Browse Topic: Frames
By its seventh flight after the first take-off, the RACER (Rapid And Cost-Effective Rotorcraft) demonstrator smoothly reached the targeted 220kts speed in stabilized forward flight, validating the high-speed compound architecture developed by Airbus Helicopters in the frame of Clean Sky 2 programme. During the flight envelope exploration, the dynamic behavior of the main rotor was carefully assessed, by monitoring the vibratory loads and validating its aeroelastic stability. Particular care was taken to validate the predicted stability domain of the Dual Rotor phenomenon, a particular case of flap-lag coupling associated with high-speed flight conditions. This paper presents the most significant results shaping the success of RACER flight test campaign. After having introduced the theoretical background and the associated analytical equations, the simulation framework based on the comprehensive analysis tool STORM is presented to discuss the numerical resolution of the stability problem. Then, the rotor dynamics loads and airframe vibratory behavior of RACER are closely examined to demonstrate the absence of any sign of instability, in the various flight conditions offered by its rotor and wing configuration. At last the flight test results are compared to the computed stability domain to assess the margins and estimate the high-speed potential of the rotorcraft.
Developed in the frame of the European Clean Sky 2 program, the RACER High Speed Helicopter Demonstrator of Airbus performed its maiden flight on April 25th, 2024. In the continuity of the previous high-speed demonstrator X3 (1st flight in 2010) the RACER is a 7/8t (15000 / 18000 lb) class compound helicopter powered by two SHE Aneto-1X engines, including a wing and two propellers. The tail rotor is removed as the two propellers control the yaw axis by differential thrust. At flight 07, with its initial default settings, it reached a true airspeed of 227 kts in level flight, exceeding its objective of 220 kts.
Over the last 90 years, many concepts of lifting payload with a single tethered fixed-wing aircraft have been proposed. In this concept, an airplane flies along a quasi-circular flight path and the payload should remain at the center of this circle. The main challenge encountered has been payload stability in hover (i.e., when the payload is fixed in space and the aircraft flies along a quasi-circular path above). In calm conditions, lengthening the tether to reach two or three kilometers (1.5 mile) has been proven to stabilize the payload in an orbit with a radius of the order of 1 meter (3 ft). However, the presence of wind has shown a drastic reduction in payload stability. At the end of the 1990s, a patent proposed to add a thruster-based stabilization device onto the payload but no further studies explored such a concept. This study proposes a new concept inspired by the former. The main difference lies in the addition of a reel-in mechanism to control and stabilize the payload in the vertical direction. This work analyzes the impact of the wind on this new concept in hover. The results have shown a maximum power requirement of 37 kW (60 hp) for the aircraft and 15 kW (20 hp) for the stabilization device to lift a 300 kg (660 lbm) payload fixed in the inertial frame with a 400 m (1,300 ft) long tether. This work has highlighted the high impact of the tether force on the towing airplane and therefore a means to reduce this impact is required.
This paper presents activities performed in the frame of MOTUS, a DGAC-funded research project, to better understand and reduce annoyance of helicopter operations. It focuses on the operational context of La Réunion island where local authorities intend to define concrete measures to answer multiple complaints from the population. In parallel with ongoing research towards a better understanding of short- and long-term annoyance thanks to both laboratory and field studies, the paper presents an in-depth analysis of helicopter operations in the area. Furthermore, specific recommendations on low noise operations are proposed to local operators in order to reduce their noise footprint and improve helicopter acceptance.
AAM concepts use multiple distributed electric motors driving propellers and rotors to augment or directly generate lift and propulsive forces. Several current concepts incorporate separate drive systems for providing vertical lift, for takeoff and landing, and propulsive thrust for wing-borne cruising flight. Measurement of loads and performance on these rotating systems is very important in both the design and development stage, as well as for certification use and ultimately supporting HUMS monitoring. However, providing instrumentation in the rotating frame and extracting their associated measurements is often problematical, as it requires some means for both power and signals to bridge the rotating interface between the blade of the rotor/propeller and the fixed frame (fuselage) system. This paper describes work conducted to leverage prior CDI development of a novel optical telemetry/instrumentation system to create a prototype unit that can support ground and flight tests, allowing for multiple installations on the many rotors that constitute current AAM configurations. The resulting hardware was designed to expand the capabilities developed previously in types and rates of data collected, on-board processing, and user configuration options, supporting NASA and commercial organizations in their testing activities.
Airbus is certifying new H160 helicopter, first serial application of the Blue EdgeTM rotor system, easily recognizable with its double leading edge swept shape. The reduction of the blade-vortex interaction noise has been the main driver of this design, studied since the 1990s, in collaboration between DLR, ONERA and Eurocopter (since become Airbus). From the project ERATO (Etude d'un Rotor Aeroacoustique Technologiquement Optimise = aeroacoustically optimized rotor), the Blue EdgeTM blade design became the trademark of the last rotor generation whose the history is summarized in Ref. 1. In 2014, a first extrapolation of this type of shape has been developed and tested in the frame of BluecopterTM demonstrator as described in Ref. 2. The five-bladed bearingless rotor flew on EC135 in order to explore a low tip speed within new optimized eco airfoils and twist distribution. At the same time, new studies of Blue EdgeTM design has been performed with other objectives: keeping the shape for the BVI acoustic reduction, multi-objective optimization of airfoils, twist and chord for better aerodynamic performances. This project, internally called PROTEGE (Pale pRincipale ecOlogique en composiTe de nouvellE GEneration – New generation of ecological composite blade), flew on H225 demonstrator. The paper presents an overview of the design development of this new blade and the results about the dynamic behavior, the aerodynamic performances and acoustic reduction in various flight conditions. The acquired results bring new elements in the Blue EdgeTM blade which strengthen the interest of this design for the BVI acoustic reduction.
