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Trackingderby.com wingsuit section

 

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The111  (D 29246)

May 23, 2006, 10:41 AM
Post #51 of 91 (11232 views)
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Re: [jakee] Trackingderby.com wingsuit section [In reply to] Can't Post

Forward drive in unpowered flight comes from a forward-angled lift vector. Why do you think returning your lift vector to near vertical will provide a boost in forward speed? In your example, what force is causing your forward speed to increase during plane out?


jakee  (C License)

May 23, 2006, 11:04 AM
Post #52 of 91 (11219 views)
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Re: [The111] Trackingderby.com wingsuit section [In reply to] Can't Post

In reply to:
In your example, what force is causing your forward speed to increase during plane out?

Lift. Although the horizontal component of total lift will be smaller, the increased AOA during the plane out, combined with your higher airspeed from the steeper dive will cause the total lift you are generating to massively increase. So although proportionally the horizontal component is smaller, in actual terms horizontal force has increased.

Again, when I say plane out I don't mean getting totally horizontal, and this increase in horizontal speed will be temporary.


KrisFlyZ  (C 34590)

May 23, 2006, 11:12 AM
Post #53 of 91 (11212 views)
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Re: [The111] Trackingderby.com wingsuit section [In reply to] Can't Post

Shut up you two TongueWinkLaugh.

Plane out VKB style....the track is still very steep just not headdown...the initial speed will help the end result because you have entered your 90 sec time slice at a higher velocity( hopefully).

Back to the issue of dive...

I mean for the prevailing conditions if horizontal speed is less than vertical speed then it is a dive...but I do see your point about just maximizing horizontal speed because glide is not a factor in a race that is limited by time. Which probably means I misinterpreted what Costyn said.

Kris.


The111  (D 29246)

May 23, 2006, 11:33 AM
Post #54 of 91 (11201 views)
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Re: [KrisFlyZ] Trackingderby.com wingsuit section [In reply to] Can't Post

In reply to:
Shut up you two TongueWinkLaugh.

But it's so fun!

In reply to:
Plane out VKB style....the track is still very steep just not headdown...the initial speed will help the end result because you have entered your 90 sec time slice at a higher velocity( hopefully).

I think we're all on the same page here. Smile

In reply to:
I mean for the prevailing conditions if horizontal speed is less than vertical speed then it is a dive...but I do see your point about just maximizing horizontal speed because glide is not a factor in a race that is limited by time.

Exactly, which I'm guessing is why Costyn raised the point in the first place... the current rules potentially encourage dirty wingsuit flight. Laugh


yuri_base

May 23, 2006, 12:48 PM
Post #55 of 91 (11183 views)
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Maximum sustained horizontal speed [In reply to] Can't Post

I think we're all right here, we just need to put the pieces together. Wink

You do get higher horizontal speed when you plane out from head down (or very steep dive). When you dive at constant speed, the total force the air exerts on your body is vertical and equal to your weight. The components of this force perpendicular and parallel to your trajectory are called lift and drag (there are no two actual separate forces). When you plane out you change the angle of attack and other aerodynamic properties of your body in such a way that the total force the air exerts on your body increases and is inclined forward, accelerating your body horizontally.

However, if you plane out as typically done with wingsuit - i.e. you try to level off as much as possible - your horizontal speed will quickly bleed and you go back to your regular forward speed. You need to maintain the high speed over the period of 90 seconds somehow.

I believe the best distance in fixed period of time can be achieved not with wingsuit, but with leg wing, because it gives you so much thrust. I recorded sustained horizontal speed of 140mph in Prodigy pants without even trying to max it. Diving with Twin Otter in Phantom, I found that flying just the leg wing allows me to hold the race for longer time. 140mph in 90s gives you 3.5 miles. In 60mph tailwind you'll get 5 miles. Larger (but not too large) wing with smooth & tight legs will give even higher horizontal speed.

To achieve maximum sustained horizontal speed, think thrust, not lift. Leg wing is the way to go.

Yuri


phoenixlpr  (D 3049)

May 23, 2006, 1:08 PM
Post #56 of 91 (11172 views)
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Re: [jakee] Trackingderby.com wingsuit section [In reply to] Can't Post

In reply to:
I'm still going to disagree with this, I think a plane out from a very high speed dive will result in (temporary) horizontal speeds greater than those that can be sustained in a less steep dive.

Notice that you can not collect so much speed that can support your horizontal flight over 90 seconds in higher agnle of attach than agle of max-out.


jakee  (C License)

May 23, 2006, 1:20 PM
Post #57 of 91 (11168 views)
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Re: [phoenixlpr] Trackingderby.com wingsuit section [In reply to] Can't Post

In reply to:
Notice that you can not collect so much speed that can support your horizontal flight over 90 seconds in higher agnle of attach than agle of max-out.

