The development of energy regeneration system and the result of flight demonstration were described in this paper. The regeneration system was designed and integrated to regenerate potential energy of aircraft to electric energy. The autors experimentally clarify the conditions to maximize regeneration efficiency. The display system and a power lever included as pilot interface in the system are configured to adjust the regenerated power without any increase of pilot workload. As the result of test flights in 2015, functions of the system are properly demonstrated and succeeded to realize stable `Regenerative Soaring' for the first time in the world.

This paper proposes the novel motor fault detection method for the multiplex motor propulsion system using a propeller as the torque reference device. The electric propulsion system has particular issues which are difficult to detect directly but essential for the flight such as a demagnetization of the motor cause of the torque reduction of the motor. Therefore, fault detection method is important to take advantage of the electric propulsion system which can configure higher redundancy system such as the distributed or multiplex propulsion system. The proposed method is demonstrated using 100 kW class four stage multiplex motor system, and it is verified that the proposed method can detect the fault motor without any additional sensor in the practical power level.

Flight tests were conducted to evaluate a paint-riblet. This study is named FINE:Flight Investigation of skiN-friction reducing Eco-coating. The paint-riblet is made from a common paint for aircrafts. The paint-riblet has fine grooves and it reduces skin friction in the turbulent boundary layer. The groove width of the paint-riblet is 100 μm, which is optimized size for flight conditions for common airlines. The paint-riblet is painted on a fuselage of an experimental aircraft in Japan Aerospace Exploration Agency. A measurement system with Pitot rake is made in order to evaluate skin friction reduction by the paint-riblet. Wind tunnel tests including high Reynolds number condition on the momentum thickness same as the flight test are conducted to investigate detailed effects of the paint-riblet. Direct numerical simulation is also conducted to investigate the flow field on the riblet. As the result, the flight data of the paint-riblet shows agreement with the drag reduction predicted by the wind tunnel test and the direct numerical simulation. This result indicates the effectiveness of the paint-riblet in the flight condition and the usefulness of the design techniques with wind tunnel and DNS in this study.

Demand for aircraft transportation has doubled in the past ten years and is expected to increase. On the other hand, electrification of the aircraft's equipment is gradually improving. As part of this electrification, mounting of electrically driven wheel is considered. Our previous research also proposed safety landing by electrically driven wheel. In this paper, we propose the total thrust control method using propeller and electrically driven wheel in ground run. This method can accelerate in constant value on dry or wet road surface. We demonstrate the effectiveness of the proposed method by simulations and basic experiments.

The concept of avoiding complete loss of thrust by a multiplexed motor system was proposed for the purpose of reducing the accidents due to engine failure of single engine aircraft. The developed multiplexed motor system consists of four motor elements and can provide totally 60 kW power. Even if one motor element loses the power during takeoff and climb, the aircraft can safely continue to climb due to the output of 45 kW from the remaining motor elements. The pilot can maneuver with the same feeling as in the conventional aircraft without any discomfort in the multiplexed motor system. The motor system and the pilot interface were mounted on a demonstrator and manned flight tests were conducted. This paper describes about the summary of flight tests in FEATHER (Flight-demonstration of Electric Aircraft Technology for Harmonized Ecological Revolution) project at JAXA and discusses the design method of the multiplexed motor system for aeropropulsion.

Demand for aircraft transportation has doubled in the past ten years and is expected to increase. Therefore, aircrafts must become more safer. Most business jets accidents occur while landing; in many times, the accidents are caused by strong cross winds and tail winds. In this paper, we propose motion control for aircraft landing, taking advantage of electric motorization of aircraft in recent years and the characteristics of electric motor. By utilizing the advantages such as fast torque response, easy distributed arrangement, and independent control, electric motors for driving the wheels, we propose a method to suppress the yaw-rate generated in crosswind landing. In this paper, we demonstrate the e ff ctiveness of the proposed method by the simulation and basic experiments. Simulation was also performed when the velocity control was incomplete due to measurement error, and showed the robustness of the proposed method.

Aircrafts are desired to be more energetically e fficient and safer due to the increasing demand of air transportations. Generally, business airplanes tend to have low stability under wind disturbances especially during landing. Due to electric motor’s high performances among motion control compared to internal combustion engines, electric airplanes, in which electric motors are used for propulsion, can satisfy the demands of both e fficiency and safety. In this paper, by utilizing electric motors’ advantages, lift control method using propeller slipstream as well as thrust control is proposed. The e ffectiveness of the proposed method is verified by simulations.

