PhD programmes

Completed doctoral research projects

Method for improving the maneuverability of a top-wing monoplane.
This dissertation is based on experimental work and describes a method for improving the maneuverability of trainer aircraft built in accordance with the classical laws of aerodynamics.

The appearance of highly maneuverable fighter aircraft automatically, so to speak, increased the requirements for aircraft designed for pilot training.

This paper presents the method for and way of achieving a planned effect consisting in an increase in the maneuverability of a modernized trainer aircraft built in accordance with the classical aerodynamics laws by means of introducing modifications worked out during an aerodynamic design process carried out with the use of wind tunnels operated by the Aviation Institute. The obtained results of model testing in wind tunnels and comparison thereof with data from tests flights conducted with the use of prototype aircraft provided evidence justifying the statement contained in the thesis according to which higher maneuverability (better aerodynamic characteristics) of a top-wing monoplane trainer aircraft built in accordance with classical aerodynamics laws can be achieved by means of equipping its wing with high-lift devices and strakes (strake, LEX) installed at the wing root.

In order to increase lift generated by the wing within the whole range of operational velocities of the aircraft and to raise the limit above which wing buffeting occurs, the author has proposed to introduce strakes (generators of vortex flow on the upper surface of the wing near the fuselage, within the symmetrical profile area, installed at the wing root).

In order to increase the lift generated by the wing at low speeds and to decrease the angle of airflow deflection behind the wing, the author has proposed introduction of high-lift devices (on the leading and trailing edges) based on the Fowler flap that generates lift not only by means of airflow deflection but also by increasing the wing area (broadening), which, as a consequence, prevented airflow separation on the bottom source of the horizontal stabilizers.

Modifications worked out by the author as options were subsequently introduced during the model completion and subjected to tests in wind tunnels.

The necessary corrections were introduced successively, depending on the achieved test results.

Introduction of prototype modifications was planned and effected in two phases.

Phase one: an I-22 ”Iryda” aircraft prototype was modified by means of installing strakes and increasing the height of the vertical stabilizer.

Phase two: another aircraft was reconstructed and provided additionally with wholly changed high-lift devices comprising double-segment slats on the leading edge and Fowler flaps.

The analyses and surveys presented in the paper have enabled positive verification of the thesis proposed in the dissertation.

The developed method for selecting components (strake, high-lift devices) and testing made it possible to provide the modernized aircraft with increased maneuverability capabilities.

The subject of this doctoral dissertation focuses on the influence of gyroscopic effects on dynamic properties of light turboprop aircraft. Gyroscopic moments are generated by the turbopropeller power units and cause coupling between longitudinal and lateral dynamics.

The main purpose of this study was to investigate the influence of the gyroscopic effects on the dynamic stability and the response of aircraft to manoeuvres following either a rapid deflection of the control surfaces or wind gust.

As a representative of the General Aviation aircraft, for which calculations were carried out, a Polish turboprop aircraft I-31T was selected. The analyses were conducted for several different mathematical models of aircraft motion, which allowed to investigate the relationship between introduced simplifying assumptions and the aircraft response, including non-linear terms in equations of motion expressing the influence of inertial coupling.

There was carried out an analysis of the sensitivity of dynamic stability versus dimensionless aerodynamic derivatives, received from different data sources. The analytical and experimental methods (measurements in the wind tunnel for the scaled model and flight test of the I23 prototype aircraft) were employed.

The results of numerical simulations were compared to the aircraft flight tests. There were also evaluated compliance of the dynamic characteristics obtained by the use of different computational packages. A number of calculations were conducted to assess trends in dynamic stability changes due to many other flight and aircraft parameters.

It was found that the gyroscopic moments are induced mainly by the propeller and their influence on dynamic stability of a light aircraft is negligible, whereas in manoeuvring flight the gyroscopic effects should be included into analyses, although for light aircraft they are not strong. Hence there were distinguished two types of gyroscopic effects depending on disturbances of steady flight. They were divided into: weak gyroscopic effects – corresponding to classical dynamic stability and strong gyroscopic effects – corresponding to rapid manoeuvres.
Conclusions include some findings about nature of the gyroscopic effects (i.e. sensitivity of flight stability versus turboprop power unit parameters) and practical recommendations for aircraft designers dealing with new configurations of General Aviation aircraft.

