This paper addresses autonomous aerial refueling between an unmanned tanker aircraft and an unmanned receiver aircraft using the probe-and-drogue method An important consideration is the ability to achieve successful docking in the presence of exogenous inputs such as atmospheric turbulence Practical probe and drogue autonomous aerial refueling requires a reliable sensor capable of providing accurate relative position measurements of su‐cient bandwidth, integrated with a robust relative navigation and control algorithm This paper develops a Reference Observer Based Tracking Controller that does not require a model of the drogue or presumed knowledge of its position, and integrates it with an existing vision based relative navigation sensor A trajectory generation module is used to translate the relative drogue position measured by the sensor into a smooth reference trajectory, and an output injection observer is used to estimate the states to be tracked by the receiver aircraft Accurate tracking is provided by a state feedback controller with good disturbance rejection properties A frequency domain stability analysis for the combined reference observer and controller shows that the system is robust to sensor noise, atmospheric turbulence, and high frequency unmodeled dynamics Feasibility and performance of the total system is demonstrated by simulated docking maneuvers of an unmanned receiver aircraft docking with the non-stationary drogue of an unmanned tanker, in the presence of atmospheric turbulence Performance characteristics of the vision based relative navigation sensor are also investigated, and the total system is compared to an earlier version Results presented in the paper indicate that the integrated sensor and controller enable precise aerial refueling, including consideration of realistic measurements errors, plant modeling errors, and disturbances

Trajectory Tracking Controller for Vision-Based Probe and Drogue Autonomous Aerial Refueling

https://people.bath.ac.uk/jldb20/pubs/Thomas.etal2014Advancesinair.pdf

Advances in air to air refuelling

Wind-tunnel data have been obtained from a tapered tanker wing and receiver aircraft model at varying vertical separation. The data are presented in derivative form and compared with theory using a flat vortex sheet model of the tanker wing wake to determine the induced angle-of-attack variation on the receiver wing, fin, and tailplane due to the tanker wing. Aerodynamic loads on the receiver are obtained by the vortex lattice method, with an allowance made for the vertical displacement of the tanker wake in the estimation of the fin side force. In the experiments, the lateral aerodynamic interference between tanker and receiver was determined by banking the tanker wing and displacing it sideways, and by yawing the receiver aircraft model. Data were obtained from open and closed test sections in order to assess the significant boundary interference effect and corrections estimated from the image vortex system of the tanker and receiver wings in the test section. In general, the theory compares favorably with the experimental data. The most significant terms are the rolling moments due to sideways and bank displacements. Significant side forces are produced due to sidewash on the fin from the tanker and receiver wings and, when displaced in yaw, the receiver experienced a loss in directional stability.

Lateral Aerodynamic Interference Between Tanker and Receiver in Air-to-Air Refueling

This paper addresses the development of multiple UAV deployment simulation models that include representative aerodynamic cross-coupling effects. Applications may include simulations of autonomous aerial refuelling and formation flying scenarios. A novel wake vortex model has been developed and successfully integrated within a Matlab/Simulink simulation environment. The wake vortex model is both sufficiently representative to support studies of aerodynamic interaction between multiple air vehicles, and straightforward enough to be used within real time or near real time air-to-air simulations. The model integration process is described, and computational results of a two-vehicle-formation flight are presented.

/pdf/simulation-of-wake-vortex-effects-for-uavs-in-close-42tj7ia7ym.pdf

Simulation of wake vortex effects for UAVs in close formation flight

Recent heightened interest in autonomous refueling of unmanned aerial vehicles has stimulated research activity in the area of aerial refueling in general. Aircraft aerial refueling research can be divided into four general areas: influence of tanker aircraft wake turbulence on the receiver aircraft, the dynamics of the drogue and hose, automatic flight control system design for aerial refueling, experiments and flight tests related to the practical implemen- tation of autonomous aerial refueling system. This survey summarizes research activities as well as the current state of knowledge in these areas.

A Survey of the Dynamics and Control of Aircraft During Aerial Refueling

Wind tunnel data from a tanker wing and receiver aircraft model at varying vertical separation have been compared with theoretical results. In the aerodynamic model the tanker wing is represented by a horseshoe vortex while the aerodynamic loads on the receiver are determined by the vortex lattice method and lifting-line theory, although an approximate method is used to determine the side force on the fin. In the longitudinal case data were obtained for low, mid and high tailplane positions and, with the exception of the pitching moment results, fairly good agreement is obtained between theory and experiment. The relatively small differences are due mainly to the wind tunnel boundary interference effect which could not be quantified for the pitching moment measurements. The lateral aerodynamic interference was determined by banking the tanker wing and displacing it sideways and by yawing the receiver model. Fairly good agreement is obtained between the theory and experiment for the most significant terms which are the rolling moments due to bank and sideways displacement. The effect of the sidewash due to the tanker wake on the receiver in yaw is found to be relatively insignificant. Over the range of bank, yaw and sideways displacements tested the results are almost linear.

The aerodynamic interference between tanker and receiver aircraft during air-to-air refuelling

The longitudinal stability and control of a large receiver aircraft was considered during air-to-air refuelling. A simple horseshoe vortex was used to model the tanker wake and approximate expressions were derived for the additional aerodynamic derivatives due to the position and attitude of the receiver aircraft within the downwash field. These derivatives were shown to depend on the mean variation of downwash with vertical displacement at the receiver wing and tailplane. The mean downwash gradients, in turn, depend mainly on the vertical separation between the tanker and receiver aircraft and the ratio of the tanker-to-receiver aircraft wing spans. Solutions of the linearised equations of motion were obtained for a range of values of the downwash gradients. The large receiver aircraft, considered in the paper, typically exhibits two divergent modes which appear to be controlled in flight by frequent alternate movement of the elevators and engine throttle.

V. Trochalidis

Papers

The aerodynamic interference between tanker and receiver aircraft during air-to-air refuelling

The longitudinal dynamic stability and control of a large receiver aircraft during air-to-air refuelling