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An all-electric General Aviation airplane was realized within the ENFICA-FC program (ENvironmentally Friendly Inter City Aircraft powered by Fuel Cells - EC funded project coordinated by Prof. Giulio Romeo). The electric-motor-driven two-seat airplane powered by fuel cells was developed and validated by flight-test in May 2010. The airplane represents the first and unique airplane flying in the world. Six test flights were successfully carried out by POLITO. The all-electrical power system was successfully tested during the experimental flights. Take-off and climbing was obtained at power of 35 kW. Level flight was attained at 150 km/h by mean of only a fuel cell power setting. 2.5 hours of effective flight were obtained during flight tests for a total path of 237 km. A new speed world record of 135 km/h and an endurance of 39 min. was established during flights conducted for the FAI Sporting Code Category C (airplane). The excellent results obtained by the flight tests can be considered as a further step in the European and World Aeronautics Science in introducing a completely clean energy (ZERO CO2 EMISSION). At the same time, more theoretical type studies have been carried out in designing an aircraft powered by hydrogen for 10-20 passengers in the regional and intercity sector”. The airplane works on hydrogen, taking advantage of the “fuel cell” technology at present available, to create an aircraft that is able to connect cities through flights while totally eliminating the environmental impact.

This article deals with the design, manufacturing, and testing of a propeller for a general aviation aircraft fuelled by hydrogen. The feasibility of the ENFICA-FC project depended on several key-enabling technologies. In order to minimize the power required from both the batteries and the fuel cell, a highly efficient electrical propulsion system was required, in which all the components would need to yield the highest possible efficiency. The choice of the propeller for this specific aircraft was more difficult, above all because the electric motor was limited as to the torque it could handle. In addition, the propeller would also have to provide the necessary airflow for the motor, electronics, and fuel cell cooling to ensure that the temperature did not exceed the limits imposed by the manufacturer. Although a designer may be aided by modern numerical design and analysis programmes to optimize propellers, structural and manufacturing constraints can influence the final choices. Finally, the calculated performance would always have to be validated with experimental tests. An optimal propeller has been designed and manufactured to be installed on the Rapid 200 FC aeroplane. Static tests on the manufactured two-blade propeller were performed by means of a static test facility. Specific tests have also been performed to check the efficiency of the propeller when installation effects (blockage and scrubbing drag effects) are included and to verify the real efficiency of the propulsion and cooling systems, with the propeller installed in the complete converted aircraft. A good agreement between the theoretical and experimental data was obtained.

The hydrogen and fuel cell power based technologies that are rapidly emerging can be exploited to start a new generation of propulsion systems for light aircraft and small commuter aircraft. Different studies were undertaken in recent years on fuel cells in aeronautics. Boeing Research & Technology Centre (Madrid) successfully flew its converted Super Dimona in 2008 relying on a fuel cell based system. DLR flew in July 2009 with the motor-glider Antares powered by fuel cells. The goal of the ENFICA-FC project (ENvironmentally Friendly Inter City Aircraft powered by Fuel Cells -European Commission funded project coordinated by Prof.Giulio Romeo) was to develop and validate new concepts of fuel cell based power systems for more/all electric aircrafts belonging to a "inter-city" segment of the market. As a result of the project, a technology demonstrator was designed, manufactured and tested: a new proton exchange membrane (PEM) fuel cell based power system was installed in the Skyleader RAPID200 that had its demonstrative flights in 2010. One of the most critical, if not the most critical, aspect of the all-electric power system adopted for demonstrator is undoubtedly prediction of fuel cell behaviour, specifically in terms of temperature control since reduced volumes and low weights (needed for the aeronautical applications) are not beneficial from a heat-management point of view. Moreover temperature control of PEM fuel cell is extremely important for a correct employment of the cell itself and, since the fuel cell is the main power generating device on the aircraft (batteries are however present as emergency back-up), temperature control becomes a very important safety issue too. In particular, as the ionic conduction of the polymeric membrane is a function of its degree of humidification, the stack temperature has to be carefully controlled to avoid phenomena of water evaporation causing an increase of ohmic drop and a decrease of stack performances. The output power of the fuel cells system is affected considerably by the change of the stack temperature. The paper will report a description of the research activity that lead to the fuel cell based power system developed for the ENFICA-FC project: the main topics will regard the design phase, including numerical and theoretical modelling (validated by flight tests) of the fuel cell system and its cooling, the results of ground testing and installation and, finally, the results of flight testing

