Aerodynamic Shape Optimisation of a Proprotor and Its Validation by Means of CFD and Experiments

The aerodynamic shape design of a proprotor for a tiltrotor aircraft is a very complex and demanding task because it has to combine good hovering capabilities with high propeller efficiency. The aim of the present work is to describe a two-level procedure and its results for the aerodynamic shape design of a new rotor blade for a high-performance tiltwing tiltrotor aircraft taking into account the most important flight conditions in which the aircraft can operate. Span-wise distributions of twist, chord and aerofoil were chosen making use of a multi-objective genetic optimiser that worked on three objectives simultaneously. A non-linear sweep angle distribution along the blade was designed to reduce the power losses due to compressibility effects during axial flight at high speed. During the optimisation process, the aerodynamic performance of the blade was evaluated with a classical two-dimensional strip theory solver. The optimised blade was than analysed by means of a compressible Navier-Stokes solver and calculations were validated comparing numerical results with experimental data obtained from wind-tunnel tests of a scaled model of the proprotor

Towards a Wind Tunnel Testing Environment for Rotorcraft Operations Close to Obstacles

The correct identification of the aerodynamic loads due to interaction between rotorcraft and obstacles requires to run computationally intensive numerical models characterized by a high level of uncertainty. Wind tunnel data can be used as a source of information to improve those models. The present paper investigates the aerodynamic interaction of a helicopter and ship airwake exploiting wind tunnel data. A series of wind tunnel experiment, using a scaled helicopter model and Simple Frigate Shape 1, has been performed to measure forces and moments acting on the rotor, while the helicopter is approaching the flight deck. In addition, the velocity components along the longitudinal symmetry plane of the rotor have been visualized using PIV technique. With the rotor positioned at the starting point of the landing trajectory, the load measurements are used to modify the distribution of the inflow over the rotor in multibody simulation environment, in order to generate same loads, including thrust, torque and in-plane moments. Then, an identification algorithm is developed to capture the effect of ship airwake on the rotor loads during the maneuvers, modeling it as an external gust to the rotor inflow. The gust velocity is obtained through an optimization algorithm with the objective of generating same load coefficients as the experiment. The simulation results show that the same load coefficients as the experiment can be generated by implementing a linear gust over the rotor with a magnitude that changes as the rotor moves through the wake of ship. The experiment showed that this test setup could be used for identification of aerodynamic interaction to be used for maneuver analysis

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

Experimental investigation of a helicopter rotor with Gurney flaps

The present work describes an experimental activity carried out to investigate the performance of Gurney flaps on a helicopter rotor model in hovering. The four blades of the articulated rotor model were equipped with Gurney flaps positioned at 95% of the aerofoil chord, spanning 14% of the rotor radius. The global aerodynamic loads and torque were measured for three Gurney flap configurations characterised by different heights. The global measurements showed an apparent benefit produced by Gurney flaps in terms of rotor performance with respect to the clean blade configuration. Particle image velocimetry surveys were also performed on the blade section at 65% of the rotor radius with and without the Gurney flaps. The local velocity data was used to complete the characterisation of the blade aerodynamic performance through the evaluation of the sectional aerodynamic loads using the the control volume approach

Experimental Investigation on the Aerodynamic Interaction Between a Helicopter and Ground Obstacles

In this study, experiments were performed to investigate the aerodynamic interaction between a helicopter and ground obstacles. A new experimental set-up was realised and validated. The motorised helicopter model, which included the fuselage, was positioned in different positions relative to a model building in order to replicate different hovering configurations. The use of a helicopter model with a six-component balance and a building model with several pressure taps allowed a database to be compiled for the loads on the helicopter and obstacle. First several tests were performed without the building in order to develop a reference database and assess the experimental set-up through a comparison with results in the literature. The measured loads were analysed to investigate the interference effects of the building model on the helicopter performance. A physical interpretation of the flow phenomena was obtained through analysis of the obstacle pressure measurements and particle image velocimetry surveys of relevant configurations

Still air resistance during walking and running

: In everyday life during terrestrial locomotion our body interacts with two media opposing the forward movement of the body: the ground and the air. Whereas the work done to overcome the ground reaction force has been extensively studied, the work done to overcome still air resistance has been only indirectly estimated by means of theoretical studies and by measurements of the force exerted on puppets simulating the geometry of the human body. In this study, we directly measured the force exerted by still air resistance on eight male subjects during walking and running on an instrumented treadmill with a belt moving at the same speed of a flow of laminar air facing the subject. Overall, the coefficient of proportionality between drag and velocity squared (Aeff) was smaller during running than walking. During running Aeff decreased progressively with increasing average velocity up to an apparently constant, velocity independent value, similar to that predicted in the literature using indirect methods. A predictive equation to estimate drag as a function of the speed and the height of the running subject is provided

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

Experimental study of a helicopter model in shipboard operations

The paper presents the experimental investigation of the aerodynamic interaction between a helicopter model and a ship model with a simplified geometry. In the first phase of the experiment, a series of wind tunnel tests were carried out in order to study the flow features on the flight deck for several wind conditions, without the presence of the helicopter. Pressure measurements and Particle Image Velocimetry surveys were performed to assess the effect of wind velocity and direction on the flow field in the landing region over the ship deck. Moreover, the effect of the Atmospheric Boundary Layer was investigated. In the second phase of the experimental campaign, a helicopter model was positioned in a series of points representative of a typical stern landing trajectory and a vertical descent above the landing spot. The landing maneuver was performed in three different wind conditions, including no-wind, head wind and wind blowing from port side of the deck. The rotor loads and moments were measured by means of a six-axis balance for all test points. The use of different measurement techniques in the present experiments provides a comprehensive database suitable for the study of the rotor-ship aerodynamic interaction. Additionally, the experimental results are used to develop an identification algorithm to be incorporated into the flight simulator environment to capture the effect of ship airwake on the rotor loads during shipboard operations

Graphene Materials Strengthen Aqueous Polyurethane Adhesives

Carboxyl-functionalized graphene platelets (GP) and graphene oxide (GO) sheets were added to a commercial aqueous adhesive dispersion of thermoplastic polyurethane (TP) (Idrotex 200 from FacGB s.r.l.). For both additives, the weight percentage was of industrial interest, 0.01 and 10.1 wt %. The addition of GP/GO was carried out in a simple and scalable-up process that can be applied to other materials and additives. Mechanical, peel tests were applied on polyurethane strips (75 mm long, IS mm wide, and 1.5 mm thick) prepared cutting extruded sheets obtained using Estane 58091, a 70D aromatic polyester-based TP. The tests with 0.01 wt % of GP showed statistically significant higher forces at first failure and maximum forces with respect to the pristine adhesive. Sample characterization was carried out with scanning electron microscopy, infrared spectroscopy, X-ray diffraction, and thermal analysis. A mechanism is suggested for the improved performance of the low-dose GP adhesive