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This paper assesses the application of a new method for system stability analysis, the weight functions method, to the longitudinal and lateral motions of a High Incidence Research Aircraft Model. The method consists of finding the number of weight functions that is equal to the number of differential equations required for system modelling. The aircraft's stability is determined from the sign of the total weight function; which should be negative for a stable model. The Aero-Data Model In Research Environment (ADMIRE) simulation, developed by the Swedish Defence Research Agency, was used for the aerodynamic aircraft modelling, with the following configu-rations: Mach number = 0-25, altitude = 500m, angle-of-attack [-10 to 30]°, elevon deflection angle [-30 to 30]°, canard deflection [0° and 25°] and rudder deflection angles [-30° and 30°]. These flight configurations were selected because they are among the flight conditions for Cat. II Pilot Induced Oscillation (PIO) criteria validation, performed on the FOI aircraft model presented in the PIO Handbook by the Group for Aeronautical Research and Technology in Europe, Flight Mechanics/Action Group 12. This aircraft model has a known instability for longitudinal and lateral motions and so a control law was introduced to stabilise its flight. [ABSTRACT FROM AUTHOR]

In this paper, a new original method based on the least squares method is presented for the conversion of unsteady aerodynamic forces from frequency into Laplace domain, in which the error is written in an analytical form of the aerodynamic forces calculated by use of the least squares method. This method is applied on an F/A-18 aircraft (14 symmetric and 14 anti-symmetric modes) for one Mach number and for a set of 14 reduced frequencies. Two different types of results are obtained and analysed: aerodynamic force approximations in the Laplace domain and flutter speeds and frequencies values. For a better comparison of these results, different lag terms numbers are used. Results obtained by this new method are better in terms of execution speed and precision than the results obtained by the use of the least squares method. [ABSTRACT FROM AUTHOR]

Two classical methods are used in the literature to approximate the unsteady generalized forces from the frequency domain Q(k) to the Laplace domain Q(s) and these methods are the least squares and the minimum state (MS). In this article, a new method is presented, called the corrected minimum state (CMS), on the basis of the standard MS approximation method. This new CMS method uses an analytical form of the error as a function of Laplace variable similar to the analytical form of the aerodynamic forces calculated with the MS method. This new method is applied to an F/A-18 aircraft and it is found that the CMS method brings improvements in the approximation results in comparison with the standard MS method. It is shown that the use of the CMS method on an F/A-18 aircraft will give better results in terms of convergence speeds and precision than the MS method. [ABSTRACT FROM AUTHOR]

The article presents information on the ground dynamics model validation through the use of landing flight test. The model performance was able to meet the tolerances set by the U.S. Federal Aviation Administration for one-engine inopertive and autorotation landings. According to the article, the mathematical model improved understanding of the behavior of the helicopter during touch down. It adds that the theory and priniciples developed in the model can be used for the validation of other helicopter landings.