More "What's that thing on that plane?"...

Tangentially related to the OP and the recent batch of airplane threads, I found this page at Boeing that has rescue information on each of their commercial aircraft. It has information like the locations of fuel tanks, APU’s, fuel lines, oxygen generators, and other stuff that would be hazardous to a firefighter. It also has instructions on where to start chopping at the fuselage if it is necessary to chop the survivors out. There is even a page telling you how to turn the engines off (assuming the pilots are no longer available). It’s really interesting stuff.

Those things also serve the purpose of mainatining the “Rule Area” to decrease drag at transonic speeds, I´ve also heard them called Kucheman Carrots, for the aerodinamic engineer that had the idea.
Basically, they keep the corss section of the wing constant along the chord.

Right-O. Sorry about that; the boundary-layer control assertion was Like Fry’s.

I got curious and checked this out with an aerodynamicist here, and he says no. Boeing airliners get no area-rule benefit from the flap track fairings. You’d have to fly much faster than our current airliners do to get any benefit.

They also are not used to control spanwise flow along the bottom of the wing.

Basically, we just try to minimize their impact on drag.

Well, that’s nice to know. I told my neighbor’s kid those pods were steerage. That’s where you have to ride if you get a really low priced ticket. :wink: If you want to meet the Travelocity Gnome, check in steerage. :cool:

Hmmm, maybe not in Boeing aircraft, Airbus planes at least do use them as anti-shock bodies (Cite, first picture )

The link to the photo on the OP shows an A-321 model, there are oversized flap track fairings there, those are indeed used as an aerodynamic device, besides reducing the drag of an exposed flap mechanism of course

I think the author of that Web page is overstating the effect of the flap tracks. While the Whitcombe bodies added to the Convair 990 and other aircraft did have a definite effect, flap tracks and similar devices are there for other reasons and have different shapes, so any profile drag reduction effect is probably wiped out by the increased surface drag of all those multiple small bits sticking out. (The Tu-95 fairings shown at the bottom of the page are there to accomodate the HUGE main landing gear - any other effects are strictly secondary.)

More detail on that. Generally airliners are designed to fly at Mach 0.80-0.85, slow enough that the extra friction drag and weight exceed any form drag improvements. The whole package is much more fuel-efficient that way. The Convair 990, which exemplified the Kucheman Carrot application, was faster than its competitors but too much more expensive to operate. The actual time gate-to-gate was only a matter of minutes, and that was even without its frequent go-arounds attributable to high approach speeds. Or so I’ve been told by an old airline captain who remembers them, anyway.

The flap track fairings, and the engine pylons if they’re there, do help resist transverse air flow on the lower surface of a swept wing at high angles of attack, maintaining controllability during a stall. But that’s not why they’re there, since an airliner is rarely stalled - they’re just to reduce drag over stuff that won’t fit inside the wing.