Why Aren't RC Flying Wings Negative Camber?

[Talon Driver]

I fortunately have an undergraduate degree in aerospace vehicles (accredited). I am not bragging just providing to you my viewpoint.

I know that the B-2 (the real jet) has a negative cambered airfoil. The reason for this is because a neutral or positive cambered wing w/o horz stab or canard is not as aerodynamically efficient as one that is negatively cambered.

The mechanics of this are that a negative camber wing's pitching moment is countebalanced by the moment arm of the CG to the aerodynamic center (AC). Using a neutral camber or even worse a positive cambered airfoil for a flying wing requires the elevon to have deflection up to provide the necessary counteraction of the CG to AC moment arm and the upward pitching moment inherent of the airfoil.

Anyone know why none of the RC flying wings do not have a negative cambered airfoil (at least the projeti and the zagi that I have seen) for greater efficiency?

Cheers,

Chuck

[pjkunz]

Reflexed or negative camber airfoils primarily effect the zero-lift pitching moment (must be positive to be trimmable). Without sweep this can only by accomplished with reflex, but with the addition of sweep, a +Cmo can be acheived with twist.

The downside of reflex: poor Clmax, possibility of aft lower surface separation, typically some drag penalty. Also many flying wings exhibit low inboard Cl's, uniformily applied reflex exacerbates this and can hurt performance

Downside of twist: planform can become a strong point design, with poor performance (particularly induced drag) away from the design trim point (CL or speed)

Typically sweep and twist is combined with low(but still negative) or slightly positive( reflexed) pitching moment sections

The zagi is sorta in the middle, the combination of sweep and the reverse tapered elevons unload the tips more than the root for a given flap deflection. A negative (up) flap defelction effectively reflexes the airfoil progressively from root to tip, allowing the root to work harder and the tips to unload.

-Pete Kunz

[Sparky Paul]

A modestly cambered with reflex airfoil is just more efficient than a purely negatively cambered airfoil. Lower drag at useable Cls..
MOF, a normal airfoil, such as a 2415, is stable inverted with no tail, for the reasons stated... the nose down pitching moment (which tries to raise the front when inverted) can be counterbalanced by a forward c.g.
I have seen at least two planes lose their horizontals in flight, and being high enough were able to complete the tuck under and maintain level but inverted flight.. the loss of weight of the horizontal moving the c.g. forward enough in those events. (Don't count on it though.)
A reflexed airfoil gives the designer a bit more latitude in positioning the c.g. as well.

[Dereck]

My aerodynamics training involves being able to spell the word and remaining awake while reading some of Lennon's book!

But I did build a half dozen tailless models using NACA 0012 and 0014, with wide-ish elevons 'reflexed' up a tad and a CG that I read someplace should be at 16%. Whether they should or not have, all but one flew pretty well.

Of course, my development budget was a little lower than the B2, so I was forced to use a little less computer enhancement of flight characteristics ;) Still, I didn't need stealth either - it's embarrassing when you have to admit you can't find your model in the pits ;)

"Efficiency" needs defining. My last but one, with a low wing, had much of the aerobatic abilities of a sports pattern model, with passable knife edge capabilities and was easily managed in snap / spin areas, if a little fast thereabouts. I figured that made it 'efficient'. If you mean the ability to stay up ages - an OS 25 and a 6oz tank took care of that pretty well too.

It also has been flown since as an electric - time to lose that pesky tailplane thing again :) . On CG placement, one of my designs was published as a freeby in a UK mag - and they left the CG off the plan. One guy actually built one, balanced it at the trad 1/3rd chord, got it up, around the sky some and back down again to a runway landing under some kind of control. It was hairy, but the model survived. Turned out we were in neighbouring clubs and he was quiet happy with his model after he talked to me and took the ballast off the tail.

[fregon45]

Mechanical engineer here, and I've done some reading on the caveats of flying wings. First, it doesn't seem quite right to me that a negatively reflexed wing would be more "efficient". It's more like a requirement for some degree of stability. With a positive cambered wing, the CG must be placed in front of the center of lift for stability. On an R/C plane this is no problem. You simply cram all of your radio equipment near the nose of the plane. The B2 has a different mission than to just fly around and do loops, though. It has to carry a big payload, which can't all be crammed in the nose. Just to make things clear, if you look at the geometry of a modestly swept, tapered flying wing, like the B2, the Center of lift is very far forward. To get the CG in front of that you have to cram all of the weight near the nose, which isn't really practical with a big payload. If you make the reflex negative, though, the lifting moment is in the oposite direction, and you can now place the CG behind the center of lift. I can't see how this would be more efficient, but more likely a necessary compromise in the design. That's how I see it.

