By Harold Andrews
Naval Aviation News
Among the many Navy aircraft that emerged under Ed Heinemann's direction at the Douglas El Segundo plant, probably the least known is the XTB2D-1. Born in the period following Pearl Harbor, it was intended to meet a clearly identified need in carrier aircraft operations, capable of carrying greater loads and/or flying longer ranges as a torpedo bomber, and also performing extended range or duration scouting missions. As events transpired, only two X airplanes were built and flown, and neither flew very many flights before being retired in 1947 for use in barrier tests.
With the greatly intensified activities that followed Pearl Harbor early in 1942, Douglas was asked to submit a proposal for a new design torpedo bomber capable of multi-torpedo attacks, high-altitude bombing or long-range scout missions; a twin-engine design was suggested based on BuAer design studies. By April, Douglas had submitted several design alternatives, recommending a single-engine airplane using the Pratt and Whitney 28-cylinder XR-4360 engine then being developed. The design proposed included a tricycle landing gear, external carrier for bombs and up to four torpedoes, powered gun turrets, a dual rotation propeller, and a three-man crew. It would be operable from Essex-class carriers. Further design development of this preferred design led to an increase in wing area and span for adequate carrier takeoff and landing performance — resulting in a 70-foot span. It was the largest aircraft seriously considered for carrier operations in that period.
A letter of intent in November 1942 initiated the program for two XTB2D-1s, powered by XR-4360-8 Wasp Major engines, driving counter-rotating four-bladed Hamilton Standard propellers. A static test airframe was also included. Airplane mock-up inspection took place in March 1943, with the power plant mock-up installation in May. During this period, the question of production was raised, Douglas finally being requested to submit a proposal for 25 additional aircraft in December. By this time design development, including the results of Douglas flight tests on flap concepts incorporating lateral control devices, resulted in design changes to include full span flaps, as well as extended-span horizontal and vertical tail surfaces to provide adequate stability. Delays in delivery of an XR-4360 engine delayed the start of full-scale power plant nacelle ground tests until March 1944, when jigs for the aircraft's construction were also being built. Production action also began in March for a total of 25 airplanes, with tooling to produce 100 aircraft per month. Over the next three months, construction of the first airplane and static test article proceeded satisfactorily and the power plant ground test running started. Club props were used since an actual eight-blade dual propeller had not yet been delivered.
June brought a complete reversal of the March production decision. Based on the successful Fast Carrier Task Force operations in the Pacific and assessment of their attack aircraft experience, and also based on the progress in aviation technologies during the early war years, the Navy turned completely to single-place attack designs (VBT class) for future needs. At Douglas, high priority development of the new XBT2D-1 (later AD/A-1) was initiated. The TB2D program was cut back to the original two airplanes, some concern for the large size and experimental features entering into the decision along with the policy change. Since the XTB2D-1 development was well along, it was continued to explore the design features, as well as to provide an ongoing backup program in case operational requirements changed again. However, it was assigned a very low priority, so Douglas could concentrate on the XBT2D-1.
The low priority and delays in propeller delivery resulted in the first flight date slipping from the fall to early 1945. Meanwhile, consideration was given to installing a jet engine in the second aircraft for flight installation experience. This was turned down, but it was agreed to complete the second airplane like the first, without the power turret and the under fuselage tub for the bomb- sight and tunnel gun. Relocation of the second crewman further aft with extensive electronic equipment was proposed as a step towards offsetting the resulting center-of-gravity shift and providing a usable military capability in the changing combat environment.
Initial taxi tests and liftoffs in February 1945 were followed by further delays due to engine problems, the first three flights occurring in May with generally satisfactory results, although the third flight ended in an emergency landing due to propeller problems. While awaiting a new propeller, modifications to reduce wing outer panel dihedral and vertical tail height were incorporated, flight testing resuming in June in preparation for ferrying to Patuxent River for Navy evaluation. Before test completion, both inboard flaps separated from the airplane while being retracted from the dive brake position. The pilot completed a successful emergency landing.
In August, the second airplane made its first flight in the same configuration as the modified first one, but the flight ended in an emergency landing due to engine failure. In fact, the dual rotation engine gearing froze on rollout. The engines were grounded pending redesign of the nose section. New propeller blades were also found necessary, and the repaired #1 as well as #2 remained grounded until May of 1946 when flight testing resumed. In June another forced landing due to reduction gear failure resulted in concern over adequate engine reliability for safe flight testing. Plans were made to substitute the different gear ratio nose section and six-blade dual rotation Aeroproducts propeller which had not experienced as many problems in other flight test installations. These were delivered in December.
During early 1947 continuation of the flight program was reviewed, and by June it was decided to accept the aircraft for barrier testing of dual rotation propeller tricycle gear aircraft, closing out the development of a design that no longer fit into the carrier aviation picture, even though it promised to meet the very ambitious design goals considered vital five years earlier.
Appreciation is extended to Dr. W. J. Armstrong and Ms. Judy Walters for assistance in making this feature possible.