's F-117 was the first true stealth aircraft, which is invisible to radar.
E 'is therefore useful to trace the history of this important development of aviation technology.
The mechanism by which a radar "sees" a target is very simple: a beam of radio waves is emitted by a transmitter, the waves bounce off "obstacles" (and therefore on target) and back, to be collected by a receiver shows that these return signals on a screen.
Each object has a surface radar equivalent: that is, its reflectivity compared to the radar waves is calculated using a comparison with the reflectivity of a flat metal surface.
The radar cross section RCS of an object is called and is expressed in measures of area. If we say that an aircraft has an RCS of 10 square meters, which means it has the same ability to reflect radar waves in a metal plate of 10 square meters.
The smaller the RCS of an aircraft, the lower the distance that can be spotted by a radar, the same power transmission.
Americans were among the first to realize the importance of reducing the RCS of an aircraft in order to make it more difficult to detect by radar, and since the early '50s began to study special paints and materials that absorb radar energy rather than reflect it.
These studies led to a series of tests made in 1958 with a Lockheed T-33 trainer covered with such materials (called RAM), during which there was - in secret - that the road was promising, although we need to work a lot these materials because they weighed a lot and endanger aircraft flying qualities.
From those experiences we went in the first operational use: the strategic reconnaissance SR-71 Blackbird reconnaissance drone and some designed in the sixties, as the Firebee and D-21, made use of materials RAM and paints to reduce the RCS.
The design of these aircraft began to take into account the need to reduce the RCS: designers and experts were in fact moving in different directions to obtain the result: the use of RAM materials were joined by the construction lines designed to avoid coupling between the surfaces that negatively affect the visibility to radar.
It began to apply construction techniques to hide or delete bolting and other irregularities that acted by real radar reflectors, they began to examine how to hide the radar compressor blades for jet engines.
With these materials and these techniques, the supersonic bomber
B-1A, which first flew in 1974, had a lower RCS even hunting as the Phantom II
ol 'F-15 Eagle
.
The U.S. was now accumulating vast experience and technological knowledge in this new field, in the utmost secrecy: at that time, in fact, no one else will even put the issue to lower the radar track of its combat aircraft.
The American designers, however, were now projected to the realization of a plane, as well as much of the energy absorbing material radar thanks RAM, presented surfaces designed to deflect electromagnetic energy balance, and enable it to obtain a virtually complete invisibility compared to radar. Unfortunately, every
optimal design for lowering the visibility radar challenged the aerodynamic requirements: an aircraft designed in that way would never be able to fly well.
This finding led to a downsizing of expectations to the point that stood only an experimental program of DARPA, called Project Harvey, who was not protected by the bond of secrecy, which included, in competition, Northrop and Lockheed .
In the mid-seventies, however, the aviation technology experienced a revolutionary development: the flight control systems operated by the computer, known by the acronym FBW (Fly By Wire). These systems
had the potential to allow the pilot of any aircraft type, regardless of its traditional aerodynamic qualities.
Suddenly we realized that it was possible to design an aircraft invisible without bothering to comply with the normal rules of aerodynamics. The program
Project Harvey, who had been selected for the project of Lockheed, thanks to new technology showed that it could make a plane invisible to radar completely: it was then that he was born the term "Stealth," which means, roughly, furtive .
Thus, in 1977, the program was renamed HAVE BLUE and fell in absolute secrecy.
HAVE BLUE led to the realization of two demonstrators, the first of which, called HAVE BLUE 1001, rolled out of Lockheed's Burbank plant secrets (the famous Skunk Works) in November 1977 and was immediately transferred in the even more secret military base at Groom Lake in a desert area Nevada, often referred to as Area 51 and the subject of legends and fantasies of all kinds.
After several months of testing and inspection, in 1978, the HAVE BLUE 1001 was destroyed in an accident and to preserve the secrecy was buried in the sand of the desert. HAVE BLUE 1002 was replaced by that suffered the same fate in 1979.
Meanwhile, back in 1978, the USAF had decided to develop an air attack by enlarging and improving the design of the two HAVE BLUE was born SENIOR TREND program.
were ordered 5 copies FSD (development and pre-production), the first of which flew in 1981.Furono all delivered by 1982.
In the same year began the delivery of the copies of the series, the first of which was destroyed during takeoff, and the new aircraft was designated F-117A Nighthawk.
In 1980 there was a leak to the press, and the Government had acknowledged the existence of a stealth program, but in fact nothing was leaked on the state of the program and new fighter aircraft could remain secret. To this end, instructional and test flights took place almost exclusively at night.
