Originally Posted by
KenV
I understand that part. What I don't understand is blades fractures occurring "at the same clock position." Every blade is at every clock position when the engine is running. You can't say "the blade at 2 o-clock tends to fail more often than the blades at the other clock positions". So what am I missing?
Lets try again-IMHO a particular spot on the fixed ( non rotating ) part of the engine casing/inlet is defined by ' clock position " The comment was made about an instrumentation device (probably a very small protrubence into the surrounding casing such as a magnetic/proximity/ device to measure rpm/temp/pressure ( approx 5000 rpm I believe ) This then could cause a minor disturbence in the airflow or a minor change in tangential/radial stress when each blade passes )
Over a period of time, given a marginally fatigued blade, this change in stress while quite small **COULD** **MAY** be sufficient to cause that blade to depart within a few milliseconds.
The point was that **IF** that is the case, then the first 'impact' point of the broken blade **COULD** be a function on fan speed and direction. so **IF** the fan speed was the same in a few cases, then the first impact point would **PROBABLY** be in the same relative clock position depending on fan direction eg 9 O'clock or 3 O'clock and x o'clock from the protrubence.
Keep in mind- the comment was re statistics and/or probability of such a comparison - NOT a fixed- proven theory.
Just my .000002 based on my injun-ear background
And after I posted this- I found tdracer comment made a few minutes before I hit save of my tome