Nathan

[frankenfoamy]

The PROJETI has such an animal
It uses little to no reflex

[Talon Driver]

CL, CG and +Cmo I understand. However, what is relfex? I think this is something that is unique to RC flying. Anyone? What is the difference between this and Crow and Differential?

Cheers,

Chuck

[Gerald]

Reflex is the up-turning of the trailing edge (or elevons) from the downward slope at aft portion of the airfoil. In some ways it has the same effect as negative camber. It is not limited to R/C flight, gliders often use it as a trim setting to neutralize lift in order to reduce drag and increase speed. Slow speed flying wings such as hang gliders and some ultralights rely on it for positive stability. One advantage of positive camber with reflex over negative camber is improved low speed stall performance.

[Sparky Paul]

"reflex" is where the trailing edge is raised.
Either by rigging the surface so the trailing edge is up, or building the upward curve into the airfoil profile.
Either works, but the purpose-designed shapes are a tad more efficient..
The reflex creates a nose-up pitching moment about the 1/4 chord point. This is counteracted by locating the c.g. ahead of the 25% chord line. As with a tailed airplane, the sensitivity of the wing will vary with the c.g. relative to the 1/4 chord point.
Here's some reflexed airfoils...

[Talon Driver]

Originally posted by Gerald
One advantage of positive camber with reflex over negative camber is improved low speed stall performance.

Please elaborate.

Cheers,

Chuck

[Talon Driver]

Paul,

Thanks for the graphics...sharp! :) I wanted to respond to another part of your entry.

Originally posted by Sparky Paul
[BThe reflex creates a nose-up pitching moment about the 1/4 chord point. [/B]

This is true. However, all positive cambered airfoils have an upward pitching moment at 1/4 chord provided they are subsonic. Which moves aft starting in the transonic region to about 1/2 chord supersonic (not a factor for E-flight).

Cheers,

Chuck

[Sparky Paul]

" all positive cambered airfoils have an upward pitching moment at 1/4 chord provided they
are subsonic."
.
No.
The usual cambered airfoil's pitching moment is nose down. The horizontal tail provides a down-force to counter act this, which is why c.g.s can go aft of the 1/4 chord point.
When the usual cambered airfoil (less horizontal) is inverted as in your 1st message, the nose down Cm is now trying to force the nose up. If the c.g. is forward of the 1/4 chord point pulling the nose down, the plane can be stable.
.
Here's a site which shows a normal plane that had the entire horizontal sawed off at the root.. reflex added to the ailerons which were mixed as elevons...removal of the servo and surfaces moved the c.g. forward enough..
http://home.earthlink.net/~pjburke1/Tailless.htm
.
and there's the profile Somethin' Extra I crashed the tail off, repaired and flew as tailless, with only a slight amount of reflex and rebalancing needed on that page.

[Tom Hunt]

Originally posted by Sparky Paul
I have seen at least two planes lose their horizontals in flight, and being high enough were able to complete the tuck under and maintain level but inverted flight..

Yup.... lost my Horiz in a midair on my Terry with another Terry during a streamer combat session (we usually get 5-6 in the air at once). She pitch inverted, stayed there and I flew it down to a safe landing using rudder and throttle! What a hoot! wish the video had been running then! I found the tail in the grass (two pieces) and she lives to fly again!

Tom

BTW the other guy survived too!

[Dereck]

SNIP
and there's the profile Somethin' Extra I crashed the tail off, repaired and flew as tailless, with only a slight amount of reflex and rebalancing needed on that page.
SNIPEND

Hi Paul
My first tailless used the wing out of a low AR conventional I designed. It was mostly lost when someone who couldn't fly real good sawed her tail off in a pylon race, the subsequent "firm landing" taking the nose off. I removed the rest of the fuselage - not that much was left - from a wing that had somehow survived. Doubled the aileron area, called them elevons, added an aesthetically matching fuselage with a short rear and big fin/rudder.

Attempt 1 suggested I needed to know more about UC positioning on tailless. Attempt 2 proved it flew.

