• Korean Journal of Remote Sensing
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• v.27 no.4
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• pp.411-420
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• 2011

In this study, a digital elevation model (DEM) in tidal flat of Suncheon Bay, one of the most ecological preserved area in the world, was generated from digital aerial stereo-images. The focal lengths for the aerial stereo-images were adjusted using ground control points (GCPs) in order to improve the accuracy of camera parameters. We proposed matching sizes suitable for generating DEM in tidal flat and a method for eliminating excessive position errors using intersection-distance($P_R$) threshold value. The accuracies of the DEM generated from the proposed method as well as the commercial S/W were compared with the elevation profiles measured by Total Station in the filed. As the results, the DEM generated by the proposed method showed better result (maximum deviation is a -21 centimeters) with detailed topography than DEM by the commercial S/W in the region. These results suggest that the DEM of tidal flat, which hardly obtained with the traditional methods, can be generated from digital aerial images by applying the proposed method in this study. We believe that the generated DEM in tidal flat can be an essential data for monitoring the sediment erosion and deposit of the tidal flat.

• Korean Journal of Applied Biomechanics
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• v.30 no.4
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• pp.293-299
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• 2020

Objective: The aim of this study was to investigate the swing and aerial motion of Kovacs, and evaluate the skill level of Kovacs by Korean adult players on horizontal bar. Method: The subjects for this study were 6 male top athletes participated in the 46th National Gymnastics against Cities and Provinces. After the motions of Kovacs were filmed by digital highspeed camcorder setting in 90 frames/s, kinematical data were calculated through DLT method. The variables were computed in the lapse time, the joint angle, the position·velocity of body COG, the inferred tension force of bar, and body COG path were simulated according to skill level of Kovacs. Results: Firstly, it was revealed that the lapse time was 1.19±0.03 s in the swing phase, and 0.83±0.03 s in the aerial phase. Secondly, it was revealed that the shoulder·hip joint motions of S1 and S2 were better than the other subjects in the swing phase, and the knee joint motions of S1 and S2 were better than the other subjects in the aerial phase. Thirdly, it was revealed that the horizontal·vertical velocity of body COG were -1.40±0.03 m/s, 3.80±0.07 m/s respectively, and the vertical positions of S1 and S2 were higher a little than the other subjects. Lastly, the skill level of Kovacs of this subjects was evaluated into 3 steps; excellent, advanced, normal. They need to train the swing motion including a giant circle, and body motions in the air. Conclusion: It would be suggested that Korean domestic players should improve to increase the vertical velocity at release instant and train to control the limbs elaborately in the air.

• Journal of Biosystems Engineering
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• v.37 no.3
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• pp.192-200
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• 2012

Purpose: Aerial application of chemicals with an agricultural helicopter allows for precise and timely spraying and reduces working labor and pollution. An attitude controller for an agricultural helicopter would be helpful to aerial application operator. The objectives of this paper are to determine the transfer function models and to estimate the handling qualities of a bare-airframe model helicopter. Methods: Transfer functions of a model unmanned helicopter were estimated by using NAVFIT and DERIVID modules of the $CIFER^{(R)}$ program to the time history data of frequency sweep flight tests. Control inputs of the transfer functions were elevator, aileron, rudder and collective pitch stick positions and the outputs were resulting on-axis movements of the fuselage. Results: Minimum realization of the transfer functions for pitch rate output to elevator control input and roll rate output to aileron control input produced second order transfer functions with undamped natural frequencies around 3.0 Hz and damping ratios of 0.139 and 0.530, respectively. The equivalent time delays of the transfer functions ranged from 0.16 to 0.44 second. Sensitivity analysis of the proposed parameters allowed derivation of minimal realization of the transfer functions. Conclusions: Handling quality of the model helicopter was addressed based on the eigenvalues of the transfer functions, corresponding undamped natural frequencies with damping ratios. The equivalent time delays of the lateral-directional motion ranged from 0.16 to 0.44 second, longer than the 0.1 to 0.15 second requirement for well-controlled typical manned aerial vehicles.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.11
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• pp.1103-1111
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• 2014

The results of control law design for a tilt-rotor unmanned aerial vehicle that has a nacelle mounted wing extension (WE) are presented in this paper. It consists of a control surface mixer, stability and control augmentation system (SCAS), hold mode for altitude / speed / heading, and a guidance mode for preprogram and point navigation which includes automatic take-off and landing. The conversion corridor and the control moments derivatives between the original tilt-rotor and its variant of the nacelle mounted WE were compared to show the effectiveness of the WE. The nacelle conversion of the original tilt-rotor starts when the airspeed is greater than 30 km/h but its WE variant starts at 0 km/h in order to reduce the drag caused by the high incidence angle of the WE. The stability margins of the inner loop are presented with the optimization approach. The outer loops for the hold mode are designed with trial and error methods with linear and nonlinear simulation. The main control parameter for altitude control of the helicopter mode is thrust command and it is transferred to the pitch attitude command in airplane mode. Otherwise, the control parameter for the speed of the helicopter mode is the pitch attitude command and it is transferred to the thrust command in airplane mode. Therefore the speed and altitude hold mode are coupled to each other and are engaged at the same time when an internal pilot engages any of the altitude or speed hold modes. The nonlinear simulation results of the guidance control for the preprogrammed mode and point navigation are also presented including automatic take-off and landing in order to prove the full control law.

