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Hybrid experimental measurement of sectional stiffness properties of the MERIT rotor blade with digital image correlation
Get PDFA method to experimentally determine the sectional stiffness properties of modern fiber composite rotor blades is presented. This study hereby follows the novel approach introduced by Sinotte and Bauchau [1, 2]. The hybrid method relies on the measurement of the strain field and combines it with a numerically determined warping field. The strain field is measured using Digital Image Correlation (DIC)-a contact-free, optical 3D deformation measurement method in order to analyze and calculate deformations. The warping displacement field is recovered from a 2D cross-sectional structural analysis using the preprocessor SONATA and ANBA4. The design and manufacturing of the herein presented test article, the first rotor blade specifically developed for the Munich Experimental Rotor Investigation Testbed (MERIT) [3, 4], is described in detail and sectional stiffness properties are calculated based on the experimentally measured strains and loads
Dynamics and stability issues of a synch-rotor aircraft
Get PDFThis paper presents an analytical framework for addressing the stability analysis of a synch-rotor configuration. By linearization about some different trim conditions, a linearized model is obtained made by the decoupled longitudinal and lateral/directional dynamics. A detailed analysis of the stability derivatives and natural modes is given, showing how relevant design parameters, proper of the intermeshing rotors configuration, affect the rotorcraft dynamical behavior. A numerical test case is discussed in support of the proposed model
Non-linear dynamics simulation-based testing to create operating envelopes for autonomos UAS inspection missions
No full textThis paper uses stitched linear and non-linear models to simulate the dynamics of an autonomous TRex-700E model helicopter in order to determine its operating envelope. The helicopter is simulated carrying out an oil rig inspection mission and the wind speed and direction are used to define its operating limits. These limits were determined by applying a series of cost functions, which use operator set performance requirements, to the velocities, attitudes, controls inputs, and position of the UAS over the course of the mission. It was found that for benign wind conditions, in this case <10 knots wind speed, the linear models provide a reasonable approximation. However, as the operating limits reached, the non-linear and linear models diverge. Therefore, to determine the operating limits in harsher wind conditions, the non-linear models would be required
Four-step simulation toolchain to assess the effectivity of noise reduction measures for shrouded tail-rotors
No full textThis paper presents a simulation tool-chain to study the effect of design changes on shrouded rotorcraft (tail-)rotors on its noise signature. Basically, the approach consists of four steps: The first step involves the simulation of the flow-field of the shrouded tail-rotor. The second step involves the computation of the noise far-field using the Ffowcs Williams-Hawkings (FW-H) equations in its Farassat 1A formulation. Both, step 1 and 2 are performed in the time domain. Afterwards, results are transformed to the frequency domain which improves computational efficiency and flexibility significantly. The third step is the computation of the acoustic transfer matrix to include the near-field effects of the structural elements of the tail-rotor. For this purpose, a high-fidelity finite-element model of the fluid domain surrounding the shrouded tail-rotor is introduced which is based on the frequency space formulation of the Helmholtz equations. The fourth and last step in the simulation tool chain is a terrain noise model which is based on acoustic ray tracing while results from the computed sound pressure level spheres serve as a source of ray release. The terrain noise simulation is capable to consider atmospheric attenuation as well as varying environmental and geographical conditions. In the present study, the prediction of the frequencies and relative sound pressure levels was demonstrated with acoustic measurement data acquired at a full-scale single component test-rig. The proposed toolchain uses the Kopter AW09’s tail-rotor as an illustrative example to study the acoustic signature for hover and two forward-flight conditions. In this context, the spatial distribution of the noise emissions as well as the noise footprint on the ground are discussed. This serves to highlight the impact of shroud near field effects. As a practical example, the effect of a generic liner implemented upon the inner surface of the shroud is discussed. For this, directivity and noise footprint on the ground are used to benchmark the effectiveness of the liner in terms of global and local noise level reduction
CityAirbus, a safe entry into remote piloted flight test world
Get PDFAirbus took the opportunity to bring its expertise to the Urban Air Mobility adventure and launched CityAirbus in 2017. This twin-quadcopter of 2.3 tons was designed as a demonstrator to explore the challenges of a full scale remotely piloted electric vehicle. After a short technical description, this article focuses on the main aspects of the safety process followed throughout the project and points out the main lessons learnt regarding the remotely piloted flight test campaign
Roller-screw inerter: a novel strut-mounted device for vibration isolation
No full textThe struts that connect the main rotor and gearbox assembly to the fuselage carry the weight of airframe and payload during flight, and guarantee smooth operation to the drive system. While performing the functions they are designed for, these struts transmit the vibratory loads originating from the main rotor periodic aerodynamic loading to the airframe with essentially negligible alleviation. One technique to cure this problem is to implement strut-mounted vibration alleviation devices, to improve ride comfort by isolating the airframe from the main rotor excitation. This work presents a novel strutmounted vibration attenuation device and demonstrates the concept through experiments and numerical analysis. The design is based on a roller screw inerter, which is mounted in parallel to the strut, sharing its attachment points. The inerter transforms the relative displacement between the two ends of the strut into a corresponding rotation of a body about an axis parallel to that of the strut. As a result, the inerter applies to its two terminals a counter-force proportional to their relative acceleration. In the ideal, frictionless case, a global isolation of the fuselage can be achieved
