• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1914-1922
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• 2004

This paper provides a comprehensive study of optimum design of a helicopter tailrotor driveshaft made of the flexible matrix composites (FMCs). Since the driveshaft transmits power while subjected to large bending deformation due to aerodynamic loadings, the FMCs can be ideal for enhancing the drivetrain performance by absorbing the lateral deformation without shaft segmentation. However, the increased lateral flexibility and high internal damping of the FMCs may induce whirling instability at supercritical operating conditions. Thus, the purpose of optimization in this paper is to find a set of tailored FMC parameters that compromise between the lateral flexibility and the whirling stability while satisfying several criteria such as torsional buckling safety and the maximum shaft temperature at steadystate conditions. At first, the drivetrain was modeled based on the finite element method and the classical laminate theory with complex modulus approach. Then, an objective function was defined as a combination of an allowable bending deformation and external damping and a genetic algorithm was applied to search for an optimum set with respect to ply angles and stack sequences. Results show that an optimum laminate consists of two groups of layers: (i) one has ply angles well below 45$^{\circ}$ and the other far above 45$^{\circ}$ and (ii) the number of layers with low ply angles is much bigger than that with high ply angles. It is also found that a thick FMC shaft is desirable for both lateral flexibility and whirling stability. The genetic algorithm was effective in converging to several local optimums, whose laminates exhibit similar patterns as mentioned above.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.5 s.149
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• pp.538-549
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• 2006

A code is developed to simulate a viscous flow field around a deformable body using the hybrid Cartesian/immersed boundary method. In this method, the immersed boundary(IB) nodes are defined near the body boundary then velocities at the IB nodes are reconstructed based on the interpolation along the normal direction to the body surface. A new method is suggested to define the IB nodes so that a closed fluid domain is guaranteed by a set of IB nodes and the method is applicable to a zero-thickness body such as a sail. To validate the developed code, the vorticity fields are compared with other recent calculations where a cylinder orbits and moves into its own wake. It is shown the code can handle a sharp trailing edge at Reynolds number of $10^5$ under moderate requirements on girds. Finally the developed code is applied to simulate the vortex shedding behind a deforming foil with flapping tail like a fish. It is shown that the acceleration of fluids near the flapping tail contributes to the generation of the thrust for propulsion.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.11
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• pp.965-972
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• 2016

This paper presents results of flight experiments on a navigation algorithm including multiplicative extended Kalman filter for estimating attitude of the guided munition. The filter describes orientation of aircraft by data fusion with low-cost sensors where measurement update is done by multiplication, rather than addition, which is suitable for quaternion representation. In determining attitude from vector observations, the existing approach utilizes a 3-axis accelerometer as a 2-axis inclinometer by measuring gravity to estimate pitch and roll angles, while GNSS velocity is used to derive heading of the vehicle. However, during accelerated maneuvers such as coordinated flight, the accelerometer provides inadequate inclinometer measurements. In this paper, the measurement update process is newly defined to complement the vulnerability by using different vector observations. The acceleration measurement is considered as a result of a centrifugal force and gravity during turning maneuvers and used to estimate roll angle. The effectiveness of the proposed method is verified through flight experiments.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.1
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• pp.35-42
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• 2020

Electromechanical Actuator(EMA) for flight vehicles generally serves to control the fin deflection angle or the thrust vector angle. This paper deals with design and development of EMA for both aerodynamic control and thrust vector control. In this paper, a novel compact EMA is proposed that can simultaneously control both the tail fin and the jet vane with one actuator and detach the jet vane after vertical launch and rapid turn of the flight vehicle so as to increase efficiency during flying to target. To do this, we designed the EMA using a push-push link mechanism and derived a mathematical model. The mathematical model is validated by comparing simulation result and experimental data. The performance and reliability of the proposed EMA have been verified through performance test, environmental test and ground test. The proposed EMA is expected to be useful as an EMA for flight vehicles because of its simple and compact structure, as well as its performance and reliability.