In May 1996, the National Museum of the United States Air Force, located at Wright-Patterson Air Force Base, Ohio, announced the receipt of a new exhibit. The Pentagon and the defense industry donated a unique aircraft to the museum, the very existence of which until recently was a secret. Only many years after the completion of work on the secret project, it was decided to transfer the no longer needed prototype to the National Air Force Museum, as well as to announce the basic information about the project. Thanks to this decision, the whole world was able to learn about a unique development - the Northrop Tacit Blue experimental aircraft.
The appearance of the project with the symbol Tacit Blue was the result of an extensive research program, the purpose of which was to create technologies for reducing the signature of aircraft. By the mid-seventies, American science and industry had time to present developments in this area, which now needed to be tested in practice. In addition, it was decided to develop a new project with a certain groundwork for the future practical application of technology. Thus, one of the future experimental aircraft was to become a demonstrator of technologies in two directions at once.
General view of the Northrop Tacit Blue aircraft. Photo National Museum of the USAF / Nationalmuseum.af.mil
Studying the theoretical part of reducing visibility, the military and researchers tried to determine the future role of promising technology in the air force, for which various options for the use of aircraft were proposed and considered. In December 1976, the US Air Force and the Advanced Projects Agency DARPA launched the BSAX (Battlefield Surveillance Aircraft Experimental) program. The goal of the project was to create a promising aircraft with the lowest possible visibility for enemy detection equipment, equipped with a set of various special equipment. Such an aircraft was supposed to "hang" over the battlefield, remaining invisible to the enemy, while conducting reconnaissance and transmitting data to its troops.
According to some sources, the BSAX program was considered as an addition to the guided weapons being created at that time. The transmission of target designation with the minimum possible delays made it possible to maximize the efficiency of the use of high-precision systems. At the same time, the possibility of joint work with formations using less advanced weapons was not ruled out. Thus, the possibility of constant presence over the battlefield with monitoring of all events gave the troops a certain advantage.
Side view. Photo National Museum of the USAF / Nationalmuseum.af.mil
The BSAX program, for obvious reasons, has received a high level of secrecy. The project was classified as a so-called. "Black", because of which, in particular, a promising stealth reconnaissance aircraft should not have any official designation capable of revealing its goals. The work was carried out under the "neutral" name Tacit Blue ("Silent Blue"). In addition, in the future, the development received several new unofficial names. The specialists who worked with the experimental machine were not left without their own nicknames.
The development of the BSAX aircraft was entrusted to Northrop. This organization had extensive experience in the construction of aircraft of the most daring appearance, and therefore could cope with the tasks set. It should be noted that the developments on the Tacit Blue project could later be used to create new aircraft with specific capabilities. In particular, since the late seventies, Northrop engineers have been working on the ATB project, which later led to the emergence of the B-2 Spirit, an unobtrusive strategic bomber.
The contours of the vehicle were formed taking into account the reduction in radar signature. Photo National Museum of the USAF / Nationalmuseum.af.mil
The main objective of the BSAX / Tacit Blue project was to reduce the signature for radar detection systems as much as possible. To fulfill such requirements, it was even allowed to reduce the basic flight characteristics of the aircraft. Since the project was exclusively experimental in nature and did not have to be brought to mass production, it was proposed to use all the newest and most daring ideas in it. According to various sources, about a dozen ideas of one kind or another were used in the design of the future aircraft, aimed at increasing stealth. The principles of absorption and reflection of electromagnetic radiation away from the source were applied.
The widest application of new ideas and solutions has led to the formation of a very unusual appearance of the aircraft. In addition, already preliminary checks of the proposed design and blowing in a wind tunnel showed the specific characteristics of the proposed appearance, because of which various new means and systems had to be used in the project. Nevertheless, the main task of the work was to reduce the visibility, so that the complication of the structure and onboard equipment was not considered unacceptable.
The tail section of the car. Photo National Museum of the USAF / Nationalmuseum.af.mil
Based on the results of the research, the necessary contours of the aircraft were determined, capable of solving the assigned tasks. It was determined that the BSAX aircraft should be built in a normal aerodynamic configuration with a low wing. At the same time, it was required to use a trapezoidal wing in plan and a V-shaped tail unit with spaced keels, as well as some other non-standard technical solutions. In particular, the need to create a non-standard fuselage was identified.
