The coupled coaxial rotors/auxiliary propeller/drive train system of a compound helicopter may exhibit torsional instability. A novel modeling strategy based on the transfer matrix method is developed and used to analyze the coupled torsional system. In contrast to the finite element method, the proposed modeling strategy offers more elegant formulations of the dynamic equations for the rigid-flexible multibody system. The highlight includes the overall transfer equation that can be directly obtained according to the topology figure of the system by introducing a virtual branch element to decouple the tree topology system as a combination of the chain systems. Besides, another virtual connection element is introduced to deal with the state vector dimension mismatch problem, improving the computational efficiency by further reducing the scale of the overall transfer matrix. A new transfer matrix of a rotor blade for lead–lag motion is derived. The influences of different flight conditions on torsional vibration are highlighted. And several suggestions on torsional vibration design are concluded.
{"title":"A Novel Modeling Strategy for the Dynamical Analysis of Coupled Coaxial Rotors/Auxiliary Propeller/Drive Train System","authors":"Xiao Wang, Laishou Song, P. Xia","doi":"10.4050/jahs.68.012003","DOIUrl":"https://doi.org/10.4050/jahs.68.012003","url":null,"abstract":"The coupled coaxial rotors/auxiliary propeller/drive train system of a compound helicopter may exhibit torsional instability. A novel modeling strategy based on the transfer matrix method is developed and used to analyze the coupled torsional system. In contrast to the finite element method, the proposed modeling strategy offers more elegant formulations of the dynamic equations for the rigid-flexible multibody system. The highlight includes the overall transfer equation that can be directly obtained according to the topology figure of the system by introducing a virtual branch element to decouple the tree topology system as a combination of the chain systems. Besides, another virtual connection element is introduced to deal with the state vector dimension mismatch problem, improving the computational efficiency by further reducing the scale of the overall transfer matrix. A new transfer matrix of a rotor blade for lead–lag motion is derived. The influences of different flight conditions on torsional vibration are highlighted. And several suggestions on torsional vibration design are concluded.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70218402","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Reynolds stresses and turbulent kinetic energy are studied in the wakes of several helicopter rotor hub geometries in forward flight. Computational fluid dynamics simulations are performed using NASA’s OVERFLOW 2.2n Reynolds-averaged Navier–Stokes solver. The simulations impose flow conditions based on previous and current experimental and numerical studies. Discrete Fourier transforms are used to examine velocity harmonics for several frequencies and compared against available experimental results. Components of the Reynolds stress tensor are computed and examined. Production and transport of the turbulent kinetic energy are examined through the rotor hub wakes at six streamwise coordinates. It was found that the scissor arms, previously found to have a significant effect on rotor hub force harmonics, also had a significant effect on the magnitudes of Reynolds stresses and turbulent kinetic energy. Integrated values of turbulent kinetic energy flux indicate that drag-reducing designs have a direct effect on turbulent kinetic energy levels in the wake.
{"title":"Computational Characterization of Unsteadiness and Turbulence in Rotor Hub Wakes","authors":"Forrest Mobley, Tristan D. Wall, J. Coder","doi":"10.4050/jahs.68.012007","DOIUrl":"https://doi.org/10.4050/jahs.68.012007","url":null,"abstract":"Reynolds stresses and turbulent kinetic energy are studied in the wakes of several helicopter rotor hub geometries in forward flight. Computational fluid dynamics simulations are performed using NASA’s OVERFLOW 2.2n Reynolds-averaged Navier–Stokes solver. The simulations impose flow conditions based on previous and current experimental and numerical studies. Discrete Fourier transforms are used to examine velocity harmonics for several frequencies and compared against available experimental results. Components of the Reynolds stress tensor are computed and examined. Production and transport of the turbulent kinetic energy are examined through the rotor hub wakes at six streamwise coordinates. It was found that the scissor arms, previously found to have a significant effect on rotor hub force harmonics, also had a significant effect on the magnitudes of Reynolds stresses and turbulent kinetic energy. Integrated values of turbulent kinetic energy flux indicate that drag-reducing designs have a direct effect on turbulent kinetic energy levels in the wake.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70218805","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The focus of this work is to integrate component-level design analyses developed for different machine elements of a twin pericyclic drive into a comprehensive design decisions framework. The integrated system loads, bearing loads, and tooth contact analysis procedure is used for designing a prototype for minimum weight within the constraints posed by assembly, component life, and system efficiency. Simultaneous sizing of the gears, bearings, and shafts was performed for given input power, speed, and reduction ratio. The effect of inertial loads due to nutational gear motion is significant on support bearing loads, and the gear bodies are designed to minimize these loads. It was demonstrated that a torque density greater than 50 Nm/kg can be achieved for a low Technology readiness level (TRL) pericyclic transmission prototype design. The test article is designed to operate at a 50-HP, 5000 RPM input with a speed reduction ratio of 32:1 and system efficiency greater than 93%.