• Korean Journal of Remote Sensing
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• v.36 no.5_3
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• pp.1013-1025
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• 2020

Unmanned Aerial Vehicle (UAV) platform is being widely used in disaster monitoring and smart city, having the advantage of being able to quickly acquire images in small areas at a low cost. Ground Control Points (GCPs) for positioning UAV images are essential to acquire cm-level accuracy when producing UAV-based orthoimages and Digital Surface Model (DSM). However, the on-site acquisition of GCPs takes considerable manpower and time. This research aims to provide an efficient and accurate way to replace the on-site GNSS surveying with three different sources of geospatial data. The three geospatial data used in this study is as follows; 1) 25 cm aerial orthoimages, and Digital Elevation Model (DEM) based on 1:1000 digital topographic map, 2) point cloud data acquired by Mobile Mapping System (MMS), and 3) hybrid point cloud data created by merging MMS data with UAV data. For each dataset a three-dimensional positional accuracy analysis of UAV-based orthoimage and DSM was performed by comparing differences in three-dimensional coordinates of independent check point obtained with those of the RTK-GNSS survey. The result shows the third case, in which MMS data and UAV data combined, to be the most accurate, showing an RMSE accuracy of 8.9 cm in horizontal and 24.5 cm in vertical, respectively. In addition, it has been shown that the distribution of geospatial GCPs has more sensitive on the vertical accuracy than on horizontal accuracy.

• Journal of Advanced Navigation Technology
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• v.8 no.1
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• pp.19-26
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• 2004

This paper deals with the automatic flight control system for an unmanned target drone which is operated by an army as an anti-air gun shooting training. By automation of unmanned target drone that is manually operated by external pilot, pilot can reduce workload and an army can reduce the budget. Most UAVs which are developed until today use high-cost sensors as AHRS and IMU to measure the attitude, but those are contradictory for the reduction of budget. This paper says the development of low-cost automatic flight control system which makes possible of automatic flight with low-cost sensors. We have developed the integrated automatic flight control system by integrating electricity module, switching module, monitoring module and RC receiver as an one module. We also prove the performance of automatic flight control system by flight test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.5
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• pp.342-349
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• 2013

A damage imposed on an unmanned aerial vehicle changes the flight dynamic characteristics, and makes difficult for a conventional controller based on undamaged dynamics to stabilize the vehicle with damage. This paper presents a neural network based adaptive control method that guarantees stable control performance for an unmanned aerial vehicle even with damage on the main wing. Additionally, Pseudo Control Hedging (PCH) is combined to prevent control performance degradation by actuator characteristics. Asymmetric dynamic equations for an aircraft are chosen to describe motions of a vehicle with damage. Aerodynamic data from wind tunnel test for an undamaged model and a damaged model are used for numerical validation of the proposed control method. The numerical simulation has shown that the proposed control method has robust control performance in the presence of wing damage.

• Journal of Aerospace System Engineering
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• v.17 no.5
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• pp.34-41
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• 2023

This paper applies the icing effect and wing rock uncertainty to small unmanned aerial vehicles (UAVs), which have recently attracted attention. Attitude control simulations were performed using various control methods. First, the selected platform, the Skywalker X8 UAV with blended wing-body (BWB) configuration, was linearized for both its baseline form, and a form with applied icing effects. Subsequently, using MATLAB SimulinkⓇ, simulations were conducted for roll and pitch attitude control of the baseline configuration and the configuration with icing effects, employing disturbance observer-based PID control, model reference adaptive control, and model predictive control. Furthermore, the study introduced wing rock uncertainty simultaneously with icing effects on the configured model-a combination not previously explored in existing research-and conducted simulations. The performance of each control Method was compared and analyzed.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.12
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• pp.1181-1188
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• 2014

In this paper, we propose a novel concept foran unmanned delivery service using a cooperative heterogeneous unmanned system consisting of a self-driving car and an unmanned aerial vehicle (UAV). The proposed concept is suitable to deliver parcels in high-density and high-rise urban or residential areas. In order to achieve the proposed concept, we will develop acooperative heterogeneous unmanned system. Customers can order goods using a smartphone application and the order information, including the position of the customer and the order time, and the package is transported automatically by the unmanned systems. The system assigns the tasks suitable for each unmanned vehicle by analyzing it based on map information. Performance is validated by experiments consisting of autonomous driving and flight tests in a real environment. For more evaluation, the landing position error analysis is performed using circular error probability (CEP).

• Journal of Mechanical Science and Technology
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• v.17 no.5
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• pp.776-783
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• 2003

A low speed wind tunnel test was conducted for full-scale model of an unmanned aerial vehicle (UAV) in Korea Aerospace Research Institute (KARI) Low Speed Wind Tunnel(LSWT). The purpose of the presented paper is to illustrate the general aerodynamic and performance characteristics of the UAV that was designed and fabricated in KARI. Since the testing conditions were represented minor portions of the load-range of the external balance system, the repeatability tests were performed at various model configurations to confirm the reliability of measurements. Variations of drag-polar by adding model components such as tails, landing gear and test boom are shown, and longitudinal and lateral aerodynamic characteristics after changing control surfaces such as aileron, flap, elevator and rudder are also presented. To explore aerodynamic characteristics of an UAV with model components build-up and control surface deflections, lift curve slope, pitching moment variation with lift coefficients and drag-polar are examined. The discussed results might be useful to understand the general aerodynamic characteristics and drag pattern for the given UAV configuration.