v1.1.0 / 01 nov 01 / greg goebel / public domain
* The rapid development of American Mach 2 combat aircraft in the 1950s inevitably led to the development of a Mach 2 strategic bomber, the "B-58 Hustler". As it turned out, a Mach 2 bomber was not a particularly practical idea; the B-58 was only produced in small numbers and did not remain in service for very long.
However, the B-58 was one of the sleekest and most impressive combat aircraft ever built, and even in the 21st century the B-58 Hustler still looks futuristic. This document describes the rise and fall of the B-58.
* The Convair company of Fort Worth, Texas, USA, began conceptual studies on a supersonic bomber in October 1946, with the investigation designated "Generalized Bomber (GEBO)". GEBO led to a second, more practical study designated "GEBO-II", begun in March 1949, when the Cold War was beginning in earnest.
This was two years after Boeing had test-flown the first modern jet bomber, the B-47 Stratojet, and three years before Boeing would test-fly the B-47's bigger and badder sister, the B-52 Stratofortress. At the time, there were no supersonic combat aircraft in operational service, and first-line bombers of the US Air Force (USAF), such as the Convair B-36, were primarily piston powered. However, aeronautical engineering was advancing by leaps and bounds at the time, and it paid to be forward-looking.
Convair engineers focused on the delta wing for the supersonic bomber. The concept of the delta wing had been invented by Dr. Alexander Lippisch of Germany in the 1930s. Although the Germans never got a powered delta-wing aircraft into the air during the war, after the war Convair had tested the delta wing on the XF-92 experimental interceptor in 1948. The XF-92 would lead along another path to the Convair F-102 Delta Dagger and its follow-on, the superlative F-106 Delta Dart.
The delta wing has a number of disadvantages: as a tailless aircraft, it cannot use flaps, and so has a long takeoff run; its low wing loading makes for a rough ride at low altitude; and it loses speed quickly on turns, limiting maneuverability. However, it is a simple, robust design that offers high straight-line speed and plenty of space for fuel tanks, and was used in many first-generation Mach-2 combat jets.
Convair engineers originally focused on "parasite bomber" schemes, involving a relatively small supersonic bomber that would be carried by a B-36 to the target area. The USAF's Strategic Air Command (SAC), which operated the service's nuclear-strike bombers, wasn't impressed by the parasite scheme. Fortunately, Convair was also working on a more conventional self-launched bomber, and after a test program involving wind tunnel models, rocket-boosted models, and radio-controlled air-dropped models, in October 1952 the USAF selected Convair to develop a full-scale supersonic bomber prototype.
The Convair supersonic bomber was to be powered by the General Electric (GE) X24A afterburning turbojet engine, then in development. The X24A would be produced as the GE J79, which would power many supersonic aircraft, such as the Lockheed F-104 Starfighter and the McDonnell-Douglas F-4 Phantom II. Initial prototypes of the supersonic bomber would be powered by the Pratt & Whitney J57 engine until the J79 became available.
Convair assigned the supersonic bomber project the designation "MX-1964". Boeing was working on a competing swept-wing supersonic bomber project with the designation of "Model 484" or "MX-1965". In mid-1952, the Air Force gave the Convair bomber the service designation of "XB-58" and the Boeing bomber the service designation of "XB-59".
In October 1952, the Air Force selected the Convair XB-58 for further development. This led to award of a contract in February 1953, specifying delivery of two prototypes of the Convair aircraft, including one "XB-58" bomber prototype and one "XRB-58" reconnaissance aircraft prototype. They were also known by the USAF "weapon system" designations of "WS-102A" and "WS-102L" respectively, and by the company designation of "Convair Model 4".
* While the XB-58 was clearly seen at the outset as a delta-winged aircraft with four J79 engines and stores in a pod carried under the belly, little else was certain, and a wide range of different configurations were considered, some with engines podded together, some with engines above and below the wing, and so on.
