Drone dynamics are affected by flight condition uncertainties, such as the surrounding structure, gust disturbance, and rotor damage, resulting in the deterioration of flight performance and safety. Real-time modeling of drone dynamics plays an important role in flight safety. In this study, the on-board measurement of downwash speed, which is an important parameter in drone dynamics, was performed using ultrasonic passing-time information. In this method, ultrasonic transmitters and receivers were arranged below the rotor, and the passing time in the downwash was estimated using an extended Kalman filter, which was designed for the constructed ultrasonic propagation dynamics model. It was validated that the proposed method is sufficiently robust to accurately estimate the downwash speed in a disturbed flow under a rotating rotor.

This study proposes a fuel efficiency prediction model using a newly defined fuel efficiency index. The process is divided into three steps: (1) define a new fuel efficiency index after identifying the limitations of the existing fuel efficiency index; (2) set up a fuel efficiency prediction model; and (3) formulate possible actions for the airline to enhance fuel efficiency and reduce carbon emissions based on the model established in the previous step. The fuel efficiency prediction model was established using the actual flight data of Airbus 330-300 (engine type: PW4168A). The flight data were obtained from the fuel management and information system of an airline. The multiple regression model is used to identify the independent variables affecting the fuel efficiency and the degree of influence of each variable. The results indicate that variables such as payload, aircraft fuel mileage deterioration, center of gravity, extra fuel loaded, flight distance, and outside air temperature affect the fuel efficiency. Some variables can be controlled and managed by airlines, others are not. The proposed fuel efficiency prediction model is expected to be utilized as a measurable method for enhancing the fuel efficiency and reducing the carbon emissions.

In this study, the landing point ellipse predicted using the Earth GRAM atmosphere model and the pinpointed landing point predicted using NCEP GFS forecast data are validated using flight data for a low-ballistic-coefficient flight vehicle with a deployable aeroshell. The equations of motion in the Earth-centered Earth-fixed (ECEF) coordinate system are used for the atmospheric re-entry trajectory calculation, combined with the atmospheric model or the forecast data. The flight data of the RATS, which was launched by the S-520-31 sounding rocket, is used for validation. It was confirmed that the actual landing point is located within the 1σ landing error ellipse calculated using Monte Carlo simulation with Earth GRAM. It was found that the closer the forecast data was to the flight data, the more accurate the forecast became, and the smaller the change in the landing point for each forecast update. The maximum likelihood trajectory using the NCEP GFS forecast data available immediately before the flight is similar in shape to the actual flight trajectory, and the difference in the landing point is approximately 1 km.

Dynamically extendable chords with controlled non-harmonic motions are studied for improving the performance of variable-speed tail rotors. A validated helicopter performance model is utilized, which consists of a rotor, a fuselage, a tail rotor and a propulsive trim method. The results show that the optimal azimuth angles for the deployment of extendable chords are 40°–50° and 130°–140° at the nominal tail rotor speed. In order to improve the efficiency of the extendable chord, a non-harmonic motion of the extendable chord is proposed. Extendable chords can reduce the blade area with high drag and lower the angle-of-attack, which can lead to significant power savings during high-speed flight. Extendable chords are more suitable to reduce the power of variable-speed tail rotors. When the tail rotor speed is reduced by 20%, the power can be reduced up to 19.4%.

A numerical simulation method of computational fluid dynamics (CFD) coupling with a trim analysis for coaxial rotor systems is described in this paper. The trim analysis is implemented using a rotorcraft flow solver, rFlow3D. Six target forces and moments, which are the thrust of the coaxial rotor system, the rolling and pitching moments for each upper and lower rotor, and the torque balance for yaw control, are considered as the trim conditions. The blade pitch angles of both upper and lower rotors are adjusted to satisfy the target trim conditions through the trim analysis by being loosely coupled with the CFD solver. Verification of the trim analysis method and validation of the prediction accuracy of aerodynamic performance are performed based on previous experimental and numerical studies in hover and forward flight using the lift-offset conditions. It is shown that the predicted hover performances of the torque-balanced coaxial rotors are in excellent agreement with the experimental data. It is also verified that the lift-offset conditions in forward flight are simulated using this established trim analysis. Furthermore, reasonable agreements with other computational results are indicated.