The only wing I've had published in two different models! It started in L'il Special", Radio Modeller in England, c 1990 and went on to feature in "Bubbles", RCM around 1993

With a root chord of around 11", the elevons were about 1/75" wide. "Reflex" amounted to a tad under 3/32" up from neutral with a NACA 0012 section (originally!) and 16% MAC CG.

Anyone still think designing model aircraft is hard ?

[Bare]

Well the question remains mostly unanswered.
The Zagi airfoil is frankly barely an airfoil by any normal standard.. in fact building a Zagi with a 'proper' , say a MH foil, results in a markedly superior abilities.
Simple fact is Toy Airplanes often have the crudest of Airfoils.. or facsimilies of..even flat plates work fine.
Am surprised by the lack of knowledge re Reflex.. it's prominent the few textbooks I' ve browsed.

[Chris Todd]

I think to summarize the answer so far, is that models tend to use reflex, especially with their elevons, to create the upward sweep needed at the trailing edge. One of the free model plans I downloaded recently was a flying wing with a decidely "upside-down" airfoil. It was a true negative camber rather than a reflex addition. So, they appear both ways. I also saw a recent report on one of the foamie wings that mentioned you had to dial-in some up elevon to make it fly. To me that says it has the wrong airfoil. It should have had some reflex without having to lose some control throw just to make it fly.
I suspect it is a case of models getting away with instabilities and strange control arrangements that no test pilot would ever climb inside if it were real. That is a big part of the fun with models, though, we can stand back and watch, and say "Wow! That was interesting!"

[Flypaper]

When you boil it down, reflex is just decalage in a conventional plane. If you could see the airfoil on the Canadian Avro Arrow, it is flat topped, curved on the bottom, with a leading edge droop.

[JRuggiero]

A picture article about the Northrup N9M in the June 2002 Air Classics magazine has a pic that shows the N9M tailless had an airfoil similar to the laminar section of a P-51 Mustang, with no reflex. Instead, according to a Web search, the wing has a 4 degree twist toward the tips.

[Talon Driver]

Originally posted by Flypaper
When you boil it down, reflex is just decalage in a conventional plane. If you could see the airfoil on the Canadian Avro Arrow, it is flat topped, curved on the bottom, with a leading edge droop.

G Cliford,

I am interested in what you mean by decalage. Fortunately, my wife speaks French and recognized the word. American Heritage doesn't show it. Despite this I'm not understanding your usage above. :confused:

I have seen pictures of the Canadian Avro Arrow...sexy jet. Too bad it was before its time (engine technology wasn't there to match the airframe). :cool:

Cheers,

Chuck

[Sparky Paul]

"decelage" is a term that describes the difference in settings between the wing and the horizontal's chord lines relative to the FRL.
Longitudinal dihedral is another way of saying it.
As that delightful blond in the DiGiornio commercial says..."It's French!"

[rpage53]

Seems that the obvious answer has been only mentioned in passing. If a negative camber was more efficient (seems unlikely since you'd be sacrificing lift to avoid a positive pitching moment -- but for the sake of argument we'll say it is) it would possibly be incapable of inverted flight. That wasn't a design criterion for the B-2 but is for our flying wings.
A symmetrical wing with elevons will perform better in all flight modes since the elevons are essentially camber-changing devices. A positively cambered wing with reflex (from elevons or airfoil design matters little) will perform better at low speed upright flight for landing but sacrifice little in high speed and inverted flight with camber changing.

I thought the negatively cambered airfoil was for near-supersonic conditions. I don't believe they are more efficient at low speeds (but then I'm a biologist).

Rick.

[Talon Driver]

All,

I was able to find some time to put my hands on my copy of "Fundamentals of Aircraft Design" by Leland M. Nicolai. I have provided an excerpt from the text for clarification on the original question. "Why Aren't RC Flying Wings Negative Camber?"
-- I put parenthesis () around my remarks w/in the entry from the above text book.
-- I put ellipsis ... to indicate omitted text.
-- I put the word "sub" in the text to denote subscript for the engineering symbols.
-- Remember "airfoils" are two-dimensional and "wings" are three-dimensional versions of airfoils. The only significance of this statement is values for an airfoil (2-D) are slightly higher than a wing (3-D).
-- The moment about a wing is only one part of the moment of the aircraft system (engine, wing and tail moments). However, for a flying wing there is only two moments about the longitundinal axis they are 1) that from the wing's camber C sub M sub 0 and 2) the moment of the CG in relation to the A.C.
-- "M" versus "m" in the below entry belwo distinguishes wing moments (M) from airfoil moments (m). Same goes for "L" and "l".