This work proposes a novel relationship between pilot workload and optic flow during visual approach-to-land maneuvers. A simulation experiment was conducted at NASA Ames Vertical Motion Simulator (VMS) to evaluate the workload associated with operating two candidate Army Future Vertical Lift (FVL) vehicles: a compound (coaxialrotor and push-prop) vehicle, and a tilt-rotor vehicle. The UH-60 was included in the evaluation as a baseline reference. Sixteen experienced military pilots flew aggressive visual approaches terminating in a hover while providing Bedford workload ratings in real time. No approach or hover guidance was displayed to the pilot. The out-the-window (OTW) environment (front and chin monitors) was digitally recorded and the optical flow of each video frame computed. Prior work identified a mathematical relationship between pilot workload and the combination of display error rate and stick rate during compensatory tracking tasks. The current work extends this relationship to visual landing approaches, where the pilot is hypothesized to track key optical variables that are available from the OTW scene. Hypothesizing that the visual approach is essentially a compensatory task, optical flow rate was combined with stick rate to compute Bedford workload estimates. Actual and estimated Bedford ratings are compared for the three aircraft models. Innovative contributions of this research include: 1) Optical flow from high resolution, high frame rate flight video is computed and analyzed for workload analysis; 2) A modelling technique is developed that produces workload estimates that closely matches actual pilot ratings; 3) A technique based on visual perceptual requirements allows optical flow to be employed in a tractable, effective manner; 4); Using a novel method, Bedford workload ratings were collected in real time without impinging on the flight task, enabling in-situ workload analysis. Lastly, the authors recently proposed a psychophysical approach which characterizes workload response for a given task in concise terms such as sensitivity to stimulus (Weber fraction), just-noticeable difference (JND), and dynamic range. This new methodology is applied to the workload results obtained for the three aircraft models and discussed, demonstrating how a psychophysical treatment to workload brings a different and relevant toolset for quantitatively examining human-machine performance.
ABSTRACT Visual-inertial odometry has demonstrated the ability to turn a traditional micro-aerial vehicle (MAV) into an advanced platform for aerial robotics. Traditional MAV platforms suffer from strict weight limitations and in some cases flight controllability issues. Qualcomm's Snapdragon Flight™ is utilized to solve both of these problems. It is chosen due to its low weight and high processing power. Results show sufficient controllability to conclude feasibility using Snapdragon Flight™ in GPS-denied environments and onboard unconventional MAV frames. This study is presented with a generic quadrotor configuration. Methods are presented for achieving generic MAV autonomy as well as extending autonomy to more unconventional MAV configurations.
ABSTRACT A model-scale, coaxial, counter-rotating rotor system with single-bladed rotors was tested in hover and compared to a comprehensive model developed in CAMRAD II. Measurements included vibratory hub and pitch link loads, as well as three-dimensional lower rotor blade deformations extracted using digital image correlation. The model flap dynamics were validated using a rotating frame modal extraction technique based on a modified Ibrahim Time Domain method. The CAMRAD model successfully predicted unsteady loads and deformations for the isolated lower rotor operated with cyclic pitch in hover. To investigate transient loads, measurements were taken in the coaxial configuration at a blade loading coefficient of 0.10 and for an isolated lower rotor at equivalent blade loading. The CAMRAD model accurately predicted the unsteady interaction thrust, as well as the blade flapping which was found to increase after upper-lower rotor blade passage. The CAMRAD model revealed aerodynamic forcing in the coaxial configuration consistent with vortex interaction of the upper and lower rotors, while higher harmonics observed in the experimental data were attributed to impulsive loading due to blade thickness effects.
ABSTRACT The use of a local frame motion formalism for finite element simulation of rotor dynamics leads to low order nonlinearity of the equations of motion. In order to exploit this reduced non-linearity, a domain decomposition strategy is implemented. The independence of the subdomains enables naturally parallel computations. The combination of these three key elements leads to significant savings in computational time, without compromising the accuracy.
ABSTRACT In this paper, detailed development of a nonlinear aeroelastic coupled trim model of a twin-cyclocopter, consisting of two cycloidal rotors (also known as cyclorotors) as main rotors and a conventional horizontal tail-rotor for anti-pitch torque and control, is presented. Coupled trim analysis requires simultaneous computation of trim controls, vehicle orientation and blade structural responses so that both blade response equations and vehicle trim equations are satisfied. To obtain the blade structural response and the hub loads in the vehicle frame for the cyclorotors, a nonlinear aeroelastic model of cyclorotor is developed. For this purpose, a high-fidelity unsteady aerodynamic analysis of a cyclorotor is developed, which includes rigorous modeling of effects such as dynamic virtual camber, effects of near and shed wake, and leading edge vortices. To include effect of blade deformations on cyclorotor performance, a structural framework consisting of fully nonlinear geometrically exact beam model and an FEM based solver is developed. An aeroelastic framework of cyclorotor is developed by coupling the aerodynamic and structural models and the coupled aeroelastic model is validated with in-house experiments with flexible cyclorotors. To obtain the performance of the conventional horizontal tail rotor a modified BEMT based model with CFD-based airfoil lookup tables is developed and validated with test data. Once the complete aeroelastic framework of cyclocopter is developed, coupled trim analysis is performed by simultaneously solving blade response equations and vehicle trim equations until trim controls, blade response, inflow and circulation converge all together. Variation of control inputs required for hover trim is investigated with change in gross-weight and longitudinal center of gravity location of the vehicle.
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