Browse Topic: Off-board energy sources
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Propeller driven rotors utilize propellers on the main rotor blade to spin the rotor. Past research efforts have highlighted dynamic issues that arise from the rotor-propeller Coriolis interaction. For this paper, a comprehensive multi-body analysis methodology, called Elastic Rotorcraft Analysis (ERA), was applied to various propeller driven rotor datasets. The focus of the modeling effort was on propeller driven rotor twirl phenomenon, which arises from rotor-propeller inertial couplings interacting with rotor blade modes. After describing the phenomenon, the paper is split into two parts: validations and predictions. In Part I of the paper, the ERA propeller driven rotor model was validated using three datasets: (i) a propeller flapping vacuum chamber experiment, (ii) a propeller/rotor loads vacuum chamber experiment, and (iii) a propeller driven rotor hover experiment. The ERA model showed good agreement with the data, and captured the important rotor-propeller Coriolis interaction. In Part II of the paper, predictions for several propeller driven rotor configurations were generated and analyzed. Loads were computed for an isolated propeller and are compared to propeller loads during propeller driven rotor operation. The analysis showed that operating the propeller on the rotor blade introduces significant inertial loads on the propeller. Finally, propeller placement along the main rotor blade span was investigated. The results of the present study agree with earlier research, which showed placing the propeller at the midspan location reduced the electrical power coefficient by nearly half compared to a tip mounted propeller.
Researchers at the National Aeronautics and Space Administration (NASA) have conducted a series of module-level 50-ft dynamic drop tests on electric Vertical Take-off and Landing (eVTOL) Energy Storage Systems (ESS) for the generation of dynamic impact data to support standards developments. The tests were conducted on zero-state-of-charge Electric Power Systems (EPS) Electric Propulsion Ion Core (EPIC) modules at the National Institute for Aviation Research (NIAR), utilizing the NIAR outdoor drop test setup and conducted by NIAR test personnel. Four total tests were conducted on modules oriented in four different orientations. During initial post-test inspections at the drop facility, it was observed that the modules experienced varying amounts of damage in various locations and forms. The damage was quantified to the maximum extent possible via photogrammetric methods such as digital image correlation and marker tracking. Post-test modules were then disassembled, and forensics were conducted, which involved inspections into various containment structures and the cells themselves. A scoring rubric was developed in order to utilize a common methodology to quantitatively assess the damage incurred into each module as way of determining the least and most amount of damage present. Results in the form of post-test inspections, digital image correlation deformations, and scoring rubric values will be all presented, along with proposed paths forward for future work.
Aircraft Certification is a mature and complex bureaucracy that has successfully ensured a very high degree of safety of aircraft design, construction, operation and maintenance. Outside of a very few doing the work, there is a general lack of knowledge of certification details. For novel technologies such as electric power, and innovative configurations such as multi-rotors, the rules are far less mature and still emerging and so also poorly understood. Within the Advanced Air Mobility (AAM) initiative, many new aircraft developments are underway using novel configurations, and the public announcements of regulatory progress toward FAA or EASA Type Certification capitalize on this ignorance by being vague or even misleading. Honeywell conceived the Regulatory Readiness Level (RRL) indicator as an objective measure of certification status to serve the AAM industry and ecosystem, with applicability across aviation. The released RRL Version 1 now enables credible, objective assessment of new aircraft progress toward FAA Type Certification, and Operational Approval for Part 135 operations, to allow consistent apples-to-apples comparisons with other aircraft in development. An emerging complementary version of the rubric for EASA Type Certification is ready for publication to enable RRL determination against the European Union criteria. Future releases will consider other Nation's regulatory authorities, supplemental types certifications (STCs), and risk-based airworthiness assessments such as the Specific Operations Risk Assessments (SORA).
Researchers at the National Aeronautics and Space Administration (NASA) have conducted a series of module-level tests on electric Vertical Take-off and Landing (eVTOL) Energy Storage Systems (ESS) for the generation of dynamic impact data to support standards developments. The tests were conducted on zero-state-of-charge Electric Power Systems (EPS) Electric Propulsion Ion Core (EPIC) modules at the National Institute for Aviation Research (NIAR), utilizing the NIAR outdoor drop test setup and personnel. Four total tests were conducted. For each test, the module was dropped at a specific orientation from a height of 50 feet while connected to a guided trolley in order to assess the effects of a 50-foot drop test on the ESS. The test velocities ranged between 46.9 and 52.8 ft/s with impact angles ranging between a flat, zero-degree impact and 18 degrees. Data were recorded in the form of temperatures, cell-level voltage, module level acceleration and digital image correlation from the tests. Accelerations were in the range of 1,500 g for a few millisecond duration, which were indicative of a shock type loading condition. No modules entered thermal runaway, and post-test inspections revealed a variety of internal deformations and damage present in the various modules tested, with specific damage occurring for specific orientations. The modules were ranked according to a custom developed scoring rubric developed by utilizing the test and post-test inspection results. The results were compiled, reported, and will be used to guide future ESS testing. Part 1 discusses the loading environments in the modules, while Part 2 will discuss the deformation and damage in the modules.
