by "Jcarr" (jcarr)
Published 09/26/2017 at 20:57
by "Jcarr" (jcarr)
Published 09/26/2017 at 20:57
Tags: Planelopnik
STARS: 2
Can one of you aeronautical engineers (or other smart Oppos) explain the physics at play with this thing?
"ttyymmnn" (ttyymmnn)
09/26/2017 at 21:01, STARS: 2
Without doing any research whatsoever, I’d say it’s some sort of fancy wing fence .
"Jcarr" (jcarr)
09/26/2017 at 21:04, STARS: 0
The press write up says something about the outer sections being laminar flow and the inside sections being tradional internal structure or something like that.
"Saracen" (manualdoucheelitist)
09/26/2017 at 21:08, STARS: 2
From the article:
“The Airbus A340 Flight Lab’s first takeoff equipped with outer wing sections designed for highly smooth airflow over their surfaces. Known as natural laminar flow, such smoothed passage of air creates less drag than the airflow on traditional wings, potentially reducing fuel burn.”
So the wings are designed to minimize turbulence of the air it’s cutting through.
"someassemblyrequired" (someassemblyrequired)
09/26/2017 at 21:12, STARS: 1
I’ve heard it’s applying glider wing technology to an aircraft wing. Flow can be laminar or turbulent - laminar moves in a very regular, predictable pattern that results in less drag (hence its use in gliders). If the flow becomes turbulent (as it would on most powered aircraft wings), the drag increases. Laminar wings have a much smaller cross section than your typical wing, which you can see in the picture.
"Jcarr" (jcarr)
09/26/2017 at 21:13, STARS: 0
Yeah, I guess I was trying to figure out how they create such smooth flow.
"ttyymmnn" (ttyymmnn)
09/26/2017 at 21:22, STARS: 1
Laminar flow dates back to the P-51. It would seem that they’ve made a wing that has two different types of air flow. I know that winglets (or wingtip wing fences on the early A320) exist to increase fuel efficiency. It would seem that Airbus is doing something with the whole outer portion of the wing. I’m no engineer, but I’ll take a look at the link.
"wafflesnfalafel" (wafflesnfalafel1)
09/26/2017 at 21:28, STARS: 1
a lighter, more efficient way to reduce flutter?
"ttyymmnn" (ttyymmnn)
09/26/2017 at 21:28, STARS: 1
I would start here. It’s a long read, but looks pretty interesting.
http://www.aviation-history.com/theory/lam-flow.htm
"ttyymmnn" (ttyymmnn)
09/26/2017 at 21:31, STARS: 2
Here we go. Laminar flow is, according to this NASA article, the “holy grail” of aeronautics because it’s super efficient. So it looks like Airbus is trying to make at least a portion of the wing work with true LF. The inner portion is a plain old wing. I think.
https://www.nasa.gov/connect/chat/laminar_flow_chat.html
"gmporschenut also a fan of hondas" (gmporschenut)
09/26/2017 at 21:35, STARS: 2
smoother airflow at high speeds..
With aircraft wing design everything is balance between lift, drag. They would have slightly lower lift at takoff speeds, but less drag allowing higher speeds or greater cruising range at altitude.
http://www.aviation-history.com/theory/lam-flow.htm
"Levitas" (levitas)
09/26/2017 at 21:42, STARS: 5
Aero engineer here (currently automotive so this might not be 100%):
It appears the outer wing section has a different cross section (or, more accurately, the airfoil). Changing the 2D geometry of the airfoil greatly influences performance characteristics; one of the geometry changes that can be made is where the thickest part of the airfoil occurs. On ‘basic’ airfoils the thickest park occurs at 25% the length of the airfoil, or quarter chord. I’ve heard some laminar airfoils shift this more rearward, maybe towards 50%.
The other important thing here is the surface. At transonic speeds, it takes very small bumps in the surface to disrupt laminar flow. By having a much smoother wing they reduce friction drag, as well as reduce interruptions in the flow.
So between the airfoil shape and the smooth surface, they should see a much more efficient (amount of lift per amount of drag) airfoil at transonic speeds. Keep in mind, this section is probably going to be mostly useless for lifting the plane at slower speeds.
Tl;dr - cross section shape is different combined with what appears to be a different surface should cause the “laminar flow” at transonic speeds.
