WingedMigrator From United States of America, joined Oct 2005, 2353 posts, RR: 56 Posted (8 years 7 months 3 days 13 hours ago) and read 13763 times:
I read in this week's Aviation Week issue that the 787 sports an external (!) keel beam that, for aerodynamic reasons, protrudes out of the belly fairing under the center wing box. Does anyone have a close-up photograph of said appendage, from the roll-out ceremony?
WingedMigrator From United States of America, joined Oct 2005, 2353 posts, RR: 56
Reply 6, posted (8 years 7 months 2 days 23 hours ago) and read 12481 times:
Quoting Jogales (Reply 2): Click on "all sizes" for a much bigger view
Thanks, that's exactly what I was looking for. Flickr is a gold mine of 787 photos, much more abundant than a.net or even Flightblogger! For example, I saw lots of shots of airplane #2.
Quoting DeltaDAWG (Reply 3): What is the reasoning? Can anyone explain the details of why it is like that?
Here is the direct, fair-use quote from the article in AWST:
Quote: The externally visible keel beam was perhaps the most surprising feature, thought to represent a first for any Boeing commercial jetliner to date. Measuring 340 in., it begins toward the aft end of the Kawasaki-made Section 43 forward fuselage and ends just aft of the front end of the Alenia Section 46 center-rear fuselage. It runs under, not through, the Kawasaki Section 11 center wing box.
In all previous models the keel beam, a strengthening structural member running forward and aft through the bottom of the fuselage, has been hidden within the contours of the fuselage itself. Although clearly visible on the 787, the structure is contained within a fairing only a few inches deep. Boeing says the beam is not a bolted add-on.
The keel beam “is a very deep structure, not externally mounted,” says 787 Chief Project Engineer Tom Cogan. “It happens to protrude by choice. We could have made the fairing bigger for appearance, but by choice we wanted the fairing to be as small as possible and that’s why you see more contouring on the bottom than people are used to.”
Viewed from either end, the beam also displays slight area ruling to reduce transonic drag rise in the belly area flow field between the large engine nacelles. “A lot of study and aerodynamic work went into this aspect of the design and this was the best solution,” adds Cogan.
There's also information about another unusual 787 design detail: those funky ram air scoops for the air packs. Looks like the extra drag from those protruding scoops will have to be weighed in the balance of the cost/benefit of using a 'bleedless' architecture.
Boeing767mech From United States of America, joined Dec 2000, 1037 posts, RR: 2
Reply 7, posted (8 years 7 months 2 days 23 hours ago) and read 12318 times:
I don't know the reason why,but the Convair 880/990's also had a external longeron running down the center line of the aircraft from just ahead of the center section and ended just forward of the aft outflow valve (not to be confused with the speed fairing on the upper crown of the airframe), They also had a smaller one around the tail bumper area.