Tanker Aircraft Research Articles

Helicopter rotor in a propeller slipstream: Aerodynamic and rotor blade flapping responses

During helicopter air-to-air refueling the helicopter's rotor can engage the tanker aircraft's wing and flap end tip vortices and the slipstream of its propellers. The tip vortices represent a swirl around an axis that is essentially parallel to the rotor longitudinal axis. The slipstream of the propellers includes a strong air jet downstream that can cover a significant amount of the helicopter's main rotor. This phenomenon was recently treated analytically for a rigid rotor by means of blade-element momentum theory and the rotor control angles required to reject the disturbance were computed. In this article, the rotor blade flapping is introduced as degree of freedom. It is shown that the rotor coning is affected by the slipstream position with respect to the rotor hub. Without retrim, the largest amount of coning and cyclic flapping occurs for slipstream positions on the retreating side of the rotor.

Research on the Motion and Dynamic Characteristics of the Hose-and-Drogue System under Bow Wave

To study the hose-and-drogue system’s motion under bow waves, this paper established a dynamic model of the hose-and-drogue system based on the multibody dynamics theory and the rigid ball-and-rod model. The wake of a tanker aircraft was taken into account in the simulation. The simulation results conformed to the general laws and verified the model’s accuracy. The equilibrium positions of the hose-and-drogue system were computed by the linear superposition of the bow waves and wake. The motion of the hose-and-drogue system was simulated and analyzed when a receiver aircraft moved at a constant speed or accelerated relative to the tanker aircraft. Since the receiver aircraft would not immediately stop after docking, the pulling force changes on the hose with and without a reel were compared. The present results are essential for improving the success rate of aerial refueling and ensuring the safety and stability of the hose-and-drogue system.

Evaluation of a real-time simulation environment for helicopter air-to-air refuelling investigations

AbstractThe ability to perform air-to-air refuelling (AAR) can dramatically extend the utility of helicopters, through effectively providing unlimited range. For helicopters, AAR is typically performed utilising the probe-and-drogue aerial refuelling method. This is a complex manoeuver, where normally both the helicopter and tanker aircraft are operating at the limits of their flight envelopes. In addition, the wake flow from the tanker aircraft can cause a significant disturbance on the refuelling helicopter. This paper presents the initial evaluation of an AAR scenario constructed within DLR’s flight simulator, the Air Vehicle Simulator (AVES), based on current procedures and pilot interviews. A mission task was defined to assess the scenario in AVES and results are subsequently discussed. For pilots unfamiliar to formation flight or HAAR, the results show the difficulty of the flying task itself at the given cueing. Measures for improvement in future investigations are suggested.

Review of Sensor Technology to Support Automated Air-to-Air Refueling of a Probe Configured Uncrewed Aircraft

As technologies advance and applications for uncrewed aircraft increase, the capability to conduct automated air-to-air refueling becomes increasingly important. This paper provides a review of required sensors to enable automated air-to-air refueling for an uncrewed aircraft, as well as a review of published research on the topic. Automated air-to-air refueling of uncrewed aircraft eliminates the need for ground infrastructure for intermediate refueling, as well as the need for on-site personnel. Automated air-to-air refueling potentially supports civilian applications such as weather monitoring, surveillance for wildfires, search and rescue, and emergency response, especially when airfields are not available due to natural disasters. For military applications, to enable the Air Wing of the Future to strike at the ranges required for the mission, both crewed and uncrewed aircraft must be capable of air-to-air refueling. To cover the sensors required to complete automated air-to-air refueling, a brief history of air-to-air refueling is presented, followed by a concept of employment for uncrewed aircraft refueling, and finally, a review of the sensors required to complete the different phases of automated air-to-air refueling. To complete uncrewed aircraft refueling, the uncrewed receiver aircraft must have the sensors required to establish communication, determine relative position, decrease separation to astern position, transition to computer vision, position keep during refueling, and separate from the tanker aircraft upon completion of refueling. This paper provides a review of the twelve sensors that would enable the uncrewed aircraft to complete the seven tasks required for automated air-to-air refueling.

