A novel airspeed detection method was developed for electrified aircraft, offering a reliable alternative to conventional air data equipment (ADE) utilizing pitot tubes. Conventional ADE systems are susceptible to failure and may pose challenges in installation on newly configured aircraft. The proposed method used monitored quantities such as rotational speed, motor torque, and current of a propulsion propeller positioned directly opposite to the airflow. The procedure for calculating propeller torque and the subsequent detection of airspeed by propeller advance ratio were formulated using the monitored quantities. Since it is inherently difficult to determine a priori the propeller characteristics, particularly the relationship between propeller torque and advance ratio, a ground-roll-based procedure was devised to identify these characteristics. Additionally, an advanced procedure was developed to estimate airspeed as well as air density by modulating rotation speed marginally during flight. Flight demonstrations employing an electrified motor glider showed minimal deviation between this method and ADE outputs, typically within a few percent. Wind tunnel tests employing the same propeller as the motor glider demonstrated that airspeed and density can be estimated within
This study proposed and evaluated a cooling system that uses liquid film evaporation for high heat flux environments on a heated rotating disk, such as the axial gap motor (AGM) used in liquid rocket engines. Cooling conditions to avoid demagnetization of the rotor were evaluated through heat conduction simulations of the rotor, and the liquid film thickness required to achieve sufficient cooling power was investigated. Furthermore, the effects of different coolants on cooling power were investigated. The results showed that the required heat transfer coefficient depended on the coolant, and a liquid film with a thickness of a few micrometers was required for effectively cooling AGMs in rocket engines. Additionally, depending on the heat generation rate, even evaporative cooling may fail to easily cool AGMs in rocket engines. Therefore, technologies to reduce the heat generation rate in the motor are required.
As air traffic systems transition towards trajectory-based operations with fewer constraints on flight planning, optimizing trajectories in flight plan generation holds promise for greater efficiency. To harness this potential, the optimizer necessitates an aircraft performance model with highly accurate fuel flow rate predictions, capable of accounting for individual aircraft performance variations over time due to daily wear-and-tear of flight operations and maintenance. This study proposes a method to construct tailored performance models using airline-acquired flight data. We demonstrate the feasibility of simultaneously estimating aerodynamic and fuel models, traditionally regarded as challenging, by incorporating vertical velocity due to climb and descent, and inertial drag due to acceleration and deceleration. This approach reduces estimation bias, enhancing the model's applicability across a wider flight envelope including climb and descent phases, thus facilitating more comprehensive trajectory optimization solutions. Hold-out validation confirms the model's accuracy, with mean fuel flow rate error below 1%. Furthermore, this method's ability to extract individual aircraft performance from flight data suggests potential applications in maintenance-related performance monitoring.
Beams consisting of lattice structure with slits for high-accuracy deployable reflectors were developed, and their mechanical characteristics were evaluated through numerical simulations and experiments. In these lattice beams with slits, slit members are placed on the side of the lattice beam where bending deformation is to be restrained. When the beam bends above a predetermined level, the slits close, and the members contact each other, thereby increasing the stiffness of the beam structure and restraining deformation from the predetermined shape. The numerical analyses were conducted by changing the stiffness of the beam material, and it was confirmed that the proposed lattice beam with slits can reduce the sensitivity of the deformation to changes in the stiffness of the beams. Then the model was printed using a 3D printer, and bending experiment was carried. The experimental result shows that the appropriately designed beam structure can be easily bent at low loads up to a designed deformation, and their stiffness increases after the slits are closed. This result indicates that beams for deployable reflectors consisting of these lattice structures deploy easily, and the deformation due to disturbance can be mitigated by increasing the structure's stiffness after deployment.
A thruster head of a water-vapor Hall thruster with a discharge channel of 15 mm in diameter and 5 mm in width was designed and developed by applying the conventional scaling law to a previously studied laboratory model. The newly designed thruster was successfully operated at discharge powers ranging from 80 to 340 W. The thrusts were estimated from the plume diagnostics, which were validated by direct measurements using a thrust stand. As a result of the performance analysis, it was revealed that the thrust exhibited a linear correlation with the discharge power, while the specific impulse and anode efficiency also varied with the discharge voltage. Unlike other internal efficiencies, higher discharge voltages did not necessarily enhance the mass utilization efficiency, especially above 250 V. This suggests that the electron temperature is less likely to increase in the high-voltage regime, possibly due to further energy losses from additional chemical processes or wall interactions.
A winglet design is discussed from the perspectives of sonic boom suppression and drag reduction at supersonic speeds. Design parameters such as dihedral and anhedral angles that were effective in reducing drag in previous studies on low-drag designs of a winglet at transonic and supersonic speeds were used in this study, and their effects on a low-boom design are examined herein. Non-dominated solutions with respect to sonic boom loudness and drag are explored using response surfaces and a genetic algorithm. Two characteristic winglets are selected from the solutions, and their drag and sonic boom characteristics are compared. Results showed that winglets affect sonic boom signatures through the shielding, cancellation, and reflection effects. The first two effects weaken expansion waves propagating to the ground, exerting a positive impact on rear boom suppression. In terms of drag reduction, the suction force of the winglet utilizing expansion waves on the upper surface of the wing should be enhanced, and the pitch trim change should be minimized to reduce trim drag. Based on these results, design guidelines to reduce both sonic boom loudness and drag are derived.