"PatBateman" (PatBateman)
09/26/2017 at 21:47, STARS: 2
"ttyymmnn" (ttyymmnn)
09/26/2017 at 21:48, STARS: 3
Yes. I’m not an engineer, more of an aviation historian. The laminar flow wing dates back to the P-51 Mustang, but in practice, the manufacturing tolerances weren’t up to snuff, and the wing wasn’t as efficient as it could be, though it was definitely a step forward. You also can’t really have a LF wing on an airliner because of all the rivets and engines and what not. So it seems that AB has split the difference, so to speak, and created a super efficient LF outer wing, with a traditional wing in the middle. And heaven knows that manufacturing tolerances and materials have come a long way since 1940. So just having 1/3 of a truly LF wing could make a huge difference in fuel burn. AB sells it as less CO2, but I’m betting that fuel costs are what is really pushing this.
"ttyymmnn" (ttyymmnn)
09/26/2017 at 21:49, STARS: 0
Ha ha, you and I cited the same article. Check out this one .
"Jcarr" (jcarr)
09/26/2017 at 21:54, STARS: 0
Thanks, that makes sense.
"Jcarr" (jcarr)
09/26/2017 at 21:55, STARS: 1
I heard it has something to do with magnets and clowns.
"WilliamsSW" (williamssw)
09/26/2017 at 22:02, STARS: 1
The thing is, I would think that this would increase takeoff and landing distances (and speeds) absent any other changes. Laminar flow reduces drag — and lift, too, I believe. I’m curious if there is an offset somewhere to avoid that.
"FTTOHG Has Moved to https://opposite-lock.com" (alphaass)
09/26/2017 at 22:14, STARS: 5
Oh hai, BS in Aerospace Engineering here, though I basically just play with guns and bombs for a living now. I’m 99% sure I get what they are doing here. It is a little hard to explain briefly, but I’ll try.
Basically when anything moves through the air, there is a physical constraint that the air right at the surface of the object moves at the same speed as the object. Far away, the air isn’t moving at all (in a perfect world with no wind anyway). Between these extremes there is a transitional region called the boundary layer.
The thickness of this boundary layer grows from the leading edge of the wing to the trailing edge. The air flow within the boundary layer can be smooth (laminar) or turbulent. Near the leading edge, the flow is always laminar. As the boundary layer grows, however, at some point it typically transitions to turbulent flow. Turbulent boundary layers grow more quickly than laminar ones and therefore cause more pressure drag.
Traditionally, this transition point moves around depending on a several factors, but two are at play here: the shape of the airfoil and the smoothness of the wing surface. In smaller aircraft, or aircraft that can get away with short chord lengths (like glider with a long span) or thin air airfoils (P-51 Mustang), it isn’t that hard to keep the flow laminar. But a big fat airfoil covered with rivets and openings makes it harder. So what Airbus have done is a combination of advanced computer aided design to optimize the airfoil and then given it a smooth, slick surface finish that helps get the rest of the way there.
FWIW, Hondajet does the same thing. Airbus just scaled the concept up from a VLJ to an airliner. It appears they are just using it for the outboard sections of the wing, but even that could cut overall drag and therefore improve efficiency significantly.
And now I realize that still wasn’t short. Hopefully its helpful though. I guess the TL;DR would be wings have boundary layers that grow as you go from leading edge to trailing edge, typically turning from laminar to turbulent mid-span somewhere. The turbulent boundary layer makes more drag, so they came up with this to push that transition further towards the trailing edge or maybe get rid of it altogether.
"gmporschenut also a fan of hondas" (gmporschenut)
09/26/2017 at 22:16, STARS: 1
bottom is more curved, top less so. The wing is more knife-like. Also you need a really smooth surface, Super flush rivits, or composite of some sort.
"Levitas" (levitas)
09/26/2017 at 23:16, STARS: 0
100% agree this is a fuel costs thing. I’m also interested in the difference between this surface and a typical painted surface, as well as any maintenance issues.
2 of my favorite classes in undergrad were aviation and space history; incredible to see how we got to where we are today. Too bad they weren’t mandatory for aerospace majors.
"Jayhawk Jake" (jayhawkjake)
09/27/2017 at 09:07, STARS: 0
Aero engineer, I work in aerospace but not on aerodynamics.
You’ve captured it well, but I’m wondering what else Airbus has done. They aren’t exactly forthcoming with all the details. They say:
First test aircraft in the world combining a transonic laminar wing profile with a standard aircraft internal primary structure
That is one of those statements that sounds impressive, but it doesn’t actually say anything. I assume it’s just a supercritical airfoil with a really smooth surface?