Cooperative Docking Guidance and Control with Application to Civil Autonomous Aerial Refueling

This paper proposes a novel concept for automatic docking of a boom-receptacle aerial refueling system adequate for civil aerial transportation. The receiving aircraft is assumed to keep straight and steady flight, and the docking maneuver is performed exclusively by the tanker and its boom system. As opposed to the conventional approach, the docking maneuver consists in a coordinated and guided motion of the tanker and the boom arm that is simultaneous with the extension of the nozzle tip. To achieve this, a cooperative guidance algorithm is derived in a systematic manner. The first step is to reduce the docking problem to a planar kinematic guidance problem. Subsequently, the cooperative guidance law algorithm is derived and applied to generate commands for the inner-loop controllers of the tanker aircraft and the boom. The ability to achieve successful docking is demonstrated using numerical simulations, and advantages of this concept are highlighted using a comparison with a baseline controller that uses separated control of the tanker and the boom in a sequential manner.

The payload-range performance of a multirole tanker transporter aircraft accounting for towline (on-station refuelling) and trail (strategic deployment) missions

This article has arisen from a general investigation into the payload-range envelope of a multirole-tanker transport aircraft and how this envelope is modified as a result of the tanker’s refuelling activities. To this end, the Breguet range equation is used in conjunction with a simple fuel budget to model different scenarios in which the tanker aircraft can perform towline or trail missions. For the common radius of action case, a closed-form solution is obtained for the payload-range variation; for instances where the outbound journey and the return journey are of unequal lengths, the governing equation is found to require a numerical solution. The act of dispensing a significant quantity of fuel whilst some distance into a flight can have a dramatic impact on the tanker’s overall range and payload capability. An assessment of this payload-range modification needs to be made prior to commencing the flight to ensure the mission can safely be accomplished, which provides the motivation for the current work. Three case studies are presented to demonstrate the efficacy of the method, and comparisons with published data show strong agreement. This model will be of use to planners wishing to investigate typical ‘ what if?’ scenarios on the overall mission.

A stochastic approximation method for probability prediction of docking success for aerial refueling

Aerial refueling is capable of increasing the endurance and flight range of aircraft. However, during the docking phase of aerial refueling, the docking risk increases as the receiver aircraft approaches the tanker aircraft. A high docking risk indicates docking failure or even flight collision. In order to guarantee docking reliability and safety, a stochastic approximation method is proposed to predict the docking success probability during the docking phase of aerial refueling. If the success probability is lower than the specified value, the receiver aircraft needs to increase its relative distance from the tanker aircraft to reduce the risk. In our method, a stochastic differential equation is used to model the relative motion between the receiver and tanker aircrafts, where the receiver aircraft flies along a predefined flight path with influence of additive wind perturbations. The correlation between the magnitude of wind perturbations and the distance between the receiver and tanker aircrafts is considered. Then, based on the established relative motion model, the probability that the receiver aircraft enters the target set during a given time interval is predicted by the Markov chain stochastic approximation method. The docking success probability is computed by propagating the transition probabilities of the Markov chain backwards starting from the target set during the time interval. Comparing with the widely used Monte Carlo method in previous studies, our method demonstrates substantial effectiveness and efficiency.

Reachability analysis on optimal trim state for aerial docking

Aerial refueling is an important capability to increase the endurance and flight range of aircraft, but it often suffers from a low success rate. The altitude and speed of the tanker aircraft in the docking phase play a great role in the docking success rate. According to this, the optimal trim state, namely the optimal speed and altitude of the tanker aircraft, is investigated through the reachability analysis method in this paper. The optimal problem is transformed to find the trim state corresponding to the maximum volume of the reachable set. First, a relative motion model of the receiver aircraft with respect to the drogue is proposed. Then, based on reachability analysis, an optimization problem is formulated and a solution procedure is given in detail. In the simulation, the volumes of reachable sets are plotted with respect to the given discrete speeds and altitudes, based on which the optimal trim state of the docking phase is determined. Finally, the determined optimal trim state is verified by using numerous docking control simulations and the degree of controllability from another aspect. The effectiveness of the proposed method is demonstrated.