No, but with 15 seconds to dive before the timing starts it may be possible to boost your speed at the beginning of the race.


phoenixlpr  (D 3049)

May 23, 2006, 1:26 PM
Post #58 of 91 (11164 views)
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Re: [jakee] Trackingderby.com wingsuit section [In reply to] Can't Post

But you have to change the angle twice...


Costyn  (D 92506)

May 23, 2006, 1:30 PM
Post #59 of 91 (11159 views)
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Re: [jakee] Trackingderby.com wingsuit section [In reply to] Can't Post

In reply to:
No, but with 15 seconds to dive before the timing starts it may be possible to boost your speed at the beginning of the race.

Yes, this wil certainly help, but wouldn't it bleed off somewhat quickly? I can't see the increased forward speed having effect for more than 10 or so seconds?

I agree with Yuri that a large leg wing will give you more forward speed, but wouldn't some arm wings then give you the opportunity to make ensure you actually make the 90 seconds? There's not that many people who can make a 105 second track from 13500ft, are there? (considering just using the tracking pants Yuri was talking about).

Also, if you just use a big leg wing, you'll tip over forwards, sending you more in a head down trajectory. Similar to what happens when backflying, opening your leg wing without having your arm wings fully stretched out (or so it seems to happen with me, at any rate).


Costyn  (D 92506)

May 23, 2006, 1:43 PM
Post #60 of 91 (11147 views)
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Re: [Costyn] Trackingderby.com wingsuit section [In reply to] Can't Post

In reply to:
As some people will probably have noticed, the Wingsuit ranking is now also available on TrackingDerby.com. And Claude did change the time to 90 seconds, making it more accessible. A side effect is of course that someone getting more altitude can now dive head-low for 90 seconds and probably cover more distance, but we've discussed this topic to death already. Smile

Ok, silly to be replying to myself, but I forgot to make a point in this post.

If the distance calculation was done on the basis of an altitude range, there would be no discussion. If you measure the horizontal distance travelled between 10000 to 4000 feet the person with the best glide ratio wins, no matter how long they take between those two altitudes.

Of course there is still the issue of tailwind, but as Claude has pointed out, you should only really be comparing people that jump at the same event with the same conditions.


jakee  (C License)

May 23, 2006, 2:10 PM
Post #61 of 91 (11149 views)
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Re: [Costyn] Trackingderby.com wingsuit section [In reply to] Can't Post

In reply to:
Yes, this wil certainly help, but wouldn't it bleed off somewhat quickly? I can't see the increased forward speed having effect for more than 10 or so seconds?

Umm, I dunno. I was really just arguing a technical point with MattTongue.


KrisFlyZ  (C 34590)

May 24, 2006, 4:34 AM
Post #62 of 91 (11112 views)
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Re: [yuri_base] Maximum sustained horizontal speed [In reply to] Can't Post

In reply to:

To achieve maximum sustained horizontal speed, think thrust, not lift. Leg wing is the way to go.

Yuri

I understand you are talking about maximum sustained horizontal speed but wanted to point out the following.

In the end the overall force vector's angle to the horizon is what results in speed(as Mr 111 pointed out earlier). The arm wings add to this forward force and thus speed.

Maintaining the angle is easier if the arm wings are collapsed but the angle can be maintained without collapsing the arm wings at all.

The way I see it
wing == wing ....round of applause please Blush...
and more force results in the forward direction from having the arm wings open...maybe not fully but enough to form an imaginary 'V' from head to the toes. The thinking is to reduce drag from having outstretched arms.

Thoughts?

Kris.


douggie  (A 40008)

May 24, 2006, 1:39 PM
Post #63 of 91 (11076 views)
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Re: [Costyn] Trackingderby.com wingsuit section [In reply to] Can't Post

This is all really stupid. Just grow some nuts and jump off a cliff and see how far you can fly. The furthest wins!


yuri_base

May 24, 2006, 1:46 PM
Post #64 of 91 (11075 views)
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Re: [KrisFlyZ] Maximum sustained horizontal speed [In reply to] Can't Post

In reply to:
Thoughts?

Yes, I got an interesting result:

To achieve maximum possible horizontal speed, one should fly at glide ratio of square root of 2 (1.41) with minimum possible drag coefficient.

This theoretical result points to leg wing as optimal for achieving max speed, since it's glide ratio lies between regular tracking (~1) and wingsuit (2-2.5).

I don't have time now to elaborate, c-ya! Wink

Yuri


pbla4024  (C 2033)

May 24, 2006, 1:51 PM
Post #65 of 91 (11070 views)
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Re: [yuri_base] Maximum sustained horizontal speed [In reply to] Can't Post

Are you sure? Shouldn't angle depend on polar curve?


