Naoki Matayoshi

Dual‐Doppler lidar observation of horizontal convective rolls and near‐surface streaks

Received 4 May 2008; revised 9 June 2008; accepted 18 June 2008; published 23 July 2008. [1] Dual-Doppler lidar and heliborne sensors were used to investigate the three-dimensional (3D) structure of the wind field over Sendai Airport in June 2007. The 3D structures of several-hundred-meter-scale horizontal convective rolls (HCRs) in the sea-breeze layer were observed by the dual-Doppler lidar. The scale of the HCRs determined by the heliborne sensors roughly agreed with that determined by the dual-Doppler lidar. Analysis of the dual-Doppler lidar data showed that the region of upward flow in the HCRs originated in near-surface low-speed streaks. This structure is consistent with the results of large-eddy simulations of the atmospheric boundary layer. The aspect ratios of the HCRs were close to those predicted by linear theories. Citation: Iwai, H., et al. (2008), Dual-Doppler lidar observation of horizontal convective rolls and near-surface streaks, Geophys. Res. Lett., 35, L14808, doi:10.1029/ 2008GL034571.

Flight Trajectory Optimization to Minimize Ground Noise in Helicopter Landing Approach

The purpose of this paper is to optimize helicopter flight trajectories to reduce ground noise in the landing approach using an optimization technique and to conduct flight experiments to confirm the effectiveness of the optimal solutions. The Japan Aerospace Exploration Agency has thus far measured helicopter noise under various flight conditions. This study builds a noise model of the helicopter in which the level of noise generated from a point noise source is a function of the flight path angle and bank angle. Then, we define optimal control problems that minimize the noise levels measured at points on the ground surface using equations of motion of 3 degrees of freedom for three-dimensional flight, and obtain the optimal controls for some flight constraints and wind conditions. The obtained optimal flights avoid the flight path angle that generates a great deal of noise and skirt the measurement points; these optimal flights are different from the conventional flight. Finally, this study verifies the validity of the optimal flight patterns by means of flight experiments with an experimental Japan Aerospace Exploration Agency helicopter. The actual flights following the optimal flights result in noise reduction and prove the effectiveness of the optimization.

Near-Optimal Control for Aircraft Conflict Resolution in the Presence of Uncertainty

In this paper, a stochastic near-optimal control method is proposed for determining aircraft conflict-resolution trajectories in the presence of uncertainty in real time. The prior work developed a stochastic optimal control method for aircraft conflict resolution based on the polynomial chaos expansion and pseudospectral methods. This stochastic optimal control method is extended to generate conflict-resolution trajectories in real time without actually solving the computationally expensive stochastic optimal control problems. The proposed near-optimal conflict-resolution algorithm is based on a recently developed surrogate modeling technique called polynomial chaos kriging, which is used to construct the surrogate models of the optimal conflict-resolution trajectories from a set of precomputed optimal solutions. The near-optimal conflict-resolution trajectories can be accurately generated in real time from the surrogate models with the information of current conditions (for example, current states). Thr...

Accuracy Estimation of Probabilistic Wake Vortex Prediction Considering Weather Information Errors

Current wake vortex separation minima are a major impediment to increasing traffic capacity since they require greater separations than radar separation minima. The concept of dynamic wake vortex separation minima, which would allow reduced separations in favorable meteorological conditions when wake durations on flight paths become shorter, would allow an increase in capacity. This paper proposes a methodology that uses a probabilistic wake vortex prediction model to probabilistically assure that wake vortex encounter risks at reduced separations are equal or lower than the risks at current separations.

Flight Test Evaluation of a Helicopter Airborne Lidar

The Japan Aerospace Exploration Agency (JAXA) has conducted ground and flight test evaluations of a prototype 1.5μm all-fiber pulsed coherent Doppler lidar produced by Mitsubishi Electric Corporation which aims to measure three-axis components of airspeed and detect atmospheric turbulence ahead of a helicopter. In the ground test, the lidar has proved its capability to detect atmospheric turbulence with a scale of several tens of meters by accurately measuring helicopter rotor downwash. For the flight test, the lidar was installed in JAXA’s MuPAL-e research helicopter and several flights were carried out to evaluate the accuracy of real-time airspeed calculation using lidar outputs and the format of a real-time pilot display. The lidar successfully measured three-axis airspeed components accurately even in low-airspeed flight regimes including hovering, backwards and sideways flight where the conventional Pitot-static system does not work and its capability as a helicopter airspeed sensor was proven. Some technical challenges were found for atmospheric turbulence detection such as increasing the detection range and improving the data analysis and presentation. These results will be utilized to establish the specifications of practical airborne lidars.

