Optimal Controller for an Autonomous Helicopter in Hovering and Forward Flight

Systematic design methodology for development and flight testing of a variable pitch quadrotor biplane VTOL UAV for payload delivery

In the last decade, with the continuous development of Drones or Unmanned Aerial Vehicles (UAVs), a wide variety of models were tested and created, highlighting two types of Drones: multicopters and fixed wings. However, recently, there has been a growing demand to explore the “mixture” between these two types of vehicles. Leading to Vertical Take Off and Landing (VTOL) models, which seek to produce an aircraft capable of having the stability characteristics of a multicopter in hover flight mode, and the speed and high flight time that a fixed wing typically provides in cruise mode (straight level flight). In contrast to the advantages of VTOLs, the challenge with this class of aircraft is that they are subject to a high degree of non-linearity, typical of the mixture between two different aircraft architectures. Additionally, like all air vehicles, they must be able to deal with aerodynamic disturbances in the air. The main objective of this work is to propose a new UAV VTOL architecture with tricopter topology. This aircraft has independent rotor inclination together with wings, vectoring propulsion forces and aerodynamic forces, in order to help control the aircraft, reduce the downwash impact and take advantage of the same rotor structure to exert vehicle movement in several directions. The vehicle uses coaxial-rotors to balance the induced torque between the rotors for every tilting angle and, additionally, to increase the thrust force. The dynamic modeling was developed based on the physical laws that govern the propulsive, aerodynamic and inertial principles. Especially highlighting the mobile center of gravity (CG) due to the fact that the vehicle is characterized as a multi-body system, capable of assuming a non-symmetrical morphology. The aircraft design was made using SolidWorks® 3D design software, considering real electrical and mechanical components in order to obtain a theoretical model of the aircraft as close to reality. The vehicle's inertia tensor was validated by comparing the inertia tensor generated by the mathematical model and the inertia tensor generated by SolidWorks®. For the simulation, the aircraft model was linearized under the hover and cruise flight conditions and the aircraft control was implemented through a cascade control strategy. A state-integrated linear quadratic regulator controller (LQRI) was used to control the linear and angular velocities of the aircraft, while a proportional derivative integral controller (PID) was used to control the aircraft's position and attitude in space. The control strategy adopted allowed for the tracking of trajectories in a satisfactory manner, even in the presence of aerodynamic disturbances.

This paper describes the development and flight testing of a tail-sitter unmanned aerial vehicle (UAV) platform that has the potential to be tube-launched. Integrated with vertical take-off and landing (VTOL) capability, the platform can perform high-endurance loiter tasks along with low-speed and hovering flights, and land vertically in limited spaces. The current design utilizes a thrust-vectored counter-rotating coaxial propeller combined with a foldable conventional fixed-wing to accomplish both vertical and horizontal flights. A feedback control strategy capable of stabilizing and controlling the vehicle in both vertical and horizontal flight was designed and implemented on a custom-designed 1.7-gram autopilot. Several tests were conducted in hover and edgewise flight with aggressive pilot inputs to demonstrate the controllability of the aircraft even in the presence of moderate wind gusts. Additionally, transition flight tests were also performed, which demonstrated the vehicle’s capability of transitioning from vertical to fixed-wing horizontal flight using thrust-vectoring-based pitch control.

The design of new helicopter rotor blades is a challenging task. The individual blade sections undergo very different flow conditions during the various flight regimes of the helicopter. In forward flight, the advancing side operates in a transonic regime where potentially shock waves can occur, while on the retreating side little flow velocities at high angle of attacks are seen up to reverse flow. In hover, the oncoming tip vortex of the previous blade drastically influences the inflow on the rotor. This paper joins the classical blade shape design with numerical optimization techniques. Opposing to the direct solution process of directly modifying the blade shape, the rotor blade is conventionally considered as a set of airfoils, a planform and a twist distribution. First, rotor airfoils are found through numerical optimization and then placed on the reference rotor. The planform and twist of this rotor are then also numerical optimized. The obtained trade-off blade for hover and forward flight drastically improved the performance over the reference HART-II blade (11% in forward flight, 5% in hover flight). In order to arrive at industrial relevant blades, further work including more disciplines becomes necessary.