The cost of stratospheric aerosol injection through 2100

This paper presents the estimated direct costs of a stratospheric aerosol injection (SAI) program through the end of this century. It displays a range of future solar geoengineering deployment scenarios that are intended to reduce anthropogenically-caused radiative forcing beginning in 2035. The scenarios reviewed herein include three commonly modeled representative concentration pathways (4.5, 6.0, and 8.5) and three possible radiative forcing targets (halving future warming, halting warming, and reversing temperatures to 2020 levels). The program relies on three successive generations of newly designed high-altitude tanker aircraft to deliver aerosols to an altitude of ∼20 km. Sulfates are assumed to be the aerosol used in conjunction with the first generation tanker, supplanted by an as-yet-determined ‘Aerosol 2’ with the later generation aircraft. The aggregate cost over the remainder of the 21st century and the annual cost in 2100 both vary by an order of magnitude between the cheapest and the most expensive scenarios. However, the cost-per-ton of deployed aerosol varies little among scenarios and the cost-per-degree-of-warming-avoided is similarly consistent. Relative to other climate interventions and solutions, SAI remains inexpensive, but at about $18 billion yr−1 per degree Celsius of warming avoided (in 2020 USD), a solar geoengineering program with substantial climate impact would lie well beyond the financial reach of individuals, small states, or other non-state potential rogue actors and would instead be the exclusive domain of large national economies or coalitions including at least one such economy.

Лесные пожары – ущербы и авиапожаротушение

<span class="myItalicChars CharOverride-3">Лесозаготовительная</span><span class="myItalicChars CharOverride-3"> отрасль и лесное хозяйств</span><span class="myItalicChars CharOverride-3">о из-за неадекватных</span><span class="myItalicChars CharOverride-3"> институциональных усл</span><span class="myItalicChars CharOverride-3">овий приносят бюджет</span><span class="myItalicChars CharOverride-3">ной системе одни убы</span><span class="myItalicChars CharOverride-3">тки. За счёт доходов</span><span class="myItalicChars CharOverride-3"> от их деятельности </span><span class="myItalicChars CharOverride-3">не могут быть обеспе</span><span class="myItalicChars CharOverride-3">чены в нужном объеме</span><span class="myItalicChars CharOverride-3"> ни лесоустройство, ни необходимые</span><span class="myItalicChars CharOverride-3"> мероприятия по защи</span><span class="myItalicChars CharOverride-3">те лесов от пожаров.</span><span class="myItalicChars CharOverride-3"> Институциональное обеспеч</span><span class="myItalicChars CharOverride-3">ение системы тушения</span><span class="myItalicChars CharOverride-3"> лесных пожаров не о</span><span class="myItalicChars CharOverride-3">твечает современным </span><span class="myItalicChars CharOverride-3">требованиям. Единой методики </span><span class="myItalicChars CharOverride-3">определения ущерба, </span><span class="myItalicChars CharOverride-3">причиняемого лесными</span><span class="myItalicChars CharOverride-3"> пожарами, в стране </span><span class="myItalicChars CharOverride-3">не существует. Применяемые критерии</span><span class="myItalicChars CharOverride-3"> определения ущерба </span><span class="myItalicChars CharOverride-3">от лесных пожаров и </span><span class="myItalicChars CharOverride-3">зон контроля не учитывают социальн</span><span class="myItalicChars CharOverride-3">ые и экологические п</span><span class="myItalicChars CharOverride-3">оследствия. Ведомств</span><span class="myItalicChars CharOverride-3">енная разобщенность </span><span class="myItalicChars CharOverride-3">авиационной техники, исполь</span><span class="myItalicChars CharOverride-3">зование крупных само</span><span class="myItalicChars CharOverride-3">лётов-танкеров не по</span><span class="myItalicChars CharOverride-3">зволяют эффективно о</span><span class="myItalicChars CharOverride-3">рганизовать тушение </span><span class="myItalicChars CharOverride-3">лесных пожаров на ранней</span><span class="myItalicChars CharOverride-3"> стадии. По мнению а</span><span class="myItalicChars CharOverride-3">второв, вся система </span><span class="myItalicChars CharOverride-3">пожаротушения требует пересмо</span><span class="myItalicChars CharOverride-3">тра</span><span>.</span>

Об одной нелинейной задаче оптимальной встречи

The paper analyzes a nonlinear problem of optimal rendezvous of two material points in the horizontal plane. The velocity of both participants is constant modulo. The aim of control is to minimize the final distance between participants under given initial conditions. The approach time is fixed. The angle between the line of sight and the velocity vector of the Participant 1 (P1) is used as a control variable. The Participant (P2) uses the proportional-navigation law. This task may be relevant when planning the approach paths of a tanker aircraft to an unmanned aerial vehicle, or in the case of intercepting an attacking unmanned aerial vehicle by a target simulator missile launched from a real target. The principle of maximum procedure allows reducing optimal control problem to the problem of analyzing the phase portrait of a system of two nonlinear differential equations. A qualitative analysis of the system is performed, the characteristic properties of the trajectories of the participants in the horizontal plane are investigated and the results of numerical solution of the boundary value problem are presented.

