The B-36D featured 2 pairs of J47-GE-19 turbojets (in pods, beneath the wings) to assist the basic 6 R-4360-41 engines, a K-3A bombing and navigation system (in lieu of B-36B's APG-24 radar) to allow a single crew member to act as radar operator and bombardier, an AN/APG-32 radar (instead of APG-3) to control the tail turret, and higher takeoff and landing weights (370,000 and 357,000 pounds, respectively. This was forty thousand more takeoff pounds than the B-36B and a 29,000 pound landing weight increase). The aircraft was fitted with snap action bomb-bay doors, as opposed to the sliding type of the preceding B-36As and Bs. The new bomb-bay doors opened and closed in 2 seconds. The K-1 not the K-3A at first equipped most B-36Ds (new productions as well as converted B-36Bs). This K-1 system was little more than a refined APQ-24. It likewise had its share of problems, chief among them the random failure of vacuum tubes. In fact, soon after the B-36s entered the inventory, more than 25 percent of their aborts were due to radar deficiencies.
Flown even sooner than Convair expected (26 March 1949), the prototype B-36D was a converted B-36B. It differed notably from ensuing B-36Ds by carrying in its pods 4 Allison J35 jet assist engines, in place of the later standard J47-GE-19s.
The first true B-36D flew on 11 July 1949, but the Air Force did not accept any of these aircraft for another year.
The first B-36Ds accepted by the Air Force in August 1950 went to Eglin AFB for testing, but SAC received some of the new productions much later. By December, the command's operational bombers included 38 B-36s several B-36Ds and about 24 B-36Bs (soon to be brought up to the D configuration). The aircraft equipped units of the Eighth Air Force's 7th Bombardment Wing.
Except for the sole B-36 simulated bombing mission to Hawaii in December 1948, no B-36s were flown overseas before 1951. Then on 16 January, 6 B-36Ds went to the United Kingdom, landing at Lakenheath Royal Air Force Station, having staged through Limestone AFB, Maine. The flight returned to Carswell on 20 January. A similar flight was made to French Morocco on 3 December, when 6 B-36s of the 11th Bombardment Wing touched down at Sidi Slimane, having flown nonstop from Carswell.
Despite 2 years of engineering test flights and high priority modifications, many of the problems in early productions remained unsolved. An early major B-36 problem was the recurring leaks in the aircraft's fuel system. The unreliable electrical system and the dangerous flight conditions that could result were also of deep concern through the end of 1949. Engine troubles were still frequent in 1950, compounded by the fact that an engine malfunctioning at a given altitude could check out in perfect order on the ground. Hence, the Air Force on 15 September approved a SAC request for "immediate procurement and installation of airborne ignition analyzers together with necessary spares and supporting equipment for all B-36, B-50, and C-124 type aircraft assigned to this command Undoubtedly, progress was being made through gradual changes and carefully devised fixes. The aircraft were nearly combat ready by 1951, but far from perfect. In October, for example, the B-36's gunnery system remained operationally unsuitable. In fact, SAC viewed the "gunnery and defensive armament as the weakest link in the present B-36 capability."
Improved containers and better sealants reduced fuel tank leakages. Changes in the electrical system had posed fire hazards during ground refueling operations. Landing gear and bulkhead failures were almost totally corrected. Nevertheless, the Air Force was not satisfied. In April 1952 it ordered a series of gunnery missions for both B-36 and RB-36 aircraft. Known as Far Away, this test was completed in July. It showed that malfunction of the B-36's defensive armament system was due in part to poor maintenance and gunnery crew errors (The problem of caring for new and highly sophisticated equipment came as no surprise to the Air Force. In early 1949, the Sperry Company had opened a school to train personnel in proper maintenance of the K radar system. SAC, however, was reluctant to let its few trained radar men attend the 8-month course, and it was just as hard to recruit qualified students). This prompted Test Fire, a field service exercise begun in September by a RB-36 squadron of the 28th Strategic Reconnaissance Wing. Test Fire ended in December, having attained its main purpose of helping to standardize maintenance and operational procedures.
