• Journal of Aerospace System Engineering
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• v.15 no.1
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• pp.72-79
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• 2021

In this study, as part of the development of an autonomous flying personal aircraft, an equivalent model of the main wing assembly of an Optionally Piloted Personal Air Vehicle (OPPAV) was developed. Reliability of the developed equivalent model was verified by eigenvalue analysis. The main wing assembly consisted of a main wing, an inboard pod, and an outboard pod. First, for developing an equivalent model of each component, components to produce the equivalent model were divided into several sections. Nodes were then created on the axis of the equivalent model at both ends of each section. In addition, static analysis with unit force and unit moment was performed to calculate the deformation or the amount of rotation at the node to be used in the equivalent model. Equivalent axial, bending, and torsional stiffness of each section were calculated by applying the beam theory. Once the equivalent stiffness of each section was calculated, information of a mass and moment of inertia for each section was entered by creating a lumped mass in the center of each section. An equivalent model was developed using beam element. Finally, the reliability of the developed equivalent model was verified by comparison with results of mode analysis of the fine model.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.6
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• pp.375-382
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• 2020

Owing to the rapid development of infrared guided weapon systems, the threat to aircraft survivability is constantly increasing, and research on infrared stealth technologies are being conducted to ensure aircraft survival. In this study, we analyze the minimum infrared signature of an aircraft according to its flight altitude by considering the characteristics of infrared guided missiles, which detect the contrast signature between the aircraft and background. We conducted computational fluid dynamics simulations for the convective coefficient, and heat transfer simulations were performed considering convection, conduction, and radiation for flight conditions. Thus, we obtained the surface temperature distribution of the aircraft and analyzed the aircraft infrared signature based on the flow characteristics around it. Furthermore, the optimum emissivity for the minimum infrared signature was derived, and the effect of the infrared signature was analyzed when this optimum emissivity was applied to the fuselage surface for each flight condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.3
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• pp.185-195
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• 2021

The flapping-wing micro air vehicle (FW-MAV) in this study utilizes the cambered wings made of quite flexible material. Similar to the flying creatures, the present cambered wing uses three different materials at its leading edge, vein, and membrane. And it is constrained in various conditions. Since passive rotation uses the flexible nature of the wing, it is important to select an appropriate material for a wing. A three-dimensional fluid-structure interaction solver is developed for a realistic modeling of the cambered wing. Then a parametric study is conducted to evaluate the aerodynamic performance in terms of the elastic modulus of leading edge and vein. Consequently, the elastic modulus plays a key role in enhancing the aerodynamic performance of FW-MAVs.

• Smart Media Journal
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• v.9 no.4
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• pp.176-186
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• 2020

The size and shape of crops are diverse, and the growing environment is also different. Therefore, when one uses a drone to spray pesticides, the characteristics of each crop must be considered, and flight conditions such as the flight height and forwarding velocity of the drone should be changed. The droplet flow of pesticides is affected by various flight conditions, and a large change occurs in the sprayed area. As a result, an uneven distribution of liquid may be formed at the wake, and the transport efficiency will be decreased as well as there would be a risk of toxic scatter. Therefore, this paper analyzes the degree of distribution of pesticides to the crops through numerical analysis when pesticide is sprayed onto the selected three crops with different characteristics by using agricultural drones with different flight conditions. On the purpose of establishing a guideline for spraying pesticides using a drone in accordance with the characteristics of crops, this paper compares the amount of pesticides distributed in the crops at the wake of nozzle flow using the figure of merit, and the sum of transported liquid rate divided by the root mean square of the probability density function.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.719-727
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• 2008

A 3-D compressible Navier-Stokes solver using overlapped grids is developed to predict a flow-field around a hovering rotor. The flow solver is verified by a parametric study with the grid spacing of wake grid, spatial accuracy and turbulence model. Computations are performed with different Chimera grid systems. Computational results are compared with the experimental data of Caradonna et al. for both blade loading and the tip vortex behavior. Numerical results show good agreements with experiments for the distribution of surface pressure and tip vortex behavior. Pressure distributions over the blade have marginal differences for different numerical methods, whereas large discrepancies are seen in the prediction of the wake behavior. Results unexpectedly show that the vortex strength from an automated cut-paste Chimera grid is weaker than that from the conventional Chimera grid.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.3
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• pp.259-267
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• 2017

