Finite element method application for determining water landing parameters of airplanes and helicopters of various types

Аuthors

Nedelko D. V.^1*, Safiullin A. F.^2*

1. Kazan National Research Technical University named after A.N. Tupolev, 10, Karl Marks str., Kazan, 420111, Russia
2. Kazan Helicopters, 14, Ulitsa Tetsevskaya, Kazan, 420085, Russia

*e-mail: airat9415@mail.ru

Abstract

The problem of safety ensuring while an aircraft forced water landing is topical due to periodic incidents while the flights over the water. According to the European Aviation Safety Agency information, the helicopters that have passed the certification procedure topple when performing water landing. This fact indicates that the process of aircraft dynamic contact water surface is insufficiently studied, and the need to account for the aircraft spatial position parameters while water landing.

Confirmation of compliance with requirements of the airworthiness standards (AP, FAR, JAR) while emergency landing and subsequent sailing of the aircraft is based on the results of model tests, which determine the aircraft behavior, the structure loading, its possible destruction and conditions of the most favorable water landing. The hydrodynamic characteristics of models of aircraft fuselages of ground and water basing in the water landing mode, and helicopter equipment with the system of emergency splashdown are studied. A method allowing study such processes at the stage of preliminary design is the finite element method application. However, validity of the results obtained in this way should be verified based on experimental data to enable further practical application of the experience gained.

The article presents the verification results of finite element models of simple geometric bodies (inclined plate, cylinder). These are simplified models that duplicate the shapes of the amphibious aircraft float, the fuselage of the ground airplane and the helicopter ballonet. Verification was perormed employing the concept of Euler-Lagrangian interaction using the generalized “structure-to-fluid” communication simulation algorithm. For the inclined plate, the lifting force coefficients were determined for various deadrise angles and trim at its gliding on incomplete width. A graphic dependence comparing the experimental and computed values was plotted. The changing of overload at the center of gravity was demonstrated for the gliding cylinder, and comparison was performed with experimental data and approximate analytical theory. In all cases satisfactory convergence of the results was obtained.

A helicopter mathematical model with a system of emergency water landing was developed to compute the depth of the ballonet sinking, which determines the level of hydrostatic and hydrodynamic loads. The general case of driving a helicopter to the approaching slope of the wave was simulated with the presence of the initial slip at the moment of contact with the water surface. Based on the graphical dependence of the ballonet transoms movements, a technique for the computed immersion depths determining was formulated. The visualization of the helicopter position change while the water landing process is demonstrated. Based on the developed finite-element model, the other parameters of water landing of a helicopter with emergency splashdown system (overloading in the helicopter center of mass, loads on the fuselage bottom, etc.) can be determined.

The article shows, that a similar approach can be employed to simulate the process of various types of aircraft water landing, including amphibious and ground ones.

Keywords:

aircraft water landing, helicopter water landing, finite element modeling, Euler-Lagrange interaction, dynamic loading process, mathematical model verification

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