Safety of flight approach for fuel tanks ALM flanges for tiltrotor application
No full textAdditive Layer Manufacturing (ALM) is a very promising manufacturing technology, which makes possible to produce components that would not have even been possible just a few years ago. Metal powder additive manufacturing produces three-dimensional parts layer by layer. This allows for almost a complete freedom of design and it overcomes the traditional limits of subtractive manufacturing techniques, such as CNC. The design process can also incorporate the use of topological optimization software, making it also possible to obtain higher integration with respect to machined parts, thus minimizing the number of components to be assembled, with advantages in terms of material waste and energy consumption. The present paper intends to be an overview of the approach which aims to guarantee the safety of flight of metal Additive layer manufactured parts of the fuel storage system of a Civil Tilt Rotor Technology Demonstrator under development in the framework of EU Clean Sky 2. Since the flight tests are already scheduled, the technologies that will be taken on-board will reach TRL6 at least. The parts under investigation are the metallic flanges, which connect the fuel hoses system to the fuel storage system (which are bladder tanks installed in the wing bays). A flowchart of the testing activities, aiming to guarantee the safety of flight, is presented, along with manufacturing, experimental and NDI results
Appraisal of handling qualities standards for rotorcraft 4-dimensional lateral-directional dynamics
Get PDFThe coupled vehicle roll-yaw-sway motion of Lateral-Directional Oscillations is often a contributor to rotorcraft Handling Qualities deficiencies. The extent of the deficiencies, and the required pilot control compensation to mitigate their effects, depend critically on the LDO damping and frequency and relative contributions from the roll, yaw and sway motions. Current rotorcraft performance/certification standards (e.g. ADS-33E-PRF/CS-29) for LDO stability have been developed from standards that date from the 1950s or from fixed-wing requirements; there has been limited flight test to support their validation. This paper builds on previous work examining the suitability of these LDO stability criteria to modern rotorcraft operations through ground-based simulation assessment covering a range of HQs, selected based on a frequency of 2.5 rad/s with varying damping and roll-yaw ratio. The underlying simulation model is a FLIGHTLAB Bell 412 model, augmented to ensure that the non-LDO HQs are Level 1. The LDO test configurations have been developed with delta-derivatives added to the nonlinear model to change the LDO frequency, damping and the magnitude ratio of the roll/yaw motion, whilst preserving yaw control sensitivity. The preliminary results demonstrate Handling Qualities generally degrade as the amount of roll in the LDO increased with a p/r = 1.5 giving a reasonable match with the military standards. If the ratio is reduced, Level 1 ratings were awarded with a lower damping. Conversely, no Level 1 ratings were returned for p/r = 2 when the LDO was triggered in the closed loop task
Stability and dynamical analysis of whirl flutter in a gimballed rotor-nacelle system with a smooth nonlinearity
No full textWhirl flutter is an aeroelastic instability that affects aircraft with propellers/rotors. With their long and flexible rotor blades, tiltrotor aircraft are particularly susceptible. Whirl flutter is known to have destroyed aircraft and in the best case it constitutes a fatigue hazard. The complexity of whirl flutter analysis increases significantly with the addition of nonlinearities, due to the more complex dynamical behaviours that emerge as a result. Most whirl flutter stability analyses in current literature are grounded in linear theory, preventing the full discovery of the nonlinearities’ effects. Continuation and Bifurcation Methods (CBM) may instead be used to fully appreciate and analyse the effects of the presence of nonlinearities. Previous CBM-based work on nonlinear gimballed hub rotor-nacelle models, representing those found on tiltrotor aircraft, are capable of whirl flutter in parametric regions declared safe by linear analysis. Furthermore, it was found that they are capable of complex behaviours including limit cycle oscillations, quasi-periodic behaviour and even chaos, though the whirl flutter implications of such behaviours has not been explored. This paper investigates the impact of a smooth structural nonlinearity on the whirl flutter stability of a basic gimballed rotor-nacelle model, compared to its baseline linear stiffness version. A 9-DoF model with quasi-steady aerodynamics, a flexible wing and blades that can move both cyclically and collectively in both flapping and lead-lag motions, producing gimbal flap-like behaviour, was adopted from existing literature. A smooth stiffness nonlinearity was introduced in the blade flapping stiffness and CBM was used to find the new whirl flutter behaviours created by the presence of the nonlinearity. Time simulations, Poincaré sections and spectral analysis were then used to investigate the various behaviours found. This in turn allowed recommendations to be made concerning preferable and/or hazardous parameter combinations of use to the tiltrotor designer
Comparison of design features of quadrotor aircraft and helicopters from the point of view of flight
Get PDFBlade flapping, control methods and rotor/rotor aerodynamic interference are some of the main differences between quadrotor aircraft and helicopters. To investigate these differences in flight performance of square formation quadrotor aircraft, a performance prediction model, including a validated rotor model, an aerodynamic model, and a propulsive trim model, is used. The square formation quadrotor aircraft with variable blade pitch or rotor speed as control means are analyzed. Compared with a helicopter rotor, from low to medium speed flight, the aerodynamic interference between the front and rear rotors dominates the power difference between quadrotors and helicopters. At high speed flight, the blade flapping and aerodynamic interference can lead to increased power, and the blade flapping can be more pronounced. Applying cyclic pitch controls in quadrotor aircraft can effectively control the blade flapping, reduce the rotor power, and increase the maximum forward speed. In general, the overall rotor power consumption of quadrotor aircraft is larger than the equivalent helicopter rotor