• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.16-26
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• 2005

The aerodynamic design of a proprotor for the Smart UAV adopting tiltrotor aircraft concept is conducted in this study. Since proprotor of tiltrotor aircraft is operated at both rotary and fixed wing mode with single configuration rotor, the proprotor has to be designed to meet performance requirements for both flight modes. The aerodynamic design of proprotor is accomplished by combining three sources of data - the proprotor performance data, the aerodynamic data of vehicle, and the performance data of engine. The performance analysis code for proprotor is based on the combined momentum and blade element theory and validated by comparison with the TRAM data. In order to design configuration for a proprotor satisfying requirements for both rotary and fixed wing mode, various kind of performance maps are constructed for many performance and configuration parameters. From the analysis the twist angle of 38 degrees and the solidity of 0.118 are decided to be the optimal geometric parameters for both operating conditions.

• Journal of Aerospace System Engineering
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• v.15 no.5
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• pp.16-23
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• 2021

Domestic and foreign manufacturers are developing VTOL UASs in various shapes in line with demand for future technologies. UASs have been developed in a shape classified as fixed/rotary wing, and verified by appropriate certification standards. However, airworthiness certification of recent VTOL UASs is strict with the absence of VTOL-specific certification standards. In this paper, criteria applicable to VTOL UAS were presented through analysis of STANAG-4671 and STANAG-4702, which are certification standards for fixed/rotary wing UAS of the North Atlantic Treaty Organization (NATO) and the Special Condition for VTOL Aircraft (SC-VTOL) of European Aviation Safety Agency (EASA). For this, the categorization criteria of general/fixed-wing/VTOL characteristics were established for each standard item and utilized for analysis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.5
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• pp.359-367
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• 2018

The vortex ring state that occurs during the descending flight of a rotorcraft generates a circulating flow like a donut near the rotating surface, and it often causes a rotorcraft fall due to loss of thrust. In this paper, we have physically identified the flow field in the vortex ring state of the quadcopter, one of the types of unmanned aerial vehicles. The descending flight of the quadcopter was simulated in a 1m subsonic wind tunnel of the Korea Aerospace Research Institute(KARI) and the Particle Image Velocimetry(PIV) was used for the flow field measurement. The induced velocity in the hovering state is estimated by using the momentum theory and the test was carried out in the range of descent rate at which the vortex ring condition could be caused. The development and the direction of the vortex ring were confirmed by the measurement of the flow field according to not only the descent rate but also propeller separation distance. In addition, the results of the study show the vortex ring state can be predicted sufficiently by measuring the flow velocity around the quadcopter.

• Journal of Advanced Navigation Technology
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• v.25 no.3
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• pp.203-210
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• 2021

In many metropolitan cities around the world, ground and underground transportation networks are saturated due to urbanization. In addition, regulations on carbon emissions to prevent global warming are becoming stricter, and eVTOL, which will be operating in complex cities, is gaining popularity as the next generation of eco-friendly transportation. In this study, the hover lift efficiency and disc loading of eVTOLs for each type were calculated by classifying eVTOLs into following types: multicopter, lift+cruise, and vectored thrust. In addition, using the aerodynamic analysis programs OpenVSP, Fluent and Javaprop, the specific battery energy required for the smooth operation of eVTOL, which will be realized in the near future, was calculated and analyzed base on reports published by Uber and airworthiness authorities of each country.

• Journal of Aerospace System Engineering
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• v.16 no.5
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• pp.78-85
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• 2022

Multicopter-type unmanned aerial vehicles (UAV) are increasingly for cargo transportation to mountainous and island regions, image information acquisition in disaster areas, and emergency rescue transport. In order to successfully perform these tasks, the aircraft structure must be able to safely support the loads induced by flight conditions while ensuring the vibration and aeroelastic stability of the prop-rotor. This study introduced a structural analysis model of a 40kg payload multicopter with an engine-generator hybrid power system. The deformation and stress distribution are investigated depending on the load conditions. In addition, the vibration characteristics and aeroelastic stability of the prop-rotor were also presented to flight speed and aircraft pitch angle. The maximum thrust generated by the prop-rotor and the landing load applied to the multicopter under normal and emergency landing conditions were reviewed., It confirmed that the structure could support without failure. In addition, it confirmed that the damping characteristics of each primary locate in the constant region according to the aircraft's flight speed and the prop-rotors rotating speed.