One important design feature was presently added in the form of "area ruling", a concept devised by engineer Richard Whitcomb of the US National Advisory Committee for Aviation (NACA), one of the predecessors organizations of the current US National Aeronautics & Space Administration (NASA). Whitcomb's area ruling was based on the concept that an aircraft would have better supersonic performance if it had as constant a cross-sectional area as possible along its length. This meant that as the wing span increased with cross-section, the fuselage diameter shrank, resulting in a "wasp-waist" or "Coke bottle" configuration that not only improved performance but generally improved an aircraft's appearance as well.
However, the XB-58 design did not really begin to converge on a solution until the spring of 1953, after Convair had been bought out by General Dynamics (GD). The final design had a delta wing with a leading-edge sweep of 60 degrees and a trailing-edge sweep of 10 degrees, with downturned wingtips. The four engines were fitted in individual nacelles slung under the wings, and a new GE T-171 Vulcan six-barreled 20-millimeter Gatling-type cannon was fitted in the tail for defense.
A single high-yield nuclear weapon was to be carried in a long belly pod. A reconnaissance pod could be fitted as an alternate payload. The pod also carried fuel and equipment. The pod was used because attempting to include the payload in the aircraft itself inflicted too much of a performance penalty.
* Unfortunately, when GD told the USAF in June 1954 that the XB-58's first flight had to be pushed back from January 1956 to June 1956, the service balked. This hardly seemed like much of a schedule slip, but the XB-58 program had already cost $300 million USD, and there were doubts among USAF brass that a Mach 2 bomber really made any sense.
Even the SAC commander, General Curtis LeMay, stated in a January 1955 memo that SAC neither wanted or needed the B-58, as the B-58's range was only half that of the B-52. There were wider issues as well: subsonic bombers could do the conventional bombing job much more cheaply, and the future of strategic nuclear strike seemed to clearly lay with the intercontinental ballistic missile (ICBM), then in development by both the USA and the USSR. LeMay's logic was hard to argue with and indeed, would grow even harder to argue with in the future.
Nonetheless, B-58 advocates won out in the short run, with the Air Force ordering 11 more "YB-58" trials aircraft in December 1955. The first XB-58 prototype took to the air on 11 November 1956. The aircraft was fitted with GE J79-GE-1 engines, with 4,035 kilograms (8,900 pounds) dry thrust and 6,575 kilograms (14,500 pounds) afterburning thrust. As it turned out, the J79 was available in time and no B-58 was ever fitted with P&W J57s. The second prototype, which was completed simply as an "XB-58" and not as an "XRB-58", first flew in February 1957.
First service delivery of the "Hustler", as it was named, was in February 1959. In the interim, 17 more trials aircraft had been ordered, for a total of 30.
* The B-58 was a spectacular aircraft in almost every regard, elegant with its long, slender, wasp-waisted fuselage and its clean delta wing, sporting four J79 engines, with the inner pair on long swept-forward pylons and the outer pair on short stub pylons. All but the first seven B-58s were fitted with J79-GE-5A or -5B turbojets, with 4,400 kilograms (9,700 pounds) dry thrust and 7,075 kilograms (15,600 pounds) afterburning thrust. Most earlier B-58s were retrofitted with these engines.
The B-58 had long, spindly-looking, strong, tricycle landing gear to allow
ground clearance for the engines and the weapons pod. Flight controls used
redundant hydraulic systems.
GENERAL DYNAMICS B-58 HUSTLER:
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spec metric english
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wingspan 17.3 meters 56 feet 10 inches
length 29.5 meters 96 feet 9 inches
height 9.6 meters 31 feet 5 inches
empty weight 25,200 kilograms 55,560 pounds
max loaded weight 80,200 kilograms 176,890 pounds
maximum speed 2,205 KPH 1,370 MPH / 1,190 KT
cruise ceiling 19,500 meters 64,000 feet
range (typical) 6,600 kilometers 4,100 MI / 3,565 NMI
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There was no room to move around, except for a crawlway between the second and third seats. The crew was essentially strapped into their seats as they would be in a fighter. The pilot had a good view through a six-piece windscreen, with his seat offset so he didn't have to stare through the center post, but the two back-seaters had to make do with small windows on either side of their seats.
