Wind-Tunnel Tests of a Tilt-Rotor Aircraft

A wide aerodynamic test campaign has been carried out on the tiltrotor aircraft ERICA at the Large Wind Tunnel of Politecnico di Milano by means of a modular 1:8 scale model in order to produce a dataset necessary to better understand the aerodynamic behaviour of the aircraft and to state its definitive design. The target of the tests was the measurement of the aerodynamic forces and moments in several different configurations and different attitudes. The test program included some conditions at very high incidence and sideslip angles that typically belong to the helicoptermode flight envelope and measurements of forces on the tail and on the tilting wings. A large amount of data has been collected that will be very useful to refine the aircraft design. In general the aircraft aerodynamics do not present any critical problems, but further optimisation is still possible. From the viewpoint of drag in the cruise configuration, the sponsons of the landing gear seem to be worth some further design refinement since they are responsible for a 20% drag increase with respect to the pure fuselage configuration. On the contrary, the wing fairing has proved to work well when the aircraft longitudinal axis is aligned with the wind, providing just a slight drag increase. Two other interesting aspects are the quite nonlinear behaviour of the side force for the intermediate sideslip angles as well as the noticeable hysteresis in the moment coefficient at very high incidence angles

Wind-tunnel tests of a heavy-class helicopter optimised for drag reduction

Wind-tunnel tests of a heavy-class helicopter model were carried out to evaluate the effectiveness of several components optimised for drag reduction by computational fluid dynamics analysis. The optimised components included different hub-cap configurations, a fairing for blade attachments and the sponsons. Moreover, the effects of vortex generators positioned on the back ramp were investigated. The optimisation effect was evaluated by comparison of the drag measurements carried out for both the original and the optimised helicopter configurations. The comprehensive experimental campaign involved the use of different measurement techniques. Indeed, pressure measurements and stereo particle image velocimetry surveys were performed to achieve a physical insight about the results of load measurements. The test activity confirms the achievement of an overall reduction of about 6% of the original model drag at cruise attitude

Stereo particle image velocimetry set up for measurements in the wake of scaled wind turbines

Stereo particle image velocimetry measurements were carried out in the boundary layer test section of Politecnico di Milano large wind tunnel to survey the wake of a scaled wind turbine model designed and developed by Technische Universität München. The stereo PIV instrumentation was set up to survey the three velocity components on cross-flow planes at different longitudinal locations. The area of investigation covered the entire extent of the wind turbines wake that was scanned by the use of two separate traversing systems for both the laser and the cameras. Such instrumentation set up enabled to gain rapidly high quality results suitable to characterise the behaviour of the flow field in the wake of the scaled wind turbine. This would be very useful for the evaluation of the performance of wind farm control methodologies based on wake redirection and for the validation of CFD tools

Proprotor–wing aerodynamic interaction in the first stages of conversion from helicopter to aeroplane mode

Tiltrotors have the potential to revolutionise air transportation since they combine the flight performance of aeroplanes with the versatility of helicopters. One of the most crucial features characterising tiltrotors is represented by the aerodynamic interaction between wing and rotor. Although this phenomenon has been largely studied using both experiments and calculation, analyses were mainly focused on helicopter operative mode and hovering condition. The present work is aimed at describing the effects due to the aerodynamic interference between wing and rotor of a tiltrotor aircraft employing the tiltwing concept solution during the first stage of the conversion manoeuvre from helicopter to aeroplane configuration. Experimental tests carried out in the open test section of the Politecnico di Milano Large Wind Tunnel with a half-span scaled powered model are reported in detail and results are illustrated in terms of rotor performance and wing aerodynamic loads. Both isolated rotor and half-span model test results are presented as function of several parameters. Overall aircraft performance during the first part of the conversion manoeuvre is finally discussed

Stereo Particle Image Velocimetry Measurements of Perpendicular Blade-Vortex Interaction over an Oscillating Airfoil

The aerodynamic interaction of a stream-wise vortex impacting on a NACA 23012 oscillating airfoil was investigated using stereo particle image velocimetry. The experimental rig enabled the study of the aerodynamic effects due to the blade pitching motion in the interaction with the vortex. The experimental study focused on the light dynamic stall regime, which represents a typical condition of the retreating blade of a helicopter in forward flight. Particle image velocimetry was applied to a measurement volume close to the airfoil upper surface in order to obtain the three-dimensional interacting flow field. In particular, the experimental results show that during the airfoil downstroke motion, the vortex impact triggers the stall of the local blade section, indicating that detrimental effects on the blade performance can be introduced by perpendicular vortex interactions

Helicopter-Obstacle Aerodynamic Interaction in Windy Conditions

The helicopter-obstacle interaction has become a challenging research topic in the last few years. The detrimental effects which can arise in this kind of aerodynamic interaction can be dramatically worsened under windy conditions, particularly when the helicopter flies inside the turbulent and extremely unsteady wake generated by an obstacle. In the present paper a comprehensive experimental survey carried out at Politecnico di Milano is described, obtained by placing a helicopter model in several positions with respect to an obstacle, in windy and not windy conditions. The experimental database comprises load measurements on the rotor in order to assess the rotor performance for different positions with respect to a cubic obstacle, steady and unsteady pressure measurements on the obstacle and Particle Image Velocimetry (PIV) measurements in the region between the rotor and the obstacle in order to highlight the features of the interacting flowfield

Wing-Rotor Aerodynamic Interference on a Tiltwing Aircraft in the First Part of Conversion Manoeuvre

Tiltwing aircraft represents a possible future evolution of conventional tiltrotors. Indeed, by making use of smaller rotors, a tiltwing is able to hover in helicopter mode, to achieve very high forward speed in cruise flight in aeroplane mode and to allow for horizontal taking off and landing. The partial tilting wing concept, introduced in 2000 in the ERICA tiltrotor design, made the tiltwing solution even more attractive. Although this promising configuration was widely studied, many aspects require further analysis. In the present work, the initial stage of the transition manoeuvre that allows a tiltwing aircraft employing the partial tilting wing solution to convert from helicopter to aeroplane mode is investigated. An extensive wind tunnel test campaign carried out in the Politecnico di Milano Large Wind Tunnel is described and the effects due to the aerodynamic interaction between wing and rotor are discussed. Aircraft performance are also discussed to assess the effectiveness of this aircraft design

Wing-Rotor Interactions on a 1/4 - Scale Tiltrotor Half-Model

In a tiltrotor aircraft, the aerodynamic interaction between wing and rotors can have a negative influence on the hovering performance and on the lifting capability. In 2011, a research activity has been started at Dipartimento di Scienze e Tecnologie Aerospaziali at Politecnico of Milano to study from both an experimental and numerical point of view the aerodynamic interference between wing and rotor on a tiltwing aircraft. A 0.25 scale model, based on the aircraft geometry defined at the very beginning of this activity, has been manufactured in–house and the experimental test rig represents only one half– wing and the corresponding rotor and nacelle. The rotor performance were evaluated in terms of figure of merit both for the isolated rotor and for the half–model configurations. Two different wing configurations (untilted and tilted) were tested to understand how the airframe affects the rotor performance. The forces generated on wing by the rotor wake were measured for a wide range of thrust coefficients for both wing configuration. Particle–image velocimetry technique was used to acquire two–dimensional images of the flow field close to the tilted part of the wing