Defects of steel units of the high-lift devices of aircraft wings caused by fretting corrosion
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DEFECTS OF STEEL UNITS OF THE HIGH-LIFT DEVICES OF AIRCRAFT WINGS CAUSED BY FRETTING CORROSION V. O. Kralya,1 O. H. Molyar,2 V. A. Trofimov,3 and A. M. Khimko1
UDC 620.178.16(045)
We study the defects of a flap actuator of the wing of an An-124 aircraft. The fractographic and metallographic investigations of the surface defects of a screw–nut friction couple are performed. A device for wear tests under the conditions of fretting corrosion is developed. Recommendations concerning the reduction of possible damage to flap actuators are proposed. Keywords fretting corrosion, corrosion defects, tribological tests, fractographic investigations, metallography, screw–nut couple.
Actuators of flaps and slats moving them after takeoff and prior to landing belong to the most critical units of the high-lift devices of aircraft wings. These actuators are designed the form of screw–nut couples with intermediate balls used to transfer forces from the screw of the drive to the nut fixed on the flap carriage. The carriage is moved along the carriage track of the high-lift devices of the wing and extends the flap along a given trajectory. The flap actuators are especially critical units operating in the zone not isolated from the environment, i.e., under the conditions of complete operating temperature range ± 60°C and under the action of all possible atmospheric influences. The failure of any actuator in the course of a flight creates emergency situation. In [1, 2], we studied a track–roll unit used for the extension and retraction of the flaps. The in-service defects of the track were described. The optimal solution for the improvement of the wear resistance of working surfaces and restoration of damaged segments of the tracks by the method of plasma spraying of molybdenum coatings was proposed. For the related (screw–nut) friction couple operating in rigid tie with the carriage and carriage track of the high-lift devices of the wing, the results of similar investigations are absent. According to their design, both these friction couples transfer the same force required to extend and retract the high-lift devices. This is why it is of interest to analyze the operation and defects of the flap actuator unit, especially in view of the fact that significant defects appear in the track–roll couple after operation as a result of vibration [2]. In what follows, we analyze the defects formed in the flap actuator unit of the high-lift devices of an aircraft wing and develop recommendations concerning the possibility of decreasing the number and preventing the appearance of defects in screw–nut friction couples. Assessment of the Fretting-Corrosion Defects in the Units of High-Lift Devices of the Wing We now analyze the defects formed in the thread part of the screw-and-nut unit of flap actuators of an An124 aircraft. 1
National Aviation University, Kyiv, Ukraine. Kurdyumov Institute for Physics of Metals, Ukrainian National Academy of Sciences, Kyiv, Ukraine; e-mail: [email protected] (corresponding author). 3 Antonov Aviation Scienti
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