This paper analyses the possibility of using photovoltaics as additional energy provider for small to medium-sized eVTOL UAVs. A simplified model for eVTOL UAVs, which covers all relevant areas of aircraft design, including aerodynamics, structural mechanics, propulsion and systems modelling, is presented. Sensitivity studies covering various design parameters, such as airfoil, wing geometry and propulsion system selection are performed to show their influence on the configurations' performance. The first result of this paper is, that a photovoltaic powered configuration can outperform a battery electric and it can be worth the effort to implement the solar cells. To achieve this, the aircraft needs to be as aerodynamic efficient as possible. Also higher efficiency solar cells increase the possible performance. Additionally there is a big influence of the time of year and the latitude onto the performance. Secondly a multi mission study is performed. This uses a more detailed model, as the preliminary study. It is to find the best solar eVTOL for a set of missions. A summary of this study's results is presented. Finally the best aircraft configuration, following this study, is presented. The main take aways are, that solar cells can have a positive effect on the overall performance of eVTOL UAVS. However some possible drawbacks are also identified, as the resulting aircraft require rather low speeds and a more complicated mission planning, because solar irradiance needs to be taken into account and monitored during the whole mission.
This paper presents an object-oriented, equation-based framework for multi-engineering modeling of a quadrotor UAV, which includes the rigid body dynamics, simplified aerodynamics, gyroscopic effects, electrical power system and battery losses, and DC motor dynamics. An open-source drone modeling library is introduced by explaining the mathematical models and multi-domain components used to model the drone. Animation and visualization techniques for the drone using CAD models are also introduced and explained. The proposed drone model is simulated under different flight scenarios using motor and power system models with different levels of detail, aiming to provide better means for design and understanding, of multi-engineering aspects of UAVs. This model provides a foundation for future UAV open-source model development, electrified power propulsion design, visualization and interaction, and system identification.
This paper analyses the possibility of using hydrogen fuel cells as main energy provider for small to medium-sized eVTOL UAVs. A simplified model for eVTOL UAVs, which covers all relevant areas of aircraft design, including aerodynamics, structural mechanics, propulsion and systems modelling, is presented. Sensitivity studies with various design parameters, including aspect ratio and design cruise speed are performed to show their influence on the configurations’ performance. A comparison between pure battery electric and fuel cell hybrid UAVs is taken. The result of this paper is, that a hydrogen fuel cell hybrid configuration can have a better performance than a battery electric and it can be worth the effort to implement the fuel cell. To achieve this, the mission should require a long endurance and have hover and transition times reduced as far as possible, which both enable the high energy density of the hydrogen system to unfold its full potential. Also, the aircraft needs to be as aerodynamic efficient as possible in order to reduce the fixed weight of the hydrogen fuel cell. Respecting these requirements and accepting a reduced versatility of the aircraft, a fuel cell hybrid eVTOL UAV can easily outperform one with a pure battery electric power supply.
ABSTRACT Rotorcraft operations in arid environments can result in the ingestion of large quantities of dust particles into turboshaft engines, where they can melt and deposit on high pressure turbine nozzle guide vanes. This can result in reduced engine life-span and in worst case scenarios, in-flight engine failure. Predicting the extent and rate at which this damage occurs has proven difficult owing to the wide range of variables relating to the dust cloud, engine and most importantly, the properties of the particulate encountered. Whilst significant work has been carried out to model the particle deposition process for both volcanic ash and coal fly-ash, there is scarce similar work for the different types of mineral dusts rotorcraft encounter. In this contribution, we assess the suitability of two opposing numerical approaches for use in a generalised, reduced-order deposition model of individual mineral particles depositing on a vane. Both models are seen to be heavily reliant upon empirical inputs, be this the thermo-mechanical properties of the particles such as their yield strength, or currently unknown experimentally determined constants. An alternative approach is therefore proposed whereby the particle yield strength is correlated using existing relationships to the Vickers hardness of the grain, a property more amenable to empirical determination. The results obtained represent the current applicability limits of the two models based upon existing empirical data and thus highlight the need for further experimentation relating to both the thermo-mechanical properties and probabilities of adhesion for both individual mineral grains and mineral dust blends.
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