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Approaches for numerical analysis and experimental monitoring of manufacturing process and damage evolution in carbon/titanium hybrid structures
Get PDFThe prediction of detailed mechanical respond in bonded Composite/Metal hybrid structure is hardly detectable due to the presents of thermal strain that depends on mismatch of Coefficient of Thermal Expansion (CTE), adhesive behavior, development of defects in adhesive layer during manufacturing or operational loads. These uncertainties could be overcome by optical fibre based monitoring systems and by a precise characterization of the manufacturing effects and damage progression on the stress-strain field. This paper presents a well-assessed monitoring technique based on strain sensors carried by optical fibers embedded in the hybrid specimen that can be used both during manufacturing process and fracture test to validate a numerical modelling approach for prediction of strain evolution. The experimental tests are conducted with two pre-damaged configurations, Balanced and Un-Balanced specimens equipped by two types of fiber coating, Naked fiber and Ormocer, to investigate the effects of thermal stress build-up on the fracture behavior. The hybrid specimens have been designed by the method that is capable of controlling thermal stress build-up. These specimens have been obtained by co-bonded process and have been suited for the Double cantilever Beam (DCB) fracture mechanic test. Validated numerical approach based on multistep explicit analyses have been used to implement the effect of thermal stress produced in the manufacturing on the simulation of fracture propagation
Towards optimisation of compound rotorcraft
Get PDFThis work presents a tool-chain development for aerodynamic analysis and optimisation of compound rotorcraft. An automation framework for geometry composition and grid generation using ICEM Hexa is proposed, and variable applications are presented. High-fidelity CFD simulations of ducted fans are first performed to validate the in-house solver HMB3. Detailed analyses of the ducted fan and comparisons against experiments and simpler methods are presented, and good correlation can be noted. A compound helicopter model is then assembled, consisting of a parametrised Dauphin-like fuselage, ducted fans for auxiliary thrust, and a main rotor. Simulation methods of several fidelity levels using steady/unsteady actuator disks and resolved blades are conducted and evaluated. Analyses of the aerodynamics and flow features are then presented
Rotorcraft simulation fidelity for low speed manoeuvring using ‘additive’ system identification
Get PDFHigh fidelity rotorcraft flight simulation relies on the availability of a quality flight model that further demands a good level of understanding of the complex nonlinearities arising from aerodynamic couplings and interferences. This paper explores rotorcraft flight dynamics in the low-speed regime where such nonlinearities abound and presents a new Additive System IDentification (ASID) approach in the time-domain to aid investigations of these complexities. The ASID approach identifies flight model parameters sequentially based on their contribution to the local dynamic response of the system, in contrast with the averaged values of conventional System IDentification (SID) approaches over a whole manoeuvre. The identified 4 degree-of-freedom model shows good predictability using flight test data from the National Research Council’s Bell 412 at hover and how the identified parameters can be used to improve the fidelity of Liverpool’s baseline FLIGHTLAB model of the Bell 412. The approach is also used to study nonlinearities attributed to Manoeuvre Wake Distortion (MWD). A cubic rate term is proposed to model the MWD nonlinearities and first results show good correlation for this nonlinear model structure, demonstrated by its capability to capture the nonlinear response and variations of the stability and control derivatives with response magnitude
On the design of a helicopter rotor blades exposed to the wind flow
No full textThe paper presents methods for calculating bending stresses in the rotor blade of a helicopter blown by a wind flow. The data obtained using the methods set out in this paper can be used in the design of the rotor blades and the determination of safe operation to ensure the required reserves for operational wind speeds. For the problem in the linear formulation, convenient calculation formulas for calculating deflections, angles of rotation and bending moments (stresses) directly through their values for the "rigid" blade are obtained. For the problem in the nonlinear formulation, a simple-to-implement computational scheme for solving the initial nonlinear equation of loading of the blade based on the method of successive perturbations of the parameters of V. V. Petrov is obtained. The results of calculations made for the tested rotor blades of the helicopter
A safety prompt method for helicopter formation flight
No full textAiming at the formation maintenance and comprehensive collision avoidance of the helicopter formation under "Leader-follower" mode, a safety prompt method is proposed. This method is based on the artificial potential field method to maintain formation and prevent collision of terrain and other formation members, which prompts helicopter to perform compound escape maneuver when it encounters obstacles and deviates from formation. After determining the research method, the safety threshold of formation maintenance and comprehensive collision avoidance during helicopter formation flying is discussed. Finally, the correctness of the method is verified by numerical simulation
Novel approach for experimental measurement of sectional stiffness properties of composite rotor blades
Get PDFA novel experimental-numerical technique is presented for evaluating the full 6 _ 6 stiffness matrices for beams. The general formulation makes the method well suited for isotropic beams with simple cross-sectional configurations or beams made of anisotropic materials with complex geometries, as typically exhibited in composite rotor blades. A 2-D finite element code, SectionBuilder, is used to generate a finite element mesh of the cross-section and evaluate the warping field. The surface strain field is experimentally measured along the span of the beams using Digital Image Correlation (DIC). Stiffness matrices are then calculated based on the experimentally measured strain data and numerical model of the cross-section, with results presented for an isotropic beam, a composite beam with bending/torsion coupling, and a composite rotor blade
Aeromechanics modelling of tiltrotor aircraft
