Origin of Convair B-58 Hustler

Last revised July 1, 2000



The Convair B-58 Hustler was the first supersonic bomber to be put into operational service, entering service with the USAF in March of 1960. Although the B-58 was destined never to fire a shot or drop a bomb in anger, it provided a key component of the Strategic Air Command's deterrent capability during the 1960s. Despite its high performance and sophisticated equipment, the service of the B-58 was destined to be rather brief, the aircraft serving with the Strategic Air Command for only a decade before being consigned to storage. Part of the reason for this rather short service was the B-58's rather high accident rate, but the major factor was the intercontinental ballistic missile, which entered service at the same time as the B-58.

The origin of the B-58 can be traced back to the period just after the end of the Second World War, at the time of the creation of the independent United States Air Force. In May of 1947, Maj. Gen. Curtis E. LeMay, at that time Deputy Chief of Air Staff for Research and Development, wrote a letter to Lt. Gen. Nathan F. Twining, chief of the Air Materiel Command, to request that work begin on a new jet- powered medium bomber that would be ready for service by the late 1950s. The bomber should have a combat radius of 2500 miles, a cruising speed of at least 500 mph, and a gross weight of 170,000 pounds. It was proposed that the development of such an aircraft would follow the development of the B-52.

General LeMay's proposal led the Air Staff to solicit ideas from the leading US maker of bombing aircraft, the Boeing Airplane Company, as well as to several other manufacturers. At this stage, the project was rather ill-defined. In October of 1947, things had begun to firm up sufficiently that the War Department submitted a requirement for a new medium bomber to the aviation industry. The aircraft was to weigh less than 200,000 pounds, have a 2000 mile radius, and be able to carry a 10,000 pound bombload. It was tentatively assigned the designation XB-55. Boeing submitted the winning proposal, and a Phase I contract was initiated with FY 1948 funds.

However, in the immediate postwar environment, funding for military projects was in short supply and it was decided that the initial design study for the XB-55 would be converted into a paper study to explore new aeronautical technologies. In particular, the Air Force began to explore the potential of delta wing configurations and began to consider the possibility of bomber designs capable of supersonic flight.

Some of this work had actually gotten started before the advent of the XB-55 project, and several companies had launched informal studies. Among the initial approaches to the design of a long-range supersonic bomber was the Generalized Bomber Study (better known as GEBO). GEBO began with the exploration of the the feasibility of a delta-winged aircraft weighing about 150,000 pounds. This began in October 1946 under an Air Force contract given to Convair, since that company had the most experience with delta-winged aircraft. Pre-GEBO studies by Convair of the abortive XF-92 delta-winged interceptor had given that company valuable experience with delta wings.

The delta wing was basically the idea of Dr. Alexander M. Lippisch, a German aeronautical engineer, although NACA had independently explored many of the advantages of delta wings during the war. In postwar years, US government agencies and many US aircraft corporations studied captured German reports on delta-winged aircraft.

By June of 1948, Convair had looked at 10,000 different configurations which explored the effects of different wing areas, aspect ratios, thickness and sweep. In addition, several different types of propulsion systems were considered, both turbojet and turboprop.

At the suggestion of the AMC, the USAF asked Convair to continue its study on the development of future long-range supersonic bombers. This study was formalized in June of 1949 with the granting of a contract for further detailed study

On January 27, 1949, the AMC was directed to cancel the XB-55, since the projected B-47 production rate had reached the point that another subsonic medium bomber would be unnecessary. However, the general requirement for a high-performance medium bomber remained intact.

One of the positive results of the cancellation of the XB-55 project was that it freed up some scarce funds for additional development. Brig. Gen. Donald Putt, Director of the Research and Development Office and Deputy Chief of Staff for Materiel, recommended that the AMC ask the aircraft industry for new and possibly unconventional proposals for intercontinental bombers. A second Generalized Bomber Study (known as GEBO II) was initiated. The design parameters were a a radius of 1200 to 2500 miles with a 10,000 pound bombload, a cruising speed of more than 450 knots, a combat altitude greater that 35,000 feet and a takeoff distance of less than 6000 feet.

