ds were ordered (BuNos 125479/125488). On August 18, 1950, 81 more Skysharks were ordered (BuNos 127962/128042). Plans were made for a Skyshark production line at El Segundo, California, and several subcontractors were identified.
In the meantime, the results of the test flight program were going from bad to worse. Not only were the engine vibrations still present, tests now uncovered problems with bearing failures, reduction gear failures, and overheating of the fuselage skin in the region of the engine exhausts. To make things even worse, the first XA2D-1 prototype crashed on December 19, 1950, killing pilot Lt Cdr Hugh Wood. An investigation later determined that the failure of one of the Model 501 units during a test dive was most likely the cause.
The second XA2D-1 (BuNo 122989) did not fly for the first time until Apr 3, 1952. During the test flight sequence, the protruding rear fuselage engine exhausts were replaced by flush exhausts. The fin and rudder were revised, and the aircraft had a bare metal finish as opposed to the blue-black paint scheme of the first prototype. The accessory gearbox was relocated from the top to the bottom of the engine. The number of compressor stages in the engine were increased from 17 to 19, which was the planned production version of the engine, the YT40-A-6A. The engine was equipped with an automatic decoupler to separate individual power units from the drive shaft in the event of a failure. However, the problems with the Allison turboprop engine were still there.
The problems with the Allison T40 seemed to be insoluble, and the Navy was now beginning to have doubts about whether the Skyshark would ever be turned into a reliable aircraft. In addition, Skyraider production was continuing at Douglas, and the plane appeared to be satisfying the Navy’s attack aircraft needs for at least the next few years. Furthermore, the Navy was developing a new confidence in the suitability of pure jet aircraft on its carrier decks. This led to a growing disenchantment with the A2D program. In mid 1952, the Navy project office in charge of the A2D recommended cancellation of the project, and later that year the Navy cancelled most of the production A2Ds that were on order, leaving only ten remaining. This cancellation had the effect of freeing up space on the Douglas production line for more AD Skyraiders and freeing up developmental money for the A4D Skyhawk.
The first production A2D-1 (BuNo 125480) flew for the first time on June 10, 1953, with George Jansen at the controls. Four more planes on the order (125479, 125481, 125482, and 125483) were delivered later in the year. The flight testing continued, but there were still problems with engine and gearbox failures, and a spate of accidents continued to beset the program. 125480 suffered a gearbox failure and crashed near Lake Los Angeles on August 5, 1954. The pilot ejected safely. The last four aircraft on the order (125485/125488) were completed, but were never flown.
In April of 1953, the second XA2D-1 (BuNo 122988) was seconded to Allison to assist them in resolving the problems with the T40 turboprop. Under the terms of the contract cancellation, Douglas was supposed to make two previously stored A2D-1s (125481 and 125484) flight ready and deliver them to Allison. 125484 was to be assigned to the naval storage facility at Litchfield Park in Arizona, but was delivered instead to Edwards AFB for use by Allison. After the completion of the tests, Allison disposed of all three of their their aircraft. One was transferred to Aberdeen Proving Grounds in Maryland for armament tests, a second was sent to the Naval Air Material Center for barrier tests, and a third went to NAS Quonset Point, Rhode Island for technical use. The remaining Skysharks at the Douglas plant were scrapped.
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