• Journal of the Korea Institute of Military Science and Technology
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• v.25 no.5
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• pp.539-544
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• 2022

This research shows the test performance of a 6 kW-scale hybrid electric power system for the high endurance drone. The power system is composed of a two-stroke reciprocal engine, starter-generator and battery, and they are integrated as one power unit. The engine is designed to provide the house for holding the starter-generator at the end of a crankshaft in turn the engine and starter-generator can maintain the same speed during the operational period. In this way, the generated power is readily controlled by just manipulating an engine throttle movement. Moreover, the starter-generator can initiate an engine operation with an aid of battery power until the combustion process becomes stabilized. In consequence, integration mechanism between an engine and generator is simplified, which results in weight reduction achieved. The duty of back-up battery is to provide a starting power to generator via a system controller in addition to covering momentarily power shortage. Therefore, the electric power system is vindicated to provide 6 kW power through a ground test.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2022.11a
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• pp.344-346
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• 2022

최근 자율운항기술개발이 활발하게 이루어짐에 따라 자율운항선 실증이 증가하고 있으며, 또한 자율운항선의 효율적 운용 특히 운항의 안전성을 위해 입출항 시기의 적절성 또한 중요해지고 있다. 이에 해상교통혼잡도를 예측하고자 하였고, AIS 빅데이터를 통해 선박별항적을 분석 및 분류하고자 하였다. 장기적 관점에서 PORT-MIS 선박입출항현황 데이터(호출번호, 입항일시, 출항일시, 전출항지, 차항지, 계선지)를 과거 AIS 빅데이터와 연결시켜 과거 항적 중 가장 가까운 항적을 찾고자 하였다. 그리고 당시 소요 시간을 반영하여 12개의 시간대별로 어느 시점에 어느 위치 구간에 선박들이 놓이게 될지 예측하였고, 특히 입출항 시기의 적절성에 핵심이 되는 13개로 모델링된 영역에 몇 개의 선박들이 항로를 지나는지에 따라 혼잡도(원활, 혼잡, 정체)를 구분하였다. 또한, 본 연구에서는 단기적 관점에서 실제 AIS가 수신된 후에도 유사한 항적을 검사해가며 혼잡도를 예측하고자 하였고, 이러한 장단기적 혼잡도 예측을 통해 미래 자율운항선입출항 지원 서비스의 안전과 그 적절성을 제공하고자 하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.8
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• pp.699-705
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• 2015

Aircraft needs high lift-to-drag ratio and weight reduction of the structure for long endurance flight with a small power. Generally high aspect ratio wing is applied to HALE(High Altitude Long Endurance) aircraft. Also high modulus, and high strength CFRP(Carbon Fiber Reinforced Plastic) has been used in primary structures. and thin mylar(membrane material) film has been applied to skin of wing. As a result, wing is more flexible than the other structures. and the stiffness of thin mylar film has an affect on dynamic stability. In this study, the membrane characteristic of mylar film has been simulated using nonlinear gap elements. And equivalent modeling method using shell elements is presented using the nonlinear simulation result. The linear equivalent model has verified using the results of nonlinear membrane method. Proposed linear equivalent shell model has applied to mode analysis for estimate the effect of mylar mechanical properties on natural frequency.

• Journal of computational fluids engineering
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• v.21 no.2
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• pp.70-80
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• 2016

The comparison of two commercial codes(FLUENT and STAR-CCM+) and an open-source code(OpenFOAM) are carried out for the aerodynamic analysis of flight vehicles at low speeds. Tailless blended-wing-body UCAV, main wing and propeller of HALE UAV(EAV-3) are chosen as geometries for the investigation. Using the same mesh, incompressible flow simulations are carried out and the results from three different codes are compared. In the linear region, the maximum difference of lift and drag coefficients of UCAV are found to be less than 2% and 5 counts, respectively and shows good agreement with wind tunnel test data. In a stall region, however, the reliability of RANS simulation is found to become poor and the uncertainty according to code also increases. The effect of turbulence models and meshes generated from different tools are also examined. The transition model yields better results in terms of drag which are much closer to the test data. The pitching moment is confirmed to be sensitive to the existence and the location of transition. For the case of EAV-3 wing, the difference of results with ${\kappa}-{\omega}$ SST model is increased when Reynolds number becomes low. The results for the propeller show good agreement within 1% difference of thrust. The reliability and uncertainty of three codes is found to be reasonable for the purpose of engineering use. However, the physical validity and reliability of results seem to be carefully examined when ${\kappa}-{\omega}$ SST model is used for aerodynamic simulation at low speeds or low Reynolds number conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.11
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• pp.908-914
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• 2013

This study has developed a small solar powered UAV and performed its flight tests. In daylight, a solar powered UAV flies by using some of electricity generated from solar cells, and stores the remainder into battery. At night it flies by using electricity from battery. A solar powered UAV should have aerodynamically efficient configurations, light-weight, strong wing and fuselage. Its electric propulsion system and solar power system should also be very efficient. In the present study the solar powered UAV and its solar power system are developed for 12 hour continuous flight and the flight tests are performed to verify its performance. The flight tests performed in fall and winter to prove the present solar powered UAV is successful in four-season 12 hour flight.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.7
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• pp.505-511
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• 2020

The circular composite tubes have been used as a main spar of HALE-UAV(High Altitude Long Endurance-Unmanned Air Vehicle). In this paper, an analytical model is presented for the prediction of the failure load of unsymmetrically stiffened circular spar using a modified Brazier approach. This model was used to predict the moment carrying capacity of the unsymmetrically stiffened circular spar. From the results, we can know that a stiffened cap placed in the top sector of a spar increased the bending capabilities. Four point bending tests were conducted to estimate the effect of the cap on the failure load and compared with the proposed model. And numerical simulations were performed to analyze the behavior of stiffened circular spar. Comparisons of the results from the proposed model with those from experiments and numerical modes show good correlation.