Early production featured conventional ejection seats, but after the deaths of aircrew in high-speed ejections, in 1962 a new "escape capsule" scheme was introduced that sealed each crewman into a clamshell capsule to improve his chances of survival in a supersonic ejection. The capsule would self-stabilize after ejection, had inflatable floatation devices for water landings, and featured a survival kit, including a radio, a survival rifle, and even a change of clothing. The escape capsule was also retrofitted to older B-58s.
The B-58's construction was as innovative as its appearance. Much of the aircraft was made of sandwich panel composed of fiberglass sheet faced by thin aluminum on each side, a scheme that proved both strong and heat resistant, as required for Mach 2 flight. In areas where the fiberglass sandwich wasn't strong enough to do the job, a similar sandwich scheme with thin aluminum sheet filler was substituted. In areas exposed to unusual levels of heat, as was the case in areas under the wing near the engine exhausts, a sandwich material based on stainless steel was used. The panels were held in place by titanium screws.
The end result was an aircraft with a remarkably low empty weight. There was a literally a price to pay, however, since fabricating the honeycomb sheets to the desired tolerances was a difficult and expensive process, and fitting the panels in place on the aircraft during manufacture was equally troublesome. Expensive high-precision jigs were required. Worse, replacing a panel in the field meant placing the entire aircraft in such a high-precision jig, which made maintenance difficult to say the least, particularly in comparison to other aircraft in the USAF inventory.
The aircraft's GE J79 engines were another marvel. They had an inlet spike that automatically adjusted for airflow and reduced the chances of high-speed engine stall. In afterburner, the engines could easily move the Hustler to its redline speed of Mach 2.2. They could provide even more thrust in an emergency, but the airframe itself simply wasn't strong enough to fly any faster.
The B-58 had a large fuel capacity, with a "wet" wing divided into fore and aft tanks, with a total wing fuel capacity of 34,100 liters (9,000 US gallons). The skin panels were fitted with gasketing to allow them to also serve as the tank walls. In addition, there were two tanks in the rear fuselage, with a total fuselage fuel capacity of 19,000 liters (5,000 US gallons). The weapons pods could also accommodate fuel, and in fact the fuel capacity of the aircraft was so great that it could not take off when fully loaded. It took off with an incomplete fuel load and then "topped off" from a tanker once airborne.
The rearmost fuselage tank was mostly intended as a ballast tank to maintain pitch trim as fuel was expended. Fuel trim proved to be a major problem during initial aircraft flight tests, and the aircraft's fuel system was correspondingly elaborate. The B-58 was fitted for boom-type inflight refueling, with a boom socket in the nose forward of the cockpit.
A considerable amount of engineering effort was expended on the Hustler's landing gear, which perched the aircraft about 2.75 meters (9 feet) off the ground with the weapons pod removed. The steerable nose gear had twin wheels and a travel of about 38 centimeters (15 inches). Each of the main gear had a total of eight wheels, with four mounted on two axles, with a travel of about 43 centimeters (17 inches). All three gear assemblies retracted backward.
The main gear tires were relatively small, only 56 centimeters (22 inches) in diameter, to allow them to fit inside the thin wings, which still had to be built with shallow fairings to permit the gear to fit. The tires were filled with nitrogen to a pressure of about 19 atmospheres (280 pounds per square inch), which was about eight times the pressure of an automobile tire.
The aircraft's tires had to bear up under tremendous loads at high rolling speeds and often blew out. Extended taxiing was ruled out and sharp turns had to be avoided. After a hot landing, the tires were often cooled by a blower system pulled out on the runway by the ground crew. In fact, on touchdown the Hustler's tires tended to tear up bits of the runway, until the Air Force figured coated the runways down with a mixture of sand and epoxy to make the surface more durable. Delta-wing aircraft tend to land fast, and so the B-58 had a ribbon-style drag parachute to reduce the landing roll.