{"title":"System and Component Level Design Procedure for High Reduction Ratio Pericyclic Drive","authors":"Tanmay D. Mathur, E. Smith, H. Desmidt, R. Bill","doi":"10.4050/jahs.67.032003","DOIUrl":"https://doi.org/10.4050/jahs.67.032003","url":null,"abstract":"The focus of this work is to integrate component-level design analyses developed for different machine elements of a twin pericyclic drive into a comprehensive design decisions framework. The integrated system loads, bearing loads, and tooth contact analysis procedure is used for designing a prototype for minimum weight within the constraints posed by assembly, component life, and system efficiency. Simultaneous sizing of the gears, bearings, and shafts was performed for given input power, speed, and reduction ratio. The effect of inertial loads due to nutational gear motion is significant on support bearing loads, and the gear bodies are designed to minimize these loads. It was demonstrated that a torque density greater than 50 Nm/kg can be achieved for a low Technology readiness level (TRL) pericyclic transmission prototype design. The test article is designed to operate at a 50-HP, 5000 RPM input with a speed reduction ratio of 32:1 and system efficiency greater than 93%.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70217184","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The hybrid gear concept, which combines a metallic outer rim of gear teeth with a composite web, has shown potential to reduce the weight of small-scale spur gears without negatively affecting vibration performance for low- and medium-speed applications. In this paper, the hybrid gear design and tooth microgeometry optimization technique that had been applied to small-scale spur gears was adapted for application to spur gears of aerospace-relevant scale, speed, and load. A single reduction drivetrain model was developed featuring large-scale hybrid spur gears, which was used to determine optimal tooth microgeometry modifications that minimized peak-to-peak transmission error. Static and dynamic transmission error analyses were then performed using the optimal microgeometries. Results were compared to those predicted for a similarly-optimized all-steel drivetrain. The application of optimal tooth microgeometries to large-scale hybrid gears led to a more significant decrease in a peak-to-peak transmission error than was observed for the small-scale gears. Similar to results for small-scale hybrid gears, the drivetrains featuring large-scale hybrid gears predicted similar dynamic transmission errors to their all-steel counterparts at low and medium speeds, while significantly different transmission errors were predicted at high speeds.