In this dissertation the analysis of disc brake temperature impact on braking torque curve in vehicle’s friction brake is presented. Scientific objective of the thesis is analysis of the braking torque versus time function induced by temperature. Temperature rise results in friction coefficient reduction, which causes a decrease of the braking process efficiency. The issues related to the design, construction, and tests of the friction brakewith emphasis on the impact of temperature on the braking torque are the subject of the dissertation. In order to determine the impact of temperature on the braking torque, a number of laboratory tests was performed. Two test stands, one for friction material testing and the other for full scale brakes testing,were used. The measurements of the braking torque, rotational speed, braking force, and temperature were performed. Temperature recording was made using infrared camera, pyrometer, and thermocouples on the stand for testing friction materials and pyrometer only on the stand for testing full size brakes. As a result of the tests, the existence of the connection between temperature and the braking torque curves was confirmed.Developed test method can be used to observe phenomena occurring in the friction contact zone, difficult or even impossible to determine using other methods of measurement.At the same time the phenomenon of sudden drop in braking torque, and its re-growth to a level of equilibrium was observed and explained.

In the next part of the dissertation, numerical (FEA) and mathematical models of friction process are presented. Numerical model was created using COMSOL Multiphisics software. As the input parameters, the results from friction material laboratory test were used. The results obtained from the simulation were compared to the laboratory ones showing high level of convergence. The same laboratory results became the source of the braking torque and temperature mathematical models. They were determined using functions estimation approach.

The thesisalso includes the state of the knowledge analysis in terms of friction phenomena, friction materials, full size brakes, laboratory tests, and numerical simulations.

At the end of the dissertation the conclusions are formulated connected to the described laboratory research and calculations, which confirm the thesis. Suggestions for further works on the topic are proposed.

An elaboration of a future aircraft design concept has become increasingly complex due to changes of the basic criteria for evaluating emerging solutions. In the past, the basic performance characteristics of an airplane were the only selection criteria. Today, more and more emphasis is placed on factors such as impact on the environment, cost-effectiveness, or comfort of travel.

The thesis presents a method to optimise parameters of a small aircraft and to be used in the initial phase of a design project taking into account the requirements of aviation safety imposed by the European Union certification specifications CS-23 and a requirement of aircraft competitiveness within the total transport system.

The basic design decisions regarding a future aircraft, including the selection of basic parameters are taken in the initial phase of a project (a definition of requirements, a conceptual design, a preliminary design). It means that most of the decisions concerning a future aircraft, including decisions significantly affecting aircraft competitiveness, for both, a manufacturer and an operator, are taken before the stage of a technical design. However, in this phase of a project, it is extremely difficult to evaluate achieving project goals due to the imprecision of requirements and design parameters, lack of knowledge of any ongoing interactions among parameters and uncertainty of analysis and calculations. A solution to this dilemma is to increase knowledge of the early stages of a design process.
The method is based on a mathematical model of aircraft and the multidisciplinary design optimisation (MDO) and the method covers the basic areas of aircraft design: aerodynamics, aircraft structure, performance and expected operating costs.

First, I determined the basic requirements for future aircraft by defining project goals accompanied by a set of basic design parameters. I select these basic parameters to define a configuration, that corresponds most accurately to the goals.
The objective function was defined as the value of the direct operating costs per 1 passenger-kilometre. Evolutionary algorithm was applied to solve the optimization problem.

The competitiveness requirements were formulated basing on a concept of the Small Air Transport system (SATs). The SATs vision was developed by the consortium within the projects of the 6th and the 7th Framework Programme of the European Union. The SATs is based on a fleet of small aircraft and rotorcraft equipped with 4 to 19 seats, and operating within an integrated and intelligent transport management system, at small airports and aerodromes. The SATs conclusion underlines significance of a fleet of turboprop aircraft.

The first stage of my study was to analyse the current state of the art in three thematic areas: the small aircraft transportation theory, the design process at the stage of concept development and preliminary design, and the modelling, computer simulation and numerical optimisation methods.
I used the analysis results to formulate a mathematical model of aircraft. It consists of four modules: a mass model, a performance model, a direct operating costs model and an optimisation algorithm.

