Lockheed Have Blue
Lockheed Have Blue was the code name for Lockheed's proof of concept demonstrator for a stealth fighter. Have Blue was designed by Lockheed's Skunk Works division, and tested at Groom Lake, Nevada. The Have Blue was the first fixed-wing aircraft whose external shape was defined by radar engineering rather than by aerospace engineering. The aircraft's faceted shape was designed to deflect electromagnetic waves in directions other than that of the originating radar emitter, greatly reducing its radar cross-section.
To design the aircraft, the Skunk Works' design team leveraged the mathematics published by Soviet physicist and mathematician Petr Ufimtsev regarding the reflection of electromagnetic waves. A stealth engineer at Lockheed, Denys Overholser, had read the publication and realized that Ufimtsev had created the mathematical theory and tools to perform finite element analysis of radar reflection.
The eventual design characteristically featured faceted surfaces to deflect radar waves away from a radar receiver. It had highly swept wings and inward-canted vertical stabilizers, which led to it being nicknamed "the Hopeless Diamond"—a pun on the Hope Diamond. The first operational aircraft made its maiden flight on 1 December 1977.
Two flyable vehicles were constructed. Both were lost due to mechanical problems. Nevertheless, Have Blue was deemed a success, paving the way for the first operational stealth aircraft, Senior Trend, or Lockheed F-117 Nighthawk.
Background
In the 1970s, it became increasingly apparent to U.S. planners that, in a military confrontation with Warsaw Pact forces, NATO aircraft would quickly suffer heavy losses. This came as a result of sophisticated Soviet defense networks, which used surveillance radars, radar-guided surface-to-air missiles, and anti-aircraft artillery to seek and eliminate enemy aircraft. Consequently, the Defense Advanced Research Projects Agency started a study on low-observability aircraft, seeking to design and produce an operational stealth aircraft. Five companies were initially invited, three of which bowed out early. The remaining two were later joined by Lockheed.Design and development
Origins
The Lockheed Have Blue was born out of a requirement to evade radar detection. During the Vietnam War, radar-guided SAMs and AAA posed a significant threat to US aircraft. For this reason, strike aircraft during the war often required support aircraft to perform combat air patrols and suppression of enemy air defenses. The 1973 Yom Kippur War again highlighted the vulnerability of aircraft to SAMs – the Israeli Air Force lost 109 aircraft in 18 days. During the Cold War, the Soviet Union developed an integrated defense network, central to which were medium- to long-range surveillance radars. SAMs and AAAs would be set up around key locations to defend them from incoming enemy aircraft. If the loss ratio of Israel during the Yom Kippur War was experienced by NATO forces during a military confrontation with the Warsaw Pact, NATO aircraft numbers would be depleted within two weeks.In 1974, DARPA secretly requested answers from five aircraft manufacturers regarding two considerations. The first was about the signature thresholds at which an aircraft is virtually undetectable. The second point was whether these companies had the capability to design and manufacture such an aircraft. Fairchild and Grumman declined to participate, while General Dynamics insisted on the use of electronic countermeasures. As a result, General Dynamics left the discussion. The remaining two companies, McDonnell Douglas and Northrop, were each awarded $100,000 for further research.
Design effort and early testing
Lockheed, having been absent from the fighter aircraft industry for 10 years, was not approached by DARPA in 1974. Ed Martin, Lockheed California Companies director of science and engineering, became aware of the research into stealth during his work at the Pentagon and Wright-Patterson AFB. Martin and Ben Rich, who at that time had recently become Skunk Works' president, briefed Clarence "Kelly" Johnson on the program. The Central Intelligence Agency gave Skunk Works permission to discuss with DARPA the stealth characteristics of the A-12, M-21 and D-21. On behalf of the company, Rich and Martin formally requested permission from DARPA to participate in the program, but the agency initially refused because there were insufficient funds; after much debate, Lockheed was allowed entry, albeit without a government contract.Preliminary designer Dick Scherrer requested possible shapes upon which he could base his low radar cross-section design. He was introduced to Denys Overholser, who recommended an aircraft with flat surfaces. Overholser later recounted his discussion with Sherrer: "When Dick Scherrer asked me... I said 'Well, it's simple, you just make it out of flat surfaces, and tilt those flat surfaces over, sweeping the edges away from the radar view angle, and that way you basically cause the energy to reflect away from the radar.'" Scherrer subsequently drew a preliminary low-RCS aircraft with faceted surfaces. At the same time, Overholser hired mathematician Bill Schroeder, with whom he had a prior working relationship – in fact, it was Schroeder who trained Overholser on mathematics relating to stealth aircraft. Kenneth Watson was hired as the senior lead aircraft designer.
During the next few weeks, the team created a computer program which could evaluate the RCS of possible designs. The RCS-prediction software was called "ECHO 1". As tests with the program proceeded, it became apparent that edge calculations by the program were incorrect due to diffraction. To overcome this, Overholser incorporated elements of research by Soviet engineer Pyotr Ufimtsev into the software.
ECHO 1 allowed the team to quickly decide which of the 20 possible designs were optimal, finally settling on the faceted delta-wing design. However, many within the division were skeptical of the shape, giving rise to the name "Hopeless Diamond" – Kelly Johnson said to Rich, "Our old D-21 drone has a lower radar cross-section than that goddamn diamond".
