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Simulation investigation of safety limits of helicopter operations
Get PDFThe paper presents results of simulations concerning some aspects of helicopter operation safety which include the H-V zone limits, loss of tail rotor aerodynamic effectiveness, operations of ship-borne helicopter and maneuver flight. For simulation investigation, two kinds of physical models of helicopter with different simplification level of real rotorcraft structure are applied. For analysis of emergency situation after power loss, the helicopter is treated as point mass of fuselage suspended beneath main rotor in form of non-deformable disk area. To define the rotor loads and blade deflections generated in boundary flight states a more precise model of elastic blades is applied which consists of deformable blade axes with sets of lumped masses distributed along blade radius. The axis model allows flap, lead-lag and pitch motion of blade. Equations of motion of rotor blades are solved applying Runge-Kutta method. Data of light helicopter were applied for simulations. The simulation investigation may help to collect data for prediction conditions of helicopter flight which can generate potentially dangerous situations
Autopilot design for the ERICA tilt-rotorcraft
Get PDFThe paper discusses the design of a full Autopilot for the ERICA tiltrotor. The structure of the whole control system is implemented by means of classic control technique. The Autopilot envisages several automatic modes, such as the typical hold modes as well as a trajectory following control mode. Both the activation logics of the Autopilot and the automatic nacelle positioning system for the flight envelope protection are also described. The whole control system is implemented in the FLIGHTLAB software environment and it is tested by means of a proper test campaign, whose most significant test simulations results are reported
Automated model based conceptual design approach for composite helicopter rotor blades
Get PDFIn this paper, an automated conceptual structural design methodology of composite helicopter rotor blades is described. Furthermore, design outputs such as blade weights of commercial aircraft blades are compared with the outputs of the tool using this methodology. The methodology applied targets to find optimum internal structure which can compensate outcomes of major rotor design parameters which are chord length, rotor radius and rotor frequency. Minimum blade weight is objected while searching necessary internal structure. Structural integrity and cross-sectional center positions affecting dynamic responses are constrained while searching for the necessary internal structure. The method applied differs from traditional blade optimization studies with the solution time and maximum parametrization of blade structural configuration. Hence, method does not target to optimize a blade structure having a detailed initial design. It aims to find a feasible design from sweep models of blade configurations with necessary mass attachments
DLR analysis on the noise emission from the RACER configuration
No full textTo answer the challenge of increasing range and speed of a rotorcraft, RACER (Rapid And Cost-Effective Rotorcraft) is developed by Airbus Helicopters. The RACER configuration incorporates an innovative “box-wing” design to provide lift and “pusher” propellers at the wing tips to generate thrust in forward flight. The noise sources from RACER do not only include conventional helicopter main rotor noise, but also propeller noise which can be significantly affected by interferences with the main rotor, wings and other parts of the configuration. Having been widely applied to the simulations of rotor and propellers, the DLR free wake code UPM and the aeroacoustic analysis tool APSIM are used for a detailed analysis and an improved understanding of the complex aerodynamics and aeroacoustics of the RACER configuration. The noise generation mechanisms of the various interactions among the propeller, the wings and the rotor as well as a variation in the sense of rotation of the propeller are numerically studied to allow finding mitigation means to reduce the interactions in the final RACER configuration. The noise from rotor and propeller emitted by the complete RACER configuration for various flight conditions is analyzed and the analysis of acoustic scattering of propeller noise by the RACER configuration is conducted
A quasi-Linear Parameter Varying (qLPV) modeling approach for real time piloted simulation of tiltrotor
No full textTiltrotors can transform from helicopter configuration to a fixed wing airplane configuration. This allows them to have a broader flight envelope. The dynamics of tiltrotors change with flight condition and aircraft configuration. Therefore, a model stitching technique based on quasi-Linear Parameter Varying (qLPV) framework is employed to develop a continuous full flight envelope flight dynamics model for the purpose of control system design and real time piloted simulation. A high order qLPV model is developed for XV-15 where discrete linear state-space models are stitched together to provide a varying model dynamics and trim characteristics over the complete flight envelope. The model is also coupled with engine dynamics, rotor speed governor, actuator dynamics and stability and control augmentation system (SCAS). Lastly, the qLPV model is implemented in FRAME-Sim, a fixed base rotorcraft flight simulation system
Effect of vortex deflection on vortex-rotor interaction