A state-of-the-art avionics suite was included. A Raytheon targeting radar was fitted in the nose, and the pilot was assisted by an autopilot that provided a "watchdog" capability, preventing the pilot from taking maneuvers that would be dangerous in supersonic flight. The bombardier-navigator, in the second seat, used a Sperry-Rand ASQ-42V electronic navigation system that was highly capable and accurate, though as it was built with 1950s technology it weighed about 550 kilograms (1,200 pounds). Today a system with better capabilities could be picked up with one hand.
The defense systems operator (DSO) sat in the third seat. He controlled a powerful electronic countermeasures (ECM) system to blind enemy radars, including an AN/ALQ-16 active jammer and an AN/ALE-16 chaff dispenser. If an enemy fighter still managed to get on the Hustler's tail, an unlikely event since the aircraft moved so fast and at altitudes above the ceilings of most contemporary fighters, the DSO could direct the Vulcan cannon in the tail "stinger" via a radarscope to engage the fighter.
The standard "MB-1C" weapons pod carried by the B-58 was a big spindle with tailfins. It was 17.4 meters (57 feet) long, 1.5 meters (5 feet) in diameter, and had a fully loaded weight of 16,325 kilograms (36,000 pounds). It carried both a W39Y1-1 multi-megatonne nuclear weapon and fuel, with the fuel stored in tanks at both ends to ensure trim.
The pod was mounted slightly off center from the aircraft's centerline so that it would begin to spin after being dropped to ensure stability. When the B-58 was parked on the runway without the pod, a counterweight had to be attached to the aircraft to keep it from tipping back on its tail.
The B-58A was originally to have been fitted with an "MA-1C" liquid-fuel stand-off missile with a range of 260 kilometers (160 miles) rather than a weapons pod. However, the guidance systems available at the time simply could not provide the necessary accuracy.
After the introduction of the B-58, the Air Force began to have doubts about the utility of a bomber that could only carry a single nuclear weapon, and so in between 1961 and 1963 all B-58s were retrofitted with four stub pylons, arranged in tandem under the wing roots, to carry Mk 43 or Mk 61 nuclear weapons.
A photo-reconnaissance pod, designated the "LA-331", was fielded, a modification of the MB-1C pod but carrying a Fairchild KA-56 panoramic camera rather than a nuclear bomb. The camera was fitted in the nose, along with a scanner system that permitted clear images at high speed and low level.
More specialized pods were considered but not fielded. An "MD-1" ECM pod was built but apparently not flown. A radar reconnaissance pod fitted with the huge Hughes "AN/APQ-69" side looking airborne radar (SLAR) was test-flown in 1959, leading to tests of the more compact AN/APS-73 SLAR in the early 1960s. A Hustler carrying the AN/APS-73 SLAR was sent over Cuba during the Missile Crisis in October 1963, and it appears this is the only time a Hustler ever overflew hostile airspace.
Problems with fuel leaks led to the development of a new "two component pod (TCP)" system that used twin stacked pods, with the upper pod carrying a BA53-Y1 nuclear weapon along with barometric sensors, and the lower pod amounting to a big drop tank that would be discarded during an operational mission once it was exhausted. Oddly, few pictures of the stacked pod system are available. Whether this was because it wasn't used very much use, or because it was simply too strange-looking to be regarded as photogenic when attached to the B-58, is difficult to say.
* After production of the first 30 trials aircraft, 86 production B-58s were built, for a total of 116 Hustlers in all. Production ended in the fall of 1962. Most of the trials aircraft were brought up to operational specification, though eight other trials aircraft were modified into "TB-58A" trainers. The primary users were the SAC 43rd Bomb Wing at Carswell, Texas, and later Little Rock, Arkansas, and the 305th Bomb Wing at Bunker Hill, Indiana, later renamed Grissom Air Force Base.
The Hustler's performance was astounding. It was capable of flying as fast or faster than any fighter it might encounter, and generally at higher altitudes than a fighter could reach. The B-58 had a blazing rate of climb, often described as "like a rocket", particularly when the aircraft was lightly loaded. The B-58 was also surprisingly maneuverable for an aircraft of its size, and although delta wings are supposed to give a bumpy flight at low altitude, the Hustler was perfectly adept at low-level penetration flights.