My next step was elaboration of the simulation model and the simulation program. The simulation model was elaborated using Mathcad software. The basic aim of the simulation model was to validate the structure of the mathematical model, the completeness of data and algorithms.
I coded the simulation program in the Visual Studio environment using C++ programming language.

Then, I carried out the optimisation of design parameters of the 9-seater and the 19-seater as an example of this method application. I compared the optimisation results of my method with the results obtained using the minimisation of the engine power method.

Moreover, I analyse the sensitivity of the objective function with respect to selected parameters of the aircraft. The results facilitate choosing the most significant variables responsible for operational costs.

The thesis includes conclusions from modelling and analysis, and the recommendations leading to improve the competitiveness of small aircraft.

The subject of this doctoral dissertation focuses on the early detection of damage to the nickel-based alloys using nondestructive methods. The degradation of the material structure is a dangerous phenomenon from the safety point of view. The deformation of the structural materials causes the structure damage and in effect destroys the material. Analysis of damage growth consists of observation of changes in the structure of the material subjected to a specified deformation. In order to determinethe degradationof materialsbothdestructiveandnon-destructive methods there are used. An important advantage ofnondestructive methodsisthat they do notrequire asampleof materialfromthe tested objectto determine itsmaterial properties.
The main purpose ofthis study was toinvestigate the possibilityto detectdefectsat an earlystage of theprocess ofdegradation of the material, with application ofcurrently used or modified methodsof nondestructive testing. A stage preceding the creation of the dominant crack is an early stage in the process of material damaging. At this stage, cracks, formed as a result of accumulation of microdamages, are below 0.5 mm in size.
To detect changesin the structureof the materialanultrasonicandeddy currentmethod are selected. Inconel718 was the materialused to testand evaluate the degradation. Inconel is a family of alloys of austenitic crystal structure based on nickel and chromium. These superalloys are characterized by high heat resistance, strength and creep resistance at high temperatures, surface stability and resistance to corrosion and oxidation. Therefore Inconel alloys are specially applied in extreme working conditions – in power engineering industry, aviation and aerospace.
The tests were conducted using a new type of specimens of variable cross-sectional area measuring part. This allowed to obtain a continuous distribution of plastic strain in that part of the specimen. The deformation that varies along the axis of the sample enables an analysis of damage induced by plastic deformation. The proposed method enables replacing a series of specimens by one sample.
Methods of material damage measuringare based on the assumptionof the correlation between the degree of damage and the measurablephysical quantitycalledthe indicator ofdamage.There was carried out an analysis concerning measures and damage indicators. In ultrasonic testing attenuation of ultrasonic waves and acoustic birefringence were selected as indicators of damage. In the case of the eddy current method there was selected a change in the phase angle of the impedance in the material. The values of these indicators were measured for specimens of the material before strength tests.
In order to obtain a certain deformation of the material samples static tensile tests and creep tests were carried out. Thedamage indicators were measured again. In the result there were obtained the values of attenuation of ultrasonic waves, the acoustic birefringence, and the phase angle shift of the eddy current, depending on level of material damage in specific areas of the specimen.
Based on Johnson’s model there were determined damage parameters in parts of the measuring specimens. The correlation between thematerial damage degree and nondestructivedamage indicators was determined.
In the summary,it has been concludedthat theappropriatenondestructivetesting techniquescan be used toassess the degree ofmaterial degradation. Using these,it is possible todetect damageat the microstructure level, resulting fromservice loadsandmaterialsrelated to the processof creepand fatigue.Nondestructivetesting techniquesallow the detectionof the changesin the structureof the materialcaused bypermanent deformationat an early stage of damage.

Aim of the dissertation

Liquid impingement erosion is a result of numerous and repetitive impacts of liquid droplets onto a solid body with degradation mechanisms similar to fatigue. The erosion models used so far are based on empirical data and limited selection of material properties.
The aim of this work is to develop a methodology for erosion life prediction of martensitic steels, based on data concerning fatigue properties.

Thesis
Prediction of service life of martensitic steels subjected to liquid droplet erosion can be performed based on fatigue material properties.

