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One of the reasons the U-2 was so vulnerable was the ease with which Soviet radar stations could track the plane. Several studies by Lockheed and the government concluded that the best way to alleviate this problem was to develop a new aircraft flying at high supersonic speeds and extreme altitude with the lowest possible radar cross section (RCS). In late 1957, the Central Intelligence Agency (CIA) invited both Lockheed and Convair to participate in a program to develop this U-2 replacement.
The Lockheed team, led by Clarence "Kelly" Johnson, explored a variety of exotic concepts but eventually settled on a relatively conventional design intended to cruise at Mach 3 at an altitude of 90,000 ft (27,430 m). Convair's approach, led by Bob Widmer and Vincent Dolson, was more unusual. The design first began as a derivative of the B-58 Hustler supersonic bomber that Convair was building for the Air Force. As shown below, the B-58 was a delta wing design that carried a large external pod underneath the centerline. This pod normally contained a nuclear weapon.
An improved version of this aircraft, called the B-58B Super Hustler, was proposed to the Air Force in 1957. The B-58B was to be faster and larger than the original B-58 so that it could carry an additional "parasite" aircraft instead of the external pod. This parasite vehicle would be carried aloft to an altitude of at least 35,000 ft (10,670 m) and a speed of over Mach 2 where its three ramjet engines could be started. The parasite would then be air launched from the B-58B mother plane and accelerate to even higher speeds for its mission. The Super Hustler parasite was to consist of two major pieces. The first was a manned vehicle with a two-person crew while the second component was an independent expendable unmanned vehicle. Though this unmanned component was originally foreseen as a bomber containing a nuclear weapon, it could also carry additional fuel to extend the range of both components combined. This capability made the parasite attractive as a possible reconnaissance aircraft.
The manned component was about 46.58 ft (14.21 m) long with a wingspan of 18.75 ft (5.72 m) and weighed approximately 10,500 lb (4,760 kg). The two crewmembers sat side-by-side while the craft's single Marquardt RJ-59 ramjet engine produced 10,000 lb (44.5 kN) of thrust at Mach 3 and 5,000 lb (22.24 kN) of thrust at Mach 4. A small turbojet engine was also added to provide power during landing when the vehicle would be traveling too slowly for the ramjet to function. It was also equipped with a wheeled nose gear and skid main gear arrangement, similar to that used on the X-15, and the fuselage nose was designed to hinge downward for improved visibility during landing, much like the Concorde.
The expendable portion of the vehicle, meanwhile, was 48.75 ft (14.87 m) in length with a wingspan of 23.33 ft (7.17 m) and weighed about 25,300 lb (11,475 kg). This component was also powered, carrying two Marquardt RJ-59 ramjets, so that it could be released from the manned vehicle to fly under its own power and deliver its nuclear payload. Being expendable, however, this unmanned vehicle carried no landing gear. Both sections of the parasite were to be constructed of stainless steel, a ceramic material called pyro-ceram, and titanium to survive the intense heat generated at Mach 4. This heating also made it necessary to cover the cockpit windows with a series of heat protection shields, and television cameras were required to give the crew outside visibility.
Because of the limited space beneath the B-58B, the manned and expendable components were to be mated to the launch aircraft in an unusual manner. The manned vehicle was placed in front with its tail connected to the nose of the unmanned component behind it. The entire assembly, once mated to the B-58, would take off from a conventional runway and climb to altitude. The Super Hustler parasite was to be released about 2,300 nm (4,260 km) from its target. At launch, the parent aircraft would accelerate to Mach 2 so that the three ramjet engines could be engaged. With the ramjets producing full power, the parasite would be released and climb to its cruse altitude of 75,000 ft (22,860 m) and Mach 4. The vehicle would reach a peak altitude of 90,000 ft (27,430 m) when approaching the target. After releasing the unmanned component, the manned section was to return to base, decelerate, engage its turbojet engine, and land on a conventional runway.
Though the Air Force expressed some interest in an improved version of the B-58, the parasite bomber was considered impractical and received no government funding. Development of a B-58B bomber continued but the CIA's interest in a supersonic reconnaissance plane sent the parasite idea down a different path. As Lockheed was working on its proposal for a U-2 replacement, Bob Widmer and Vincent Dolson at Convair resurrected the parasite concept and dubbed the vehicle the "Fish." The Fish was to be carried by a modified version of the B-58B Super Hustler with a lengthened fuselage, more powerful engines, and carrying an additional crewman to launch the parasite.
The Fish itself was also modified from the original parasite concept and became a single manned vehicle instead of separate manned and unmanned components. The Fish employed a sophisticated lifting body fuselage shape and could reach a top speed of Mach 4.2 at 90,000 ft (27,430 m) with a maximum range of 3,900 nm (7,220 km). Powering the Fish during its Mach 4+ dash over the target were two of the same Marquardt ramjets that would have been used on the earlier parasite. The Fish was also to be equipped with two turbojets to return and land under its own power. Both the engine nozzles and the leading edges of the wings would have been constructed of pyro-ceram to withstand high temperatures as well as absorb radar waves for improved stealthiness.
