Rolls-Royce Limited. Bristol Engine Division Parkside. Stress Department. Olympus...

PA1716/5/11/2/254

Rolls-Royce Limited. Bristol Engine Division Parkside. Stress Department. Olympus HP turbine rotor blade failures

1978

Hand-written un-signed report. 1 Critical rpm band indicated by MES review is 83 - 91% Nh. This is coincides with the IF-6th engine order where the max AR was 55%. 2 The original SF1, which was introduced to avoid the 4th engine order combined disc and blade mode of vibration involving the 'thin' disc, avoided 81-87% LP pm in the case of he Mk.202 engine and 82.5 - 90% LP pm from the Mk.301 engine (ie rpm at 15C deg). 3 The equivalent LP rpm from the HP rpm band given at 0 is as follows:- Mk.202 70-83% LP rpm; Mk.301 69.5-83.5% LP rpm. 4 The failures to date have all been on Mk.301 engines (ie 3 cases in Service) and the bias has always been towards the Mk.30. May be due to more excitation ie higher operating pressure (HOP). 5 Because of 4 it would indicate that the fit of the blades at the root and the outer shroud is not the critical feature leading to the failures, but must be related to the rpm at which the blade is likely to resonate plus the (HOP). 6 Since the recent failures have occurred after the SFI was withdrawn, this also would tend to support comments at 5. 7 Since the likely speed band to avoid is now wider than before (ref 1 and 3) this may lead to compliance problems. Also, most of the band would have been flown in prior to the withdrawal of the SFI and apparently did not produce failures. This would also indicate that the area to worry about is the overlap and this is indicated below: Drawing of Mk.301 showing old SFI and Mk.202 showing new band. The overlap of the Mk.202 is 81-83% LP rpm. The overlap of the Mk.301 is 82.5-83.5% LP rpm. Using the above speed bands the HP rpm. Avoided is 90/91% for the Mk.202 and; is 90.5/91% fo the MK.301. To allow or scatter, the band for both marks could be made 80-85% LP rpm, which would avoid HP rpms between 89/92.5%. It could also be argued that since with the original SFI, there were no failures, that this should be re-introduced. This would encompass the top end of the 6h EO resonance condition covered by the ovelap condition. Olympus engine operation: In circuit 35 67/70% rpm. Approach 75 75-78% rpm. Roller 93% rpm. At below 5,000 not operated between 80-90% LP rpm.

English

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