Docking Controller for Autonomous Aerial Refueling With Adaptive Dynamic Surface Control

The docking controller for autonomous aerial refueling (AAR) is intractable considering the high precision requirement and the complex disturbances of multiple environment flows. To solve the problems in the docking phase of AAR, such as the uncertainties of the aerodynamic parameters of receiver aircraft and the disturbances acting on the receiver aircraft, an adaptive dynamic surface control (ADSC) scheme based on radical basis function neural network (RBF-NN) is presented in this paper. Firstly, a nonlinear model of longitudinal dynamics of the receiver aircraft relative to the tanker aircraft is established, which incorporates the tanker vortex term. Secondly, a nonlinear strict-feedback form is introduced to design an adaptive dynamic surface controller with RBF-NN. Thirdly, the upper bounds of the “total disturbances” are estimated with the adaptive law, and the uncertain aerodynamic parameters of receiver aircraft are estimated with RBF-NN. It is proved that the proposed controller can guarantee the uniform boundedness of all the signals in the closed-loop system using Lyapunov theory. Finally, simulation results demonstrate the effectiveness of the proposed controller for the docking control of AAR.

Fault-Tolerant Control for Autonomous Aerial Refueling against Actuator Fault in Receiver UAV

This paper investigates the fault-tolerant control problem of a receiver unmanned aerial vehicle (UAV) against actuator fault and wake vortex induced by the tanker aircraft under the aerial refueling formation flight conditions. In autonomous aerial refueling (AAR), the relative distance of the receiver UAV with respect to the tanker aircraft/UAV is essential for the flight safety of the receiver UAV and the tanker aircraft/UAV. To design the fault-tolerant controller for the receiver UAV, disturbance observer technique is used to estimate the lumped uncertainties including wake vortex and actuator fault. Based on the estimated lumped uncertainties, backstepping architecture is utilized to construct the control scheme. Furthermore, it is shown that the relative forward distance and the relative perpendicular distance tracking errors are uniformly ultimately bounded. Finally, simulations are presented to show the effectiveness of the proposed fault-tolerant control scheme.

Relative position control design of receiver UAV in flying-boom aerial refueling phase

This paper proposes the design of the relative position-keeping control of the receiver unmanned aerial vehicle (UAV) with the time-varying mass in the refueling phase utilizing an inner-outer loop structure. Firstly, the model of the receiver in the refueling phase is established. And then tank model is set up to analyze the influence of fuel transfer on the receiver. Subsequently, double power reaching law based sliding mode controller is designed to control receiver translational motion relative to tanker aircraft in the outer loop while active disturbance rejection control technique is applied to the inner loop to stabilize the receiver. In addition, the closed-loop stabilities of the subsystems are established, respectively. Finally, an aerial refueling model under various refueling strategies is utilized. Simulations and comparative analysis demonstrate the effectiveness and robustness of the proposed controllers.

Fault-Tolerant Adaptive Model Inversion Control for Vision-Based Autonomous Air Refueling

The practical autonomous air refueling of unmanned air system tanker aircraft to unmanned air system receiver aircraft will require an integrated relative navigation system and controller that is tolerant to faults. This paper develops and demonstrates a fault-tolerant structured-adaptive-model-inversion controller integrated with a reliable relative-position sensor for this autonomous air-refueling scenario using the probe-and-drogue method. The structured-adaptive-model-inversion controller does not depend on fault-detection information, yet reconfigures and provides smooth trajectory tracking and probe docking in the presence of control-effector failure. The controller also handles parameter uncertainty in the receiver-aircraft model. In this paper, the controller is integrated with a vision-based relative-position sensor, which tracks the relative position of the drogue, and a reference-trajectory generator. The feasibility and performance of the controller and integrated system are demonstrated with simulated docking maneuvers with a nonstationary drogue, in the presence of system uncertainties and control-effector failures. The results presented in the paper demonstrate that the integrated controller/sensor system can provide successful docking in the presence of system uncertainties for a specified class of control-effector failures.

