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In-service data from two Bombardier business jets, a Global 5000 and a Global Express XRS, have been compared. Flight data has been analyzed from both airframes with comparable number of ground-air-ground cycles. Individual flight phase have been examined and compared between the two airframes. Primary emphasis has been placed on airframe usage. The influence of primary mission on ground-air-ground cycles has been highlighted in the form of ground and flight loads, as well as dynamics of the flights. It is demonstrated that safe-life maintenance approach may have to be adjusted to account for the airframe usage.

Presented here are analyses and statistical summaries of data collected from 11,299 flight operations recorded on 6 BE-1900D aircraft during routine commuter service over a period of three years. Basic flight parameters such as airspeed, altitude, flight duration, etc. are shown in a form that allows easy comparison with the manufacturer's design criteria. Lateral ground loads are presented for ground operations. Primary emphasis is placed on aircraft usage and flight loads. Maneuver and gust loads are presented for different flight phases and for different altitude bands. In addition, derived gust velocities and various coincident flight events are shown and compared with published operational limits.

Data obtained from digital flight data recorders are used to assess the actual operational environment of propellers on a fleet of Beech 1900D aircraft in commuter role. Information is given on various aerodynamic parameters as well as those pertaining to engine and propeller usage. The takeoff rotation has been identified as the most demanding phase of flight in terms of unsteady loads exerted on the propeller blades. Special attention is paid to ground operations.

Some of the methods used for experimental detection and examination of wake vortices are presented. The aim of the article is to provide the reader a brief overview of the available methods. The material is divided into two major sections, one dealing with methods used primarily in the laboratory, and the second part devoted to those used in field operations. Over one hundred articles are cited and briefly discussed.

An algorithm is developed and validated for automatic avoidance of restricted airspaces. This method is devised specifically for implementation with an advanced flight control system designed for general aviation application. The algorithm presented here implements two inputs to the aircraft; the bank angle, and the airspeed, while the control system always ensures coordinated maneuvers. Unlike collision avoidance systems, the current method is not designed to serve in an advisory role, but to assume complete control of the aircraft if necessary. It is demonstrated that in order to implement this technique, the aircraft must be assigned an immediate domain whose size would have to depend on the aircraft performance and flight conditions. The strategy is designed such that as the domain surrounding the aircraft approaches that of the restricted airspace, aircraft control would switch gradually away from the pilot and to the controller, which would initiate an evasive maneuver.

An envelope protection scheme is proposed for responding to a microburst. This approach is based on limiting the allowable maximum inertial deceleration of the aircraft when flying at low airspeeds. This technique is shown in simulations to be very effective at preventing stall and resulting in minimal loss of altitude. It is speculated that the same scheme can also protect an aircraft in the event of other forms of windshear encounters, such as making a sudden turn to downwind.

An experiment is performed to investigate the feasibility of using a water tunnel to study the aircraft wake vortex behavior in ground effect. Two blades are used to generate the vortices, simulating an aircraft wake. The ground plane is modeled with a splitter plate. Vortex mean positions are determined using an optical technique. The results show all the critical properties of an aircraft wake in the vicinity of the ground. The vortices are shown to descend monotonically until they start interacting with the ground plane. The minimum height to which the filaments sink is shown to compare favorably with that predicted by numerical methods and the operational data obtained from lidar. The vortex span is shown to increase at the same rate as that estimated from an empirical model based on lidar data as well. Vortex rebound is observed with maximum heights comparing well with other predictions. Partial comparison is also presented with a numerical scheme developed for AVOSS application.

Dynamic interactions of pairs of co-rotating vortex filaments, typical of those emanating from wing tips and flap tips are studied. Time history of the motion of individual filaments has been obtained in a water tunnel using an optical method. It is demonstrated that before their merger, co-rotating vortex filaments tend to oscillate along preferred directions. Also, the motion appears to be unstable with increasing amplitude over a wide range of frequencies. These conclusions are shown to be consistent with analytical predictions. It is also shown that the merger location correlates well with the vortex strength. Comparisons with analytical and computational results are provided where appropriate.

