The Largest Security-Cleared Career Network for Defense and Intelligence Jobs - JOIN NOW

Weapons of Mass Destruction (WMD)


XB-35 Flying Wing

Hampered by mechanical failings, the N-9 flight test program prevented the acquisition of reliable flight data through 21 September 1943, when the N-9MB, last of the N-9s, initially flew. Engines excepted, the N-9MB included all latest design features of the XB-35, but the model's flight testing did not help the XB-35's cause. By the end of November, test results indicated that the XB-35's range would most likely be 1,600 miles shorter than anticipated and that the bomber's highest speed would be at least 24 miles per hour below previous estimates. Such disappointing prognostics were not overlooked. General Arnolde himself began to question the merits of the extensive B-35 production plans.

Production of 200 B-35s, as planned in November 1942, was formalized on 30 June 1943 by Contract W535-ac-24555, which called for delivery of the first "flying wing" by June 1945. But Martin had already begun to lose personnel to the draft before the contract was signed. In mid 1943, projected delivery rates were reduced by 50 percent, and Martin pointed out that changes requested by Northrop amplified the many risks shrouding the aircraft's manufacture. In August, Martin reiterated its concern for the shortage of engineers and the project's uncertainties, adding that perhaps further production expenditures should be postponed. By March 1944, the Baltimore plant still lacked tooling, and Martin had rescheduled delivery of the first B-35 to 1947. Not surprisingly, the AAF's headquarters canceled the Martin production contract on 24 May 1944. The decision, however, did not spell the end of the "flying wing." In November, the Air Technical Service Command's Engineering Division reported that the XB-35 project seemed worthwhile "even if the B 35 never becomes operational."

In December 1944, some 6 months after the Martin production contract was nullified, modification requests began to alter the B-35 development contract. The AAF decided that Northrop would build the first 6 B-35 prototypes (YB-35s) on the XB-35's pattern, with certain exceptions affecting individual aircraft. Soon afterward, Northrop was authorized to build 2 of those 6 prototypes as all jet models, a change so important that it actually marked the beginning of a new program. In 1945, after 2 YB-35s had been added to the first YB-35 lot to replace the 2 earmarked for jet conversion, the AAF told Northrop to manufacture the remaining 5 airplanes to more advanced specifications, a directive that automatically entailed the aircraft's redesignation as YB-35A.

In the meantime, Northrop, like Martin, had its share of problems. The poor showing of the N-9 and the impact of the war had not helped the experimental program. In 1941, Northrop believed the first XB-35 could be delivered in November 1943. But by May 1944, the best estimate for the XB-35's first flight was August 1945, another optimistic prediction that would not materialize.

The initial flight of the first XB-35, from Hawthorne to Muroc Army Airfield, California, took place at long last on 25 June 1946 and lasted 45 minutes. Two AAF test pilots, after maneuvering the first XB-35 during its initial and second flights, termed the experimental flying wing "satisfactory, trouble free." Yet, once again, this encouraging appraisal was to prove wrong.

Gear box malfunctions and propeller control difficulties prompted the XB-35's grounding on 11 September 1946, less than 3 months after the aircraft's first flight. Flying was not resumed until February 1948, after many modifications had taken place that affected the aircraft's engineering as well as the entire experimental program.

The first XB-35 underwent only about 24 hours of testing, all of which were accumulated in 19 contractor flights. The second XB-35, also covered by Contract W-535-ac-21920 of November 1941, fared even worse. First flown on 26 June 1947 (a slippage of 3 years), the plane was tested for approximately 12 hours. As in the first XB-35's case, Northrop pilots did the testing. Only 8 flights were accomplished.

Since most of the serious troubles encountered during testing were attributed to the XB-35's dual rotation propellers and gear boxes, significant modifications were undertaken. In February 1948, flights of the first XB-35 were resumed, this time with single rotation propellers and simpler gear boxes installed. The new installation began to operate without exhibiting any particular mechanical difficulties, but test pilots immediately reported considerable vibration and reduced performance. Moreover, the modified XB-35's landing gear doors still failed to close after gear retraction, a malfunction that had plagued the 1947 tests.

The cost of the first XB-35 had initially leaped from an estimated $2.9 million to a substantial $14 million, and other financial setbacks were on the way. In February 1947, Northrop reported that the 2 all jet prototypes (YB-49s) and the first 6 YB-35s (built to XB-35 specifications) were either complete or nearing completion. However, the originally allocated $23 million would cover construction of only 3 or 4 of these aircraft. An additional $8 million would probably finance completion of these 8 planes, and $16 million would make it possible to complete all 13 (counting the 5 YB-35As included in the program changes of 1945). On 28 May 1947, $12 million was approved for cost overruns $4 million below Northrop's estimate. At the end of January 1948, Northrop again reported that an additional $4.4 million would be required to complete all 13 aircraft.

