Flow Control for Unmanned Air Vehicles

: Currently, Unmanned Air Vehicles (UAVs) are too large to penetrate buildings for situational awareness and reconnaissance, emplace important sensors, and sample and return material. While a variety of Micro Air Vehicles have been built and flown that use propellers and flapping wings for lift generation, Nano Air Vehicles (NAVs), defined as weighing less than 10 grams with wingspans less than 7.5 cm, have yet to be flown. NAV-scale actuators and wings with the requisite range of motion, power, and efficiency do not exist. In this project, we used a newly developed micromachining process based on Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE), for PZT chips to fabricate novel, high performance actuators for NAVs. A novel T-beam actuator was fabricated using ICP-RIE etching from the front of a bulk PZT chip. Masked electrode deposition created active and passive regions in the PZT structure. With a T-shaped cross section, and bottom and top flange and web electrodes, a cantilevered beam can bend in-plane and out-of-plane with bimorph actuation in both directions. One of these T-beam actuators was fabricated and experimentally tested. An experimentally validated model predicted that the cross-section geometry can be optimized to produce higher displacement and blocking force.

A series of experiments was carried out to investigate the effects of active flow control on the aerodynamic characteristics of a cranked-delta-wing model at a subsonic speed. A dielectric barrier discharge (DBD) plasma actuator was used to improve the aerodynamic performance of the half-span cranked-delta-wing model at various angles of attack. The model had inboard and outboard sweepback angles of 57 and 38 deg, respectively. The surface pressure distribution was obtained at five streamwise stations and at two ray stations. All data were obtained at a constant Reynolds number of 0.27×106 and at various angles of attack: 0 deg≤α≤36 deg. The results showed that the pulsed DBD plasma actuator improved the aerodynamic performance of the cranked-delta-wing model by preventing flow separation at high angles of attack. The deep stall angle of attack was delayed up to 6 deg, and the poststall suction coefficient was increased approximately 30% at an angle of attack of about α=34 deg when the pulsed DBD plasma was applied at its optimum condition (F+≈1 and duty cycle=10%). It was found that the pulsed plasma actuator suppressed the wake flow in the forward portion of the wing at poststall angles of attack, thus delaying the flow separation. However, the effects of the DBD actuator at very high angles of attack on the flow reattachment process at the rear portion of the wing for the present DBD setting were seen to be minimal. The induced flow by the pulsed DBD plasma actuator influenced the vortex merging phenomena and delayed the onset of the outer vortex burst at prestall angles of attack.

Flight dynamics modeling and analysis of a fixed-wing nano air vehicle (NAV) is studied. In the process of developing a NAV, this paper explains, longitudinal and lateral dynamics and performance analysis of 75mm wing span NAV. The performance and trim analysis is carried out with aerodynamic data found by simulating a typical nano air vehicle geometric configuration in XFLR5 and integrating this data with Matlab. Longitudinal and lateral dynamics are analyzed both for coupled and uncoupled model, and difference is projected by considering only aerodynamic coupling.

Insects that use a Weis-Fogh clap and fling mechanism, where their wings clap together and fling apart, show an increase in thrust per unit muscle mass compared to conventional flapping insects. This has motivated the development of macroscale clapping winged ornithopters with four wings. Most clapping wing ornithopters use electric motors with gears and linkages that are inefficient at the sub-millimeter (meso)scale. Piezoelectric actuators are attractive for Nano Air Vehicles (NAVs) because they have high power density, high efficiency, and new fabrication processes have been developed at this scale. Recently developed piezoelectric T-beam actuators are monolithically fabricated from bulk PZT and function like unimorph actuators without the need to bond passive layers. These bending actuators drive a novel four-winged clapping NAV that produces thrust. This paper studies thrust force generation of a clapping wing NAV using a model-based approach. A three degree of freedom dynamic model of the clapping wing nano air vehicle is derived including unsteady aerodynamic forces and torques. The model is validated using experimental data from a NAV prototype.

The use of dielectric barrier discharge plasma actuators for hingeless flow control over a 47-deg 1303 unmanned combat air vehicle wing is described. Control was implemented at the wing leading edge to provide longitudinal control without the use of hinged control surfaces. Wind-tunnel tests were conducted at a chord Reynolds number of 4.12 x 105 and angles of attack ranging from 15 to 35 deg to evaluate the performance of leading-edge plasma actuators for hingeless flow control. Operated in an unsteady mode, the actuators were used to alter the flowfield over the lee-side wing to modify the aerodynamic lift and drag forces on the vehicle. Multiple configurations of the plasma actuator were tested on the lee side and wind side of the wing leading edge to affect the wing aerodynamics. Data acquisition included force-balance measurements, laser fluorescence, and surface flow visualizations. Flow visualization tests mainly focused on understanding the vortex phenomena over the baseline uncontrolled wing to aid in identifying optimal locations for plasma actuators for effective flow manipulation. Force-balance results show considerable changes in the lift and drag characteristics of the wing for the plasma-controlled cases compared with the baseline cases. When compared with the conventional traditional trailing-edge devices, the plasma actuators demonstrate a significant improvement in the control authority in the 15- to 35-deg angle-of-attack range, thereby extending the operational flight envelope of the wing. The study demonstrates the technical feasibility of a plasma wing concept for hingeless flight control of air vehicles, in particular, vehicles with highly swept wings and at high angles of attack flight conditions in which conventional flaps and ailerons are ineffective.