{"title":"Analysis of Large-Scale Hybrid Aerospace Spur Gear Drivetrains","authors":"Sean Gauntt, S. McIntyre, R. Campbell","doi":"10.4050/jahs.68.012004","DOIUrl":"https://doi.org/10.4050/jahs.68.012004","url":null,"abstract":"The hybrid gear concept, which combines a metallic outer rim of gear teeth with a composite web, has shown potential to reduce the weight of small-scale spur gears without negatively affecting vibration performance for low- and medium-speed applications. In this paper, the hybrid gear design and tooth microgeometry optimization technique that had been applied to small-scale spur gears was adapted for application to spur gears of aerospace-relevant scale, speed, and load. A single reduction drivetrain model was developed featuring large-scale hybrid spur gears, which was used to determine optimal tooth microgeometry modifications that minimized peak-to-peak transmission error. Static and dynamic transmission error analyses were then performed using the optimal microgeometries. Results were compared to those predicted for a similarly-optimized all-steel drivetrain. The application of optimal tooth microgeometries to large-scale hybrid gears led to a more significant decrease in a peak-to-peak transmission error than was observed for the small-scale gears. Similar to results for small-scale hybrid gears, the drivetrains featuring large-scale hybrid gears predicted similar dynamic transmission errors to their all-steel counterparts at low and medium speeds, while significantly different transmission errors were predicted at high speeds.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70218465","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper presents numerical calculations, on coaxial rotor systems, that show the variations of rotor thrust share with lift offset, system thrust, and advance ratio. The calculations are based on a coupled analysis between the U.S. Army's Rotorcraft Comprehensive Analysis System (RCAS) and a viscous vortex particle method. The level of agreement between calculations and experimental data is good in hover and mixed in edgewise flight. In hover and zero lift offset–a condition in which the upper rotor typically produces more thrust than the lower rotor–changing system thrust does not significantly alter the rotor thrust share. For advance ratios up to approximately 0.25, independently increasing lift offset increases the lower rotor thrust; this is an aeroelastic phenomenon that is eliminated with rigid blades. Independently increasing advance ratio leads to three distinct regions with different thrust sharing behaviors; these behaviors are governed by changes to the longitudinal skew of the upper rotor wake and its proximity to the lower rotor.
{"title":"Variations in Thrust Sharing for Torque-Balanced Lift-Offset Coaxial Rotors","authors":"J. Ho, H. Yeo","doi":"10.4050/jahs.68.022008","DOIUrl":"https://doi.org/10.4050/jahs.68.022008","url":null,"abstract":"This paper presents numerical calculations, on coaxial rotor systems, that show the variations of rotor thrust share with lift offset, system thrust, and advance ratio. The calculations are based on a coupled analysis between the U.S. Army's Rotorcraft Comprehensive Analysis System (RCAS) and a viscous vortex particle method. The level of agreement between calculations and experimental data is good in hover and mixed in edgewise flight. In hover and zero lift offset–a condition in which the upper rotor typically produces more thrust than the lower rotor–changing system thrust does not significantly alter the rotor thrust share. For advance ratios up to approximately 0.25, independently increasing lift offset increases the lower rotor thrust; this is an aeroelastic phenomenon that is eliminated with rigid blades. Independently increasing advance ratio leads to three distinct regions with different thrust sharing behaviors; these behaviors are governed by changes to the longitudinal skew of the upper rotor wake and its proximity to the lower rotor.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70218719","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Linghai Lu, Dheeraj Agarwal, G. Padfield, M. White, N. Cameron
High-fidelity rotorcraft flight simulation relies on the availability of a quality flight model that further demands a good level of understanding of the complexities arising from aerodynamic couplings and interference effects. This paper explores rotorcraft flight dynamics in the low-speed regime where such complexities abound and presents a new heuristic approach in the time domain to aid identification of nonlinear dynamics and fidelity assessment. The approach identifies flight model parameters “additively,” based on their contribution to the local dynamic response of the system, in contrast with conventional approaches where parameter values are identified to minimize errors over a whole maneuver. In these early investigations, identified low-order, rigid-body, linear models show good comparison with flight-test data. The approach is extended to explore nonlinearities attributed to the so-called maneuver wake distortion and wake skew effects emerging in larger maneuvers. The results show a good correlation for the proposed nonlinear model structure, demonstrated by its capability to capture the time response and variations of the stability and control derivatives with response magnitude.
