Sharif Digital Repository

This work presents a novel approach to redefine a "Safe Aircraft" based on systems engineering fundamentals. We aim todemonstrate the possibility as well as suitability of the "Functional-Aircraft" instead of currently employed concept of "Physically-defined-Safe-Aircraft". The current work is consistent with ever-increasing number of flights; as it suggests that any aircraft that can complete its mission should not declare emergencies due to any physical malfunction. With proper simulations, wedemonstrate the feasibility of "Functionally Safe" concept as oppose to the "Physically Safe" aircraft. The process revolves around standard and well-known documents such as FTA and FMEA; which are... 

The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so called 'Quad-tree forms'. The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the 'cost map', lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different... 

In this paper, we address aircraft conflict detection on a mid-term horizon. We adopt a probabilistic approach and provide a simple method to estimate the probability of two aircraft getting closer than some minimum predefined distance, based on a commonly adopted Gaussian model of the deviation from their planned trajectories. A key feature of our method is that the probability estimate is accompanied by a deterministic accuracy certificate. This is achieved by adopting a geometric approach to conflict probability estimation and jointly computing a lower and an upper bound on the conflict probability. These bounds can be inspected and refined if the resulting accuracy of the probability... 

Increasing competition in the transport commercial market has resulted in many changes in the aircraft design process. There is a great tendency to include economic factors such as "affordability" In the design process. On the other hand, the so-called market dynamics are also getting complicated and a design team has to deal with many uncertainties as far as the business environment is concerned. This leads to the need for new decision-making tools in the early stages of the design process. This paper introduces a decision-making algorithm based on fuzzy logic systems which provides a structured approach to deal with uncertainties in the aircraft preliminary design. The developed tool leads... 

This work describes a new mathematical model to predict the so-called aircraft handling qualities via proper positioning of aircraft mass in the early stages of the design process. The methodology aims to help make handling qualities and therefore pilot rating an integral part of the design process. The main idea is to And proper mass distributions for an aircraft in given flight conditions based on the well-known quantitative measures of flying qualities described in military standards. The proposed methodology allows aircraft designers to associate a density to different segments of an aircraft and have a prior insight about an optimum arrangement of internal parts such as fuel tanks,... 

This paper describes an approach to mid-term probabilistic conflict detection between two aircraft flying at the same altitude. The key distinguishing feature of the proposed method is that it analytically estimates the conflict probability, in the presence of a fully correlated wind field. The method uses a two-step approach. First, the mean and the covariance of the aircraft relative position are computed analytically. Then, the conflict probability is estimated such that a desired level of accuracy is obtained. Numerical results, conducted using a simulator incorporating a fully correlated wind field model, show the effectiveness of the approach versus the competitors. Finally,... 

In this paper, a hierarchical method for trajectory design for cooperative combat missions (CCM) is presented. In a military environment, in addition to physical constraints (aircraft dynamics and mountains) there are threats made by Radars or Artillery. So an important constraint, "Avoid Threats", is added to physical constraints. Major steps in trajectory design are: "Target Assignment", "Path Planning", "Path Smoothing and Trajectory Design". The most important points and a brief algorithm for each step is presented in this paper. Finally the method is applied to special case and the results presented. ©2008 IEEE  

Traditionally, flying and handling quality evaluation of an aircraft in various flight phases is aimed at pilot workload assessment to guarantee a successful mission. Subsequently, Different levels of acceptability are defined for the aircraft based on the additional work required by the pilot to achieve a desired performance level, feting scales are usually numerical, which pilots utilize as a mean to quantify their subjective opinion about an existing aircraft after hours of flying. Cornell aeronautical laboratory used their own scales in flying qualities research for many years and Cooper of NASA originated a ten-point numerical scale that was used more universally. When Harper of Cornell... 

In this manuscript, a new concept of 2D-semi-optimal-circular-3-arced-path manoeuvres with constant speed for multiple aircraft cooperative conflict resolution is presented. This type of manoeuvres is based on appropriate commands to heading, speed and manoeuvreing time. According to aircraft turning dynamics, each aircraft manoeuvre is composed of three tangent circular arcs. The optimality of manoeuvres is based on the minimisation of weighted sum of kinetic energy for aircraft two-legged manoeuvres. In comparison, aircraft with lower weight factors bear more responsibility to resolve the conflicts. The effectiveness of the proposed algorithm for real time conflict resolution is... 

In this paper, the problem of designing optimal conflict-free maneuvers for multiple aircraft encounters is studied. The proposed maneuvers are based on changes of heading, speed and maneuvering time. The optimality of maneuvers among the conflict-free constraint is based on minimization of a certain cost function based on kinetic energy of either aircraft involved. Some suitable priority weight factors are incorporated into the cost function so that optimal resolution maneuvers are such that aircraft with lower priorities assume more responsibility in resolving the conflicts. As for considering aircraft turning dynamics, the circular 3-arced path with constant speed are proposed for each... 

Purpose - The purpose of this paper is to describe optical flow-based navigation of a very light fixed-wing aircraft in flight between obstacles. Design/methodology/approach - The optical flow information of two cameras mounted on the aircraft is used to detect the obstacle. It is assumed that the image processing has been completed and the optical flow vectors have been obtained beforehand. The optical flow is used to detect the obstacles and make a rapid turn manoeuvre for the aircraft. Findings - It is shown that using the optical flow feedback by itself is unable to give a rapid turn to the aircraft and its rate should be employed into the control law. Six degree-of-freedom flight... 

A novel adaptive model-based predictive controller for attitude and trajectory tracking of a vertical take-off and landing(VTOL) aircraft in the simultaneous presence of model uncertainties and external disturbances is introduced in this study. Animportant challenge of designing the model-based controllers is developing an accurate model, especially in the presence ofmodel uncertainties. In this study, first, the nominal model of a ducted-fan air vehicle, which is a multi-input multi-outputnonlinear system with non-minimum phase behaviour, is given as the test case of this research. After that, two modified robustand adaptive model predictive controllers are proposed for tracking a... 

In this work we show how Artificial Intelligence (AI) could effectively be used to expedite the decision making process in the early stages of the aircraft design process. We employ both Fuzzy Logic (FL) and Neural Network (NN) as two different schemes of the AI. The developed tools are intended to help to select the proper combination of engine thrust, wing area and the aircraft weight without going through elaborate details of other direct approaches. We further show how the AI could be applied to the specific class of light business jets which serves to validate these schemes. The results indicate the effectiveness of the AI approach in the preliminary aircraft design process. The actual... 

Aircraft landing problem is to assign an airport's runways to the arrival aircrafts as well as to schedule the landing time of these aircrafts. In this paper, first a mixed integer goal programming model is developed. Then, due to the complexity of the problem, which is NP-hard, we design a hybrid meta-heuristic applying simulated annealing framework. The computational results show that the proposed algorithm can obtain the optimal solution for instances up to 100 aircrafts, and also it is capable of finding very high quality and comparable solutions for the problems with up to 500 aircrafts and 5 runways in a short time  

The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so-called "quad-tree forms". The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the "cost map," lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different...