• Journal of Aerospace System Engineering
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• v.10 no.1
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• pp.59-65
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• 2016

Korea Aerospace Research Institute (KARI) is developing an electric-driven HALE UAV in order to secure system and operational technologies since 2010. Based on the 5 years of flight tests and design experiences of the previously developed electric-driven UAVs, KARI has designed EAV-3, a solar-powered HALE UAV. EAV-3 weighs 53 kg, the structure weight is 21 kg, and features a flexible wing of 19.5 m in span with the aspect ratio of 17.4. Designing the main wing and empennage of the EAV-3 the amount of the bending due to the flexible wing, 404 mm at 1-G flight condition based on T-800 composite material, and side wind effects due to low cruise speed, V_cr = 6 m/sec, are carefully considered. Also, unlike the general aircraft there is no center of gravity shift during the flight. Thus, the static margin cuts down to 28.4% and center of gravity moves back to 31% of the Mean Aerodynamic Chord (MAC) comparing to the previously developed scale-down HALE UAVs, EAV-2 and EAV-2H, to minimize a trim drag and enhance a performance of the EAV-3. The first flight of the EAV-3 has successfully conducted on the July 29, 2015 and the test flight above the altitude 14 km has efficiently achieved on the August 5, 2015 at the Goheung aviation center.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.4
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• pp.469-477
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• 2015

In this study, the characteristics of main wind direction, vertical temperature and wind speed profile near the Moseulpo airfield for HALE UAV(High Altitude Long Endurance Unmaned Aerial Vehicle) is investigated. The results are summarized as follows, main wind direction is governed by air mass according to season and local wind such as land-sea breeze. The directions of landing and take-off of HALE UAV will be selected as the south-east direction in June ~ August, north-west direction in October ~ March, and south-east direction at daytime in April ~ May, September. Annual variation of temperature at 100 hPa showed that temperature in summer season is lower than winter season. On the other hands, wind speed at 250 hPa in winter season is higher than summer season. The threshold values of temperature and wind speed for HALE UAV flight are $-75^{\circ}C$ and $90ms^{-1}$, which were determined by 5 % frequency value($1.96{\sigma}$), respectively.

• Journal of the Korean Institute of Gas
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• v.19 no.6
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• pp.22-27
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• 2015

Hydrogen features highest energy density per mass and is expected to be desirable as a fuel of HALE(High altitude long endurance) UAV(Unmanned aerial vehicle). A reciprocating internal combustion engine is known to be a reliable and economic power source for this kind of UAV. Therefore, the combination of hydrogen and engine is worth of doing research. Test bench with 2.4L Spark-Ignited engine was prepared for the experiment in which start and combustion characteristics at idle condition were examined in this study. Stable hydrogen supply system and a universal ECU(Engine control unit) were also utilized for the test engine. Equivalence ratio and spark timings at idle operation were investigated and compared to the data of gasoline engine. The results will be a starting point for full-scale research of hydrogen engine for HALE UAV.

• Atmosphere
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• v.27 no.3
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• pp.359-370
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• 2017

In this study, the oceanic Total Precipitable Water (TPW) retrieval algorithm at 16 km altitude of High Altitude Long Endurance Unmanned Aerial Vehicle (HALE UAV) is described. Empirical equation based on Wentz method (1995) that uses the 18.7 and 22.235 GHz channels is developed using the simulated brightness temperature and SeeBor training dataset. To do radiative simulation, Satellite Data Simulator Unit (SDSU) Radiative Transfer Model (RTM) is used. The data of 60% (523) and 40% (349) in the SeeBor training dataset are used to develop and validate the TPW retrieval algorithm, respectively. The range of coefficients for the TPW retrieval at the altitude of 3~18 km with 3 km interval were 153.69~199.87 (${\alpha}$), 54.330~58.468 (${\beta}$), and 84.519~93.484 (${\gamma}$). The bias and RMSE at each altitude were found to be about $-0.81kg\;m^{-2}$ and $2.17kg\;m^{-2}$, respectively. Correlation coefficients were more than 0.9. Radiosonde observation has been generally operated over land. To validate the accuracy of the oceanic TPW retrieval algorithm, observation data from the Korea Meteorological Administration (KMA) Gisang 1 research vessel about six clear sky cases representing spring, autumn, and summer season is used. Difference between retrieved and observed TPW at 16 km altitude were in the range of $0.53{\sim}1.87kg\;m^{-2}$, which is reasonable for most applications. Difference in TPW between retrieval and observation at each altitude (3~15 km) is also presented. Differences of TPW at altitudes more than 6 km were $0.3{\sim}1.9kg\;m^{-2}$. Retrieved TPW at 3 km altitude was smaller than upper level with a difference of $-0.25{\sim}0.75kg\;m^{-2}$ compared to the observed TPW.