The111  (D 29246)

May 24, 2006, 2:05 PM
Post #66 of 91 (11063 views)
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Re: [pbla4024] Maximum sustained horizontal speed [In reply to] Can't Post

Yes, it will depend on airframe (wingsuit + body type). There is no magic number.


KrisFlyZ  (C 34590)

May 25, 2006, 2:59 AM
Post #67 of 91 (11037 views)
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Re: [douggie] Trackingderby.com wingsuit section [In reply to] Can't Post

In reply to:
This is all really stupid. Just grow some nuts and jump off a cliff and see how far you can fly. The furthest wins!

Laugh I agree.

For us folks that do not have a cliff in the backyard...this is a way of amusing ourselvesTongue. It is also good spaceout material when I am sitting at my desk and have nothing to do.

Kris.


KrisFlyZ  (C 34590)

May 26, 2006, 3:19 AM
Post #68 of 91 (10991 views)
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Re: [yuri_base] Maximum sustained horizontal speed [In reply to] Can't Post

In reply to:
In reply to:
Thoughts?

Yes, I got an interesting result:

To achieve maximum possible horizontal speed, one should fly at glide ratio of square root of 2 (1.41) with minimum possible drag coefficient.

Yuri

That's BS!! Everyone knows that number must be PHI (1.618) Tongue.

Kris.


yuri_base

May 30, 2006, 9:17 PM
Post #69 of 91 (10941 views)
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Maximum horizontal speed @ G = 1.414 [In reply to] Can't Post

In reply to:
In reply to:
To achieve maximum possible horizontal speed, one should fly at glide ratio of square root of 2 (1.41) with minimum possible drag coefficient.

That's BS!! Everyone knows that number must be PHI (1.618) Tongue.

Here we go:

In equilibrium flight (straight flight at constant speed), the vector sum of lift L and drag D is equal to weight W, therefore,

W = sqrt(L^2 + D^2)

If d is the density of the air, S is the surface area of the wing, V is the speed, the lift can be expressed as

L = 1/2*Cl*d*S*V^2

where Cl is the lift coefficient.

Drag is

D = 1/2*Cd*d*S*V^2

where Cd is the drag coefficient.

Thus,

W = 1/2*d*S*V^2*sqrt(Cl^2 + Cd^2)

Total speed V is the vector sum of horizontal and vertical components Vx and Vy:

V^2 = Vx^2 + Vy^2

So,

W = 1/2*d*S*(Vx^2 + Vy^2)*sqrt(Cl^2 + Cd^2)

The glide ratio G is the ratio of the Lift/Drag, or horizontal/vertical speed:

G = L/D = Vx/Vy = Cl/Cd

From this we have

Cl = G*Cd
Vy = Vx/G

and

W = 1/2*Cd*d*S*Vx^2/G^2*(G^2+1)^(3/2)

The horizontal speed is

Vx = sqrt(2*W/S/d/Cd*G^2*(G^2+1)^(-3/2))

For given weight W, air density d, wing surface area S, and drag coefficient Cd, the maximum horizontal speed will occur at maximum of this function:

F(G) = G^2*(G^2+1)^(-3/2)

The derivative F'(G) must be zero at maximum:

dF/dG = 2*G**(G^2+1)^(-3/2) - 3/2*G^2*(G^2+1)^(-5/2) = 0

From here we find that

G^2 = 2

G = sqrt(2) = 1.414

Fmax = 0.385

Vxmax = 0.88*sqrt(W/S/d/Cd)

So, for given drag coefficient Cd, the maximum horizontal speed is achieved at the glide ratio of square root of 2, or 1.414 - not the Da Vinci "code" Phi. Wink

E.g. for exit weight 200lbs (W = 90kg*9.8m/s^2 = 882N), d = 1.25kg/m^3, S = 0.8m^2,

Vx = 42m/s*sqrt(G^2*(G^2+1)^(-3/2)/Cd) = 94mph*sqrt(G^2*(G^2+1)^(-3/2)/Cd)

The 2-D graph of this function Vx(G, Cd) is in the attachment, and you can see that given Cd, the maximum horizontal speed is achieved at G = sqrt(2) = 1.414.

To summarize, to achieve the maximum horizontal speed, glide at ratio 1.4 (angle to horizon 35 degrees) with as little drag as possible (that is, gliding with your body parallel to the relative wind, arms not wide spread, smooth & tight suit). You can achieve this with the leg wing alone or with the leg wing and small arm wings.

