Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16840
N. Taymourtash, G. Gibertini, G. Quaranta, A. Zanotti
State-space representation of the dynamic inflow is an essential element in rotorcraft flight mechanics modeling and simulation. Identification of a reliable low-order model which is able to predict the transient response of the inflow as well as the steady part, becomes even more important during the maneuvering flights. The objective of this paper is to exploit an experimental setup, consists of a helicopter model and a simplified ship geometry, to investigate the possible effect of the wake interactions with environmental elements such as ground effect or airwake of the ship, on the time constants associated with the buildup of the inflow states. A series of wind tunnel tests were performed, simulating various flight conditions, including hover and forward flight, inside and outside of the ground effect, and the rotor over the deck of the SFS1 at two different positions with respect to the ship super-structure, with the wind coming from two different directions. After trimming the rotor at each flight condition, a sequence of pitch excitation commands were applied to the collective, lateral and longitudinal cyclic in order to excite the induced flow of the rotor. The frequency analysis of the measured aerodynamic loads shows the variation of the time lag, while rotor is operating in the same trim condition, but different positions with respect to the ground or the flight deck.
{"title":"Experimental Investigation of Unsteady Inflow for a Helicopter Model in Shipboard Operations","authors":"N. Taymourtash, G. Gibertini, G. Quaranta, A. Zanotti","doi":"10.4050/f-0077-2021-16840","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16840","url":null,"abstract":"\u0000 State-space representation of the dynamic inflow is an essential element in rotorcraft flight mechanics modeling and simulation. Identification of a reliable low-order model which is able to predict the transient response of the inflow as well as the steady part, becomes even more important during the maneuvering flights. The objective of this paper is to exploit an experimental setup, consists of a helicopter model and a simplified ship geometry, to investigate the possible effect of the wake interactions with environmental elements such as ground effect or airwake of the ship, on the time constants associated with the buildup of the inflow states. A series of wind tunnel tests were performed, simulating various flight conditions, including hover and forward flight, inside and outside of the ground effect, and the rotor over the deck of the SFS1 at two different positions with respect to the ship super-structure, with the wind coming from two different directions. After trimming the rotor at each flight condition, a sequence of pitch excitation commands were applied to the collective, lateral and longitudinal cyclic in order to excite the induced flow of the rotor. The frequency analysis of the measured aerodynamic loads shows the variation of the time lag, while rotor is operating in the same trim condition, but different positions with respect to the ground or the flight deck.\u0000","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"7 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130582215","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16761
C. Mballo, J. Prasad
This paper considers synthesis of a load alleviation scheme based on active rotor control for helicopter component life extension. The proposed load alleviation scheme is formulated in a model predictive framework. Using a reduced order coupled body/rotor/inflow dynamic model onboard the vehicle, real-time estimates of component loads arising due to vehicle maneuvers are generated. The load estimates in turn are used in an optimal control formulation to obtain the higher harmonic individual blade control (IBC) inputs needed to reduce selected harmonics of component loads. The performance of the proposed component load alleviation using IBC scheme is implemented in a comprehensive nonlinear model of a generic helicopter. Nonlinear model simulations show that significant individual harmonic load reduction can be obtained with very little impact on the maneuver performance and minimal impact on the uncontrolled harmonics of component loads.
