Can we increase the wing area vertically?

[Langbein]

The bird wing principle once more:

http://www.flightlevel350.com/aviation_video.php?id=8467

At this one one can se the front slats is actuated at the moment the weight off wheel switches is operated both at take off and landing.

http://www.flightlevel350.com/aviation_video.php?id=6349&vcm

And in the end possible the best exaple of a heavy lift low speed design using the slat and the flap (pluss nose up) to give increased lift at low speed.

http://www.flightlevel350.com/aviation_video.php?id=4419


In the end .. some low speed propeller aircrafts is made with "rubber boots" for deicing on the wing front. Those does not use leading edge slats, but the prinsipple of increasing the "thickness" of the airstream are still the same.

Which aircraft model is designed and flown from prinsiples unlike those described above ?

 

[russ_watters]

I don't know which of my "applications" you are thinking about.

Sorry - lost track of the thread and thought you were the OP... and I think we had somewhat of a miscommunication there because of it. The OP is misuing the word "thick" to indicate an increased chord length. It appears you were using the word "thick" in the more conventional sense, which then makes most of what you said correct.

 

[Langbein]

OK. No problem. The idea just struck me that the OP might have ment something that I did not understand at first reading :-)

By the way, I'm not sure that my english and my teminology is 100 % as I haven't looked into these textbooks for a while. (But used to work with that stuff for a couple of years.)

 

[Langbein]

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

 

[The_Thinker]

Wow! Guys thanks for all the info... I've really learned a lot from this... A lot of stuff that I had no idea about... Now I have a better understanding... Although a some of it is over the head...

Anyway...
Yeah, I am familiar with the F-16, and the hydraulic design on that, thanks for the all links Langbein...

But... yeah I get the general Idea... by increasing the chord length one can get more lift at low velocities, which is why planes land nose up, showing more of their wing to the wind, that is as you put it a thicker airstream (I hope I got this right...) but, the system would be very inefficient... Hope I got the point right...

 

[Langbein]

The increase of the cord length while the slat and the flap is extended is a part of the effect. The main effect will be as the slat in front goes down which will permit the the aircraft nose to go up so wing to meet more air in the vertical direction. The extended plaps will increase this effect, and the extended flaps will also make a drop in the pressure at the upper side of the wing, and a pressure buildup under the wing, and then all in all, a lor more lift and a even more increase in drag.

For setting the aircraft down while landing the increased drag is a good thing to reduce the forward speed. As much as possible lift at as small speed as possible while doing aerodynamically breaking, makes a smooth and nice landing. For landings you typically use a lot of slat and flaps, espesially at the last final. Landing without flaps will be an emegency sitation for most airplanes, as this situation will reqire a rather high landing speed, to keep the aircraft flying until landing.

For takeoff you use not that amount of slat/flap because the drag will be to great.

For the Sukhoi Su-27 the slats is something that you use also for doing airshows .. Didn't know that before I saw the film - quite interesting :-)

In the end I found two links that explain the slat/flap thing quite easy:

http://travel.howstuffworks.com/airplane13.htm

http://travel.howstuffworks.com/airplane14.htm

 

[FredGarvin]

Just be careful with "How Stuff Works." I treat them like Wkipedia in that they are a good first source, but try not to take them as gospel without corroborating sources. I once read an article they did on counter-rotating helicopters that was so badly wrong it was apparent that they never even looked at one let alone understood what was going on.

You guys are pretty close to what is going on, but I have to add one little thing...The effect of slats and flaps is to increase the AoA of the wing without altering the orientation of the fuselage. For example, in the slides that show the flaps in Langbein's first link, the flap in the down position took a wing chord with essentially no AoA and took it to approximately 20°, without changing the orientation of the major section of the airfoil. To really see the effect, draw a line from the center of the leading edge to the tip of the flap, that is your AoA.

 

[Langbein]

"The effect of slats and flaps is to increase the AoA of the wing without altering the orientation of the fuselage."

That's true. It can be used that way. Sorry for the inaccuracy.

 

[Langbein]

"I once read an article they did on counter-rotating helicopters that was so badly wrong .."

How does the Cariolis effect work on counter-rotating helicopters. Will the "90 degres delyed forces" be canceled out or what ? Will you have to have two set of swash plates where one is tilted to the left and one to the right when you want to get forward ? (It should work this way, shouldn't it ??)

 

[FredGarvin]

The Coriolis acceleration is not at issue. You are referring to precession and no, the counter rotation has no effects on the gyroscopic precession. It still is there. However, they do cancel out torque created by the other head, hence no need for a tail rotor.

