Downloaded from https://www.everyspec.com AMCP 706o19 Ellxamol!e No, 14 (Re. ,2) A turbojet engine in experiencing blade-fattgue failures due to wexesive vibra- tions at resonance. A test to to be run to determine whether a relationship exists be- twen bench-measured blade resonance points and the actual rpm at which the blade reaches resonance. If this is established, it may be possible, by nondestructive bench miasurements, to determine the acceptability of blades for actual engine use, reducing or eliminating this engine failure mode. Thirty bWades are seleoted at random and tested sequentially.
The test conslsts of building up engine speed and recording the rpm at which resonance occurs and the resonant frequency. The test data are given in Table 2-22. Compute the linear re- gression equation and the associated statistical quantities. Procedure EXAMDle 1. Plot the data to see what * 1. See Fig. 2-13. They look reasonable enough. they look like L 2. Calculate the deviations 2. Fill in the x oolumn in Table 2-22. from the mean for the bench resonant frequen- otes. 3. Calculate SOA. 3. Ztx -223,266.70. 4. Calculate zIyg. 4. Ziy, -322,200. 5. Calculate zjxJyi. S. jxjyj .- 2,608,330. 6. Calculate 9 and it from 6, 9-.10,740 Eqs. 2-60 and 2-61. A 11.683 a - 1085.1. 7.
Calculate each it, (4 7. 0 - 50175.5 -Y# - A + 9) then 224.0. calculate of - (Ez /- * - 2). 8. Estimate Var $I}and 8. Var{S}. 50178.2/30- 1672.5 -40.92 Var Use Eqj. .2-63. Var {o}w 50178.2/223, 206,; - 0. 2%,7 = 0.47412 ".In,,,q I i', . . .. ; , '