• Journal of Advanced Navigation Technology
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• v.27 no.4
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• pp.374-381
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• 2023

This study focuses on the implementation of C-band radio navigation in the 5.03 ~ 5.15 GHz terrestrial band to cooperate with GNSS navigation mainly used in existing UAMs. This is one of the navigation technologies that can fully satisfy the requirements of Title 14 of CFR-135.165. According to the FAA, the use of two or more independent navigation sources for aircraft is proposed for aircraft. This study proceeded with the link budget derivation through radio wave propagation path loss analysis, and antenna shape design for miniaturized Doppler VOR, and DME design with enhanced positional distance resolution compared to conventional aircraft. The ground navigation system which is the result of this study, consists of a VOR/DME ground station and a terminal that can be mounted on UAM. Significant performance was confirmed through the production and testing of each prototype.

• Journal of Aerospace System Engineering
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• v.18 no.3
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• pp.56-64
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• 2024

In this study, a drop impact tester was developed to comprehensively conduct basic testing and academic research on the drop impact characteristics of aerospace structures. A drop tester enables accurate assessment of the dynamic stresses and deformations that occur when an aircraft collides with the ground, thereby enabling the verification of important design factors, such as safety and mechanical strength. The drop tester consists of an electromagnet to attach and drop the test object, a crane to adjust the drop height of the test object, and a drop support structure for vertical drops. Numerical analysis of the drop test object for the test was performed, and basic tests were performed using the drop impact tester. Through the analysis and test results, the structural shape of the landing gear was analyzed, and the behavior of each part was evaluated.

• Composites Research
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• v.18 no.6
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• pp.9-18
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• 2005

With the wide applications of fiber-reinforced composite material in aero-structures and mechanical parts, the design of composite joints have become a very important research area because the joints are often the weakest areas in composite structures. This paper presents an analytical study of the stress distributions in mechanically single-fastened and multi-fastened composite laminates. The finite element models which treat the pin and hole contact problem using a contact stress analysis are described. A dimensionless stress concentration factor is used to compare the stress distributions in composite laminates quantitatively In the case of single-pin loaded composite laminate, the effects of stacking sequence, the ratio of a hole diameter and the width of a laminate (W/D ratio), the ratio of hole diameter and distance from edge to hole (E/D ratio), friction coefficient and clamping force are considered. In the case of multi-pin loaded composite laminate, the influence of the number of pins, pitch distance, number of rows, row spacing and hole pattern are considered. The results show that P/D ratio and E/D ratio affect more on stress distributions near the hole boundary than the other factors. In the case of multi-pin loaded composite laminate, the stress concentration in the double column case is better than the other cases of multi-pin loaded composite laminate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.8
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• pp.611-620
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• 2018

For the past decades, the analytic model for distributed surface roughness has been developed to improve the accuracy of the icing simulation code. However, it remains limitations to validate the developed model and determine the empirical parameters due to the absence of the quantitative experimental data which were focused on the surface state. To this end, the experimental study conducted to analyze the ice covered surface state from a micro-perspective. Above all, the tendency of the smooth zone width which occurs near the stagnation point has been quantitatively analyzed. It is observed that the smooth zone width is increased as growing the ambient temperature and freestream velocity. Next, the characteristics of the ice covered surface under rime and glaze ice have been analyzed. For rime ice conditions, ice elements are developed as the opaque circular corn in the opposite direction of freestream. The height and interval of each circular corn are increased as rising the ambient temperature. For glaze ice conditions, numerous lumps of translucent ice can be observed. This is because the beads formed by gravity concentrate and froze on the lower surface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.219-226
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• 2010

The stamping process is widely used in fabricating various sheet-parts for vehicle, airplane, and electronic devices due to its low processing cost and high productivity. Recently the use of thin sheets with corrugated structures has rapidly increased for the production of energy devices, e.g., heat exchangers and fuel cells. However, it is very difficult to make corrugated structures directly in the stamping process due to their geometrical complexity. To solve this problem, this paper proposes a multi-step stamping process with a combined heat treatment process: a sequence of the first stamping, heat treatment, and second stamping. By multi-stamping, we obtained successful results in fabricating very thin corrugated structures with thicknesses of $100{\mu}m$; these are applicable as part of a plate-type heat exchanger.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.3
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• pp.257-268
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• 2018

