Experimental studies of the influence of a gyroscopic damping system on the aeroelastic characteristics of a large aircraft model with elastic pylon-mounted engines under the wing

During production of modern large transport aircraft, engine arrangement mounted on the elastic pylons under the wing is widely used. This arrangement of engines has certain advantages, however, there are also significant dynamic features due to the fact that the partial frequencies of vertical and horizontal (lateral) vibrations of elastic pylon-mounted engines are close to the wing bending and torsional natural frequencies of low modes. It is this frequency spectrum that determines the dynamic response of the aircraft as a whole to external disturbance input, and also significantly affects the dynamic stability of the aircraft. A number of technical solutions have been proposed to damp vibrations of the elastic pylon-mounted engines, including the implementation of the “freed engine” principle. To increase the dissipative parameters of the pylon-mounted engines vibrations, this paper proposes to use special devices – powered gyroscopes, which are the main part of the gyroscopic damping system. Numerous theoretical studies of the possibility of using powered gyroscopes have shown that the stability of a dynamic system can be increased by introducing additional gyroscopic, dissipative and potential forces into it. It is known that a method of direct gyroscopic stabilization is proposed to control aeroelastic oscillations of aircraft structural elements. The article proposes to use powered gyroscopes to damp lightly damped vibrations of pylon-mounted engines of a large aircraft. In order to assess the possibility of practical application of the gyroscopic damping system (GDS), experimental studies were conducted on a dynamically similar flutter model (DSFM) of a large aircraft type An-124 with four pylon-mounted engines under the wing. The studies included two stages: frequency and flutter tests. A gyroscopic device made according to the scheme of a rate gyroscope, which was installed inside the engine nacelle, was used as the GDS. The article presents the results of the experiments to assess the effect of the GDS on the dynamic characteristics of the DPFM. The analysis of the normalized amplitude-frequency characteristics of vertical and horizontal oscillations in the center of mass of the outboard engines shows a significant (by 1.5...5 times) decrease in the peak values of the oscillation amplitudes across the entire frequency range covered. The results of the experimental studies of the effect of the GDS on the flutter characteristics of the aircraft model showed a significant (7...15%) flutter speed enhancement at all levels of aircraft refueling. At the same time, with the gyroscopic damping system powered on, the self-oscillations are sluggish and incoherent, and the flutter modes change from one to another due to the gyroscopic coupling of the longitudinal and lateral motion.

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