Development of an Airborne Ultrasonic Velocimeter and its Application to Helicopters

The Japan Aerospace Exploration Agency (JAXA) has been developing a new air data sensor, called an ultrasonic velocimeter (USV), based on the ultrasonic anemometer commonly used in ground-based meteorological observation. For airborne use, JAXA has modified the probe and realized the operational velocity range of 0–100m/s to cover almost the entire flight envelope of small airplanes and helicopters. The USV has a great advantage particularly as a helicopter airspeed sensor since it measures three-axis airspeed components even at low airspeeds where a conventional Pitot-static system is ineffective. Two USV installations on a helicopter, at the tip of a nose boom and at the bottom of the fuselage, were evaluated by flight test. The USV successfully measured two- or three-axis airspeed components at airspeeds down to 5–10m/s forward speed. For practical use, there still remains a technical problem to find a more suitable location for the USV probe where position error, i.e. the effects of rotor downwash and flow around fuselage, does not change greatly throughout all flight conditions.

Airport Terminal Traffic Simulation Applying Reduced Wake Vortex Separation

The Japan Aerospace Exploration Agency has developed an airport terminal traffic simulation environment that dynamically minimizes aircraft wake vortex separation by considering wake vortex behaviors from meteorological information and using GBAS-based curved approach paths. A traffic simulation of Tokyo International airport using four intersecting runways revealed that the capacity could be increased by up to 12% by reducing separations without additional risk of wake vortex encounter. This result demonstrates the benefit to airport capacity of reducing wake vortex separations dynamically.

In-Flight GPS-Signal-Reception Anomalies of Helicopters

I T IS difficult to find appropriate installation points for global positioning system (GPS) antennas on helicopters, because structures such as rotors and engines that are located above the fuselage may degrade GPS positioning accuracy. Even for fixedwing airplanes that have no such obstacles on the fuselage, an inflight GPS antenna performance study has revealed that large bias errors can be caused by distortions in the GPS antenna pattern due to other antennas nearby [1]. The effects of such problems are not so great when GPS usage is limited to en-route navigation. However, they will be more significant in approach and landing with vertical guidance (APV) or precision approaches using a GPS satellite/ ground-based augmentation system (SBAS/GBAS), such as the Federal Aviation Administration’s GPS wide/local area augmentation system (WAAS/LAAS). Although the minimum operational performance standards (MOPS) for WAAS/LAAS airborne equipment [2,3] specify an airborne accuracy model that includes an airframemultipath based on flight test data from large commercial jet transports [4], there is little quantitative flight test data for helicopter GPS antenna performance, and it is thought to be difficult for helicopters to meet the MOPS specifications. This paper presents in-flight GPS-signal-reception anomalies, such as GPS signal masking and multipath that degrade positioning accuracy, observed using the Japan Aerospace Exploration Agency’s (JAXA) research helicopter.

Numerical Simulations and Measurements of the Helicopter Wake in Ground Effect

When a helicopter takes off, lands, or makes hovering or taxiing flights in ground effect, its downwash interferes with the ground. Encounters with such highly turbulent helicopter wakes have resulted in the two small fixed-wing aircraft crashes in the United Kingdom. Due to these accidents, the Japan Aerospace Exploration Agency is investigating the helicopter wake structure in ground effect, especially during taxiing, by means of computational fluid dynamics and flight testing. The base computational fluid dynamics code is structured grid solver rFlow3D, which has systematically been developed for helicopter applications at the Japan Aerospace Exploration Agency. The rFlow3D solver is a highly versatile computational fluid dynamics code that can numerically simulate flows around helicopters with a wide range of Reynolds and Mach numbers and can perform rotor trim analysis with elastic blade deformations. In the flight experiment described herein, the Japan Aerospace Exploration Agency research helicopte...

Reduced Wake Vortex Separation Using Weather Information

Current wake vortex separation minima are a major impediment to increasing traffic capacity since they require greater separations than radar separation minima. The concept of dynamic wake vortex separation, which allows reduced separations in favorable weather conditions when wake durations on flight paths become shorter, would allow an increase in capacity. The Japan Aerospace Exploration Agency (JAXA) has developed a methodology that calculates a reduced wake vortex separation that is equally safe as current separation minima. The methodology uses a probabilistic wake vortex prediction model to probabilistically assure that the wake vortex encounter risks at reduced separations do not exceed those at current separation minima. JAXA has also developed an airport terminal traffic simulation environment to demonstrate the traffic capacity gain at a congested airport when reduced wake vortex separations are introduced and take-off/landing sequences are optimized. The simulation result showed a greater than 10% capacity gain, and confirmed the effectiveness of the proposed methodology.