Scope of dissertation
• Based on available publications, a literature review on liquid droplet erosion has been presented with an emphasis on material degradation mechanisms.
• Existing models of service life prediction under erosion were analyzed. The following aspects were taken into consideration: impingement loads caused by single droplet impacts, used material properties, structural aspects and thermodynamic erosion conditions.
• A test matrix and investigation plan was elaborated for two types of martensitic steels: 17-4PH and X20Cr13 – materials commonly used in the design of turbomachinery equipment. Tests were setup to match the typical operating conditions.
• As a result of these studies, similarities between the erosion and fatigue mechanisms were evaluated. Among the methods used were: visual examination, magnetic particle inspection, microfractography using scanning electron microscopy, microstructural studies using transmission electron microscopy and X-ray residual stress measurement.
• Analyses and simulations of liquid impacts onto a solid body were performed with numerical methods, such as: finite element method (FEM) and due to complex fluid-structure interactions, presence of fragmentation effects and large deformations smooth particle hydrodynamics (SPH). Obtained results were used to evaluate the stress levels induced by impinging water droplets.
• Based on fatigue approach, a methodology was developed for estimation of erosion incubation period. The stresses and strains generated by a single droplet impingements are evaluated from numerical experiments. Depending on their level, two different methods were used: for high or low cycle fatigue. The randomness of droplet impacts during erosion tests is included with a simplified statistical model. Verification and validation of the developed methodology was performed based on experimental test data.
Conclusions
1. Literature review has shown existence of similarities between the erosion and the fatigue phenomena:
• existence of incubation period, analogous to fatigue life under fluctuating loading;
• increase or decrease of incubation period length as a function of erosion conditions (i.e. impingement speed);
• presence of limiting conditions for erosion occurrence (i.e. minimum speed with other parameters remaining constant) for materials having an endurance limit (such as carbon steel);
• lack of limiting conditions for erosion occurrence (i.e. lack of minimum speed with other parameters remaining constant) for materials (such as aluminum alloys) which do not have a defined endurance limit.
2. Analysis of existing erosion models showed numerous and significant limitations in their applicability. These were found to come from simplifications in model design (being based on empirical data), or lack of sufficient material properties to express the erosion resistance.
3. Degradation mechanisms under erosion showed numerous similarities to fatigue. As a consequence of repetitive load cycles caused by water droplets impingements, the target material has suffered from surface microdeformation and accumulation of microstructural defects. After a the incubation period was reached, the material degradation took form of fatigue microcracks initiation and propagation.
4. The analyzes and simulations of liquid droplet impingements showed that the generated stress levels are sufficient to exceed the fatigue strength of martensitic steels such as 17-4PH. The source of stresses was both: the hydrodynamic interaction between the liquid and the solid, as well as formation of a shock wave. Depending on the erosion conditions, two possible scenarios were observed (for typical turbomachinery operating conditions):
• single impingements generate stresses exceeding the fatigue strength of a given material, however too low to cause plastic yielding;
• single impingements generate stresses exceeding the elasticity limit of a given material.
5. The accuracy of the developed incubation period estimation methodology for models based on low and high cycle fatigue was verified against ASTM G73 test data. It was found to be comparable to typical accuracy of methods used for evaluation of fatigue life.

Recommendations
• Some of the existing simplifications in proposed methodology originate from current limitations in modeling of fatigue on a microscale and under high strain rates. Any progress in those fields should be used, leading to further refinement of erosion prediction accuracy.
• Present study was focused on martensitic stainless steels. Nevertheless, materials such as cobalt based Stellite alloys or titanium alloys are known to exhibit remarkably good erosion characteristics, with comparable tensile properties. Taking into consideration their different physical and fatigue properties, application of fatigue based approach to LDE prediction on those groups of materials should be a part of further research.
• Considering the fact that turbomachinery equipment is designed to poses years of service lifespan, further study should focus on implementation of methods used to estimate infinite life of the material. Ongoing work is focused on feasibility study of Goodman diagram and Haigh diagram application with mean stress correction to liquid droplet erosion problems.
• With known design parameters and operating conditions on erosion (i.e. impact angle, surface roughness), further work should be related to development of design criteria, so that the stress levels produced by a single droplet impingements would be reduced, leading to increase in erosion resistance.

