Re: Engine rotation

From:         drinkard@bcstec.ca.boeing.com (Terrell D. Drinkard)
Organization: Boeing Commercial Airplane Group
Date:         01 Apr 94 13:11:41 PST
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Followups:    1
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In article <airliners.1994.1051@orchard.chicago.com>,
Clemens Emmanuel Tillier <ctillier@flagstaff.princeton.edu> wrote:
>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.

Typical Western engines turn clockwise as seen from behind.  Russian
engines turn counterclockwise.  Making them all turn the same way has more
than economic implications.  It also eliminates the 'critical' engine - cf
P-38 Lightning with its special gearbox to reverse propeller direction on
the right(?) engine.  The engine with the gear box is more likely to fail,
but does reduce the amount of rudder required to hold the ship straight
when the other engine fails.  But, if you put enough rudder on the bird to
begin with, this is not a problem.

>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?

I would not call it negligible, it is rather substantial, but you are
correct if you mean it is not the limiting design case.  If this case
doesn't design the structure, then I guess you can neglect it, making it
negligible.  :-)

>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?

Geez, that's a pilot technique question.  I'd have to ask around; I don't
know.

>(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.)

Did the right wing tip raise up?

Terry


-- 
Terry
drinkard@bcstec.ca.boeing.com
"Anyone who thinks they can hold the company responsible for what I say has
more lawyers than sense."