· · · Aerospace Engineering reports

Dit memorandum geeft- een overzicht van de geluidsgegevens en stijgprofielen, die door het NLR worden toegepast bij berekeningen van de geluidsbelasting door vliegtuigen in de omgeving van diverse vliegvelden. Tevens worden de zgn."noise footprints" weergegeven.

The concept of Introduction of biaxial loads in a specimen made of sheet material using soft clamps of unidirectional aramld composite sheet is presented. Using this concept it Is possible to generate realistic biaxial tensile stress states in specimens made of sheet materials without the introduction of unwanted fatigue critical areas.

From recorded Distance Measurement Equipment (DME) data during Microwave Landing System (MLS) flight trials performed at London Gatwick Airport (April 21 - 26, 1989) using the NLR Fairchild Metro II Laboratory Aircraft, the position of the aircraft was determined by post-processing and compared with the MLS- and ILS-derived positions. This report presents an empirical determination of the expected accuracy of a rho-rho DME solution. Also the difference between the DME position, derived from measured DME/N data, and the MLS (or ILS) position is presented.

This report contains a summary of the main conclusions and recommendations from extensive work performed by the Flight Mechanics Action Group on Handling Qualities (FM/AGOl) of the Group for Aeronautical Research and Technology in Europe (GARTEUR). The work of this Action Group, which involved cooperation between research institutes of France (ONERA), Germany (DLR), the United Kingdom (RAE), and the Netherlands (NLR), was performed with the ultimate aim to establish handling qualities guidelines for future transport aircraft with advahced flight control and display systems. The work of the Action Group started in 1982 with the consultation of aircraft industries within the participating countries concerning their opinion on anticipated manual control aspects for future transport aircraft. The underlying report may be regarded as the overall result of the work performed on the basis of this consultation, which resulted in a number of handling qualities guidelines.

This report compares the mechanical properties, fracture toughness and fatigue crack growth properties of the damage tolerant/medium strength aluminium plate alloys 2024-T351, 2324-T39, 8090-T651 and 8090-T8171. The main objective, in view of previous work, was to determine whether damage tolerant 8090-T8171 plate can advantageously replace the industry standard damage tolerant 2024-T351 alloy. From the results it may be concluded that the 8090 alloys possessed combinations of strength and fracture toughness intermediate between those of 2024-T351 (lower) and 2324-T39 (higher). And in the in-service inspectable fatigue crack growth regime the 8090 alloys demonstrated better or equivalent fatigue crack growth properties compared with the 2000 series alloys. In view of these results, and the fact that 8090-T8171 had a much improved short transverse fracture toughness compared to the earlier 8090-T651 material, it is concluded that from an engineering property viewpoint there would appear to be significant advantages in replacing 2024-T351 by 8090-T8171.

This paper reviews currently available information on corrosion and fatigue in aircraft as a background to discussing the assessment of corrosion and fatigue damage. The main topics are: - aircraft operating environments and loads - corrosion - fatigue - corrosion and fatigue - corrosion and fatigue damage assessment. Aircraft structures are susceptible to corrosion and fatigue damage, which concentrate at structural joints. There is a likelihood of interactions between corrosion and fatigue, especially as aircraft become older. However, it is uncertain whether in-service corrosion habitually leads to fatigue cracking, and it is also difficult to be specific about the relations between the environments and load histories that aircraft see in service. There is a need for ad hoc investigations to determine the in-service environmental contributions to fatigue initiation and crack growth. Structural areas removed from ageing aircraft should be invaluable sources of information for these investigations. At present there is no established methodology for assessing the effects of corrosion on fatigue in order to estimate service lives and specify inspection intervals. This paper suggests approaches to corrosion and fatigue damage assessment that are based on current methods of fatigue analysis.