In January of 1950, Convair, as part of its work on GEBO II, began to explore a parasite concept. They proposed a fairly small delta-winged aircraft which would be carried part-way to its target underneath a B-36. The aircraft was to carry a two-man crew and would have four turbojet engines. The aircraft would have a composite construction, with a droppable pod containing a bomb bay, a radar scanner, three expendable engines, and the fuel. Launch weight was 100,000 pounds, but landing weight was only 17,900 pounds. Maximum altitude was 48,500 feet. Maximum speed over the target was Mach 1.6, and service ceiling before bomb drop of 52,000 feet. No defensive armament was to be carried, since it was expected that the high performance of the aircraft would make it immune to interception.

The Air Force was highly interested in this parasite concept, but there was some opposition. Many felt that a parasite bomber would be much more expensive than a single aircraft designed to accomplish the same mission, and that the mothership/parasite combination would be quite vulnerable to attack while attached.

In April of 1950, the GEBO II specification was changed to provide for a radius of 3500 to 4500 miles, with speeds as great as Mach 1.5. This changed specification was based on Convair's parasite proposal. By the fall of 1950, Convair had settled on a 100,000-pound aircraft powered by five engines. Three engines would be expendable, with one of the engines being mounted in the centerline pod itself and one expendable engine being mounted in a pod underneath each wing. The centerline pod would also contain fuel and a single nuclear weapon. The main module had a delta wing with two turbojets in partially buried wing nacelles. Once airborne, the B-36 would carry the parasite 2000 miles toward the target, release it and return to base. The parasite would then use its five engines to accerate to a Mach 1.3 cruising speed. Over the target, the speed would increase to Mach 1.5. The parasite would then release the pod containing the nuclear warhead and return home at Mach 1.3. Once safely out of the combat zone, the aircraft would drop its two wing-mounted expendable engines and complete the trip back home at Mach 0.9. The aircraft would have no defensive armament, but it would be equipped with a full suite of electronic countermeasures equipment.

In the meantime, the Boeing Airplane Company, now freed up by the cancellation of the XB-55 project, began to study the possibility of a high-performance medium bomber. Performance objectives included a combat radius of 3000 miles at an altitude of 50,000 feet. The aircraft would be capable of supersonic speed of Mach 1.3 within 200 miles of the target. After looking at several different configurations, the Air Force selected the Boeing Model 484-405B as having the highest potential. The 484-405B was a fairly conventional design, with a low aspect ratio, high-mounted wing with a sweepback of 47 degrees. A bomb bay similar in size to that of the B-47 would be provided. Gross weight was 200,000 pounds. The aircraft was to be powered by four Pratt & Whitney J57-P-5 afterburning turbojet engines. The engines were to be mounted side-by-side, two in the inboard section of each wing. Because the wing was thin in order to make it possible to achieve supersonic performance, the fuel had to be housed entirely within the fuselage. The fuselage housed a pressurized cabin for a crew of three. A remotely-controlled tail turret was to be fitted.

By the end of 1950, the Bombardment Branch of the Air Materiel Command's Aircraft and Guided Missiles Section began to prepare a detailed military specification for both the Boeing and Convair proposals. Based on the AMC proposal, which was in turn based on input from both the Boeing and Convair design studies, requests were made for funds for beginning projects. The supersonic bomber was now officially a part of the Air Force's future plans.

On January 26, 1951, following the completion of the detailed study, Convair proposed that it develop a long range supersonic reconnaissance bomber. The project was given the number MX-1626 by the AMC under contract AF33(038)-21250. The contract called for partial Phase I development (initially without a mockup) of a bomber/ reconnaissance aircraft based on the GEBO II studies. However, the Convair proposal now had only three engines rather than five, with two being permanently mounted in the wing nacelles and one expendable engine being mounted in the droppable pod.

In February, the competing Boeing project was given a development contract by the AMC under the designation MX-1712 and contract AF33(038)-21388. Boeing's contract called for Phase I development of two bomber/reconnaissance aircraft through wind tunnel testing, engineering, and mock-up. Initial flight dates for both designs were tentatively set for late 1954.

