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 helicopter-mode 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.

The first part of the history of composites in aerospace emphasised materials with high specific strength and stiffness. This was followed by a quest for reliable manufacturing techniques that guaranteed sufficiently high fibre volume fractions in complex structural parts with reasonable cost. Further improvements are still possible leading, ultimately to an extension of the functionality of composite structures to non-mechanical functions. Reduction of material scatter and a more probability-based design approach, improved material properties, higher post buckling factors, improved crashworthiness concepts and improved NDI techniques are some of the evolutionary measures that could improve the performance of current composite structures. Modular design, increased co-curing, hybrid material structures, hybrid fabrication methods, innovative structural concepts and reduced development times are more revolutionary steps that could bring today’s solutions further. Manufacturing engineering is also important for achieving revolutionary change. Function integration such as embedded deicing, morphing,, and boundary-layer suction are among the next steps in weight and cost reduction, but now on the system level.

Although the deployment of carbon fibre structural components has enjoyed wide success on smaller aircraft, their acceptance on larger transport airframes is less sanguine – especially in the case of primary structure applications where the increasing out of plane loads found on the larger airframes have exposed the weak interlaminar properties of the layered material system. This has led to an overreliance on mechanical attachments to suppress these through thickness failures, which ultimately degrades structural performance and increases manufacturing costs. Until these resin dominated failure modes can be dealt with more effectively, without adversely affecting the in plane properties of the laminate, the true weight-savings potential afforded by carbon fibre material systems will be difficult to attain. This paper describes how researchers at NASA-LaRC and The Boeing Company are working to develop a next generation stitched composite design solution that addresses the fundamental challenges in achieving improved structural performance and reduced fabrication costs for large carbon fibre airframe structures.