This paper discusses the development of flight dynamic model and control law to enable autonomous autorotative landing for small unmanned helicopters. For this, a novel modeling and system identification approach based on acceleration prediction model is proposed for accurate simulation of the plant dynamics during the unpowered descent f light of the unmanned helicopter. The flight dynamics model identified using the flight test data obtained through manual autorotation flights of the unmanned helicopter is implemented on a real-time computer to create a hardware-in-the-loop simulation (HILS) setup to design and tune a PID controller in the HILS environment to facilitate safe landing of the helicopter in the event of unpowered flight. This controller is then validated on a small unmanned helicopter using open source PixHawk 2.0 flight controller board to demonstrate autonomous autorotative landing starting from different height and velocity conditions. For vertical autorotation experiments performed, the controller is observed to maintain steady autorotative descent through application of suitable negative collective to maintain rotor RPM and then arrests the rate of descent by flaring at the appropriate height, which is defined as a function of descent rate, to ensure landing at near zero vertical speed.

Nowadays, Unmanned Air Vehicles (UAVs) have become more and more important. These vehicles are employed in many applications from military operations to civilian tasks. Under situations where global positioning system (GPS) and inertial navigation system (INS) do not function, or as an additional sensor, vision systems can be used. In recent years omnidirectional camera usage has experienced a remarkable increase. In many fields innovative research has been done by this camera which captures 360° view in a single frame. However, employment of omnidirectional cameras in UAVs is very new. In this paper, we present the use of catadioptric systems in UAVs. The parallel lines that exist on many structures in an urban environment are used by the algorithm for the estimation of the attitude of the UAV. After explanation of the algorithm, the UAV modelling and control will be presented. Various simulations have been done to present the effectiveness of the estimation algorithms as well as the UAV controllers. Finally, we will present the experiments and the results of the estimation and control algorithms on a real model helicopter.

Large-eddy simulation (LES) is employed to investigate the use of plasma-based actuation for the control of flapping motion of a wing section at low Reynolds number. The SD7003 airfoil section and imposed oscillatory motion of the investigation are representative of micro air vehicle (MAV) applications. Dielectric-barrier-discharge (DBD) plasma actuation is utilized to modify the transitional flow and improve aerodynamic performance. Solutions are obtained to the Navier-Stokes equations, that were augmented by source terms used to represent plasma-induced body forces imparted by the actuator on the fluid. A simple phenomenological model provided the body force resulting from the electric field generated by the plasma. The numerical method is based upon a high-fidelity time-implicit scheme, an implicit LES approach, and domain decomposition in order to perform calculations on a parallel computing platform. Solutions are obtained for combined periodic pitching and plunging motion about an 8 degree mean angle of attack at chordbased Reynolds numbers of 30,000 and 60,000. Baseline simulations without control are compared to cases employing plasma actuation in order to assess eects on performance. Comparison is also made with experimental data, and a grid resolution study is performed for validation purposes. Plasma-based control is able to mitigate, but not completely eliminate, the massive separation that occurs during the unsteady motion. It is shown that plasma actuation can reduce drag by 80% over the flapping cycle, and increase the lift to drag ratio by a factor of five.

In this chapter, preliminary sizing and performance calculations of unmanned air vehicles (UAV), with relation to its propulsion system, are explained. Starting with the mission profile of the air vehicle, which is one of the important design drivers, the UAV is sized for the requirements. The requirements in design consist of a set of target values (e.g., payload amount to be carried, range, endurance time, cost, etc.). Additionally, the parameters within mission profile such as cruising altitude and speed of aircraft affect engine type, power level required, fuel quantity, and therefore general dimensions and the gross weight of the aircraft. It is often an iterative process to size the air vehicle and engine together. UAV is designed in a loop of calculations in which sizing, flight performance, and engine performance are done for each phase of the mission or flight profile to satisfy the overall design mission and requirements.

An important subproblem in the area of cooperative control of multiple, autonomous, unmanned air vehicles is the determination of the minimum-time optimal paths for the agents to fly from one destination to the next. The tasks for the air vehicles are usually tightly coupled in time, and hence estimates of the times taken for each air vehicle to fly from one destination to the next is highly critical for correct assignment of tasks. In this article, we discuss the existence and uniqueness of minimum time solutions for the trajectory planning problem for a Micro Air Vehicle (MAV) under wind conditions. We show that there exists a minimum time solution for the trajectory planning problem with a minimum turn radius constraint for the air vehicle, and for a non-zero, time-varying wind vector field satisfying certain easily checked sufficient conditions. We also prove uniqueness for almost every combination of initial and final conditions in the case of a wind vector field that can vary with time but is constant in the spatial variable at each time instant.