The experiments described had three main objectives: First, to validate the recommendations for an improved Man Machine Interface (MMI) design based on a Phase I experiment on the human factors of data link in glass cockpits. Second, to investigate the effect of directly loading data linked Air Traffic Control (ATC) instructions into the various avionic systems (gating) on crew performance and finally, to study the effectiveness of different alerting schemes to ATC uplinks.The experiment was performed by the National Aerospace Laboratory (NLR) using their moving base Research Flight Simulator (RFS) which was configured to represent realistic , gate to gate, flight operations. A total of 9 crews participated for 6 flights lasting appr. 50 minutes each. Flight scenarios were routed from Amsterdam airport to London airport and back. Each pair of flights was performed with a different level of gating and associated procedures. Alerting schemes were studied, varying the use of distinctive aural alerts and the use of different alerting schemes depending on "message criticality". Results showed a dramatic increase in the crew acceptance levels of data link, as compared to the Phase I experiments, validating the recommendations based on these studies. Succesful factors were: putting more emphasis on operational relevant page layout and the use of more practical procedures. Further results showed a preference for auto loading the Flight Management System (FMS) type of information as compared to an auto loading capability including Mode Control Panel (MCP) entries. Finally the results suggested that an alerting scheme using a distinct but 'non-annoying' aural alert should be prefered.

This report provides an overview of the emerging technology Distributed Artificial Intelligence, in particular in the area of Distributed Problem Solving (DPS). DPS refers to coarse-grained (task-level) problem decomposition resulting in a number of expert or knowledge-based systems, generally called agents of which each exhibits some intelligence. The DPS technology has features that may reduce system design complexity through a highly modular approach and, consequently, may reduce life cycle costs through improved maintainability. These problems of complexity and maintenance are often faced with the design of complex critical applications (including many aerospace applications). DPS can provide a more natural solution with respect to system design, development, and maintenance. This report surveys DPS methods and techniques that have potential benefit for these critical applications. The two main approaches in DPS are discussed: blackboard systems and multi-agent systems. Further, the technology is evaluated along a number of criteria relevant for the envisaged applications. Based on this evaluation it is recommended to consider DPS technology in complex modular (decomposable) critical systems and let it be a driving technology for the overall system architecture.

The present review gives a brief summary of the work performed in the Netherlands in the field of aeronautical fatigue, during the period from March 1993 until March 1995. The contributions come from three different sources, namely: The National Aerospace Laboratory (NLR) • The Department of Aerospace Engineering, Delft University of Technology (DUT) Fokker Aircraft B.V. The names of the principal investigators and their affiliation are presented between brackets at the end of each topic title

In this paper the capabilities of an automated CFD system which is currently available at NLR are demonstrated. Transonic flow around the AS28G wing/body configuration and hypersonic flow through a generic three-dimensional mixed-compression airbreathing inlet are simulated. An assessment of the level of automation of the current CFD-system is made. The problem-turnaround time lies within the order of a week for both applications

An investigation was made of the effect of starter notch geometry on flight simulation fatigue crack growth in three damage tolerant aluminium sheet alloys, 2024-T3, 2091-T84 and 8090-T81. Changing the starter notch geometry resulted in significant differences in initial nonstabilized fatigue crack growth behaviour. However, there was only a slight effect on the rankings of the alloys for the in-service inspectable fatigue crack growth regime. Based on the results, a proposal for further investigation was made. This proposal should enable determining the influence of several important factors on flight simulation fatigue crack growth in damage tolerant aluminiuiTi sheet alloys. These factors are starter notch geometry, alloy yield strength, spectrum clipping level, and the specimen or sheet thickness. The proposal also provides an opportunity to try to bridge the gap that currently exists between short and long fatigue crack growth under flight simulation loading.

In this paper linear time-invariant dynamical systems described by a combination of differential equalities and static inequalities in state-space formulation are investigated. Of special interest is the contact problem: the effect (of the boundary) of the constraint set on the behaviour of the system. This effect is studied by dividing the state-space in number of disjunct subsets. It is shown that these subsets are invariant under linear state feedback. Algoriüims are presented that calculate all these subsets in a finite number of steps. In our framework a specific place is reserved for modelling the laws of collision, i.e. physical modelling, which are regarded as external factors. Our main results are a system theoretical framework in which we describe what happens upon contact, and a precise definition of the constrained state-space system in terms of its restricted behaviour. The results presented here can be considered as an extension for restricted linear systems of the classic positive invariance theory for linear systems.