By mid 1948, the XB/RB-35 program had started to show definite signs of an approaching demise. To begin with, a propeller driven bomber could not match the performance of jet bombers already in development and nearing the production stage. In addition, the "flying wing" in its mid 1948 configuration was less stable than a conventional wing fuselage aircraft, and thus made an inferior bombing or camera platform. The factor that kept the program alive was the multi million dollar investment in the aircraft's development, with no tangible gain for the operational forces. Such failing most likely accounted for the Air Force's decision to get a reconnaissance version of the jet equipped YB-35s, first ordered in 1945. The decision, as formalized in June 1948, called for the production of 30 aircraft, due to be known as RB-49As. As it turned out, the RB-49 project, like other "flying wing" ventures, proved unsuccessful. In the meantime, and again because of the money involved, the Air Force continued to attempt rescuing the original XB-35 program. For example, a study was underway in mid 1948 to determine the feasibility of producing the B-35 for the air refueling role.

Proposals for conversions and modifications of the experimental B-35s increased during the second half of 1948. Both contractor and Air Force still hoped that a tactical or strategic mission could be found for the aircraft. Yet, the odds were not encouraging. In August, Northrop indicated that existing experimental contracts could be completed with the funds already allotted if no further changes were made, but Air Materiel Command promptly pointed out that such a procedure would be self defeating. Changes were necessary, the command insisted, to solve the vibration problems created by the single rotation propellers. Also, the XB-35's intricate exhaust system caused tremendous maintenance difficulties, and the cooling fans of the R-4360 engines were beginning to fail due to metal fatigue. The only solution, the Air Materiel Command believed, was to convert every B-35 prototype to a 6 jet configuration.

By the end of 1948, modification plans had evolved further. Five YB-35s and 4 YB-35As were to be equipped with Allison J35-A-17 jet engines (6 per aircraft), fitted with cameras, redesignated RB-35Bs, and used for reconnaissance. In addition, 1 YB-35A was earmarked for static tests, a second YB-35B, after being re-engined with 6 Allison jets, was to serve as a reconnaissance prototype for the B-49 program, and a third jet converted YB-35A would be fitted to serve as a test bed for the T-37 turboprop engine being developed by the Turbodyne Corporation, a Northrop subsidiary. Referred to as the EB-35B, the test bed aircraft (last of the 13 prototypes included in the B-35 experimental program) would be capable of carrying 2 T-37 engines, although only 1 would be initially installed. Finally, a flexible mount gear box would be fitted in the second XB-35 to try stopping the vibrations caused by the aircraft's single rotation propellers. All this, the Air Materiel Command calculated, could probably be done with an additional $13 million.

By the end of fiscal year 1948, development costs of the experimental B-35 had reached $66,050,506 (Including $1,644,603, which paid for conversion of 2 YB-35s to 6 jet equipped B-49 prototypes). More than one third of this amount had been spent on the first contract (535-ac-21920). This cost plus fixed fee contract, as amended in January 1942, gave the Air Force 2-XB 35s for a final sum of $25,632,859, some $21 million more than originally estimated by the AAR. The remaining $40,417,647 covered the second and last cost plus fixed fee contract (535-ac-33930) which, as supplemented by Change Order No. 11, totalled $24,417,647, excluding cost overruns of $12 and $4 million, approved respectively in April 1947 and April 1948.

Faced with a $13 million modification proposal at a time when money was especially scarce, Air Force enthusiasm for the B-35 conversion program fell sharply. In August 1949, the 2 XB-35s and the first 2 YB-35s were scrapped. And while the decision did not signify the official end of the program, its fate was determined soon afterward. In November, the Air Staff canceled plans to convert remaining YB-35s and YB-35As, pointing out that no requirements existed that a "flying wing" could fulfill as efficiently as more conventional aircraft.

A total of 15 XB-35s were accepted. Two XB-35s and 13 YB-35s were paid for and also accepted, in theory. In actuality, the Air Force hardly took possession of the B-35 lot. Some of the aircraft were diverted to the B-49 program, and most others, although finally completed, were immediately scrapped.

Scrapping of the remaining YB-35 types started in December 1949 and ended in March 1950, when the disassembling of the EB-35B test bed began.



NEWSLETTER
Join the GlobalSecurity.org mailing list



 
Page last modified: 24-07-2011 04:34:17 ZULU