In this paper, edge-finishing automation using an active position/force control system is discussed. The architecture for a robust edge-finishing control system is developed, and the implementation of this con trol system on an xy table for the purpose of finishing planar parts is discussed. The control system combines position/force control with a fuzzy logic controller to compensate for part tolerance and fixturing errors. The cutting process is modeled using an empirically derived set of equations that relate tool contact forces and variances to the final chamfer depth that results on the part. The paper demonstrates that tangential force and normal position control is the preferred method for task-level control of edge-finishing processes because kinematic instability that develops when finishing highly curved parts can be avoided. Motion planning at the task level preserves spatial accuracy and prevents this phenomenon from developing. Experimental eval uation of the system on a sample workpiece shows the system is capable of consistent edge finishing in the presence of workpiece position uncertainty.

Aerodynamic characteristics of rigid coaxial rotor by wind tunnel test and numerical calculation

This allows unregistered users to read the abstract as a teaser for the complete chapter. The formulas for calculating the variation of aerodynamic coefficient of iced blade airfoil were introduced according to rotor icing test data from NASA and the formulas for aerodynamic force and moment of rotor icing were deduced. Further, the model of flight dynamics for helicopter icing was built. Icing effect on trim characteristics and stability of certain single-rotor helicopter in hover and forward speed was studied. The results show that whether in hover or forward flight, when the helicopter iced, the amount of the collective control, the longitudinal control, and the lateral control of the rotor, the tail rotor collective control as well as the roll angle increases, while the pitch angle decreases; the longitudinal long-period and short-period mode goes more stable, and the same as the lateral helical mode, while the roll mode and Dutch roll mode go more unstable.

The Rotor Blown Wing (RBW) is a tailsitter Vertical Takeoff and Landing (VTOL) Unmanned Aerial System (UAS) configuration that leverages cutting-edge autonomous flight controls through Sikorsky's MATRIX™ technology to create a highly capable, efficient, and scalable technology platform. By combining the benefits of fixed- and rotary-wing aircraft, the RBW configuration eliminates the need for traditional UAS launch and recovery infrastructure. This paper describes the RBW-5 prototype, a 100-pound, dual 5-foot diameter proprotor demonstrator, and discusses the comprehensive evaluation of its design and operability through a combination of flight tests, wind tunnel experiments, and computational fluid dynamics (CFD) simulations. The results demonstrate the maturity of the UAS and highlights key accomplishments of the RBW-5 program, including successful autonomous takeoff and landing and transitions between hover and forward flight, the extraction of critical "blown-physics" underlying RBW aerodynamics, and the validation of CFD models against unpowered and powered wind tunnel data.

In the present study, the parametric study was performed to analyze the effect of the tab on the aerodynamic performance and characteristics of rotor blades. Also, the tab shape was designed to improve the aerodynamic performance of rotor blades. A computational fluid dynamics solver based on three-dimensional Reynolds averaged Navier–Stokes equation using an unstructured mesh was used for the parametric study and the tab design. For airfoils, the effect of length and angle of a tab was studied on the aerodynamic characteristics of airfoils. In addition, including those parameters, the effect of a span of a tab was studied for rotor blades in hovering flight. The results of the parametric study were analyzed in terms of change of the aerodynamic performance and characteristics to understand the effect of a tab. Considering the analysis, the design of tab shape was conducted to improve the aerodynamic performance of rotor blades. The simply attached tab to trailing edge of the rotor blades increases the thrust of the rotor blades without significant changing of aerodynamic characteristics of the rotor blades in hovering and forward flight.

In this work, optimization methodologies of the kinematics of flapping wings in forward and hover flights are considered. Particularly, local and global optimization algorithms are combined with the unsteady vortex lattice method (UVLM) to determine the most efficient kinematics. In the first problem, the kinematic optimization of a three-dimensional flapping wing in forward flight with active shape morphing is aimed at maximizing the propulsive efficiency under lift and thrust constraints. Results show that due to the quasi-concavity of the objective function associated with the flapping kinematics employed in forward flight, local gradient-based optimizers perform very well in terms of accuracy and computational cost. In the second problem, the objective is to identify the optimized kinematics of a twodimensional hovering wing that minimize the aerodynamic power under lift constraint. The results show that using a hybrid optimization algorithm (combination of local and global schemes) accelerates the convergence to optimal points and avoids being trapped at local minimum points. While the efficiency of using a local optimizer, a global optimizer, or a hybrid of the two depends on the nature of the problem and associated design space, it is determined that hybrid optimization is best suited for determining local minima.

This paper describes the development and flight testing of an autonomous flight control system that allows for different levels of pilot interaction in both hover and forward flight. Three modes of operations are described, fully coupled autonomy, additive control, and piloted decoupled attitude-command. These modes are demonstrated on the Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL) JUH-60A Black Hawk integrated with Obstacle Field Navigation (OFN) and Safe Landing Area Determination (SLAD) algorithms that both use a line scanning LADAR as their primary sensor. The paper will describe the control system, its performance, and demonstrate how it was used to transition into these modes while flying mission scenarios through mountainous terrain at speeds from hover to 100 kts.

