Aircraft Design最新文献

The paper shows the logical process carried out in order to define, in a preliminary way, concepts of cost-effective Unmanned Offensive Airplane Vehicles (UOAV). In particular, the goal is to explore the feasibility of a system whose size and performances are reduced if compared with the ones expected by UAVs now under development. However, they are more affordable and quite effective. On the basis of mission requirements, some configurations have been considered and they will be presented by describing the logical paths explaining the evolution from each one to the others. All concepts presented will be examined and technically considered, in particular the last one. This concept will also be the object of a preliminary comparative evaluation from the point of view of efficacy and costs. From the educational point of view, this study is considered as a first step towards a more detailed activity which foresees an important involvement of students.

A novel approach to assessing aircraft system feasibility and viability is presented, with special emphasis on modeling and estimating the impact of new technologies. The approach is an integral part of an overall stochastic, life-cycle design process under development by the authors, which is to address the new measure for system value: affordability. Stochastic methods are proposed since the design process is immersed in ambiguity and uncertainty, both of which vary with time as knowledge increases about the system behavior. The specific task addressed in this paper of examining system feasibility and viability is encapsulated in the five steps of the Concept Feasibility Assessment approach. The rationale and technical foundations of each step are explained, and the approach is compared to more traditional, deterministic means for examining a design space and evaluating technology impacts. Finally, the techniques are implemented on a supersonic transport design problem to highlight the power of the approach on a problem of significant interest to the international aerospace community. Several innovative avenues for viewing the design and technology spaces are employed in assessing first feasibility and then viability for the problem.

This paper presents a numerical simulation of the external and engine inlet flows for the F-18 aircraft at typical high-angle-of-attack flight conditions. Two engine inlet mass flow rates, corresponding to flight idle and maximum power, were computed. This was accomplished using a structured, overset grid technique to couple the external and internal grid systems. Reynolds-averaged Navier–Stokes solutions were obtained using an implicit, finite-differencing scheme. Results show a strong coupling of the external and engine inlet flows, especially at the maximum power setting. Increasing the mass flow rate through the inlet caused the primary vortex breakdown location to move downstream. This trend is also observed in flight tests performed on the F-18. A reversed flow region upstream of the inlet duct is visible in the faired-inlet and flight-idle computations. This flow reversal is not present in the maximum power setting computation. These large-scale changes in flow structure highlight the importance of simulating inlet conditions in high-angle-of-attack aircraft computations.

In recent years neural networks have been proposed for identification and control of linear and non-linear dynamic systems. This paper describes the performance of a neural network-based fault-tolerant system within a flight control system. This fault-tolerant flight control system integrates sensor and actuator failure detection, identification, and accommodation (SFDIA and AFDIA). The first task is achieved by incorporating a main neural network (MNN) and a set of n decentralized neural networks (DNNs) to create a system with n sensors which has the ability to detect a wide variety of sensor failures. The second scheme implements the same main neural network integrated with three neural network controllers. The contribution of this paper focuses on enhancements of the SFDIA scheme to allow the handling of soft failures as well as addressing the issue of integrating the SFDIA and the AFDIA schemes without degradation of performance in terms of false alarm rates and incorrect failure identification. The results of the simulation with different actuator and sensor failures with a non-linear aircraft model are presented and discussed.

A large database of currently manufactured turbofan engines with a bypass ratio of at least 2.0 was compiled in 1996. Key parameters (dry weight, length, fan diameter, nacelle diameter, cruise thrust, air mass flow, bypass ratio, total pressure ratio, take-off specific fuel consumption, and cruise specific fuel consumption) were plotted, most as a function of take-off thrust. The resulting plots are a rich source of basic information, which can be used to quickly define an engine for use in a preliminary airplane design. The database is sorted by take-off thrust and can also be used to determine if an existing engine can be used in the proposed airplane. Relationships are suggested for use in preliminary design.

This paper presents experimental observations of two-dimensional air flows with a Reynolds number of 170 passing a stationary circular cylinder and its active control of transition to turbulence. One of the potentials of this research application is in aircraft design.

A hot-wire sensor was located in the upper shear layer of the cylinder at about 0.9d streamwise and about 0.8d above the cylinder axis. After the phase of the feedback signal shifted 180°±2° and the amplifier gain was adjusted, perturbations were imposed at vortex-shedding frequency on the wake of the cylinder on both sides of the wind tunnel. The induced perturbations were significant and the Karman vortex street responded vigorously to the feedback of the signal from the hot-wire sensor in the wake of the cylinder at vortex-shedding frequency. Thereafter, the amplitudes of velocity fluctuations were significantly reduced in the Karman vortex street. The Karman vortex street was studied at various locations spanwise to examine the extent of the response of the longitudinal components of velocity fluctuations in the wake. The amplitude of velocity fluctuations was measured with the hot-wire probe positioned at x/d=2 off the center about 1/2 diameter spanwise in the wake of the cylinder. Finally, the vortex street was studied at various locations to examine variability of the longitudinal components of the velocity fluctuations. The free stream velocity of the wind tunnel maintained uniformly at U_∞=80.4 cm/s during the experiment.

A new formula is presented for estimating the maximum take-off weight of an initial short-haul jet transport aircraft design in terms of its main specified mission characteristics: design payload, range and field length at sea level ISA. The formula is based on an approximation of numerical modelling results for designs optimised with respect to geometry, powerplant and aerodynamic characteristics. The method provides an accurate prediction of the take-off weight in the initial design phase and also allows evaluation of the take-off weight sensitivity with respect to changes in the specification.

Regional transports in the 10–22 passenger category will be jet-powered in the near future. The rationale for this predicted development is discussed in this paper. Based on operational and affordability factors the desired mission requirements for these airplanes are determined. It is shown that the cost of these airplanes must be kept under very tight control. One approach to achieving this is to develop a family of two airplanes, a single fuselage 10-passenger airplane and a twin-fuselage 22-passenger airplane. These airplanes are to have a large amount of commonality. Several design challenges and certification issues are also discussed.