The Lockheed F-117A “Stealth” fighter in one of the most sophisticated warplanes ever built, almost invisible to radar, the F-117 has revolutionized air warfare.
At first, the aircraft was operated under conditions of total secrecy, but during the US intervention in Panama in 1990 and during the first Gulf War in 1991 the U.S. Air Force deployed it openly.
In 1974, the US Defense Advanced Research Projects Agency (DARPA) initiated a program known as PROJECT HARVEY, after a well-known comedy about an invisible giant rabbit, that requested designs of an “experimental survivable testbed (XST)” aircraft with a low RCS. Lockheed was not among the companies contacted by DARPA with this request, but in 1975 Ben Rich, an engineer who had worked on the secret Lockheed U-2 and SR-71 reconnaissance aircraft, got wind of the project and lobbied the government successfully to have Lockheed included.
Rich had the services of two Lockheed employees, mathematician Bill Schroeder and computer scientist Denys Overholser, to work on the XST program. Schroeder realized that it would be much easier to compute RCS if the shape of an aircraft could be reduced to a set of flat surfaces, or “facets”. Schroeder approached Overholser with the idea, and within five weeks Overholser had written a computer program named “Echo I” that could determine the RCS of a “faceted” aircraft. Armed with Echo I, Schroeder came up with an initial XST design that he called the “Hopeless Diamond”, and handed Ben Rich a sketch of it in May 1975.
In response, Rich asked how big the RCS of a practical version of the Hopeless Diamond would be: As big as a T-33? A Piper Cub? A condor? An eagle? An owl? Schroeder shot back: “Ben, try as big as an eagle’s eyeball.”
By October 1975, the DARPA XST competition had been reduced to two finalists: one from Northrop, and a refined version of the Lockheed Hopeless Diamond. The Northrop entry was a delta with a faceted fuselage, with the jet engine mounted on the back and the intake above the cockpit.
The Lockheed design had a tenth of the RCS of the Northrop design. It was so invisible to radar that a radar operator performing tests on the model at White Sands, New Mexico, thought it had fallen off the pole. Bird droppings increased the RCS by 50 percent, and so the model had to be regularly cleaned. Lockheed won the competition in April 1976. The Northrop team was heartbroken, even though their engineers admitted Lockheed had the better design. They returned to their calculations and would eventually catch up with Lockheed at the stealth game, with the B-2 Spirit bomber.
When the Carter Administration took office in early 1977, Bill Perry, an influential defense undersecretary for research and engineering and later defense secretary in the Clinton Administration, learned of how dramatic the results of the model tests had been. Perry immediately saw to it that program became secret. Responsibility was transferred from the mostly-civilian DARPA to the USAF Special Projects Office, and funding was increased. Orders went out stating that the word “stealth” was not be used in unclassified documents, and the program was assigned a meaningless two-word codename: HAVE BLUE.
The first of the two HAVE BLUE demonstrators was intended for aerodynamic tests. Faceting had an interesting consequence: unlike almost every other aircraft ever built, HAVE BLUE’s wings did not have a curved cross-section, being composed instead of flat planes. Its aerodynamics were suspicious, and in fact the machine was so unstable that it had to be controlled by a computerized fly-by-wire system. The first prototype was needed to ensure that the design could fly at all. The second would be a more finished product that would be used for stealth demonstrations.
The HAVE BLUE prototypes were 17.25 meters (38 feet) long, with a wingspan of 10.2 meters (22.5 feet) and a weight of 5.67 tonnes (12,500 pounds). Each was powered by a pair of General Electric J85-GE-4A engines with 13.1 kN (1,340 kgp / 2,950 lbf) each, obtained from Navy T-2B Buckeye trainers. Other scavenged equipment included the fly-by-wire system, modified from the F-16A fighter; and ejection seat, landing gear, and cockpit instrumentation taken from an F-5 fighter.
The Air Force was impressed by the flight tests of the HAVE BLUE 1001 test aircraft, and in mid-1978 Lockheed suggested two designs for an actual weapons system: a medium bomber with four engines and a two-man crew, and a single-seat twin-engine strike fighter. The Air Force preferred the strike fighter concept, and issued a design contract to Lockheed for such an aircraft in November 1978. The aircraft was given the code name ‘Senior Trend’.
