Can we increase the wing area vertically?

[caslav.ilic]

[In air] The whole point is to be able to change the AoA without using pitch control. That way the fuselage can remain relatively in the same position while the wing "thinks" it's at a higher AoA.

The critical angle of attack, after which the wing will stall, for a conventional clean wing is about 15 degrees. At landing approach this is not too much with regards to forward visibility for subsonic-nosed airplane. Also, in this case it is not directly the fuselage AoA which matters, but pitch angle to the runway, which is further 3-5 degrees less than AoA due to descent path angle. Given that stall angle shouldn't actually be approached too near, the total fuselage pitch angle would come at less than 10 degrees -- which is inside normal tail strike clearances, at least by the books :) (except for a stubby-legged, high-wing, tail-pipe aircraft like Crusader).

If it's on the ground, then flaps and slats aren't really going to do much of anything, will they? What's your point?

I meant during takeoff.

A moveable wing like that is simpler than a flap system? I'd debate you on that point. It may or may not be. I would lean towards the latter.

I don't see why should it not be less complicated? All the load carrying elements are there anyway, it only needs pivot instead of rigid connection at rear spar and hydraulic instead of rigid connection at the front spar (or vice-versa for low-wing aircraft). That compared to flaps and slats which need a lot more hydraulic and telescoping elements and control links spread along the wing leading and trailing edges, all dead weight, and also complicating the wing structure and aeroelastic effects. Or, compared to simply increasing the landing gear height to provide more tail strike clearance. At least the Crusader designers considered pivoting the whole wing a better bet than increasing the landing gear height by 70-90 cm, and Crusader does have extremely stubby legs (they didn't nickname it "Hog" for no reason :)

But this is all moot, for the simple fact that a cruise-efficient airplane cannot afford enough wing area for clean wing near critical AoA to produce enough lift at landing. The slats and flaps both work to raise the effective critical AoA, but the flaps reduce the zero-lift AoA, whereas slats don't affect it; in fact, the slats are there precisely to allow higher effective AoA to be used, they do nothing at otherwise admittable AoAs. In sum, with flaps and slats deployed, the geometric AoA may be even greater, and so the fuselage may be at even greater pitch-to-runway attitude compared to that with clean wing. For example, see the http://adg.stanford.edu/aa241/highlift/highliftintro.html (the bottom-most diagram on the page), where it is shown that the geometric critical AoA is increased by 5 degrees with flaps and slats deployed, rather than decreased. This means that if a clean wing could provide enough lift for landing, flaps and slats would immediately be deleted altogether.

--
Chusslove Illich (Часлав Илић)

 

[russ_watters]

I don't exactly understand this "leading-edge flaps instead of slats" -- these are not synonymous in English?

Leading edge flaps are just hinged, well, flaps. There is no slot:

Leading edge flaps perform a similar function to slats (see above.) The difference is that leading edge flaps increase the camber of the wing, and do not create a slot.
As a result LE flaps increase lift at all angles of attack, and do not delay the stall as effectively as slats.

http://selair.selkirk.bc.ca/aerodynamics1/controls/Page5.html

I think the argument is getting buried in the minutae now, though, with what the bigger benefits are.

 

[FredGarvin]

I meant during takeoff.

Ahhhhh...Now I see.

I don't see why should it not be less complicated? All the load carrying elements are there anyway, it only needs pivot instead of rigid connection at rear spar and hydraulic instead of rigid connection at the front spar (or vice-versa for low-wing aircraft). That compared to flaps and slats which need a lot more hydraulic and telescoping elements and control links spread along the wing leading and trailing edges, all dead weight, and also complicating the wing structure and aeroelastic effects. Or, compared to simply increasing the landing gear height to provide more tail strike clearance. At least the Crusader designers considered pivoting the whole wing a better bet than increasing the landing gear height by 70-90 cm, and Crusader does have extremely stubby legs (they didn't nickname it "Hog" for no reason :)

I can see a lot of flight control complications by doing that. The Crusader had flaps anyways, because the wing incidence couldn't solve all of the problems with slow approach speeds but I think they also had other issues to deal with that are natural constraints due to carrier based aircraft. Also, the Crusader's wing was a 2 position setting, either up or down whereas flaps have multiple settings.

I think the argument is getting buried in the minutae now, though, with what the bigger benefits are.

Yeah. I think we've beaten this horse pretty well.

 

[gaming_addict]

Normally the leading edge slat is used to increase lift at low speed takeoff and landing only, but it looks like this Sukhoi Su-27 is flying with the slat extended all the time (while doing the airshow) to increase lift and manouverability at low speed. I think I have not seen that befor (??!)

http://www.flightlevel350.com/aviation_video.php?id=4663&vcm

Just to clear, Su-27 slat automatically deploy once a certain angle of attack(or stall angle) is reached.

When Su-27 which has high wingloading(relatively speaking) must have high angle of attack in low speed maneuvers in order to turn or stay aloft. The craft must be maneuvering well past the AoA needed to deploy the slats. Not only the su-27 is doing thing but also a host of modern jet fighters like F-16.

..Also to add, I've read this thread and some concepts are not absolute, some thick wings can be used for high speed travel, an example is the 'supercritical airfoils' which is in use with modern airliners. Will actually produce less drag at high subsonic that non critical airfoils that could be much thinner. It also produces superior lift at low speeds so most airliners use it, even the B-2 bomber