• Journal of Aerospace System Engineering
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• v.16 no.6
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• pp.114-122
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• 2022

This paper explores three-dimensional unsteady computational fluid dynamic (CFD) analyses with an overset grid technique to analyse the wake effect created by a rotating propeller on a hand-launched unmanned aerial vehicle (UAV). Additionally, the influence of actual aileron deflection on the equilibrium condition of the rolling moment is examined in various hand-launched take-off conditions. The results of this study demonstrate the importance of initial aileron deflection in increasing the initial rolling stability during the hand-launched take-off process. Furthermore, an aerodynamic database is constructed to rapidly predict the aileron set values required for different take-off speeds and angle-of-attacks.

• Journal of Aerospace System Engineering
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• v.16 no.3
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• pp.84-92
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• 2022

The electro-hydrostatic actuator (EHA) recently has been used in flight control fields for aircraft because of its benefits of minimizing oil leakage and weight, improving safety, and etc. while independently operating the hydraulic power source and eliminating complex hydraulic piping. The aircraft of which EHA is installed inside, has the thermal management issue of EHA, because of its limited cooling source as compared with the aircraft which installs the traditional central hydraulic system. So, the thermal analysis model which predicts the thermal characteristics of EHA, is required to resolve this thermal management issue. In this study, an oil circulation circuit inside the hydraulic power module comprised of hydraulic pump and electrical motor for EHA was applied. This is for the purpose of developing the internal rotary group of hydraulic power module, which operates under the conditions of high rotation speed and hydraulic pressure. After formulating an appropriate thermal analysis model, the thermal analysis results with oil cooled or no oil cooled hydraulic control module were compared and reviewed, for the purpose of predicting the thermal characteristics of EHA.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.9
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• pp.607-616
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• 2019

Free body diagram analysis is done for key parts of pilot stage of LLV (Load Limit Valve) which is used to protect overload for static structural test of aerospace flight vehicle. It is shown through the analysis that diameter ratio($D_2)^{ten}/D_2)^{comp}$) of two poppets in a pilot stage must be equal to piston area ratio($A_{comp}/A_{ten}$) of a hydraulic actuator for making a poppet open consistently at constant force applied by an actuator. The result of the analysis is verified by measuring geometries of the poppets in the four different LLVs which are corresponding to four actuators with different capacity and have been used after being imported in this laboratory. Results of "Adjuster resolution tests" with two different pilot stages show the max. deviation of Fi(actuator force in instant of opening poppet) from average Fi obtained for each turn of adjuster is 0.3KN and max. deviation of the Fi normalized by average Fi of each turn of adjuster is 3.7%. From the results, it is verified that the two pilot stages with same poppet diameter ratio make a poppet consistently open at Fis within ${\pm}3.7%$ deviation from the average Fi. The deviation is shown to be caused from frictional force of O-ring in the poppet. Additionally, design factors for poppet spring and adjuster, which are also key parts of the pilot stage, are distinguished and procedure for deciding the factors are also shown in this study.

• Journal of Aerospace System Engineering
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• v.12 no.6
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• pp.9-16
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• 2018

This paper describes how to find out the optimum position of the reaction wheel assembly (RWA) to minimize image quality degradation through the integrated system jitter prediction combining the micro-vibration test with finite element analysis considering optical coefficients. Micro-vibration generated from RWA that is widely used for satellite maneuver, is one of key factors that degrades the quality of satellite image. Due to varying vibration characteristics of each RWA, its accommodation position may affect image quality even though the same company manufactured them. To resolve this issue, an integrated system jitter prediction is conducted with all possible RWA accommodation location, and finally we determine optimal RWA position from the analysis results.

• Journal of Aerospace System Engineering
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• v.13 no.2
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• pp.26-33
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• 2019

Control moment gyro (CMG) employed as satellite actuators, generates a large torque through the steering of its gimbals. Although each gimbal holds a high-speed rotating wheel, the wheel imbalances induces disturbance and degrades the satellite control quality. Therefore, the disturbances ought to be detected and identified as a precaution against actuator faults. Among the method used in detecting disturbances is the state observers. In this paper, we apply a continuous second order sliding mode observer to detect single disturbances/faults in CMGs. Verification of the algorithm is also done on the hardware satellite simulator where four CMGs are installed.