Convair KINGFISH

The KINGFISH reconnaissance aircraft design was the ultimate result of a series of proposals designed at Convair as a replacement for the Lockheed U-2. KINGFISH competed with the Lockheed A-12 for the Project OXCART mission, and lost out to that design in 1959.

Background

Before the U-2 became operational in June 1956, CIA officials had estimated that its life expectancy for flying safely over the Soviet Union would be between eighteen months and two years. After overflights began and the Soviets demonstrated the capability of tracking and attempting to intercept the U-2, this estimate was adjusted downward; in August 1956, Richard Bissell reduced the number to six months.

In order to extend the useful life of the U-2, the CIA started Project RAINBOW, which added various countermeasure in order to confuse the Soviet radars and make planning an interception more difficult. According to the few published reports, RAINBOW consisted of a series of wires strung along the leading edges of the aircraft that were supposed to cancel out the radar reflection of the airframe by "broadcasting" a similar return but out-of-phase. Several RAINBOW-equipped flights were made, but the Soviets proved to be able to track the aircraft regardless. The weight of the equipment also had the side-effect of lowering the maximum altitude the aircraft could cruise at, make it more vulnerable to interception. RAINBOW was cancelled in 1958.

As early as 1956 Bissell had already started looking for an entirely new aircraft to replace the U-2, with an emphasis on reducing the radar cross section as much as possible. High-altitude flight would still be useful to avoid visual interception by aircraft, but did little to help against missiles. But by reducing the RCS, the radars guiding the missiles would have less time to track the aircraft, complicating the attack.

In August 1957 these studies turned to examining supersonic designs, as it was realized that supersonic aircraft were very difficult to track on radars of that era. This was due to an effect known as the blip-to-scan ratio, which refers to the "blip" generated by an aircraft on the radar display, compared to the time it takes for the radar to complete one scan of the entire sky, a 360 degree sweep. In order for a blip to be visible to the operator, the aircraft has to move slowly enough that the radar makes numerous "hits" on it at roughly the same location, each return adding slightly to the single blip on the display. An aircraft moving at high speeds would cover ground so quickly that its blip would be smeared out over the display, rendering it invisible.

By the autumn of 1957 so many ideas had been submitted that Bissell arranged for the formation of a new advisory committee to study the concepts, led by Edwin Land. It appears this may have been organized as Project GUSTO. The committee first met in November to arrange for submissions. At their next meeting, on 23 July 1958, several submissions were studied. Kelly Johnson presented a design which could cruise at Mach 3 for extended periods in order to take advantage of blip/scan spoofing. Convair proposed a two-part aircraft that was launched in the air from a newer version of the B-58 Hustler that was then being studied. The Navy introduced a submarine-launched inflatable rubber vehicle that would be lifted to altitude by a balloon, boosted to speed by rockets, and then cruise using ramjets. Johnson was asked to provide a second opinion on the Navy design, and the committee arranged to meet again shortly.

At the next meeting, in September 1958, the designs had been further refined. Johnson reported on the Navy concept and demonstrated that it would require a balloon a mile wide for launching; the submission was then dropped. Boeing presented a new design for a convert|190|ft|m|sing=on long liquid hydrogen powered inflatable design. Lockheed presented several designs; the Lockheed CL-400 Suntan was a large hydrogen-powered conventional design that looked like a scaled-up F-104 Starfighter, the G2A was a subsonic design with a low radar cross-section, and the A-2 was a delta wing design using zip fuel-powered ramjets. Convair entered their parasite design, now intended to fly at Mach 4.

FISH

Convair's parasite design matured between its first conception and the version submitted in 1958. The earlier version had been one part of a two-part design, the rear portion being an unmanned booster powered by a single ramjet, and the front portion a manned aircraft with two of the same ramjets. The two parts would be suspended under the B-58B "Super Hustler", flown to a speed of Mach 2 at convert|35000|ft|m|abbr=on, and released. All three ramjets would fire for "boost", after which the rear portion would fall away. The unmanned booster could also be used as a weapon, if armed.

