Re: A 777 with four engines.

Date:         25 Aug 98 00:53:45 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
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>The problem with an engine failure (or worse obviously, a reverser
>deployment giving us negative thrust) is the asymetrical thrust (center of
>thrust not on the aircraft centerline) and the resultant yaw. The limiting
>factor is then how much rudder you have to counteract that yaw.

The cascades of the thrust reversers (at least on the PW4000-equipped
767s) are ahead of the wing, so thrust reverser deployment causes
airflow disruption which in turn causes loss of lift, in addition to
the yaw effect you describe.  Studies based on wind-tunnel tests after
the Lauda Air crash showed a 25% loss of lift with the engine at maximum
climb power, leading to a roll rate of about 28 degrees per second
within four seconds.  It was found that full aileron and rudder had to
be applied within 4-6 seconds.  Any longer and recover was not possible.

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