No full textA numerical investigation into the influence of different aerodynamic interaction models on the trim behaviour of tiltrotor aircraft was undertaken. The study simulated the entire conversion corridor and compared a baseline case, with no interaction accounted for, with simulations that included different interaction models: rotor-induced download on the wing; wing downwash at the tailplane; and the rotor wake effect at the tailplane. The entire conversion corridor was simulated using a reduced-order blade element/ strip theory framework. The influence of the interactions models was compared for the trimmed pitch attitude and control stick position. The most important interaction to account for was the wing downwash at the tailplane. This interaction was found to have a pronounced effect on the trim state at all operating points and in_uenced the predicted conversion corridor boundaries
Design methodology of force feedback laws through helicopter control loop simulation
No full textThe latest evolution of pilot controllers, referred to as ASSU (Active Side Sticks Units) provides static and dynamic tactile force (or haptic) feedback to the pilot at the grip. Combined with FBW (fly-by-wire), this promising technology has enhanced safety levels compared to the original mechanical linkage systems they have started to replace, while offering vast improved benefits in terms of carefree handling and pilot situational awareness. In the framework of a PhD thesis, the Information Processing and Systems Department (DTIS) of ONERA and SAFRAN Electronics & Defense have started a cooperation to evaluate the interest and the different possibilities offered by the ASSU technology to improve safety and handling qualities of rotary wing aircraft. Up to now, the design and tuning of these functions were essentially performed thanks to numerous simulator sessions or flight tests with pilots. More than just providing a set of values for the required parameters defining the cueing function (hopefully an optimal set of parameters), it is expected that the approach presented here would reduce the number of piloted simulation tests and associated difficulties of the availability of pilots, the significant amount of time and material resources. This paper describes the work done during the first half of the thesis. The main objective of this work is to develop a design methodology based on the simulation of the entire helicopter control loop (also including the pilot in some form) and enabling the definition and parameterization of cueing functions. Moreover, some objective criteria will be defined and used to design the force feedback laws, bringing additional means of evaluation and validation than the classical subjective rating scales
Phantom blade model - advanced methodology for actuator disk modeling
Get PDFA good prediction of the unsteady behavior of the aerodynamic interactions between rotating and fixed parts is of great importance in the design of a helicopter, in particular for rear parts conception. In the present work, an unsteady actuator disk-like approach named Phantom Blade Model (PBM) is presented and results obtained are confronted to other numerical approaches and test data. This method allows (1) improved modeling of the rotor downwash and of the aerodynamic interactions compared to the classic, steady, actuator disk and (2) reduced pre-processing and computational times compared to high-fidelity CFD models with meshed blades. First, two academic cases for which experimental data is available, namely an isolated two-bladed rotor in hover and a ROBIN fuselage equipped with a four-bladed rotor in level flight, are used as validation cases for the PBM. Good agreement is observed with both tests and meshed-blades simulations, with reduced simulation time - 48% and 63% less CPU hours, respectively. Then, the PBM is applied to the Bluecopter® in forward flight, in which PBM is used for both main rotor and Fenestron®. Comparison between high-fidelity CFD/CSM simulations of a full helicopter, flight tests and unsteady actuator disk applied to a flying aircraft as presented here is new. Results with PBM of unsteady loads and pressure at the horizontal stabilizer are considerably close to the complete helicopter CFD/CSM simulations. Both numerical methods fairly capture the amplitudes, but slightly overestimate the average pressure compared to test data
Autorotation: physiological measures of workload
Get PDFThe workload assessment to perform a full autorotation on the AS-350 aircraft (Airbus Helicopters) was performed during a Flight Test Campaign with 80 flight hours and 227 data collection procedures, considering 10 pilots with different piloting skill levels, among such military pilots, flight instructors, and test pilots. During the tests, these pilots were subjected to unexpected engine failures, to evaluate the actual reaction time of each pilot, and to test the ability to make a safe landing under the conditions prescribed by the aircraft manufacturer. The testing method used began with unexpected engine failures when only the lead test pilot knew that the engine failure would be simulated. In the sequence, several points of autorotation were performed, from the simplest profile to the most complex. All the procedures have registered the performance parameters and handling qualities of the aircraft, along with the physiological parameters of the pilots. The aircraft was equipped with dedicated instrumentation for in-flight testing and the pilots have been instrumented with an Electroencephalogram (EEG), Electrocardiogram (EKG), Respiration Belt and Galvanic Skin Response (GSR), Eye Tracking and Face Recognition Camera equipment. This instrumentation was employed to determine physiological markers that could determine the pilot workload, quantitatively, reducing the subjectivity of measures that use only qualitative scales of evaluation, such as Handling Qualities Rate (HQR) and Bedford Workload Scale (WL). In this work, only the preliminary results of the analysis obtained by the Galvanic Skin Response markers will be presented. Major potential applications of the results from the present research range from cockpit design guidelines and human-machine interface systems for supporting pilotage such as more effective alarm systems, interactive cockpits, enhancement of active autopilots with semi-automatic flight commands. Besides that, the results and conclusions from this research can also improve processes and methods for the training-based formation of pilots, along with the development of flight simulators with physiological measurements parameters quantification, feeding back data for a piloting performance assessment