The Senior Trend aircraft was a direct outgrowth of the HAVE BLUE prototypes, with many changes to turn the design into a practical combat aircraft. HAVE BLUE’s wings had a sharp sweep of 72.5 degrees, which gave it the flatiron flight characteristics that had led to the loss of the first prototype. As a result, the sweep of Senior Trend’s wings was reduced to 67.5 degrees, and the wings were extended as far back as possible.
Senior Trend was about twice as big as HAVE BLUE. It was 20 meters (65.9 feet) long, with a wingspan of 13.2 meters (43.25 feet), and an empty weight of 13.6 tonnes (30,000 pounds). The canopy was heavily framed and had poor visibility. The mid-air refueling receptacle was positioned behind the cockpit. The door over the receptacle had serrated edges to reduce radar reflection, as did the landing gear doors and canopy leading edge.
Senior Trend was mostly built out of aluminum, though titanium was used around the engines. It was powered by twin General Electric F404-GE-F1D2 turbofans, like those of the F/A-18 Hornet fighter but without afterburners, providing 48.1 kN (4,900 kgp / 10,800 lbf) thrust each. The intakes were covered by grilles, which were electrically heated to prevent them from icing up. The pilot could also activate lights on either side of the cockpit to allow him to check the intake grilles for icing.
The first production aircraft, number 785, was delivered to Groom Lake in the spring of 1982. It crashed and was destroyed on take-off on 20 April, badly injuring the pilot, Bob Ridenauer of Lockheed, who never flew again. The accident was traced to reversed wiring in the flight control system. Number 786 was delivered to Groom Lake in June and used for flight testing.
Senior Trend 787 was the first of the black aircraft to be flown by the 4450th Tactical Group, making its first operational flight on 15 October 1982. By Christmas, several more Senior Trend’s had been delivered to TTR, and the F-117A Nighthawk, as the aircraft had been formally named, was in business.
As the F-117s trickled into Tonopah, operations evolved into a schedule. Flight crews were shuttled there each Monday afternoon on a chartered airliner from Nellis Air Force Base, after spending the weekend home with their families. On arriving at Tonopah, they would be given a briefing on the night’s mission.
Hangar doors were not opened until an hour after dark. For the first year of operations, flight operations were restricted to the Nellis range. Permission to perform off-range operations had to be given by the President himself. Flight routes were defined to avoid populated areas, and some routes were not used if the Moon was more than 50% full. Pilot communications and transponder signals were defined so that the aircraft mimicked an A-7.
Training flights were conducted in two waves, one early and one late in the night. The missions simulated precision strikes on local targets, such as the crossroads of two dirt roads or a shanty in the wilderness. The missions ended before sunrise, since it was found that a pilot found it hard to go to sleep if he went to bed after sunrise.
The enthusiasm for the F-117 grew to the point where the Air Force wanted more of them. The original plan had been for a single squadron of 18 aircraft, organized for special operations, but the plan was expanded to an entire wing, with three 18-aircraft squadrons. Lockheed would build a total of 59 production F-117s, with the second squadron activated in July 1983, and the third going into operation in October 1985. A total of over $6 billion USD would be spent building the F-117s.
During Operation Desert Storm F-117’s were stationed at King Khaled Air Base in Saudi Arabia. Their new home was at the southern tip of Saudi Arabia, well out of range of Iraqi Scud tactical ballistic missiles, and was well-equipped with hardened shelters. It became known as “Tonopah East”, with the similarities in environment possibly being a factor in the selection of the name. The F-117 pilots soon began an intensive training program, since few of the pilots had combat experience in any sort of aircraft.
On 12 January 1991, the US Congress voted to allow the use of force to remove the Iraqis from Kuwait, in support of a UN resolution demanding that Saddam pull out of the country. On 15 January, the deadline specified by the UN resolution expired. The next day, F-117 pilots were briefed for their strikes. During the operation, the 40 assigned F-117’s flew almost 1,300 combat sorties. They dropped almost 2,000 tons of bombs, during 6,900 flight hours.
In February 2006, the Pentagon proposed to speed up retirement of the F-117 Nighthawk and U-2 spy plane to save about $2 billion. To make room for the new F-22 Raptor stealth fighter, and the unmanned reconnaissance drone RQ-4 Global Hawk, the Pentagon wil retire all 52 F-117s in 2008 and the U-2s by 2011.