Fault Diagnosis in Air Data Sensors for Receiver Aircraft in Aerial Refueling

Multiple air-data sensors placed on different positions on an aircraft are usually expected to provide identical measurements. This is because aircraft are assumed to fly in no-wind or uniform wind conditions. There are cases, however, where an aircraft flies in nonuniform wind vector field with significant variations in magnitude and direction over the dimensions of the aircraft. For example, in an aerial refueling operation, the receiver aircraft needs to fly within the nonuniform wind field induced by the wake of the tanker aircraft. This paper shows that an air-data sensor fault detection and isolation algorithm, if developed with an underlying assumption of identical sensor measurements, yields very high false detection rate when the aircraft enters the wake of another aircraft. This paper also presents a novel modification to the redundant-sensor-based fault detection and isolation algorithm that eliminates this problem. The new method is based on a model of the wind field as a function of relative position with respect to the tanker aircraft. This model is used to compute the expected values of air-data sensor measurements given the position of the receiver aircraft relative to the tanker.

Detection and Tracking Strategies for Autonomous Aerial Refuelling Tasks Based on Monocular Vision

Detection and tracking strategies based on monocular vision are proposed for autonomous aerial refuelling tasks. The drogue attached to the fuel tanker aircraft has two important features. The grey values of the drogue's inner part are different from the external umbrella ribs, as shown in the image. The shape of the drogue's inner dark part is nearly circular. According to crucial prior knowledge, the rough and fine positioning algorithms are designed to detect the drogue. Particle filter based on the drogue's shape is proposed to track the drogue. A strategy to switch between detection and tracking is proposed to improve the robustness of the algorithms. The inner dark part of the drogue is segmented precisely in the detecting and tracking process and the segmented circular part can be used to measure its spatial position. The experimental results show that the proposed method has good performance in real-time and satisfied robustness and positioning accuracy.

공중재급유를 위한 상대운동방정식 유도 및 검증

This paper addresses the derivation of 6-DOF equation of Tanker and Receiver's aircraft for aerial refueling. The new set of nonlinear equations are derived in terms of the relative translational and rotational motion of receiver aircraft respect to the tanker aircraft body frame. Further the wind effect terms due to the tanker's turbulence are included. The derivation of absolute dynamic equation for tanker aircraft written in the inertial frame is calculated from the relative dynamics equations of receiver. The derived relative and absolute equations are implemented the simulation in the same flight conditions to verify the relative motion and compare the trim results by using the MATLAB/SIMULINK program.

Estimation of Receiver Aircraft States and Wind Vectors in Aerial Refueling

A square root unscented Kalman filter is used to estimate the states of a receiver aircraft and the components of the wind the aircraft is exposed to as it flies behind the tanker aircraft. The wind is the superposition of time-varying prevailing wind, turbulence, and the tanker’s wake-induced wind. The system update of the estimator uses the nonlinear aircraft model, augmented by a nonlinear wind model, obtained from the translational dynamics of the aircraft. The aircraft state estimates are successfully used in controlling the position of the receiver aircraft relative to the tanker flying straight level and making turns. Although the performance of the estimation and control is very dependent on the covariance and correlation time constants of the sensor measurement errors, the estimated state feedback performs better than measured state feedback with higher levels of measurement noise and turbulence intensity.

Derivation of the Dynamics Equations of Receiver Aircraft in Aerial Refueling

This paper describes the derivation of a new set of nonlinear, 6{DOF equations of motion of a receiver aircraft undergoing an aerial refueling, including the efiect of timevarying mass and inertia properties associated with the fuel transfer and the tanker’s vortex induced wind efiect. Since the Center of Mass (CM) of the receiver is time{varying during the fuel transfer, the equations are written in a reference frame whose origin is at the CM of the receiver before fuel transfer begins and stays flxed at that position even though the CM is moving during the refueling. Due to the fact that aerial refueling simulation and control deal with the position and orientation of the receiver relative to the tanker, the equations of motion are derived in terms of the translational and rotational position and velocity with respect to the tanker. Further, the derivation of the equations takes into account the momentum transfer into the receiver due to the fuel transfer. The receiver aircraft before fuel transfer is treated as a rigid body made up of ‘n’ particles. The dynamic efiects due to fuel transfer are modeled by considering the mass change to be conflned to a flnite number of lumped masses, which would normally represent the fuel tanks on the receiver aircraft. Once the refueling begins, by using the design parameters such as the shape, size and location of the individual fuel tanks and the rate of fuel ∞owing into each of them, the mass and location of the individual lumped masses are calculated and fed into the equations of motion as exogenous inputs. The new receiver equations of motion are implemented in an integrated simulation environment with a feedback controller for receiver station-keeping as well as the full set of nonlinear, 6{DOF equations of motion of the tanker aircraft and a feedback controller to ∞y the tanker on a U-turn maneuver.