Experiments and model predictions for fatigue crack propagation in riveted lap-joints with multiple site damage

In this paper, the growth of long fatigue cracks up to failure in aircraft components is studied. A deterministic model is presented, able to simulate the growth of fatigue through cracks located at rivet holes in lap-joint panels. It also includes criteria to assess the link-up of collinear adjacent cracks in a MSD scenario. To validate the model, a fatigue test campaign was carried out on riveted lap-joint specimens in order to produce experimental crack growth and link-up data. Accurate measurements of naturally occurred surface cracks were automatically performed by the Image Analysis technique, thus allowing the tests to run 24 h a day. The comparison between experimental tests and numerical simulations is good, thus confirming the model as a useful tool for the assessment of fatigue life of aircraft riveted joints

A solution to detect and avoid conflicts for civil remotely piloted aircraft systems into non-segregated airspaces

The capability to ‘‘detect and avoid’’ potential collisions is one of the main technical challenges restricting widespread operations of unmanned aircraft into non-segregated airspaces. In fact, to operate into prescribed environments, an unmanned aircraft needs an onboard technology to replace the capability of the human pilot to ‘‘see and avoid’’ collision hazards. Such a technology is a ‘‘sense and avoid’’ system. This article focuses on the ‘‘avoid function’’ of such a system and proposes a suitable solution. The approach to the problem is to schematize a generic obstacle through a moving ellipsoid that represents the region of space the unmanned aircraft must not violate. The obtained solution enables situations of potential conflict to be detected and avoided through a set of such as speed changes in magnitude and/or direction. Thousands of test cases have been considered to validate this solution. Simulations show that the proposed algorithm is able to detect and avoid situations of potential conflict in the three-dimensional space and in real-time, even without the assistance of a human operator. As such, it can be considered as a fundamental step for the development of a prototype of ‘‘sense and avoid’’ system for promoting the integration of unmanned aircraft into non-segregated airspaces

Fault-Tolerant Control of a Dual-Stator PMSM for the Full-Electric Propulsion of a Lightweight Fixed-Wing UAV

The reliability enhancement of electrical machines is one of the key enabling factors for spreading the full-electric propulsion to next-generation long-endurance UAVs. This paper deals with the fault-tolerant control design of a Full-Electric Propulsion System (FEPS) for a lightweight fixed-wing UAV, in which a dual-stator Permanent Magnet Synchronous Machine (PMSM) drives a twin-blade fixed-pitch propeller. The FEPS is designed to operate with both stators delivering power (active/active status) during climb, to maximize performances, while only one stator is used (active/stand-by status) in cruise and landing, to enhance reliability. To assess the fault-tolerant capabilities of the system, as well as to evaluate the impacts of its failure transients on the UAV performances, a detailed model of the FEPS (including three-phase electrical systems, digital regulators, drivetrain compliance and propeller loads) is integrated with the model of the UAV longitudinal dynamics, and the system response is characterized by injecting a phase-to-ground fault in the motor during different flight manoeuvres. The results show that, even after a stator failure, the fault-tolerant control permits the UAV to hold altitude and speed during cruise, to keep on climbing (even with reduced performances), and to safely manage the flight termination (requiring to stop and align the propeller blades with the UAV wing), by avoiding potentially dangerous torque ripples and structural vibrations

Does Social distancing affect the processing of brand logos?

Social distancing and isolation have been imposed to contrast the spread of COVID-19. The present study investigates whether social distancing affects our cognitive system, in particular the processing of different types of brand logos in different moments of the pandemic spread in Italy. In a size discrimination task, six different logos belonging to three categories (letters, symbols, and social images) were presented in their original format and spaced. Two samples of participants were tested: one just after the pandemic spread in Italy, the other one after six months. Results showed an overall distancing effect (i.e., spaced stimuli are processed slower than original ones) that interacted with the sample, revealing a significant effect only for participants belonging to the second sample. However, both groups showed a distancing effect modulated by the type of logo as it only emerged for social images. Results suggest that social distancing behaviors have been integrated in our cognitive system as they appear to affect our perception of distance when social images are involved