The MX-1626 was a two-seat delta-winged aircraft consisting of two main components--a lower droppable bomb-pod and an upper main return component. The return component was a complete aircraft with a tricycle undercarriage to be used only for landing. The aircraft was to be launched from a trapeze which extended downward from its mother craft, but there is a Convair drawing showing the installation of a jettisonable landing gear that permitted takeoffs when the pod was fitted. The return component featured a delta wing with an area of 1200 square feet and a total span of 47 feet. The fuselage was 82 feet long. At the rear of the fuselage was a triangular-shaped vertical tail. A pair of nonafterburning General Electric J53-GE-X25 turbojet engines were mounted in midwing pods. The long pointed pod was integrated into the bottom of the aircraft, and featured three large fins separated by 120 degrees. The free-falling bomb pod was to be roll-stabilized by the control surfaces in the two upper tails. A third J53 engine was to be mounted inside the pod and would be expended when the pod itself was dropped. A maximum speed over target of Mach 1.7 was anticipated, and a maximum total mission radius (carrier plus parasite) of 4000 nautical miles was anticipated.

Convair's parasite proposal turned out to be very short-lived. The parasite idea had arisen at a time when cost factors were particularly important, and it was thought that such an approach would provide a cost-effective answer to the problem of long-range strategic bombing. However, it soon became apparent that the two aircraft would require complex navigational equipment so that they could find each other on the return part of the mission. While joined, the two aircraft would be especially vulnerable to attack. In addition, the two-aircraft attack system would be much more expensive to build and maintain than a single bomber. Consequently, in December of 1951 the MX-1626 design was drastically revised. The parasite idea was abandoned in favor of a single aircraft that would be capable of being refuelled in midair. The third expendable engine in the bomb pod was eliminated, and afterburners were added to the aircraft's remaining two engines. A landing gear capable of supporting both landings and takeoffs would have to be provided. Gross weight rose to about 126,000 pounds and the number of crew members rose to three (pilot, navigator-bombardier, and defense systems operator).

On February 1, 1952, the USAF issued General Operational Requirement SAB-51, where SAB stood for Supersonic Aircraft Bomber. It called for a multi-mission strategic reconnaissance bomber capable of carrying 10,000 pounds of bombs. It had to be capable of operating in all weather conditions, and had to be able to achieve a combat radius of 5000 miles with a single outbound inflight refuelling. It had to be capable of supersonic performance at altitudes of 50,000 feet or more and of high subsonic performance at lower altitudes. It was considered important that the aircraft be fairly small, since this would reduce the radar reflectivity and make the aircraft harder to detect. The Air Force wanted production to begin within five years.

On February 26, 1952, the SAB-51 GOR was revised in a document which came to be known as Directive Number 34. It was conceded that it was unrealistic to expect the rapid development of a high-altitude, long- range supersonic bomber that could also be suitable for low-altitude high speed missions. Consequantly, the low-altitude performance requirement was dropped. Following discussions with the Air Council and representatives of the ARDC, SAC, the Rand Corporation, and the Scientific Advisory Board, the Air Force endorsed this recommendation, and the revised SAB became formalized on September 1, 1952 as SAB-52-1. However, the Air Force still wanted the aircraft by 1957.

At the end of February 1952, General J. W. Sessums, ARDC Deputy for Development recommended that it would be better to forego the traditional industry-wide competition that would ordinarily be held for the supersonic bomber project. Time and money would be saved if contractors could be selected on the basis of the proposals already submitted. Although the AMC felt that the Boeing and Convair proposals offered the best hope for a supersonic bomber, the AMC had requested informal proposals from other manufacturers, including Douglas, Lockheed, Martin, and North American. However, only two of the last four companies actually submitted proposals, and these were not very interesting. Shortly thereafter, the Wright Air Development Center endorsed this strategy and called for a competition between Boeing and Convair, the only two companies to have submitted proposals that were of any significant interest. The Air Force was now committed to the advanced bomber project, and placed heavy emphasis on the MX-1626 and MX-1712 programs. It requested that two parallel Phase 1 projects be initiated, thus engaging Boeing and Convair in an official competition. It was anticipated that contracts would be issued to both competitors in the fall of 1952 for detailed designs and mockups, followed by the selection of a winning design in February or March of 1953. The emphasis would continue to be on minimum size and maximum altitude and speed performance.

