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robibird

Wingsuit and Laminar Airfoil-explanation

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Yuri,

shorter wool threads: good idea- sewing threads: not good I think - the air doesn't catch them as good as wool thread (everyone uses wool-threads ...)

the wool thread video shows a ws experiment with a semi-elastic leading edge. I hoped I can reach cleaner, smoother airflow separation and better airflow over the first third of the upper wing surface.

anyway, it turned out that semi-elastic leading edge is buckling too much generating a dead air area with previous turbulence. with non elastic leading edge it looks just a little different, still separating very early.

by the way, the airflow over the legwing is very interesting too -much more potential of improving the ws, I think. I use a vertical rib between legwing and backspoiler which keeps the backspoiler away from getting sucked on top of the legwing for example - with very good results. but this is another topic...

aero rig, aero helmet, and off we go with 1:3,5 ;)

andi
www.pressurized.at

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From discussion with Øyvind, it looks they used windtunnel data (among other things) to refine the pitch angle to achieve L/D=1.8 in real flight, the maximum of the L/D curve for G-3 they measured in the tunnel. Although initial L/D=1.6 test flight was impressive by itself, they improved that with the help of windtunnel.

With a lot of useless research going on in universities (see, for example, all this research on birds... interesting articles, but pointless), it seems some bored doctorate students in aeronautics might be interested doing some research in wingsuits. There's so much talent and money wasted there, it's not even funny.

Maybe I'll bribe some with Russian Vodka? :)



I assume that was a joke. The military is VERY interested in bird and insect flight right now, as part of the micro UAV program. Micro UAV's are likely to be the next generation of tactical battlefield sensors, useful even in cities and inside buildings.
...

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

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Andi,

Very cool! I agree, there's a lot of inefficiency going on in the legwing. I'll experiment with exposing the leading edge of the legwing and let it fly, not just deflect air.

Perhaps it's a good idea to first think about wingsuit as a flying body composed of inefficient elements and see which ones are the biggest contributors to inefficiency. If total inefficiency is 100% and we determine that:

50% inefficiency is contributed by brick rig
30% by leg wing
10% by arm wing
5% by helmet
5% by other factors

- then it doesn't make sense to put a lot of effort to make an improved arm wing first or speed helmet if the brick rig destroys so much of performance. Making a smaller/flatter/integrated rig is a priority then. Then leg wing takes the next priority, etc.

How these inefficiencies can be estimated? By removing them (keeping other inefficiencies in place). Here is where windtunnel can help. Measure how much max L/D changes with rig/no rig, with legwing/no legwing, armwing/no armwing, head/no head. It'll be a crude estimate, because all elements affect each other, but gross inefficiencies can be identified this way.

3.5 in 2007. Now we're talking! :)
Yuri
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So I tied threads and nylon strands to the rib sewing on my wingsuit and guess what?

The first 30% of the wing of the phantom is the sleeve. except very close to the body but even there its just an inch short.

Should still be interesting video if I can get the camera mounting sorted.

Kris.

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This is not good!
when u doing this Kris, make it so that you make the knot on one side of a thread. guide the thread from the bottom to the surface w the needle and that is it. make the thread longer than you need , friction between the thread and the material you putting the thread through will be enough to hold the thread in position. When you finish installing , measure the size you want to have and cut it.
the way you did is not good , also thread looks stiff too.
on the top you should avoid and bumps made by knots
Use bright color soft medium thin wool thread.
also there is no reason not to make this on the sleeve part of the wings too...

hope this explanation will help
Robert Pecnik
robert@phoenix-fly.com
www.phoenix-fly.com

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I think you'll have better success using a different type of thread. Yarn tufts like the ones in the attached links work well and they need to be placed over the entire surface being tested. In the case of Jean-pierres testing, the tufts covered the entire suit, to include the helmet and rig.

Wing tufts

Model tuft test

Tufts top view

Video of tufts
"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

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Thanks Robi. I got what you are saying.

Will change to thin wool(wool might be easier to get Scott) over the next week. I just realized that my rig will be out of date for the planned trip to Belgium next weekend so I will have to pack my reserve tomorrow(under supervision)....so will only be able to do one jump tomorrow.

I will stick the wool with duck tape to the sleeve as well.

Kris.

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To throw some numbers in, I claculated a Reynolds number for each arm wing on the Rigor Mortis to be 2666666 (no jokes about all the 6s...).

The Reynolds number for a laminar flow has to be less than 2100 so we are about 1270 times over it!

This should clear any doubt.
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I claculated a Reynolds number for each arm wing on the Rigor Mortis to be 2666666 (no jokes about all the 6s...)



Curiously enough, the Reynolds number for the whole body of a person 5'7" tall (175cm) at 120mph is equal to 6,666,666.

Re = density*speed*length/viscosity

density of air in standard conditions = 1.229 kg/m^3
speed 120mph = 53.6246992m/s (appoximately ;))
length 1.75m
viscosity of air in standard conditions = 1.73E-5 (metric units)

Re = 1.229*53.6246992*1.75/0.0000173 = 6666666 :)
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To throw some numbers in, I claculated a Reynolds number for each arm wing on the Rigor Mortis to be 2666666 (no jokes about all the 6s...).

The Reynolds number for a laminar flow has to be less than 2100 so we are about 1270 times over it!

This should clear any doubt.



Suitable airfoil design delays the laminar to turbulent transition to far higher Re numbers, by maintaining a negative pressure gradient over much of the chord. Many aircraft now have wings that maintain laminar flow over a large fraction of their area, at high Re.

Generally the benefit is only possible over a very limited range of AoA, though. I agree that it is NOT worth pursuing in a wingsuit.

