B-45 Tornado
Like the trouble plagued but eventually successful and long lasting B-47, the B-45 officially originated in 1944, when the War Department called for bids and proposals on an entire family of jet bombers, with gross weights ranging from 80,000 to more than 200,000 pounds. These were ambitious requirements considering the kind of airplanes being planned at the time in the United States and elsewhere. Yet, the emergence of unrealistic requirements was a common practice that would endure for decades. From experience, government officials most likely rationalized that inflating the requirements was the only way to get at least the minimum acceptable. Late in 1948, engineers of the Air Materiel Command began to point out the pitfalls of this practice. But their concern did not prevail. In 1952, many in the Air Staff also recommended caution and their efforts achieved some degree of success. Nevertheless, as the "weapon system concept" gained momentum, it became evident that the Air Force believed increasingly that mission objectives had to come first and that technology could be made to satisfy such objectives.
Unofficially, the roots of both the B-45 and B-47 aircraft could be traced to 1943, when the Army Air Forces, aware of Nazi Germany's advances in the field of jet propulsion, asked the General Electric Company to design something better than the TG-100 axial flow turboprop engine that was being developed for the Consolidated Vultee's 2 experimental P-81 escort fighters (the mass production of which did not materialize). The AAF's demands were met with General Electric's development of the 4,000 pound thrust TG-180 and the TG-190 engines, of which various models were to power subsequent bomber and fighter aircraft (The TG-180, eventually built in large quantities by the Allison Division of the General Motors Corporation, became the J35; the TG 190, continuously produced by the General Electric Company, became the J47).
For its part, North American began to attempt satisfying the AAF's requirements for a jet bomber with a design for an easy to build airframe, conventional in concept and straightforward in its aerodynamic form. Model 130, as the design was labelled in early 1944, was a mid-wing monoplane with dihedral tailplane and a retractable landing gear. North American planned to propel its new bomber with 4 jet units, grouped in horizontal pairs, 1 pair on each side of the fuselage outboard of the tailplane.
The AAF initiated the procurement of the future B-45 with Letter Contract AC-5126. This document, issued on 8 September 1944, called for the development and testing of 3 experimental B-45s, all of which were to be based on North American design 130. In time, as production of the aircraft appeared probable, North American altered the overall configuration of 1 of its 3 XB-45s. The selected vehicle was actually completed as a tactical model and, although seldom referred to as YB-45, assumed the role of a standard prototype.
The AAF originally intended to schedule a formal competition between the various contractors working on projects to satisfy the War Department's requirements of 1944. In 1946, since the early production of a jet bomber seemed highly desirable, the AAF decided to forgo the planned competition. Instead, available designs would be reviewed to determine which model could be obtained first. Four contractors were involved: North American, working on the XB-45; the Boeing Airplane Company, engrossed in the development of the swept wing, 6 jet XB-47; the Consolidated Vultee Aircraft Corporation (Convair), engaged in the XB-46; and the Glenn L. Martin Company, builder of the XB-48. The military characteristics, issued by the AAF on 17 November 1944 and embodied by the 4 projects, were specific but not restrictive. The B-45 and B-47 aircraft, the only 2 programs that went beyond the experimental stage, stemmed from the same requirements but ended having very little in common. Both were ordered as "medium" bombers, but in contrast to the B-47, which retained its medium bomber designation, the B-45 became a light bomber. The fact that the B-45, weighing 47,000 pounds and having a combat radius of 764 nautical miles, was finally listed as "light" also showed how swiftly concepts changed. Five years before, the World War 11 B-17G Flying Fortress, which weighed 37,672 pounds and had a combat radius of 873 nautical miles, was considered "heavy."
But while the XB-45 and XB-46 were nearing completion and flights of these aircraft were scheduled for 1947, the XB-47 and XB-48 in 1946 were still in the early stages of development, and 2 years might elapse before the end of their fabrication and initial flight testing. Pressed for time, the AAF opted to appraise the XB-45 and XB-46 immediately and to postpone consideration of the XB-47 and XB-48 until they flew. Then, if either the XB-47 or the XB-48 proved superior enough to supplant the new bomber being produced (which the XB-47 did) that aircraft would be bought. The AAF anticipated that the B-47's performance characteristics would exceed those of the B-45, but realistically believed that the swept wing, underslung engine nacelles, bicycle type landing gear, and other experimental features of the Boeing design would require an extended period of development. The XB-48, although more conventional than the XB-47, featured a 3 engine installation in each wing and would incorporate the bicycle type landing gear of the B-47. The XB-48 might prove to be superior to the XB-45, but any potential production of the Martin design remained several years away.