Flow fields around a KARI-11-180 airfoil, SDM and transonic body are numerically simulated by using an unstructured meshes based compressible flow solver developed at KAIST. RANS equations are solved to analyse the flow fields and Roe's FDS method is adopted to evaluate convective fluxes. Turbulence effect of the flow fields is modeled by a SA model, SST model and ${\gamma}-{\widetilde{Re}}_{{\theta}t}$ model. It is found that smaller drag coefficients are predicted for the KARI-11-180 airfoil when a transition phenomenon is considered and small deviations exist between CFD and EFD results. For the SDM, flow separation is observed at a leading edge and calculated aerodynamic properties show similar tendencies to experimental results. A shock wave on main wings of the transonic body is successfully captured by the present flow solver at a Mach number 0.9. Estimated pressure profiles by means of the present CFD method also agree well with those of wind tunnel results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.8
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• pp.662-669
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• 2012

The effect of aspect ratio (AR) on the aerodynamic characteristics of a flapping wing was examined to analyze the design parameters of an insect-based MAV. The experimental model constructed with 4-bar linkages was operated in a water tank with the condition of a low Reynolds number. A water-proof micro-force load cell was fabricated and installed at the root of the wing which is made of a plexiglas. The wing shapes were based on the planform of a fruit fly wing. The ARs selected were 1.87, 3.74 and 7.48 and the Reynolds number was fixed at $10^4$. For AR=1.87 and 3.74, distinct lift peaks which indicate unsteady effects such as 'wake-capture' were observed at the moment of the start of the wing-stroke. However, for AR=7.48, no unsteady effects were observed. These phenomena were also observed in the delayed rotation case. The results indicate that a larger AR provides better aerodynamic performance for the insect-based flapping wing which can be applied in MAV designs.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.4
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• pp.297-305
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• 2011

In this study, the aeroelastic analysis of rotorcraft in forward flight has been performed using dynamic inflow model to handle unsteady aerodynamics. The quasi-steady airload model based on the blade element method has been coupled with dynamic inflow model developed by Peters and He. The nonlinear steady response to periodic motion is obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim for stability analysis. The aerodynamic and structural characteristics of dynamic inflow model are validated against other numerical analysis results by comparing induced inflow and blade tip deflections(flap, lag). In order to validate aeroelastic stability of dynamic inflow model, lag damping are also compared with those of linear inflow model.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.4
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• pp.74-80
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• 2014

This paper describes the development of the dual-thrust flight motor for enhancing the hit probability of unguided rockets. We designed dual-thrust flight motor by shape modification of the double base propellant with high burning rate, and confirmed the dual-thrust performance by static firing tests. The test results showed the thrust ratio of about 1:7.6 between sustaining phase and boosting phase, and had a quietly normal dual-thrust characteristics. And the results showed that there was not the fire extinction phenomenon of propellant due to the pressure drop.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.4
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• pp.289-296
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• 2017

In this paper, geometrical optimization for newly designed flapping mechanism for insect-like micro air vehicle is presented. The mechanism uses strings to convert rotation of motor to reciprocating wing motion to reduce the total weight and inertial force. The governing algorithm of movement of the mechanism is established considering the characteristic of string that only tensile force can be acted by string, to optimize the kinematics. Modified pattern search method which is complemented to avoid converging into local optimum is adopted to the geometrical optimization of the mechanism. Then, prototype of the optimized geometry is produced and experimented to check the feasibility of the mechanism and the optimization method. The results from optimization and experiment shows good agreement in flapping amplitude and other wing kinematics. Further research will be conducted on dynamic analysis of the mechanism and detailed specification of the prototype.