Browse Topic: Lightweighting
Emerging technologies in the field of electrified propulsion systems offer a promising solution to reduce the dependence on fossil fuels and improve efficiency. However, the design of high-power density electric machines introduces new challenges, including limited passive cooling potential and the issue of the weight of electric motors. To address these challenges, this paper considers analysis and design methods for high torque-to-weight ratio axial flux motors. A magnetic equivalent circuit model coupled with a lumped parameter thermal network is developed for design space exploration and optimization. This inexpensive analytical model predicts the performance of a single-stator dual-rotor axial flux motor based on geometry, loading condition, and slot and pole pair combination. To enable comparisons against real-world data, the optimization study was demonstrated using the hover mission requirements from the Research Aircraft for eVTOL Enabling techNologies (RAVEN) vehicle to minimize the mass of the motor. In tandem with the analytical model, a higher-fidelity finite element model was also developed, and good agreement between predicted power and efficiency was demonstrated across a range of axial flux motor designs. The lightest weight design that satisfied the hover mission requirements was the 12 pole pair 27 slot (12PP 27S) configuration with a fixed weight of 9.28 kg. The analytic model undersized the output power of the electric motor by approximately 9% across a range of slot and pole pair combinations.
The paper describes a method for optimal design of a helicopter tail shaft that considers rotordynamic effects from long shaft assembly. The tail shaft transmits power from the main gearbox (MGB) to the tail rotor of the helicopter and operates at high speeds that may exceed 6000 rpm. While higher speeds allow for weight reduction, they also pose risks associated with supercritical operation, necessitating careful design optimization. The objective of the optimization is to maximize the first three transverse natural frequencies with the constraint of the safety parameter (avoidance of the resonance/critical zone) while minimizing the weight of the system. A Non-Dominated Sorting Genetic Algorithm (NSGA-II) is used to obtain the solution to this multiobjective optimization problem, which involves shaft design variables such as length, outer diameter, and wall thickness. In addition, the optimization framework also incorporates system related design variables, including the stiffness of tail shaft bearing supports, the location of bearings, and coupling characteristics, to comprehensively evaluate and enhance the system performance. A rotordynamics model utilizing Timoshenko beam finite elements is deployed to predict natural frequencies.
In order to maximize range, a substantial portion of the interior volume of aircraft is allocated for fuel containment. To ensure the safety of aircrew and passengers, these systems must contain fuel and retain critical structural integrity in the event of a crash, self-seal and retain structural capability in the event of penetration, and suppress fire in the event of proximate ignition. Traditionally, light weight aircraft such as rotorcraft have accomplished these functions with heavy self-sealing bladder offset and isolated from primary structure. Boeing and the US Army Combat Capabilities Development Command Aviation & Missile Center's Aviation Development Directorate (ADD), together with the Joint Aircraft Survivability Program Office, have developed and demonstrated a structurally integrated fuel containment system that efficiently tolerates crash, self-seals, and suppresses fire at a lower weight and volume than traditional systems, thus maximizing space and weight capacity for fuel and payload.
The Mars Helicopter is a 1.8 kg coaxial rotorcraft designed to demonstrate aerial mobility at the surface of Mars after deployment from the Mars 2020 rover. In this paper, the authors present the development of the Mars Helicopter rotor system from preliminary design through fabrication and testing of the flight hardware. The vehicle has a 1.21 m counter-rotating coaxial rotor system which is driven by electric motors and which features collective and cyclic controls on both the upper and lower rotor sets. The rotor blade design is characterized by the low Reynolds number (∼104), high Mach number (∼0.7), high stiffness (first flap frequency ∼1.9/rev), and minimum mass. Airfoil design focused on minimizing drag at the low operating Reynolds number while maintaining sufficient spar depth for structural requirements, and the blade planform was based on a minimum induced loss profile with modifications to reduce mass of the outboard blade sections for increased flap frequency. The swashplate and servos were designed to provide actuation of the rotor at up to 12Hz bandwidth while minimizing system mass and volume, and the primary structure of the rotor blades and hubs relies heavily on molded carbon fiber composites and ceramic ball bearings.