This study addresses the residual thrust concept in hybrid thrusters. In this phenomenon, thrust is generated by the gasification of heated fuel post-firing, particularly after long-duration maneuvers. Residual thrust is significantly lower than nominal thrust. However, it poses challenges for attitude control and orbit design in small satellite missions because it can cause postural instability. The residual thrust in hybrid thrusters has not been evaluated to date. This study represents a pioneering study in this field. We conducted a simulation incorporating the rocket equation, unsteady heat conduction equation, fuel pyrolysis characteristics, and radiation from the nozzle and injector to the fuel. Subsequently, we estimated the residual thrust after firing. This estimation technique was applied to a single-port fuel. Simulation results indicate that the residual thrust can exceed 0.3 N for up to 6 s after firing if the fuel regression rate is 0.01 mm/s immediately after firing. The results showed that the residual thrust effect is greater for smaller regression rates. Thus, a thruster for slowly regressing fuel can generate more significant residual thrust than that for regressing fuel quickly, even if the same Delta is designed.
Aircraft trajectory generation is one of the key technologies for realizing and researching a highly efficient air traffic system. Fast-time simulations are used for the initial evaluation of newly proposed operational concepts, and the employed scenarios must be faithful to actual aircraft operations and include a wide range of possible future events. In addition, since aircraft trajectories are influenced by numerous complex factors, incorporating these factors into the generation process is essential to improve the fidelity of the generated trajectories. This study employed a deep generative model to capture these factors, with surrounding traffic conditions selected as a representative example. In particular, a flow-based generative model was employed to obtain the generation probability of the trajectory to allow evaluation based on the probability of events occurring in the simulation. The generated trajectories were confirmed to be consistent with the operational flight envelope and surrounding traffic using publicly available track data.
The L-band digital aeronautical communications system (LDACS) is a broadband, secure digital communications system based on cellular technology, designed specifically for aeronautics applications. It enhances the safety and efficiency of air traffic management (ATM) by supporting innovative paradigms such as 4D trajectory-based operations (TBO). Given that the LDACS frequency band is also allocated for aviation surveillance and navigation equipment, ensuring electromagnetic compatibility (EMC) with these systems is critical. The determination of requirements for collocating LDACS and aeronautical surveillance systems in L-band has already started, recently. However, realistic and solid measurement findings are necessary to determine the condition for co-existence. This study investigates the EMC between LDACS and surveillance transponder (XPDR) to establish the required attenuation levels for their onboard coexistence. Two transponders are used as devices under test (DUT): one tailored for small aircraft and the other for large aircraft. Through a combination of experimental analysis and estimations, the study identifies the attenuation levels necessary for LDACS-XPDR coexistence. These findings enable the implementation of measures such as antenna separation or out-of-band rejection filters to facilitate the effective integration of LDACS and XPDR onboard aircraft.
Weather avoidance algorithms play a crucial role in significantly enhancing aircraft safety during flight operations, particularly in the presence of severe weather conditions. This paper presents a novel obstacle avoidance strategy based on the use of alternative paths to circumvent obstacles during the cruise phase. The objective of this study is to assess the benefits of using strategic information to address tactical avoidance issues. Firstly, the new strategy is simulated in a dynamic space populated with weather obstacles. Subsequently, the proposed strategy is compared to a classical avoidance maneuver in several dynamic simulations, varying the size of the obstacles. The results show that including strategic information on dynamic rerouting can be of significant benefit to both the pilot and air traffic controller, providing a supportive decision-making tool for bad weather avoidance.
This paper describes a guidance system for efficient orbits of space solar power systems (SSPSs), with a particular focus on the use of quasi-geostationary Earth orbit (QGEO). SSPSs consist of a space solar power satellite and a ground site. The satellite collects solar energy in space and converts it into electromagnetic waves, then transmits the energy to the ground site on Earth. In general, the SSPS satellite is planned to be placed in geostationary Earth orbit (GEO), but this is highly challenging due to the limited space available in GEO since it is already occupied by satellites for telecommunications and Earth observation. Therefore, this paper describes the use of QGEO for SSPSs. We analyzed the received power on the ground site when the satellite is controlled in QGEO with a model of wireless power transfer and compared it with one controlled in GEO. Our findings showed that the received power under the QGEO condition with an inclination of 10 degrees and an eccentricity of 0.1, when the ground site was on the equator, was 6.8% higher than that under GEO condition. We conclude that the received power in QGEO is comparable to or higher than that in GEO.
