A New Dimension in Performance and Safety
Birth of the Project
As the fs35 started to look less and less like a construction site and more like a proper airplane, we started considering ideas for our next project. In 2017, it was announced that one could apply for support for promising ideas from the Luftfahrtforschungsprogramm (LuFo, Aerospace Research and Development Program) of the Federal Ministry for Economy and Energy, which was very appealing for the members of the Akaflieg Stuttgart. At around the same time, two ideas came to the forefront. The first proposal, named fs36-Velo, involved an elastic wing leading edge, allowing for a slot-free high-lift device. The second proposal was for a sailplane which would experiment with an electrical control system, the fs36 FlyByWire.
Both proposals were approved, though unfortunately as an Akaflieg, we would be unable to complete both projects. We informed the Projektträger Luftfahrtforschung (PT-LF, Project Sponsor for Aerospace R&D) and after much consideration and a feasibility study, we decided to proceed with only the fly-by-wire proposal. Our proposal specifies the design and construction of a demonstrator for a fly-by-wire control system in a sailplane, where the control surfaces are solely driven by electromechanical actuators. The Akaflieg will deal with designing and building the plane itself while the Institut für Luftfahrtsysteme (ILS, Institute for Aerospace Systems) of the University of Stuttgart will be responsible for the flight computer and necessary software.
Of course, that raises the question, why should one build a sailplane with a fly-by-wire control system?
The topic of safety is an important one in the field of sailplanes. According to the Bundesstelle für Flugunfalluntersuchung (BFU, Federal Bureau of Aircraft Accident Investigation), 49% of all fatal accidents between 1996 and 2009 were a result of an entry into an uncontrolled flight situation. The development of a fly-by-wire sailplane can help prevent this via the isntallation of a stall protection or even a complete envelope protection system. In addition, further automization allows for the integration of a flight path control system that can assist pilots in avoiding collisions and airspaces.
Apart from increased safety, a fly-by-wire system enables an improvement in flight performance. Through the replacement of a mechanical control system with actuators and cables, new paths are opened in terms of flexibility. For example, it’s possible to control a larger amount of aileron surfaces with variable deflections without having to design a complicated mixer. Furthermore, by limiting the flight envelope or by adding an active flutter prevention system, it’s possible to lighten the structure.
Since as students it’s difficult to complete such a complicated project alone, we’ve secured the ILS as a LuFo project partner. The institute itself has gained much experience in the field and has even installed an automated avionic platform in a DA42. Its using this experience that they develop the flight computer to fit our requirements.
From the revival of the fs34 …
Even with a proposal at hand, the question still remained of what kind of airplane exactly that we want to build as a demonstrator. As ambitious aspiring engineers, we wouldn’t be satisfied with simply converting a standard production sailplane. Only a concept which will also demonstrate the performance advantage of a fly-by-wire control system would suffice. So we decided to look back into our history and realize an old, unfinished project, the fs34.
… to the fs36
As with the fs34, the fs36 is to be equipped with Fowler flaps. The aircraft is designed to be able to thermal with other planes when its flaps are extended while at the same time, benefiting from the reduced drag during high speed flight with retracted flaps.
Due to the amount of time the fs35 project took to be completed, we have decided to finish this project at a much quicker rate. To this end, we’re restricting the amount of innovative ideas and concepts that we will incorporate in the project and we will use the fuselage of a standard production sailplane. Modern construction methods should also help us build the plane faster.
Currently, the fs36 project is in its design phase. Aspects such as aerodynamics and structure of the wings and components in the fuselage are being dealt with. Furthermore, we’re testing the waters and gaining experience from construction tests.
Articles to specific aspects of the project will be published soon in our news section.
|Wing area||ca. 8,5 – 10 m²|