Re: Inflight engine shutdowns vs. speedups?

From: (JVRusso)
Organization: America Online, Inc. (1-800-827-6364)
Date:         22 Mar 95 02:34:21 
References:   1
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  As I work in the field of testing jet engines, I have shut down engines
(both on purpose and in emergencies) from full power a number of times. It
is true that due to thermal effects the rotor and static hardware due cool
at different rates. Most times as soon as the high rotor stops turning it
locks up and can not be turned for several hours. BUT, that is not due to
blades touching shrouds, it id due to knife edge seals under the blade
root rubbing against their seal lands. There are much tighter clearances
in the seals, especially in commercial enignes, which have larger
clearances, and rely on active clearance control to reduce the clearances
  I have never seen any long term damage as a result of "hot shutdowns".
The worst that happens is that you have to wait a few hours to borescope
since you can't rotate the high rotor. We try to prevent that in a test
stand by getting on starter motors as soon as N2 gets to sub-idle speeds
during spool down.
  Hope that helped!