Aerodynamic characteristics of the black-tailed gull were investigated for two configurations in gentle and strong breezes. Firstly, the wing is twisted down, so the area of separation on the upper surface of the wing gradually expands and there is no sudden decrease in lift. Secondly, the crosswind characteristics change with the difference in shape. For flat wing configurations in gentle breeze, the rolling moment occurs such that the ventral side of the bird faces upwind, which can be called the dihedral effect for an upper-winged aircraft. While gull wing configurations in strong breeze, the rolling moment occurs such that the back side of the bird faces upwind, which can be called an active rolling control to keep flying straight. To confirm the flow around the wings, numerical analyses visualized the area where separations occurred. This study showed that by utilizing the 3D models of the bird, nondeformed models were analyzed to investigate the basic aerodynamic characteristics of the bird. In addition, by comparing the results with those of the experiments on the taxidermy bird, it will be possible to confirm the effects of the deflection of the wings and the surface texture, and to approach morphing technology from the bird.
Twist morphing wings require both high bending stiffness and low torsional stiffness. To address this challenge, lattice structures are investigated because they can achieve anisotropic properties by rearranging the lattice shape. We developed a twist morphing wing made from a periodic cubic lattice. Although flight testing was successful, a quantitative aerodynamic evaluation was needed. In this study, a cubic-lattice twist morphing wing was wind tunnel tested at 10 m/s and angles of attack from 14 degrees to 20 degrees. First, to investigate the wing's fundamental aerodynamics, the non-morphed state was compared to a polystyrene wing. The results showed that, despite slight differences, the overall aerodynamic characteristics were similar and the twist morphing wing's lift-to-drag ratio was higher. Next, the aerodynamic characteristics were examined on the morphing wing. Twisting the wings asymmetrically generated lift differences between the left and right wings, like an aileron. Symmetrical twisting provided a flapping functionality, altering the aerodynamic characteristics over a wide range at the same attack angle without changing the aircraft's attitude. These results quantitatively demonstrate that twist morphing wings made from cubic lattices can achieve aerodynamic performance comparable to that of rigid wings while enabling flexible and efficient alteration of aerodynamic characteristics through wing twisting.
Well-executed strategic air traffic flow management (ATFM) such as ground delay programs and controlled enroute delays account for numerous uncertainties. Such initiatives aim to minimize unnecessary airborne and ground delays while maintaining sufficient arrival runway pressure. This can be achieved through setting a cap on the maximum allowable airborne delay, i.e. the GDP buffer. Previous studies have shown that the ideal buffer is influenced by anticipated traffic levels. This study examines the uncertainties in departure time predictions, such as those arising from delayed passengers, maintenance problems, or late aircraft arrivals, and explores their impact on buffer efficiency and potential losses due to inappropriate buffer selections. Cumulative ground delay, airborne delay and throughput loss (capacity loss) are used as metrics. A day of arrival traffic at a hub Japanese airport is modeled and the ATFM necessity is demonstrated. To investigate operational aspects such as predictability and air traffic control workload, the number of flights with airborne delay exceeding the buffer is evaluated for several departure time prediction uncertainty models. It is concluded that modeling departure time uncertainties is important for optimal buffer selection. These results also highlight the importance of actual operational data which will allow for such models to be developed.
We have been studying debris capture by shooting a metal harpoon into it. Potential harpoon tip shapes have been investigated, but their penetration behavior has not been studied in detail. Therefore, we employed numerical simulations to investigate penetration behavior. Friction between the harpoon and the target was found to have a significant influence on penetration behavior and the influence of this friction was especially strong when the harpoon was shot into the target at a large oblique angle. Friction suppresses slippage on the target surface, allowing the kinetic energy of the harpoon to be used for penetration, leading to a reduction in penetration velocity. The influence of tip shape on the penetration behavior was also investigated, revealing the deformation of the target in detail in stress distribution diagrams. When the tip shape of a harpoon was sharp (1-point contacting double-bladed or conical), and the harpoon hit the target at a point, a high-stress region was generated near the impact point, and a small fracture hole was created at the beginning phase of the penetration. After that, the harpoon tip is trapped in this fracture hole, suppressing slippage and improving penetration. Therefore, the effect of friction is reduced.
Satellite-borne multi-aperture imagers are a promising optical system for high-resolution Earth observation. A significant challenge to realize such an imager is to develop an in-orbit fine phasing method to complete precise piston-tip-tilt alignment between sub-apertures to achieve diffraction-limited imaging performance. This study demonstrated the use of the simulated annealing algorithm for iterative scene-based fine phasing. One advantage of this approach is the correction capability of the piston-tip-tilt misalignment with a minimal hardware configuration. Numerical simulation revealed the relationship between fine phasing performance and the temperature parameters in the algorithm. Besides, algorithmic comparison with the stochastic parallel gradient descent algorithm, another approach capable of scene-based fine phasing, is also presented. Furthermore, we developed a miniaturized multi-aperture imaging system with 37 hexagonal mirror segments for our laboratory-scale optical experiments. The demonstration experiment showed the high-accuracy fine phasing results for typical extended scenes obtained by optical remote sensing.