On 2 August 1946, the AAF endorsed the immediate production of the B-45. The decision did not specifically spell the end of the XB-46, but it was a poor omen. Already reduced to only 1 plane, the experimental B-46 program actually lingered until August 1947, when the AAF terminated the whole venture. Several factors accounted for the selection. First, the AAF concluded that the XB-46's projected performance most likely would be inferior to that of the XB-45. Second, the XB-46's fuselage was not configured to hold all required radar equipment. Finally, since the XB-45's design only departed slightly from proven configurations, it was the most logical choice prior to testing of the experimental model. The AAF's decision of 2 August prompted within 1 week the negotiation and signature of Contract AC-15569, which called for an initial lot of 96 B-45As (North American Model N-147), plus a flying static test version of the experimental type (NA Model N-130). The cost of the contract was $73.9 million.
On 17 March 1947, the first of the 3 experimental B-45s made its initial flight. The 1 hour flight, from Muroc Army Airfield, California, was conducted under stringent speed restrictions because the aircraft's landing gear doors did not close properly when the landing gear was retracted. This problem could have been avoided by installing new and available landing gear uplocks, but this time consuming installation was postponed. (As soon as World War II ended, most manufacturers had to compete fiercely for the few, limited orders. This was reason enough for North American not to delay the XB-45's flight). Nevertheless, the XB-45's demonstration was impressive. No large multi-engine jet bomber had ever been flown before (Douglas's experimental twin jet B-43, an outgrowth of the company's XB-42 Mixmaster, flew almost 1 year before the XB-45, but the XB-43 was very small and the 2 could not be compared. In the same vein, 2 German developments appearing in 1944 presented no true challenge. One of them, the Arado Ar-234, introduced by the Luftwaffe as a jet bomber, was so tiny that it rightly belonged to the fighter category. The Junkers Ju-287 only flew as a prototype designed to test a radical wing, Germany's nearing collapse presumably preventing completion of the aircraft). And, of primary importance from the manufacturer's standpoint, even though a B-45 production order had already been secured, the XB-45 flight preceded that of the still potentially competitive XB-46.
The Air Materiel Command planned an extensive test program for the 3 experimental airplanes developed by North American; each of the 3 was to be instrumented for a specialized phase of the program (In the late fifties, the various testing phases to which all aircraft were submitted were supplanted by testing categories. However, the changes affected the testing program's terminology more than its scope). The testing, however, was marred at the start by an accident that killed 2 of North American's crack test pilots and destroyed their aircraft. This accident was attributed to an engine explosion, but other contributing factors later came to light. These accounted for most of the changes specified in the B-45's production articles. Meanwhile, flight testing of the remaining XB-45s went on. Air Force pilots did not participate extensively in the initial tests. They flew only about 19 hours, while the contractor logged more than 165 flight hours on the 2 surviving aircraft. This total was accumulated in 131 flights, conducted before the Air Force took delivery of the planes. The Air Force accepted 1 XB-45 on 30 July 1948; the other, on 31 August. The acceptances were conditional because the pressurization systems of both planes did not function.
After North American fixed the pressurization of the XB-45 cabins, additional tests were undertaken. Air Force pilots flew a total of 181 hours in 1 XB-45 between August 1948 and June 1949, when an accident damaged the aircraft beyond economical repair. The remaining XB-45, although constructed to serve as a prototype, had limited testing value due to an initial shortage of government furnished equipment. Still, the Air Force put another 82 hours of flying time on the plane. A USAF flight test crew delivered the airplane to Wright Patterson AFB, Ohio, where equipment was installed for bombing tests at Muroc AFB, California. Unfortunately, the YB-45 proved to be an unsatisfactory test vehicle because it required excessive maintenance. Only 1 mission was accomplished between 3 August and 18 November 1949, and that mission was to evaluate the long awaited components. The airplane was used for high speed parachute drops after November 1949, but on 15 May 1950, it was transferred to the Air Training Command to serve as a ground trainer.
As might be expected, the crash of an XB-45 precipitated a thorough investigation. As suspected, special wind tunnel tests confirmed that the aircraft's insufficient stabilizing area had contributed directly to the accident. The lack of ejection seats, moreover, had practically eliminated the pilot and co pilot's chances for survival. As a result, 2 ejection seats were installed in the other experimental planes, while an advanced ejection system was being devised for the forthcoming production aircraft. In addition, future B-45s would be equipped with wind deflectors, placed in front of the escape doors from which the other 2 crew members (bombardier-navigator and tail gunner) would have to bail out in case of an emergency. North American also altered the structural configuration of the production vehicle. Most noticeable was a redesign of the nose panel. Finally, the aircraft's stabilizer area was increased, and the tailplane was lengthened from 36 to almost 43 feet.
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