Re: MD-80: Lawn Dart or Efficient Design?

From:         "Keith R. Thompson" <>
Organization: Earthlink Network, Inc.
Date:         21 Oct 96 02:29:21 
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> In article <airliners.1996.1635@ohare.Chicago.COM>, "David G. Davidson"
> <> writes:
> >727 APU installation is the best of the three, but also far from ideal.
> Can anyone describe to me what the 727 APU installation actually is?

The B-727 was originally designed without provision for an APU and was
later added to the design at the behest of the airlines. Because the engine
and aft airstair configuration ruled out mounting the APU in the tail,
Boeing basically cut a hole through the keel in the forward part of the
main gear wheel wells and mounted the APU there.

Air for the APU is drawn from the left wheel well and exhausted through a
port in the top of the right wing near the fuselage. The APU uses a flow
multiplier which draws from the right wheel well.

The main problem with this installation is that in extremely hot
environments, high temperatures in the wheelwell when the APU is operating
can result in a Lower Aft Body overheat warning light illuminating on the
engineer's panel. That's why under these conditions ground crew will
frequently drop the main gear doors if the aircraft will be idle for
awhile. This aids airflow to the APU and reduces the likelihood of getting
the warning light.

Keith R. Thompson
Denver, CO