Next generation of composite civil aircrafts and unconventional configurations, such as High Altitude Long Endurance HALE-UAV, exhibit aeroelastic instabilities quite different from their rigid counterparts. Consequently, one has to deal with phenomena not usually considered in classical aircraft design. Alternative design criteria are needed in order to maintain the safety levels imposed by the regulations and required for certification. The A2-Net-Team project aims to build a multi-disciplinary network of researchers with complementary expertise to develop analytical methods used for a better understanding and assessment of the factors contributing to the occurrence of critical aeroservoelastic instabilities. Along with modeling and numerical investigations a test article will also provide the opportunity to modify and calibrate theoretical models, to highlight and explore their limits, to recommend the necessary modifications and future pertinent investigations. The objective of this paper is to provide the authors' point of view on a consistent scaling procedure applicable when investigating the flutter stability of a full-size high aspect-ratio composite wing structure by means of an economical laboratory wind tunnel test model. Sizing and technological development aspects are discussed along with a detailed design procedure to gather the necessary data for the model manufacture. To exemplify the procedure a wooden model is fabricated and used to provide insight into the scaling procedure and verify the acquired data. Finally a dynamically scaled composite model is defined for a wind tunnel aeroelastic test.

Some main activities have been developed as part of the HELINET research project which was financed in January 2000, by the European Commission, (Fifth Framework Program in the IST action), to develop a European project in the field of stratospheric platforms. From the aeronautical point of view the following items were studied: (1) the design of an autonomous high altitude long-endurance unmanned air vehicle (HALE-UAV) platform capable of remaining aloft for very long periods of time (between 6 and 9 months) using a solar-powered and fuel cell system and to gain a complete understanding of the feasibility of a near-term aerodynamic HALE concept, in particular as far as stratospheric platforms are concerned (mainly dependent on high efficiency and reliability of solar cells, fuel cells and electric motors), (2) an evaluation of the production and service costs and an assessment of the safety and regulatory aspects of the platform, and (3) the manufacturing of a scale-sized technological demonstrator and the execution of static tests on it up to the ultimate load. The first HELIPLAT® (HELIos PLATform) configuration was worked out, on the basis of a preliminary parametric study. The platform was a twin-boom tail type monoplane with eight brushless motors, a long horizontal stabilizer and two rudders. A scaled-prototype was designed to demonstrate the feasibility of this configuration and to perform some structural static and dynamic tests on it. The main CFRP structures were manufactured by CASA (Spain): the principal wing and horizontal tail tubular spars, booms, vertical tail spars and some reinforced ribs. These parts were delivered to the Aerospace Engineering Dept. (DIASP) at the Politecnico di Torino (POLITO) and assembled using special joints while some other necessary parts were manufactured by POLITO-DIASP. A parallel activity was performed to define the structural test configurations and structural test frame. The manufacturing activities and the development of the structural test system is described in the first part of the paper. Static and dynamic experimental tests were performed in two phases (2003 and 2004) on the prototype and the results of the static tests are presented in this paper and compared with numerical and theoretical computations.

High Altitude Long Endurance (HALE) aircraft exhibit aeroelastic behavior that is quite different from conventional flight vehicles. For such aircraft, large static structural deformations that occur during standard flight conditions could severely reduce the flutter speed. Limit cycle oscillations may occur, reducing their operational life. In this paper, a non-linear aeroelastic model is proposed as a design/diagnostic analysis tool. A geometrically exact non-linear structural model for large deformations by Hodges and Dowell, modified according to Da Silva second order geometrical non-linear terms, has been adopted. The structural model has been coupled with an unsteady aerodynamic model for an incompressible flow field, based on the Wagner aerodynamic indicial function, in order to obtain a non-linear aeroelastic model. Within the analysis, linear and non-linear static and dynamic aeroelastic responses have been considered. The approach enables one to expedite the calculation process. In addition to analytical and computational results, a high aspectratio wing model has been selected as a candidate for a feasibility study case and to validate the theoretical model. Preliminary tests have been conducted and more experiments are underway.

This paper presents the design and manufacture of the first European Very Long-Endurance Stratospheric Unmanned Air Vehicle, HeliPlat® (HELIos PLATform). This vehicle is a monoplane with eight brushless motors, a twin-boom tail type and two rudders. A computer program has been developed to carry out the platform design. To minimize airframe weight, high modulus carbon fibre composite material has been used extensively. Airfoil coordinates and wing planform have been optimized in order to achieve the best possible aerodynamic efficiency by using integral panel/boundary-layer methods and also to obtain the minimum possible induced drag with respect to local Reynolds airfoil. To this effect, several wind-tunnel tests were carried out so as to compare the analytically predicted airfoil performances. After an initial configuration had been worked out, a scale technological demonstrator (wing span 24 m) was designed, manufactured, and tested under shear, bending, and torsion loads. Finite element analysis was also carried out in order to predict the static and dynamic behaviour of both the full-size and scale model versions of the HeliPlat structure. The preliminary static test resulted in a high correspondence.