The Nighthawk is a plane far from the drawing innovation: the fuselage is flat, one with the wings to form a kind of wedge, the rear tail fins are made of two different angles with very wide, which serve as both rudder rudders that orizzontali.Le surfaces are flat, faceted in order to deflect the waves radar.Il aircraft is powered by a pair of modern turbofan F404 without postbruciatore.L 'weapons, not to compromise the quality stealth, is transported in a cargo bay inside the fuselage, designed to accommodate two guided bombs Paveway laser class of 1,000 kg each.
The F-117 has no internal cannon and has no radar: navigation and attack relies on an inertial navigation system, a FLIR sensor for the vision sensor and a front view of the DLIR terrain and laser illumination of targets.
speed is subsonic.
features stealth aircraft have been obtained thanks to the extensive use of RAM materials and the particular facet of the surfaces. The air intakes are shaped so as to hide the fans of turbofan. It 'called for special treatment of surfaces and detail: it was shown that even a ledge a few tenths of a millimeter (eg, a screw or bolt is not perfectly even the droppings of the birds) to undermine the invisibility to radar, which However it is not absolute.
The Nighthawk, in fact, a surface radar (RCS) equivalent in the range of 0.001 to 0.003 square meters, lower than that of a small bird.
The track has been reduced infrared, hiding the discharge nozzles with a grid system and mixing the flue gas with cold air.
The USAF plans to acquire only 18 copies of the series, to equip a single squadron dedicated to special operations, but the enthusiasm for the qualities demonstrated by stealth aircraft was such that it was decided to order a total of 59 horses, with which three squadrons were equipped, all operational by 1985.
The need to fly only at night to preserve the secrecy of the aircraft resulted in the loss of certain aircraft and related pilots, because of the "spatial disorientation" caused by the flight without external references.
For this reason, in 1988 the Pentagon decided to disclose the existence of the plane, and first released a doctored photo and of poor quality. But it was not until 1990 that the aircraft was finally unveiled to the public during an actual event.
Meanwhile, the Nighthawk had a baptism of fire in December 1989 some F-117 bombs with laser struck military targets in Panama in Operation Just Homes "aimed at ousting the dictator and capture Noriega.
The real challenge came in January 1991, when U.S. forces and their allies waged the war of liberation of Kuwait, invaded by the troops irakene.Gli F-117 did what they were designed: they reached their targets without being seen by the network of Iraqi radar and destroy them with laser-guided bombs, thus paving the way for successive waves of about 40 aircraft attacco.I Nighthawk located in the 1271 bombing missions carried out without any loss, dropping 2,040 laser-guided bombs, destroying a total of 1,677 targets.
In the years following the F-117 were again used in attacks against Iraq's air defense positions in response to frequent violations of peace agreements. In such circumstances, the Nighthawk HARM anti-radar missiles also employed. The
Nighthawk Black day was 28 March 1999, when a specimen in bombing mission over the skies during the Serbs "Kosovo War" was shot down near Belgrado.Sono many assumptions were made about this killing, ranging from the presence of Serbian spies close to the Aviano Air Base from where the fighter had taken off, to the degradation of stealth characteristics following the opening of doors for the release of the hold internal bombe.In effects of the F-117 took off from Aviano to bomb targets Serbs, under the gaze of onlookers and journalists, and always walked the same routes during the same hours. And actually opening the doors of the hold significantly degrades the stealth for a few seconds, enough to use an active radar-guided missile or semi-active, but enough to alarm a an anti-aircraft particularly vigilant and know in advance that the route of the aircraft. One such location was, and had not been reported intelligence militare.I Serbs launched some ground to air missiles (SA-6 according to American sources, SA-3 SA-2 or as otherwise) and used it to drive a radio control system with sensors, optical / IR, allowing them to hit the velivolo.Il pilot was rescued by a SAR mission, while the wreckage and were taken by the Serbs - it seems - at the disposal of Russian technicians, before being transferred to a museum. The
Nighhawk has undergone to various training programs, the first named OCIPE and the last, in 2000, called SCF, which has made it compatible with the new GPS-guided weapons and replaced the RAM with paint newly designed products, lighter and stronger and that require less maintenance. The hunt is still in service with the USAF, but it is expected to be replaced by the new F-35
.
course, for its special characteristics, the F-117 was not offered on the export market, except to the RAF, but without success.
The formula of the F-117 has been partially superseded by more recent developments in technology.
In fact, the new stealth aircraft, such as 'F-22
el'
F-35 , unable to obtain levels of invisibility to radar comparable to those of the Nighthawk, without recourse to faceted surfaces, but adopting the softness and raccordate.Ciò allowed to make hunting "invisible" while ensuring that excellent performance in terms of speed and maneuverability, the quality with which the Nighthawk had to give up.
still stealth technology, introduced by the F-117, is a closely guarded secret from American designers, and continues to provide a significant margin of superiority in combat.
