Engine rotation

From:         ctillier@flagstaff.princeton.edu (Clemens Emmanuel Tillier)
Organization: Princeton University
Date:         25 Mar 94 11:33:15 PST
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I was wondering about engines-- more specifically which way they
rotate, and what effect this has.  What I've observed seems to
indicate that all the engines of a particular aircraft rotate the same
way, usually CCW seen from the front.  The best guess I can make is
that this cuts down on costs, since making them all the same is
cheaper.

I also guess that the torque applied to the airframe in flight
(through various forms of friction and drag within the engines) is
essentially negligible.  Is this true?

What about the torque from spooling up in flight, e.g. for an aborted
landing?  Does this make the plane pull to the left appreciably?

(What prompts me to ask is something I observed the other day: I was
looking out over the left wing of a 747, and when the engines spooled
up for the takeoff roll, the wingtip briefly sank a few feet.)

Regards,
Clem Tillier
Princeton, New Jersey, USA
<ctillier@phoenix.princeton.edu>