A non-linear model of large radial tyres for the simulation of aircraft braking

A model is presented of the in-plane behaviour of a radial tyre, suitable to be employed within the simulation of aircraft braking. The model is developed on the basis of an energy-balance approach that allows the determination of the effects of braking on rolling friction and on the lever-arm of vertical load. The model is tuned and validated through the correlation between simulated and experimental results relevant to a large aircraft tyre. The method proposed is tuneable on a specific tyre using a limited number of parameters, that are those usually recorded during standard braking tests and it is extendible to the braking tests of an aircraft. This would overcome the limitations intrinsic of current tyre dynamometer facilities that are able to test large aircraft tyres over a modest range of vertical loads compared with those experienced under service conditions

Models of Wheel Contact Dynamics: an analytical study on the in-plane transient responses of a brush model

This paper deals with the dynamics of the contact between the pneumatic tyre and the ground, in particular with reference to braking manoeuvres of aircraft. The transient response of the braking force is analytically evaluated in terms of the transfer functions that link the variation of the braking force to the variation of physical inputs affecting the interaction between the tread and the ground, in the longitudinal plane. The proposed models have been formulated in order to account for the effects of different reference conditions of steady braking on gains, zeros and poles of such transfer functions

ACT-TILT project (Work Package 1.2.1) - Hinge moments estimation - Summary of results

This paper summarises the results obtained by the staff of the University of Pisa and TELEAVIO Srl concerning a preliminary estimation of the hinge moments on the aerodynamic control surfaces of the tilt rotor (operating in the "Fixed Wing" mode), carried out in order to allow the pre-design of the actuators of the flight control system. The estimation was accomplished by means of two different methods (provided by ESDU and Hoerner ), whose results are then compared. The basic hypotheses are that the aerodynamic surfaces work in the linear range of incidence and control deflection. Nevertheless, an estimation of the hinge moments in the post-linear range of control deflection is also given

PROCEDURE FAULT-TOLERANT PER SISTEMI DATI-ARIA PER VELIVOLI AD ELEVATE PRESTAZIONI

Nel lavoro si illustrano i risultati e gli sviluppi più recenti delle attività di ricerca condotte presso il Dipartimento di Ingegneria Aerospaziale dell’Università di Pisa sui sistemi dati-aria per moderni velivoli Fly-By-Wire. Dette attività sono state svolte in collaborazione con le società AleniaAermacchi ed AleniaSia nell’ambito dello sviluppo del sistema di comandi di volo dell’addestratore M346. Il sistema Dati-Aria studiato consente la determinazione dei principali parametri di volo (an-golo di incidenza, angolo di derapata, numero di Mach e pressione statica ambiente) ed è do-tato di opportune ridondanze che gli consentono di tollerare due avarie conservando la piena funzionalità. I parametri di volo vengono determinati elaborando opportunamente le misure di angoli di flusso e pressioni locali fornite da quattro sonde poste nella parte prodiera della fusoliera. Nel lavoro si riassumono brevemente le caratteristiche del sistema e si affrontano alcuni ar-gomenti particolarmente delicati, connessi con lo sviluppo degli algoritmi di elaborazione delle misure e con la loro calibrazione a seguito dei risultati di prove di volo. In particolare si illustrano alcune soluzioni metodologiche adottate per evitare potenziali instabilità negli algoritmi di calcolo. Si descrivono inoltre algoritmi di interpolazione dei dati sviluppati per contenere l’occupazione di memoria nei computer di bordo e le problematiche di integrazione dei dati di galleria con i dati di volo. Si riassumono infine gli aspetti chiave degli algoritmi di monitoring e voting, originali e non convenzionali, che è stato necessario sviluppare per il sistema in esame

ABS 1.0 (Aircraft Braking Simulation package): Check Manual

Reports of the Department of Aerospace Engineering of the University of Pis

Una procedura fault-tolerant per la determinazione dei parametri di volo mediante sonda multi-pressione