In May 1975, the Skunk Works produced an internal report titled, "Progress Report No. 2, High Stealth Conceptual Studies." Within it was a concept study called "Little Harvey," including Kelly Johnson's drawing of an aircraft with smoothly blended shapes. Johnson advocated for the use of blended shapes as the best way to achieve stealth, while Ben Rich advocated for faceted angles. Rich won the argument with Johnson, a rare occurrence.
The design effort produced a number of wooden models. A 24-inch long model, made of balsa wood, demonstrated placement of internal structure and access doors. An Air & Space article noted "The model shop found it nearly impossible to make all the flat surfaces come to a single point in one corner. Engineers later encountered the same difficulty fabricating the prototype on the factory floor." For early tests of the design, two ⅓-scale wooden mock-ups were constructed. One model, coated in metal foil, was used to verify ECHO 1's RCS calculations, while the other was earmarked for wind tunnel tests. Afterwards, a model was moved to the Grey Butte Range radar-testing facility in the Mojave Desert near Palmdale, which allowed more accurate tests of the aircraft's RCS. In the event, the aircraft's RCS level confirmed ECHO 1's predictions. This meant Ben Rich won a quarter from Johnson, who previously insisted that the D-21 had less RCS than Have Blue.
Experimental Survivable Testbed
In the summer of 1975, DARPA informally invited Lockheed, Northrop and McDonnell Douglas to develop an aircraft under the name "Experimental Survivable Testbed". McDonnell Douglas, having identified the thresholds at which aircraft were deemed undetectable, was unable to design and produce such an aircraft. Phase 1 of XST would see both Lockheed and Northrop build full-scale models to test their RCS, construct flyable vehicles, and wind-tunnel test their designs. Following Phase 1, a sole contractor would be selected to continue with the construction and flight testing of two demonstrators as part of Phase 2. Northrop's and Lockheed's designs were generally similar, though the former's submission featured more angular and flat surfaces. The company used "GENSCAT", software similar to ECHO 1, to calculate the RCS of its designs.On 1 November 1975, Lockheed and Northrop were each awarded $1.5-million contracts to proceed with Phase 1 of XST. During a four-month period, the two companies were each required to construct full-scale wooden mock-ups, which would then be evaluated at the USAF's Radar Target Scatter test facility at White Sands, New Mexico. To test the design's radar returns, Lockheed erected a $187,000 specially built pole upon which the model would be perched. In March 1976, a Lockheed model was transferred to the range before being tested; the following month Lockheed was pronounced the winner because the Northrop XST had a much higher side hemisphere RCS. DARPA, having realized the progress accumulated throughout the study, urged the Northrop team to remain together. The agency would later initiate the Battlefield Surveillance Aircraft-Experimental, which evolved into the Tacit Blue and, ultimately, the B-2 bomber.
Construction and further tests
Skunk Works now had to design, construct and flight test two crewed demonstrators as part of Phase 2, or Have Blue. To build the demonstrators, Ben Rich had to raise $10.4 million from the Lockheed management, which was secured by June. Phase 2 encompassed three main objectives, which were the validation of: reduced visibility in the radio wave, infrared, and visual spectrums and reduced acoustical observability; acceptable flying qualities; and the "modeling capabilities that accurately predict low observable characteristics of an aircraft in flight".Construction of both Have Blue demonstrators used leftover tools from the C-5 program. Final assembly of HB1001 was originally scheduled to be completed in August 1977, before being ground tested until mid-October. The secret roll-out was envisaged to occur on 23 October, after which the aircraft would be dismantled and transported to the test area. On 1 September, however, with HB1001 partially complete, Lockheed machinists went on a four-month strike. A group of managers took over the job of assembly, which was completed in six weeks, with ground tests beginning on 17 October.
While superficially similar to the later F-117, the Have Blue prototypes were smaller aircraft, about one quarter the weight of the F-117, with a wing sweep of 72.5° and inward-canted vertical tails. Radar-absorbent material, developed in a Lockheed laboratory, was applied to the aircraft's flat surfaces – for the windscreen, special coatings were applied to give them metallic characteristics. The aircraft's gross weight of 9,200–12,500 lb enabled the aircraft to use the landing gear from the Northrop F-5 fighter. The aircraft's powerplants were two General Electric J85-GE-4As from the T-2C Buckeye. Because stealth took precedence above all else, the aircraft was inherently unstable. As a result, a quadruple redundant fly-by-wire flight control system was integrated into the aircraft to give it normal flying characteristics. The flight control system was borrowed from the F-16. The overwing engine inlet was covered by a low-RCS grid; blow-in doors were constructed at the upper fuselage to admit additional airflow during takeoffs, when more air is needed.
Throughout the one and a half months after the start of ground tests, HB1001, the first of two demonstrators, underwent tests in preparations for the first flight. Flight instrumentation was checked first, followed by a thorough shakedown of the aircraft. In early November, two semi-trailers were parked parallel to each other outside Building 82; a camouflage net was thrown over the top to cover the demonstrator during outdoor engine runs. During the engine tests, a local resident complained about the noise, but Have Blue retained its secrecy. HB1001 received a layer of iron-coat paint; during the weekend of 12–13 November, the aircraft received a camouflage scheme devised by Alan Brown, Have Blues chief technical engineer. The scheme, consisting of three colors, each with three tones, was used to deceive any casual onlooker from recognizing the design's characteristic faceting. The aircraft was disassembled, loaded onto a C-5, and on 16 November, the aircraft was flown from Burbank Airport to Area 51 at Groom Lake, Nevada. Upon touchdown, the aircraft was reassembled before undergoing another round of testing prior to the first flight. After four taxi tests, HB1001 was ready for test flights.