Date: 16 Sep 97 02:35:25 From: Gregory.A.Addington.email@example.com (gregory addington) Organization: ND / AFRL References: 1 2
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In article <airliners.1997.2130@ohare.Chicago.COM>, firstname.lastname@example.org (Charles Crosby) wrote: >Marc Schaeffer (email@example.com) wrote: > >: I wonder to what extend the hump of the 747 contributes to the total >: fuel consumption at cruise speed and cruise altitude. Can the >: aerodynamical disadvantages of the 747-hump be evaluated by some formula >Area-rule considerations indicate that the hump causes very little (if any) >additional drag at cruising speed. At low speed there is more of a >disadvantage, but this is fairly unimportant on a long-distance aircraft, >which spends little time at low speed. Kuethe & Chow (Foundations of >Aerodynamics, Wiley) have a graph on page 298 of their book indicating >that the change from short hump to longer hump (as on the -300 and -400 >models) pushed the drag-rise Mach-number up significantly. >Considering the cross-section area plot on the same page, de-humping >a 747 may well result in an increase in drag, in which case the hump causes >negative fuel consumption ;-) C.Y. Chow used this example for his lecture on the area rule when he taught fluid mechanics at the University of Colorado. Quite interesting! Which has made me wonder: from a picture I saw of the freighter version of the 747-400, it looks as though it has the short-style hump. Was it a bad camera angle, or is this true? I can understand why the long hump would have no use from the cargo standpoint (really tough to get pallets up those little stairs ;-) ), but why would the reduction in drag not be advantagous? A weight vs. range trade, maybe? GA Greg Addington Doctoral Candidate, University of Notre Dame | Any opinions,statements, Aerospace Engineer, USAF Research Laboratory | etc, expressed herein are USAF PALACE Knight recipient | not necessarily those of email: Gregory.A.Addington.firstname.lastname@example.org | the U.S. Government; they www: www.nd.edu/~gaddingt | may not be even my own.