The main and largest unit of the Northrop Tacit Blue aircraft is the fuselage of the original design. Its bow has a relatively high upper unit, made in the form of a curved part and equipped with a glass cockpit. Behind such a bow was the central compartment, which had sloping sides and a horizontal roof, connected by curved panels. Provided for the upper air intake, made in the form of a depression, smoothly mated with the rest of the fuselage. The tail section of the fuselage served as a fairing and had a tapering shape. The bottom of the fuselage was made in the form of a curved unit of the required dimensions. Its tail section also had a tapering section.
The interior of the cockpit. Photo National Museum of the USAF / Nationalmuseum.af.mil
A characteristic feature of the fuselage of the Tacit Blue aircraft is the "separation" of the upper and lower units by means of an additional plane. A horizontal plane with a V-shaped anterior cut was located in front of the nose. This plane was wider than the fuselage, and its lateral parts were connected to similar units on the sides. In the tail section of the aircraft, the plane expanded slightly, forming an assembly with attachments for the tail assembly. To improve aerodynamics and optimize the distribution of radio waves, additional "influxes" smoothly mated with other elements of the fuselage.
The aircraft received a trapezoidal wing of medium aspect ratio, located with a noticeable shift towards the tail. On the trailing edge of the wing, the placement of ailerons was provided. Instead of the "traditional" tail unit, the experimental aircraft received a V-shaped system with two planes collapsed outward. For use as elevators and rudders, the planes were made all-turning.
Both metal and plastic parts were used in the design of the Silent Blue airframe. In addition, it is known about the use of special radio-absorbing materials, coatings, etc. The combination of various materials made it possible to create an aircraft structure with an acceptable combination of key indicators, as well as meeting the basic requirements of the customer.
Airplane prototype in flight. Photo by US Air Force
The aircraft fuselage layout was simple enough. A single crew cabin was placed in the bow compartment, behind which there was an instrument compartment for placing the main equipment. The tail was given for the installation of engines. The remaining volumes contained fuel tanks and other units of one purpose or another.
As a power plant in the Northrop Tacit Blue project, two Garrett ATF3-6 turbofan engines with a thrust of 24 kN each were used. The engines were proposed to be mounted in the aft fuselage, side by side. To supply atmospheric air to the engines, the aircraft received an air intake of a characteristic design. In front of the descending part of the tail of the fuselage there was a depression, to the rear end of which a common channel of a relatively large width was connected. Passing along the fuselage skin and bending, the air intake channel supplied air to the engine compressors. It was proposed to remove the reactive gases of the engines outside using a common pipe located in the tail of the fuselage. The gases escaped through an elongated nozzle placed above the tail section of the additional fuselage plane.
Test flight. Photo National Museum of the USAF / Nationalmuseum.af.mil
Even at the stage of blowing in a wind tunnel, it was found that the proposed appearance of the airframe, which completely suits the creators from the point of view of stealth, will not be able to provide the required stability in flight. Because of this, a digital redundant fly-by-wire control system was introduced into the project. The stability of the aircraft was now supposed to be monitored by automation. The pilot's task, in turn, was to monitor the operation of the systems and control the aircraft in accordance with the flight program. The main controls were a "fighter" type handle, a pair of levers for controlling the operation of engines and a pedal. At the pilot's workplace there were several panels with all the necessary devices.
The Pave Mover radar station was considered as the aircraft's payload. This product consisted of a large antenna device and modern computing equipment, which made it possible to track the ground situation, detect stationary and moving objects, etc. In the future, an improved version of this station could become a standard payload of a serial reconnaissance aircraft. In addition, it was planned to use the developments on this project in the future when creating promising aircraft for long-range radar surveillance and control.
The BSAX / Tacit Blue project mainly used the latest ideas and solutions. Nevertheless, with the aim of a certain reduction in the development cost, it was decided to apply some of the existing units and assemblies. So, the three-point landing gear with the front strut was borrowed without significant changes from the production Northrop F-5 fighter. The cockpit housed an ACES II ejection seat.
A unique specimen in the museum. Photo National Museum of the USAF / Nationalmuseum.af.mil
The total length of the experimental aircraft was supposed to be 17 m, the wingspan was 14.7 m. The height in the parking lot was 3.2 m. The maximum take-off weight was determined at the level of 13.6 tons. which the maximum speed reached only 462 km / h. Service ceiling - 9, 15 km. It is easy to see that the Northrop Tacit Blue should not have had high flight performance. However, the experimental technology demonstrator aircraft did not need them.
