• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.3
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• pp.207-212
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• 2010

This paper presents a spiral descending path and a landing guidance law for net-recovery of a fixed-wing unmanned aerial vehicle. The net-recovery landing flight is divided into two phases. In the first phase, a spiral descending path is designed from an arbitrary initial position to a final approaching waypoint toward the recovery net. The flight path angle is controlled to be aligned to the approaching direction at the end of the spiral descent. In the second phase, the aircraft is guided from the approaching waypoint to the recovery net using a pseudo pursuit landing guidance law. Six degree-of-freedom simulation is performed to verify the performance of the proposed landing guidance law.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.3
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• pp.398-404
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• 2020

In this paper, we propose a new design method of signal constellation of the spiral quadrature amplitude modulation (QAM) exploiting a modified gradient descent search algorithm and its binary mapping rule. Unlike the conventional method, the new method, which uses and the constellation optimization algorithm and the maximum number of iterations as a parameter for the iterative design, is more robust to phase noise. And the proposed binary mapping rule significantly reduces the average Hamming distance of the spiral constellation. As a result, the proposed spiral QAM constellation has much improved error performance compared to the conventional ones even in a very severe phase noise environment. It is, therefore, considered that the proposed QAM may be a useful modulation format for coherent optical communication systems and orthogonal frequency division multiplexing (OFDM) systems.

• International Journal of Aeronautical and Space Sciences
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• v.1 no.1
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• pp.1-12
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• 2000

The wake geometries of a two-bladed rotor in axial flights using a time-marching free-wake method without a non-physical model of the far wake are calculated. The computed free-wake geometries of AH-1G model rotor in climb flight are compared with the experimental visualization results. The time-marching free-wake method can predict the behavior of the tip vortex and the wake roil-up phenomena with remarkable agreements. Tip vortices shed from the two-bladed rotor can interact with each other significantly. The interaction consists of a turn of the tip vortex from one blade rolling around the tip vortex from the other. Wake expansion of wake geometries in radial direction after the contraction is a result of adjacent tip vortices begging to pair together and spiral about each other. Detailed numerical results show regular pairing phenomenon in the climb flights, the hover at high angle of attack and slow descent flight too. On the contrary, unstable motions of wake are observed numerically in the hover at low angle of attack and fast descent flight. It is because of the inherent wake instability and blade-vortex-interaction rather then the effect of recirculation due to the experimental equipment.