From page 7-11

7.5 Effect of Airfoil; Camber:

All airfoil sections have about the same lift curve slope of 2 pi per radian (this is the slope of the line of C sub L w/ respect to angle of attack, this is the slope not the maximum value of C sub L). The amount of camber determines the value of the angle for zero lift, alpha sub 0L = 0. Airfoils with positive camber have negative values (nose up pitching moment is positive) of C sub m sub a.c. (Moment coefficient about the aerodynamic center), whereas a symmetric section has C sub m sub a.c. = 0. If the wing must have positive C sub m sub a.c., such as a tailless design for static longitundinal stability, then the camber must be negative. The B-58 has a swooped up trailing edge, called inverse camber or reflexed trailing edge, to give it negative camber and a positive C sub m sub a.c. ...

The designer should (Back to my original question) should determine the lift coefficient that the aircraft requires during a critical mission phase, such as cruise. Then the camber is selected to give a C sub L sub min, called the design C sub L, close to the required C sub L. ...

The designer must be careful in his selection of positive camber as it is accompanied by a negative C sub M sub a.c. and must be trimmed by a down aft tail load for statically stable aircraft.

So, what is the design points for an RC flying wing?

Originally posted by rpage53
A symmetrical wing with elevons will perform better in all flight modes since the elevons are essentially camber-changing devices. A positively cambered wing with reflex (from elevons or airfoil design matters little) will perform better at low speed upright flight for landing but sacrifice little in high speed and inverted flight with camber changing.

Rick.

Rick, I think you pretty much said it all. To paraphrase, it depends on your design point.

For the RCer. If you want your flying wing to fly inverted equally to upright pick a symmetrical airfoil (no mention here for thickness ratio) and you will automaticaly crank in reflex to keep the nose up by obtaining the required positive C sub M sub a.c. because you are making the wing have negative camber. A positive pitching moment is required to counter the foward CG of a statically stable flying wing.

If you want to design a flying wing aircraft that people sit in (they do not like long term inverted flight because it makes your head hurt) and want that plane to cruise straight and level for a long time then select a negative cambered wing.

Before I close I ealier mentioned that a positive cambered wing has a positive pitching moment. Sparky Paul corrected me. He was right. I realize where I got this false data. If you take a straight wing that is relatively homogeneous in its weight distribution (no servos etc) and toss it into the air it will pitch up. If you do not want to do this to a good wing take a light weight yard stick and toss it into the air and you will notice that it rotates about its span axis as it falls to the ground. This pitching up action is due to a nose up pitching moment (but not the moment about the wing's (in this case a flat plate) A.C.). This pitching moment is generated by the A.C. being at quarter chord which is in front of the CG which is at half chord (hopefully your yard stick is homogeneous wood). Remember A.C. in front of the CG is an unstable condition. As the yard stick's leading edge pitches nose up it continous to rotate until its former trailing edge becomes the leading edge upon which it pitches up, etc. This is why the yard stick will constantly rotate leading edge up until it hits the ground.

So, in closing "Why Aren't RC Flying Wings Negative Camber?"

The answer is:

A) if you want to fly inverted equally to upright pick a symmetrical airfoil, but you'll pay the price in landing a little faster than a reflexed positive camber (maybe one-three knots).

B) if you want your wing to land very slow pick a positive cambered airfoil to get the higher C sub L, but you'll pay the price in top end speed and (two to three knots) and lesser ability to fly inverted.

C) if you want your wing to fly for duration pick a negative cambered airfoil to get the positive C sub M sub a.c., however you won't turn up you tailpipe as well nor land a slow (unless you want to loop inverted and land inverted).

RCers are looking for choice A first then B, but never C.

Cheers,

Chuck

[desertwind]

I asked the chap who flies the Planes of Fame N9M one time about the stability design of that plane. He said it does have reflex, at least some, toward the center (you can see it as well). It also has a somewhat negative camber in the central area, and it has that 4 degree washout. The sweep also has quite an effect, I hear. I guess the idea was to give some of each of the various ways to make it stable. Maybe only one stability design trait is too restrictive or makes for too many side effects on its own.

