Flight Test Results Research Articles

Flight Test Result for the Ground-Based Radio Navigation System Sensor with an Unmanned Air Vehicle.

The Ground-based Radio Navigation System (GRNS) is an alternative/backup navigation system based on time synchronized pseudolites. It has been studied for some years due to the potential vulnerability issue of satellite navigation systems (e.g., GPS or Galileo). In the framework of our study, a periodic pulsed sequence was used instead of the randomized pulse sequence recommended as the RTCM (radio technical commission for maritime services) SC (special committee)-104 pseudolite signal, as a randomized pulse sequence with a long dwell time is not suitable for applications requiring high dynamics. This paper introduces a mathematical model of the post-correlation output in a navigation sensor, showing that the aliasing caused by the additional frequency term of a periodic pulsed signal leads to a false lock (i.e., Doppler frequency bias) during the signal acquisition process or in the carrier tracking loop of the navigation sensor. We suggest algorithms to resolve the frequency false lock issue in this paper, relying on the use of a multi-correlator. A flight test with an unmanned helicopter was conducted to verify the implemented navigation sensor. The results of this analysis show that there were no false locks during the flight test and that outliers stem from bad dilution of precision (DOP) or fluctuations in the received signal quality.

Aircraft health and usage monitoring system for in-flight strain measurement of a wing structure

This paper presents an aircraft health and usage monitoring system (HUMS) using fiber Bragg grating (FBG) sensors. This study aims to implement and evaluate the HUMS for in-flight strain monitoring of aircraft structures. An optical-fiber-based HUMS was developed and applied to an ultralight aircraft that has a rectangular wing shape with a strut-braced configuration. FBG sensor arrays were embedded into the wing structure during the manufacturing process for effective sensor implementation. Ground and flight tests were conducted to verify the integrity and availability of the installed FBG sensors and HUMS devices. A total of 74 flight tests were conducted using the HUMS implemented testbed aircraft, considering various maneuvers and abnormal conditions. The flight test results revealed that the FBG-based HUMS was successfully implemented on the testbed aircraft and operated normally under the actual flight test environments as well as providing reliable in-flight strain data from the FBG sensors over a long period of time.

DEVELOPMENT AND EVALUATION OF A UAV BASED MAPPING SYSTEM FOR REMOTE SENSING AND SURVEYING APPLICATIONS

Abstract. In recent years, unmanned aerial vehicles (UAVs) have increasingly been used in various application areas, such as in the remote sensing or surveying. For these applications the UAV has to be equipped with a mapping sensor, which is mostly a camera. Furthermore, a georeferencing of the UAV platform and/or the acquired mapping data is required. The most efficient way to realize this georeferencing is the direct georeferencing, which is based on an onboard multi-sensor system. In recent decades, direct georeferencing systems have been researched and used extensively in airborne, ship and land vehicle applications. However, these systems cannot easily be adapted to UAV platforms, which is mainly due to weight and size limitations. In this paper a direct georeferencing system for micro- and mini-sized UAVs is presented, which consists of a dual-frequency geodetic grade OEM GPS board, a low-cost single-frequency GPS chip, a tactical grade IMU and a magnetometer. To allow for cm-level position and sub-degree attitude accuracies, RTK GPS (real-time kinematic) and GPS attitude (GPS compass) determination algorithms are running on this system, as well as a GPS/IMU integration. Beside the direct georeferencing, also the precise time synchronization of the camera, which acts as the main sensor for mobile mapping applications, and the calibration of the lever arm between the camera reference point and the direct georeferencing reference point are explained in this paper. Especially the high accurate time synchronization of the camera is very important, to still allow for high surveying accuracies, when the images are taken during the motion of the UAV. Results of flight tests demonstrate that the developed system, the camera synchronization and the lever arm calibration make directly georeferenced UAV based single point measurements possible, which have cm-level accuracies on the ground.

