FVA 14 - Ringflügel
A few years after the Second World War, a chair for aircraft construction was again established in Aachen, and the FVA could justifiably hope for expert scientific support. It was decided to tackle a very unconventional and spectacular project: the construction of a ring-wing glider. The aim of the work was to investigate the flight characteristics of such an aircraft. Because of the omission of non-supporting parts, it was hoped to achieve minimal construction weight, on the one hand, and some outwitting of induced drag, on the other, because of the apparent absence of wingtips. In addition, such a project deviating from the normal shape seemed a very suitable object of study for a student association, since it raised many interesting questions of aerodynamics, strength and manufacturing. Of course, one did not want to be satisfied with theoretical calculations and wind tunnel measurements, one rather wanted to see the project through to the completion of a large-scale model ready for flight. A small moddl of a ring wing had already flown successfully.
In May 1952, the “Kleine Aachener Luftsport-Zeitung” published an article dealing with the special characteristics of a ring wing. From this it becomes clear from which considerations the project FVA-14 had arisen: “Next something would have to be said about the aerodynamics of the ring wing. A small physical experiment is quite interesting. Let a circular disk made of paper, which is weighted with a paper clip, sink to the ground and determine the sink rate! One will find out that the sinking speed decreases, if one cuts a hole with a sufficiently large diameter in the center of the circular disk. The result of this experiment justifies the development from the circular disk wing to the ring wing. The characteristics of the ring wing differ considerably from those of the pure circular disk wing, at least in the rate of descent. The separation of the flow does not occur as suddenly with the ring wing as with the circular disk wing. Also, the glide stability of the former is considerably greater.
If you now take a closer look at an airplane, you will see that there are two main elements that enable this machine to fly: They are the wings, which generate lift, and the empennage, which controls the wings and gives them the necessary attitude stability. The arrangement of these two elements relative to each other can be quite different. The tail unit can be arranged as a tail behind the wings, but it can also be located in front of or attached to them. The various designs known as “flying wing only,” “duck,” etc., are well known. In all these cases, the tail unit has the function of exerting a leverage force with respect to the center of gravity of the aircraft.
However, it is also possible to take a second wing as the control element. The two wings should control each other. In this arrangement, however, the front wing must have the larger effective angle of attack in all flight attitudes at different angles of attack). The center of gravity must therefore be closer to the front wing than to the rear wing. We thus arrive at the concept of a stable tandem airplane.
If, in this tandem arrangement, the ends of the front wing are now swept backward and those of the rear wing swept forward in exactly the same way, so that the ends of both merge into each other, we obtain a ring-shaped wing system. It is not important whether this system is round, oval or triangular.
The aerodynamic properties of these annular airfoil systems have not yet been fully explored. However, it has been proven that it is possible to build longitudinally stable flying machines based on these systems. Some types of these airplanes showed quite remarkable flight characteristics. It is also quite possible to assume that the induced drag of annular wings is lower than that of normal wings with the same aspect ratio.
Like circular disk wings, ring wings have the remarkable property that the lift force increases steadily with the angle of attack up to relatively large angles, without any sudden stall or breakaway of the flow. In all types known so far, the maximum lift seems to be at an angle of attack of about 30°. Since such large angles of attack do not occur unintentionally during flight, it is quite understandable that airplanes with ring wings have very good flight characteristics.
Another remarkable property of the ring wing was noted by the Englishman Tilgham Richards. He found that the center of pressure of such wing systems is almost stationary during flight, or that it is possible to achieve a wandering of the center of pressure which is practically stable up to an angle of attack of 18°. In ring wings, in fact, no case of longitudinal instability has yet become known, although the center of pressure has often been moved relatively far back.”
Unfortunately, under the circumstances of the time, the first wind tunnel tests could not be carried out until 1955 in the wind tunnel of the State Mechanical Engineering School, and the theoretical investigations were also completed only very slowly, so that the construction of the large-scale design was further advanced than the scientific research and calculation of the project would have allowed in normal times. During the wind tunnel tests, it was found that the ring wing also had disadvantages compared to normal aircraft.
The longitudinal stability behavior exhibited a nasty naughtiness: In high-speed flight, the airplane had a tendency to seek the inverted position via a top-heavy moment. An improvement in the flight characteristics, possible within certain limits, led to considerable losses in flight performance because of the very small aspect ratio. These changes would have required extensive and costly modifications to the large-scale design, which was almost complete in its shell. Under these circumstances, the FVA decided not to complete the large-scale version. After another two years, the shell was smashed by the FVAers with axe blows because it took up too much space in the workshop.
Malicious tongues claim that the “ring wing” was built around a workshop pillar by mistake and therefore had to be smashed!