Catastrophic damage to fixed-wing unmanned aerial vehicles (UAV) is most likely to occur during the landing stage. Vision-based autonomous landing methods for small UAV have been proposed in literature to address the issue. This paper improves on previous work on vision-based landing via a controlled collision with a large inflatable airbag. In the proposed method the UAV steers towards a large, multi-coloured, dome-shaped airbag using visual feedback obtained from a UAV-mounted camera. A multi-colour airbag is proposed to facilitate a robust and efficient colour-based detection method for real-time detection of the dome in images. A proposed visual servoing controller translates the dome location into desired pitch and yaw rate commands to achieve an exponential decay of the image error. A model predictive UAV controller that achieves desired roll and yaw rates is designed and tested in simulations. The lateral and longitudinal UAV dynamics were decoupled and a linear discrete state space model of the dynamics was obtained via system identification. The proposed dome landing method has been implemented on the FlightGear flight simulator and has presented successful landings in simulations over multiple trials.
Unmanned Aerial Vehicles (UAVs) have been widely used in intelligence gathering, psychological operations, laser designation, range-finding, and communication. In this paper, the design of a fixed-wing UAV is presented. A target detection and localization method is proposed for the developed UAV. The hardware construction, along with the selection of necessary components, is introduced. In order to facilitate modular code development and integration of control laws with simulation and hardware, a hardware-in-the-loop simulator is proposed. The flight control law is developed and tested using the hardware-in-the-loop simulator. Wifi is used for monitoring the state variables of the aircraft. Simulation and experimental results demonstrate the performance of the developed system.
It is well known that a big aviation market in the world is air transport of passengers and goods and buoyant aerial vehicles are one of the potential candidates for such applications. Aerodynamic and stability characteristics of such vehicles are critical issues of design and any new such design should exhibit longitudinal and directional stability. A generic model of hybrid buoyant aerial vehicle, consisting of fuselage similar to a hull of airship, was numerically tested by using Aircraft DATCOM to get first-hand knowledge about the general trends of aerodynamic and stability parameters. Most of such tools are limited to well-defined conventional aircraft configurations. But based on the presented results, it can be revealed that such tools can be used for hybrid buoyant aerial vehicles as well. Presented results will be validated in future by wind tunnel testing.
To improve aircraft performance in adverse service environments, specific coatings are applied to critical surfaces to improve (i) erosion, (ii) corrosion, (iii) hydrophobic, or (iv) icephobic properties. Although protective coatings are available in all four groups, aerospace applications require combinations of properties that are not readily available, for example hydrophobicity together with erosion resistance. The combination of hydrophobic (or icephobic) and erosion properties is difficult to obtain. Known hydrophobic or icephobic materials are usually polymers that are too soft to provide required erosion resistance and durability in aircraft service conditions. Conversely, physical vapour deposited coatings that are erosion resistant and durable, typically do not have adequate hydrophobicity. However, recent studies on amorphous carbon (a-C) coatings indicate that these materials have potential for combined hydrophobic and erosion applications through doping or compositional changes. Thus, this paper reports on improving the hydrophobic and erosion resistance properties of nonhydrogenated a-C coatings doped with a single element such as chromium (Cr), silicon (Si), aluminum (Al), or titanium (Ti) up to 12 at.%. All coatings are produced using unbalanced magnetron sputtering and characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, nanoindentation, and water contact angle measurements. The most prospective compositions are evaluated for erosion resistance and ice adhesion strength testing. Overall, the best combination of hydrophobic and erosion properties is obtained for a-C doped with 10 at.% of Al, whereas the ice adhesion results against bare steel substrate have been inconclusive.
Ion propulsion is a technology that offers low thrust but high specific impulse for small spacecraft. The propulsion system can be used for attitude control and deep-space missions. A disadvantage ion thrusters have is the high cost of the propellant. Xenon is a widely used propellant for ion thrusters; however, it is expensive. In addition, the manufacturing of the ion thruster can be costly. This paper presents a low-cost ion thruster that uses nitrogen and argon as its propellant. The thruster is named capacitive discharge ion thruster (CDIT) because the plasma is generated by a capacitive discharge. The force, specific impulse, mass efficiency, power efficiency, and thrust efficiency of the CDIT using nitrogen is 0.564 mN, 2 300 s, 0.44, 0.75, and 0.34, respectively, at a mass flow rate of 25 µg/s.
In this work, friction stir welding (FSW) of 3.18 mm thick AA6061-T6 sheets in the butt- and lap-joint configuration was investigated with the objective of industrializing the process using low-cost serial industrial robots. The influence of weld pitch on the welding defects, microstructure, hardness, and bend performance of butt and lap welds was examined to identify process operational windows for both joint types. In parallel with these trials, a methodology based on kinetostatic analysis was developed to identify and evaluate viable robotized scenarios for FSW. On the basis of the experimental FSW process development results, this methodology was then applied to identify optimized FSW scenarios for the fabrication of large integrated AA6061 structural components with stringer-to-skin and skin-to-skin joints. Candidate workcell layouts are also presented.
