• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.10
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• pp.962-968
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• 2008

An experimental study of the aerodynamic characteristics of a stealth configuration, the test techniques developed for the testing in the Low Speed Wind Tunnel of Agency for Defense Development(ADD-LSWT), and the lessons learned have been presented. The main objectives of this test are to determine the aerodynamic characteristics of a stealth configuration and to measure the flow field characteristics with a 5-hole pressure probe. The test results are discussed and the effect of the leading edge shape on the aerodynamic characteristics is also given.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.6
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• pp.467-473
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• 2007

Flow visualization study to qualitatively define the flow field over a stealth UCAV(Uninhabited Combat Air Vehicle) configuration in a water tunnel has been conducted to clarify the basic aerodynamic performance. The test was performed at freestream velocity of 12.7 cm/sec which was corresponding to a Reynolds number of $1.4{\times}10^4$ based on mean aerodynamic chord. The development and breakdown of vortices illuminated by using dye were compared to the previous force and moment data. It was shown that the effect of the vortices generated by the main-body and junction are dominant in the low angle-of-attack region. However, in the high angle-of-attack region, the vortex generated by the fore-body mainly influenced the aerodynamic performance of the model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.4
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• pp.297-305
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• 2018

The role of UCAV is to carry out various missions in hostile situations such as penetration and attack on the enemy territory. To this end, application of RF stealth technology is indispensable so as not to be caught by enemy radar. The X-47B UCAV with blended wing body configuration is a representative aircraft in which modern RCS reduction schemes are heavily applied. In this study, a model UCAV was first designed based on the X-47B platform and then an extensive RCS analysis was conducted to the model UCAV in the high-frequency regime using the Ray Launching Geometrical Optics (RL-GO) method. In particular, the effects of configuration of UCAV considering IR reduction on RCS were investigated. Finally, the effects of RAM optimized for the air intake of the model UCAV were analyzed.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.4
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• pp.429-436
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• 2018

The RCS value of maritime ship is indicator of ship's stealth performance and it should be particularly measured for navy ship to ensure survivability on the battlefield. In the design phase of the navy ship, a RCS prediction should be performed to reduce RCS value and achieve ROC(Required Operational Capability) of the ship through configuration control. In operational phase, the RCS value of the ship should be measured for verifying the designed value and obtaining tactical data to take action against enemy missile. During the measurement of RCS for the ship, ship motion can be affected by roll and pitch in accordance with sea state, which should be analyzed into threat elevation from view point of enemy missile. In this paper, we propose a method to measure and analyze RCS of ship in 3-dimensions using a ship motion measuring instrument and a fixed RCS measurement system. In order to verify the proposed method, we conducted a marine experiment using a test ship in sea environment and compared the measurement data with RCS prediction value which is carried by prediction SW($CornerStone^{TM}$) using CAD model of the ship.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.1
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• pp.81-89
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• 2017

This study investigates store separation characteristics of an unmanned aerial vehicle having generic stealth configuration over unsteady flow of an internal bay. Free-drop wind tunnel tests are conducted to simulate bomb releases from an internal weapons bay while high-speed camera images are taken. The images are analyzed to examine the effects of flow velocity, angle of attack, flap deflection and the ejector force application on the store separation trajectories. For the free-drop wind tunnel tests, Froude Scaling is applied to match the dynamic similarity for the bomb model, and the ejector force is simulated by using small pneumatic cylinders. The results indicate that the test bomb model safely separates from the internal bay at the given test conditions and configurations. It is also observed that the effects of the flow velocity and ejector force application have greater impacts on the separation trajectories than those of angle of attack and flap deflection.

• The Journal of the Acoustical Society of Korea
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• v.30 no.2
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• pp.63-72
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• 2011

Since the detection probability is critically dependent on the target strength (TS) in active sonar and on the radiated noise level (RNL) in passive sonar, the acoustic materials for echo reduction (ER) and transmission loss (TL) are widely used for the stealth of underwater targets. In this paper, a measurement system based on the small water tank, for the frequency range of greater than 30 kHz, is developed and verified using reference targets. In order to design the water tank and the geometry of test samples, a program is developed to calculate the arrival time of interfering signals due to the reflection from water tank walls and also due to the diffraction from the edge of the test samples. Considering all the interfering signals, an optimal experimental configuration for water tank and test samples is designed and used throughout the experiment. Next, the signal processing algorithms to estimate ER and TL are developed based on the measured propagation loss reflecting the geometric spreading characteristics of the transducer. Finally, a set of reference targets such as aluminium plate and perfectly reflecting plate are used in a small water tank to verify the developed measurement system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.1
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• pp.1-9
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• 2018

Lambda wing type Unmanned Combat Aerial Vehicle(UCAV) which adopts Blended Wing Body(BWB) has relatively less drag and more stealth performance than conventional aircraft. However, Pitching moment is rapidly increased at a specific angle of attack affected by leading edge vortex due to leading edge sweep angle. Wind tunnel testing and numerical analysis were carried out with UCAV 1303 configuration on condition of 50 m/s of flow velocity, $-4^{\circ}{\sim}28^{\circ}$ of the range of angle-of-attack. The effect of wing twist for longitudinal stability at the various angles of attack was verified in this study. When negative twist is applied on the wing, Pitch-break was onset at higher angle of attack due to delayed flow separation on outboard of the wing. On the other hand, pitch-break was onset at lower angle of attack and lift-to-drag ratio was increased when positive twist is applied on the wing.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.3
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• pp.232-242
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• 2015

For stealth performance consideration, many UAV designs are adopting tailless lambda-shaped configurations which are likely to have unsteady dynamic characteristics. In order to control such UAVs through automatic flight control system, more accurate estimation of dynamic stability derivatives becomes essential. In this paper, dynamic stability derivatives of a tailless lambda-shaped UAV are estimated through numerically simulated forced oscillation method incorporating dynamic mesh technique. First, the methodology is validated by benchmarking the CFD results against previously published experimental results of the Standard Dynamics Model(SDM). The dependency of initial angle of attack, oscillation frequency and oscillation magnitude on the dynamic stability derivatives of a tailless UAV configuration is then studied. The results show reasonable agreements with experimental reference data and prove the validity and efficiency of the concept of using CFD to estimate the dynamic derivatives.