{"title":"Individual Blade Control for Component Load Alleviation using a Model Predictive Control Formulation","authors":"C. Mballo, J. Prasad","doi":"10.4050/f-0077-2021-16761","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16761","url":null,"abstract":"\u0000 This paper considers synthesis of a load alleviation scheme based on active rotor control for helicopter component life extension. The proposed load alleviation scheme is formulated in a model predictive framework. Using a reduced order coupled body/rotor/inflow dynamic model onboard the vehicle, real-time estimates of component loads arising due to vehicle maneuvers are generated. The load estimates in turn are used in an optimal control formulation to obtain the higher harmonic individual blade control (IBC) inputs needed to reduce selected harmonics of component loads. The performance of the proposed component load alleviation using IBC scheme is implemented in a comprehensive nonlinear model of a generic helicopter. Nonlinear model simulations show that significant individual harmonic load reduction can be obtained with very little impact on the maneuver performance and minimal impact on the uncontrolled harmonics of component loads.\u0000","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130269987","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16883
Tom DuBois, John Kisor, R. Matthews, M. Orlovsky
From a military operations perspective, the primary goals of the Modular Open Systems Approach (MOSA) [Ref. 1] are Affordable Life Cycle Cost (ALC), Maintain Capability Overmatch (MCO), and Faster-to-Field (FtF). Achieving these goals is directly related to the ability of the architecture to enable reuse and interoperability. The importance of this association is amplified with the assumption of a Family of System (FoS) acquisition where mission-level capabilities are needed by multiple products. Accordingly, the value of MOSA to architecture development in a FoS acquisition is directly related to the ability of the resulting architecture to enable reuse and interoperability of capabilities across the products that comprise the FoS. Not only is the resulting architecture a key enabler, but the governance of that architecture is also critical to long-term success for a FoS with products that are not on the exact same development timeline. Model-Based Engineering (MBE) within a digital thread offers structures and processes that assist both architecture development and governance while integrating the best features of Model-Based Systems Engineering (MBSE) [Ref. 2], DevSecOps [Ref. 3, 4, 5, 6], open system standards, and Agile methodologies [Ref. 7]. However, the usage of such structures and processes needs to be done carefully to avoid situations in which the process itself can enable the intended or unintended consequence of sacrificing the benefits of MOSA while implementing the process. Without the right discipline, even developers with the best intentions for achieving MOSA benefits can end up building architectures, components, and build processes that inhibit the realization of MOSA benefits and complicate governance to an intractable level [Ref. 8]. Another concern is organizations that actually seek flaws in the development or governance processes and use those flaws to claim compliance with MOSA while at the same time embedding locks to guarantee future business contrary to MOSA goals. This paper will identify the discipline needed to achieve the benefits of MOSA in a FoS acquisition and recommendations for architecture development and life cycle governance. Building upon previous work [Ref. 9], this paper will present use cases and examples of pitfalls to avoid with suggestions on how to avoid them. The most significant recommendation provided in this paper is the development of a component-based architecture to be used as a basis to identify opportunities for reuse and interoperability across products and how to use it to establish a governance framework for an FoS-based acquisition. This paper describes the steps to derive a component-based architecture starting with a modeled reference architecture. Derivation follows the pattern endorsed by the US Government in their Comprehensive Architecture Strategy [Ref. 10] and includes process steps for iterative top-down decomposition and bottom-up re-composition. This paper presents study r
{"title":"Approach to Architecture Development Assuming a Modular Open Systems Approach (MOSA) for a Family of Systems (FoS) Acquisition","authors":"Tom DuBois, John Kisor, R. Matthews, M. Orlovsky","doi":"10.4050/f-0077-2021-16883","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16883","url":null,"abstract":"From a military operations perspective, the primary goals of the Modular Open Systems Approach (MOSA) [Ref. 1] are Affordable Life Cycle Cost (ALC), Maintain Capability Overmatch (MCO), and Faster-to-Field (FtF). Achieving these goals is directly related to the ability of the architecture to enable reuse and interoperability. The importance of this association is amplified with the assumption of a Family of System (FoS) acquisition where mission-level capabilities are needed by multiple products. Accordingly, the value of MOSA to architecture development in a FoS acquisition is directly related to the ability of the resulting architecture to enable reuse and interoperability of capabilities across the products that comprise the FoS. Not only is the resulting architecture a key enabler, but the governance of that