Nonlinear Dynamic Modeling of a Fixed-Wing Unmanned Aerial Vehicle: a Case Study of Wulung

Developing a nonlinear adaptive control system for a fixed-wing unmanned aerial vehicle (UAV) requires a mathematical representation of the system dynamics analytically as a set of differential equations in the form of a strict-feedback systems. This paper presents a method for modeling a nonlinear flight dynamics of the fixed-wing UAV of BPPT Wulung in any conditions of the flight altitude and airspeed for the first step into designing a nonlinear adaptive controller. The model was formed into 10-DOF differential equations in the form of strict-feedback systems which separates the terms of elevator, aileron, rudder and throttle from the model. The model simulation results show the behavior of the flight dynamics of the Wulung UAV and also prove the compliance with the actual flight test results.

Cooperative Path Following of Multiple Multirotors Over Time-Varying Networks

This paper addresses the problem of time-coordination of a team of cooperating multirotor unmanned aerial vehicles that exchange information over a supporting time-varying network. A distributed control law is developed to ensure that the vehicles meet the desired temporal assignments of the mission, while flying along predefined collision-free paths, even in the presence of faulty communication networks, temporary link losses, and switching topologies. In this paper, the coordination task is solved by reaching consensus on a suitably defined coordination state. Conditions are derived under which the coordination errors converge to a neighborhood of zero. Simulation and flight test results are presented to validate the theoretical findings. Note to Practitioners-This paper presents an approach which enables a fleet of multirotor UAVs to follow a set of desired trajectories and coordinate along them, thus satisfying specific spatial and temporal assignments. The proposed solution can be employed in applications in which multiple vehicles are tasked to execute cooperative, collision-free maneuvers, and accomplish a common goal in a safely manner. An example is sequential monitoring, in which the UAVs have to visit and monitor a set of points of interest, while maintaining a desired temporal separation between each other. In this paper, we also simulate a scenario in which the vehicles, positioned in a square room, are required to exchange position with each other. It is shown that the proposed control algorithm not only ensures that the UAVs arrive at the final destinations at the same time, but also guarantees safety, i.e., the vehicles avoid collision with each other at all times.

Analysis of Flight Test Results of the Optical Ice Detector

Analysis of Flight Test Results of the Optical Ice Detector

헬리콥터 능동진동제어시스템의 수리온 적용 및 성능 분석

The most decisive factor of major sources of a helicopter is the main rotor system and the rotor-induced vibration is one of the technical challenges which should be resolved to ensure comfort for crews and passengers. Passive vibration reduction devices are adopted in conventional helicopters and several types of passive devices are also used in Surion. In recent years, foreign helicopter manufactures have increasingly applied the application of AVCS (active vibration control system) because of their superior performance with lower weight compared to passive device. In addition to weight reduction, AVCS has advantages maintaining its performance over aircraft configuration changes and flight condition changes. The technology demonstration program was performed in order to validate the performance of AVCS when applied to Surion, and optimization process for finding optimal configuration of sensors and actuators. Optimal configuration was produced using ground and flight test data, and its performance was evaluated and compared with flight test result.

HIFiRE-5 Flight Test Results

The Hypersonic International Flight Research Experimentation (HIFiRE-5) is a hypersonic flight test vehicle designed to investigate the aerothermodynamics of a three-dimensional geometry. It is a 7-deg minor-axis half-angle elliptic cone with a aspect ratio and 2.5 mm nose radius. The flight test occurred in April 2012, but the upper stage of the sounding rocket failed to ignite, resulting in a peak Mach number of about 3 instead of the target of 7. The instrumentation (almost 300 thermocouples and 50 pressure transducers) performed well and provided a wealth of supersonic aeroheating and boundary-layer transition data. The pressure transducers indicated the expected dependence upon angle of attack and yaw and offer a check for the inertial measurement unit. Heat flux was calculated from paired thermocouples and boundary-layer transition locations were identified from the heating rates. Two boundary-layer transition mechanisms were encountered during the supersonic descent. One mode leads to transition over the acreage of the vehicle and correlates well with ; the other mechanism causes the leading-edge boundary-layer transition to advance rapidly over a small range of freestream and is suspected to be roughness-induced. The good performance of the instrumentation increases confidence in the success of a repeat flight.