By 1958 the concept had been simplified, and reduced to a single larger aircraft. Code-named FISH, the aircraft was based on a lifting body design that bears some resemblance to the ASSET of a few years later. It differed in having the nose taper down to a flat horizontal line instead of the rounded delta of the ASSET, and the fuselage was not as large at the rear. Two vertical control surfaces were placed on either side of the fuselage at the rear, and a small delta wing covered about the rear third of the aircraft. It was to be powered by two Marquardt RJ-59 ramjets during the cruise phase, providing a cruise speed of Mach 4 at convert|75000|ft|m|abbr=on, climbing to convert|90000|ft|m|abbr=on as it burned off fuel. In order to handle the intense heat generated by skin friction at these speeds, the leading edges of the nose and wings were built of a new "pyroceram" ceramic material, while the rest of the fuselage was made of a honeycomb stainless steel similar to the material for the proposed B-70 "Valkyrie". After completing its mission, the aircraft would return to friendly airspace, slow, and then open intakes for two small jet engines for the return flight at subsonic speeds.

Lockheed's entry had also changed during the research phase. Their original submission was the A-2, another ramjet-powered design, but one that was ground-launched using large jet engines. The committee didn't find either entry particularly interesting, and when the Super Hustler was cancelled by the Air Force in 1958, the entire FISH concept was put in jeopardy. There was some work on converting the existing A-model Hustlers as FISH carriers, but this appeared to have limited capabilities for launching the FISH, and the Air Force was unwilling to part with any bombers regardless. The committee asked both companies to return with another round of entries powered by the Pratt & Whitney J58 turboramjet.

KINGFISH

Convair turned to a completely new design, similar to their earlier entries in name only. The new KINGFISH design had much in similar with the F-106 Delta Dart featuring a classic delta wing layout. It differed in having two of the J58 engines buried in the rear fuselage, and twin vertical surfaces at the rear. The intakes and exhausts were arranged to reduce radar cross section, and the entire aircraft had the same sort of angular appearance as the later F-117. The leading edges of the wings and intakes continued to use pyroceram, while other portions used a variety of materials selected for low radar reflection, including fiberglass. The new engines reduced the cruise speed to Mach 3.2 compared to the FISH's Mach 4.2, but range was increased to about 3,400 nm (6,300 km).

In August 1959 the teams met again to present their latest designs. Lockheed had produced an aircraft similar to the KINGFISH, the A-11, but it was more "conventional" in layout. Although the A-11 had somewhat better performance than KINGFISH, the panel generally preferred Convair's design due to its much lower RCS. Johnson expressed skepticism of Convair's claimed RCS and complained that they had given up performance to achieve it; "Convair have promised reduced radar cross section on an airplane the size of A-12. They are doing this, in my view, with total disregard for aerodynamics, inlet and afterburner performance."

In the end it was not performance that decided the outcome; Lockheed had proven its ability to design advanced aircraft in secret with the U-2, which was on-time and under-budget, whereas Convair had massive cost overruns with the B-58 and no secure facility similar to the Skunkworks. Lockheed promised to lower the RCS in a modified version of the A-11 known as the A-12, and that sealed the deal.

Aftermath

Some small-scale work on the KINGFISH continued even after the choice of the A-12, in case the A-12 ran into problems. This did not occur, and the KINGFISH funds soon disappeared.

The CIA continued studies into even higher performance aircraft, and studied replacing the A-12 under Project ISINGLASS. ISINGLASS focused on a new design blending features of the General Dynamics F-111 and KINGFISH, possible due to General Dynamics having moved Convair's work to their Fort Worth site. The new design aimed to produce a new reconnaissance aircraft capable of reaching up to Mach 5 at an altitude of convert|100000|ft|m|abbr=on. The CIA felt that the extra performance would not be enough to protect it from missile systems already capable of attacking the A-12, and nothing came of the project.

Ironically, the entire idea of spoofing radars through their blip/scan turned out to not work. The high-temperature exhaust turned out to be a fair radar reflector at certain wavelengths, although Lockheed proposed adding caesium to the jet fuel to help mask this effect. As the entire technique relied on problems in the radar display systems, upgrades to these systems could render the entire idea moot. In the end, the A-12 was considered too vulnerable to defenses and flown over secondary nations like Vietnam. The failure of the A-12's attempts to avoid radar was proven when the Vietnamese proved able to track the A-12 with some ease, even firing on it on occasion and causing minor damage on one occasion in 1967. [ [http://www.blackbirds.net/sr71/oxcart/successortou2.html The U-2's Intended Successor:Project Oxcart, 1956-1968] ]

References

* [http://www.blackbirds.net/sr71/oxcart/successortou2.html The U-2's Intended Successor:Project Oxcart, 1956-1968]
* [http://www.aerospaceweb.org/question/planes/q0287.shtml Convair Super Hustler, Fish & Kingfish]