Re: 777 engine RPM

Date:         11 Sep 97 03:35:28 
From:         kls@ohare.Chicago.COM (Karl Swartz)
Organization: Chicago Software Works, Menlo Park, California
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>Anyone have knowledge of the approx rotational speed of 777 engines
>(inner core and fans) at take-off and cruise?  I'll split the beer I
>win if the fans do <30,000 rpm.

I don't have any hard numbers, but it's easy enough to come up with a
decent estimate.  Have you ever noticed how some jets have a distinct
buzz at takeoff power?  (The DC-10 is a notable example.)  That's due
to the tips of the fan blades going supersonic.

The speed of sound varies with temperature and barometric pressure,
but at average conditions at sea level it's about 760 mph.  The fan
of a PW4000-series engine for a 777 has a diameter of 112 inches.
(http://www.pweh.com/lce/pw4074.html) Some simple math says that if
the tips of the blades on a fan of that size are moving at 760 mph,
the fan is turning at 2,280.9 rpm.

Given how much less than 30,000 rpm that is, I'd say you ought to
win a keg of beer from whomever your bet was with!

--
Karl Swartz	|Home	kls@chicago.com
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Moderator of sci.aeronautics.airliners -- Unix/network work pays the bills