Get PDFVortex-rotor interaction has been studied mostly with “rigid” straight-line vortices (longitudinal, lateral and or-thogonal to the rotor disk). Vortex deformation during encounter with the rotor was only addressed by means of CFD codes. This paper investigates the interaction by a simplified vortex deflection model, where the in-teracting vortex is convected in parallel to the wake tube of the rotor once it penetrates the rotor disk. The consequences on rotor controls required to keep the trim constant are compared to former results obtained with a rigid (undeflected) vortex model
Investigation of the effects of autorotative flare index variation on helicopter flight dynamics in autorotation
Get PDFAutorotation is a flight condition whereby the engine of a helicopter is no longer supplying power to the main rotor system, which is driven solely by the upward flow of the air moving through the rotor. For helicopters, autorotation is a common emergency procedure performed by pilots to safely land the vehicle in the event of a power failure or tail-rotor failure. In the classic analysis of dynamic stability of helicopters in powered flight, it is common practice to neglect the effect of variation of rotor angular velocity, as the rotorspeed is constant. However, this assumption is no longer justified in case of autorotative flight. Therefore, the rotorspeed becomes an additional degree-of-freedom in autorotation, giving rise to a new stability mode that couples with classical rigid-body modes. The present paper aims at understanding the role of the rotorspeed degree-of-freedom in modifying the stability characteristics in autorotation of rotor systems with different autorotative flare indexes. Results show that the helicopter dynamics are considerably affected in autorotation as a consequence of the fact that the rotorspeed degree of freedom couples with the heave subsidence mode. Therefore, autorotation requires a different control strategy by the pilot and should not be mistakenly considered only as an energy management task. Furthermore, the autorotative flare index, used to characterize the autorotative performance during the preliminary design phase of a new helicopter, provides only energy information. Indeed, this paper demonstrates that high values of this index, representative of good autorotative performance in terms of available energy over required energy, may lead to degraded stability characteristics of the helicopter in autorotation
Enhanced gust load recovery for the AW609 tiltrotor
Get PDFThe prediction of dynamic gust loads for a tiltrotor is a challenging task since it requires to take in account several components such as the flexibility of the airframe and of the rotor, their aerodynamic properties and the effect of the automated flight control systems. The characterization of the aerodynamic forces acting on the tiltrotor, in particular, can be very difficult and the direct use of unsteady aerodynamic forces from simplified panel methods can lead to a wrong definition of the dynamic properties of the rigid modes of the aircraft. A correction of the unsteady aerodynamic forces using tabulated stability derivatives can then be used to recover the proper aircraft dynamics. The use of a reduced basis for the characterization of the structural dynamics can lead to a poor accuracy of the predicted loads, and the mode acceleration method can be used to solve this problem. The present paper describes the advantages obtained using the mode acceleration method for load recovery and presents a procedure for the correction of aerodynamic forces using tabulated aerodynamic coefficients, showing their effect on the gust loads
Influence of contact points of skid landing gears on helicopter ground resonance stability
Get PDFSoft-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 slope landing studies and investigations of non-linear landing gear effects, this work focuses on a systematic study of partial skid contact using different landing modelling approaches and contact definitions. Special focus is given to different methods of contact simulation, using 3d spring-damper elements and polygonal contact elements. This paper is part of a larger study to investigate the influences of partial ground contact and soft terrain on helicopter dynamic stability during landings. It is the long-range objective to reduce the necessity of extensive 2ight tests prior to helicopter certification processes
Aeromechanics investigation of tiltrotor transition maneuver
No full textAeromechanics analysis is performed using the comprehensive analysis code RCAS (Rotorcraft Comprehensive Analysis System) to study the transient conversion maneuver of a tiltrotor. The analytical model is based on the XV-15 research tiltrotor aircraft in size and dynamic characteristics. A generic (not representative of XV-15) tiltrotor control system is developed to simulate conversion maneuver. The calculation begins with a trim analysis at hover, which is followed by the conversion maneuver. During the maneuver analysis, the pilot control model is activated to fly the aircraft following a desired airspeed profile and zero altitude change. Time histories of vehicle dynamics, rotor controls, rotor flapping, rotor performance and blade structural loads are investigated for various transient conversion maneuver flight conditions. The aircraft longitudinal acceleration is larger for the faster conversion (shorter conversion time) and for the higher cruise speed (conversion end speed). The aircraft acceleration during the transient maneuver has a significant influence on the rotor performance and loads