Вы здесь

Lockheed A-12: The CIAs Blackbird and other variants

Lockheed A-12: The CIAs Blackbird and other variants

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.

Although not part of Project Rainbow or Gusto, Project Suntan’s CL-400 design provided Johnson with important insights into possible fuel and power plant options for a U-2 replacement. (Lockheed Martin)


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.

Johnson proposed that his Archangel I design be powered by two J58s and built from titanium B 12 °CVA. Together with Gusto 2A, the designs were received with interest by Dr Richard Bissell, the DCI’s Special Assistant for Planning and Coordination, but would come to nothing. (Lockheed Martin)

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.

On July 23, 1958, Johnson attended a meeting at which he presented Archangel I and Gusto 2A. Bissell was present and Johnson noted in his log that both designs were “well received.” A Navy commander also present alluded to a Navy idea for an inflatable aircraft, and Bissell requested Kelly’s comments on the concept. On July 31 the advisory panel met to formally discuss both Lockheed concepts, during which Bissell noted that reasonable progress was being made, but that he thought the way forward would become clearer after their September meeting.

Having been provided with details about the intriguing Navy concept, Johnson conducted a thorough evaluation for Bissell. Under the Navy project name Champion, Goodyear was proposing a reconnaissance vehicle with inflatable wings that could be rolled up whilst in transit aboard an aircraft carrier, then inflated for launch. It was envisaged that the ramjet-powered vehicle would be lifted to altitude by balloon and would cruise at 125,000–150,000ft. A quick calculation by Johnson determined that the balloon would need to be over a mile in diameter! A more detailed study followed during which a tug aircraft was also evaluated, but the unreliability of the concept for reconnaissance over highly sensitive areas was enough to ensure that the design didn’t progress.

This wind tunnel model shows Convair’s FISH concept being carried beneath the underside of its B-58 launch aircraft. (Lockheed Martin)Powered by two J58s and two wingtip-mounted ramjets, Johnson’s Archangel II design precluded provision for reducing RCS, so yet again he was reminded of President Eisenhower’s requirement for an “invisible” aircraft. (Lockheed Martin)

On August 18, Johnson made a note in his log to conduct studies into a modified version of Archangel I utilizing ramjets on the wingtips to gain a further 10,000ft in altitude. However, Archangel II made no concessions to reducing RCS and during meetings held in Washington, DC and Boston from September 17–24, Johnson was once again reminded that the President required a replacement reconnaissance aircraft that was invisible to radar.

The Land Panel convened in Boston on September 22–23, and both Johnson and Widmer presented their designs independently. The panel decided to terminate further studies into Champion, voiced interest in the Convair design, but rejected Archangel II primarily on the grounds of its poor RCS. Gusto 2A, the panel contended, required further development.

Five days after the Boston meeting, Johnson began making notes on what would become his A-3 design. Consisting of two wingtip-mounted ramjets and two JT-12A turbojets, Johnson assigned the concept to Dan Zuck, Ed Baldwin, and Henry Combs. Continuing the angel theme, the team referred to them as Cherubs, since they were smaller than Archangel, and they worked on several design permutations. On October 30 Ed Baldwin completed the final A-3 design, which had a length of 62.3ft, a span of 33.8ft, and weighed in empty at 12,000lb. Despite the relatively low levels of thrust generated by the two turbojets, the A-3 could reach Mach 3.2 at a cruise altitude of 95,000ft and had a range of 4,000nm. But weight issues dogged the design and when “LD” MacDonald and his team conducted RCS measurements on two scale models, the returns averaged out as the same for those of the U-2, which were much greater than those for the all-metal Gusto 2S, which were themselves larger than for Gusto 2A, which incorporated RAM.

On November 12, 1958, Johnson and Widmer presented their designs to the Land Panel — Johnson the A-3 and Widmer FISH. Three days later the panel communicated its findings to James Killian — the President’s science advisor. Their recommendation was that FISH be selected, but should this design later prove unable to meet “the desired technical features” the panel would wish to review other alternatives before recommending firmly a second choice (the A-3). Bissell called Johnson with the bad news on November 26, pointing out that actually the two designs compared quite favorably, but that the crunch issue had again been RCS, an area in which Convair was clearly ahead.