The B-58 set a number of records, including a low-level flight covering 1,930 kilometers (1,044 nautical miles) at altitudes of under 150 meters (500 feet) with an average speed of 1,100 KPH (610 knots), and a dash climb to a maximum altitude of 26,025 meters (85,360 feet). One Hustler flew from Los Angeles to New York and back in four hours, 41 minutes.
In October 1963, another B-58 appropriately named GREASED LIGHTNING flew from Tokyo to London, and despite the fact that it had to slow down for five aerial refuelings, its average speed over the 14,850 kilometer (8,028 nautical mile) flight was 1,726 KPH (933 knots). Cruise speed for five hours of the journey was 2,276 KPH (1,230 knots) at an altitude of 16,160 meters (53,000 feet), and the aircraft would have had an even higher average speed if it had not lost an afterburner late in the mission.
The Hustler was a very demanding aircraft, only very experienced flight crews were assigned to the type, and some aircrew were frightened of it. This was not because it was badly engineered, simply because it was pushing the envelope of aircraft design and left little margin for error. Ignoring the prescribed ranges of angle of attack in takeoff, landing, and cruise could be deadly. Loss of an engine at high speed could cause the aircraft to yaw drastically and tear itself to pieces. Loss of hydraulic control demanded an immediate bailout.
A total of 26 of the 116 B-58s built were lost in accidents, and the type had the unfortunate distinction of suffering fatal crashes twice at the Paris Air Show, once in 1961 and again in 1965. The TB-58A rebuilds were performed to help deal with the difficulties in flying the type.
* By the late 1960s, the argument over the manned supersonic bomber that had gone back and forth since the Hustler's development tipped decisively against it. The B-58 was an amazing aircraft, but it was just too expensive to operate. To the extent that SAC still believed in the manned bomber, the subsonic Boeing B-52 could do the job, and for the cost of operating two B-58 wings SAC could operate six B-52 wings. Some SAC brass also disliked the B-58 because of its high accident rate.
The B-58 never fired a shot in anger. Although the war in Southeast Asia was in full blaze by the mid-1960s, the Hustler was simply not cost-effective for conventional attacks, though in 1967 the Air Force did experiment with several B-58s for conventional strike in "Project Bullseye". The four stores pylons were modified for the carriage of conventional bombs and flown on low-level strike test missions out of Eglin AFB in Florida. Some rumors have it that B-58s were painted in jungle camouflage in place of the normal natural metal finish for these tests, but there is little evidence that this is true.
The last B-58 was removed from operational service in early 1970. The type's operational career only spanned a decade, a modest interval for a modern military aircraft. Seven survive on static display and one derelict is apparently being rebuilt, but it seems very unlikely the Hustler will ever fly again.
* A wide range of B-58 variants were considered, though in practice only one version of the B-58 was built, including some minor variations and experimental fits.
Trials aircraft were designated "YB-58". Production aircraft were designated "B-58A", or usually just B-58 as there never was a B-58B. Trainers were designated "TB-58" or "TB-58A", and were intended to give new B-58 pilots the necessary familiarization required to fly their demanding aircraft. This could not be done very well in a standard B-58 as there was no copilot seat, meaning a pilot new to the type was on his own on his very first flight. The second seat position was modified to accommodate a flight instructor, and distinctive additional rear windshield panel extensions were added to give the instructor a decent view. Most combat systems were removed.
Hustlers fitted with the LA-331 reconnaissance pod were designated "RB-58" or "RB-58A". It seems that RB-58As also carried some specialized equipment to control the pod and support the reconnaissance mission.
B-58s were used in limited numbers as test aircraft. One particularly impressive test configuration involved the fit of the huge YJ93 engine for the North American XB-70 bomber to the third B-58 built, replacing the aircraft's weapons pod. This aircraft was designated the "NB-58A".
