Efficient flight operations are crucial for the sustainable development of aviation. Continuous descent is a potential solution in a terminal airspace. At present, descent is evaluated based on the length or duration of level flight segments only. Typically, modern flight management systems calculate optimal descent profiles with level segments added only for necessary deceleration. If no wind disturbance is present, the aircraft can follow the path calculated and achieve the optimal descent. In practice, however, differences between the predicted and actual wind require changes to the descent profile such as adding thrust, drag, or flying additional level segments. This research analyses different descent control strategies and investigates their effects on fuel burn, flight time and path deviation. Monte Carlo simulations are conducted to account for various wind conditions. Results show that even strategies with level segments increased by an average of 22% can result in lower fuel burn. Therefore, it is concluded that level segments by themselves are not a sufficient metric for descent efficiency and a strategy for lower fuel burn descents is proposed.
A regional navigation satellite system is a prospective candidate for use in the Korean navigation satellite system (KNSS), which will have South Korea and the remainder of East Asia as its service area. However, orbit design is a prerequisite for any navigation satellite system. This paper implements a conceptual design process prior to orbit design for an indigenous KNSS. Orbits are examined in terms of suitability, and an orbit combination based on the dilution-of-precision (DOP) performance is presented. Through simulation, an orbit combination capable of providing a stable DOP for the Korean Peninsula is proposed. Moreover, the orbit combination proposed incorporates design constraints such as satellite unavailability or potential position errors in the north-south direction, with the Korean Peninsula as a reference position. The simulation results suggest that the KNSS requires an orbit combination involving geostationary orbit (GEO) and elliptically inclined geosynchronous orbit (EIGSO), along with backup satellites in EIGSO; thus, the proposed system consists of 11 satellites in total.
A method to correct wind tunnel test data for the additional drag caused by roughness elements in a fully turbulent boundary layer is proposed using drag polar curves obtained from wind-tunnel tests. It is assumed that boundary layer over a wind tunnel model is fully turbulent at high absolute angle of attack both with and without roughness elements from the results of measurements using Preston tubes, and that the additional drag due to the roughness elements is constant over the entire range of the angle of attack. The additional roughness drag is estimated using the axial force data obtained from internal balances. The method proposed was validated using the data from wind tunnel tests with the same Mach number with two models obtained from two different wind tunnels. The differences in the values of minimum drag coefficient obtained from the two wind tunnels tests corrected by this method were smaller than those corrected using a conventional method, and they were well within the uncertainties in terms of the drag coefficient. Furthermore, the additional roughness drag can be estimated by this method when applying wind tunnel data obtained using only a single roughness height.
Wind tunnel experiments are performed to investigate the aerodynamic characteristics of a quadrotor helicopter in a uniform flow. At first, the thrust and drag coefficients of a single rotor under low-Reynolds number conditions are measured to deduce the basic design parameters of the rotor. Second, the aerodynamic interference between two rotors in a tandem configuration is investigated. It is experimentally found that the thrust coefficient of the rear rotor is a maximum of 11% lower than that of the front rotor during forward flight. Moreover, it is found that the interference effect of the front rotor on the rear rotor can be predicted qualitatively using a theoretical formula on the basis of the Biot-Savart Law. Finally, it is shown that the theoretical predictions of the thrust coefficient and drag coefficient agree well with the experimental results of a quadrotor helicopter model within limited ranges of the inflow ratio and advance ratio.
A magnetically suspended control sensitive gyroscope (MSCSG) is a type of gyroscope with integrated attitude control and attitude angular measurement. The rotor of the MSCSG is a split-type sphere with different radii, so that the external force of the rotor can always pass the center of the gyro rotor. This is advantageous for providing precise control. The rotor is driven by a Lorentz force magnetic bearing (LFMB) capable of tilting in all directions and controlling attitude with precise torque. Its control precision depends directly on the uniformity in the magnetic density of the LFMB. To make the magnetic density distribution more uniform, a new LFMB is proposed. A cross-sliding mode controller is designed to control the rotor tilt. The Lyapunov theory is introduced to design the method proposed, thus the closed-loop system is Lyapunov stable. Numeric simulations are developed to demonstrate the effectiveness of the control method proposed, and the results illustrate that this method can inhibit disturbances effectively for both new LFMB and traditional LFMB. Furthermore, the tracking accuracy and dynamic performance of the new LFMB are significantly better than the traditional one.