The Douglas B-66 Destroyer was originally envisaged as a replacement for the World War 2-era piston-engined Douglas B-26 Invader in the tactical bombing role for both day and night operations. On June 14, 1951, the USAF issued a formal requirement for a tactical bombing aircraft to meet this need. The initial requirement specifically asked for a reconnaissance vehicle, but in August the requirement was amended to include tactical bombing as well.
Several companies responded with proposals to meet this requirement. North American proposed an improved version of its B-45 Tornado four-jet bomber. Boeing proposed an adaptation of its B-47 Stratojet six-jet medium bomber. Martin proposed a version of the B-51 3-engined low-level bomber. Most promising, however, was Douglas's proposal of a land-based version of the Navy's XA3D-1 Skywarrior twin-engined carrier-based strategic bomber that was then currently under development. However, the XA3D-1 was not scheduled to fly for yet another year and was somewhat of an unknown quantity.
On August 29, 1951, Douglas formally issued a proposal for an adaptation of its XA3D-1 to meet this requirement. On November 29, 1951, the USAF Aircraft and Weapons Board announced that the Douglas design had been approved. The designation B-66 was assigned on January 12, 1952.
The Air Force originally thought that the B-66 would be more or less an off-the-shelf copy of the A3D, so there would be no need for prototype XB-66. Instead, a small initial batch of pre-production aircraft designated RB-66A (Douglas Model 1326) would be acquired for test and evaluation purposes. There would be two separate production versions that would be acquired--a reconnaissance version designated RB-66B and a bomber version designated B-66B. The reconnaissance version would have the higher priority, and would be equipped with night photography capability and would carry electronic countermeasures and reconnaissance equipment.
The general operational requirements were issued on January 21, 1952. A fast, highly-maneuverable tactical reconnassance bomber was called for, with a 1000-nautical mile radius. It had to be capable of carrying at least a 10,000 pound load of atomic weapons, conventional bombs, or photographic flash bombs. The plane had to be capable of carrying large amounts of electronic equipment without adversely affecting its normal performance. In addition, defensive armament had to be carried and electronic countermeasures equipment was required to deal with enemy radars. Finally, the aircraft had to be simple and easy to maintain and had to be able to operate from makeshift or temporary runways.
Letter Contract AF 33(600)-9646 was issued on February 12, 1952, calling for the acquisition of a test quantity of 5 RB-66As. It was decided that it would not be worthwile to acquire any examples of the Navy A3D because by now it was anticipated that the Air Force version would be quite different. The definitive contract was signed on December 4, 1952. 127 production aircraft were ordered in Letter Contract AF 33(600)-16314, signed on April 24, 1952.
The design of the B-66 was assigned to a Douglas-Long Beach team under the direction of John C. Buckwalter. Work on the project began in early 1952. The B-66 shared the same basic configuration of the A3D, with a high-mounted sweptback wing with negative dihedral. The two engines were mounted in pods attached to underwing pylons. The crew of three were seated together in a cockpit in the forward part of the nose. The main landing gear members retracted into wells in the rear fuselage.
The first step in the design was the elimination of the features of the Navy A3D that were specific to its carrier-based role, such as folding wings, arrester gear, and catapult harnesses. This was fairly simple to do.
The next step was not so straightforward. An early problem was the fact that the A3D did not have ejector seats, the crew escaping the aircraft via a chute in the rear of the cockpit. Since the B-66 would be flying at low altitudes and at fairly high speeds (the A3D was envisaged as a high-altitude strategic bomber), upward-firing ejector seats for the three crew members had to be provided. The use of ejector seats in turn required that the cockpit canopy be extensively revised to accommodate the escape hatches needed for the ejecting crew. In addition, the cockpit itself had to be extensively revised, with the pilot sitting centrally forward and the navigator and gunner/reconnaissance system operator seated immediately aft.