They go on to describe:
On the wings, there are hundreds of points to measure the waviness of the surface to help Airbus’ engineers ascertain its influence on the laminarity – which is the first time that Airbus has used such a testing method on an aircraft. Other ‘firsts’ are the use of infrared cameras inside the pod to measure wing temperature and the acoustic generator which measures the influence of acoustics on laminarity. In addition, there is also an innovative reflectometry system, which measures overall deformation in real-time during flight.
So basically they made a really smooth surface and are studying how smooth it stays in flight. Makes sense. The goal must be to determine just how much impact skin warping and vibrations have on laminar flow.
Interestingly the inboard pod on the test section must be there to act as a boundary layer separator.
I’m certain the goal is to develop a surface that improves drag because a small percent decrease in drag across an entire airline fleet is a lot of fuel money saved.
"Jayhawk Jake" (jayhawkjake)
09/27/2017 at 09:08, STARS: 1
I think they’re just using the outer section as their test, kinda like how Pratt & Whitney grafted turboprops onto airplane’s noses to test them.
The big pod inboard is definitely there as a boundary layer separator to isolate the outer test section. I suspect the intention is to eventually make an entire wing based on what they learn here.
"ttyymmnn" (ttyymmnn)
09/27/2017 at 09:13, STARS: 0
Somehow, I think it would be cooler if they just left the outer portion of the wing LF.
"Jayhawk Jake" (jayhawkjake)
09/27/2017 at 09:19, STARS: 0
It’s pretty important to distinguish between “natural laminar flow” and “laminar flow” here I think.
Airbus is researching natural laminar flow. That means the shape and surface itself promotes LF. LF itself can be achieved artificially by messing with the boundary layer, but that takes space, mechanisms, and weight such that the benefit is usually washed out by whatever you do to get there.
Boeing recently has been messing with a different idea to achieve a similar thing:
http://www.boeing.com/features/2015/05/bca-active-flow-control.page
Active flow control essentially injects air into the boundary layer to prevent separation, or in other words to promote laminar flow, which makes the tail surface significantly more efficient. More efficient tail = smaller tail = far less drag at cruise.
NASA has messed with laminar flow a lot, not surprisingly, including experiments with boundary layer suction most notably on the F-16XL. Here’s a huge PDF from Dryden talking about laminar flow, note I have not read it just found it while looking up information on the F-16XL
https://www.nasa.gov/centers/dryden/pdf/88792main_Laminar.pdf
"Jayhawk Jake" (jayhawkjake)
09/27/2017 at 09:20, STARS: 0
Nah, this has little to do with flutter. It’s all about drag
"Jayhawk Jake" (jayhawkjake)
09/27/2017 at 09:37, STARS: 1
That may ultimately be the way to go. Essentially extend the engine pod to act as a BL separator and make everything outboard NLF.
"ttyymmnn" (ttyymmnn)
09/27/2017 at 09:42, STARS: 0
I think this is actually pretty exciting.
"ttyymmnn" (ttyymmnn)
09/27/2017 at 09:45, STARS: 0
I’ll have to go back and look, but I think I made a post about the smaller Boeing tail a couple of years ago. Good info though, thanks. I remember reading many years ago about using holes to suck the boundary layer air in.
http://www.nytimes.com/1991/11/21/us/device-is-found-to-reduce-air-s-drag-on-jet-wings.html
Getting LF without mechanics would be a big deal.
"Jayhawk Jake" (jayhawkjake)
09/27/2017 at 10:47, STARS: 0
I don’t think it’s realistically achievable though.
It’s not hard to make a smooth surface in an ideal environment, especially with composites - you can eliminate rivets in wing skins by essentially gluing rib caps to the wing surface, thereby moving the fasteners between the skin and the ribs to the rib web. Airbus is essentially researching how to maintain that smoothness in flight with this project, in that regard it seriously seems more like a research aircraft rather than a developmental aircraft, if that makes sense.
The problem is can you actually maintain NLF? Probably not. First and foremost airplanes need “stuff” to function. Leading edge slats, deicing devices, landing lights, etc...all of these create drag and break up the boundary layer preventing NLF. Then there’s the question of how sensitive is the BL to disruption? This is what Airbus is trying to answer. When the wing bends and the skin “wrinkles” is that enough to upset it? Does the vibration of the engines upset it? Theoretically any ice buildup or even dirt would upset it.
"ttyymmnn" (ttyymmnn)
09/27/2017 at 10:54, STARS: 0
in that regard it seriously seems more like a research aircraft rather than a developmental aircraft, if that makes sense.
Makes perfect sense.