Survey of Certifiable Air Data Systems for Urban Air Mobility

In the near future, vertical take off and landing aircraft of the urban air mobility sector will be integrated into the civil airspace and they will be characterised by several levels of autonomous flying capabilities. Many countries worldwide are funding several researches to identify and develop enabling technologies to make urban air mobility as safe as modern aviation. One of the most critical aspect of those aeroplanes rely on the reduced fuselage dimensions and available space on board to welcome all those safety critical systems commonly used on commercial aviation. The air data system is one of the safety critical system that is equipped with several probes and vanes, protruding externally from the aircraft fuselage, and some of its functionalities are adequately redundant for general aviation and large aeroplanes. Even though an airworthiness standard applicable to urban air mobility is not ready yet, worldwide there are several efforts that will lead to type certification standards in next years. This work presents a brief survey of certified technologies available for sensing solutions feeding air data systems and solutions based on synthetic sensors certifiable in a couple of years. The survey relies on certified and certifiable innovative data sensing units for realistic urban air mobility applications. To this aim, a safety assessment analysis is presented in order to support the validity of the certifiable air data sensing solutions presented in this paper

Safety Analysis of a Certifiable Air Data System Based on Synthetic Sensors for Flow Angle Estimation

This work deals with the safety analysis of an air data system (ADS) partially based on synthetic sensors. The ADS is designed for the small aircraft transportation (SAT) community and is suitable for future unmanned aerial vehicles and urban air mobility applications. The ADS’s main innovation is based on estimation of the flow angles (angle-of-attack and angle-of-sideslip) using synthetic sensors instead of classical vanes (or sensors), whereas pressure and temperature are directly measured with Pitot and temperature probes. As the air data system is a safety-critical system, safety analyses are performed and the results are compared with the safety objectives required by the aircraft integrator. The present paper introduces the common aeronautical procedures for system safety assessment applied to a safety critical system partially based on synthetic sensors. The mean time between failures of ADS’s sub-parts are estimated on a statistical basis in order to evaluate the failure rate of the ADS’s functions. The proposed safety analysis is also useful in identifying the most critical air data system parts and sub-parts. Possible technological gaps to be filled to achieve the airworthiness safety objectives with nonredundant architectures are also identified

ThrustPod: a novel solution for vertical take-off and landing systems

The work introduces a patented solution, named ThrustPod, to adapt the state-of-the-art fixed-wing aircraft for vertical take-off and landing operations. The proposed system is conceived to overcome the need of tilting surfaces or rotors and to overcome the aerodynamic low performance of multicopters. The ThrustPod is applicable to very light and general aviation aircraft and next generation air vehicles that aim to operate on urban and regional routes. The proposed solution is based on retractable thrusters to provide the required vertical thrust for the take-off and landing phases. The more suitable thrusters can be adopted, e.g. ducted fans or propellers. Another characteristic is the modularity as the ThrustPod can be scaled on different vehicle categories. In fact, the proposed solution can be used on different fixed-wing aircraft to provide vertical and take-off capabilities or to design novel airframes. The work proposes an integrated preliminary design process to optimise both the aircraft and the ThrustPod configuration to define fuselage length, thruster’s arrangement, power budget, energy management and performance evaluation of a potential aircraft for urban air mobility applications. The aim of the present work is to present a preliminary design application to evaluate advantages and drawback with respect to the most promising urban air mobility vehicles

Range Estimation Of A Novel Concept Electric Aircraft Based On Modified Breguet Equation

The electric vertical-take off and landing aircraft are able to perform vertical flights, equipped with an electric propulsion and energy storage system. This kind of aircraft has gained more importance during the last decades, in particular for urban aerial mobility. Its design is function of several project specifications, among them the range to cover a cruise flight mission profile. The present work is intended to show a modified Breguet equation for the range estimation applied to a novel electric aircraft concept. The advantage of this equation is to avoid the knowledge of parameters which are difficult to be found a-priori in a preliminary design phase. It is worth noticing that the modified Breguet estimated range needs further corrections to obtain a correct effective cruise range. For this reason, the estimated range is compared with the effective cruise range obtained with an energy balance equation. Results show that the estimated and theoretical range values are very close and comparable, hence the modified Breguet equation for electric aircraft is correct. In order to validate the present results, a comparison with several urban air mobility aircraft is performed

Sensitivity Analysis of a Neural Network based Avionic System by Simulated Fault and Noise Injection

The application of virtual sensor is widely discussed in literature as a cost effective solution compared to classical physical architectures. RAMS (Reliability, Availability, Maintainability and Safety) performance of the entire avionic system seem to be greatly improved using analytical redundancy. However, commercial applications are still uncommon. A complete analysis of the behavior of these models must be conducted before implementing them as an effective alternative for aircraft sensors. In this paper, a virtual sensor based on neural network called Smart-ADAHRS (Smart Air Data, Attitude and Heading Reference System) is analyzed through simulation. The model simulates realistic input signals of typical inertial and air data MEMS (Micro Electro-Mechanical Systems) sensors. A procedure to define the background noise model is applied and two different cases are shown. The first considers only the sensor noise whereas the latter uses the same procedure with the operative flight noise. Flight tests have been conducted to measure the disturbances on the inertial and air data sensors. Comparison of the Power Spectral Density function is carried out between operative and background noise. A model for GNSS (Global Navigation Satellite System) receiver, complete with constellation simulator and atmospheric delay evaluation, is also implemented. Eventually, a simple multi-sensor data fusion technique is modeled. Results show good robustness of the Smart-ADAHRS to the sensor faults and a marginal sensitivity to the temperature-related faults. Solution for this kind of degradation is indicated at the end of the paper. Influences of noise on input signals is also discussed