[Fred Bronk]

OK, and what does this have to do with power systems?? :rolleyes:

FB

[Buzz_Man]

I'm interested in aerodynamics and how things really work. I have the bare basics understood but there's so much more to learn & it's all facinating.

Lately, I've also been wondering about forward swept wings - there seem to be some really great advantages in using this design with several well proven models (Bird of Prey & XBow, for example). I'm wondering why fsw's aren't more popular - is it mainly because folks choose not to think outside the box, balance problems, too unconventional looking, or what?

(hope this isn't getting too sidetracked, or off topic)

[Daniel G]

Wow.
Fred must really take moderating seriously to find a 3 year old thread, just to move it. ;) :D

[Buzz_Man]

Fred must really take moderating seriously to find a 3 year old thread, just to move it.Are you KIDDING?! I was told most moderators at this place get over 60K just for moderating these forums. Fred, we all know you're just doing your job, but I feel it's also important to recognize the fact that you do a great job - well worth every penny they pay you. Keep up the fantastic efforts and THANK YOU for making it possible for the many of us who enjoy hangin out here. It's a great place in large part because of the wonderful (& very necessary) moderators.

Now, let's go flyin'.
:)

[Don Sims]

60K??!! :eek: All I get is a hard time!! FRED!!!! I want my cut of the big bucks please!!

[digsy]

I'm interested in aerodynamics and how things really work. I have the bare basics understood but there's so much more to learn & it's all facinating.

Lately, I've also been wondering about forward swept wings - there seem to be some really great advantages in using this design with several well proven models (Bird of Prey & XBow, for example). I'm wondering why fsw's aren't more popular - is it mainly because folks choose not to think outside the box, balance problems, too unconventional looking, or what?

(hope this isn't getting too sidetracked, or off topic)

I may be wrong but as I understand it, forward sweep encourages a negative dihedral effect. It also encourages a strong roll movement (which requires larger rudder surfaces).

And thinking about it - 2 wing tips hitting the ground (instead of a nose in a swept back wing) sounds like a recipe for splitting the airplane in 2.


Digsy

[raptor22]

The nastiest thing about forward swept stuff is that it has AWFUL aeroelasticity. in other words, if you have jsut a little flex at higher speeds you will rip the wing off.

I spoke to a guy who came into the hobby store I work for who was trying to make a very fast turbine model with forward sweep. he went through several very expensive crashes before he found a layup of 4-layer carbon that would not destroy his plane when he touched the stick. This layup, as you may expect, was a very expensive and complex combo of different carbon types.

So, short story, when a FSW plane goes fast, it flies like crap. That when it does fly.

BTW: when I say fast, i mean 100+. Not some 400-powered BOP or whatever.

--Alex

[sloper steve]

Why Aren't RC Flying Wings Negative Camber?
-not enough people cutting them and not a big enough market to motivate people to make the 5-6 attempts to get it right-
Or maybe nobody has wanted to just go slow and rightside up.

I came close with my CNC by making an undercamber root and symmetrical tip with lots of twist.
It needed more twist to compensate for the strong moment at the root.

It can be done and the result is a slostik style flying wing.

[PaulVi]

So, short story, when a FSW plane goes fast, it flies like crap. That when it does fly.

BTW: when I say fast, i mean 100+. Not some 400-powered BOP or whatever.

--Alex

You have seen Ritewing / Aeroworx Skyvak right... I have the video looks very stable in slow and fast flying style... I will be posting the video soon so we can see the effects of speed on a FSW

[andrewwells13]

Sylvan Aircraft has an undercambered wing in the experimental phase. Is this the same as negative camber??

http://www.rcgroups.com/forums/showthread.php?t=603675

[myxlplyx]

SpeedWing.Net (http://www.speedwing.net/) has had one for over a year:

Mini SpeedWing EX (http://www.speedwing.net/mini-speedwing-ex-p-296.html)

[-=SLaPPiE=-]

Jerry Smiths Outlaw is a fast Delta (glow conversion :rolleyes: ) w/ a neg. cambered wing.
The Telink Mini Tornado and Toro 300 are negative camber.

I learned from the Tornado, and build about all my wings with negative camber.