An advanced flight control system, which has been demonstrated to compensate for unanticipated failures in military aircraft, is proposed for use in general aviation. The method uses inverse control to decouple the flight controls and to modify the handling qualities of the aircraft, while employing artificial neural networks in order to compensate for any modeling error. These errors can stem from any differences between the model and the actual aircraft. Therefore, they can include in-flight hardware failures, rendering the system fault tolerant and reducing the necessity for multiple levels of redundancy. The proposed system is verified in simulations for longitudinal flight and is shown to be able to track pilot-commanded velocity and flight path angle. Also, one example is presented for in-flight changes of the configurations (flap deployment) where the controller is shown to adapt rapidly to these changes without a need for compensation by the pilot.

The aerodynamics of a typical Le Mans configuration is investigated numerically and experimentally. The purpose of the investigation has been to gain a better understanding of the aerodynamic characteristics of such configurations in extreme off-design conditions. Computational modeling is performed with a low-order panel method, while flow visualization is accomplished with dye injection in a water tunnel using a 1/24-scale model. At low angles of attack, excellent agreement is shown between the streamline patterns observed experimentally and those predicted computationally, despite the large differences in Reynolds numbers. Experimental results indicate presence of attached boundary layers over a large part of the car at very high angles of attack. Furthermore, strong vortical structures are detected around sharp edges of lower part of the car at these extreme attitudes.

The authors explore the possibility of designing the flap system on a given wing for enhanced Crow instability. The problem motivation in terms of increased traffic volume and increased safety is described. A brief review of the technical literature is given. An exploratory two-dimensional potential flow formulation is presented. A generic wing and flap combination is used for trade-off studies. The authors show that the frequency with which the flap-tip and the wing-tip vortex filaments swirl around each other can be tuned to match that which corresponds to the largest rate of amplitude growth in the wake. The extent of the analysis being two-dimensional, the authors suggest careful wind- or water-tunnel testing in three dimensions to validate the concept.

In nonlinear cases, the SDG method requires multidimensional search procedures. However, in linear cases only one-dimensional search procedures are required to identify the critical gust load conditions. In this study the application of the backpropagation ANN method as a multi-dimensional modeling tool has been proposed to model or identify the global and local extrema of one-dimensional gust load responses. The maximum and minimum response values of ramp-step input gust profiles were considered to investigate the ANN modeling capability and effectiveness. The actual SDG analysis for nonlinear cases was hypothesized to be performed over a large and sparse domain, therefore the ANN could be trained to quickly identify the region of the domain containing the global extrema. The SDG analysis, then, could be concentrated on a smaller region thereby reducing computation time.

A comparative analysis has been performed on the Boeing 727-100 using three conceptual design codes. These programs were: The Aircraft Synthesis Program, ACSYNT, Advanced Aircraft Analysis, AAA, and RDS-Student. The objective of this study was to investigate differences in the conceptual design methodologies of these three programs. All three codes showed reasonable prediction of drag in the subsonic flow regime. However all three programs had difficulty predicting transonic drag rise characteristics. The principal cause was the inability to accurately predict the critical drag rise Mach number. Difficulties in estimating the shape of the drag rise curve, relative to the critical Mach number, also contributed to the errors in drag prediction. AAA and RDS-Student gave reasonable predictions of maximum lift coefficient. ACSYNT could not model the triple-slotted flap system on the 727-100. The three codes showed a consistent trend towards under-prediction of empty weight.

The architecture and training of artificial neural networks are briefly described. Five applications of these networks to design and analysis problems are presented; three in aerodynamics and two in flight dynamics. The aerodynamics cases are those of a harmonically oscillating airfoil, a pitching delta wing, and airfoil design. The flight dynamic examples involve control of a super maneuver and a decoupled control case. It is demonstrated that highly nonlinear aerodynamic cases can be generalized with sufficient accuracy for design purposes. It is shown that although neural networks generalize well on the aerodynamic problems, they appear lacking comparable robustness in modeling dynamic systems. It is also shown that generalization appears to become weak outside of the training domain.