On the Preliminary Structural Design Strategy of the Wing of the Next-Generation Civil Tiltrotor Technology Demonstrator

The T-WING project is a Clean Sky 2 research project aimed at designing, manufacturing, qualifying and flight-testing the new wing of the Next-Generation Civil Tiltrotor Technology Demonstrator (NGCTR-TD), as part of the Fast Rotorcraft Innovative Aircraft Demonstrator Platforms (FRC IADP) activities. Requirements, design strategy, methodology and main steps followed to achieve the composite wing preliminary design are presented. The main driving requirements have been expressed in terms of dynamic requirements (e.g., limitations on natural frequencies), aeroelastic requirements, i.e., compliance with European Aviation Safety Agency (EASA) CS-25 and CS-29 Airworthiness Requirements), structural requirements (e.g., target wing structural mass), functional requirements (e.g., fuel tanks, accessibility, assembly and integration, etc.) and wing preliminary loads. Based on the above-mentioned requirements, the first design loop is performed by targeting an optimal wing structure able to withstand preliminary design loads, and simultaneously with stiffness and inertia distributions leading to a configuration free from flutter within the flight envelope. The outcome from the first design loop is then used to refine the model and compute more reliable flight loads and repeat aeroelastic analysis, returning further requirements to be fulfilled in terms of wing stiffness and inertia distributions. The process is iterated till the fulfillment of all the project requirements

Wing structure of the next-generation civil tiltrotor: From concept to preliminary design

The main objective of this paper is to describe a methodology to be applied in the preliminary design of a tiltrotor wing based on previously developed conceptual design methods. The reference vehicle is the Next-Generation Civil Tiltrotor Technology Demonstrator (NGCTR-TD) developed by Leonardo Helicopters within the Clean Sky research program framework. In a previous work by the authors, based on the specific requirements (i.e., dynamics, strength, buckling, functional), the first iteration of design was aimed at finding a wing structure with a minimized structural weight but at the same time strong and stiff enough to comply with sizing loads and aeroelastic stability in the flight envelope. Now, the outcome from the first design loop is used to build a global Finite Element Model (FEM), to be used for a multi-objective optimization performed by using a commercial software environment. In other words, the design strategy, aimed at finding a first optimal solution in terms of the thickness of composite components, is based on a two-level optimization. The first-level optimization is performed with engineering models (non-FEA-based), and the second-level optimization, discussed in this paper, within an FEA environment. The latter is shown to provide satisfactory results in terms of overall wing weight, and a zonal optimization of the composite parts, which is the starting point of an engineered model and a detailed FEM (beyond the scope of the present work), which will also take into account manufacturing, assembly, installation, accessibility and maintenance constraints

Maneuver Load Controls, Analysis and Design for Flexible Aircraft

L'obiettivo principale della Tesi di Dottorato è stato quello di definire metodologie numeriche per il disegno e l’analisi di un sistema di alleviazione del carico di manovra che tenga conto dell’elasticità della struttura, nonché di quantificare i benefici derivanti dall’utilizzo di tali sistemi in termini di allungamento della vita a fatica. Le metodologie sviluppate sono di tipo teorico/numerico. Nel corso del primo anno è stata messa a punto una metodologia per il calcolo dei parametri di equilibrio del velivolo elastico in manovra quasi-statica bilanciata ed un metodo per ridurre il carico strutturale alare. Nel corso del secondo anno è stata messa a punto una metodologia per il calcolo dell’efficacia aeroelastica di una superficie mobile quando essa è utilizzata per alleviare il carico da manovra simmetrica non stazionaria. L’attività del terzo anno è consistita nel disegno concettuale di un sistema automatico di controllo dei carichi da manovra in volo longitudinale. E’ stata definita l’architettura del sistema aero-servo-elastico a loop chiuso per il controllo simultaneo del fattore di carico e del momento flettente nella stazione dell’ala più sollecitata. Sono state eseguite applicazioni numeriche su velivolo a configurazione non convenzionale e a configurazione classica (joined-wing UAV e CS-25 business jet). Infine, è stato stimato il miglioramento della vita a fatica derivante dall’utilizzo di un sistema automatico di controllo dei carichi, per elementi strutturali alari dimensionati a momento flettente. I risultati numerici ottenuti in termini di riduzione del carico di manovra sono rilevanti. Sono state registrate diminuzioni del momento flettente alla radice alare fino ad oltre il 30%, sia in caso di velivoli a configurazione fortemente non convenzionale (joined-wing), sia in caso di velivoli classici. La principale limitazione della metodologia consiste nel fatto che il carico è osservato e controllato in un’unica stazione alare, generalmente la più caricata che, in caso di architetture fortemente non convenzionali, potrebbe non coincidere con la radice alare. Tuttavia è possibile generalizzare il metodo introducendo altre superfici mobili dedicate all’alleviazione del carico per il controllo simultaneo in più stazioni. Appare difficile che sistemi di “load control” possano portare alla riduzione del peso strutturale data la reticenza degli Enti Certificanti ad accettare che la progettazione strutturale sia eseguita “a carico ridotto” senza prevedere eccessive ridondanze dei sistemi. D’altro canto l’allungamento della vita a fatica costituisce un beneficio di fortissimo interesse industriale. Sono stati stimati allungamenti della vita a fatica fino ad oltre il 50%, per elementi strutturali dimensionati a momento flettente

U-HARWARD: a CS2 EU funded project aiming at the Design of Ultra High Aspect Ratio Wings Aircraft

International audienceThe paper introduces the EU funded project CS2-U-HARWARD, started, in response to the call JTI-CS2-2019-CFP10-THT-07: Ultra-High Aspect ratio wings, aiming at the use of innovative aerodynamic and aeroelastic designs in a multi-fidelity multi-disciplinary optimal design approach to facilitate the development of Ultra-High aspect ratio wings for medium and large transport aircraft. The structure of the project, the main goals as well as the preliminary results obtained together with the due final considerations are reported

Wing Structure of the Next-Generation Civil Tiltrotor: From Concept to Preliminary Design

The main objective of this paper is to describe a methodology to be applied in the preliminary design of a tiltrotor wing based on previously developed conceptual design methods. The reference vehicle is the Next-Generation Civil Tiltrotor Technology Demonstrator (NGCTR-TD) developed by Leonardo Helicopters within the Clean Sky research program framework. In a previous work by the authors, based on the specific requirements (i.e., dynamics, strength, buckling, functional), the first iteration of design was aimed at finding a wing structure with a minimized structural weight but at the same time strong and stiff enough to comply with sizing loads and aeroelastic stability in the flight envelope. Now, the outcome from the first design loop is used to build a global Finite Element Model (FEM), to be used for a multi-objective optimization performed by using a commercial software environment. In other words, the design strategy, aimed at finding a first optimal solution in terms of the thickness of composite components, is based on a two-level optimization. The first-level optimization is performed with engineering models (non-FEA-based), and the second-level optimization, discussed in this paper, within an FEA environment. The latter is shown to provide satisfactory results in terms of overall wing weight, and a zonal optimization of the composite parts, which is the starting point of an engineered model and a detailed FEM (beyond the scope of the present work), which will also take into account manufacturing, assembly, installation, accessibility and maintenance constraints