As anticipated by the Air Force, Test Fire also confirmed the overall conclusion of Far Away that the B-36's defensive armament was nearly as bad as ever. Various pieces of equipment needed to be redesigned and the fire control system was barely adequate. In light of this, Hitmore was launched in early 1953. This third project pooled the efforts of the Air Force, General Electric, and Convair (the prime contractor). It required the modification of 6 B-36s to further assess the actual airborne accuracy of the fire control system. In addition, these planes made separate test flights to gauge the operational efficiency of the gunnery system. The Hitmore results proved encouraging. By mid year no critical problems had been uncovered. The B-36's defensive armament could be made to work well, after numerous but minor modifications.
Several B-36Ds received the special modifications initially applied to a number of the B-36Js (sixth and last of the B-36 model series). Approved in February 1954, the modification contract extended over 11 months. The first modified B-36D, flown in June by Convair, was returned to the Air Force the same month. The modified B-36Ds were identified as Featherweight B-36D-111s. Like other featherweight B-36s, they were to be used for high altitude operations. Hence, they had been stripped of all armament except the tail turret. Convair had also removed all non essential flying and crew comfort equipment from the modified planes. To shed even more weight, the Featherweights carried a 13 man crew, 2 fewer than the standard B-36D.
Just 26 B-36Ds came off the production lines. But modification of most of the B-36Bs accepted by the Air Force gave SAC a sizeable B-36D contingent.
Except for 1 B-36D received in fiscal year 1952 (August 1951), all B-36Ds were accepted by the Air Force in FY 51-5 in August 1950, 5 in September, 1 in October, 2 in November, 1 in December, 3 in January 1951, 6 in March, and 2 in April.
Production ended in June and the Air Force accepted its twenty sixth B-36D in August.
Each production aircraft cost $4.1 million- Airframe, $2,530,112; engines (installed), $589,899; propellers, $184,218; electronics, $55,974; ordnance, $30,241; armament, $747,681.
Other Configurations: RB-36D, GRB-36D, and RB-36D-111.
In December 1956, SAC's operational inventory counted 250 B/RB-36s of one kind or another. Only 11 B-36Ds remained, after some 6 years of service. It was merely a matter of months before the last of the Ds would be gone.
In August and September, B-36s of the 92d Heavy Bomb Wing completed the first mass flight to the Far East, visiting bases in Japan, Okinawa, and Guam. Nicknamed Operation Big Stick, this 3 day exercise came shortly after the end of hostilities in Korea and demonstrated U.S. determination to try every means possible to keep peace in the Far East. On 15 and 16 October, the 92d Heavy Bomb Wing left Fairchild AFB, Washington,62 bound for Andersen AFB in Guam and 90 days of training. This move was the first time an entire B-36 wing was deployed to an overseas base. Fairchild's severe winter climate adversely affected the 92d Wing's combat readiness. The B-36Ds were still prone to fuel cell leaks, and their usual staging from Fairchild to even colder areas made matters worse. The wing had not yet been able to trade its Ds for either Hs or Js that promised better fuel cell scalant.
A number of B-36Ds were converted for reconnaissance purposes. The RB-36D carried cameras and electronics, as required by the aircraft's principal missions: all purpose strategic reconnaissance, day and night mapping, charting, and bomb damage assessment. The RB-36D carried a crew of 22; the B-36D, a crew of 15. 24 of this variant were produced.
Development of the RB-36D coincided with that of the jet podequipped B-3611 later identified as the B-36D. As in the bomber's case, General LeMay strongly influenced the procurement decision that soon followed. Only 3 strategic reconnaissance candidates remained in November 1948, when the Board of Senior Officers met to review the Air Force's needs for long range reconnaissance aircraft. The jet pod equipped B-36 emerged as the board's first choice. The B-47 was second, as also favored by the SAC Commander. The B-54, officially canceled within several months, was third and last. The RB-49, once a strong contender, was not even discussed. Its fate had been sealed during the summer, when problems had arisen in testing the B-49 Northrop's latest tactical configuration of the unconventional B-35 "flying wing. "Moreover, development of the RB-49 would have been time consuming and expensive, 2 commodities the Air Force could not afford.
General LeMay commanded the B 29 strikes against Japan in World War II, and one of his first actions upon taking charge of the Strategic Air Command was to insist on a quick supply of strategic reconnaissance planes. Speedy conversion of the B-36As and delivery of the RB-36Es ahead of the RB-36Ds attested to the urgency of the SAC Commander's request.
Due to severe materiel shortages, the new RB-36Ds did not become operationally ready until nearly half a year after delivery to SAC.
