Re: ETOPS Question

Date:         01 Dec 97 02:33:56 
From:         Matthew Willshee <96mjw@eng.cam.ac.uk>
Organization: University of Cambridge, England
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On 29 Nov 1997, John van Veen wrote:
> When the combustion temperature, maybe 1100 degrees, of the fuel burning
> in the APU is considered, there isn't much difference between -45
> degrees and +90 degrees.  Both temperatures are very cold relative to
> how warm it will get.  Maybe someone who knows more about this has a
> comment.

I should think that the limiting factor on cold starts is oil temperature.
If the oil is very cold then it will be too viscous to pump around the oil
system.  This can lead to problems with bearings and local overheating of
the oil (because the cold oil is too thick to pump into the hot bearing
chambers to replace the heated oil there).

As to the temperature scales mentioned in John's post don't really apply.
The oil will cold soak down to ambient temperature, but when the APU is
running, the oil is cooled to stop it decomposing.  I think about 100
degrees celsius is a reasonable maximum temperature for an oil system, but
I may be wrong here.

____
Matthew Willshee                               E-Mail: mjw44@cam.ac.uk
Churchill College, Cambridge, CB3 0DS                : 96mjw@eng.cam.ac.uk