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The early Boeing 737 models had wings with triple-slotted flaps that appeared to be derived from the 727. When the 737 was redesigned as the Next Generation series (dash 600 through 900), these flaps were dropped in favor of a double-slotted design.

Why did Boeing choose to make this change, and what were the trade offs? Did it impact performance? I had always been under the impression that early 737s were reasonably capable on shorter and rougher runways.

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One of the biggest differences that you will see between the flaps on the two is that the NG (photo on the right) has continuous span flaps while the classic has split inboard and outboard flaps.

737 Classic Flaps 737NG Flaps

Combined with the longer wing on the NG, this gives the new flaps more surface area, so they don't need to be quite as effective. Overall, the NG actually has better performance than the classic, mainly because of the redesigned wing which is 25% larger and has winglets; both of which help out.

Even though the performance is better with comparable triple-slotted flaps, the double-slotted flaps are lighter (which helps with overall aircraft performance) and have fewer moving parts. This makes them more reliable and they require less maintenance. Most new aircraft designs are moving to either double or even single slotted flaps because of this simpler design and the fact that today's runways don't require the extra performance that would be gained by the more complicated flaps.


Photo Credits:
737 Classic Flaps
737NG Flaps

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  • $\begingroup$ Don't double-slotted flaps have less drag for the same lift (though maximum lift possible is less)? $\endgroup$ – Qantas 94 Heavy Jan 20 '14 at 1:45
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    $\begingroup$ @Qantas94Heavy Yes, double-slotted flaps have less drag and less overall lift than triple-slotted flaps, both of which are positive design factors for the triple-slotted flaps. (When putting flaps down for landing, drag is a good thing in a jet!) $\endgroup$ – Lnafziger Jan 20 '14 at 1:55

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