{"title":"A New Heuristic Approach to Rotorcraft System Identification","authors":"Linghai Lu, Dheeraj Agarwal, G. Padfield, M. White, N. Cameron","doi":"10.4050/jahs.68.022005","DOIUrl":"https://doi.org/10.4050/jahs.68.022005","url":null,"abstract":"High-fidelity rotorcraft flight simulation relies on the availability of a quality flight model that further demands a good level of understanding of the complexities arising from aerodynamic couplings and interference effects. This paper explores rotorcraft flight dynamics in the low-speed regime where such complexities abound and presents a new heuristic approach in the time domain to aid identification of nonlinear dynamics and fidelity assessment. The approach identifies flight model parameters “additively,” based on their contribution to the local dynamic response of the system, in contrast with conventional approaches where parameter values are identified to minimize errors over a whole maneuver. In these early investigations, identified low-order, rigid-body, linear models show good comparison with flight-test data. The approach is extended to explore nonlinearities attributed to the so-called maneuver wake distortion and wake skew effects emerging in larger maneuvers. The results show a good correlation for the proposed nonlinear model structure, demonstrated by its capability to capture the time response and variations of the stability and control derivatives with response magnitude.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70219102","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fang Wang, Yu-Dong Wang, Xiang Gao, Yulin Ye, Rui Liu, Han Gao, Jie Jin
The slinger is an important configuration of an aeroengine combustion chamber. It is well matched to smaller gas turbines that are more sensitive to cost than larger and more sophisticated models. The slinger combustor is inherently low cost itself, by eliminating fuel injectors and much of the fuel tubing and manifolding and also reducing costs in the requirements of the main fuel pump by operating at fuel delta pressures significantly lower than conventional fuel systems. The slinger's inherent drawbacks of increased combustion liner surface area and less atomization are less of a concern in a lower temperature, lower cost small turbines. The slinger's internal flow is of great significance to fuel atomization. This paper conducts experiments and numerical simulations on the slinger fuel injector. Numerical analysis and high-speed photography of the fuel slinger were applied to investigate the film flow pattern inside the slinger and the liquid phase distribution inside the combustion chamber to predict the flow field in an aeroengine combustion chamber. The transient Reynolds-averaged Navier–Stokes method, the volume of fluid method, and the discrete phase method were adopted in the simulation, and a high-speed camera and the rotational rig were used to perform the experiments. The nonaxisymmetric flow was present in the slinger and the combustor space. In the simulation results, the total mass-flow rate varies with time. Each hole's mass-flow rate value in the slinger is also different at the same time. The Sauter mean diameter (SMD) difference for each injection orifice is relatively small compared with the SMD difference caused by a rotation rate. The spatial distribution of the spray is also uneven as shown in the result of different single discharge channels' mass-flow rates. The experimental photos confirmed the simulation outcomes. The general theoretical analysis was made that these nonaxisymmetric phenomena were driven by the combined action of centrifugal force, surface tension, and instability phenomenon.
{"title":"Exploration on Nonaxisymmetric Flow Phenomenon in a Slinger Injector","authors":"Fang Wang, Yu-Dong Wang, Xiang Gao, Yulin Ye, Rui Liu, Han Gao, Jie Jin","doi":"10.4050/jahs.67.032011","DOIUrl":"https://doi.org/10.4050/jahs.67.032011","url":null,"abstract":"The slinger is an important configuration of an aeroengine combustion chamber. It is well matched to smaller gas turbines that are more sensitive to cost than larger and more sophisticated models. The slinger combustor is inherently low cost itself, by eliminating fuel injectors and much of the fuel tubing and manifolding and also reducing costs in the requirements of the main fuel pump by operating at fuel delta pressures significantly lower than conventional fuel systems. The slinger's inherent drawbacks of increased combustion liner surface area and less atomization are less of a concern in a lower temperature, lower cost small turbines. The slinger's internal flow is of great significance to fuel atomization. This paper conducts experiments and numerical simulations on the slinger fuel injector. Numerical analysis and high-speed photography of the fuel slinger were applied to investigate the film flow pattern inside the slinger and the liquid phase distribution inside the combustion chamber to predict the flow field in an aeroengine combustion chamber. The transient Reynolds-averaged Navier–Stokes method, the volume of fluid method, and the discrete phase method were adopted in the simulation, and a high-speed camera and the rotational rig were used to perform the experiments. The nonaxisymmetric flow was present in the slinger and the combustor space. In the simulation results, the total mass-flow rate varies with time. Each hole's mass-flow rate value in the slinger is also different at the same time. The Sauter mean diameter (SMD) difference for each injection orifice is relatively small compared with the SMD difference caused by a rotation rate. The spatial distribution of the spray is also uneven as shown in the result of different single discharge channels' mass-flow rates. The experimental photos confirmed the simulation outcomes. The general theoretical analysis was made that these nonaxisymmetric phenomena were driven by the combined action of centrifugal force, surface tension, and instability phenomenon.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70217773","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A multiobjective design optimization technique for hybrid gears with sinusoidally shaped interlocks has been developed and applied to a hybrid spur gear. The hybrid gear concept consists of a metallic outer ring to support high tooth contact stress bonded to a composite inner web for weight reduction. Three design objectives were minimized for various geometric parameters controlling the composite–steel interface. Borg MOEA, a multiobjective evolutionary algorithm, was used to generate Pareto-optimal solutions for this design problem. Candidate designs were chosen from the Pareto-optimal set for more detailed analysis. From the results, we infer that the spur hybrid gear studied herein has the potential to decrease gear weight by approximately 27–45%, at the expense of a 22–34% increase in tooth pitch-point deflection, and that the optimal interface has between 15–20 cycles of the sinusoid with an amplitude of 0.25–0.35 mm.