The financing of the Phase I development of two parallel projects was extremely difficult to support, especially during a period of financial austerity. The Boeing MX-1712 program had benefited somewhat from the XB-55 cancellation, which freed up some Boeing developmental funding for the new project, but Convair's MX-1626 was experiencing a severe funding problem. In late February, the MX-1626 program was almost cancelled due to the lack of funds, and the project remained in some danger until May 15, when enough additional funds were obtained to keep the project going.

In June of 1952, Convair proposed that they move the engines to nacelles placed underneath the wing. The engines were to be either two J75-P-1s, two J67-W-1s, four J57-P-7s, four J73s, or two J77s.

Directive 34 had also dictated that the project use the weapons system concept, in which the equipment, weapons, electronics, and components of the aircraft would be developed as an integrated whole to ensure that each component would be compatible with the others. By mid-1952, both Boeing and Convair had made considerable progress in bringing their projects into compliance with the weapons system philosophy. In the process of making their designs conform with the requirements of Directive 34, Convair's MX-1626 was now known as MX-1964 and Boeing's MX-1712 was now called MX-1965. The USAF designations B-58 and B-59 were tentatively assigned to the two competing projects, even though no production orders were yet forthcoming.

In the summer of 1952, the Wright Air Development Center concluded that a less costly alternative would be to select just one of the two competitors even before the design and mockup stage was reached. The small bomber concept was endorsed by the Air Force Council and by General Hoyt S. Vandenberg, who was Chief of Staff of the Air Force. However, General Curtis LeMay, head of the Strategic Air Command, generally favored larger bombers with longer ranges. SAC felt that high performance alone would not necessarily assure mission success, and that the small supersonic bomber's lack of range would prevent it from operating without midair refueling from most forward bases. Despite SAC's objections, the Wright Air Development Center recommended that the Boeing/Convair competition be stopped. Even though the Air Force thought that Convair's estimates of the MX-1964's supersonic drag and gross weight were overly optimistic, the Air Force felt that the Convair design was superior to the Boeing proposal, since they felt that the Boeing design would offer insufficient supersonic capabilities, and on November 18, 1952, General Vandenberg formally announced that Convair was the winner of the contest.

On December 2, 1952, it was announced that the designation of the new bomber would be B-58. The Deputy Chief of Staff for Development endorced a production schedule based on the four-year procurement of 244 B/RB-58s. The first 30 would be used for testing, and they would be reworked on the production line as problems appeared and were solved. This plan was based on the "Cook-Cragie" philosophy, in which the prototype phase was skipped. This plan, named for General Laurence C. Cragie, Deputy Chief of Staff for Development, and Orval R. Cook, Deputy Chief of Staff for Materiel, was rather risky and was really applicable only when there is a fairly high degree of certainty that the aircraft is actually going to go into production. The F-102 interceptor had been designed according to this principle.

On February 12, 1953, the Air Force gave Convair the go-ahead to begin detailed Phase I work on the XB-58 and XRB-58. At this point, only the basic concept had been approved, not any detailed design. On March 20, the Air Force indicated its acceptance of a firm configuration with a 60-degree delta wing with the trailing edge swept forward by ten degrees. A small amount of leading edge camber was provided to reduce drag due to lift. The aircraft was to be powered by four General Electric J79 turbojet engines, with the two inboard units mounted on underwing pylons and the two outboard engines mounted on the wing upper surface.

Even though Convair had been selected over Boeing, many revision of the MX-1964 design were to follow. At the same time, development problems with Convair's F-102 interceptor confirmed the Air Force's suspicion that the initial estimates of the aerodynamic drag of a delta winged aircraft had been overly optimistic. NACA engineer Richard T. Whitcomb's ideas on the Area Rule had been verified in December of 1952, which suggested that the cure for excessive transonic drag was to equalize the cross-sectional area at all points along the fuselage, thus producing a narrow ("coke bottle") fuselage in the region of the wing. The crew was to be three--a pilot, a navigator/bombardier, and a defensive system operator. The defense was to be one 30-mm gun mounted in a remotely-controlled tail position.

