Effect of Flaps on B737

[tae9141]

I read a phrase from B737 FCTM and it says as below:-
"The leading edge devices ensure that the inboard wing stalls before the outboard wing."
Is this because of how inboard lead egde flap is situated or is it different theory that supports aforementioned idea?

[Tomaski]

I read a phrase from B737 FCTM and it says as below:-
"The leading edge devices ensure that the inboard wing stalls before the outboard wing."
Is this because of how inboard lead egde flap is situated or is it different theory that supports aforementioned idea?

While we tend to think of a wing stalling at a single AOA value, usually the stall begins in one area and spreads to other regions as the AOA is increased. It is desirable to have the stall begin in areas away from the roll control devices (usually the wing root) so lateral control can be maintained approaching and even into the the stall. That said, the stall characteristics of a clean wing can be significantly different than when in the landing configuration, particularly with swept-wing aircraft which have a tendency to stall at the wing tips. Leading (and trailing) edge devices changes the effective camber and chord line of the wing, and the amount of this change can vary along the cross section from wing root to tip. Effective design of these devices, sometimes with the addition of vortex generators, will ensure that roll authority is retained in the landing configuration in inadvertent high-AOA situations (e.g. windshear).

[ImbracableCrunk]

Couldn’t this simply be in reference to the inboard stall strips?

[hans brinker]

While we tend to think of a wing stalling at a single AOA value, usually the stall begins in one area and spreads to other regions as the AOA is increased. It is desirable to have the stall begin in areas away from the roll control devices (usually the wing root) so lateral control can be maintained approaching and even into the the stall. That said, the stall characteristics of a clean wing can be significantly different than when in the landing configuration, particularly with swept-wing aircraft. Leading (and trailing) edge devices changes the effective camber and chord line of the wing, and the amount of this change can vary along the cross section from wing root to tip. Effective design of these devices, sometimes with the addition of vortex generators, will ensure that roll authority is retained in the landing configuration in inadvertent high-AOA situations (e.g. windshear).

Yes, because of how inboard lead edge flap is situated ( as compared to the outboard flap) .

Tomaski is totally correct IMO, just trying to keep it simple.

[Tomaski]

For further reading: Airflow Control (https://www.aopa.org/news-and-media/all-news/1995/october/01/airflow-control)

Excerpt:

Leading-edge devices did not come into vogue, however, until the advent of swept-wing, turbojet airplanes. Such wings have a particularly nasty trait: the wingtip stall. Instead of the stall's occurring near the wing root and propagating outboard (as with straight wings), the stall of a swept wing begins near the wingtip. This can result in strong nose-up pitching moments, sharp and uncommanded roll rates, and reduced aileron authority. Aircraft designers obviously go to great length to preclude the possibility of such a stall.

One solution is to install slats or — as in the case of the Boeing 727 — a combination of slats and leading-edge flaps. It is natural to wonder why Boeing uses inboard flaps and outboard slats on the "three-holer." The answer is both simple and clever. Because the leading-edge flap is less effective in delaying a stall than a slat, the inboard section of the wing is forced to stall first, thus preventing the possibility of a tip stall.

[tae9141]

Thanks everyone for your participation!