We have studied the damage mechanism of a metallic thin plate by the highly energetic fragments generated from high explosive(HE) warhead. The penetration process has presumed that the velocity of a fragment is in the range of 350 m/s to 3353 m/s, the thickness of Aluminum 2024 target plate is in the range of 1 mm~6.3 mm thick. The mass of fragment with hemisphere nose shape is in the range of 0.32 g to 16 g. The analytical solution for penetration process has been derived by using the report of the project THOR. The results of analysis implied that the closed forms by an exponentially decay function well fit the change of the ballistic limit velocity, loss velocity and loss mass of fragment as the mass of fragment and the thickness of target plate increase.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.9
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• pp.822-829
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• 2015

In this paper, the piezoelectric-hydraulic pump with a piezostack actuator as a driving source has been designed, fabricated, and evaluated for its application to UAV's brake system. The performance requirements of the piezoelectric-hydraulic pump were decided based on the requirements analysis of the target aircraft brake system. The geometric design of the piezoelectric-hydraulic pump to meet the performance requirements of the pump was conducted, and all components of the pump including the spring sheet type check valves were machined with close tolerance. By constructing a test apparatus for the performance check of the piezoelectric-hydraulic pump, the performance characteristics of the pump, such as the outlet flow rate for load-free condition and the outlet oil pressure for closed loop condition, have been evaluated. It has been found by the performance test result that the developed piezoelectric-hydraulic pump satisfies the design requirements effectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.47 no.12
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• pp.831-840
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• 2019

Flush Air Data Sensing system (FADS) estimates air data states using pressure data measured at the surface of flight vehicles. The FADS system does not require intrusive probes, so it is suitable for high performance aircrafts, stealth vehicles, and hypersonic flight vehicles. In this study, calibration procedures and solution algorithms of the FADS for a sphere-cone shape vehicle are presented for the prediction of air data from subsonic to supersonic flights. Five flush pressure ports are arranged on the surface of nose section in order to measure surface pressure data. The algorithm selects the concept of separation for the prediction of flow angles and the prediction of pressure related variables, and it uses the pressure model which combines the potential flow solution for a subsonic flow with the modified Newtonian flow theory for a hypersonic flow. The CFD code which solves Euler equations is developed and used for the construction of calibration pressure data in the Mach number range of 0.5~3.0. Tests are conducted with various flight conditions for flight Mach numbers in the range of 0.6~3.0 and flow angles in the range of -10°~+10°. Air data such as angle of attack, angle of sideslip, Mach number, and freestream static pressure are predicted and their accuracies are analyzed by comparing predicted data with reference data.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.4
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• pp.255-267
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• 2020

Under SLD conditions, due to the large size of droplets, physical phenomena such as wall-droplet interaction and deformation have a significant effect on the icing process. Accordingly, many studies have been conducted in order to computationally simulate SLD effects. As one of the efforts, post-processing method have been proposed to describe wall-droplet interaction effect, which modified collection efficiency using Wright model. However, since the model doesn't properly consider the wall condition, it still overestimated collection efficiency and impingement limit. To solve this problem, impingement areas were divided into 3 different regions, and the post-processing method was introduced with the new wall-droplet interaction model developed based on Bai and Gosman rebound model. In order to consider the effect of deformation, the most suitable model was selected by comparing the deformation models used in the various icing codes. As a result, the modified post-processing method showed improved accuracy in predicting the impingement limits and collection efficiency by further estimating mass flux loss due to rebound, and it was observed that the result was the closest to the experimental data when the deformation effect was included by using Wiegand model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.7
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• pp.471-478
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• 2022

This paper is about research and development of Korea Aerospace University's Solar-Powered UAV System that named of KAU-SPUAV, and describes the design process of the 4.2 m solar UAV that succeeded in a long flight of 32 hours and 19 minutes at June 2020. In order to improve the long-term flight performance of the KAU-SPUAV, For reduce drag, a circular cross-section of the fuselage was designed, and manufactured light and sturdy fuselage by applying a monocoque structure using a glass fiber composite material. In addition, a solar module optimized for the wing shape of a 4.2 m solar drone was constructed and arranged, and a propulsion system applied with the 23[in] × 23[in] propeller was constructed to improve charging and flight efficiency. The developed KAU-SPUAV consumes an average of 55W when cruising and can receive up to 165W of energy during the day, and its Long-term Endurance was verified through flight tests.