NLR participates in the ECARF (European Computation Aerodynamics Research Project) "Optimum Design" project, developing an algorithm for multi-point airfoil design. Within the ECARP project a test case has been defined for two-point design with the aid of well-specified target pressure distributions. It appears that optimization of pressure distributions requires the application of efficient nonbased optimization algorithms. The investigation described in this report has been carried out in order to examine the possibilities of genetic algorithms. In this report the problem description is given, as well as how genetic algorithms can be used to optimize the problem. Next, the simulator is described which has been used to conduct some smallscale experiments. Finally, results from these simulations are presented. Summarized, the results are: - Genetic algorithms cam be used successfully to optimize pressure distributions. - Software in the public domain can be used to solve the optimalization problem. Only some problem specific operators have been added. - The current implementation of the genetic algorithm generates different minima depending on the starting point. - The results suggest that the current choice of the initial population plays an important role in the outcome of the genetic algorithm. - Although the genetic algorism uses about 100 times more function evaluations than the application of the Simplex algorithm to the present constrained minimalization problem, the efficiency of the genetic algorithm can be improved by improving the function formulation, by specifying more appropriate initial populations and by applying problem specific mutation and recombination operators.

A worst case gust shape has been derived for turbulence or gust patches, assuming only that the average spectrum of such patches is known. The maximum value of the response can be calculated quite easily. The result differs from the PSD-method. Some examples of worst case inputs and outputs are given, also for nonlinear systems.

Aspects of the requirements for and the calculation of design loads due to atmospheric disturbances are discussed. Special attention has been paid to the relation between discrete gusts and continuous turbulence. It is recommended that a worst case gust model, as described in this report, be further developed.

This paper was presented at the Specialty Meeting on Airborne Radars and Lidars, Toulouse, France, July 1992.

Effective management of forest resources requires suitable, up-to-date information on the state, extent and distribution of forest. Remote Sensing data can provide this information. FAO has initiated a feasibility study on a global operational forest cover monitoring network using satellite remote sensing data within the framework of the Tropical Forestry Action Plan. The study indicates that the use of remote sensing data for global forest cover monitoring is of great importance. To enable this, provisions are required to allow operational pre-processing of remote sensing data to well defined and standardized products. A scenario for the development of a Forest Assessment and Monitoring Environment (FAME) is presented. Firstly, Pilot FAME is developed, aiming at providing a suitable infrastructure for forest management using satellite remote sensing data to compile information on global forests. Secondly, PFAME is upgraded to improve its functionality and to introduce Forest Management Systems. Thirdly, PFAME is extended by introducing remote sensing data from other newly launched sensors. By introducing this three-step approach, uniform and validated remote sensing end products will become available for use in sustainable forest management providing information on the state, extent and distribution of tropical forests. Paper presented at the International Symposium "Operationalization of Remote Sensing", 19-23 April 1993, ITC Enschede, The Netherlands.

The schlleren observation technic[ue can be used in microgravity experiments. Alignment features for the gratings of a multiple source sharp focusing schlieren system have been analysed. Measurements have been performed to verify the theoretical predictions which show good agreement with the analysis results. The analysis allows for the alignment to be carried out using tele-operation or automation.

A preliminary investigation is reported of the development of a Structure Relevant (SR-) specimen, which maintains the essential features of a stiffened panel configuration, in order to study damage growth behavior at limited cost. Several SR-specimens were fabricated, damage was applied, either through impacts or by the insertion of artificial delaminations, compression loads were applied, and C-scan damage areas and internal damage configurations were determined. The failure mode of one series of SR-specimens consists of three phases: a first phase of stable delamination buckling with increasing amplitude but no growth, a second phase of rapid delamination growth until the delamination jumps across the stiff doubler area, causing a significant load redistribution, and a final phase with slow delamination growth in the base skin zones at the edges of the specimen, until total failure occurs at a gross strain of 0.006. The failure mode of another series of specimens could not be described in sufficient detail, due to a lack of instrumentation. In this case the failure mode probably consists of failure due to bending, at a gross strain of 0.006, while the artificial delaminations did not grow until final failure. Delamination growth was observed to follow preferred interfaces, adjacent to 90-degree layers. It is concluded, that the SR-specimen proposed can be used for damage tolerance studies.

Flight simulation fatigue crack growth tests are necessary for verification of aircraft damage tolerance analyses and crack growth prediction methods, and also for comparing candidate materials for aircraft structural applications. However, such tests involve complicating issues that have emerged from many investigations on aluminium alloys since the late 1960s. These issues are reviewed to provide guidelines for further testing.