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yuri_base

Deriving L/D from swoop

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Yo!

It just dawned on me that when you swoop your glide ratio is infinite (you guys are pro's and know this since you dragged your foot on the ground for the first time; it takes years for the retards like me ;)) and thus in the wingsuit equations - which are actually applicable to any non-powered gliding flight - from

L/D = (G*(g - ay) + ax)/(g - ay - G*ax)

with G = infinity it follows that

L/D = g/|ax|

In other words, if you simply take a video of the swoop and calculate the deceleration from it (for example, by having an object of known length in the frame or even simply using wing's chord as a unit of length), you simply divide g by that deceleration and get the lift to drag ratio at each moment. Since the speed is purely horizontal during the swoop, it's easy to measure the angle of attack when you're on the rears and bingo! - you have L/D as a function of AoA (as well as for different brake inputs when you transition to brakes). And since during the swoop lift is precisely equal to weight, you get lift as function of AoA and since you know L/D from the first step, you know drag as a function of AoA, too! Complete polar curve can be derived by just taking a video of the swoop.

A simple idea for you canopy researchers - PD, Brian, and others. :)
I thought I am a laureate of Nobel Prizes in wingsuiting and BASE only, but now I won the Nobel Prize in canopies, too! ;)

The first person to derive the lift L(AoA) and drag D(AoA) characteristics of their canopy from the swoop is my hero and deserves the honor to buy me a beer (tall silver Sapporo, please :))

Yuri
Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio

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L/D = (G*(g - ay) + ax)/(g - ay - G*ax)

with G = infinity it follows that

L/D = g/|ax|



Edited because I realized (post-coffee)

L/D is not (g - ay)/|(-ax)|

because of the totally horizontal assumption and ay goes to 0. Got it now.

First time I saw the other post. Nice.
Shit happens. And it usually happens because of physics.

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Edited because I realized (post-coffee)

L/D is not (g - ay)



You are 100% correct, Sir. L/D flying is not gay. Flocking is. :)
Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio

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The first person to derive the lift L(AoA) and drag D(AoA) characteristics of their canopy from the swoop is my hero [..]



Something tells me we'll soon have a swoop course with retro-reflective photoelectric sensors on each gate at the Ranch.

Just make sure you bury the wires deep enough so the swoopers don't trip on them ;)

BTW, is that what they use for measuring speed in competitions?

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We can totally use lazy Gardiner cops as aerospace scientists standing with radar guns next to swoop course anxiously waiting for fresh L/D data!

Here's another idea: g divided by deceleration ax is nothing but the cotangent of the angle that apparent gravity (for the swooper) makes with the vertical. Therefore, we don't even need to measure speed as a function of time to measure the deceleration, we can simply use any device that indicates the apparent gravity - like a plumb-line in decelerating train. Plumb line would be affected by drag, a better indicator would be a disk with one half heavier that the other, or a small vessel with liquid. The cotangent of the measured angle is nothing but crystal pure L/D! :)
Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio

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Here's another idea: g divided by deceleration ax is nothing but the cotangent of the angle that apparent gravity (for the swooper) makes with the vertical. Therefore, we don't even need to measure speed as a function of time to measure the deceleration, we can simply use any device that indicates the apparent gravity



Cute idea but since you're trying to measure is the angle between apparent gravity and true gravity, you need both your device (whichs gives you apparent gravity) and also a way to measure where true gravity is pointing. The latter is what's hard to obtain as the entire system (parachute / container / jumper) is moving.

I vote for the photo cells B|

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Plumb line would be affected by drag,



What do men in womens clothes have to do with it. :S

Are you talking about the chow fairy? :o


:P
Stupidity if left untreated is self-correcting
If ya can't be good, look good, if that fails, make 'em laugh.

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You are right, in a "black box" with an apparent gravity pointer there is no way to determine the direction of true gravity, but if you stick your head outside the box and see where the ground or water is, you can. This method requires taking the video of the swoop so you measure the angle the half-black, half-white disk (with one half heavier than the other) makes with the ground.

But what I was thinking - there's even better way and I already have all the electronics for it! Simply take an accelerometer with you. Accelerometer measures apparent gravity. The vector sum of its components along the axes of the accelerometer is the vector of apparent gravity:

g1 + g2 = g'

(here prime denotes apparent gravity, vs. true gravity g)

So it's nothing but Pythagorean theorem:

g1^2 + g2^2 = g'^2

On the other hand, you're moving with horizontal deceleration ax (that's horizontal component of apparent gravity for you) and the vertical component is simply g (because your vertical acceleration ay = 0). So

ax^2 + g^2 = g'^2

From these two equations it follows that

ax^2 = g1^2 + g2^2 - g^2

and finally

L/D = g/sqrt(g1^2 + g2^2 - g^2)

DONE!!! :)
I already have a device that I built for wingsuits - Z-Device, it already has accelerometer and data recorder. For the purpose here, we don't need the vane and Pitot tubes, so I can remove them and give you the belly mount with two black boxes.

How does the weekend WX look? ;)
Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio

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Thank you for impressing us with your brilliance!

Oh hey... Are you still on the Bounce Bingo list? http://www.dropzone.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=1759796;
Are people at the Ranch still trying to murder you by half way collapsing your slider? http://www.dropzone.com/cgi-bin/forum/gforum.cgi?do=post_view_flat;post=1763663;
Did you end up suing the DZ or calling FAA and DEA about that issue?

How is the chemical treatment going?

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Great success! B|

Here's the result of Vadim's swoop at the Ranch. He used toggles which explains relatively low L/D. It'd be interesting to see the results for risers as well as for different canopies.

The device works in horizontal flight, and it does not need to be actual swoop: you can practice high in the air and level off using the accuracy trick.

Zee best is yet to cum! ;)

Yuri


P.S. Two accelerometers were used that recorded data independently (blue and red lines on the graph).
Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio

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I made a mistake - was looking at the wrong place in data, it's hard to identify the actual landing (~20-30 data points) in the sea of noisy data (~5000 points). That L/D = 0.6 was an artifact of applying the theory that requires horizontal flight, while it was in fact the front riser turn.

Here's what I think is the actual landing.
Android+Wear/iOS/Windows apps:
L/D Vario, Smart Altimeter, Rockdrop Pro, Wingsuit FAP
iOS only: L/D Magic
Windows only: WS Studio

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yawn



Honestly what is the purpose of a response like this? The topic bores you yet you took the time to read the whole thread and then post a reply?



Exactly ;)
"Don't make me come down there" - God.

My site:http://www.skystudio.nl/video.html
Some of my vids: http://www.youtube.com/user/TomSkyStudio

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