Aircrafts are desired to be more energy efficient and safer due to the increasing demand for air transportations. However, generally speaking, nowadays commercial airplanes tend to loss stability under wind disturbances, especially during landing. On the other hand, electric airplanes (EAs) are believed to satisfy the two demands because electric motors are used for the propulsion. Especially, as the actuators, electric motors can improve the control performances of EAs compared with internal combustion engines (ICEs). In this paper, by utilizing electric motors' advantages, lift control method using propeller slipstream is proposed for safe landing, which might be a key technology to innovate the design of EAs. Moreover, simulations and experiments are conducted to verify the effectiveness of the proposed method.

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Electrical airplanes (EAs) have become practical in the recent years. Considering the increase of demand on smaller aircraft and the attention to environmental issues, the demand on small EAs is expected to grow in the coming decade. However, the accident rate of small aircrafts is higher than that of larger aircrafts, so ensuring higher safety of EA is very urgent. Modeling and thrust control of EAs have been proposed previously by the authors' research group. However, this model and control method is not suitable when the propeller revolution speed is near and below zero. In this paper, the improved thrust control method based on new EA propeller plant is proposed. This method is necessary for design of airspeed control method, which can be expected to improve the safety of EA. A towing test method which allows plane's dynamical experiment on ground is also proposed. Real flight experiment was the only conventional method test a plane's dynamics. However, the test piece needs to be a complete airplane to conduct a real flight. Moreover, it is impossible to observe the response a particular input without interferes from other factors. The proposed method allows component technology to be tested in dynamical situations. The effectiveness of the proposed methods is verified through simulations and experiments.

In the recent years, attention has been gathered in the research field of electric airplanes (EAs), which have electric motors as a power source. EAs have many advantages including low environmental impact and safety. The flight range per charge, however, is shorter than that of conventional airplanes. This paper proposes a range extention control system (RECS) which extends the flight range of EAs by control. It is shown that the power consumption can be minimized by optimizing thrust distribution on multiple propellers with different properties. The effectiveness of the proposed method is verified by simulations and experiments.

Electrical airplanes (EAs) have become practical in the recent years. Considering the increase of demand on smaller aircraft and the attention to environmental issues, the demand on small EAs is expected to grow in the coming decade. However, the accident rate of small aircrafts is higher than that of larger aircrafts, so ensuring higher safety of EA is very urgent. In this paper, the new thrust control method based on new EA propeller plant is proposed. This method can be applied to new advanced flight control systems of EA, which can be expected to improve the safety of EA. The effectiveness of the proposed method is verified through simulations and experiments.

The concept of a passive hybrid system consisting of fuel cell stacks, Li-ion battery packs, and two diodes was tested. The diodes take the place of the DC/DC converter that is usually used to align fuel cell and battery voltages, thereby directly connecting the fuel cell and the battery. Prototype equipment was built for collecting characteristic data on the static and dynamic behavior of the hybrid system. The measurement results indicate that increasing the operation efficiency and simplifying the system were possible by applying the direct hybridization concept. The dynamic behavior results showed an interesting combination of output signals from the fuel cell stack and the battery pack. The quick response of the battery output completely compensated for the delay in fuel cell output response, indicating that the direct hybrid system is also applicable to high-frequency electric loads such as brushless DC motors. The ability to recharge without a DC/DC converter was also successfully validated for the direct hybrid system. From the measurement results, the design method, and the system sizing, this passive hybrid system appears promising for application in the Antares DLR-H2 electric aircraft test bed.

Three-dimensional laminar boundary layers are susceptible to cross-flow instability and streamline-curvature instability, both of which lead to growth of longitudinal vortices. It is practically difficult to distinguish one instability mode from the other in the natural process of laminar-turbulent transition. Unlike plane-wave disturbances, however, the point-source disturbances evolve into dispersive development of their different components, which will result in separate appearance of two instability modes downstream of a point source. Continuous excitation from a small hole is applied to the boundary layer on a yawed circular cylinder evolving into a wedge-shaped pattern downstream of the hole, while a pulsed jet through a tiny hole is used to generate disturbances of a wave-packet type in the flow on a rotating-disk. Spatial development of localized disturbances corresponding to these experimental configurations can be described by linear stability analysis based on the complex ray theory. Comparison between experimental results and theoretical calculations shows qualitative and even quantitative agreement for either case.