Advantages of Neural Network Based Air Data Estimation for Unmanned Aerial Vehicles

Redundancy requirements for UAV (Unmanned Aerial Vehicle) are hardly faced due to the generally restricted amount of available space and allowable weight for the aircraft systems, limiting their exploitation. Essential equipment as the Air Data, Attitude and Heading Reference Systems (ADAHRS) require several external probes to measure significant data as the Angle of Attack or the Sideslip Angle. Previous research focused on the analysis of a patented technology named Smart-ADAHRS (Smart Air Data, Attitude and Heading Reference System) as an alternative method to obtain reliable and accurate estimates of the aerodynamic angles. This solution is based on an innovative sensor fusion algorithm implementing soft computing techniques and it allows to obtain a simplified inertial and air data system reducing external devices. In fact, only one external source of dynamic and static pressures is needed. This paper focuses on the benefits which would be gained by the implementation of this system in UAV applications. A simplification of the entire ADAHRS architecture will bring to reduce the overall cost together with improved safety performance. Smart-ADAHRS has currently reached Technology Readiness Level (TRL) 6. Real flight tests took place on ultralight aircraft equipped with a suitable Flight Test Instrumentation (FTI). The output of the algorithm using the flight test measurements demonstrates the capability for this fusion algorithm to embed in a single device multiple physical and virtual sensors. Any source of dynamic and static pressure can be integrated with this system gaining a significant improvement in terms of versatility

A Data-Driven Approach to Identify Flight Test Data Suitable to Design Angle of Attack Synthetic Sensor for Flight Control Systems

Digital avionic solutions enable advanced flight control systems to be available also on smaller aircraft. One of the safety-critical segments is the air data system. Innovative architectures allow the use of synthetic sensors that can introduce significant technological and safety advances. The application to aerodynamic angles seems the most promising towards certified applications. In this area, the best procedures concerning the design of synthetic sensors are still an open question within the field. An example is given by the MIDAS project funded in the frame of Clean Sky 2. This paper proposes two data-driven methods that allow to improve performance over the entire flight envelope with particular attention to steady state flight conditions. The training set obtained is considerably undersized with consequent reduction of computational costs. These methods are validated with a real case and they will be used as part of the MIDAS life cycle. The first method, called Data-Driven Identification and Generation of Quasi-Steady States (DIGS), is based on the (i) identification of the lift curve of the aircraft; (ii) augmentation of the training set with artificial flight data points. DIGS’s main aim is to reduce the issue of unbalanced training set. The second method, called Similar Flight Test Data Pruning (SFDP), deals with data reduction based on the isolation of quasi-unique points. Results give an evidence of the validity of the methods for the MIDAS project that can be easily adopted for generic synthetic sensor design for flight control system applications

Experimental Analysis of Neural Approaches for Synthetic Angle-of-Attack Estimation

Synthetic sensors enable flight data estimation without devoted physical sensors. Within modern digital avionics, synthetic sensors can be implemented and used for several purposes such as analytical redundancy or monitoring functions. The angle-of-attack, measured at air data system level, can be estimated using synthetic sensors exploiting several solutions, e.g. model-based, data-driven and model-free state observers. In the class of data-driven observers, multilayer perceptron neural networks are widely used to approximate the input-output mapping angle-of-attack function. Dealing with experimental flight test data, the multilayer perceptron can provide reliable estimation even though some issues can arise from noisy, sparse and unbalanced training domain. An alternative is offered by regularisation networks, such as radial basis function, to cope with training domain based on real flight data. The present work's objective is to evaluate performances of a single layer feed-forward generalised radial basis function network for AoA estimation trained with a sequential algorithm. The proposed analysis is performed comparing results obtained using a multilayer perceptron network adopting the same training and validation data

DEFINITION OF THE FLEXIBLE AIRCRAFT LONGITUDINAL MODEL FOR A PRELIMINARY CONTROL DESIGN

Developing control system of high aspect ratio aircraft can be challenging due to flexibility involved in the control loop design. A model based approach can be straightforward to tune the control system parameters and, to this aim, a reliable aircraft flexible model is necessary. This paper aims to present the approach followed to design the longitudinal control strategy considering the aircraft simulator in the loop. The elastic modes are calculated from the lumped mass geometrical model and an aerodynamic properties from a reference aircraft. The approach and the model validation have been done in partnership with Leonardo Aircraft, as a thesis topic. Beginning with verification of the trim conditions, the flexible dynamic modes are compared to the rigid ones in order to highlight the relevant changes in the aircraft modes. A preliminary design of the longitudinal control strategy is herein proposed to achieve the dynamic response objectives