architecture is also critical to long-term success for a FoS with products that are not on the exact same development timeline. Model-Based Engineering (MBE) within a digital thread offers structures and processes that assist both architecture development and governance while integrating the best features of Model-Based Systems Engineering (MBSE) [Ref. 2], DevSecOps [Ref. 3, 4, 5, 6], open system standards, and Agile methodologies [Ref. 7]. However, the usage of such structures and processes needs to be done carefully to avoid situations in which the process itself can enable the intended or unintended consequence of sacrificing the benefits of MOSA while implementing the process. Without the right discipline, even developers with the best intentions for achieving MOSA benefits can end up building architectures, components, and build processes that inhibit the realization of MOSA benefits and complicate governance to an intractable level [Ref. 8]. Another concern is organizations that actually seek flaws in the development or governance processes and use those flaws to claim compliance with MOSA while at the same time embedding locks to guarantee future business contrary to MOSA goals. This paper will identify the discipline needed to achieve the benefits of MOSA in a FoS acquisition and recommendations for architecture development and life cycle governance. Building upon previous work [Ref. 9], this paper will present use cases and examples of pitfalls to avoid with suggestions on how to avoid them. The most significant recommendation provided in this paper is the development of a component-based architecture to be used as a basis to identify opportunities for reuse and interoperability across products and how to use it to establish a governance framework for an FoS-based acquisition. This paper describes the steps to derive a component-based architecture starting with a modeled reference architecture. Derivation follows the pattern endorsed by the US Government in their Comprehensive Architecture Strategy [Ref. 10] and includes process steps for iterative top-down decomposition and bottom-up re-composition. This paper presents study r","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128848823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16730
C. Lanouette, J. Hirsch
Integrating the vertical flight in our modern environment is an engine of progress for any technological product. H160 helicopter is a good illustration of the most recent market evolution. Recently certified by the European Union Aviation Safety Agency (EASA) in July 2020, the last Airbus Helicopters' multi-role twin-engine rotorcraft introduced the latest technological innovations for the benefit of all: passengers, pilots, operators, population. Comfort improvement and sound reduction are some examples of added values of this helicopter where the Blue Edge(TM) main rotor blade is exploited as a new technological mean as presented in Ref. 1 and Ref. 2. Nevertheless, such progress is only achievable if the expectations of continuous improvements on the safety and the airworthiness are satisfied. The paper presents the optimization studies of the serial design, the means of compliance and substantiations according to the latest standard of certification regulations applied on the Blue Edge(TM) main rotor blades with a special focus on the fatigue tolerance and threat assessment.
{"title":"Lift Off of H160 with Blue Edge(TM) Blade","authors":"C. Lanouette, J. Hirsch","doi":"10.4050/f-0077-2021-16730","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16730","url":null,"abstract":"\u0000 Integrating the vertical flight in our modern environment is an engine of progress for any technological product. H160 helicopter is a good illustration of the most recent market evolution. Recently certified by the European Union Aviation Safety Agency (EASA) in July 2020, the last Airbus Helicopters' multi-role twin-engine rotorcraft introduced the latest technological innovations for the benefit of all: passengers, pilots, operators, population. Comfort improvement and sound reduction are some examples of added values of this helicopter where the Blue Edge(TM) main rotor blade is exploited as a new technological mean as presented in Ref. 1 and Ref. 2. Nevertheless, such progress is only achievable if the expectations of continuous improvements on the safety and the airworthiness are satisfied. The paper presents the optimization studies of the serial design, the means of compliance and substantiations according to the latest standard of certification regulations applied on the Blue Edge(TM) main rotor blades with a special focus on the fatigue tolerance and threat assessment.\u0000","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"151 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126752838","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16772
Ahmad Haidar, Luca Belluomini, A. Trezzini
The certification of the Leonardo Helicopters AW609 tiltrotor includes certifying, for the first time, the tiltrotor drive train architecture in a civilian aircraft. This paper presents a Simulink-based linear analysis that predicts torsional stability across the flight envelope as well as sensitivity to important design parameters. The paper also describes the ground and flight-test methodology carried out in the certification test campaign. The post-processing of experimental data is summarized, and results from the certification test campaign are presented as model correlation.