In this paper, the flight dynamic model of Vertical Take-Off and Landing (VTOL) aircraft which equips a propeller-wing-flap system that produces slipstream is established. The complete aircraft is modeled by combining experimental results, theoretical calculation, and empirical data. Firstly, the propeller deflected slipstream effects and the parameters of ducted fan are obtained by bench test. The DATCOM are used for generating the aerodynamic coefficients. Then, the 6-DoF nonlinear flight dynamic model in both hover and forward flight conditions are deducted by employing the assumption of linear superposition. The gyro effect and gravity are considered. Finally, specific trim conditions in hovering, transitional and level flight states are determined, and dynamic characteristics at trim are studied by both full model simulation and linear system analysis obtained through small-perturbation theory. It is found that the aircraft is critically stable in hovering condition. The damping ratio of short-period mode is relatively small, and the phugoid mode divergence in the transition state. The aircraft is less well damped in the level flight condition. The built model accurately reflects the dynamic characteristics of the VTOL aircraft and provides help for the design of the flight control system afterward.KeywordsSlipstreamVertical Take-off and Landing (VTOL) aircraftBench testDynamic modeling

The paper describes a methodology to extract linearized state-space dynamic inflow model from a generic and high fidelity aerodynamic analysis for single and coaxial helicopter rotor systems. Both hover and forward flight are studied including maneuvering and the results are demonstrated by a free-wake analysis. The proposed methodology which is founded on a Single Frequency Analysis is computationally efficient and provide the entire frequency-domain behavior of the wake inflow states. Besides being able to incorporate any advanced computational tool, the present methodology takes advantage of exact wake states and thus adequately encompasses high frequency responses. The paper also extends the methodology to the case where states of higher harmonics are required and to the case of heaving, rolling and pitching rotor disc. For a single rotor system the results resemble the well known classical dynamic inflow model. For coaxial rotor system in hover, the high mutual couplings between the rotors are clearly demonstrated and affect the resulting system matrices. An important feature of the present methodology lays in the fact that the entire formulation is non-dimensional and the in-flow analysis is completely separated from the loads analysis, which enables a consistent generalization of the results.

For the last 40 years high - capacity Unmanned Air Vehicles have been use mostly for military services such as tracking, surveillance, engagement with active weapon or in the simplest term for data acquisition purpose. Unmanned Air Vehicles are also demanded commercially because of their advantages in comparison to manned vehicles such as their low manufacturing and operating cost, configuration flexibility depending on customer request, not risking pilot in the difficult missions. Nevertheless, they have still open issues such as integration to the manned flight air space, reliability and airworthiness. Although Civil Unmanned Air Vehicles comprise 3% of the UAV market, it is estimated that they will reach 10% level within the next 5 years. UAV systems with their useful equipment (camera, hyper spectral imager, air data sensors and with similar equipment) have been in use more and more for civil applications: Tracking and monitoring in the event of agriculture / forest / marine pollution / waste / emergency and disaster situations; Mapping for land registry and cadastre; Wildlife and ecologic monitoring; Traffic Monitoring and; Geology and mine researches. They can bring minimal risk and cost advantage to many civil applications, in which it was risky and costly to use manned air vehicles before. When the cost of Unmanned Air Vehicles designed and produced for military service is taken into account, civil market demands lower cost and original products which are suitable for civil applications. Most of civil applications which are mentioned above require UAVs that are able to take off and land on limited runway, and moreover move quickly in the operation region for mobile applications but hover for immobile measurement and tracking when necessary. This points to a hybrid unmanned vehicle concept optimally, namely the Vertical Take Off and Landing (VTOL) UAVs. At the same time, this system requires an efficient cost solution for applicability / convertibility for different civil applications. It means an Air Vehicle having easily portability of payload depending on application concept and programmability of operation (hover and cruise flight time) specific to the application. The main topic of this project is designing, producing and testing the TURAC VTOL UAV that have the following features : Vertical takeoff and landing, and hovering like helicopter ; High cruise speed and fixed-wing ; Multi-functional and designed for civil purpose ; The project involves two different variants ; The TURAC A variant is a fully electrical platform which includes 2 tilt electric motors in the front, and a fixed electric motor and ducted fan in the rear ; The TURAC B variant uses fuel cells.

Design and experimental study of a new flapping wing rotor micro aerial vehicle