Yoshinori Okuno

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.

Measurement-Integrated Simulation of Wake Turbulence

Large eddy simulation of wake turbulence was performed by integrating the lidar measurements. Four-dimensional variational method was applied to integrate lidar measurements with the three-dimensional large eddy simulation. In addition, a bogus vortex technique was adopted to ensure the existence of wake vortices in the flow field. The validation of the method was performed by idealized test cases using virtual lidar measurement which is produced by the reference simulation of a vortex pair. The results of the validation cases showed the convergence of vortex parameters such as a circulation to that of reference simulation case. It is also confirmed that the velocity distribution on a measurement plane agrees with reference one.

FLIGHT EXPERIMENTS FOR AIRCRAFT NOISE MEASUREMENT USING "TUNNEL-IN-THE-SKY" DISPLAY

A series of flight experiments to measure aircraft noise were conducted using the National Aerospace Laboratory of Japan’s MuPAL-e research helicopter and MuPAL-α research airplane. In addition to longitudinal flight profiles such as level, climbing and descending flight, steady turns were flown to measure noise in the plane of the main rotor tip-path of the helicopter and in the wing tip direction of the airplane. The use of “Tunnel-In-the-Sky” (TIS) displays presented on the programmable cockpit display systems enabled precise tracking of the desired flight paths. Flight data such as aircraft position, attitude, and air data obtained from on-board data acquisition systems were used to determine accurately the direction of noise propagation. This paper presents the obtained noise directivity patterns, as well as the flight profiles and their errors to demonstrate the effectiveness of applying TIS display technology to noise measurement flight experiments.

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.