RB-66A-cont

Douglas RB-66A Destroyer (Continued)

     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 canceling 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 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.
Sources:
1. Post World War II Bombers, Marcelle Size Knaack, Office of Air Force History, 1988.

2. McDonnell Douglas Aircraft Since 1920, Volume 1. Rene Francillon, Naval Institute Press, 1988

3. United States Military Aircraft Since 1909, Gordon Swanborough and Peter M. Bowers, Smithsonian Institution Press, 1989.