The subject of proposed thesis is a multidisciplinary optimization of inverted joined-wing. In a result of the research an optimization algorithm of whole configuration of joined-wing with electric propulsion is proposed. The optimization process is a global search optimization suitable for preliminary design of joined-wing. Modular algorithm based on automatic geometry generator, FEM solver and aerodynamic panel method is developed. Whole process is optimized to decrease huge computation cost to the minimum.
The general optimization objective is to maximize the range of aircraft for assumed mission, as it is the major disadvantage of electric aircrafts. The payload and battery capacity are fixed. Global, local geometry and structural parameters are selected as a design variables.
Optimization is performed in serial manner – structure optimization is conducted inside aerodynamic optimization step. During structure optimization, strength is checked for few sizing load cases obtained from loads envelope. Only structural parameters are variable at this stage. In the aerodynamic loop objective function is optimized by changing only geometrical parameters.
For optimization purpose a meta-model of response surface is created and then used in next steps. Final optimization is conducted using two stage process. The first stage is the global one and it uses genetic algorithms. The second stage which is gradient based optimization is the local stage that improves first estimation of optimum.
Based on proposed algorithm a program was coded and some tests were done. Aerodynamic calculations were validated by wind tunnel tests conducted in Institute of Aviation. Next, three optimization test cases for UAV and VLA aircrafts were performed. Additionally, a modification of algorithm was proposed that allows to obtain specified longitudinal stability margin. Based on results of prepared optimizations it was proven that proposed algorithm can be successfully used to improve the range of inverted joined wing aircraft.

The thesis presents the analysis of results of experimental investigation which was a part of the research on the catalytic decomposition of highly concentrated hydrogen peroxide. Manganese oxide ceramic supported catalysts were used in the framework of research. Test and preparation stands as well as test equipment were designed in order to perform the activity. Catalyst beds, similar to those used in rocket propulsion, were utilized in the investigation.
The main task was to assess the possibility of application of various heterogeneous ceramic supported catalysts to decompose 98% hydrogen peroxide inside unheated catalyst beds of mono- and bipropellant rocket engines. In order to perform the activity, the number of catalysts supported mainly on α- and γ-alumina were prepared. The active phase for these catalysts were manganese oxides, doped with oxides of several transition metals.
The investigation consisted of four main stages. Initially 46 samples of catalysts were tested inside the catalyst chamber using the unified procedure and test sequence. That enabled to compare performance and select those catalysts that met defined criteria with the highest score. Selected catalysts were then applied to the second stage of the investigation that was performed using a new test setup. The crucial stage of the activity was to define, prepare and test composite catalyst beds. These structures were made by layered distribution of various ceramic supported catalysts, separated by wire mesh screens. Finally the lifetime test of one selected catalyst bed configuration was performed in order to assess the possibility of application of such a structure in a rocket engine.
Based on the results of the performed research the final conclusions were drawn. Further work for the extension of recent investigation was suggested as well.
The investigation was a part of the project “Research on composite catalyst beds for decomposition of hydrogen peroxide to be applied in a monopropellant thruster”, funded by the European Space Agency in the framework of PECS programme. The project was realized in the Institute of Aviation by the research team from Space Technology Department.

This doctoral dissertation aims at examination of Light Aircraft Transport System (LATS) safety. Analysis of statistical data concerning operations of small aircraft undoubtedly indicates on large disparities in the area of safety and reliability level compared to big commercial transport. The main reason behind this is the fact that development of safety related technologies is mostly driven by big airline industry resulting with lack of physical possibility of adopting them to the small aircraft re­quirements and non-proportional price of the item. Therefore, there is a strong need for identification of other solutions enabling improvement of light aircraft safety level without high increase of take-off weight and operational costs. The study focuses on commercial operations on light propeller-driven aircraft with take-off weight below 5760 kg and seat capacity under 10.

The primary objective of the study was analysis of room for improvement in the area of light aircraft safety through:

  • Identification of issues critical for the safety issues and consideration of possi­bilities of limiting their impact;
  • Optimal selection of technical and operational specifications of the aircraft fleet and the whole System.

The methodology was based on identification of the typical mission profile of the LATS aircraft and set of 26 critical safety issues with regard to their weights on par­ticular flight phases. There was result increase in mission reliability with insignificant increase in aircraft operational costs.

