Aircraft designers continue to strive to create technologies to make flying safer and more efficient. This is how the experimental NASA AD-1 appeared, which was and remains the only jet aircraft on the planet with an asymmetric rotary wing, made using the technology of "scissor wings". And, despite the fact that such a concept contradicts one of the main features of the liners - the symmetry of their design, the engineers of the famous American department decided to try it. But with the obvious prospects of the project, the only way that turned out to be possible for NASA AD-1 is to replenish the museum exposition.
Experimental aircraft NASA AD-1 was developed by specialists at the Ames Research Center - a branch of the government agency of the US National Aeronautics and Space Administration. The prototype was assembled and tested at NASA's Dryden Flight Research Center in Edwards, California.
Basically, NASA AD-1 is the embodiment of the concept of tilted or so-called "scissor wings" on airplanes. The abbreviation AD-1, which stands for Ames-Dryden-1, refers to a small jet airliner, whose wing in flight was able to rotate around a central axis - thus providing the most effective airspeed angle at the right time.
In total, during the period from 1979 to 1982, when the aircraft was undergoing tests, it made 79 flights, during which both the effectiveness of the concept of a rotary wing in general was tested, and data was collected regarding the aerodynamics and level of controllability of this type of wing in conditions of various speeds. and oblique angles of the wing.
However, the basic principles of the concept, which became the basis for the development of the AD-1, appeared much earlier than the aircraft itself. One of the first to actively study non-trivial wing types was Robert T. Jones, an aerodynamic and aeronautical engineer, an employee of the same NASA Ames Research Center at Moffett Field in California. In his spare time from the main work, he was engaged in research on the concept of a variable sweep wing.
In fairness, it should be clarified that he did not take data for his research from nowhere: a similar concept was already implemented as part of a project to create an X-5 aircraft back in the fifties of the last century. As a result of his research, Jones proposed an interesting idea: swinging the wings back - this should be used to delay shock waves and compressibility as the aircraft approaches the sound barrier. It was assumed that in this way the car would fly more efficiently at high speeds.
After conducting research in wind tunnels, Jones came to the conclusion that the construction of a supersonic transport aircraft with inclined wings would increase the aerodynamic characteristics of the machine, in comparison with counterparts with fixed wings: according to Novate.ru, it was assumed that it would be at least twice as economical. The result of these searches was the development in the early seventies of a prototype on a reduced scale. It was put together by the Ames Industrial Company, based in Bohemia, New York, at a cost of nearly $ 240,000.
Known design solutions and individual technical characteristics of the original aviation concept. For example, the plane was lifted into the air using two Microturbo TRS18-046 turbojet engines, each of which was capable of developing a thrust of about 0.98 kN, and the AD-1 itself - a maximum speed of more than 320 km / h. However, in the operational documents, the last indicators were limited - for safety reasons, a threshold of 270 km / h was set.
The prototype AD-1 was almost 12 meters long and had a wingspan of ten meters (in a horizontal position), a height of just over two meters, and the mass of the aircraft was 973 kilograms. Fiberglass reinforced plastic and rigid foam were chosen as the material for the main structure. Among the design features of the prototype, one can single out a fixed chassis of a tricycle configuration, characterized by a small length and fasteners in close proximity to the fuselage in order to reduce drag.
However, the most interesting is, of course, the embodiment of the unique concept of the aircraft wing. True, the path to its creation turned out to be very long. The fact is that traditionally the wings have been optimized to maximize one of the two main functions - either lifting the car during takeoff and landing, or increasing the speed during flight.
Accordingly, the designers found themselves in the search for a compromise, because maximizing one ability inevitably led to a decrease in the effectiveness of the second. A striking example of such a trend was the choice of the type of wing, depending on which characteristic is preferable for a particular model: if it was supposed to improve performance at low speeds, in particular, during takeoff, then fixed structures were chosen, and if priority was given to operation at high speeds - swept …
It was the problem of this compromise that prompted a whole group of aircraft designers to think about creating such a wing concept in order to "kill two birds with one stone." One of these enthusiasts was engineer Jones, who, while working at the NASA facility, came to the conclusion that aircraft become less maneuverable and efficient when they reach high speeds. And he saw a way out of the situation in the acquisition of the ability to turn by the wings. And tests on this concept have demonstrated an improvement in the aircraft's performance at high speed. At the same time, Jones suggested that to achieve the same results, it would be enough to turn back only one wing.
Inspired by the results of his research, engineer Jones showed his concept to the agency's management. It was only then that it was rejected, considering it too difficult to implement. However, there were still unconditional advantages on Jones' side that could be obtained if the concept was implemented: for example, significant fuel savings were observed, which would make it possible for the aircraft to reach lower takeoff speeds and significantly increase the range at cruising speed.
In the fifties, research and testing in the wind tunnel continued, which confirmed the viability of Jones's idea, but two decades later, NASA management gave the go-ahead to develop a working prototype with a rotary "scissor wing". Moreover, the initial concept was finalized by Ames Research Center and Bert Rutan - the authors of the AD-1 project itself: if Jones assumed the design of a winged aircraft with a fixed angle of inclination, then the prototype wing had a variable sweep due to the use of electric motors that were switched by the pilot in the cockpit.
In 1979, the prototype was completed and ground and vibration tests of the airframe began, which are carried out immediately before flight tests. Their results were very promising: it turned out that the wings were 15% stronger than previously calculated. The first test flight took place on December 21, 1979 at Edwards Air Force Base in California, and a total of 79 flights were made, during which the aircraft wings were located in various configurations. And they reached the maximum tilt angle - sixty degrees - only in 1982.
The testing period showed that in most characteristics it met the expectations of both Rutan and Jones. But the concept also had disadvantages: for example, there was a reduced lateral stability of the machine, as well as the appearance of oscillations with certain configurations of the wings. Another problem was the deterioration of the aircraft's controllability at temperatures above 50 degrees - this deficiency was noted by many test pilots who flew the AD-1.
In addition, NASA assigned this project the status of "high-risk development", so they did not modify the aircraft, but decided to simply close the project. The AD-1 last took off on August 7, 1982, at the Experimental Aircraft Association's annual exhibition in Oshkosh, Wisconsin. And after that, the prototype of the unique aircraft was first returned to NASA Dryden, and after a while it became part of the exposition of the Hillier Aviation Museum in California.
Want to know more about yet another type of swept aircraft? Then read: Why does it not fly in the opposite direction: all the pros and cons of the forward-swept wing