Yuri


(This post was edited by yuri_base on May 30, 2006, 10:14 PM)
Attachments: HorizontalSpeed.xls (43.0 KB)


The111  (D 29246)

May 30, 2006, 9:42 PM
Post #70 of 91 (10933 views)
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Re: [yuri_base] Maximum horizontal speed @ G = 1.414 [In reply to] Can't Post

Wingsuits are not airplanes.

Some of your assumptions do not apply.

For example, "S" is not a constant in a wingsuit. As a sidenote, that is why polar curves may not be a very accurate way to describe wingsuit flight either.

Airplanes change their AOA by moving small metal components at the ends of rigid surfaces. We reshape our entire bodies.


(This post was edited by The111 on May 30, 2006, 9:43 PM)


yuri_base

May 31, 2006, 7:26 PM
Post #71 of 91 (10873 views)
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Re: [The111] Maximum horizontal speed @ G = 1.414 [In reply to] Can't Post

The result is actually quite generic, it is based only on these two assumptions:

1. Gravity is the only engine.
2. Aerodynamic force is proportional to the square of speed (which is true for high Reynolds numbers typical for wingsuit flight).

It's just simple physics: the gravitational "thrust" is equal to weight W times the sine of glide angle A. When the glide ratio is high, the thrust T = W*sin(A) is too low to achieve high horizontal speed. On the other hand, when the glide ratio is low, the thrust is high, but the horizontal component of your speed Vx = V*cos(A) is low.

The maximum speed is somewhere in the middle. This golden middle happens to be at sqrt(2) = 1.4.

It doesn't have to be precisely 1.4. The range 1.2-1.6, as can be seen from the graph, is almost "flat" in terms of horizontal speed. The crucial task is to achieve minimum drag while maintaining this 1.2-1.6 glide ratio. 1.2 can easily be achieved even with the Prodigy leg wing, but to maximize speed, a smoother and tighter pants and low profile rig will help.

I'll measure the glide and speed on Phantom leg wing this weekend.

Yuri


yuri_base

Jun 5, 2006, 6:53 PM
Post #72 of 91 (10817 views)
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Phantom leg wing results [In reply to] Can't Post

Did one jump with leg wing on Phantom (arm wings collapsed). Tracked in the direction of jump run first with a slow turn for the first 40s, then turned 90 and tracked for about 15s in the direction approximately perpendicular to the wind. Then sharp turn towards DZ and flew both wings for another 40s.

Maximum ground speed achieved on perpendicular to wind leg was about 135mph, with glide ratio approx. 1.4. Vertical speed data is so noisy it's not even funny. Vista C was mounted on the side of the helmet. I guess, increased total speed creates even larger fluctuations in dynamic pressure than when flying both wings.

Total speed (~160mph) builds up incredible pressure on leg wing, it's almost impossible to keep the wing wide open and I thought it's going to explode any second!!! Arm wings are bitch to keep collapsed, too. After the jump I felt as exhausted as after 20 WS jumps. Pirate

What can I say... It's a fuckin' Rocket!!! Smile

Yuri
Attachments: Phantom Leg Wing.gif (14.0 KB)


Premier LouDiamond  (D 25931)
Moderator
Jun 5, 2006, 7:42 PM
Post #73 of 91 (10810 views)
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Re: [yuri_base] Phantom leg wing results [In reply to] Can't Post

Quote:
Vertical speed data is so noisy it's not even funny....Vista C was mounted on the side of the helmet

What you are seeing there is called coordinate truncation. Since the GPS calculates its position it has to figure for doppler shift of the signal from each satellite.When you get a truncated log like you have, the speed calculations are pretty useless. My guess is that the location(side) of the GPS receiver is why you are seeing a truncated track like that. There is also the possibility of a multipath error occuring due to the receivers location which contributed to the truncated log. If you are really bored, Google the topic and wade through the extremely boring details or just try relocating the receiver to the top of your helmet so it has a clear view of the sky.


yuri_base

Jun 5, 2006, 7:53 PM
Post #74 of 91 (10809 views)
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Re: [LouDiamond] Phantom leg wing results [In reply to] Can't Post

In reply to:
My guess is that the location(side) of the GPS receiver is why you are seeing a truncated track like that.

Why is the horizontal speed data smooth, then?


Premier LouDiamond  (D 25931)
Moderator
Jun 5, 2006, 8:18 PM
Post #75 of 91 (10804 views)
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Re: [yuri_base] Phantom leg wing results [In reply to] Can't Post

Without seeing your entire track log, I would guess that you experienced a multipath error and/or Position Dilution of Precision(PDOP). Google it for an in depth description as there is no short way to explain both here.Have you always mounted the receiver on the side of the helmet and have you always seen these types of spikes in your tracks?


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