A rare shot of the HB 1002 in flight - the exotic shape of the aircraft and the strong forward sweep of the wing leading edge are clearly visible. Note the faceted elevons, moving tail planes and a retractable knife antenna on the lower surface of the right wing plane.
Aviation in the first years after the war, it developed so fast that radar equipment could not keep up with them, and the task of reducing the radar visibility of aircraft became less relevant. However, some work in this area was still underway. For example, the outstanding American aircraft designer Clarencel “Kelly” Jonson, when designing the high-altitude reconnaissance “Lockheed” U-2, sought to minimize the dimensions of the machine, making it thus less noticeable to radars. In the Soviet Union, studies were conducted to reduce radar visibility through the use of special radar absorbing materials and structures. In particular, the Myasishchev Design Bureau considered ways to reduce the effective dispersion surface of the strategic ZM bomber.
With the advent of anti-aircraft missile systems equipped with high-altitude rockets and powerful radar stations in the USA and the USSR at the end of the 1950-ies, the issue of reducing the radar visibility of aircraft became again relevant.
After all, the main means that avoided detection by the enemy locators was, at that time, going to extremely low altitudes, and this led to an increase in crew fatigue, excessive fuel consumption and an overall decrease in combat capabilities. This implies the main idea of a strike aircraft that has a low visibility: it must fly over a territory covered with anti-aircraft defense equipment at high and medium altitudes. As a result, the crew’s awareness of the situation is improved, the search for ground targets at long ranges is facilitated and the trajectory of the fall of bombs becomes more steep, which increases the accuracy and increases the penetrating power of bombs. The possibility of flying at medium altitudes increases the efficiency of laser illumination of targets with its own guided weapons.
The first major attempt to reduce the effective dispersion surface was the Lockheed SR-71 supersonic high-altitude reconnaissance program, which was also developed under the guidance of Johnson. The layout of the aircraft was mainly determined by aerodynamic requirements, but its features (cross-sectional shape of the fuselage, the shape of the engine nacelles, their conjugation with the wing, keels with a slight deviation to the inside) contributed to the reduction of the effective dispersion surface. The company also developed a radio absorbing internal awl-shaped construction with a plastic honeycomb core. It was used in lateral tides, elevons, and wing socks of the original version of this aircraft, which was designated A-12. On its basis, SR-71 was created (for the first time, the 22 of December of the 1964 of the year took off for the first time). His radio absorbing material was preserved in the design of the elevons and wing socks. SR-71 was covered with a special paint having a high thermal emissivity, which reduced the skin temperature during cruising altitude flight. The use of ferrite as its basis made it possible to reduce the aircraft’s radar visibility due to a more uniform reflection of electromagnetic waves. The effective dispersion surface of the SR-71 and A-12 aircraft was smaller than that of the U-2. The later developed remotely piloted aircraft D-21 (launched from the B-52 and SR-71 bomber) had even less visibility. Late versions of U-2 also covered with ferrite paint.
As a rule, U-2 and SR-71 belong to the first generation of inconspicuous aircraft, F-117A is considered a representative of the second. The creation of this aircraft was preceded by a long research and development work, which in the United States were conducted with 1965 year. The stimulus for these works was the appearance in the USSR of the C-75 and C-125 anti-aircraft missile systems, which demonstrated quite high efficiency in Vietnam and the Middle East. Hopes for on-board electronic countermeasures did not materialize - the missile systems were quickly improved, and the containers with equipment reduced the combat load of the aircraft. In the US, in 1972-1973, the civilian four-seater Eagle pistol aircraft, created by Windecker, was tested, mainly made of plastic, and its further development was experienced YE-5A. YE-5A had a fiberglass skin and internal structure using radio absorbing materials. The trials were crowned with success, and in 1973, the United States Air Force, in conjunction with the Defense Advanced Research Projects Agency, DARPA, launched secret research projects, the main purpose of which was to create a low-profile jet combat aircraft. Leading aviation concerns were given a special assignment. Boeing, LTV, Grumman, Northrop and McDonnell-Douglas responded to him. Lockheed did not qualify for the mission, as it had not been involved in fighter aircraft for the past 10 years. But despite this, she submitted for the consideration of DARPA an initiative proposal, which in November 1975, together with the project of the company Northrop, chose for further work on experimental Stealth Technology (XST, an experimental technique of low visibility). The company "Lockheed" all further work on the "stealth" was engaged in the Department for Advanced Development, located in the city of Palmdale, California (semi-official name "Skunk Works"). It was there that previously created the U-2 and SR-71.