Emerging microelectronic technologies are expanding functionalities for future decades of vertical lift platforms, enabling both manned and unmanned rotorcraft to fully and safely participate in the NextGen National Airspace System. Specifically, for rotorcraft, benefits from expanded multi-functionality and reduced weight and space requirements, for both mandatory and desired optional avionics, are entering advanced development and flight-testing stages prior to being available to all users. One has only to think about the incredible, multifunctional capabilities of a smartphone to imagine what is possible in avionics with today's advanced technology. This presentation discusses achievements that only a few years ago were beyond imagination – miniaturized avionics that fully employ tiny but powerful digital processors and software defined multi-functional systems on a single chip are rapidly obsoleting the "black boxes" of the past. For both manned and unmanned rotorcraft systems, the benefits must be validated; and when proven valid, are immense in terms of lighter weight, tiny form factors, and lower costs. This presentation also addresses validation of ADS-B2, which depends on verification of GPS signals with technological approaches that counter potential malicious spoofing, jamming and interference.
The development of Vertical Take-off and Landing (VTOL) vehicles for the Urban Air Mobility (UAM) markets presents a need for light weight vehicle structures with effective occupant protection capabilities. The National Aeronautics and Space Administration (NASA) has been working to fill that need, recently developing a cadre of concept vehicles to help characterize UAM design feasibility. This paper describes a study, using these concept vehicles, to evaluate the use of advanced composite structure and energy attenuating designs in the UAM vehicle design space. A finite element model (FEM) of a single passenger quadrotor concept vehicle was developed in LS- Dyna® and simulated under nominal and off-nominal vertical impact conditions. A variety of energy attenuating design mechanisms were implemented within this model to quantify their effectiveness in improving occupant safety. The use of carbon composites in both the energy attenuation mechanisms and vehicle structure was evaluated. The results of this study found significant reduction in occupant injury risk with the implementation of energy absorbing composite crush tubes and landing gear within the vehicle design. Additionally the use of a carbon fiber as a structural material was found to provide significant weight reduction while maintaining similar occupant loads to that predicted with an aluminum structure. This work provides a preliminary evaluation of design mechanisms and materials that may be used to optimize occupant protection capabilities within the UAM market.
There is a constant push within the rotorcraft community to increase performance while simultaneously reducing weight in all systems. For rolling element bearings, this translates to a demand for alternative materials with lower density and improved mechanical properties. This combination of new materials and increasingly demanding application conditions goes beyond historical experiences and defined design and analysis standards. A consequence of this is that tests of these new technologies occasionally result in failure. This was the case during a recent series of gearbox tests during which two different bearing designs failed due to cage issues. The two bearing designs included cages manufactured out of different materials, and the cages failed due to two distinct failure modes (wear and structural fatigue). These test results were used to validate computational results from SKF's proprietary multibody dynamics software, BEAST (BEAring Simulation Tool). A combination of elemental testing and computational analysis is now being used to explore the feasibility of alternative material substitutions to avoid the high cost and long lead time of additional full scale testing.
This study develops an optimization technique for a sinusoidal interlock design of a hybrid spur gear consisting of a metallic outer ring to support high contact stress bonded to a composite inner web for weight reduction. Two objectives (mass and shear traction on the metal-composite interface under static loading conditions) were minimized for four design variables subject to two constraints. Borg MOEA, a multi-objective evolutionary algorithm developed at The Pennsylvania State University, and an in-house finite element solver were used to generate Pareto-optimal solutions to this design problem. Two of the designs were then analyzed in greater detail to determine stress distributions throughout the gear. In the future, this technique will be refined and applied to optimization of more representative rotorcraft gears, with the aim of reducing drive train weight and meeting performance requirements.
ABSTRACT The US Army's Aviation Development Directorate (ADD) has successfully collaborated with its industry partners to reduce system parasitic weight for aviation platforms through multifunctional structures technology development. In short, this can be generalized as achieving weight savings by replacing the combination of aircraft structure and an independent, add-on mission enabler with a singular system that performs the functions of both structure and mission enabler. This extensive multifunctional technology development for aviation structural applications has yielded significant weight savings over parasitic designs. Technologies demonstrating this structural multifunctionality for weight reduction include integrally armored helicopter floor, lightweight integrally armored helicopter floor, lightning-protected structure, structural antenna aperture, helicopter empennage antenna structure, combat tempered aft fuselage, blast attenuating aircraft structure, and highly durable floor armor for rotorcraft. The significance of weight savings that can be enabled via multifunctional structures technology development is clear. One case study exercise indicates a platform-level mission enabler weight savings of 17.8%. This significance of weight savings is analogous to other studies showing synergistic benefits from technology integration at the technology and system (platform) level.