Important elements of the framework for numerically evaluating the usage of reactive aluminum particles in solid-propellant rocket motors are brought forward, and where possible, predicted model results are correlated to established experimental observations. A principal purpose in using inert or reactive particles is for the suppression of axial pressure wave development in the motor. In this study, a primary focus is placed on evaluating the qualitative trends associated with the time-dependent reduction in size of the reactive aluminum particles as they move downstream in the central internal flow. To narrow the scope of this preliminary study, the reactive particle size regression is stipulated to occur at a designated uniform rate for a given simulated firing. Individual transient internal ballistic simulation runs for a reference composite-propellant cylindrical-grain motor show the evolution of the axial pressure wave for a given initiating pressure disturbance, and for particle loading, initial pa...
Module discretization and consolidation was performed on morphing wing profiles optimized for climb, cruise, and descent flight regimes. Wing profiles were created using an optimization algorithm based on their aerodynamic performance for the three flight regimes. A module discretization method was applied for the three cases and the minimum number of modules were found for each case without significantly sacrificing performance. The three wing profiles were then consolidated into a single final wing using a newly proposed method for combining closely aligned joints based on a weighting scale for each flight regime. When the final wing’s performance was compared to the original wing profiles a reduction of 5% and 2% was observed for climb and descent configurations, respectively. The cruise configuration was found have a 3% increase when compare to the original profile. The final wing was found to successfully maintain aerodynamic performance during module discretization and consolidation process.
Composite materials are widely used in the aerospace industry. It is a great challenge to achieve high-quality parts with reduced damage level when drilling the faces of composites. This is due to ...
The goal of this work was to identify the optimum combination of the main process parameters, i.e., the internal pressure and end feeding (load path), for tube hydroforming to minimize the thickness reduction, while satisfying the failure constraint defined by the forming limit diagram of the material. To perform process design optimization with minimum experimentation, the LS-OPT software was utilized in combination with a finite element model (FEM) that simulated a round to square tube hydroforming (THF) process for stainless steel 321 in LS-DYNA. The load path obtained through the optimization procedure was applied to the THF process and the tube expansion and the thickness results obtained from the FEM were compared with the experimental results in the critical regions of the hydroformed tube.
Part quality is an important aspect in the aerospace industry to avoid unpredictable and irreversible damages and to ensure a long lifecycle. To ensure quality, nondestructive testing techniques are applied on parts, and one of the most frequently used in the aerospace industry is eddy current testing (ECT). However, high-cost, time-consuming ECT is still mainly performed manually. In this case, reliability and repeatability of inspection results are also limited due to their high dependence on the human operator. As part of an effort to robotize ECT with a six degree-of-freedom manipulator arm and thus, free oneself from the many drawbacks of manual inspections, the authors previously proposed a coverage path planning methodology dedicated to complex aeronautical surfaces. However, orientation of the probe along these paths was not initially considered during this previous work, although it is just as important as position information given that the probe must keep a normal orientation with respect to the surface to inspect it reliably. Following on from this previous work, the computation of these orientations along every point of the path is presented in this paper. Furthermore, another coverage path planning methodology is developed to inspect with ECT around a probable defect whose position is assumed to be known a priori. After positions and orientations along inspection paths are computed, a simulation with a robotic simulation software (MotoSim) is made to generate the joint trajectories of a manipulator arm MotoMan SV3XL and to teach it the automated inspection task. Afterwards, experiments using this manipulator, with a mock-up that represents a probe, are realized. After these first experiments, it is observed that the motion of the robot is what one can expect during an efficient inspection around a known indication.
This paper introduces a new class of Bug algorithm that combines local planning with global information to guarantee convergence. Existing Bug algorithms are typically designed for 2D robot navigation in 2D environments and do not integrate vision information within their planning algorithm. In this paper a new algorithm, uavisBug, is proposed for small quadrotor UAV navigation in a 3D environment. On-board vision perception is incorporated to enable 3D way-finding behaviors in an initially unknown environment. The proposed algorithm shows non-oscillatory behaviors in the UAV's flight in proximity of obstacles. It is also immune to potential local minima exhibited by artificial force field approaches. In addition to system and sensors modeling, UAV control, UAV pose estimation, and fast environment mapping are also included. Simulation results are used to validate the proposed approach.
Kapton membranes are one of the major components of ultra-light inflatable gossamer space antenna structures. Although they are lightweight, their flimsy nature makes them particularly susceptible to various kinds of disturbances in space environments that can corrupt the accuracy of the antenna measurements. One of the key challenges with these membranes pertains to wrinkle formations due to disturbances and flatness control. In this paper, Macro-Fiber Composite (MFC) based actuators are designed for removing wrinkles in a Kapton membrane formed due to mechanical loadings. Three actuator configurations are fabricated and tested for a square membrane and are compared through force–displacement testing. The benefits of pre-activated MFCs in bimorph configurations are established. Wrinkle control experiments along with numerical studies using the finite element analysis software ABAQUS demonstrate that the proposed actuators are promising candidates for flatness control of Kapton membranes.
