Re: Good 'ole 727

Date:         31 Mar 2000 22:25:44 
From:         "John M. Hunt" <johnmhunt@ipa.net>
Organization: Internet Partners of America
References:   1 2 3
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bizfixer@aol.comspamo (Bizfixer) wrote:

>rwi@whidbey.com commented on unsuitability of a 2-engine version.  I add
>thte following bit of history.
>---
>
>Saw your interesting letter to one of the airliner newsgroups dtd. 08 Jan.
>
>You apparently bailed out in 1980 when there was no suitable engine for
>a 727 'bijet'.  The engine choices at the time, as studied by Lockheed
>& Boeing were 747 class  "heavies" and required complex pylons and
>fuselage extension.  Perhaps that's why wing wake problems. (It
>obviously didn't affect engines #1 & #3 in -100 or -200 configs.)
>
>In 1986, we (Volpar Aircraft) had both companies' data and were looking
>at the high bypass CFM56-5, which was an easy fit, plenty of power, and
>required no fuselage extensions.  Engineering analyses showed no wake
>problems, but we ran out of $$ before wind-tunnel testing.  The Chinese
>loved the idea (a co-production deal), but insisted that we imprison
>their personnel after hours.
>
>Boeing didn't want to cooperate (in spite of potential spares business)
>and top execs simply said, "We build new planes, not improve old ones."
>Lockheed was buried in other projects and simply not interested, perhaps
>based on their prior studies.  I think it would have worked.

There was a post in one of the groups about six months ago regarding
an extensive study (possibly by NASA) regarding the possibility of
fitting modern engines (presumably the CFM56 or IAE V2500) on Boeing
727s in positions 1 and 3.  Apparently there was very serious concern
about compressor stalling on the modern engines as a result of
picturesque changes in intake air flow direction arising from wing
wake in all of the various configurations.

It seems likely that the ancient engines of the 727 were considerably
less vulnerable to intake airflow compressor stalls than their modern
considerably more exotic counterparts.  If memory serves me correctly,
the only really high bypass ratio rear  mounted engines now flying are
the IAE V2500s on some (all?) of the MD90s.

Since the wing of the 727 is considerably more sophisticated than that
of the DC9 family, and can operate at unusually high lift
coefficients, it is probable that the wing wake intake airflow problem
is inherently more severe on the Boeing 727 than on the DC9/MD80
families.

John M. Hunt
johnmhunt@ipa.net