Being virtually alike, the B/RB-36Ds shared the same problems and received similar improvements.
As in the B-36D's case, some RB-36Ds were changed to the featherweight configuration. These RB-36D 111s retained a large crew, 19 instead of 22. The Convair modification contract extended from February 1954 to the following November. The first modified RB-36D 111 was flown in August, and returned to the Air Force in the same month.
The Air Force carried these 24 aircraft as RB-36D productions. In contrast, 8 of them initially appeared on the contractors' records as B-36Bs. The fine line between Convair and USAF ledgers was of no consequence-it did not affect costs nor the aircraft's operational capability.
The Air Force took delivery of 3 RB-36Ds in June 1950. It accepted the other 21 in FY 51 between July 1950 and May 1951. The Air Force never acquired more than 3 RB-36Ds in 1 month.
Delivery of the 24th RB-36D spelled the end of this aircraft's production.
The GRB-36D/RF-84 combination, better known as the FICON (fighter conveyor) or carrier parasite program, came into being in the early fifties. The RB-36s were becoming more and more vulnerable, and no new form of defense was readily available. The Air Force therefore looked to the past for solutions. As a result, it planned in 1951 to put a parasite RF-84 in the RB-36's bomb bay. The parasite plane would be released about 800 or 1,000 miles from the target and within a relatively safe area. The pilot of the RF-84 would continue on to the target, obtain high or low level photography as desired, then return to the mother aircraft. An alternate FICON mission would be long range, high speed bombing. No real problems arose, but it took longer than thought to bring the FICON project to fruition.
A carrier parasite combination had been tried before for somewhat different purposes. It had long been known that heavily laden bombers could not cope with interceptors. Studies undertaken in 1944 to afford some protection to the then yet to be flown B-36 envisioned a pilotless, remote control, fast fighter that could be carried to the battle area in one of the bomb bays of the huge long range bomber. However, this was given up in favor of a pilot operated fighter that would be more maneuverable in facing repeated attacks. The tiny, folding wing XF-85 Goblin which ensued was developed by the McDonnell Aircraft Corporation in late 1945 and first flown in August 1948. Because no B-36s were readily available, it was test dropped from a B-29. The project, however, never went past the experimental stage. The Goblin production was abandoned for a number of technical and financial reasons, but danger was the primary obstacle. The Air Force believed the odds of retrieving a fighter in the midst of a raging battle were poor. Moreover, if the bomber was shot down before the fighter was launched, both crews would be lost. Finally, if the bomber was destroyed after the launching, the short range Goblin would also be doomed.
Flown in January 1952, the FICON composite prototype comprised a modified, standard RB-36D and a straight wing Republic F-84E Thunderjet. Extensive flight tests soon demonstrated the FICON concept was practical. The parasite's straight wings posed no great difficulties. Sweeping down the tail of a forthcoming F-84 prototype (YF-84F) would enable it to fit in the RB-36 bomb bay. Elimination of the YF-84F's tail flutter by using faired bomb bay doors removed the last stumbling block.
Contracts awarded Convair and Republic in the fall of 1953 called for modifying 10 RB-36Ds and 25 RF-84Fs, respectively. This was far below the number of aircraft SAC had in mind-30 RB-36s and 75 RF-84s. Still, modification of only 35 was to take time. To begin with, the carrier RB-36Ds turned out to be featherweight configurations of the big reconnaissance bomber, and none of these were available before 1954. Furthermore, the reconfigured planes had to be modified to carry the additional mechanisms for stowing, aerial servicing, releasing and retrieving the F-84F parasites. Specifically, this meant that each carrier was equipped with a straight beam extended down from the bottom of the airframe. Each modified parasite featured a retractable probe, mounted on the forward top fuselage section to ease hook up. Actually, the technical operation of FICON was simple. Carriers and parasites could fly out of different bases. The parasite could be picked up in midair enroute to the target area, or by ground hook up prior to takeoff. Night operations were also possible. The first GRB-36D 111 carrier was delivered in February 1955, 6 months ahead of the first parasite RF-84F (subsequently identified as the RF 84K). The FICON B-36s served with SAC's 99th Heavy Strategic Reconnaissance Wing.
The RB-36D followed the B-36D's phaseout pattern. That of the FICON aircraft was much the same.
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