Because of the low altitudes and high speeds that were anticipated, the airframe structure had to be strengthened. The wing had a revised planform with a reduced thickness/chord ratio at the root. New ailerons and flaps were fitted. In addition, the 30-inch radar antenna of the A3D had to be replaced by a 45-inch antenna for the APS-27 and K-5 bombing and navigation radar. Since the R/B-66 had to be capable of operating from semi-improved or temporary airfields, larger landing gear tires were required. New emergency air brakes, wing spoilers, improved lateral controls, and a two percent reduction in the wing angle of incidence were needed to minimize Dutch roll. The hydraulic system had to be revised and the fuel system had to be redesigned. The photo-navigator station had to be relocated, and the aircraft had to be fitted for inflight refuelling. For the reconnaissance mission, a battery of four cameras was to be mounted in the center fuselage bay. A new remotely-controlled General Electric tail turret with two 20-mm cannon was fitted as the defensive armament.
One of the more significant changes was the need for different engines. The XA3D-1 was to be powered by a pair of 7000 lb.s.t. XJ40-WE-3, with production A3D-1s using the 7500 lb.s.t. J40-WE-12. Unfortunately, the J40 turned out to be completely unsuitable and was the cause of the failure of several combat aircraft projects of the era. Alternatives had to be considered. Westinghouse offered a new version of the J40, but this was unsuitable because of its excessive fuel consumption and because it offered a thrust of only 7250 pounds. The General Electric J73 was better, but it was ruled to be unsuitable because of its higher cost and its longer development cycle. Douglas preferred the Pratt and Whitney J57 turbojet (which it had selected for the J40 replacement in the A3D), but this engine was already committed to other combat aircraft projects that had a higher priority than the R/B-66 and the Air Force didn't think that the manufacturer could produce enough engines to meet the demand. This left the Allison J71, which was built by a division of the General Motors Corporation. It offered a thrust of 9750 pounds. This engine was deemed to be an acceptable alternative, and a production order specifying the J71 engine was signed on August 5, 1952.
The mockup was inspected at Douglas in late June of 1952. The Air Force was fairly pleased with what they saw, but they recommended that the landing gear be redesigned to accept a heavier load of 83,000 pounds.
The first of five RB-66A pre-production aircraft (52-2828/2832) flew at Long Beach on June 28, 1954, with George R. Jansen in command. It was a short hop to Edwards AFB. The aircraft was powered by a pair of 9570 lb. s.t Allison YJ71-A-9 engines. In the first few test flights, the aircraft was found not to handle very well, the landing gear doors did not function properly, and the vision from the cockpit was poor. The first RB-66A was formally accepted by the USAF in June, but the plane remained with Douglas for correction of the defects.
The four remaining RB-66As were accepted between August and December of 1954. Because of the early performance and handling problems that were encountered, speed and load restrictions had to be imposed which in turn impeded the progress of flight testing. The aircraft flight control system proved to be unreliable, the aircraft's wings vibrated excessively, and the aircraft had the dangerous property of pitching up unexpectedly. Because of these difficulties as well as due to schedule slippages, the Air Force began to consider the possibility of cancelling the B-66 project and started looking around for a substitute.
The B-66 program was on the verge of cancellation at this point, but it was concluded that it would be far too expensive at this stage to cancel the program outright and try to find a substitute. In addition, many of the problems with the RB-66A had already been identified and progress was being made in correcting them. Consequently, the Air Force decided that it was better to retain the program, but the number of planes ordered was cut back by 48. In the meantime, it was found that a parachute brake would have to be provided, as well as the need for the addition of an anti-skid device. The cockpit enclosure had to be revised and the cockpit instruments had to be relocated. Gradually, the problems with the B-66 were identified and corrected, and the aircraft turned out to be a fairly reliable design. The control system was reconfigured, the tail turret was reconfigured, and better engine pylons were installed. The J71-A-9 engines were replaced by production J71-A-11 engines. The buffeting was reduced to an acceptable level, and the the aircraft's speed was increased to 550 knots. The Air Force was now sufficiently pleased with the progress on identifying and fixing the problems that the delivery of production RB-66Bs was expected by the end of 1955.
None of the five RB-66As were ever used operationally by the USAF. However, the first RB-66A was bailed to General Electric for testing of the 11,200 lb.s.t CJ805-3 turbojet. It was later used to test the 16,00 lb.s.t CJ805-23 aft-fan engine.
52-2828/2832 Douglas RB-66A-DL Destroyer