Investigation on effects of time-frequency characteristics of ship airwake on helicopter flight characteristics

A conventional helicopter flight dynamics model, which can be coupled with ship airwake date, is developed in this study. In the method, the ship airwake data is obtained by the high-accuracy DES model, and a strategy which can transmit CFD data to the flight dynamics model is established based on the "one-way" coupling idea. Then, the SFS2 ship model and UH-60A helicopter are chosen as a combination to investigate the influences of the spatial and temporal characteristics of ship airwake from the aspects of control margins and unsteady level. The time-averaged simulation results show that for the counterclockwise-rotor helicopter, although pilot could have more collective pitch margin under crosswind condition compared to the headwind condition, he might possess much less pedal margin due to the sidewash in the airflow. The unsteady results indicate that the unsteady loading level of the helicopter would increase significantly under the crosswind condition compared to the headwind condition due to the increase of turbulent density in the airwake. Furthermore, for the conventional helicopter, the disturbances on the forces and moments which along the rotor hub (i.e., thrust and yaw moment) are the critical factors that increasing the pilot workload during the landing procedure.

Study on longitudinal stability of ducted vertical take-off and landing fixed-wing UAV

The longitudinal flight stability of the ducted vertical take-off and landing fixed-wing UAV during the flight state of hovering and transition is studied. Firstly, based on the Blade-Element Momentum Theory (BEMT) and experimental data, a coaxial dual-rotor ducted aerodynamic model and a thrust ducted aerodynamic model based on characteristic cross-section calculations are established. The model parameters are identified according to the experimental data. Secondly, a UAV flight dynamics model with thrust duct deflection is established according to the six-degree-of-freedom equations. Finally, the case UAV was used to solve the longitudinal balance and stability analysis of hovering and transition state with the established model method, and compared with the hovering experimental results. The results show that the UAV flight dynamics model combined with the ducted dynamic model established in the article can accurately describe the longitudinal flight stability characteristics of this type of aircraft.

Exploration of high-altitude dynamic soaring based on six-degree-of-freedom model

Dynamic soaring is an emerging flight range-extension technology that effectively reduces UAV's energy consumption by deriving wind energy from lateral gradient wind fields. Comparing with the small UAV's near the surface, the application of dynamic soaring technology in the high-altitude long-endurance flight requires the additional consideration of the influence of sustained side wind, the influence of the sideslip angle cannot be ignored. This puts higher requirements on the flight dynamics model. In this paper, the dynamic model for the high-altitude dynamic soaring based on the six-degree-of-freedom equation is modeled to replace the traditional mass point model; the energy change principle of the high-altitude dynamic gliding is derived; the effect of the high-altitude wind field on the dynamic soaring UAV is analyzed; and the way to get optimal wind field energy acquisition and energy saving efficiency are analyzed. The results show that the dynamics model based on the six-degree-of-freedom equation can more realistically reflect at high altitude; the application of dynamic soaring can effectively improve the range of the high-altitude UAV; the wind direction at high-altitude wind field has a significant effect on the dynamic soaring efficiency.

The Investigation on L 1 Adaptive Control of the Tilt-Rotor Aircraft

Considering the uncertainty of the flight dynamics model of the tilt-rotor aircraft in different flight modes, an L 1 adaptive controller for full flight modes control system of tilt-rotor aircraft is designed. Taking advantage of the separation of robustness and adaptive design of the L 1 adaptive controller, adaptive gain, and low-pass filter are designed to achieve the desired control performance and meet the requirements of flight quality. The simulations of XV-15 tilt-rotor aircraft in helicopter mode and airplane mode are carried out. Then, the simulation of conversion mode is further carried out. The results show that the tilt-rotor aircraft can track the reference signal well under the L 1 control system. In addition, the changes of states as well as controls in conversion mode flight are quite smooth which is very meaningful for engineering application.

Analysis on controllability and stability of quad-tilt-rotor aircraft in helicopter mode

The controllability and stability of quad-tilt-rotor aircraft in helicopter mode are modeled and analyzed, which will provide a theoretical guidance for the subsequent control system design. First of all, the flight dynamics model is established considering rotor-wing interference and verified with relevant experiments. Then, a control strategy for helicopter mode is proposed with trim characteristic analysis. Finally, corresponding control efficiency and cross coupling are calculated and analyzed along with characteristics of the stability derivatives and eigenvalues. The results show that the value of heading control efficiency is much smaller than that of other channels. The longitudinal force and pitch moment caused by vertical control input increase with the increase of the velocity. Yawing moment caused by lateral control input shows similar variations. The velocity stability becomes worse with the increase of the velocity. The stability of all other modes is augmented as velocity increases except the spiral mode.

Parameterized Model of Flight Dynamics of the Transport Helicopter

The article addresses investigating the possibilities of making a parameterized flight dynamics model in a mixed reality environment. The purpose was to obtain a model for a Mi-17 helicopter. The Mi-17 VI helicopter flight test characteristics were used to evaluate the above model. As a comparative criterion, compatibility between the model’s selected characteristics and the real object was adopted. Simulation tests were conducted on a cabin simulator set made via MR (mixed reality) technology. Test results confirmed the possibility of reconstructing the selected helicopter type’s flight dynamics using the parameterized model.

The Effects of Icing on Aircraft Longitudinal Aerodynamic Characteristics

To study the effects of ice accretion on the longitudinal aerodynamic characteristics of an aircraft, a two-part method for predicting longitudinal aerodynamic derivatives of iced aircraft is proposed. For the aircraft with a flight test, a parameter identification system based on maximum likelihood criterion and a longitudinal nonlinear flight dynamics model is established. For the aircraft without a flight test, an engineering prediction method of aerodynamic derivatives based on an individual component CFD calculation and narrow strip theory is established. According to the flight test data of DHC-6 Twin Otter aircraft from NASA, the longitudinal aerodynamic parameters of both clean and artificially iced aircraft are obtained. Additionally, the longitudinal aerodynamic derivatives of the iced aircraft are calculated. Then, the correctness of the prediction method is verified by comparing the calculated results with the identification results. The comparison of these results shows that the prediction method is correct and accurate, and it can be used to calculate the effects of icing on the aircraft longitudinal aerodynamic parameters.

Giant Big Stik R/C UAV Computer Model Development in JSBSim for Sense and Avoid Applications

Open-source aerospace simulation packages often lack unmanned aerial vehicles (UAVs) models, limiting the study of their interaction with other elements in the airspace. These events, which are a consequence of encounters between manned and unmanned aircraft, have recently attracted interest due to the uncertainties created by UAVs in real environments. In this paper, a fit-for-purpose flight dynamics model specific for sense and avoid (SAA) strategies in near mid-air collision scenarios is developed based on existing model development practices and adjusted from flight data. The Giant Big Stik is recognized as the representative aircraft for testing SAA manoeuvres due to its capabilities. The simulation platform is based on the JSBSim open-source flight dynamics model, and the SAA application is carried out following the current regulations and flight recommendations for UAVs in Canada. Through this methodology, the error between the real and the computer model is reduced in every step that is minimal for the SAA application. The relevance of this paper is also shown in future applications, where this model will be incorporated into more complex simulations with manned aircraft for the study of avoidance manoeuvres that will serve the safe integration of UAVs into the airspace.