Flightline: 174 - Douglas B-66 Destroyer
Developed from the A3D naval strategic bomber, the B-66 mainly flew recon and electronic warfare missions over Vietnam for the USAF.
The outbreak of the Korean War in 1950 caused the USAF to seek a replacement for the WWII-era B-26 (aka the A-26). Four aircraft were proposed: North American Aviation offering a variant of the B-45 Tornado, Boeing offering a modified B-47, Martin advancing the XB-51 and Douglas offering a variant of the A3D Skywarrior. In November 1951 the USAF, having been suitably impressed by Douglas' offering, awarded a contract for five pre-production RB-66A Destroyers. Despite having initially expressed an interest in keeping the B-66 as close to the design of the A3D as possible, shifting interests and differing mission goals and operating conditions resulted in the Destroyer having only a superficial resemblance to its Navy cousins. Aside from the expected "de-navalization" steps of removing the wing-folding mechanism, arresting hook and catapult attachment point, the USAF also called for a redesign of the cockpit, shifting the pilot's seat forwards and having the navigator and gunner/recon systems officer seated side-by-side behind him. The B-66, intended to operate at low altitude and not facing the same weight limitations as the Whale, was fitted with ejection seats, which required reworking the canopy to accommodate hatches. Owing to the change to low-altitude operations, the fuselage was made stronger, and the wing was redesigned, with a greater area, thinner airfoil, new flaps and ailerons, and a different angle of incidence. As the radar of the B-66 was larger, the nose was reshaped. The landing gear was modified for rough field service, including larger main gear tires. The USAF, fearing a shortage of the A3D's J57 engines, specified GE/Allison J71s instead, despite the reduced power and increased fuel costs incurred. As with the later A3D-2 model, the USAF B-66s were fitted with refueling probes.
Orthograph of the B-66. | Illustration: aviastar
Despite the eventual scope of the changes made to the original A3D design, the RB-66A's maiden flight was conducted on 28 June 1954, only slightly behind schedule. The flight test program uncovered a number of issues with the B-66's design, including handling problems, a poor field of view from the pilot's seat, vibration in the wings and a tendency to pitch up unexpectedly. Douglas was able to iron out the bugs, however, and delivery of the production RB-66B model soon followed, with the first flight occurring on 4 January 1955. A change in focus by the USAF saw the production of the B-66B bomber variant capped at 72 however, with the all-weather photo-recon RB-66B having a run of 145 aircraft. The two variants were externally identical, but the B-66 had a lengthened bomb bay and the capacity of the aft fuel tanks was greater. The wings of the B-66 were also fitted with a single pylon each rated for a 500 gallon drop tank. The B-66 was rated for a higher take off weight, and could carry 15,000 pounds of conventional or atomic bombs, and was fitted with a K-5 bombing system, which included an APS-27 radar. The RB-66B, on the other hand, could carry a smaller number of photoflash bombs and could be fitted with a number of camera systems. Both versions had a twin 20mm cannon mount in the tail, though this was removed and substituted with ECM equipment in a dovetail fairing as was also done with the A3D-2.
B-66B (s/n 53-506) in flight. | Photo: USAF
An RB-66B (s/n 53-415) after the tail stinger was removed and replaced with the ECM dovetail. | Photo: USAF
The Destroyer entered USAF service in 1956, with the RB-66 serving as the primary photo-recon asset for the Tactical Air Command (TAC), with many aircraft stationed in the UK and Germany. The B-66, with no real bombing mission to fulfill, found a second life as an electronic countermeasures aircraft, with 13 planes converted to EB-66B specs under Project BROWN CRADLE and were stationed, as part of the 42nd Tactical Reconnaissance Squadron, at RAF Chelveston, with aircraft also rotated out of an alert pad in France at the height of the Cold War. In the mid-1960s, the aircraft were fitted with QRC-95 "Green Dragon" jammers under BIG SAIL, which added large antennas on the top and sides of the aircraft. The EB-66B was joined by the RB-66C (later redesignated EB-66C), 36 purpose-built ELINT/EW variants fitted with radio and radar receivers, jamming equipment, and chaff dispensers. Various pods could also be carried on wing pylons. All of this gear was controlled by four electronics warfare officers (EWOs), each in downward-firing ejection seats, in a pressurized compartment in the bomb bay. The maiden flight of the RB-66C was on 29 October 1955, and production was completed in 1957. Early examples retained the twin 20mm stinger, but this was replaced by the same ECM fairing as was retrofitted to other A-3 and B-66 models, and the gunner's position was deleted. A further 52 RB-66Bs were also modified into EB-66E ECM aircraft.