An Unmanned Air Vehicle (UAV) is an unmanned, remotely controlled, small air vehicle. It has an important role in anti-surface warfare. This implies over-the-horizon detection, classification, targeting and battle damage assessment. To perform these tasks several UAVs are needed to assist or interchange with each other. An important problem is to determine how many UAVs are needed in this respect. The answer depends on the characteristics of the UAV and its mission. The UAV availability problem is very complex and the usual method to solve such a problem is simulation. A disadvantage of simulation is that it can be very time-consuming. Hence it is not very suitable for sensitivity analysis. Moreover, since simulation gives mere approximations and is not very generic, theoretical insights are hardly gained. In this paper we show how such a complex problem can still be tackled analytically by using a basic model from reliability theory, viz., a 1-out-of-n system with cold standby, ample repair facility and general life time and repair distributions.

A two-dimensional body that moves suddenly in a viscous fluid can instantly generate vortices at its sharp edges. Recent work using inviscid flow theory, based on the Birkhoff–Rott equation and the Kutta condition, predicts that the ‘starting vortices’ generated by the sharp and straight edges of a body – i.e. the vortices formed immediately after motion begins – can be one of three distinct self-similar types. We explore the existence of these starting vortices for a flat plate and two symmetric Joukowski aerofoils immersed in a viscous fluid, using high-fidelity direct numerical simulations (DNS) of the Navier–Stokes equations. A lattice Green's function method is employed and simulations are performed for chord Reynolds numbers ranging from 5040 to 45 255. Vortices generated at the leading and trailing edges of the flat plate show agreement with the derived inviscid theory, for which a detailed assessment is reported. Agreement is also observed for the two symmetric Joukowski aerofoils, demonstrating the utility of the inviscid theory for arbitrary bodies. While this inviscid theory predicts an abrupt transition between the starting-vortex types, DNS shows a smooth transition. This behaviour occurs for all Reynolds numbers and is related to finite-time effects – there is a maximal time for which the (self-similar) starting vortices exist. We confirm the inviscid prediction that the leading-edge starting vortex of a flat plate can be suppressed dynamically. This has implications for the performance of low-speed aircraft such as model aeroplanes, micro air vehicles and unmanned air vehicles.

This paper describes the latest efforts to develop an Automated UAV Mission System (AUMS) for small vertical takeoff and landing (VTOL) unmanned air vehicles (UAVs). In certain applications such as force protection, perimeter security, and urban surveillance a VTOL UAV can provide far greater utility than fixed-wing UAVs or ground-based sensors. The VTOL UAV can operate much closer to an object of interest and can provide a hover-and-stare capability to keep its sensors trained on an object, while the fixed wing UAV would be forced into a higher altitude loitering pattern where its sensors would be subject to intermittent blockage by obstacles and terrain. The most significant disadvantage of a VTOL UAV when compared to a fixed-wing UAV is its reduced flight endurance. AUMS addresses this disadvantage by providing forward staging, refueling, and recovery capabilities for the VTOL UAV through a host unmanned ground vehicle (UGV), which serves as a launch/recovery platform and service station. The UGV has sufficient payload capacity to carry UAV fuel for multiple launch, recovery, and refuel iterations. The UGV also provides a highly mobile means of forward deploying a small UAV into hazardous areas unsafe for personnel, such as chemically or biologically contaminated areas. Teaming small UAVs with large UGVs can decrease risk to personnel and expand mission capabilities and effectiveness. There are numerous technical challenges being addressed by these development efforts. Among the challenges is the development and integration of a precision landing system compact and light enough to allow it to be mounted on a small VTOL UAV while providing repeatable landing accuracy to safely land on the AUMS. Another challenge is the design of a UGV-transportable, expandable, self-centering landing pad that contains hardware and safety devices for automatically refueling the UAV. A third challenge is making the design flexible enough to accommodate different types of VTOL UAVs, such as the AAI iSTAR ducted-fan vehicle and small helicopter UAVs. Finally, a common command-and-control architecture which supports the UAV, UGV, and AUMS must be developed and interfaced with these systems to allow fully autonomous collaborative behaviors. Funded by the Joint Robotics Program, AUMS is part of a joint effort with the Air Force Research Laboratory and the Army Missile Research Development and Engineering Command. The objective is to develop and demonstrate UGV-UAV teaming concepts and work with the warfighter to ensure that future upgrades are focused on operational requirements. This paper describes the latest achievements in AUMS development and some of the military program and first responder situations that could benefit from this system.

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.

GPS enhances the ability of UAV system to control the air vehicle, an electronic map displays dynamically the position results and happenings around the UAV. To combine GPS and electronic map, visual UAV dynamic location and navigation is realized.