Investigation of Missile Control Surface Effects on F-16 Limit-Cycle Oscillation

Tactical aircraft with thin wings and heavy external wing stores are susceptible to aeroelastic limit-cycle oscillations. This investigation applies both frequency-domain and time-domain solutions using aeroelastic computational models to predict limit-cycle oscillation onset, frequency, and amplitude on an F-16. The test configuration uses missile shapes with reconfigurable aerodynamic and mass properties. Statistical analysis of flight-test results identifies significant experimental variables of missile aerodynamic configuration, flight condition, and aircraft fuel state. Furthermore, statistical analysis permits the normalization of flight-test results for direct comparison to aeroelastic models. Results of the comparison show that flight-test data analysis mostly supports the prediction trends, but the magnitude of the aerodynamic effects due to the canards and fins is much less significant in the test data.

An Automated Battery Management System to Enable Persistent Missions With Multiple Aerial Vehicles

This paper presents the development and hardware implementation of an autonomous battery maintenance mechatronic system that significantly extends the operational time of battery powered small-scaled unmanned aerial vehicles (UAVs). A simultaneous change and charge approach is used to overcome the significant downtime experienced by existing charge-only approaches. The automated system quickly swaps a depleted battery of a UAV with a replenished one while simultaneously recharging several other batteries. This results in a battery maintenance system with low UAV downtime, arbitrarily extensible operation time, and a compact footprint. Hence, the system can enable multi-agent UAV missions that require persistent presence. This capability is illustrated by developing and testing in flight a centralized autonomous planning and learning algorithm that incorporates a probabilistic health model dependent on vehicle battery health that is updated during the mission, and replans to improve the performance based on the improved model. Flight test results are presented for a 3-h-long persistent mission with three UAVs that each has an endurance of 8-10 min on a single battery charge (more than 100 battery swaps).

Design and validation of the power supply and distribution system for circumlunar return and reentry spacecraft

Considering the main characteristics of the circumlunar return and reentry mission, this paper briefly describes the functions, key technology indexes of the power supply and distribution system, and the solutions of power supply system for multi-cabin spacecraft. Through the following key technologies such as high specific mass energy ration Zn-AgO battery design, multi-mode intelligent nickel hydrogen battery charge strategy and multi-bus current balance control scheme, the design problem that high reliability light weight supply and distribution system has been solved in the complex space environment of circumlunar return and reentry spacecraft. The on-orbit flight test results show that the performance of power supply and distribution system is reliable and excellent. The power supply and distribution system analysis and design methods for circumlunar return and reentry spacecraft which are proposed in this paper have been validated on orbit. It met the requirements and ensured the circumlunar return and reentry spacecraft mission succeeded, and it can provide a reference for lunar and deep space exploration in future.

Development and evaluation of hybrid seat cushions for helicopter aircrew vibration mitigation

This article investigates the use of novel energy-absorbing materials to reduce vibration transmitted through helicopter pilot seat cushions. A type of engineered material known as the hybrid air cushioning system was integrated into the design of helicopter seat cushions in addition to conventional foam materials. The prototype seat cushions were preliminarily evaluated as the bottom seat cushion on a Bell-412 nonarmored pilot seat through mechanical shaker tests. The promising cushion designs were further evaluated on a Bell-412 helicopter through extensive flight tests. The pilot whole-body vibration levels were assessed in accordance with ISO 2631-1:1997 standard. The flight test results demonstrated that the prototype cushions were able to reduce significantly the pilot whole-body vibration. Therefore, the integration of hybrid air cushioning system with Bell-412 seat cushion can serve as a low-cost solution to mitigate the vibration levels transmitted to helicopter pilots.