This method only works if there is some taper to the wing from root to tip on the top and bottom.
Just find a table with a nice flat edge, and sand the root with your sanding bar on the edge of the table with the wing right side up. This will remove foam from the lower part of the root first and will create the negative camber.

You will find that this creates a very flat top on your wings, and will create some new challenge when selecting spanwise spar locations (top or bottom).
I just use the Dave Brown CF Ribbon for spanwise spars.

I sure don't notice any ill effects at speeds around 80 to 100 mph, but I do notice an improved low speed flight range. I like to throttle back into the wind and fly without any forward motion or fly backwards. I want my junk to have the widest speed range and I feel like the negative camber is a good thing for slow to mid speed wings. I don't really have the equipment to push my junk into the 150+mph range, so I can't say how it will affect the real high speed wings.

BTW, I'm doing this with the MH-45 airfoil.

Rich

[raptor22]

You have seen Ritewing / Aeroworx Skyvak right... I have the video looks very stable in slow and fast flying style... I will be posting the video soon so we can see the effects of speed on a FSW

Yes, I Chris sent me pics right after he cut out the first prototype. Very interesting looking machine.

My post was in reference to the fact that FSW planes have divergent aeroelastic properties without some VERY creative structural design. Which means that it only takes a tiny amount of flex to make a big difference in how the airplane flies. The result is that *most* foam FSW planes don't fly well at high speed.

However, I have every confidence that chris can create a stiff enough structure. It was just a general structural statement, not an aerodynamic one.

As an interesting anecdote, when I was working at my LHS I had a regular customer for awhile who was working on an extremely fast turbine powered FSW canard type plane. By extremely fast, I mean over 250 mph. He destroyed three VERY beefed up full carbon airframes before he got the layup down to make the wing positively divergent. The general flight pattern he was seeing was an airplane that performed excellently at low to medium speeds...but as soon as he would go into a high speed turn the wingtips would flex up and the airplane would violently pitch upwards....at which point it would crash.

[raptor22]

Most of you guys are misunderstanding the OP's idea. He wasn't talking about an UNDERCAMBERED wing, where the bottom of the wing is concave. He was talking about negative camber, where a standard non-flying-wing airfoil is essential turned upside down to get a positive pitching moment.

This has not been found to be as effecient as a proper flying wing airfoil with positive camber.

[-=SLaPPiE=-]

Most of you guys are misunderstanding the OP's idea.

wHOA! I just read back. My bad. I know nothing about upside down airfoils.

[Twizter68]

I'm interested in aerodynamics and how things really work. I have the bare basics understood but there's so much more to learn & it's all facinating.

Lately, I've also been wondering about forward swept wings - there seem to be some really great advantages in using this design with several well proven models (Bird of Prey & XBow, for example). I'm wondering why fsw's aren't more popular - is it mainly because folks choose not to think outside the box, balance problems, too unconventional looking, or what?

(hope this isn't getting too sidetracked, or off topic)

I can't answer as for models, but for full size A/C, the reason the FSW concept was abandoned was two-fold.
1) The materials available at the time the X-29 was built were not up to the stress loads the A/C was generating.
2) Pilots could not handle the amount of G's the plane can pull....

The FSW concept is fantastic, in an aerodynamic sense, for maneuverability; it reduces/eliminates tip stalling, by forcing the stall towards the root. The A/C itself was capable of incredible maneuvers, too bad the Pilots could not withstand the G's it would pull...look for FSW versions of the UCAV in the future!

[Brandano]

I doubt that excessive G forces could be a problem. the SU26-29 family of acro planes are stressed to +12 and -12 G's with a contingency factor of 2, meaning that the airframe will actually break at + and - 24 G's. The pilot doesn't wear a G suit, and will likely be dead soon if he keeps 10 positive G's for more than a few seconds. And a FBW system will limit the amount of G's in any case. AFAIK the X29 can only pull about +9 G's, don't know about the negative, and that is plenty good enough for a fighter. The real advantage isn't in the amount of G's the plane can pull, but in the better airflow over the control surfaces. The real issue with forward swept designs is that wing deformations are diverging, tending to bend the wing more and more as the wing bends. Modern composites allow engineers to design a wig that will "twist" properly as the AOA increases, but that wasn't available in the past. The main reason why FSW isn't used nowadays is that it just isn't worth it, a conventional wing will do the same job just fine, and be less expensive