Re: interesting ETOPS stats from UAL

Date:         16 Jun 98 02:15:14 
From:         "S.L." <look@the.sig>
Organization: Applied Research Laboratories - The University of Texas at Austin
References:   1 2 3 4 5
Followups:    1
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JF Mezei wrote:
>
> Gerard Foley wrote:
> >   Their minds must be back in the piston engine era, when the take off
> > stress was the major cause of engine problems.
>
> Has this changed with jet engines ? I would have though that it would
> still have been during takeoff that jet engines failed. (Although one

Yes and no ;-)

Turbine engines are affected by power setting, but not to anywhere NEAR
the degree that piston engines are. The stress on every single component
of a piston engine goes up dramatically at high power settings, greatly
increasing the risk of failure. With turbines, the main increase in
stress is due to higher combustion temperatures, and if they stay below
a critical value, the life of the engine isn't compromised much. You
don't have to worry about connecting rod bearings seeing 100X the force
per unit area they do at cruise, exhaust valves seeing many times the
temperature they do at cruise settings, valve retainers getting hammered
harder on each cycle (A common hazard with piston engines was sucking in
a valve and having it punch a hole in a piston), connecting rods
stretching at higher RPMs, cylinder blocks flexing at high torque
settings, etc. Jets just "spin faster and burn hotter". So the risks of
high-power setting failures are far less than with piston engines.

--
Stephen Lacker
Applied Research Laboratories, The University of Texas at Austin
slacker@arlut.utexxas.edu (Remove the extra 'x' to mail me)