RB-66C (later EB-66C) ECM aircraft were constant companions of USAF bombing missions early in the Vietnam war. | Photo: USAF
Originally an RB-66B, this EB-66E is being prepped for a mission at Takhli RTAFB in 1968. | Photo: USAF
The last production variant of the Destroyer was the WB-66D, a weather reconnaissance version which first flew on 26 June 1957 with the final delivery of the 36th aircraft in 1958. They were structurally similar to the RB-66C (even retaining the tail gun), but carried meteorological instruments rather than reconnaissance gear. The standard crew of three were joined by two systems operators in the former bomb bay. The WB-66 had a short service life, and the type was retired in the mid-1960s.
A preserved WB-66 at Warner-Robbins Air Museum in Georgia. | Photo: Greg Goebel
Unlike with their Navy cousins, the bomber variant of the Destroyer didn't see any service, but the recon and EW versions saw heavy use during the Cold War and during Vietnam. RB-66Cs monitored Russian and Cuban signals and radar during the Cuban Missile Crisis, and EB-66B, RB-66C and EB-66E Destroyers flew numerous missions over Europe, especially the inter-German border. On 10 March 1964, an RB-66C from the 19th Tactical Recon Squadron, flying on a photo-reconnaissance mission from the Toul-Rosières Air Base in France, strayed across the border into East Germany due to a compass malfunction and was intercepted and shot down by a Soviet MiG-21. The crew ejected from the stricken aircraft and, following a brief period of detention, were repatriated to the United States. The following year, EB- and RB-66 Destroyers were deployed to Takhli Air Base in Thailand and began flying missions in support of South Vietnamese and US missions. ECM Destroyers escorted USAF F-105 Thunderchiefs on bombing missions over North Vietnamese targets, but after an EB-66 was short down by a MiG-21, they switched to standoff jamming, flying outside the North's airspace and blinding their long range radar.
Flying under the protection of a "Big Sail" EB-66B, F-105s drop their bombs. | Photo: USAF
Although powerful, the B-66 was slow and cumbersome in the face of North Vietnamese MiGs, and time was catching up with the line. Miniaturization allowed strike aircraft to carry their own self-defense ECM pods starting in the late 60s, and faster, more nimble planes like the EA-6, EF-111 began to enter service, along with more direct solutions like the Suppression of Enemy Air Defense (SEAD) missions flown by F-105 and F-4 Wild Weasels. B-66s began to be withdrawn in the early 1970s, and by 1975 all of the Destroyers had been removed from front-line service. Many of the aircraft were scrapped in place, with the remainder being flown to AMARC for eventual recycling. Out of the 294 B-66s completed, only six remain on display, 3 WB-66s, two RB-66Bs and a single RB-66C.
An WB-66D on display at the Museum of Aviation, Robins AFB. | Photo: Dsdugan
RB-66C, s/n 54-0465, on display at the main gate of Shaw AFB, SC. The markings are from the 363rd Tactical Reconnaissance Wing which flew the RB-66 at Shaw Air Force Base during 1965-1974. | Photo: USAF
One of the major issues facing aviation engineers is drag, that is, disturbed air surrounding the plane which reduces the possible speed and range of a given design. One possible solution under study was active laminar flow control, or boundary layer suction, under which a portion of the disturbed air was drawn into the wing, restoring laminar flow. Studies found that if 80% of wing is in laminar flow, then overall drag could be reduced by 25%. In order to test the idea, NASA contracted the Northrop Corp to build two X-21A test aircraft by modifying two WB-66Ds (s/n 55-0408 and 55-0410) with new wings and the needed equipment to run and test the system. The existing wings were removed and a new pair, longer and with more area, with the sweep reduced from 35° to 30°. Each wing was made up of a porous honeycomb structure, and the skins featured 800,000 span-wise slots through which boundary layer air was drawn into the wing. The J71 engines and their pylons were removed, and replaced by GE XJ79-GE-13 non-afterburning turbojets mounted in pods attached to the rear of the fuselage sides. Bleed air from these engines was fed into bleed-burn turbines housed in fairings under the wings, which sucked in the turbulent boundary layer air. The aircraft flew with a crew of three, a pilot and two flight engineers, in the cockpit and seats were provided for two flight test engineers in the lower fuselage bay.
Line drawing of the X-21A, with cutaway detail showing internal arrangements. | Illustration: Chuck Davis
Maiden flight of the X-21A was on 18 April 1963, and the two X-21s were tested by Northrop, USAF and NASA personnel until 1968. The flight program proved that the idea of active control worked, the system was not ready for use. The surface slots were vulnerable to clogging by dust, insects and even moisture. Under certain conditions, rapid cooling of the air over the slots would cause ice crystals to form, disrupting the laminar flow and causing handling problems. Maintaining the numerous skin slots, passageways and ducts proved to be the undoing of the program, and the X-21s were retired. The aircraft were placed into storage at Edwards AFB for a time, but were eventually stripped of useful equipment and used as photographic targets. Both aircraft remain at the base, but have not been restored.
One of the X-21As in flight. | Photo: USAF
The decaying hulk of one of the X-21s. | Photo: Estate of Bob Seidemann