Re: A 777 with four engines.

Date:         06 Aug 98 11:26:35 
From:         ranfaa@my-dejanews.com
Organization: Deja News - The Leader in Internet Discussion
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In article <airliners.1998.1138@ohare.Chicago.COM>, "Richard Rea" <rrea@xmission.com> wrote:
> The Warden wrote in message ...
> >Me who doesn't have much faith in new technology thinks that 4 engines are a
> >greater safety factor, despite the extra cost. Also, if something happens
> >and rudder control is lost, the two outboard engines could be pressed into
> for that gust of wind that pushed them off of the runway and made
> >the wing dig into the ground (if that had not happened, they would have
> >landed safely). Personally, I think the 777 should be a trijet, at least...
>
>  (e.g. Sioux City - DC10 - total loss of hydraulics, Japan - 747 - rear
> pressure bulkhead failed and blew off part of the vertical tail).
>
> Does anybody know of a case where a plane was controlled successfully using
> asymmetric control of the engines?

The japanese b747 bulkhead blow out illustrates the lag effects inherent in
any attempt to control the aeroplane just using asymmetric thrust,
or in their case all thrust and just attempting to use pitch effects
to try and maintain height and some directional control. Turn means
the nose drops so thrust must be applied on all engines to start a
nose up pitch.	How much? then as the turn is stopped or all thrust
must be reduced to prevent unwanted climb. In theory it may seem
possible but  in practice ????? Regarding the question of asymmetric
thrust to control direction; I have a photo of a b52 that lost almost
all the vertical fin after striking cat near the rockies many years
ago now. It was controlled with some effort and successfully landed.
This is an aeroplane with with a fair distance between the two
critical outboard engines and because of the relatively low power
involved, the asymmetry would not be that great. Add to this the fact
that the other 8 engines could be set at a constant thrust for speed
control then a potential disaster was averted. I don't suggest for
one second that it would have been easy, there was great airmanship
and crew co-operation displayed in this incident that was in the
highest traditions...etc.

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