Johnson’s Arrow design was the result of a request by the Land Panel to undertake a “sanity check” of Convair’s radical FISH proposal. Lockheed highlighted similar operational problems with the design, namely the unreliability of ramjets in cruise and a power deficiency of the proposed single JT-12 turbojet to be used during the landing phase. (Lockheed Martin)

On December 22, Convair was given the go-ahead to proceed with further detailed design development of FISH. Twelve aircraft were to be bought and it was thought that a minimum of one B-58 launch-aircraft would be required for every four FISH. Since Strategic Air Command (SAC) was operating a wing of B-58 Hustler bombers from Carswell AFB in Texas, the base provided ready cover and security for Project FISH — the close proximity of the base to Convair’s Fort Worth plant was also an advantage.

A major operational disadvantage of FISH was its reliance upon a carrier aircraft for launch. The effect upon Johnson of the Land Panel’s decision to reject the A-3 caused him to focus his next set of designs on reducing RCS values to a minimum, whilst retaining the vehicle’s ability to launch itself independently. Therefore, beginning on November 26 and over the next two months, Johnson and his team began working on designs designated A-4, A-5, and A-6. The designs utilized an idea of Frank Rodgers to incorporate chines beginning at or near the nose that blend into the fuselage and merge into the leading edge of the wings. In addition, the designs were of small physical size and vertical surfaces were hidden above the wings. However, at the beginning of January 1959, before design studies had been completed on the A-6, Johnson instructed his team to work on a series of small, non-stealthy designs, designated A-7 through A-9. Powered by a single J58 turbojet and two ramjets, none of the designs were subsequently judged to be viable — their range was inadequate, typically 1,640nm — and despite their size, the RCS was too great.

Following the November 12 meeting, Convair began developing production plans, awarding subcontracts for the design of various sub-systems, in addition to conducting work that would refine and test various elements of their FISH design. But it was during the nearly 300 hours of wind tunnel testing of 1/17th scale models that problems were identified. Firstly the drag coefficient acting on the B-58 with FISH in place was nearly double that of a “clean” aircraft. This meant that instead of the usual three minutes to accelerate from subsonic speed to Mach 2, it would take nearly nine. In addition, FISH needed to be lengthened in order to improve stability and carry additional fuel; this meant that the B-58 needed to be 5ft longer. Neither of these were issues for the B-58B, as it was both longer and had uprated J79-9 engines; the problem was that the new bomber was unfunded.

Yet another design with no concessions made to “stealth,” the A-10 was built to cruise at Mach 3.2 and 90,500ft. It is seen here undergoing RCS tests to determine how effective the addition of RAM applied to slope the sides of the fuselage and engine nacelles might be. (Lockheed Martin)KINGFISH, inverted, undergoing RCS testing. Note the serrated leading and trailing edges into which would later be fitted dielectric wedges to further reduce the aircraft’s RCS. The intakes located above the wing would also contribute to lowering the design’s radar return. (Lockheed Martin)

Following the failure of both his small stealthy and non-stealthy designs, Johnson returned to his Archangel I concept of a purely performance-driven design with no concessions to reducing RCS. The A-10 and A-11 designs were the results of pursuing that philosophy.

Utilizing the J93 turbojet, the A-10 was 16,000lb lighter than Archangel I and was therefore able to gain an additional 2,500ft at mid-mission altitude. It was able to cruise at Mach 3.2 at 90,500ft and had an operational radius of 2,000nm. However, it transpired that the J93 engines were 18 months behind the development of the J58; so in March 1959 the Lockheed team began work on what they believed would be their final major design, the A-11. Designed specifically to utilize air refueling, it would therefore have a range of over 13,000 miles and be able to complete an eight-hour round-robin mission from the United States, thus negating the inherent political and security issues associated with operating such aircraft from a foreign base.

Страницы


В нашей электронной онлайн библиотеке вы можете бесплатно и без регистрации прочитать «Lockheed A-12: The CIAs Blackbird and other variants» автора Crickmore Paul на телефоне, андроиде, айфоне, айпаде. Сейчас вы находитесь в разделе „DESIGN AND DEVELOPMENT“ на странице 2. Приятного чтения.