The Effects of Using an Angle of Attack System on Pilot Performance and Workload during Selected Phases of Flight

In-flight loss of control (LoC-I) is the number one fatal accident category for light airplanes. The most common type of LoC-I accident involves a stall/spin and inadequate airspeed management and is frequently cited as a causal factor. An aircraft stalls when the critical angle of attack is exceeded and this may occur at any indicated airspeed, hence the use of airspeed as an indication to the proximity to stall is unreliable. This is of particular importance during the take-off, approach and landing where stall margins are reduced. Military aircraft commonly use angle of attack (AoA) devices to indicate proximity to the stall and these have been in continuous use for almost 60 years. More recently, with the simplification of light airplane design approval requirements, an increasing number of AoA designs are appearing on the market, installed in light airplanes to complement airspeed indication and stall warning systems, to notify pilots of proximity to the stall. This paper reviews a selection of current types of AoA devices and presents the preliminary results of practical flight testing and flight simulation experiments to investigate the effects of using an AoA on pilot performance and workload during selected phases of flight. The results have implications for the operational use of current AoA devices and future AoA design.

四旋翼无人机地面站控制软件的设计与实现

本文介绍了飞行监控系统软件的组成、设计原理和工作流程，以及采用的关键技术，并说明了系统在联试过程中出现的问题和处理方法；飞行试验结果表明，本系统能够实时显示无人机的飞行姿态、飞行轨迹、位置及参数，实现任务航线的编辑、装订与显示，发送飞行控制指令，实时性高，操作方便。 The structure, design theory, working process and key technique for flight surveillance and control system are introduced in this paper. The problem and solution in the combined debug are showed. Flight test results show that the system can display attitude, track, position and parameters in real-time, realize the edition, fix and display of route, send flight control command, and work continuously for days without exception.

Flight Dynamics Analyses of a Propeller-Driven Airplane (I): Aerodynamic and Inertial Modeling of the Propeller

This paper focuses on aerodynamic and inertial modeling of the propeller for its applications in flight dynamics analyses of a propeller-driven airplane. Unsteady aerodynamic and inertial loads generated by the propeller are formulated using the blade element method, where the local velocity and acceleration vectors for each blade element are obtained from exact kinematic relations for general maneuvering conditions. Vortex theory is applied to obtain the flow velocities induced by the propeller wake, which are used in the computation of the aerodynamic forces and moments generated by the propeller and other aerodynamic surfaces. The vortex lattice method is adopted to obtain the induced velocity over the wing and empennage components and the related influence coefficients are computed, taking into account the propeller induced velocities by tracing the wake trajectory trailing from each of the propeller blades. Aerodynamic forces and moments of the fuselage and other aerodynamic surfaces are computed by using the wind tunnel database and applying strip theory to incorporate viscous flow effects. The propeller models proposed in this paper are applied to predict isolated propeller performances under steady flight conditions. Trimmed level forward and turn flights are analyzed to investigate the effects of the propeller on the flight characteristics of a propeller-driven light-sports airplane. Flight test results for a series of maneuvering flights using a scaled model are employed to run the flight dynamic analysis program for the proposed propeller models. The simulations are compared with the flight test results to validate the usefulness of the approach. The resultant good correlations between the two data sets shows the propeller models proposed in this paper can predict flight characteristics with good accuracy.

