B-58 Hustler Design
The B-58 had a delta wing design that included many firsts for strategic bombers. It had four turbojet engines with afterburners, and was the first supersonic aircraft with engine pods mounted outboard on the wings. The wings had a span of 56 feet, 10 inches and were swept 60; the length was 96 feet, 9 inches; the height at the tail was 29 feet, 11 inches; and the maximum takeoff gross weight was 160,000 pounds. The crew consisted of a pilot, navigator, and defensive systems operator seated in tandem. While a retrofit provided each crew member an individual ejection capsule for supersonic bailout, the cramped crew cockpit made long missions like airborne alert very exhausting for the crew.
The configuration of the B-58 was characterized by a delta wing and the absence of a horizontal tail. The wing had 60° sweepback at the leading edge, an aspect ratio of 2.09, and airfoil sections that varied in thickness ratio from 3.46 percent at the root to 4.08 percent at the tip. Conical camber was employed in the leading edge to reduce drag at lifting conditions and thus increase cruising efficiency. (A conically cambered wing is one which has a leading-edge camber shape formed from part of the surface of a cone whose apex is located at the longitudinal plane of symmetry of the wing. The amount of camber accordingly increases progressively with spanwise distance from the fuselage.) Absence of a horizontal tail for trimming prevented the use of any trailing-edge high-lift devices. Elevons for pitch and roll control extended from the side of the fuselage to the outboard engine nacelles. All the controls were power operated.
The four General Electric J-79 turbojet engines were located in individual nacelles suspended below the wings on sweptforward pylons - an arrangement analogous to that employed on the B-47 and B-52. Area ruling was employed in the high-fineness-ratio fuselage with the single vertical fin and rudder mounted at the rear. Crew members consisting of pilot, bombardier-navigator, and defense-systems operator were housed in a tandem arrangement to aid in maintaining the desired long, narrow shape of the fuselage. Each crew station was an individual rocket-powered escape module capable of providing safe crew egress even at Mach 2.0. The entire crew compartment as well as the wheel wells and electronics bay were pressurized and air-conditioned. Cooling of the tires and electronic equipment was required because of the high temperatures generated by prolonged flight at Mach 2.0. Landing gear consisted of a tricycle design with each main gear having eight wheels arranged in two rows of four. The large number of wheels was used to maintain the landing-gear footprint pressure within acceptable limits while, at the same time, allowing the use of small diameter wheels capable of being stored in the thin wing with only small fairings bulging from the lower wing surfaces. The conventional nose gear had two wheels; a braking chute was provided to assist in stopping the aircraft on landing rollout.
A large streamlined pod under the fuselage of the aircraft served the dual purpose of housing a nuclear warhead (bomb) and several thousand gallons of fuel. Large amounts of fuel were also carried in the wings and fuselage. The pod was divided into two main parts: the portion containing empty fuel tanks was to be jettisoned on the outboard flight to the target, and the other component containing the warhead, as well as additional empty fuel tanks, was then to be dropped at the target. The B-58 might thus be considered as a sort of two-stage system. Armament on the aircraft consisted of a single six-barrel 20-mm rotary cannon controlled by the defense-systems operator.
The B-58 did not have a bomb bay but could carry one nuclear weapon externally with the centerline fuel pod fitting over it. Four weapons, whether nuclear or conventional, could be carried on external hard points if the fuel pod was eliminated, thus degrading the aircraft's range further. With fewer aircraft deployed, a larger payload was needed to deliver as many weapons as its predecessor, the B-47. But the amount of space available for modifications was less than that for the B-47. In an era of improving SAM technology, ECM modifications have been continually needed to meet the evolving threat, and space was not available for additional ECM.
To give a light, strong, stiff structure for the thin high-fineness-ratio elements of the aircraft, the B-58 made extensive use of aluminum honeycomb panels. Most of the outer covering of the aircraft consisted of such panels having outer and inner aluminum skins bonded to a honeycomb of aluminum and fiber glass. In addition to its light weight, this type of structure had a smooth exterior surface. In service, however, problems were encountered in ascertaining and maintaining the integrity of the bonded joints.
With a gross weight of 163,000 pounds and a maximum speed of 1,321 miles per hour (Mach 2.0) at 63,150 feet altitude, the B-58 was an impressive aircraft by any standard. This performance was dramatically demonstrated in a number of record flights. Perhaps the most notable of these was the May 26, 1961, nonstop flight of 3 hours and 19 minutes from New York to Paris. Average speed for the 3,669 mile flight was 1,105 miles per hour; three in-flight refuelings by KC-135 aircraft were required. Interestingly, almost 34 years earlier on May 20 and 21, 1927, Charles A Lindbergh required 33.5 hours to make the first nonstop flight from New York to Paris - a remarkable advancement in aeronautical technology during a time period of just a little more than three decades.
In spite of the spectacular records set by the B-58, the aircraft was woefully deficient in range performance. Without in-flight refueling, the radius of action, including a 450-mile supersonic dash, was only 1,500 miles. With no supersonic dash, the maximum radius increased to 2000 miles, thus indicating the relatively poor supersonic cruising efficiency of the aircraft. Ferry range at subsonic speeds was 4025 miles. With in-flight refueling, a target distance of 4,300 miles, including a supersonic dash of 500 miles, was possible. After weapons delivery, the aircraft had a range of 1,500 miles - hopefully enough to reach a friendly base but not enough to reach the point of departure. With in-flight refueling, ferry range was 6,995 miles.
The limited range capability of the B-58 can be directly traced to the compromises required in its aerodynamic design. The Mach 2.0 dash requirement dictated the use of a delta wing with leading-edge sweep angle of 60° and a low aspect ratio of about 2. As a consequence, the value of the maximum subsonic lift-drag ratio, without the fuel and weapons pod, was only 11.3 (compare this with the value of 21.5 for the B-52G); an even lower value would be expected with the pod attached. The value of (L/D)max at Mach 2.0 was slightly greater than 5. Thus, the aircraft was not capable of efficient cruising flight at either subsonic or supersonic speeds. Aircraft configuration design for highly efficient cruising flight at subsonic speeds is well understood, as demonstrated by the B-47 and B-52 as well as by the numerous highly efficient jet transports described in the following chapter. Unfortunately, the design of a highly efficient and practical supersonic cruising aircraft still remains somewhat elusive although much progress has been made since the design of the B-58. Still more elusive is a configuration concept that enjoys high cruising efficiency at both subsonic and supersonic speeds, such as required by a commercial supersonic transport. Variable sweep, however, offered a means for achieving good subsonic cruising efficiency in combination with a reasonably efficient supersonic dash capability.
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