JeffroK
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From the files of Joe Baugher
http://www.joebaugher.com/usattack/a2d.html
Douglas XA2D-1 Skyshark
The Douglas A2D Skyshark was intended as a successor to the Douglas AD Skyraider. It appeared at a time when the Navy was reluctant to use pure jet aircraft on its aircraft carriers, and it was powered by a turboprop engine. Although it had substantial performance improvements over the Skyraider, there were serious reliability problems with its engine, and the program was cancelled after only a few examples were built, and the aircraft never entered operational service with the Navy.
On June 25, 1945, with the war in the Pacific still in progress, Douglas was asked by the Navy to explore the possibility of producing a turboprop-powered carrier-based attack aircraft. At that time, the Navy was reluctant to consider pure jet aircraft for its carriers because of the high fuel consumption of the jet engines of the day and the resulting short ranges and low endurance times. Nevertheless, it was assumed that Navy attack planes might eventually be called upon to go up against an enemy equipped with jet fighters, and the Navy wanted an aircraft that could survive in such an environment and deliver its weapons successfully on the target. It was thought that an engine thrust approximately twice that which was currently available in the most powerful piston engines would be required to make it possible for an attack aircraft to be able to fly unescorted against enemy jet fighter opposition and still have an useful range and payload. The XBT2D-1 (the prototype of what later would be the AD Skyraider) had only just flown a couple of months earlier. The aircraft, if it were ordered, would have been naturally designated XBT3D-1.
Douglas initially followed three separate strategies. The first was the Model D-557A which was to be owered by two General Electric TG-100 turboprops housed in wing nacelles, the second was the Model D-557B which was powered by a pair of nose-mounted TG-100 engines driving contrarotating propellers, and the third was the D-557C powered by as single Westinghouse 25D engine. These proposals went as far as the construction of a mockup, but plans to convert a XBT2D-1 to turboprop power were cancelled after developmental problems were encountered with the turboprop engines.
In the meantime, the Navy had contacted several aircraft engine manufacturers to develop the turboprop engine further. The Allison Division of General Motors submitted a proposal for a twin axial-flow turbine mounted in parallel and driving a contrarotating propeller via a common reduction gearbox. A Navy contract was awarded to Allison in December of 1945 for development of this engine under the designation XT40-A.
By late spring of 1947, the Navy had revised its requirements. Not only did the new attack aircraft have to be able to defend itself against enemy jet fighters, it now had to be able to participate in air-to-air combat. It was also necessary that the aircraft be able to operate from CVD-55 Casablanca class carriers. A combat radius of 600 nautical miles with a reduced bomb load was required.
Although the requirements were indeed difficult, Douglas went ahead and submitted a proposal, based on the Allison XT40 engine. The new aircraft was designated XA2D-1, and on September 25, 1947 two prototypes were ordered (BuNos 122988 and 122989).
Initially, the XA2D-1 was to have been a fairly straightforward adaptation of the AD Skyraider airframe to accommodate the T40 engine, but it soon became apparent that in order to take full advantage of the additional power that would be available from the XT40, the airframe would have to be entirely redesigned. The result was essentially an entirely different aircraft, one which bore only a superficial resemblance to the Skyraider.
Like the Skyraider, the XA2D-1 was a low-winged aircraft, but the wing root thickness ratio was reduced from 17 percent to 12 percent. The wing leading edge was no longer straight, but with a significant wing root extension. The wing had a moderate taper in plan and thickness. It was hinged at the midsection (just outboard of the main underwing pylon) for folding aboard aircraft carriers. The main undercarriage members retracted backwards and rotated through 90 degrees to lie flat in wheel wells inside the wing. Both the tailwheel and the arrester hook were fully retractable.
The fuselage was somewhat longer and deeper than that of the Skyraider. The cockpit was somewhat farther forward than it was on the AD series of aircraft, which provided good visibility during landing. The cockpit was pressurized, and was covered with a canopy which slid to the rear. Unlike in the Skyraider, the canopy was not entirely transparent--there were two oval glass panels on either side of the pilot, plus a glass panel immediately above the pilot's head. The pilot was equipped with an upward-firing ejection seat.
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.
Armament was to be 4 20-mm T31 cannon in the wings, with 200 rounds per gun. The offensive armament was to be carried entirely externally, 11 stations being fitted. The three major stations (one underneath the fuselage and one under each inner wing) could carry a 200-lb bomb, a torpedo, a rocket, or a 300 US-gallon drop tank. The minor outer underwing stations could each carry a single 5-inch HVAR rocket or equivalent store.
Provision was also made for the Skyshark to carry the AN/APS-19A radar, with the scanner being located inside the extreme nose of the propeller spinner.
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.
Only one Skyshark is believed to survive today. It is 125485, which never flew. Instead of being scrapped by Douglas, it was used (minus its engine) for ground radar calibration at the Los Angeles International Airport. It was later given to the Planes of Fame museum. I am unaware of its current status.
Specification of Douglas XA2D-1 Skyshark
Engine: One Allison XT40-A-2 coupled turboprop, 5100 eshp Performance: Maximum speed 501 mph at 25,000 feet. Cruising speed 276 mph. Initial climb rate 7290 feet/minute. Service ceiling 48,100 feet. Combat range 637 miles. Maximum range 2200 miles. Weights: Empty weight 12,900 pounds. Loaded weight 18,700 pounds. Maximum weight 22,960 pounds. Dimensions: Wingspan 50 feet 0 inches, Length 41 feet 2 1/2 inches, height 17 feet 0 3/4 inches, Wing area 400 square feet. Armament: Four 20-mm cannon in wings. Maximum external ordnance load 5500 pounds.
Serials of Douglas A2D Skyshark
122988/122989 Douglas XA2D-1 Skyshark
c/n 7045/7046
125479/125488 Douglas A2D-1 Skyshark
c/n 7590/7599
125485/125488 completed but not flown
127962/128042 Douglas A2D-1 Skyshark
contract cancelled
132793/133042 Douglas A2D-1 Skyshark
contract cancelled.
134438/134445 Douglas A2D-1 Skyshark
contract cancelled.
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