Experimental study on self-excited vibration of helicopter supercritical shafting with floating splines

In order to avoid self-excited instability during the development and engineering application of supercritical shafting with floating splines,the self-excited vibration mechanism of short shaft was qualitatively analyzed and vibration stability tests of floating splines under different conditions were carried out by taking the supercritical horizontal shafting of a certain helicopter as research object. The results showed that internal friction force was the fundamental cause for self-excited vibration of the short shaft,and its characteristic frequency was the first natural frequency of the short shaft. Under normal installation condition,the shafting operated smoothly, and the amplitude of self-excited vibration was below 0.1 mm. The worse the grease lubrication state was,the more serious the damage of the tooth surface was. The maximum amplitude of self-excited vibration without grease was 0.9 mm. When the fit clearance of the locating surface exceeded the limit,self-excited vibration and tooth surface damage would be caused. When the spline side clearance exceeded the limit to a certain extent,only tooth surface damage would be caused. When both of them exceeded the limit,the maximum amplitude of self-excited vibration was 4.77 mm,which was very prone to instability. Moreover,self-excited vibration mostly occurred under small load. In practical application,vibration monitoring should be strengthened,spline inspection steps should be refined,and coaxiality of tail shaft should be controlled to ensure work safety. © 2024 Journal of Propulsion Technology. All rights reserved.