{"title":"AW609 Civil Tiltrotor Drive Train Torsional Stability Analysis and Certification Test Campaign ","authors":"Ahmad Haidar, Luca Belluomini, A. Trezzini","doi":"10.4050/f-0077-2021-16772","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16772","url":null,"abstract":"\u0000 The certification of the Leonardo Helicopters AW609 tiltrotor includes certifying, for the first time, the tiltrotor drive train architecture in a civilian aircraft. This paper presents a Simulink-based linear analysis that predicts torsional stability across the flight envelope as well as sensitivity to important design parameters. The paper also describes the ground and flight-test methodology carried out in the certification test campaign. The post-processing of experimental data is summarized, and results from the certification test campaign are presented as model correlation.\u0000","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"46 6","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114124377","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16708
G. Gress
This paper describes and reports on the status of an electric vertical take-off and landing (eVTOL) aircraft type being developed at Athena Aero Corp that began life as a concept entry in the Boeing-sponsored GoFly Challenge initiated in Sept. 2017. Known as a duct-winged inertial bicopter, the concept was intended to satisfy the Challenge’s basic requirements of giving the pilot an unobstructed forward view within a 90-degree cone and of being able to: 1.take off and land (essentially) vertically, 2.transport a 200 lb. person six times around two pylons a half-mile apart at a speed of at least 30kts, and 3.stay aloft for 20 minutes with a 10-minute fuel/energy reserve, all in a single flight. Additionally, the aircraft could be no larger than 8.5 ft. in any direction and had to be quieter than 85 dB at 50 ft. on take-off.
{"title":"Duct-Winged Inertial Bicopter: Theory, Design and Testing","authors":"G. Gress","doi":"10.4050/f-0077-2021-16708","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16708","url":null,"abstract":"\u0000 This paper describes and reports on the status of an electric vertical take-off and landing (eVTOL) aircraft type being developed at Athena Aero Corp that began life as a concept entry in the Boeing-sponsored GoFly Challenge initiated in Sept. 2017. Known as a duct-winged inertial bicopter, the concept was intended to satisfy the Challenge’s basic requirements of giving the pilot an unobstructed forward view within a 90-degree cone and of being able to: \u00001.take off and land (essentially) vertically, \u00002.transport a 200 lb. person six times around two pylons a half-mile apart at a speed of at least 30kts, and \u00003.stay aloft for 20 minutes with a 10-minute fuel/energy reserve,\u0000all in a single flight. Additionally, the aircraft could be no larger than 8.5 ft. in any direction and had to be quieter than 85 dB at 50 ft. on take-off. \u0000","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125266750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16905
Manogna Ammalladene-Venkata, Christine Groitl, Omkar Halbe, Christian Seidel, Christoph Stahl
Aviation statistics identify collision with terrain and obstacles as a leading cause of helicopter accidents. Assisting helicopter pilots in detecting the presence of obstacles can partly mitigate the risk of collisions. However, only a limited number of helicopters in operation have an installed helicopter terrain awareness and warning system (HTAWS), while the cost of active obstacle warning systems remains prohibitive for many civil operators. In this work, we apply machine learning to automate obstacle detection and classification in combination with any commercially-available airborne optical sensor. While numerous techniques for learning-based object detection have appeared in the literature, many of them are data- and computation-intensive. Our approach seeks to balance the performance in regards to the detection and classification accuracy on the one hand, and the amount of training data and runtime performance on the other hand. Specifically, our approach combines the invariant feature extraction ability of pre-trained deep Convolutional Neural Networks (CNNs) and the high-speed training and classification ability of a novel, proprietary frequency-domain Support Vector Machine (SVM) method. In this paper, we present the CNN+SVM method for efficient obstacle detection and classification. We describe the experimental setup comprising datasets of pre-defined classes of obstacles – pylons, chimneys, antennas, towers, wind turbines, flying aircraft – from airborne video sequences of low-altitude helicopter flight. We analyze the performance results using average precision, average recall, and runtime performance metrics on representative test data. Finally, we present a simple architecture for a real-time, on-board evaluation of automatic vision-based obstacle detection.
