Based on statistics of 30 test run data of three typical intershaft bearing of aircraft engine

a principle to avoid synchronous impact was acquired. The statistics of test run data shows that it is dangerous area when integer multiple of the frequency of aerodynamic force and fault characteristic frequency of intershaft bearings are close in range of 2%

aircraft engine should not work under this state for long. Afterwards

a optimization iterative dynamics design approach for rotor with intershaft bearings was proposed. Blade number or high/low pressure rotor speeds ratio should be adjusted until the range of the dangerous area less than 10% of aircraft engines running range. The approach can reduce intershaft bearings dynamic load

let it free from synchronous impact

and eventually increase its fatigue life.