Simple, approximate relations are developed that allow rapid, yet accurate, estimates of the principal mass characteristics of modern civil transport aircraft. The method is based upon an ‘aircraft mass hypothesis’ combined with data taken from Type Certificates and manufacturers’ information for 44 different Boeing and Airbus aircraft types and variants. This hypothesis links the masses of the various aircraft components, including the operational items, and the maximum payload mass to just two parameters; the passenger cabin floor area, as exemplified by the ‘design passenger number’ and the ratio of maximum zero fuel mass to maximum take-off mass, as exemplified by the non-dimensional ‘design range’. In this context, the ‘design range’ is defined as the maximum possible range when the aircraft is operating at its maximum zero fuel mass. This approach leads to the formulation of three basic ‘laws’ for aircraft mass. Special consideration is given to the identification and separation of those components that are fixed either by the design, or the certification process, and those that are free, within defined limits, to be chosen by the operator.

It is generally recognised that fuel can be saved on long haul routes if non-stop flights are broken down into a number of short stages. As fuel costs rise, these savings may eventually become economically attractive to airlines. ‘Staging’ may also play a role in the reduction of aviation’s impact upon climate change. To allow an accurate estimate of the potential benefits, an analytic model has been developed from first principles, with closure provided by data from existing aircraft. The analysis captures the relevant parameters and their influence is quantified. It has been found that significant savings are only available for distances greater than about 5,500km and a stop at the halfway point is either the best, or close to the best, strategy. For the longest routes, optimal staging with existing long range aircraft can give savings of up to 12%. However, if aircraft optimised for the stage lengths are used, this may be increased to up to 28% and, if the floor area per passenger is reduced to the short haul level, a limiting value of about 45% may be possible. The aircraft design passenger number and, provided it is constant, the load factor have little, or no, effect upon the percentage savings. Maximum use of staging on all current routes longer than 5,500km could reduce the total fuel consumed by between 3% and 20%, with a consequent reduction in global fleet annual fuel burn of between 1% and 6%. However, the savings for a given route are reduced as aircraft become more efficient.

The Swiss Airforce is operating F/A-18C/D Aircraft since 1997. Since the aircraft’s structural design is different from the version operated by the US Navy it was necessary to carry out a structural integrity study (ASIP) which was done by The Boeing Company in St. Louis. To validate this study a full scale fatigue test facility was build at RUAG and operated from 2003 to 2005. When operating this facility difficulties were encountered with the aerodynamic loads data provided by Boeing (insufficient, not well documented, questionable data). As a result RUAG looked for alternative methods to provide the aerodynamic loads, and a large investment was made in the development of a Computational Fluid Dynamics (CFD) tool. The Navier Stokes Multi Block (NSMB) solver, which was developed in an international collaboration, was adopted. In a first phase the code was validated by comparing results of CFD calculations with wind-tunnel results, results from literature and flight test data results. In the second phase, discussed in this paper, a Fluid Structure Interaction (FSI) tool was developed to permit unsteady aero-elastic simulations. Particular attention is focused on the vertical tail since this component of the F/A-18 fighter is very sensitive to fatigue due to unsteady loads generated by buffeting phenomena.

A helicopter model has been identified and validated for flight conditions defined by altitudes, speeds, loadings and centre of gravity positions. To identify the helicopter models, 2-3-1-1 multistep control inputs were performed by the pilot to excite all helicopter modes. Then, each estimated signal has to remain in tolerance margins defined by the Federal Aviation Administration. Three methods were used to observe the system outputs from its states: a fuzzy logic method, a linear method optimised with a neural network algorithm and a classical method. Because of random effects when gathering data, classical method did not give good enough results. The fuzzy logic method was not robust enough so that output plots showed peaks that could be felt by the pilot. Then, because the model could be implemented in a simulator for the pilot training, the pilot feedback is very useful in order to compare the reality with the results of the mathematical model. When the outputs are obtained from the measured state variables, the linear method gave the best results.

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.