Nel lavoro si illustrano i risultati di studi per lo sviluppo di una sonda dati-aria, dotata di 21 prese di pressione, principalmente destinata alla stima degli angoli di incidenza e derapata e della velocità di volo su piccoli velivoli non abitati. I dati di pressione, misurati grazie a sensori di tipo MEMS, vengono elaborati mediante reti neurali. Grazie alla realizzazione di tre canali di calcolo indipendenti, ognuno dei quali utilizza 5 delle 21 misure di pressione, è stato possibile ottenere un sistema two-fail-operative. Il rilevamento dei guasti e la conseguente riconfigurazione del sistema viene effettuato grazie ad algoritmi originali basati sul confronto con opportuni valori di soglia predefiniti delle differenze di pressione misurate da gruppi di 4 o 5 sonde

OBJECT-ORIENTED MODELLING OF FLIGHT CONTROL ACTUATION SYSTEMS FOR POWER ABSORPTION ASSESSMENT

In the work, the object-oriented approach provided by the Modelica-Dymola environment is used to perform a comparison between different technologies for aircraft actuation systems in terms of power absorption characteristics. Starting from the same set of basic design, three actuators characterised by different technological solutions (servohydraulic, electro-hydrostatic and electromechanical) have been defined, and the related “object-models” have been developed and characterised in terms of dynamic performances. In parallel, the model of a basic flight control system with two ailerons, two elevators and one rudder has been created, including models for the aerodynamic hinge moments calculation and the simulation of elasticity of the actuator structural links. The models have been then used to obtain three types of actuation systems: a traditional servohydraulic one, a “more-electric” plant with all electro-hydrostatic actuators, and an “allelectric” system. Each system is finally tested with the same command time history by reproducing a sample flight manoeuvre, and the power absorption characteristics are analysed and discussed

Power absorption assessment of flight control actuation systems via object-oriented modelling

As a result of the constant trend to technology innovation and integration of functions, modern airborne systems and equipments are characterised by high complexity and multi-physicality. A relevant case is that of the flight control actuators, whose technology solutions recently had a rapid evolution, moving from the traditional servo-hydraulic, to electro-hydrostatic, towards electro-mechanical architectures. The study, the design and the performance characterisation of such systems, as well as the assessment of novel solutions in the early phases of the project, can therefore be problematic (or, at least, time-consuming) if the designer/analyst does not have technical expertise in all the engineering domains. In this context, the object-oriented modelling provides a convenient design approach, since system prototyping and simulation can be carried out easily, rapidly and efficiently. In the work, the object-oriented modelling provided by the Modelica-Dymola environment is used to perform a comparison between different technologies for aircraft actuation systems in terms of power absorption characteristics. Starting from the same set of basic design requirements (working stroke stall force, maximum no-load velocity, settling time of the actuator position response, etc.), three actuators characterised by different technology solutions (servo-hydraulic, electro-hydrostatic and electro-mechanical) have been defined, and the related “objectmodels” have been developed and characterised in terms of dynamic performances. In parallel, the model of a basic flight control system with two ailerons, two elevators and one rudder has been created, including the aerodynamic hinge moment simulation and the simulation of elasticity of the actuator structural links. The actuator models have been then used to obtain three types of actuation systems: a traditional servo-hydraulic one, a “moreelectric” plant with all electro-hydrostatic actuators, and an “all-electric” system. Each system has been finally tested with the same command time history by reproducing a sample flight manoeuvre, and the total power absorption has been analysed. Simulation confirms the superiority of the all-electric solution for energy savings, but it also highlights the necessity of completing the study taking into account the thermal aspects

Caratterizzazione sperimentale della risposta in rigidezza dell’attuatore HT

Il presente lavoro documenta le attività condotte presso il Dipartimento di Ingegneria Aerospaziale dell'Università di Pisa sulla caratterizzazione sperimentale della risposta in rigidezza dell’attuatore di Horizontal Tail del velivolo Alenia Aermacchi M346. Gli esperimenti sono stati effettuati applicando all’attuatore sia carichi statici che dinamici, ed in corrispondenza di diverse condizioni operative, ottenute introducendo artificialmente avarie idrauliche ed elettriche. Ulteriori prove sono state effettuate variando i parametri del controllo in ciclo chiuso sulla posizione dell’attuatore, usando come riferimento le versioni 3.9.9.1 e 3.9.9.2 della AIM Card dello stesso. Al fine di valutare l’attendibilità dei risultati sperimentali ottenuti, essi sono stati confrontati con quelli a disposizione di Alenia SIA (unità di Genova), forniti dai laboratori della Smiths Aerospace Wolverhampton, società responsabile della fornitura ad Alenia Aermacchi dell’attuatore oggetto di studio