The Fish concept was a risky proposal since it relied on unproven ramjet engines and required launching from a mother plane that did not yet exist. Indeed, it had yet to be proven that the B-58B launch platform could achieve the Mach 2.2 speeds needed for the ramjet engines to be started, and calculations by Convair engineers suggested the Fish was too heavy to allow the B-58B to do so. However, the final nail in the coffin came in June 1959 when the Air Force cancelled the B-58B altogether. The Fish concept was all but doomed in light of this decision, although converting the existing B-58A into a suitable mother plane was explored. Nevertheless, the B-58A was smaller and slower than the proposed B-58B and converting the older aircraft was considered impractical because of high cost and technical difficulties. The parasite concept was also criticized for being difficult to support logistically.
These issues left the Super Hustler/Fish proposal as no longer feasible, but Lockheed's competing design was also unacceptable because its RCS remained considerably higher than desired. Both the Convair and Lockheed proposals were rejected in July 1959 when the design teams were told to try again. Lockheed continued to refine its concept by exploring methods of reducing RCS while Convair was given a contract to develop a new design without the worrisome ramjet engines and mother plane required for the Fish. Both companies were also encouraged to use the J58 turboramjet engine for propulsion.
In abandoning the Fish, Convair developed a completely different concept bearing only a superficial resemblance to its predecessor. Known as the Kingfish, this aircraft took advantage of many technologies previously developed for the F-102 and F-106 fighters as well as the B-58. Among these innovations were a stainless steel honeycomb skin, the delta wing design, and crew escape capsules that eliminated the need for pressurized suits. The Kingfish carried a crew of two in tandem and was powered by a pair of J58 engines mounted within the fuselage instead of along the wings as in Lockheed's competing design. Unlike its parasite predecessors, these engines allowed the Kingfish to both takeoff and land under its own power without needing a launch aircraft. These turboramjet engines reduced the cruise speed to Mach 3.2 compared to the Fish's Mach 4.2 using ramjets, but range was increased to about 3,400 nm (6,300 km).
The Kingfish's greatest strength, however, was its RCS. The plane's relatively small size with engines buried inside the fuselage was a significant contributor to its stealth technology, and the Kingfish also retained pyro-ceram material along the wing leading edges and engine nozzles to absorb radar waves. In addition, the engine inlets were to be made of a fiberglass material further contributing to a low RCS. Nevertheless, Lockheed's Kelly Johnson remained dubious about these advanced materials and felt that Convair engineers had emphasized RCS "with total disregard for aerodynamics, inlet and afterburner performance."
By August 1959, both Convair and Lockheed had completed their designs and submitted proposals to a selection panel composed of Department of Defense, CIA, and Air Force personnel. This board pitted the Convair Kingfish against the Lockheed A-12, a close relative of what would eventually become the SR-71. The following table gives an overall comparison of the competitors.
| Lockheed A-12 | Convair Kingfish | |
|---|---|---|
| Max Speed | Mach 3.2 | Mach 3.2 |
| Max Range [nm] | 4,120 | 3,400 |
| Initial Cruise Alt [ft] | 84,500 | 85,000 |
| Max Cruise Alt [ft] | 97,600 | 94,000 |
| Radar Cross Section | (higher) | (lower) |
| Unit Cost (w/o engines) | $8.05 million | $10.1 million |
Although the Lockheed design had a slight edge in cost and most performance categories, some judges favored the Kingfish because of its much lower RCS. However, Lockheed was deemed the winner and issued a contract to proceed with further development and construction of test vehicles. One of the reasons for this decision was Convair's history of cost overruns and production delays during development of the B-58 that Air Force officials feared might also occur with the Kingfish. Lockheed, by comparison, had demonstrated its ability to produce an advanced aircraft on time and under budget during the U-2 program. Lockheed also had a history of building and testing new planes in complete secrecy, including the P-80 and U-2, at its highly secure Skunk Works facility. The Kingfish also remained a rather unconventional design incorporating a number of untried technologies, and it is likely that the concept was considered too risky.
Even after the contract award, however, Convair continued receiving some funding to develop the Kingfish as a backup should the Lockheed A-12 be a failure. When that did not happen and the A-12 proved to be a highly successful aircraft, further work on the Kingfish was finally halted. The concept was revived briefly once again during the mid-1960s when the Convair division of General Dynamics proposed merging technologies from its Fish and Kingfish vehicles with the F-111 fighter. The goal of this effort was to create a high-speed reconnaissance aircraft capable of reaching up to Mach 5 at an altitude of 100,000 ft (30,480 m). However, this concept was still considered too vulnerable to Soviet air defenses and did not progress any further.
Though nothing ever came of the Kingfish, it is still interesting to note how similar the overall shape of the
vehicle is to the F-117 that would come 20 years later. The F-117 and
its Have Blue prototype were the first aircraft designed specifically for low RCS. Both they and the Kingfish
share a similar boxy fuselage shape, engine location, flat underside, and several structural concepts suggesting
that the Convair designers may have been ahead of their time in the stealth revolution.
- answer by Jeff Scott, 31 December 2006
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