The BSAX project was based on the most daring and original ideas, which led to a noticeable delay in work. The construction of a prototype aircraft of a new type started only in the early eighties. In one of the shops of the Northrop company, while observing all secrecy measures, an unusual aircraft of non-standard shapes was gradually formed. In the near future, this aircraft was presented for testing.
The prototype of the new aircraft differed from other equipment in its unusual appearance. Quite naturally, this led to the emergence of a lot of jokes and new nicknames. For its characteristic appearance, Tacit Blue was called "Flying Brick", "Whale", "Alien School Bus", etc. In addition, the nickname "Shamu" was used, which was the name of several killer whales from the SeaWorld Aquarium in San Diego. The names "Whale" and "Shamu" led to the fact that the nickname "whalers" stuck to the specialists working on the project. Fortunately, they did not live up to such a nickname, thanks to which the prototype aircraft has survived to this day.
The tail section of the fuselage close-up. Photo Wikimedia Commons
During the first weeks of 1982, the Northrop Tacit Blue prototype aircraft underwent preliminary ground tests. According to available data, the so-called. Area 51, Nevada, at Edwards Air Force Base, California. The car was sent on its first flight on February 5. After that, regular flights began, the purpose of which was to test the operation of various onboard systems, as well as to determine the effectiveness of the measures used to reduce the signature. For obvious reasons, a certain part of the information on the results of such tests is still not subject to open publication.
During the tests, the experienced "Kit" usually made three or four sorties a week. Nevertheless, at certain times, test pilots had to lift the car into the air several times a day. Apparently, the change in the intensity of the tests was associated with certain modifications, as well as the introduction of any innovations in the aircraft's own equipment or ground equipment.
Tests of the Northrop Tacit Blue prototype aircraft continued for three years. During this time, 135 flights were performed with a total duration of about 250 hours. As part of the checks, specialists from Northrop, the DARPA agency and the Air Force managed to collect a large amount of data on the means of reducing the visibility, their effectiveness, etc.
Silent Blue is transported to the new showroom on October 7, 2015. Photo National Museum of the USAF / Nationalmuseum.af.mil
In addition, the advantages and disadvantages of the project were identified in terms of flight data. So, already during the first test flights, the conclusions of aerodynamic research were confirmed. The aircraft did not really exhibit stable behavior. It is widely known the statement of one of the creators of the project, designer John Cashhen: "at that time it was the most unstable aircraft of all that a man lifted into the air."
The main task of the BSAX / Tacit Blue project was to test the basic ideas and solutions for reducing the aircraft's signature for radar detection systems. It was also planned to study the possibility of using such a machine as a carrier for a radar station and to determine its general characteristics. In 1985, the test program was fully completed, after which the experimental aircraft was sent for storage. Now specialists from the aviation industry and related industries should study the experience gained and apply it in new developments.
As subsequent events showed, the original appearance of the prototype aircraft in its current form was no longer used. The unusual shape of the airframe gave some reduction in visibility, but seriously worsened the basic flight data and made it difficult to control the aircraft. In addition, the ongoing work on the study of the shapes and contours of aviation technology has already yielded some results in the form of more convenient designs.
Airplane nose close-up. Photo National Museum of the USAF / Nationalmuseum.af.mil
The developments on the Pave Mover radar station were soon implemented in the AN / APY-7 project. Since the beginning of the nineties, stations of this type have been installed on Northrop Grumman E-8 Joint STARS reconnaissance and combat control aircraft. This aircraft was created on the basis of the civilian Boeing 707, the development of which did not use any means of reducing the visibility, but at the same time it is able to fully solve the assigned tasks.
The experimental project BSAX / Northrop Tacit Blue allowed American specialists to study in more detail the problems of reducing the radar signature of aircraft. In addition, he made it possible to conduct a preliminary check of various radar systems, both aviation and ground. As a result, the aircraft, nicknamed "Whale" or "Shamu", did not go into series production, but contributed to the creation of new types of equipment, which were subsequently brought to mass production and operation.
After the completion of the tests, in 1985, the only built prototype of the Tacit Blue aircraft was sent for storage. A unique sample of aviation technology was idle for ten years. Only in the mid-nineties, it was decided to declassify the aircraft and part of the data about it, as well as transfer the surviving prototype to one of the aviation museums. In this case, it was possible to free up space at one of the air bases, as well as save an interesting sample for posterity. The following year, the only Northrop Tacit Blue was donated to the National Air Force Museum, where it is preserved to this day. Since last autumn, Flying Brick has been in the newly built new showroom.