{"title":"Deep Learning Based Obstacle Awareness from Airborne Optical Sensors","authors":"Manogna Ammalladene-Venkata, Christine Groitl, Omkar Halbe, Christian Seidel, Christoph Stahl","doi":"10.4050/f-0077-2021-16905","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16905","url":null,"abstract":"\u0000 Aviation statistics identify collision with terrain and obstacles as a leading cause of helicopter accidents. Assisting helicopter pilots in detecting the presence of obstacles can partly mitigate the risk of collisions. However, only a limited number of helicopters in operation have an installed helicopter terrain awareness and warning system (HTAWS), while the cost of active obstacle warning systems remains prohibitive for many civil operators. In this work, we apply machine learning to automate obstacle detection and classification in combination with any commercially-available airborne optical sensor. While numerous techniques for learning-based object detection have appeared in the literature, many of them are data- and computation-intensive. Our approach seeks to balance the performance in regards to the detection and classification accuracy on the one hand, and the amount of training data and runtime performance on the other hand. Specifically, our approach combines the invariant feature extraction ability of pre-trained deep Convolutional Neural Networks (CNNs) and the high-speed training and classification ability of a novel, proprietary frequency-domain Support Vector Machine (SVM) method. In this paper, we present the CNN+SVM method for efficient obstacle detection and classification. We describe the experimental setup comprising datasets of pre-defined classes of obstacles – pylons, chimneys, antennas, towers, wind turbines, flying aircraft – from airborne video sequences of low-altitude helicopter flight. We analyze the performance results using average precision, average recall, and runtime performance metrics on representative test data. Finally, we present a simple architecture for a real-time, on-board evaluation of automatic vision-based obstacle detection. \u0000","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122789155","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16767
Reinhard Lojewski, C. Kessler
Soft-in-plane rotor systems are susceptible to a self-induced vibration phenomenon called ground resonance. This dynamic instability results from lag motions of the rotor blades coupling with airframe degrees of freedom while the helicopter is in ground contact. As an addition to previous studies of nonlinear landing gear effects, this work presents the Matrix Pencil Method as a useful additional tool for signal analysis of perturbed nonlinear systems. Contrary to simple logarithmic decrements of decaying time-series, the Matrix Pencil Method allows additional insight into the underlying structure. This makes the method interesting for ground resonance. Additionally, the Lyapunov Exponent Method is introduced to highlight and analyze nonlinear effects in helicopter substitute models.
{"title":"Analysis Methods for Ground Resonance in Partial Ground Contact ","authors":"Reinhard Lojewski, C. Kessler","doi":"10.4050/f-0077-2021-16767","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16767","url":null,"abstract":"\u0000 Soft-in-plane rotor systems are susceptible to a self-induced vibration phenomenon called ground resonance. This dynamic instability results from lag motions of the rotor blades coupling with airframe degrees of freedom while the helicopter is in ground contact. As an addition to previous studies of nonlinear landing gear effects, this work presents the Matrix Pencil Method as a useful additional tool for signal analysis of perturbed nonlinear systems. Contrary to simple logarithmic decrements of decaying time-series, the Matrix Pencil Method allows additional insight into the underlying structure. This makes the method interesting for ground resonance. Additionally, the Lyapunov Exponent Method is introduced to highlight and analyze nonlinear effects in helicopter substitute models.\u0000","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131270441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16716
R. Healy, F. Gandhi, J. McCauley, O. Sahni
This study investigates the interactional aerodynamics of hovering side-by-side rotors in ground effect. The 5.5 ft diameter, 3-bladed fixed-pitched rotors are simulated using CFD at a targeted 5 lb/ft2 disk loading. Simulations are performed using the commercial Navier Stokes solver, AcuSolve, with a detached eddy simulation (DES) model. Side-by-side rotors are simulated at two heights above the ground (H/D = 0.5 and H/D = 1), and with two hub-hub separation distances (3R and 2.5R). The performance of side-by-side rotors in ground effect are compared to isolated rotors out of ground effect. Between the side-by-side rotors in ground effect, a highly turbulent mixing region is identified where the wakes of each rotor collide. The flow fountains upwards, as well as exits outwards (along a direction normal to a plane connecting the two rotor hubs). The fountaining between rotors reaches up to 1.5R above the ground, and as blades at H/D = 0.5 traverse the highly turbulent flow, strong vibratory loading is induced, and a larger thrust loss is observed outboard between the rotors. Side-by-side rotors at H/D = 0.5 with 2.5R hub-hub spacing produce peak-to-peak thrust oscillations up to 16% the steady thrust. Rotors positioned higher, at H/D = 1 are above the turbulent mixing flow, and produce significantly lower vibratory loads. The spacing between rotors at H/D = 0.5 and 3R hub-hub separation allows strong vortical structures to develop between the rotors which move from side-to-side over multiple revolutions. When the vorticity is positioned closer to one of the rotors, it produces a greater lift deficit over the outboard region and higher vibratory loading. For rotors closer together, at H/D = 0.5 and 2.5R separation, the vortical structures between rotors are constrained to a more concentrated area, and show less side-to-side drift.