Experimental investigation of stochastic parafoil guidance using a graphics processing unit

Control of autonomous systems subject to stochastic uncertainty is a challenging task. In guided airdrop applications, random wind disturbances play a crucial role in determining landing accuracy and terrain avoidance. This paper describes a stochastic parafoil guidance system which couples uncertainty propagation with optimal control to protect against wind and parameter uncertainty in the presence of impact area obstacles. The algorithm uses real-time Monte Carlo simulation performed on a graphics processing unit (GPU) to evaluate robustness of candidate trajectories in terms of delivery accuracy, obstacle avoidance, and other considerations. Building upon prior theoretical developments, this paper explores performance of the stochastic guidance law compared to standard deterministic guidance schemes, particularly with respect to obstacle avoidance. Flight test results are presented comparing the proposed stochastic guidance algorithm with a standard deterministic one. Through a comprehensive set of simulation results, key implementation aspects of the stochastic algorithm are explored including tradeoffs between the number of candidate trajectories considered, algorithm runtime, and overall guidance performance. Overall, simulation and flight test results demonstrate that the stochastic guidance scheme provides a more robust approach to obstacle avoidance while largely maintaining delivery accuracy.

Numerical Predictions of Static-Pressure-Error Corrections for a Modified T-38C Aircraft

The objective of this work was to highlight modeling considerations for estimating the required static-pressure-error corrections using computational fluid dynamics. This work was performed to complement the U.S. Air Force Test Pilot School activities that used a T-38C aircraft with a previously untested Pitot-static system. Before the flight test, it is highly desirable to have an estimate of how any modifications will affect sensor performance, and to possess the capability to explain any discrepancies from previous test programs. Estimates of this kind are only obtainable via wind-tunnel tests or through modeling and simulation. This work presents the computational fluid dynamics requirements and methodologies needed to estimate the static-pressure-error correction of a T-38C in the subsonic, transonic, and low supersonic regimes. Estimates are validated with flight-test results, and proposed solutions for further reduction of static-pressure error via modifications to the flight-tested Pitot-static-probe geometry are included.

Multiplicative Extended Kalman Filter for Relative Rotorcraft Navigation

This paper details the fundamentals of a new approach to navigation for aerial vehicles in confined indoor environments without access to global-position measurements. The approach departs from the common practice of navigating within a globally referenced map, and it instead keeps the position and yaw states relative to the current node in the map. The approach combines elements of graph-based simultaneous localization and mapping with a multiplicative extended Kalman filter. The filter provides accurate state estimates at a fast rate and provides the information necessary for a simultaneous localization and mapping algorithm to maintain a pose graph. Specific details for the relative multiplicative extended Kalman filter are provided. The relative estimation approach is validated with hardware flight tests, and results are compared to motion capture ground truth data. In addition, flight-test results using estimates in the control loop are provided.

Onboard instrumentation of the Yak-42D “Roshydromet” new-generation research aircraft for measuring and registering flight parameters and atmospheric thermodynamic parameters

Given is a brief description and technical characteristics of onboard hardware-and-software complex for measuring flight parameters and atmospheric thermodynamic characteristics; also, described is the complex for registering these parameters from the Yak-42D “Roshydromet” new-generation research aircraft measurement system. Described are the basic principles of the construction of the onboard system for the registration of heterogeneous measurement data recorded with different frequency and following different protocols of data transmission. Presented are the results of flight tests of aircraft systems for the measurement and registration of navigation parameters, air temperature, wind speed, wind direction, and turbulence. Noted is the reliable operation of hardware and software packages which enable carrying out the acquisition and registration of data. Described is the method for taking account of airflow aerodynamic disturbances caused by the aircraft. Presented are the values of error corrections for the readings of pressure and temperature sensors depending on the construction of sensors and their placing at the research aircraft. Given are the results of the comparison of air temperature and wind speed measured by aircraft instruments and radio sounding method. Demonstrated is the reliability of the obtained data.

Using Wind Tunnel Tests for Slung-Load Clearance, Part 2: Other Loads

The first new load is the TRIO container that can be flown in three configurations with different heights. The second new load is a ribbon bridge interior bay section. Wind tunnel results with models of the new loads exhibit in general good agreement with flight-test results. The results of the new loads strengthen further the approach of using wind tunnel tests to accelerate slung-load clearance, as well as reduce risk and cost.