The first prototype XST "Heav Blue" company Lockheed
The technical requirements for the XST aircraft were stringent requirements, mainly to the size of its effective dispersion surface. The analysis has shown that the use of radio absorbing materials and individual "barely noticeable" structural elements will be small, and fundamentally new solutions are required. The real way out of this situation was the widespread use of low-reflective forms. If before that the contours of the aircraft were determined mainly by aerodynamics, now it was relegated to the background, and the main attention was paid to developing the configuration of the airframe to reduce its reflectivity. The strongest reflectors of electromagnetic energy by that time were already known. These are the so-called shiny (mirror) points, which reflect the energy exactly in the direction from which the wave came, the joints of the surfaces (corner reflectors), and the sharp edges of the bearing surfaces. The low-reflective configuration of the airframe, therefore, should have been distinguished by an integral arrangement with no protruding elements and a minimum number of edges. To do this, it was necessary to ensure a smooth pairing of the fuselage and wing. Inside the wing it was necessary to place the engines and target load. In addition, it was necessary to minimize the size of the vertical flat surfaces or eliminate them (these are the strongest reflectors, since the aircraft is irradiated with ground-based radar stations mainly at a gentle angle). Keels, if they persist, deviate from the vertical. Direct radar irradiation of engine compressors is prevented by using curved air intake ducts.
To the greatest extent, these requirements are satisfied by a “flying wing” with smooth contours, which, in addition to the low-reflective configuration, has a large internal volume for installing engines and placing loads. In the United States, confirmation of the low effective dispersion surface of such a layout was first obtained at the end of the 1940-s, when coastal radar air defense systems located south of San Francisco were bombarded with a YB-49 Northrop bomber. Later during the NATO maneuvers, the Americans noted the complexity of the radar tracking of the British bomber "Vulcan", which was not inferior in size to the B-47, but its reflected momentum was several times less.
It was possible to assume that the developers of the XST aircraft would choose a scheme close to Vulcan, especially if we consider that the traditional disadvantage of this layout — insufficient longitudinal stability — could be eliminated by electric remote control systems that appeared by that time. But the magnitude of the effective dispersion surface of an aircraft is influenced not only by the geometric shape and electromagnetic properties of its surface, but also by the ratio of the dimensions of the aircraft to the wavelength of the irradiating radar, and the irradiation angle. This greatly complicates the determination for the “flying wing” of the optimal shape of the surface of complex curvature. The limited capabilities of 1970 computers, as well as the complexity of mathematical modeling of an effective dispersion surface, did not allow solving a similar problem at that time. It turned out to be easier to determine the dependence of the effective dispersion surface on the irradiation angle for the combination of flat surfaces. As a result, Northrop and Lockheed companies in their XST projects decided to use a circuit with a multi-faceted (faceted) hull shape close to the “tailless”. This configuration does not eliminate brilliant points, however, with a certain orientation of edges and flat surfaces, it makes it possible to combine reflection angles from several structural elements, thus reducing their number and removing from the sector the most likely radiation directions. This means that in these directions, the facet form ensures a significant reduction in the level of the reflected signal in all wavelength ranges of the irradiating radar station. That is, the aircraft becomes almost invisible to the air defense radar.
HB 1002 is preparing for the first flight. The aircraft had all the features of an “invisible plane”, including a radio-absorbing coating, but did not have a bow rod - as on the first aircraft. The design of the machine was made primarily of aluminum.
Both companies presented similar XST projects. Both aircraft, in addition to the body of the facet shape, had a large-swept wing, two-fin plumage with keels tilted inward to shield the engines output nozzles. The main difference between the projects was the location of the air intakes: the Northrop company offered one dorsal air intake, located just behind the pilot’s cabin, and Lockheed two lateral air intakes.