Applied methods originated from statistical analysis and theory of probability. Of the special importance was Reliability Diagrams theory enabling modelling of Mean Time Between Incident or Accident (MTBIA). Mathematical model was calibrated with use of statistical data gathered and processed in the framework of analysis of 194 NTSB accident and incident reports occurred in the United States between 2008 and 2013.

The main result of the dissertation was distribution of incidents and accidents occur­rence intensity for particular flight phases. Mathematical model also had capacity of calculation of expected LATS safety level for set of various operational scenarios. In summary, it has been concluded that the most critical problems concerning light air­craft safety are: engine reliability in cruise phase responsible for about one fourth of incidents and accidents; pilot spatial disorientation during cruise phase leading to more than 16% of occurrences; airmanship errors, especially during touchdown phase (4%) accounting for 12% of accidents as well as pilot errors resulted from operations on non-certified or non-towered airports respectively leading to: 7.5% and 5.5% of events.

Additionally, it has been claimed that optimal selection of the technical specification of the aircraft fleet as well as operational features of the whole System would improve the LATS safety level 3,5-fold and increase in the value of MTBIA by 230%. Never­theless, it was concluded that despite the identified potential for the progress in the considered area, the further efforts aimed at safety issues are unavoidable. LATS cannot be considered as acceptably safe, both in terms of technical reliability and human factor performance. The most critical issues are: engine reliability improve­ment, pilot training effectively preventing errors leading to spatial disorientation, airmanship during touchdown or errors committed before engine start. Part of the executed work was supported by the results of ESPOSA and ASCOS FP7 projects.

This thesis concentrates on the problem of identification, estimation and risk analysis in the area of laboratory processes in defined condition for  laboratories participating in accreditation process and laboratories offering their services outside this process.

This thesis presents evaluation model of risk and defined ways of risk management in the identified sources of uncertainty focusing in the area of technical and organizational area of laboratories and specifies a roadmap of risk.

This paper defines a methodology for the approach to the risk assessment in research laboratories. Indicates sources of information related to the risk and tools for their analysis. This paper presents also the results of analyzes based on the conducted questionnaire and the results of internal and external audits in the area studied laboratories. The implementation in line with laboratories strategy have a significant impact on improving the functioning of the laboratory activities.

Analysis of the results conducted questionnaire is based on the tools such as analysis of the risk structure index (named WSR), grid percentile calculation of risk, risk coefficient analysis between perspectives and their strength and linear regression analysis and ranking. To carry out the analysis of raw data from the results of internal and external audits author uses the following tools: analysis of the percentage of risk, analysis of Pareto distribution of risk analysis and analysis of standardized risk ranking.

The above-mentioned methodologies of analysis of questionnaire results and audit were the original solution in terms of risk undertaken subject in laboratory practice.

Ability to manage effectively the risk in the context of the highest quality of services to the customers will allow laboratories to gain a competitive advantage.

In this dissertation has been presented how geometry of the combustion chamber in compression ignition engine with direct injection influence on the emission of the nitrogen oxides. The choice of the nitrogen oxides had been supported by its special harm to health, the environment and the difficulty in reducing at the level of the formation and elimination from exhaust gases.

The emission of the nitrogen oxides depends on many engines construction factors and fuel injection parameters. In this dissertation, plenty of attention, was put on the analysis of the describing these phenomena literature. It has permitted to eliminate its influence on conducted research beyond the geometry of combustion chamber. Testing was performed on five combustion chambers, which varied in diameter and depth of the chamber but chosen in this way to ensure the same compression ratio.

As a result of the research and simulations it has been confirmed that there is connection between the diameter of the combustion chamber and the level of nitrogen oxide emission.

Presented simulation of turbulence and its effects on the stream of fuel has allowed to prove the thesis which were based on the attached stream theory disintegration and other researchers study concerning on the effect of droplet size and droplet residence time in the combustion zone. Air turbulence and fuel injection in the cylinder and in the combustion chamber simulations were carried out in SolidWorks Flow Simulation. A mathematical movement model of fuel drops in swirling air was developed and its results cover with the simulations made in SolidWorks Flow Simulation.

All conclusion which are included in this dissertation, based on researches and simulations, confirm the thesis of work. The conclusion of this dissertation may provide a guidance in the design of toroidal combustion chambers.

Doctoral research projects in progress