{"title":"Design Optimization of a Hybrid Spur Gear Including Tooth Bending Effects","authors":"Sean Gauntt, Sean Mcintyre, R. Campbell","doi":"10.4050/jahs.67.042009","DOIUrl":"https://doi.org/10.4050/jahs.67.042009","url":null,"abstract":"A multiobjective design optimization technique for hybrid gears with sinusoidally shaped interlocks has been developed and applied to a hybrid spur gear. The hybrid gear concept consists of a metallic outer ring to support high tooth contact stress bonded to a composite inner web for weight reduction. Three design objectives were minimized for various geometric parameters controlling the composite–steel interface. Borg MOEA, a multiobjective evolutionary algorithm, was used to generate Pareto-optimal solutions for this design problem. Candidate designs were chosen from the Pareto-optimal set for more detailed analysis. From the results, we infer that the spur hybrid gear studied herein has the potential to decrease gear weight by approximately 27–45%, at the expense of a 22–34% increase in tooth pitch-point deflection, and that the optimal interface has between 15–20 cycles of the sinusoid with an amplitude of 0.25–0.35 mm.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70218244","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper investigates the upward scalability of a cycloidal rotor (also known as a cyclorotor) from an aeromechanics standpoint while utilizing a two-dimensional computational fluid dynamics (CFD) solver and a lower order aeroelastic model. The CFD results show that the nondimensional thrust remains almost unchanged with increasing Reynolds number, while the nondimensional torque and power decrease significantly from Re=104 to 105, which clearly shows that the cycloidal rotor scales up favorably from thrust production and aerodynamic efficiency standpoints. The structural scalability study shows that as the cyclorotor size is increased, the blade weight per unit thrust remains constant; however, the blade stress increases monotonically if the rotor geometry is kept similar. This monotonic increase in the blade stress is found to be independent of the blade structural design. To bound the blade stress with increasing size, the diameter of the cyclorotor needs to be increased at a faster rate compared to the blade span, which reduces the rotor aspect ratio (blade-span/rotor-diameter). Proper scaling laws necessary to bound the blade stress are formulated. Utilizing these insights, an optimization framework based on a genetic algorithm is developed to determine optimal cyclorotor configurations for a thrust range from 1 to 1000 lb.