If I understand your point about the swashplates correctly, yes, each rotor head has it's own swasshplate. However, due to mixing and flight control issues, it's not quite as cut and dry as you describe. There is some tilting of the rotor disk, but the swashplate effects the pitch of each blade in an articulating rotor head. Each blade pitch changes at a specific point in the rotation, depending on the cyclic input. If the collective is changed, the entire swashplate moves at the same inclination.

 

[russ_watters]

You guys are pretty close to what is going on, but I have to add one little thing...The effect of slats and flaps is to increase the AoA of the wing without altering the orientation of the fuselage.

Hmm, didn't think about that - how big of an issue is that? Older planes used to have leading-edge flaps instead of slats, so their geometric angle of attack didn't change much, if at all when they were deployed. Is the major benefit just that you don't need tall landing gear and a droopy nose like on the Concorde?

 

[caslav.ilic]

The effect of slats and flaps is to increase the AoA of the wing without altering the orientation of the fuselage.

Hm, I wouldn't really put it that way. If airplane is in the air, it can change AoA by pitch control. If it's on the ground, it could do the same by telescoping nose wheel strut. In fact, the Vought Crusader even had variable incidence wing, which could pivot by seven degrees on takeoff/landing. Any of this would be simpler and structurally lighter than the slats/flaps mechanism, hence no need for them only to increase AoA.

More precise would be to say that slats/flaps increase the critical value of the effective AoA (the one measured from the zero-lift AoA), i.e. the value where the lift stops increasing with increase in effective AoA.

--
Chusslove Illich (Часлав Илић)

 

[caslav.ilic]

Older planes used to have leading-edge flaps instead of slats, so their geometric angle of attack didn't change much, if at all when they were deployed. Is the major benefit just that you don't need tall landing gear and a droopy nose like on the Concorde?

I don't exactly understand this "leading-edge flaps instead of slats" -- these are not synonymous in English? The way I had it, slat is just a short name for leading-edge flap, and as trailing-edge flaps they come in several designs. But all the slat designs are having qualitatively the same effect on aerodynamics, so either way I think there shouldn't be any differencing between them for purposes of this discussion.

Flaps increase effective AoA and decrease the geometric (fuselage) AoA at critical effective AoA, which is a benefit at landing. Slats too increase the critical effective AoA, but also the geometric AoA (i.e. they don't change the zero-lift AoA), and therefore would by themselves require an increased fuselage incidence. Therefore at landing slats are used as an addition to flaps, when even more lift is needed than by flaps alone. (Slats can be used by themselves in maneuvering flight, as they don't increase the drag as much as flaps, have nose-up pitching moment thus reducing trim drag, and simple slotted slats can even be deployed automatically when needed by a mechanical spring system.)

Regarding Concorde, it couldn't make use of flaps because the delta wing with flaps would have too high nose-down pitching moment with nothing to counter it. Delta wings also don't use slats, as they kind of get them "naturally": at high AoA starts the shedding of leading-edge vortices, which act in a manner similar to slats, increasing critical effective AoA and not changing the the zero-lift AoA (in fact, these LE vortices are even better, as the lift curve goes upwards "superlinear" from that point on). So Concorde had to land at very high AoA to exploit the LE vortices for enough lift at low speed, hence the droop nose.

--
Chusslove Illich (Часлав Илић)

 

[FredGarvin]

Hm, I wouldn't really put it that way. If airplane is in the air, it can change AoA by pitch control.

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.

If it's on the ground, it could do the same by telescoping nose wheel strut.

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?

In fact, the Vought Crusader even had variable incidence wing, which could pivot by seven degrees on takeoff/landing. Any of this would be simpler and structurally lighter than the slats/flaps mechanism, hence no need for them only to increase AoA.

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.

More precise would be to say that slats/flaps increase the critical value of the effective AoA (the one measured from the zero-lift AoA), i.e. the value where the lift stops increasing with increase in effective AoA.

I would say that that is an aspect of it all, not the more precise statement.

 

[FredGarvin]

Hmm, didn't think about that - how big of an issue is that? Older planes used to have leading-edge flaps instead of slats, so their geometric angle of attack didn't change much, if at all when they were deployed. Is the major benefit just that you don't need tall landing gear and a droopy nose like on the Concorde?

I think those early systems were more of a way to help the flow remain attached on the wing at high AoA. I could be wrong there. There really isn't much of an "issue" per se as an added benefit of just getting that much more angle out of the same wing.

 

[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