PSI - Issue 16

Andrzej Gębura et al. / Procedia Structural Integrity 16 (2019) 184 – 191 Sylwester Kłysz, Andrzej Gębura, Tomasz Tokarski / Structural Integrity Procedia 00 (2019) 000 – 000

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rotation cycle of a kinematic pair) than in the case of the eccentricity defect. If tribological phenomena are considered (excessive abrasion due to the contact point of spline causing the accumulation of stresses and temperature increase), then the skews of splined couplings shall be treated as a dangerous manufacturing defect leading to intensive abrasion of a splined coupling in the form of ‘barrel - shaped’ defects developed by Gębura (1999), Gębura and Stefaniuk (2017) . During operation, the clearance-free skew (skew without clearances in bearing supports) of splined couplings or toothed couplings is almost non-present – most frequently it is associated with radial clearances. Such combination of two defects: skew and radial clearances is exhibited in the FAM-C method in the first form of a subharmonic rated rotational speed, i.e. pulsation component of angular speed will be two times longer – Fig. 4b, detail T i = 80 ms – than the duration period of the full shaft rotation – Fig. 4a, detail T i = 4 ms. 5.3. Structure of Mi-24 accessory gearbox Fig.5 illustrates a diagram of the accessory gearbox of Mi-24 helicopter. This diagram also shows a transmission system in the accessory gearbox. It can also be noted that a gear wheel Z70 cooperates only with one gear wheel (Fig. 5 detail Z30), i.e. there is an asymmetry of dynamic forces during operation. It can pose a threat to the transmission system since such displacement can constitute an unbalance of the mechanical system. Gear wheel Z35 no. 1, and Z30 are installed on the so-called intermediate shaft – Fig. 5, element 6. On one side, the shaft is hollowed internally and has internal splines. These splines are used to ensure the connection with the drive shaft of GT-4PCz6 generator no. 1 – Fig. 5, element 1. The rotor of this generator has a significant moment of inertia and constitutes a reliable spatial fixation of the extension of the intermediate shaft.

Fig. 4. The waveform of the instantaneous frequency by the changes in skew value of transmission shaft by angle: a) β = 0,2 o , b) β = 0,5 o obtained with the FAM-C method on a reduction gear from Mi-2 helicopter (TUN-75/R) in laboratory conditions: T i – period of modulations of pulsation component of angular speed (here: on the waveform reflected with the FAM-C method synchronized with the waveform of instantaneous rotational speed). From the other side of the intermediate shaft, a centrifugal fan (Fig. 5, element 3) with a little moment of inertia is installed. In the centre of this shaft, as it was previously mentioned, gear wheels Z30 and Z35 no. 1 are mounted. Thanks to them, mechanical power is transferred to the tail rotor. The anti-torque of tail rotor changes depending on the angle of attack of its blades and sometimes obtains the significant values developed by: Padfield (1998), Żurek (2006). The input power (from main transmission WR-24) is transferred on the gear wheel Z66. From here, there is a flow of power, through gear wheels Z35 to two generators TG-4PCz6 in the direction of a tail rotor. The wheel Z33 has a symmetrical loading but on the power output in AGB there is no such symmetrical loading – gear wheel Z70 is loaded on one side by wheel Z30 – Fig. 5, element Z70. If there are radial clearances in bearing mounting of the axle of gear wheel Z70, then they will cause the undamped radial movements of this axle. The mutual radial