FVA 25 - UL-Ente
After the arduous and lengthy construction of the FVA-20, the motivation for a new, large prototype project was not exactly overwhelming and so it took until 1984 to build up the necessary enthusiasm. This was triggered by the emergence of ultralight aircraft as a new class of aircraft that had much lower certification hurdles than a conventional aircraft, opening up the possibility that designers could see the first flight of their work within their student years.
However, unlike the ‘wire frames with covering’ on the market at the time, the FVA-25 was to be manufactured with the new materials of the time, carbon and aramid fibers. This then brought up the discussion of configuration, which led to the duck configuration after the conventional hang glider and briefly discussed flying wing variants. After the initial design, the key data were defined as follows:
|Wingspan main wing||10 m|
|Wing aspect ratio||7|
|Main wing surface||14 m²|
|Wingspan canard||4,09 m|
|Neutral point distance wing canard||3 m|
|Vertical-Separation wing-canard||1 m|
|Max. Speed||160 km/h|
|Max g-load||-3 bis +6 g|
The wing was to be made with two spars of CFRP and spar webs and ribs of rigid PVC foam, and the planking was to be aramid fiber. The design of the elevator was identical, but the main wing was still supported by a V-brace.
The fuselage was formed by a triangular girder of rigid PVC foam with CFRP tubes in the corners, to which the engine, elevator, pilot seat and landing gear were directly attached. The connection to the wings is via CFRP tubes and a connector, which also houses a rescue system. The rudders in the main wing winglets are also made of CFRP. All CFRP components are protected externally by aramid layers.
Construction was very instructive, especially at the beginning, for the FVA members, most of whom had no construction experience. In 1985, the spar was built, and at the same time, the planking was also completed and mounted on the unfinished wing. Further construction then took a little longer, partly because parts of the FVA turned their attention to the construction of the FVA 27. In 1988, the final part, the fuselage, was finally produced. As the project progressed, it was converted into a tubular steel structure and, with the connecting piece to the wings, had a mass of only 23 kg. In addition, the 25 was to receive nosewheel control and its winglet rudders were to be decoupled from it.
One of the last problems was the engine. A 40 kg 50 hp engine was to be used in order to have a high power reserve during the first phase of flight testing. This engine brought the overall design very close to the certification limit of 150 kg empty mass. A 20 kg lighter engine was then to be used in the final variant, but it later became apparent that the empty mass would be about 270 kg. This problem threatened the project until it was resolved by a change in regulations that increased the allowable weight limit of ULs from 150 kg empty mass to 400 kg maximum takeoff mass.
After most of the parts were manufactured, assembly of the FVA-25 and testing of the power train began in 1989, until the Canard took off for the first time in 1992 during initial taxi tests. At this point, the problem of certification came into play and began to delay the project even further, as there was neither the awareness of when to deal with certification nor the experience with the process. In addition, due to the already advanced project time and some incidents, there was a dwindling motivation among the active people, who were mostly occupied with other projects.
When in 1994 finally extensive proofs for the certification had been provided, it was added that the LBA had handed over the certification of ULs to the DAeC, which demanded a much too high fee. In the second half of the year, the project was considered to be moved to France and to be flown there with a French license, but this was not carried out in the end.
In 1996, the project was about to be abandoned, the prototype was to be abandoned due to lack of space, and the project was nearly discarded as a failure. Then, however, a fellow aviator from Belgium approached the FVA to save the prototype. He took the FVA-25 with him to the airfield Arlon-Sterpenich where the first flight of the FVA-25 took place in 1997. The feedback was good aerodynamics, too weak engine and strong top-heavy behavior, but the UL duck was flown. Thus the FVA-25 project was successfully completed after all.