ABSTRACT Rotorcraft propulsion systems are continually looking to improve power density; that is reducing weight and increasing power capacity and efficiency. In order to advance rotorcraft propulsion system technology, NASA Glenn Research Center (NGRC) contracted Boeing Vertical Lift to perform system level benefit assessments of designing composite materials into rotorcraft transmission gear and shaft systems. In general, the environment inside a typical rotorcraft transmission creates issues for typical composite materials. In flight critical gears and shafts, design challenges and safety risks associated with introducing composite materials must be understood and accounted for in the design. Boeing was able to develop a technical approach for the system study that covered a relatively large population of rotorcraft main transmissions. This technical approach evaluated rotorcraft from various size classes and configurations and applied parametric estimating methods to assess the performance impact of composite hybrid technologies inside transmissions, in the rotating frame. Parametric weight estimating showed that composite hybrid technologies account for an average 9% weight savings over the baseline transmissions. More weight savings may be observed when various other aircraft systems are considered. Tandem and Tilt-rotor aircraft use similar transmissions at the forward/aft rotor head and left/right side of the aircraft, respectively, doubling estimated weight savings of a single transmission. Other aircraft systems, such as airframe, landing gear, and fuel systems benefit from reduced propulsion system weight, and, therefore, lighter weight aircraft are possible when propulsion system weight is reduced. In this paper, a systems level technical approach is summarized which was used to assess the performance impacts of introducing composite materials inside helicopter transmissions, in the rotating frame. Existing composite technologies, technical challenges, and general material selection guidance were used to develop the technical approach. Transmissions from a multitude of rotorcraft configurations and power classes were studied to build a database of expected performance gains. Component designs were developed using composite materials to varying levels of fidelity in order to develop data used for parametric weight estimating. The component designs are compiled and averaged with similar, existing designs in order to build a robust dataset for weight estimating purposes. Using information developed during the component design phase, technical challenges were defined.
ABSTRACT Resin pre-impregnated fiber reinforced plastic components are integral to the advancement of rotorcraft due to their highly customizable configuration, outstanding dynamic properties, and light weight. The complexity of their fabrication introduces numerous manufacturing challenges; chief among these is the internal location of individual plies of material. Industry standard solutions are commensurately complicated and require highly specialized equipment and personnel. In order to mitigate this, the Sikorsky-Boeing SB>1 DEFIANT™ Technology Demonstrator team developed the use of additively manufactured (AM) ply locating templates as a simple, low cost alternative. An AM template eliminates many of the issues associated with industry standard ply location techniques and tools. They are elegantly simple to use while being extremely ergonomic; they are extremely cost effective, and require no capital equipment to support them; and they are flexible and quick to implement.
ABSTRACT The ability to construct a composite, semimonocoque, damage-resistant, cargo floor for a rotary wing application using an IM7 graphite/polyetheretherketone (PEEK) composite with in-situ tape-placement fabrication technology has been demonstrated. Through an evolutionary process, a damage-tolerant thermoplastic composite cargo floor was designed according to realistic requirements, and subelement representative structures were developed to verify the design viability and approach. The fabricated and tested structural composite floor subelements demonstrated the feasibility of the technology, illustrated the ability to customize the design to meet unique cargo floor properties (e.g., cargo-loading features), and validated the maturity of the approach and fabrication technology for rotary-wing applications.
ABSTRACT Current VTOL aircraft design processes require significant changes in computational methodologies resulting from innovations in distributed hybrid and electric propulsion technology. Electric VTOL (eVTOL) aircraft design offers radically different configurations by eliminating limitations in weight, size and location of Internal Combustion Engines (ICE) and associated fuel systems. Hybrid Distributed Electric Propulsion (HDEP) solutions, to include eVTOL, allow designers to incorporate a greater number of smaller, lightweight propulsors throughout the airframe structure as necessary to meet complex mission requirements. Additional benefits of HDEP versus fossil fuel counterparts, include reduced acoustic and thermal signatures and lighter and smaller structures. Because of the many advantages of DEP, it is quickly becoming the preferred choice for autonomous aircraft design. This paper addresses the necessary changes to VTOL Synthesis to include DEP and Autonomy for HDEP aircraft. Two of the authors, Dr. Daniel P. Schrage and Mr. Kaydon Stanzione have substantial expertise and experience in VTOL aircraft design and the methodologies for vehicle synthesis. They will use this expertise and experience to identify and present the necessary changes in the VTOLTradeoff Environment (VTE) for HDEP VTOL aircraft design and assessment. The VTE will also be focused on using an Overall Evaluation Criterions (OEC) for the VTE that address value as a ratio of System Effectiveness to Life Cycle Cost (LCC). The third author, Dr. Apinut "Nate" Sirirovisuth, a research fellow in the Georgia Tech's Integrated Product Lifecycle Engineering (IPLE) Laboratory, and a Cost Research Analyst at PRICE Systems has significant experience in VTE modeling efforts and is an expert in affordability analysis for advanced aerospace systems.
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