{"title":"Understanding Upward Scalability of Cycloidal Rotors for Large-Scale UAS Applications","authors":"Atanu Halder, Moble Benedict","doi":"10.4050/jahs.67.042002","DOIUrl":"https://doi.org/10.4050/jahs.67.042002","url":null,"abstract":"This paper investigates the upward scalability of a cycloidal rotor (also known as a cyclorotor) from an aeromechanics standpoint while utilizing a two-dimensional computational fluid dynamics (CFD) solver and a lower order aeroelastic model. The CFD results show that the nondimensional thrust remains almost unchanged with increasing Reynolds number, while the nondimensional torque and power decrease significantly from Re=104 to 105, which clearly shows that the cycloidal rotor scales up favorably from thrust production and aerodynamic efficiency standpoints. The structural scalability study shows that as the cyclorotor size is increased, the blade weight per unit thrust remains constant; however, the blade stress increases monotonically if the rotor geometry is kept similar. This monotonic increase in the blade stress is found to be independent of the blade structural design. To bound the blade stress with increasing size, the diameter of the cyclorotor needs to be increased at a faster rate compared to the blade span, which reduces the rotor aspect ratio (blade-span/rotor-diameter). Proper scaling laws necessary to bound the blade stress are formulated. Utilizing these insights, an optimization framework based on a genetic algorithm is developed to determine optimal cyclorotor configurations for a thrust range from 1 to 1000 lb.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70218261","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ariel Walter, M. McKay, R. Niemiec, F. Gandhi, Christina M. Ivler
Fixed-pitch, variable-RPM quadcopters of increasing size are simulated in hover. Three aircraft sizes are considered, with rotor diameters of 4, 6, and 8 ft (1.2, 1.8, and 2.4 m) and gross weights of 300, 680, and 1200 lb (136, 308, and 544 kg) respectively. Control design is performed for each aircraft using CONDUIT®, first using standard ADS-33E-PRF handling qualities specifications. Froude scaling is then applied to the specifications in order to design more comparable, aggressive controllers for the two smaller aircraft. Piloted commands and gust inputs are simulated in the time domain in order to estimate the necessary motor current margins needed for adequate maneuverability local to hover. Of the maneuvers considered, a yaw rate step requires the highest current margin for the smallest aircraft, while the longitudinal velocity step requires the highest current margin for the others, regardless of the Froude scaling of the handling qualities metrics. Using the maximum current values from these simulations, the motor weight fraction is 8.3–10.6% for the 300-lb vehicle, 11.6–13.0% for the 680-lb vehicle, and 15.8% for the 1200 lb. Motor weight requirements can be reduced on the larger two aircraft by flying with the pitch and roll axes exclusively in the attitude command, attitude hold mode, rather than translational rate command. In this case, step commands in yaw rate are limiting for the 680-lb vehicle (10.7–11.8% motor weight fraction) and heave commands are limiting for the 1200-lb vehicle (13.6% motor weight fraction). Estimated motor weight requirements are also reduced by decreasing the rotor inertia and introducing additional filtering into the aircraft commands.
{"title":"Hover Handling Qualities of Fixed-Pitch, Variable-RPM Quadcopters of Increasing Size","authors":"Ariel Walter, M. McKay, R. Niemiec, F. Gandhi, Christina M. Ivler","doi":"10.4050/jahs.67.042010","DOIUrl":"https://doi.org/10.4050/jahs.67.042010","url":null,"abstract":"Fixed-pitch, variable-RPM quadcopters of increasing size are simulated in hover. Three aircraft sizes are considered, with rotor diameters of 4, 6, and 8 ft (1.2, 1.8, and 2.4 m) and gross weights of 300, 680, and 1200 lb (136, 308, and 544 kg) respectively. Control design is performed for each aircraft using CONDUIT®, first using standard ADS-33E-PRF handling qualities specifications. Froude scaling is then applied to the specifications in order to design more comparable, aggressive controllers for the two smaller aircraft. Piloted commands and gust inputs are simulated in the time domain in order to estimate the necessary motor current margins needed for adequate maneuverability local to hover. Of the maneuvers considered, a yaw rate step requires the highest current margin for the smallest aircraft, while the longitudinal velocity step requires the highest current margin for the others, regardless of the Froude scaling of the handling qualities metrics. Using the maximum current values from these simulations, the motor weight fraction is 8.3–10.6% for the 300-lb vehicle, 11.6–13.0% for the 680-lb vehicle, and 15.8% for the 1200 lb. Motor weight requirements can be reduced on the larger two aircraft by flying with the pitch and roll axes exclusively in the attitude command, attitude hold mode, rather than translational rate command. In this case, step commands in yaw rate are limiting for the 680-lb vehicle (10.7–11.8% motor weight fraction) and heave commands are limiting for the 1200-lb vehicle (13.6% motor weight fraction). Estimated motor weight requirements are also reduced by decreasing the rotor inertia and introducing additional filtering into the aircraft commands.","PeriodicalId":50017,"journal":{"name":"Journal of the American Helicopter Society","volume":null,"pages":null},"PeriodicalIF":1.5,"publicationDate":"2022-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70218337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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