METHOD OF DETERMINATION OF SERVICE LIFE OF HELICOPTER MAIN ROTOR BLADES WITH HOLLOW METAL SPAR AND SPAR BREAK ALARM SYSTEM AND METHOD OF CONTROL OF FLIGHT OF HELICOPTER WITH SUCH BLADES Russian patent published in 1999 - IPC

FIELD: study of materials through determination of physical properties. SUBSTANCE: tests pertaining to propagation of cracks in blade spar are conducted on full-scale test rig; cracks are made by application of artificial stress concentrators; time and rate of propagation of cracks are measured for various initial lengths of cracks and for various points of their location both over contour of section and along length of spar. Then static spar breaking tests are conducted after which critical length of crack at which spar is finally broken by maximum operational load is determined on basis of test results and statical analysis of fractographic materials. Then repetition of probable initial lengths of through cracks at moment of their detection is estimated, after which parameters of function of distribution of time of propagation of crack is estimated. Guaranteed minimum rated operating time is determined and limiting time of blade operation from moment of appearance of through crack in spar is assigned. It is good practice to determine service life of blades and to set modes of flight in control of flight. EFFECT: high safety of helicopter flights. 3 cl