On August 18, 1957, Pratt & Whitney had completed its first Model 304 engine and less than a month later, static tests were initiated. During October initial engine runs took place, followed by a second series in December. A second engine began tests on January 16, 1958 and on June 24 an improved engine, Model 304-2, was delivered and tested.
All seemed to be running according to schedule: the Air Force had allocated $95 million to Project Suntan; Johnson had ordered no less than 2½ miles of aluminum extrusion for airframe production; the 304 engine continued to perform as planned; Air Products was constructing a large hydrogen liquefaction plant in Florida for fuel production, and MIT was working on an inertial guidance system. But over the next six months something continued to bother Johnson. Despite having successfully sold the aircraft to the Air Force, it was becoming increasingly apparent to him that the CL-400’s severe range limitations couldn’t be designed out of the aircraft. The design fell short of its estimated original lift-over-drag ratio by 16 percent. Stretching the fuselage to increase fuel capacity would result in only a 3 percent increase in range. Pratt & Whitney estimated that no better than a 5–6 percent improvement in specific fuel consumption could be achieved with its Model 304 engine over a five-year period of operation. Such low growth potential, coupled with the associated logistical problems of pre-positioning liquid hydrogen to OLs, convinced Johnson that “the aircraft was a dog.” In March 1957, during a meeting with James Douglas Jr, then Secretary of the Air Force, and Lt Gen Clarence Irvin, deputy Chief of Staff for material, Kelly bluntly informed them of his misgivings and by the middle of that year, others were voicing similar concerns. In February 1958, and at Kelly’s insistence, Suntan was canceled. The Skunk Works returned almost $90 million and the Air Force perhaps lost an opportunity to wrestle the strategic reconnaissance overflight program away from the Agency. However, Project Suntan had provided Lockheed with an improved understanding of high-speed flight as well as confirmation that hydrocarbon fuel, and not hydrogen, was the best choice for the proposed flight regime. It also provided Johnson with a major change of direction for Project Gusto.
Supersonic Gusto
The dichotomy was the relationship between “stealth” and performance, and this would be a recurring theme throughout Johnson’s design submissions for a U-2 replacement. A conventional design was most likely to deliver the required performance, but these criteria often proved to be too easily detected by radar; whereas a design emphasizing stealth struggled to deliver the prerequisite performance. Johnson was also concerned at the speed of Soviet radar development which, coupled with the inevitable use of more diverse radar frequencies, would, he was convinced, further complicate the search for a panacea to these conflicting paradigms. Therefore on April 21, 1958, probably as a hedge against these problems, Johnson began sketching his first Mach 3 design for the Agency. As with his Suntan design for the Air Force, this primarily put extreme speed and altitude performance at the heart of vehicle “survivability,” rather than stealth. He named the design in his notebook “U-3” (this notebook would subsequently become known as his “Archangel” notebook — Skunk Works insiders often referred to the highflying U-2 as “Kelly’s Angel,” but as this new design represented another performance leap, “Archangel” seemed the logical extension). He also recorded the basic design requirements and his preference for choosing two higher thrust-to-weight ratio J58 engines over the J93. Then over a number of days, he continued to refine and further investigate the high-speed design, before reporting his findings to Bissell.
A team from the SEI conducted a blip-scan analysis of Johnson’s U-3 proposal. By taking into account the design’s speed, altitude, and RCS, they were able to evaluate the dwell time (the length of time the aircraft remained within a radar beam) and therefore its probability of detection. Three different frequency bands — 70, 600, and 3,000 megacycles per second — were considered in these computations and the subsequent report was highly significant; becoming known as the “Blip-Scan Study,” it set specific performance targets for the U-2 follow-on: a speed of Mach 3, an altitude of 90,000ft, and an RCS of not more than 10m2 and preferably less than 5m2.
Convair’s competitor
In the spring of 1958, Bissell flew to Fort Worth, Texas, where he met Robert H. Widmer, head of advanced development at the Convair Division of General Dynamics. Bissell told Widmer that he required a reconnaissance aircraft capable of flying undetected at 90,000ft with a 4,000-mile range and 2,000lb payload — as with Lockheed, Bissell kept his initial requirements simple and without a written specification. Bissell states in his memoirs that he brought Convair into the project on a point of due diligence and also to assuage any criticism when it came time to possibly award a multi-million dollar contract. However, others on the inside track have gone on record as saying it was done because Johnson was more concerned about taking an aerodynamic quantum leap, rather than minimizing the RCS of a U-2 successor (the latter being something that President Eisenhower himself had insisted upon). Therefore, this precipitous action also provided Bissell with leverage to use against Johnson when he thought the Skunk Works boss was not focusing enough on RCS design issues.
Convair’s first proposal in the competition was based upon a radical variation of a design called Super Hustler. This nuclear bomber would have used a modified B-58 Hustler bomber to carry aloft a two-stage parasite aircraft, the aft section of which would later be jettisoned to increase overall range. The front, manned, section carrying the weapon was to have been powered by ramjets for cruising and a turbojet for landing. It was an interesting concept, but the proposed reconnaissance variant required a number of significant changes, not least because jettisoning sections of an aircraft over hostile territory was hardly covert! In addition, Super Hustler just was not stealthy. So a team of seven principal design engineers, under Donald R. Kirk, began working on what they referred to as the First Invisible Super Hustler or FISH.
Consisting of the front section only of the Super Hustler design, crew numbers for FISH were reduced from two to one. Its offset, pressurized cockpit escape capsule (a feature that would latter be incorporated into the company’s F-111 design) meant that the pilot didn’t require a full pressure suit (unlike the Lockheed designs), which greatly reduced crew fatigue. To provide the pilot with a view of the outside world when in flight, two TV cameras were mounted in the nose. Once launched from the B-58, the two ramjet engines would burn high-energy fuel. To reduce FISH’s RCS, the designers changed both the leading and trailing edges of the wing from straight lines to arcs of circles, and the inlet was also redesigned. In addition, the steel-honeycomb wings of this Mach 4 hot-rod incorporated the wedge-shaped dielectric inserts invented by Ed Lovick; but due to the high thermodynamic temperatures encountered at such speeds, their composition was changed and instead consisted of a ceramic, Pyroceram, impregnated with graphite. The project was codenamed Idiom by Bissell’s office and on June 22, 1958, the work was formally moved into Gusto.