Another B-58 was used to test the AIM-47 missile weapons system for the Lockheed YF-12A, an interceptor version of the SR-71 Blackbird reconnaissance aircraft. This B-58 was fitted with an extended nose to accommodate the ASG-18 radar for the missile and was affectionately known as "Snoopy", after the long-nosed beagle in the popular PEANUTS comic strip. The missiles were fired from a modified weapons pod, with such tests conducted from May 1962 to February 1964.
GD proposed a "B-58B" in 1958, featuring uprated J79-9 engines, a fuselage stretch, canards, and a conventional weapons capability. A B-58A was slated for conversion to a B-58B prototype, but the program was cancelled. A "B-58C" was also proposed, involving a larger aircraft powered by two or four Pratt & Whitney J58 engines, used on the SR-71 Blackbird, with 14,740 kilograms (32,500 pounds) thrust each. The B-58C would have had Mach 3 performance, but the Air Force wasn't buying.
Proposals were considered for using the B-58 as a strategic missile launcher, and Lockheed built a 9.15 meter (30 foot) long solid fuel "air launched ballistic missile (ALBM)" derived from the company's X-17 test booster. The ALBM was test-launched four times in 1958 and 1959, with two successful launches.
In the fourth and last launch, on 22 September 1959, the ALBM was launched into space to take a picture of an American Explorer satellite under "Project Snap Shot". This was a proof-of-concept test with applications for satellite inspection and anti-satellite interception, but that particular launch failed. The B-58 ALBM program was then abandoned, though the B-52-based "Skybolt" ALBM program persisted for a few more years.
A screwball scheme was proposed in which the Hustler would launch a high-speed ramjet-powered expendable aircraft to penetrate enemy airspace at speeds of up to Mach 4. The expendable aircraft would be piloted, but most of the aircraft would be discarded before the piloted section returned to base. Nothing came of this idea directly, though the basic concept would be revived with the Lockheed D-21 unmanned ramjet reconnaissance drone of the 1970s.
There were even schemes for building a supersonic transport based on the Hustler. One military transport concept involved a Hustler simply fitted with a modified pod with accommodations for five passengers, to be used when getting important personnel to a location was critical and cost wasn't a problem. More practically, GD also considered a commercial Hustler transport derivative with the fuselage stretched by about 50% and seating for 52 passengers. This concept was designated the "Model 58-9". Nothing came of these ideas, either.
* The B-58 was in general a much more advanced aircraft than the B-52, but in the year 2001, the B-52 is still flying operational missions, while the B-58 has been grounded for over three decades. The logic that argued against the supersonic manned bomber was simply too hard to dispute. Strategic strike could be performed by missiles, while conventional strike could be performed by attack aircraft and, increasingly, cruise missiles.
Two North American XB-70 supersonic heavy bombers would be built in the 1960s, but only as test aircraft. Supersonic B-1 bombers would be built in the 1980s, but only about 100 were manufactured, even less than the B-58. Only about 20 Northrop B-2s were built, and they weren't even supersonic.
It is possible that the USAF may field another heavy bomber, but if so it will most likely be an economical, relatively low cost aircraft with extremely long range and heavy payload capability, dispensing cruise missiles and other stand-off weapons from outside defended airspace.
In hindsight, it is remarkable that the B-58 ever entered service at all. Whether it was a good use of taxpayer's money is arguable. However, it is almost impossible to not be pleased with the result.
* I wrote this document as something of a "knock-off" on what I thought would be a fairly straightforward writeup on an attractive aircraft. It was straightforward, but led to more detail and work than I had expected. It always does.
I have to mention that some Hustler fans have written data sheets on a Hustler variant with eight J79 engines, and even a twin-fuselage variant with ten engines. I suspect these sheets were released on 1 April of some year.
* Sources include:
I also picked up some details on the more exotic variants from Joe Baugher's exhaustive website on US military aircraft.
* Revision history:
v1.0 / 01 nov 00 / gvg
v1.1.0 / 01 nov 01 / gvg / Minor detail update.