In the early sixties, the CIA and the US Air Force ordered Lockheed to develop and build a promising high performance reconnaissance unmanned aerial vehicle. The task was successfully solved within the framework of the D-21 project, based on the most daring decisions and ideas. The technical and technological part of this project is still of great interest.
A special challenge
On May 1, 1960, the Soviet air defense successfully shot down an American U-2 plane and thereby showed that such equipment could no longer work with impunity on the USSR. In this regard, the search for alternative solutions began in the United States. Lockheed's secret department, known as the Skunk Works, soon came up with the concept of a one-off high-speed reconnaissance UAV capable of photographic reconnaissance.
The proposed idea interested the customers, and in October 1962 there was an official order for the preliminary study of the project. In the shortest possible time, it was possible to complete the formation of the general appearance and begin aerodynamic tests. Based on the results of the first successes, in March 1963 a full-fledged design contract was signed. At that time, the future drone bore the designation Q-21. It was later renamed D-21.
The first version of the project, known as the D-21A, proposed the use of a UAV with an M-21 carrier aircraft. The latter was a two-seat modification of the A-12 reconnaissance aircraft with a pylon between the keels and some other devices for working with UAVs. In December 1964, an experienced M-21 made its first export flight with a D-21 on board.
On March 5, 1966, the first drone was launched from a carrier aircraft. Despite certain difficulties and risks, the separation and the beginning of an independent flight went without problems. In the future, several more similar tests were carried out. On July 30, the fourth launch ended in an accident. The UAV was unable to move away from the carrier and hit its tail. Both cars collapsed and fell. The pilots ejected, but one of them could not be saved.
Based on the test results of the experimental complex, it was decided to abandon the carrier in the form of the M-21. The updated D-21B reconnaissance project proposed launching from under the wing of a B-52H bomber. The initial acceleration of the drone was to be carried out using a solid propellant booster. Tests of such a complex began in the fall of 1967, but the first successful launch took place only in June 1968.
Trials 1968-69 proved the high characteristics of the new reconnaissance complex. Thanks to this, a large order appeared for serial equipment for the further operation of the Air Force and the CIA. In November 1969, the first "combat" flight took place to shoot a real object of a potential enemy.
The D-21A / B UAV could reach a maximum speed of M = 3.35 at an altitude of about 3600 km / h. At the same time, he was able to automatically fly along a given route, go to the area of the designated target and take photographs of it. Then the drone lay down on a return course, dropped a container with reconnaissance equipment in the desired area and self-destructed.
The development of an aircraft with such characteristics and capabilities at that time was very difficult. However, the set tasks were solved by using the most modern materials and technologies. Some ideas and developments were borrowed from existing projects, while others had to be created from scratch. In a number of cases, it was necessary to take a noticeable technical risk, which entailed new difficulties.
One of the main tasks of the Q-21 / D-21 project was the creation of a glider capable of providing a long flight at speeds over 3M. Such a design had to have the required aerodynamic characteristics, as well as withstand high mechanical and thermal loads. When developing such a glider, the experience of the A-12 project was used. In addition, some design solutions and materials were borrowed.
The D-21 received a cylindrical fuselage with a frontal air intake fitted with a tapered central body. Externally and in design, the fuselage was similar to the nacelle of the A-12 aircraft. The glider was equipped with a "double delta" wing with a triangular main part and developed long bends. A similar scheme has already been tested in a full-size aircraft project and has shown compliance with the basic requirements.
The airframe of such shapes was proposed to be made entirely of titanium. Other metals were used only as part of other systems and assemblies. The outer and inner surfaces of the airframe in contact with hot air received a special ferrite coating, also taken from the A-12 project.
Initially, the possibility of using the Pratt & Whitney J58 engine developed for the A-12 was considered, but this led to an unacceptable increase in the cost of the project. An alternative was found in the form of the RJ43-MA-11 ramjet engine from Marquard Corp. - This product was used on the CIM-10 Bomarc anti-aircraft missile. For the D-21, it was modified: the updated RJ43-MA20S-4 engine was distinguished by an increased operating time, which corresponded to the profile of the reconnaissance flight.
A new automatic control system was developed specifically for the D-21, capable of guiding the UAV along a given route. It used inertial navigation devices borrowed from the A-12. Due to the complexity and high cost, the control system was made salvable.
A drop container called Q-bay with a parachute system and inflatable floats was provided in the nose of the fuselage. Inside this container were placed the control system and navigation equipment, as well as all cameras with film cassettes. At the final stage of the flight, D-21A / B had to drop a container, which was then picked up by an airplane in the air or by a ship from the water. The search for Q-bay was carried out using a built-in radio beacon. Previously, similar technologies were used to search and rescue film containers launched from reconnaissance satellites.
The first D-21 drones were built in 1963-64, and small-scale production soon began. Before stopping it in 1971, Lockheed had produced 38 products in two main modifications. Some of these UAVs were used in tests and in real reconnaissance flights.
At the first stage of the project, in 1964-66. there were five sorties of the M-21 aircraft with the D-21A UAV on the pylon. Of these, four provided for the reset of the apparatus - three were successful, and the last ended in disaster. Tests of the D-21B lasted from 1967 to 1970, during which time they carried out 13 flights, incl. with imitation of the solution of reconnaissance tasks.
Combat use included only four flights. The first of them took place on November 9, 1969 and ended abnormally. The D-21B UAV successfully reached the Chinese training ground Lop Nor, took photographs - and did not go back. He continued his flight, ran out of fuel and, with some damage, "sat down" on the territory of the Kazakh USSR, where he was discovered by the Soviet military.
On December 16, 1970, the second launch took place for reconnaissance of Chinese objects. The UAV successfully completed the survey, returned to the specified area and dropped the Q-bay container. It was not possible to catch it in the air, and the rise from the water failed - the product, along with the equipment and films, sank. The third flight on March 4, 1971 ended with similar results, the container was lost.
The last flight of the D-21B took place a few weeks later, on March 20. The device, for unknown reasons, fell on the territory of the PRC, not far from the landfill to which it was heading. After this failure, the CIA and the Air Force were finally disillusioned with the D-21B project and decided to stop using such equipment.
Considering the results of the tests and actual use of the D-21A / B, you can see the main reasons for the failure. Thus, the lack of reliability of the control system became a serious problem. In particular, it is for this reason that the secret UAV after the very first "combat" sortie went to a potential enemy. In addition, unexpected problems arose with the search and rescue of the container with the equipment - however, the drone's own fault in this was minimal.
With all this, the D-21A / B UAV was technically complex and expensive. The average cost of each such product, taking into account the development work, reached $ 5.5 million in 1970 prices - about 40 million today. It should be noted that the cost of a single drone was significantly reduced due to the repeated use of a container with the most expensive components.
The designers at Lockheed / Skunk Works were given a very difficult task, and they generally coped with it. The resulting reconnaissance apparatus showed the highest tactical and technical characteristics, but still did not fully meet the requirements of real operation. The D-21 product turned out to be too complex, expensive and unreliable.
Perhaps, further refinement of the design would have allowed to get rid of the identified problems, but it was abandoned. In addition, they abandoned the concept of a supersonic long-range unmanned reconnaissance aircraft. As a result, bold and promising technical solutions, despite their high potential, did not find further application.