How about active flow control? Anyone?
...

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

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How about active flow control? Anyone?


Anyone what?!
The Ws is on the field since 1996 - Patrick
1998 I made my prototype, also mainly french jumpers were playing w their stuff
1999 BM started, also many other jumpers were playing w their own suits, different types, etc...
Now is 2007.
Suits started at 1:1 GR, nowdays some flying over 1:2.5GR Is this good answer to your Q?!
:)
Robert Pecnik
robert@phoenix-fly.com
www.phoenix-fly.com

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How about active flow control? Anyone?


Anyone what?!
The Ws is on the field since 1996 - Patrick
1998 I made my prototype, also mainly french jumpers were playing w their stuff
1999 BM started, also many other jumpers were playing w their own suits, different types, etc...
Now is 2007.
Suits started at 1:1 GR, nowdays some flying over 1:2.5GR Is this good answer to your Q?!
:)


The active flow control I'm referring to is where air is pumped through slots, typically near the LE, by an actuator. Not passive devices like vortex generators, or the gizmos on my Skyflyer.

In our lab. we have shown separation delayed to very high AoA with pumped airfoils.
...

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

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Yet we know it works



Why do you say this?



Here is why I believe that it works...as always, I maybe wrong.

Because Patrick(RIP) who did quite a bit of wingsuit testing in the wind tunnel had concluded that the deflector would reduce turbulence behind his rig and give him something like 10-15% more forward speed.

Because Robi put one on his high performance suits. I believe that Robi would not put anything(other than a logo or two :P) on his suits that has no functional value.

VKB have also said something about how the design of the Butt deflector is wrong...the design of the rig that they flew with the G3 suit was designed to address this issue... maybe?

So we arrive at the question. If the air does not even stay attached for the first 10 inches of the arm wing....why do we have a huge butt deflector which takes a lot of sewing work from a manufacturing perspective.

Kris.

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If the airflow is turbulent after 30% of the arm wing what good is a butt deflector? Yet we know it works...so what am I missing?



The way i understand it, there are three main reasons for this:

1. Even if the flow over the airfoil becomes turbulent (say) 30% along the chord, doesn't necessarily mean no lift will be generated by the wing (the efficiency will depend on how turbulent the air is). So the airfoil will still produce lift towards the rear of the wings.

2. After the flow has transitioned from laminar to turbulent air, it can "reattach" to the airfoil, in effect causing a bubble of separated (turbulent) air. This is one of the advantages of operating at low Reynolds numbers.

3. Even if the shape of the butt deflector isn't producing lift, it is still going to vastly reduce the turbulent air behind the blunt (bottom) edge of the rig, resulting in reduced drag on the entire system.

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This deflector is still an issue.
On low angle of attack it has probably major roll and it helps a lot ( VKB cockroach suit B| )
On WS it is questionable how much effect the back deflector has.
Way to find out this is to experiment w it.
From my experience it helps and benefit of having it can be noticed only on performance jumps, were glide is the main and only goal.
If the suit is flown in dirty position the real help is gone because bit of forward movement is there due the air deflecting not lift generated.:)
Robert Pecnik
robert@phoenix-fly.com
www.phoenix-fly.com

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The active flow control I'm referring to is where air is pumped through slots



Precisely what I was referring to. Think it's possible? What kind of relative pressure do you need from the output pumps? Depending on how high it needs to be (and I think it's pretty low) the equipment you'd have to wear could be pretty small. And it could obviously greatly delay seperation. I think it very well may be worth it's weight in GR.

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Suitable airfoil design [...] is NOT worth pursuing in a wingsuit.

How about active flow control? Anyone?



Are you saying that making the airfoils more efficient by:

1. Forming a nice leading edge to complete the efficient aerodynamic profile.

2. Making butt deflector smaller (or removing it altogether when we have thin/integrated rigs) and letting the leg wing to be a real wing on its own with efficient profile, its own upper surface airflow, nice leading edge, etc.

3. Assuring that the balance of all aerodynamic forces leads to the optimal AoA for max L/D without flyer disturbing his body position too much as to hurt L/D.

4. Making the parts that are horrendously inefficient L/D-wise (body) to have minimal destructive L/D impact on the whole system to not dumpen the contribution of high L/D parts - for example, making the body (fuselage) have zero AoA, just like it's done in gliders/airplanes.

- is NOT worth pursuing, but equipping a jumper with pumps and batteries is? ;)

First things first, we're in the stone age of wingsuiting yet...

That we're in the stone age, is proved by that only in 2007, we're starting to talk about the No.1 essential things in aerodynamics, such as balance and angle of attack.
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why do we have a huge butt deflector which takes a lot of sewing work from a manufacturing perspective.



Let me proclaim a 100% correct theorem I hope no fool will dare to contest.

23% larger back deflector allows for 23% larger logo.

;)
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The active flow control I'm referring to is where air is pumped through slots



Precisely what I was referring to. Think it's possible? What kind of relative pressure do you need from the output pumps? Depending on how high it needs to be (and I think it's pretty low) the equipment you'd have to wear could be pretty small. And it could obviously greatly delay seperation. I think it very well may be worth it's weight in GR.



Some very impressive results have been obtained with piezo actuators which have minimal power. Even the precise details of the airfoil don't seem important in delaying the separation. We're going to build some R/C models for flight tests, since all our data come from wind tunnel tests so far.
...

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

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vortex lift

Kline-Fogleman stepped airfoils ("Most of the modified shapes were significantly worse than the basic airfoil but two showed some positive effect on coefficient of lift and lift to drag ratio.")

more discussion about Kline-Fogleman airfoil
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