This paper describes an efficient methodology to perform ground vibration tests (GVT) using Experimental Modal Analysis and flight vibration tests of light aircraft. The objective is to extract structural dynamics properties of the whole aircraft while overcoming major challenges such as time, cost, and aircraft availability to assess flutter clearance compliance with the certification requirements. The paper provides details of the approach taken to perform a successful GVT and in-flight vibration test that includes the aircraft configuration, test instrumentation, data analysis techniques, and test procedures to extract necessary information to perform flutter clearance certification from the GVT and flight vibration test. Typical test methodology, test instrumentation, software, and procedures used to obtain the modal parameters, namely natural frequency, damping ratio, and mode shapes, are presented in this paper. In flight tests, the modal parameters were obtained from operational data without a known excitation source.
This paper discusses the concept of simple blowing directly from the trailing edge of the wing of an aircraft to provide increased lift, especially during the take-off and landing maneuvers. Although a noticeable increment in coefficient of lift has been obtained to replace or even augment the effect of classic flaps, its application as a means to exert immediate and instantaneous control on stability and control would be an added benefit. Indeed, if such a concept could truly be optimized to replace the physical presence of traditional flaps in an aircraft, the benefits in weight savings and comparative simplicity in design and operational adoptability would be enormous. The jet blowing has been applied at the trailing edge of an airfoil and a 3-D wing at a variety of jet-ejection vector angles with respect to the chord line; a noticeable increase in lift has been recorded using both configurations.
Due to the complexity of real structures and in-service environment, the probability of detection (POD) curve generated from a laboratory environment and simple coupon samples may not be representative of in-service nondestructive inspection capability and experience. A study was carried out to assess the capability of a recent Berens model to estimate the POD using in-service inspection data. This paper presents the Berens model as well as the results of five case studies, where two types of mean POD curves were estimated and compared with each other. The first POD estimation used the standard POD method, described in the Military Handbook 1823, and used both hit and miss (detected and nondetected cracks) data. The second POD estimation used the Berens model and only hit (detected cracks) and percentage of crack detection (number of detected cracks per number of inspected sites) data. It is shown that the a90 values estimated by the Berens model are close to those from the first POD approach, especially when the percentage of crack detection is known. The study demonstrated the possibility of using the Berens model for estimating an “effective” POD curve from in-service data, where often not all data required by the standard POD approach are available.
An analytical formulation of the drag characteristics of arbitrary three-dimensional surface roughness in the fully rough regime of turbulent boundary layer flow is introduced. An expression was derived for the equivalent sand grain roughness, introducing a universal roughness correlation parameter. The coefficients of the roughness parameter were determined based on Schlichting's database. This yielded a linear correlation of equivalent sand grain roughness over the complete range of roughness frontal solidity. Applications to regular and irregular distributions were undertaken. Results are presented for a sand-roughened sample, and the data uncertainty and sensitivity to input parameters are determined.
In lunar exploration, dust poses a significant problem due to its pervasiveness, adherence, and abrasiveness, causing premature failure of mechanisms. Successful operation of autonomous equipment in the harsh lunar environment requires innovative methods of dust protection, especially for exposed connection interfaces. In eventual robotic lunar exploration missions, lunar dust control will be a major factor affecting mission lifetimes and operations. Biomimetic inspired concepts are developed to design an interface allowing electrical connection between a lunar rover and interchangeable instruments. A proof-of-concept prototype of the interface has been constructed to demonstrate system functionality under laboratory conditions.
Future aircraft designs such as the blended wing body have the potential to reduce fuel consumption from 20% to 30% compared with the classical configuration. This also gives the opportunity to integrate the engines into the wing. Burying the engines brings many benefits including noise shielding and a theoretical increase in propulsive efficiency owing to boundary layer ingestion (BLI). However, BLI causes nonuniformity in the flow stream at the inlet, which can reduce the pressure recovery and increase the distortion coefficient at the engine fan face. These factors reduce the overall efficiency and stall margin of the engine, in turn reducing the potential benefits of the design. The primary objective of this research was to identify, with a parametric study, the geometric design variables of the S-shaped diffuser, which has an impact on the nonuniformity of the flow stream in the case of BLI by the engine as well as its role in distortion and pressure recovery variation. The secondary objective is to propose an optimization process aimed at reducing fuel consumption based on a CFD analysis coupled to a thermodynamic module. Results showed that the length of the diffuser and the aspect ratio of its air intake are the two most important geometric variables affecting the installation. They also showed a reduction in fuel consumption of 0.8% between the worst and optimal configurations. However, the study concluded that the optimized diffuser still exhibits an unacceptable level of distortion, which can compromise the durability of the engine components.
The objective of this paper was to design a set of proper speed controllers for reaction wheels in the presence of unknown coulomb friction and parametric uncertainties. The controller goal was to change the rotational speed of reaction wheels to adjust the satellite to a desired attitude. The mathematical model of a satellite that utilizes three reaction wheels as actuators was developed by angular kinematics and kinetic equations. Variable-structure control theory was then applied on the reaction wheel via a real-time microcontroller-based Hardware in the Loop. The simulated satellite response to wheel speed shows that the sliding mode speed controller is effective, and a small attitude angle could be tracked more effectively than with a Proportional–Integral–Derivative speed controller.