In the first phase of the XST program, companies created models on the scale of 1: 3 to evaluate the effective dispersion surface. In 1976, they began to experience them in anechoic chambers. In the middle of the same year, Lockheed won the competition, receiving a contract to build a pair of experimental aircraft under the Have Blue program. A. Brown, an engineer at Lockheed, argued that the success of his company was largely due to the use of Soviet technical literature, first and foremost, the theoretical work of Ufimtsev, an employee of the Institute of Radio Engineering and Electronics of the USSR Academy of Sciences. His article on computational methods for determining the effective dispersion surface, published in a short-run, agency-wide journal in 1962, was translated into English in 1971 and used in Lockheed during the development of the Echo program that was used to calculate bodies of various configurations. Americans themselves write that this made it possible for 30-40 to reduce the percentage of development costs for XST, and then F-117. The tests in the chambers made it possible to specify the configuration of the aircraft, which was developed on the basis of calculations under the Echo program. After that, purging took place in high- and low-speed wind tunnels. They spent 1920 hours. After that, Lockheed manufactured a full-scale radar model, on which the design details were finally completed. In a short time it was built two flight copies.
The experimental "Have Blue" turned out to be small (the length was 14,4 m, including the nose bar) subsonic single aircraft. The aircraft was equipped with two engines, J85-GE-4A "General Electric", taken from the training deck aircraft "North American" T-2В almost unchanged. The sweep angle of the delta wing along the leading edge was 72,3 degrees. The aircraft had neither air brakes nor flaps, since their installation inevitably increased the effective dispersion surface. The only control surfaces are simple elevons and a pair of rolled-in keel piled inside. Basically, the airframe was made of aluminum, using steel and titanium in the most heat-stressed components. The pilot piloted the plane with the help of a side grip and pedals. The signals from them were perceived by the electrical remote control system, which had no mechanical duplication. During the tests, the mass of the machine varied from 4200 to 5680 kg, of which 1600 kg was fuel.
However, the design, which allowed to reduce the level of reflection of the radar signal, was the reason for the fact that the car was difficult to manage and maintain. The strength of the design also left much to be desired, the prototypes even got the nickname "Hopeless Diamond".
At the end of 1980, the aviation community, filled with rumors and bits of information, was eager to uncover the secrets of the stealth technology. Aviation-related artists painted sketches and images of a mysterious airplane. But as soon as the F-117 declassified, all of them - like the one shown in this figure - turned out to be far from reality.
The first engine launch of the experimental “Have Blue” took place at 04.11.1977 on the Skunk Works site, which was adjacent to the airport of Berbank. Due to the high secrecy of the product, the aircraft was installed between two trailers, and a camouflage net was pulled from above. Racing engines were performed exclusively at night, after the airport was closed. Then the plane was disassembled and on board the C-5A 16 November delivered to the place of flight tests - a secret base Groom Lake (Nevada). 1 December 1977 test pilot Bill Park lifted the first “Have Blue” into the sky, which was designed to study the characteristics of handling and stability. The 36 flight took place; however, the 4 of May 1978 of the year, while landing at a high vertical speed, the aircraft hit the surface of the runway. As a result of the accident, the right chassis support was seized in a semi-folded position. The pilot tried to shake it out three times, attaching it to the lane with the left wheel, but did not succeed. Then the Park rose to a height of 3 km and catapulted after producing all the fuel. The second copy, made directly for the study of the characteristics of visibility, took off on July 20 and within a year carried out the 52 flight, completing the test program in full. The final phase of testing included a “game” with real air defense, when the aircraft was tried to be “found” by all available means. Experimental aircraft "Have Blue" showed low visibility in the radar, acoustic and infrared ranges, proving the possibility of creating a subtle combat aircraft.
Aircraft performance characteristics:
Wingspan - 6,86 m;
The length of the aircraft - 14,40 m;
The height of the aircraft - 2,28 m;
Wing area - 105,90 m2;
- empty aircraft - 4060 kg;
- Maximum take-off - 5670 kg;
- fuel - 1588 kg;
Engine type 2 turbojet engine General Electric J85-GE-4A;
Thrust - 2x1338 kgf;
Maximum speed - 966 km / h;
Cruising speed - 456 km / h;
Flight duration - 1 h;
Practical ceiling - 10200 m;
Crew - 1 man.
Based on materials: