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robibird

Wingsuit and Laminar Airfoil-explanation

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As I read here many times word ''laminar'', and as I see that so many times this word is placed in wrong context I would like to provide additional information.

Wingsuit and Laminar Airfoil

Laminar Flow is the smooth, uninterrupted flow of air over the contour of the wings, fuselage, or other parts of an aircraft in flight. Laminar flow is most often found at the front of a streamlined body and is an important factor in flight. If the smooth flow of air is interrupted over a wing section, turbulence is created which results in a loss of lift and a high degree of drag. An airfoil designed for minimum drag and uninterrupted flow of the boundary layer is called a laminar airfoil.
Laminar flow airfoils were originally developed for the purpose of making an airplane fly faster. The laminar flow wing is usually thinner than the conventional airfoil, the leading edge is more pointed and its upper and lower surfaces are nearly symmetrical. The major and most important difference between the two types of airfoil is this, the thickest part of a laminar wing occurs at 50% chord while in the conventional design the thickest part is at 25% chord.
The effect achieved by this type of wing design is to maintain the laminar flow of air throughout a greater percentage of the chord of the wing and to control the transition point (point at which laminar flow is converted in to turbulent flow). Drag is therefore considerably reduced since the laminar airfoil takes less energy to slide through the air. Laminar airfoils are used for fast airplanes, or on high performance sailplanes. Also, Burt Rutan is using these airfoils in his designs very often.
But laminar airfoils have also some undesirable characteristics. They have to be manufactured very carefully and with high degree precision. Also, they require very smooth surface (did you ever wonder why competition sailplanes have high polish surface?), and any disturbance can lead to significant reduction or almost complete loss of performance. An extreme example were some airplanes that were using laminar airfoils that were not able to sustain level flight in heavy rain, because water on the wings disturbed laminar airfoil and reduced available lift.
Wingsuit is typical example of aerodynamic body that is completely unsuitable for the use of laminar airfoils, for number of reasons:
1. Wingsuit is not rigid. Wingsuits are more like parachutes, semi-rigid airfoils. Each wingsuit flyer is different in shape and size, and maintains slightly different body position in flight. In order to function as intended, laminar airfoil geometry has to be designed, manufactured and maintained to a great precision. Even if we manage to design and build laminar airfoil suit, you can only, for example, bend you elbows slightly during the flight and the wing will be completely out of shape (and out of performance). Or bend you knees slightly in flight. Put on different rig. Wear different helmet. Or just look to a side or behind you during the flight…There is infinite number of things you can do during the flight to completely nullify any potential advantage of laminar airfoil. Also, we cannot look only arm wings on the wingsuit. With its short span wings, wingsuit looks more like space shuttle then like high performance sailplane. Therefore, you have to look the complete flying body, which has actually a lot of areas that are causing interference and disturbing the airflow (head, shoulders, rig, arm wing and body attachment, knees, feet, etc.). Also, no matter what type of fabric we try to use, since wingsuit is not rigid, we will have huge problem to keep surface very smooth. Anything but absolutely perfect tailoring, manufacturing, fitting and maintaining of the body position in flight would lead to bends, ripples and wrinkles in fabric that would prevent laminar flow.
2. Laminar airfoils in general have sharper leading edge. The leading edge on the wingsuit in general has the shape of the arm, and this is not very sharp. If we try to put some kind of rigid leading edge, we can severely compromise safety, but if we try to add some kind of soft leading edge, then we are back to the problem of maintaining the proper shape of the airfoil during the flight i.e. proper body position. Also, laminar airfoils are particularly sensitive to any change in shape. For instance, modern high performance sailplanes have slider that can wipe dirt and bugs from the wing leading edge in flight, in order to maintain performance; otherwise their glide ratio could drop by 10 % or more.
3. Laminar airfoils in general have unfavorable stall characteristic. In general, they lose lift rapidly without warning and they do that at lower angles of attack then conventional airfoils. I don’t think that you would like to fly a suit that stalls very easy with no warning signal (imagine canopy that stalls that way, no one would like to jump it).
4. Wingsuit flight speeds are not very appropriate for laminar airfoils. Simply, we are still way to slow and we are operating at to high angles of attack to use and fully exploit the benefits of laminar airfoils.
I have mentioned similarity in shape between wingsuit and space shuttle. For lift generation, space shuttle relies heavily on generation of vortices over the whole airframe. These vortices are accelerating the air flow around space shuttle, thus generating higher pressure difference i.e. more lift. We can assume that the same thing is happening with the airflow around the wingsuit (and it is rather difficult to obtain experimental confirmation for that, as I explained some time ago). So, in the end, some vortices (turbulence) does not have to be a bad thing in the end.
Robert Pecnik
robert@phoenix-fly.com
www.phoenix-fly.com

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Thanks for the post Robi.

Based on some of the reading I have been doing...

http://www.desktopaero.com/appliedaero/fundamentals/reno.html

At the reynolds numbers that we can put wingsuits in, flow is mostly turbulent and cannot be called laminar. Airflow most likely seperates from the wing before it reaches the trailing edge. My guess is that the word laminar is used by people to mean mostly attached airflow.

You know that sometimes when flying a wingsuit it feels like something external is pulling us up and forward(only happened to me once). I associated that with lift being created by airflow being attached until the point that it made the contribution from the upper surface count. There is a very short clip in the Year of the Robibird video that shows this...atleast I interpreted it that way.

While playing with spoons under a tap, I found that the flat less curved spoons(spoon a) created more force than the spoons with a lot of curvature(spoon b). The flow was staying attached for the whole way(like in my avatar pic ) with spoon a and seperating much sooner for spoon b.

Do you think that lesser curvature of the upper surface means a better chance of the airflow seperating further down the chord of the wing?

Kris.

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well, very important is to repeat again and again...
The gravity is our only engine and the speed is our only friend - if we want to fly not fall.
In general, ticker profile gives you lover stall speed but higher drag, and opposite. It is all about trade here , just like on the canopies...kind off...
The frame on The year of.... you can see on the video is the moment when the suit reach the the stall speed and starts to fly. ( I think you talking about the shoot which was taken from the ground w long lens )
Long ago when I was using the skyflyer 1 and 3, main problem I found was the instant loss of performance due the sensitivity to the stall. (best performance was very near the stall, so small mistake or tiredness caused the loss of lift )
V. generation of my suit resolve this problem , but as natural consequence it become clear that this suit has to be flown in specific way. Yes! It requires more flights , more jumps and more thinking... However, once the flier nailed the sweet spot there was more than clear that suit is fast, and that it works on creating lift , not just deflecting air.
Proudly I can say that I haven't saw any other suit in BASE environment which was able to cover such distance. ( talking about BASE performance jumps, what I saw and what I was told, and what I have personaly done too. )

For example, Yuri K. who is in my opinion by far the best performance flier took half a season to nail V2 . He came to the point to gave it up, but he was stubborn enough to try and try...so much that he changed the flying style also in order to get max performance he can reach at this moment.

Another issue I see at the moment in general WS activity is constant improving of the fliers.
For example, RW discipline started so that people were using ''X'' position, in order to fly stable. Later it changed to kind of ''frog'' position, later in to ''box'' and now ''mantis'' is the way to go! From ''X'' to ''mantis'' it took around 30 years. Same I see in WS flying. Where WS is actively out on the field about 7-8 years...In some parts of the world people flying ( flocking ) differently than in another, but for sure it will come to the point were the flocks will be made so that bodies will be in fast mode w stretched legs, so to say clean, not dirty. I just hope that this path will not require another 30 years or so, because I'll be damn old to participate.
:([:/]
Robert Pecnik
robert@phoenix-fly.com
www.phoenix-fly.com

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For example, Yuri K. who is in my opinion by far the best performance flier took half a season to nail V2 .

There may be hope for me yet! Actually I nailed the V-2 for several seconds last year.

Thanks for the laminar flow discussion, it considerably changes my perception of w/s aerodynamics.
Sometimes you eat the bear..............

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Thanks for the post Robi.

Based on some of the reading I have been doing...

http://www.desktopaero.com/appliedaero/fundamentals/reno.html

At the reynolds numbers that we can put wingsuits in, flow is mostly turbulent and cannot be called laminar. Airflow most likely seperates from the wing before it reaches the trailing edge. My guess is that the word laminar is used by people to mean mostly attached airflow.

You know that sometimes when flying a wingsuit it feels like something external is pulling us up and forward(only happened to me once). I associated that with lift being created by airflow being attached until the point that it made the contribution from the upper surface count. There is a very short clip in the Year of the Robibird video that shows this...atleast I interpreted it that way.

While playing with spoons under a tap, I found that the flat less curved spoons(spoon a) created more force than the spoons with a lot of curvature(spoon b). The flow was staying attached for the whole way(like in my avatar pic ) with spoon a and seperating much sooner for spoon b.

Do you think that lesser curvature of the upper surface means a better chance of the airflow seperating further down the chord of the wing?

Kris.



Flow separation towards the rear of an airfoil can be delayed considerably by energizing the boundary layer at the front. This can be done with turbulator strips, vortex generators, and other means. Also, delta planforms delay flow separation compared with straight or swept back wings.
...

The only sure way to survive a canopy collision is not to have one.

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Robi, it's hard to argue that to wait for something 30 years sucks. ;) That's why more restless brains and hands are joining the efforts to improve the performance. The first fruits are juicing and riping as we speak...

A lot of sweet L/D juice can be squeezed by extending the wing forward on the leading edge. The wing profile that we use now has no analogs in 100+ year old aerodynamics, because it's so inefficient. What we have now is a massive, several inches thick, leading "bulge" of the arm that brings a massive layer of air to a full stop from 120mph to 0. Headdown fallers hold a significant portion of their weight by their hands stretched almost like ours. Unlike them, however, we only have a fraction of the weight as our thrust. At L/D=3.0, our thrust is only 32% of the weight, or about 60lbs. for a 200lbs. jumper. Reducing the drag of by using sleeker airfoils will allows us to fly even faster.

In experiments with inflated tubes inserted in the sleeve to form a more aerodynamic leading edge, I experienced the same balance as without them and ~15lbs. on my ankles. So the improved wing created ~15lbs. of additional lift. And decreased the drag in process, too.

There's a lot of improvement that can be achieved in wingsuits. The first step is to fully understand what's going on. What exactly the angles of attack in different flying regimes and lift and drag coefficients at different angles are, and if we balance suits properly or just think we do.

L/D=3.x suits coming in the near future will only remotely resemble current suits...
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L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
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wonderful discussion, wouldn't it be great to obtain "laminar flow"

sometimes I wonder if the "wind" is just "blowing past"......... that were just "sail's" deflecting air.
but then sometime's you see a tiny wing get so much lift, and fly so fast, you gotta wonder if there's some physics going on here. Does the air wrapping around the wing create lift? of course, can we obtain the angle of attack to produce this affect? ...........how do you spell Brunuli?

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...........how do you spell Brunuli?



I assume you mean Bernoulli.



exakerly :-) isnt the Bernoulli effect wonderful, the high pressure above an airfoil creates lift, SOOOOO how much laminar flow do we need to get Bernoulli effect, if the "wind" leaves the top surface then this has to be lessened,

Gyro told me once that he thought parachutes didn't even get perfect laminar flow,.

But they get lots of lift from the airfoil they use

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wonderful discussion, wouldn't it be great to obtain "laminar flow"



Robi's entire post was about why we don't and won't get laminar flow - and why even if we did it wouldn't really do us much good.
Do you want to have an ideagasm?

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Yuri's chart, 4th one down; classic aerofoil section of a hang glider (and also good for a wingsuit) - the importance of stability in flight for flexwings can't be emphasised enough. If you don't have superb pitch stability (quite common with a lot of wingsuit pilots) then the wing won't develop much lift anyway. The more you push out, the finer the stability point becomes; ultimately the limit of suit performance is us! ;)
--
BASE #1182
Muff #3573
PFI #52; UK WSI #13

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no, whole post was about what ''laminar'' means.. I noticed that people here like to say Laminar , laminar without really understanding what is laminar flow

:)



My apologies for misunderstanding then!:$

But true laminar flow is not really a possibility for us, yes?
Do you want to have an ideagasm?

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jakee,
to design the wing w laminar air flow characteristics is still true task in modern aviation and can be done only on rigid profiles. as ws is not rigid, all theory around having laminar airflow over WS is pointless because small change of the any part of our body would ruin all the performance even if we get close to such design.

Important is to understand that I am talking about Laminar airflow and not about airflow which support us nicely when we flying w WS or canopies...
Robert Pecnik
robert@phoenix-fly.com
www.phoenix-fly.com

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jakee,
to design the wing w laminar air flow characteristics is still true task in modern aviation and can be done only on rigid profiles. as ws is not rigid, all theory around having laminar airflow over WS is pointless because small change of the any part of our body would ruin all the performance even if we get close to such design.



Yep, that is what I was getting at:)
Do you want to have an ideagasm?

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Hi there, I just want to put my 2 cents in...

To get out any calculated performance of a specific airfoil it has to be made very conform to the polar coordinates. Meaning that the wing has to be built in such a way that it matches the polar coordinates as perfect as possible.

Even when very smooth and polished the airfoil must not differ more than 3% of the theoretic polar coordinates (cross section). Otherwise you will get out less performance out of the wing. With our wingsuits and the elastic wing structure we are far from optimal conditions.

The most precise ribs will not prevent the wing from distorting between the rib sections because of the air pressure inside of the wing. so the airfoil between the ribs will always look different because it is shaped by the air pressure.

but even worse:

At the first 30% of the profile (from the leading edge) the most part of the lift will be generated. This fact is reason enough to manufacture the first 30% of the airfoil as precise, clean and smooth as possible.

As a wingsuit designer you don't overcome the problem that you have to consider that the pilots arm need space and you have to skip the ribs here.
so you not even can put ribs into that important wing section which is most responsible for the lift. Not the 3% correctness of the airfoil is now the most determining factor - it's the missing airfoil!

Maybe I'm alone here with the statement that I think the airfoil shape is not important at all! As long as it is drop-shaped to reduce drag. 90% lift generated from the wings comes from vortex forces!

and that is what I like most of robi's statement:

"I have mentioned similarity in shape between wingsuit and space shuttle. For lift generation, space shuttle relies heavily on generation of vortices over the whole airframe. These vortices are accelerating the air flow around space shuttle, thus generating higher pressure difference i.e. more lift. We can assume that the same thing is happening with the airflow around the wingsuit (and it is rather difficult to obtain experimental confirmation for that, as I explained some time ago). So, in the end, some vortices (turbulence) does not have to be a bad thing in the end."

In my opinion this statement gets it to the point.
though it's not assuming anymore, it's fact that we fly our wingsuits due to vortices. Our accurate lift theory is not the classic lift distribution of rectangle wings. With our wings we belong to the delta wings, getting lift due to vortex forces. For lift we don't need a clean airflow ower the upper wingsurface only for reducing drag!.
That's the reason why we get more performance out of the wings when we fly faster. the vortices get stonger and suck more on our wings and body(!)

Have anyone filmed the airflow over the upper wing surface? I was astonished when I watched the wool threads dancing against the flight direction. I will try to get a video here soon.

Thats how I understand the aerodynamic of wingsuit flying so far. It had been said here before - I just want to strengthen the theory of vortex forces at that point.

anybody who find spelling mistakes can keep them ;)

andi
www.pressurized.at

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Thanks Andi, that was really insightful. Actually, this whole thread is! So where did you attach the wool threads? At various parts along the upper skin? That would indeed be an interesting experiment. I'm gonna have to try that sometime.

So when would you be flying optimally? When the threads are or are not dancing around? If they're dancing around it means we're getting the vortices right?
Costyn van Dongen - http://www.flylikebrick.com/ - World Wide Wingsuit News

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Have anyone filmed the airflow over the upper wing surface? I was astonished when I watched the wool threads dancing against the flight direction. I will try to get a video here soon.



There is a great video from quite a few years back from Adrain Nicholas and his wife testing suits in this way. The docu shows them using threads in/on the wing and testing the suit at various angles in the windtunnel, and filming the white threads in blacklight...
JC
FlyLikeBrick
I'm an Athlete?

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Robi,

It is 6:36-6:38 in the video.

Andi,

I found this article a few weeks ago and posted a thread. Looks like it must be included in this discussion.

http://www.aerodyn.org/Wings/larw.html

I heard from someone that you were jumping with little video cameras attached to the wing. Was it 2005? Were the wool threads dancing against the direction of airflow even near the leading edge?

Attached pic is from this article on the wikipedia.

http://en.wikipedia.org/wiki/Stall_%28flight%29

If the wool thread was in the portion of the wing past the point where the airflow had seperated, we cannot predict how it would behave.

Also when we are gliding at less than 2.5 and not maintaining a steep pitch...the angle of attack is above 15 degrees. If super smooth airplane wings cannot bent the air around at that angle...is there much flow over any significant amount of the top surface of the WS wing ?

I guess I want to associate the few secs of flight on one BASE jump with enough attached airflow to cause the sensation and it did. 90% of the lift coming from vortices seems a bit much to me. There is a lot of surface area increase because of wearing a wingsuit and lots of air deflection from the bottom surface.

The article on aerodynamics of low aspect ratio wings says that Clmax occurs at high AoA...as high as 30. But we know for a fact(from the field... by experimentation) that at 30 degree AoA our flights suck. The article does not say how the drag coefficient varies with AoA so...


Kris.

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Have anyone filmed the airflow over the upper wing surface? I was astonished when I watched the wool threads dancing against the flight direction. I will try to get a video here soon.



There is a great video from quite a few years back from Adrain Nicholas and his wife testing suits in this way. The docu shows them using threads in/on the wing and testing the suit at various angles in the windtunnel, and filming the white threads in blacklight...




John-Pierre Knapp gave his presentation again at PIA and he included a good deal of video and empirical data from his testing both in the wind tunnel and in the sky using the S-fly wingsuit. One of the videos shown was of airflow over the entire suit using wool threads. Hopefully he will make the video publicly available as it depicts more than I care to attempt to describe here.

But what became plainly clear to see after watching his seminar was what has been said here many times before. The fact that were are not a rigid wing, but one that can constantly change shape while in flight,makes it extremely difficult to obtain exact data/numbers by the same person, let alone compare two different people to gain difinitive data/numbers (Yuri, this seminar was right up your alley but I think it would bust many of your bubbles.If you get the chance, I recommend you watch this presentation). The data gathered in the tunnel using a rigid model was clearly discernable and reproduceable, however, the data collected on a human differed from the model and even more so from the data collected on a skydive.

It became apparent that the jumper is the biggest variable in the equation and flying in anything other than an optimal position for that person and suit will create vastly different results. That aside, the one thing that was evident was that in the optimum position for the suit(S-fly), the airflow over the suit showed where the aerodynamics could be improved or where it was very efficient. In all, it was a very interesting seminar even if you're not a number cruncher.
"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

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. That aside, the one thing that was evident was that in the optimum position for the suit(S-fly)



access or expert?

Could you at least post what that was shown to be? I know there were a few others and I talking about the expert a few mths ago so it could be useful info.

Were the tests based upon a solid flat suit or one where the user could also bend/drop their knees a little?

thx scott

Where is my fizzy-lifting drink?

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I don't have his presentation so I can't post his data findings. The suit used was an S-fly version of what is now known as the expert. This test is not new by any means as I remember it being covered in ParaMag quite some time ago. The presentation is way more detailed and has actual data/videos from the test than the article that was published in paramag.
"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

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The article on aerodynamics of low aspect ratio wings says that Clmax occurs at high AoA...as high as 30. But we know for a fact(from the field... by experimentation) that at 30 degree AoA our flights suck. The article does not say how the drag coefficient varies with AoA so...


Kris.



Cd increases tremendously at high AoA in low aspect ratio and delta wings. Even if they have not (technically) stalled, their flight becomes "mushy".
...

The only sure way to survive a canopy collision is not to have one.

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