21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-1.4.4

ANALYSIS OF TRANSIENT DYNAMIC BEHAVIOUR OF A FIRE FIGHTING AIRCRAFT AFTER THE WATER BOMB DROPPING

Gorai Z., Sznajder J., Goetzendorf-Grabowski T.*
Institute of Aviation, Poland; *Warsaw University, Poland

Keywords: transient dynamic behaviour, fire fighting aircraft, water bomb dropping

Paper presents an analysis of the water bomb dropping from firefighting aircraft. The major objective is to select the most important parameters, being responsible for effectiveness of water drop and aircraft safety. Also to establish a simple, computational -effective, numerical code, being able to solve simultaneously the flight dynamics equation of motion and to determine aerodynamic forces and moments, which are functions of flight parameters and time history of the motion. Unsteady incompressible potential flow over the whole aircraft dropping the water bomb is sequentially solved using low order panel methods. Constant strength source and doublet panels distributed over aircraft surface constant strength doublet panels over flat wake and constant strength source together with linear strength doublet panels distributed over the vertical water column being able to properly imitate the downward outflow of growing velocity, are used to solve the Dirichlet's boundary condition. A comparison between results of classical flight dynamics model (linearization around steady, before-water-drop flight plus stability derivatives used to represent disturbed forces and moments) and results of an unsteady model (current forces and moments computed by unsteady panel method' stability derivatives are not used in this model) was performed. Paper discuses advantages and weak points of both approaches -classical, based on stability derivatives concept and a modern, based on unsteady aerodynamics.

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