{"title":"A Computational Investigation of Side-by-Side Rotors in Ground Effect","authors":"R. Healy, F. Gandhi, J. McCauley, O. Sahni","doi":"10.4050/f-0077-2021-16716","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16716","url":null,"abstract":"\u0000 This study investigates the interactional aerodynamics of hovering side-by-side rotors in ground effect. The 5.5 ft diameter, 3-bladed fixed-pitched rotors are simulated using CFD at a targeted 5 lb/ft2 disk loading. Simulations are performed using the commercial Navier Stokes solver, AcuSolve, with a detached eddy simulation (DES) model. Side-by-side rotors are simulated at two heights above the ground (H/D = 0.5 and H/D = 1), and with two hub-hub separation distances (3R and 2.5R). The performance of side-by-side rotors in ground effect are compared to isolated rotors out of ground effect. Between the side-by-side rotors in ground effect, a highly turbulent mixing region is identified where the wakes of each rotor collide. The flow fountains upwards, as well as exits outwards (along a direction normal to a plane connecting the two rotor hubs). The fountaining between rotors reaches up to 1.5R above the ground, and as blades at H/D = 0.5 traverse the highly turbulent flow, strong vibratory loading is induced, and a larger thrust loss is observed outboard between the rotors. Side-by-side rotors at H/D = 0.5 with 2.5R hub-hub spacing produce peak-to-peak thrust oscillations up to 16% the steady thrust. Rotors positioned higher, at H/D = 1 are above the turbulent mixing flow, and produce significantly lower vibratory loads. The spacing between rotors at H/D = 0.5 and 3R hub-hub separation allows strong vortical structures to develop between the rotors which move from side-to-side over multiple revolutions. When the vorticity is positioned closer to one of the rotors, it produces a greater lift deficit over the outboard region and higher vibratory loading. For rotors closer together, at H/D = 0.5 and 2.5R separation, the vortical structures between rotors are constrained to a more concentrated area, and show less side-to-side drift.\u0000","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"47 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127694759","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-10DOI: 10.4050/f-0077-2021-16871
R. Hallez, E. Lorenzo
Increasing complexity in modern aircraft systems and structures makes it challenging for engineers to develop aircraft within time and budget constraints. This is particularly true in the context of new Vertical Take-off and Landing (VTOL) vehicle development where many disruptive aircraft configurations are being studied. Ground and flight testing help to validate aircraft structural dynamic performance and prove that the aircraft meets certification requirements. Several experimental techniques have been developed lately to help getting deeper insight into aircraft structural dynamics and are helpful to accelerate the verification and certification process of new VTOL vehicles. Some of these methods have been recently industrialized and are available in commercial hardware and software solutions. This includes techniques for contactless measurements based on digital image correlation as well as methods for accelerated modal testing and identification of non-linearities in aircraft structures. These methods are presented here and positioned in the context of accelerated VTOL aircraft development.
{"title":"State-of-the-art Experimental Techniques for VTOL Structural Dynamics","authors":"R. Hallez, E. Lorenzo","doi":"10.4050/f-0077-2021-16871","DOIUrl":"https://doi.org/10.4050/f-0077-2021-16871","url":null,"abstract":"\u0000 Increasing complexity in modern aircraft systems and structures makes it challenging for engineers to develop aircraft within time and budget constraints. This is particularly true in the context of new Vertical Take-off and Landing (VTOL) vehicle development where many disruptive aircraft configurations are being studied. Ground and flight testing help to validate aircraft structural dynamic performance and prove that the aircraft meets certification requirements. Several experimental techniques have been developed lately to help getting deeper insight into aircraft structural dynamics and are helpful to accelerate the verification and certification process of new VTOL vehicles. Some of these methods have been recently industrialized and are available in commercial hardware and software solutions. This includes techniques for contactless measurements based on digital image correlation as well as methods for accelerated modal testing and identification of non-linearities in aircraft structures. These methods are presented here and positioned in the context of accelerated VTOL aircraft development.\u0000","PeriodicalId":273020,"journal":{"name":"Proceedings of the Vertical Flight Society 77th Annual Forum","volume":"43 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2021-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133309028","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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