The first development engineering inspection took place on August 17/18, 1953. At this stage, the B-58 mockup was known as Configuration II. The requirements matched fairly closely with the specifications issued by Convair in August of 1952 as well as with the USAF demands issued in the September 1952 GOR. At this stage in the design, the fuselage of the B-58 still consisted of an upper component and a lower pod that were integral with each other rather than being separated by a pylon. The return component had a flat fuselage undersurface once the disposable pod component had been jettisoned. In addition, nose gear requirements were complicated by the fact that both the pod and the return component required a nose gear. In the development engineering inspection of August of 1953, it became obvious that this pod would have to be completely redesigned. In October of 1953, the Air Force authorized Convair to shorten the pod to a length of 30 feet and to separate it from the fuselage by a pylon. In addition, the search radar was taken out of the pod and put in the nose of the upper compartment. The droppable nose gear was eliminated, and external fuel tanks were added to compensate for the fuel lost due to the shorter pod, and the postions of the navigator/bombardier and defensive systems operator were reversed.

The revised B-58 design was known as Configuration III. External fuel tanks were added to the wing tips in the interest of longer range. Configuration III also omitted the jump seat which had been requested in the original military characteristics. However, there were still problems being uncovered by the wind tunnel testing at the Wright Air Development and at the NACA. In 1953, the contractor and the Air Force had decided to mount the four turbojet engines inside two split-cell strut-mounted underwing nacelles, reminiscent of the inner two-engine pod of the B-47 Stratojet. It was thought that this configuration would save weight, ease engine maintenance, and facilitate retrofit of J57 engines with new J79s. However, wind tunnel testing indicated that the split-cell nacelles induced extra drag on the pod-carrying B-58. These problems caused a postponement of the Configuration III mockup from May to September 1954.

It was planned that the first 30 aircraft would be used for tests and evaluation. The first 18 of these would be powered by Pratt & Whitney J57 engines, while the remainder would be powered by four General Electric J79-GE-1 turbojets (known in the prototype form as the J73-X24A).

By August of 1954, what was to prove to be the final B-58 configuration was chosen. The engines were now mounted inside four individual underwing pylons, and all fuel was contained internally and in the podded lower component. The fuselage was aligned to the modified transonic area rule for supersonic speeds. The external wing tanks were eliminated, and the tail area was increased to 160 square feet.

In the meantime, the Strategic Air Command was still unhappy with the B-58. A mid-1954 staff study had actually excluded the B-58 from its projected 51-wing bomber force of 1958-1965. There were fears from even the B-58's most fervent supporters that even the latest configuration might not meet all the requirements of the military specification, but they still believed that the aircraft should be built even if the Air Force could not actually use it as originally intended. By this time, almost 200 million dollars had been spent. There was some thought to reorienting the program to a research and development effort, and even some thought to cancelling the program altogether. In June of 1955, a decision was made to restrict the program to just 13 aircraft. However, on August 22, 1955, this decision was reversed again and the B-58 was once again authorized for production. A wing of B-58s would be ready for service by mid 1960. However, there was at this time no mention of which branch of the Air Force that this wing would actually belong to.

In December of 1955 a definitive contract was issued to Convair for 13 aircraft and 31 pods. A second Letter Contract, AF33(600)-32841, issued on May 25, 1956, provided additional money to maintain B-58 production at a minimum sustaining rate through October of 1956. In the fall of 1956, the Air Force would decide if it should buy more aircraft.

Sources:


  1. American Combat Planes, Third Enlarged Edition, Ray Wagner, Doubleday, 1982.

  2. Post World War II Bombers, Marcelle Size Knaack, Office of Air Force History, 1988.

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

  4. Convair B-58 Hustler: The World's First Supersonic Bomber, Jay Miller, Aerofax, 1997.