Baigiamajame magistro darbe nagrinėjamas koncepcinio ultralengvojo lėktuvo „Kiras“ skrydžio stabilumas. Išilginio stabilumo charakteringi parametrai skaičiuoti rankiniu būdu bei Athenos sūkurių tinklelio principu veikiančia AVL stabilumo analizės programa. Šoninio judesio spiralės režimo tikrosios reikšmės, Fugoido, trumpojo periodo bei „olandiško žingsnio“ svyravimų tikrosios reikšmės įvertintos AVL. Darbas taip pat apima svyravimų dekremento, periodo T 1/2, laiko t 1/2, svyravimų ciklinio dažnio wn, ciklų skaičiaus N 1/2 ir kt. analizę esant skirtingam lėktuvo judesiui. Ankstyvoje projektavimo stadijoje buvo rastas ultralengvojo lėktuvo spiralinis nestabilumas. Ši klaida ištaisyta priartėjimo metodu keičiant uodegos geometriją ir sparno skersinį V kampą. Skaičiavimais bei kompiuteriniu skrydžio judesio modeliavimu įvertinus rezultatus buvo sukurta nauja kilio geometrija. Galiausiai pateikiamos baigiamojo darbo išvados ir siūlymai. Darbo apimtis – 54 p. teksto be priedų (67 p. su pried.), 9 iliustr., 10 lent., 12 bibliografinių šaltinių. Atskirai pridedami darbo priedai. / Stability analysis of conceptual design ultralight aircraft “Kiras” is presented in this master’s thesis. Longitudinal stability is evaluated by manual counting and Athena vortex – lattice based AVL program. Lateral derivatives, such as eigenvalues of spiral mode, “dutch roll“, Phugoid and short period oscillations were estimated by AVL . Thesis involves analysis of damping ratio, period T 1/2, time t 1/2, ocsillation circular frequency wn, number of cycles N 1/2 of distinct aircraft motions. The range of eigenvalues for specified run cases were automatically generated by AVL eigenmode meniu. At early phase of ultralight aircraft design, spiral instability was found. This problem fixed by approach method by correction of tail geometry and wing dihedral. According to the counting results and computerized motion analysis of an airplane, the corrected geometry of vertical tail is offered. Finally, the conclusions were made. Thesis consist of: 54 p. text without appendixes (67 p. with), 9 pictures, 10 tables, 12 bibliographical notes. Appendixes included.

This report focuses on the utilisation of flight mechanics in the context of aircraftconceptual design to assess stability, control, and motion characteristics. The pri-mary objective is to acquire the equations of motion and implement longitudinalstability and control criteria using Pacelab Aircraft Preliminary Design 8.1, a com-mercial software tool. The equations and criteria employed in this study are derivedfrom an extensive review of relevant literature.By incorporating a dedicated Flight Mechanics chapter within the software, it be-comes possible to evaluate aircraft concepts under varying conditions. To ensureaccuracy and validity, DATCOM+ and OpenVSP were employed for testing andverification purposes.The key aspects covered in this report include flight mechanics, its implementationin Pacelab APD 8.1, determination of aerodynamic derivatives, formulation of equa-tions of motion, and their application to the B747 aircraft model. The emphasis liesin assessing longitudinal stability and control, including specific characteristics suchas the phugoid and short period modes.This report provides valuable insights into the integration of flight mechanics withinthe Pacelab APD 8.1 software for aircraft conceptual design. The results contributeto a better understanding of stability and control parameters and their impact onaircraft performance.

This thesis describes the development of a series of codes for trim and longitudinal stability analysis of a helicopter in forward flight. In general, particular use of these codes can be made for parametric investigation of the effects of the external and internal systems integrated to UH-60 helicopters. However, in this thesis the trim analysis results are obtained for a clean UH-60 configuration and the results are compared with the flight test data that were acquired by ASELSAN, Inc. The first of the developed trim codes, called TRIM-CF, is based on closedform equations which give the opportunity of having quick results. The second code stems from the trim code of Prouty. That code is modified and improved during the course of this study based on the theories outlined in [3], and the resultant code is named TRIM-BE. These two trim codes are verified by solving the trim conditions of the example helicopter of [3]. Since it is simpler and requires fewer input parameters, it is more often more convenient to use the TRIM-CF code. This code is also verified by analyzing the Bo105 helicopter with the specifications given in [2]. The results are compared with the Helisim results and flight test data given in this reference. The trim analysis results of UH-60 helicopter are obtained by the TRIM-CF code and compared with flight test data. A forward flight longitudinal dynamic stability code, called DYNA-STAB, is also developed in the thesis. This code also uses the methods presented in [3]. It solves the longitudinal part of the whole coupled matrix of equations of motion of a helicopter in forward flight. The coupling is eliminated by linearization. The trim analysis results are used as inputs to the dynamic stability code and the dynamic stability characteristics of a forward flight trim case of the example helicopter [3] are analyzed. The forward flight stability code is applied to UH-60 helicopter. The codes are easily applicable to a helicopter equipped with external stores. The application procedures are also explained in this thesis.

General aircraft dynamic stability theory was used to predict the natural frequencies, damping ratios and time constants of the dynamic modes for three specific small UAVs with wingspans on the scale from 0.6 meters to 1.2 meters. Using USAF DatCom methods, a spreadsheet program for predicting the dynamic stability and handling qualities of small UAVs was created for use in the design stage of new small UAV concept development. This program was verified by inputting data for a Cessna-182, and by then comparing the program output with that of a similar program developed by DAR Corporation. Predictions with acceptable errors were made for all of the dynamic modes except for the spiral mode. The design tool was also used to verify and develop dynamic stability and handling qualities design guidelines for small UAV designers. Using this design tool, it was observed that small UAVs tend to exhibit higher natural frequencies of oscillation for all of the dynamic modes. Comparing the program outputs with military handling qualities specifications, the small UAVs at standard configurations fell outside the range of acceptable handling qualities for short-period mode natural frequency, even though multiple test pilots rated the flying qualities as acceptable. Using dynamic scaling methods to adjust the current military standards for the short period mode, a new scale was proposed specifically for small UAVs. This scale was verified by conducting flight tests of three small UAVs at various configurations until poor handling qualities were observed. These transitions were observed to occur at approximately the boundary predicted by the new, adjusted scale.