Re: ETOPS Question

Date:         25 Nov 97 03:26:07 
From:         Steve Lacker <look@the.sig>
Organization: Applied Research Laboratories - The University of Texas at Austin
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David Lesher wrote:
> (C. Marin Faure) writes:
> >All ETOPS twins must be able to immediately start their APUs at cruising
> >altitude even after hours of cold-soaking.
> Could you not just heat the APU's normally, given you will be
> starting it ASAP if you lose an engine anyhow?

"Heating the APU normally" is descending into warm air and allowing it
to warm up due to the ambient temperature :-)

> ISTM you're not
> short of waste heat in-flight but maybe I'm wrong.

You're short of waste heat if all the engines are windmilling and you
need to start the APU. Even if an engine is running, I think there's
probably no provision for "heating" the APU from engine bleed air.

> On the ground, standby power Diesels have their water-jackets kept
> warm to ensure they will start quickly and easily.

Diesels are VERY different beaties from APUs. APUs don't have water
jackets, for one thing. Also, I doubt that there is a provision for
pre-heating the lubricating oil either (weight penalty) and besides, hot
lubricating oil *still* won't heat a cold-soaked combustor on a turbine
engine (an APU is just a turboshaft engine, after all).

> And how are ETOPS APU's started; is bleed air an option, or just
> electricity?

AFAIK, APUs are electric start.

Stephen Lacker
Applied Research Laboratories, The University of Texas at Austin
PO Box 8029, Austin TX 78713-8029
512-835-3286 (Remove the extra 'x' to mail me)