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Paletta N.,Centro Italiano Ricerche Aerospaziali | Paletta N.,Aerospace Structural Design and Analysis Group | Belardo M.,Centro Italiano Ricerche Aerospaziali | Belardo M.,Aerospace Structural Design and Analysis Group | Pecora M.,Centro Italiano Ricerche Aerospaziali
Journal of Aircraft | Year: 2010

In this paper a method of alleviating wing structural load of a flexible aircraft during a symmetric balanced maneuver is presented. An application on the unmanned aircraft in development at the Italian Aerospace Research Center, high-altitude performance demonstrator, characterized by a joined-wing configuration, is illustrated. This load alleviation technique enables a desired value of the bending moment on a fixed wing control station to be obtained. The load reduction is achieved by deflecting a suitable set of flight-control surfaces, by always keeping the vertical load factor constant to preserve the maneuvering performance. The main hypotheses are: significant aeroelastic effects, linear behavior of aerodynamics and structure, and unvarying tensor of inertia under structural deflections. High-altitude performance demonstrator is a scaled performance demonstrator of an 80m-wing span high-altitude and long endurance unmanned aircraft in a joined-wing configuration. The advantages in terms of performance, fatigue life extension, and weight reduction can be achieved from the integration of an onboard load alleviation system. The results show that the attainable value of load alleviation in terms of bending moment reduction at the wing root is 37%. Moreover, the test-case analyses show that the maximum value of the alleviation increases with respect to the dynamic pressure although the load distribution varies because of significant aeroelastic effects. Copyright © 2010. Source

Belardo M.,Aerospace Structural Design and Analysis Group | Paletta N.,Aerospace Structural Design and Analysis Group | Di Palma L.,Italian Aerospace Research Center | Pecora M.,Aerospace Structural Design and Analysis Group
Journal of Aerospace Engineering | Year: 2014

Abstract The Italian Aerospace Research Center (CIRA) is currently designing an unmanned aerial research system that is lightweight and has high-structural flexibility, code named the High Altitude Performance Demonstrator (HAPD).The project is framed within the Italian Aerospace Research Program, under the Unmanned Aerial Vehicle (UAV) Chapter. This unmanned aerial system is mainly aimed at developing and validating advanced modeling methodologies for flexible aircrafts. A compendium of the system is provided in this paper, together with a deeper discussion of how CIRA developed the structural and aeroelastic design of HAPD. Some experimental tests performed to validate the main concepts are also presented. The vehicle has an unconventional joined-wing configuration that mitigates undesired extreme flexibility, but that results in a more complicated design. First, aeroelasticity has been taken into account from the preliminary stages of design because flexibility significantly affects aircraft behavior. Second, the HAPD structure is redundant with regard to constraints (because of its joined wing), thus making the internal forces dependent on the stiffness distribution. For these reasons, the availability of an integrated methodology that can support the structural design is mandatory. The output of such a methodology consists of primary structure stiffness distributions (fuselage, wings, and vertical tail), compatibly with the absence of any aeroelastic instability, and structural failure under operative loads. © 2014 American Society of Civil Engineers. Source

Picardi F.M.,University of Naples Federico II | Paletta N.,Aerospace Structural Design and Analysis Group | Belardo M.,Aerospace Structural Design and Analysis Group | Pecora M.,Aerospace Structural Design and Analysis Group
Journal of Aerospace Engineering | Year: 2014

The development of reliable and computationally efficient analysis capabilities for aeroelasticity represents one of the most intriguing challenges of modern times. In this paper, an automatic procedure for flutter clearance assessment under damage has been set up. The whole procedure is efficient in managing flutter calculations when a stiffness or inertia change occurs in a substructure of the aircraft, where the change is meant to be caused by a damage occurring during flight. The efficiency is reached by means of a substructuring approach. The procedure has been set up on a business jet in which damage cases on a trunk of the horizontal tail are processed. The method has the advantage to be effectively used when flutter occurrence has to be evaluated on a statistical basis because of its computational efficiency and reliability. Statistical quantities such as cumulative density function and probability density function related to flutter speed by means of hit or miss Monte Carlo simulations have been calculated in order to show the potentiality of the method when approaching a stochastic analysis. The damage database that has been processed by Monte Carlo is not significant from a statistical point of view. Nevertheless, the aim of the paper is to set up the procedure, which is deemed a useful tool to quickly assess flutter clearance under damage, especially for military aircrafts, subjected to the extent of damages that can effect the aeroelastic performance. It has been estimated that a statistical significant number of cases (71,428 cases) would require 80 h of computational time with a laptop of moderate performance. © 2014 American Society of Civil Engineers. Source

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