All airliners have AUXILIARY POWER UNITS to generate electrical power
for services whilst the engines are not running. Typically what power
do these APUs generate.

renniebett-ga:

It is difficult to say what is typically generated, as auxiliary power
units are sized to the requirements of the aircraft in which they are
deployed. An APU for a small regional jet, for example, would produce
as little as 10 kVA, whereas an APU for a Boeing 747 can produce up to
180 kVA.

So, the best way to Answer your question, is to provide you with the
following link where you will find statistics on many APUs:

Venik's Aviation - Auxiliary Power Units
http://www.aeronautics.ru/archive/reference/Auxiliary_Power_Units/Canada.htm

(click to the last page for the American manufacturers)

Hope this helps!

Regards,

aht-ga
Google Answers Researcher

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Request for Answer Clarification by renniebett-ga on 20 Feb 2004 06:55 PST

Thank you for your answer. Are APUs turboshaft engines with a rotary
shaft output and if so what is the likely output shaft speed. EG does
it drive an electrical generator at 1800 rev/min to produce AC current
at 60hz. Additionally do you think it would be possibleto buy a time
expired APU from an aircraft breakers yard.

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Clarification of Answer by aht-ga on 20 Feb 2004 09:45 PST

renniebett-ga:

You are correct in that APUs are typically gas turbines with rotary
output. Rotor speeds vary from manufacturer to manufacturer. For
example see:

http://www.motorsich.ru/eng/product/auxpp/ai-8.shtml

You can also see additional technical specifications for some APUs here:

http://www.hs-powersystems.com/prodindex.htm

The output shaft speed is not directly related to the electrical power
produced by any alternator driven by the turbine. Typically, a
constant speed drive assembly is used to ensure that no matter what
the output shaft speed is, the electrical system is constant. See the
following presentation for more information regarding aircraft power
systems:

http://www.tech.purdue.edu/at/courses/at403/Aircraft_electrical_systems.ppt

As you will see from that presentation, many commercial aircraft
operate at 115 VAC @ 400 Hz, with many devices onboard operating at 28
VDC as supplied by a transformer rectifier. There are also some
systems that operate at 26 VAC, primarily fluorescent lighting
systems.

As for sourcing a used APU from an aircraft breakers yard, it seems
that this is indeed possible. For example, here is the website of a
used parts broker:

http://www.aog-spares.com/index.php

And, here is the website of a hobbyist who owns several used APUs
sourced from breakers:

http://www.users.zetnet.co.uk/gas/lucas.htm

If you are interested in how the FAA tests APUs for certification, check out:

http://www1.faa.gov/certification/aircraft/APU_Auxiliary_Power_units.htm

If you require more information than I have provided, I would
respectfully suggest that you post an additional Question with an
appropriate price, to reflect the research time required.

Thanks!

aht-ga
Google Answers Researcher