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dthames

Tracking away, down angle

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>I find it hard to wrap my head around the physics but from what I understand a
>steeper angle of attack will result in more lift which will result in more horizontal
>distance.

You might get more speed - but you will not get more lift or more distance, because you'll get to pull altitude a lot faster. Several times I have watched people try to track off in a steep dive beneath me, only to get to pull altitude 5 seconds earlier than me, and have to pull while I cover another 500 feet.

I would also point out that looking down on these people is a very good position to be in; if they do manage to pull right under you you can avoid their canopy. If you pull under someone else you just have to hope that they avoid _you._ In such cases, high man is generally in a much better position.

Another thing I would point out is that bigway jumpers in general use booties. This is important because it means that if you turn outwards and drop your feet you get a) a lot of drive and b) a lot of drag. This in effect makes it easier to start the track from a slower fallrate.

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A successful track has NOTHING to do with time. Start thinking about covering the greatest horizontal distance for a given loss in altitude.
Using a diving track, you may well get to a given horizontal distance faster than me, but by tracking flatter, I'll be much further away when I reach your altitude.



I disagree but also don'[t really care. I have studied the aerodynamics so I can be familiar with them on solos (off of cliffs) when the time comes. I have no experience with tracking in big ways like I already admitted so obviously people like bill von will be better.

I know what I have studied though is that speed will translate into more lift which will equal further horizontal distance. you will arrive at deployment altitude faster and be further from your starting point.

it is the same idea behind a wingsuiter diving and then pulling into a horizontal glide. we trackers just have less lift because of our poor aerodynamic shape.


I love it when my students comment on my backsliding!!!
Anyone who thinks we, in free fall, generate lift has no understanding of what's going on.
This is the paradox of skydiving. We do something very dangerous, expose ourselves to a totally unnecesary risk, and then spend our time trying to make it safer.

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>Anyone who thinks we, in free fall, generate lift has no understanding of what's going on.

We definitely do; it's how we move around. But compared to any other aircraft out there it's a small factor compared to drag.


We move around by manipulating drag and force from the relative wind.
If we truly could generate lift, then we could fall at a slower rate than normal coming out of a dive. A glider can pull out of a dive and climb. We have to work just to slow down to normal free fall speed.
This is the paradox of skydiving. We do something very dangerous, expose ourselves to a totally unnecesary risk, and then spend our time trying to make it safer.

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I can explain lift a little more:

We do generate lift -- it just isn't of the really efficient, strong type that you get off of an airfoil, where the lift can be many times stronger than the drag that's being created at the same time. Our lift is normally less than the drag being created.

So when someone cups while tracking to "shape their body like a wing", they aren't actually functioning as a wing -- even if that body shape is actually useful in improving lift.

Technically lift is the force perpendicular to the direction of travel, so it doesn't matter if it is lift like a properly functioning wing or not. And drag is parallel to the travel. So for example if one is descending under a ram air parachute, you are being supported in an upwards direction against gravity mainly by the lift, but also by the drag back along your angle of descent.. Lift isn't straight up, unless one is flying horizontally.

If one can't create enough lift to plane out of a dive and fly level, it may not be much lift, or there's too much drag compared to the lift, but it is technically still lift.

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Hey, if you wanna see some awesome tracking, check this little guy out:
http://www.youtube.com/watch?v=3vhgC_g1cmU
Looks pretty flat to me :)



The case of the flying snakes , Chrysopelea paradisi, is definitely an interesting and tricky one. I'm looking at one of the journal papers that team wrote.

They (the snakes, not the researchers) do seem to stay fairly flat relative to the horizon but the angle of attack varies a lot. The very start of the flight is nearly flat to the horizon due to a good push off, then it gets very steep before it gets much aerodynamic movement going, and then it begins to flatten out. Tests from a 10m tower weren't high enough to clearly establish an equilibrium glide at the end, but it tended to be about a glide ratio of 2.2 or better near the end, which is surprisingly good. During the glide the snakes do flatten their bodies somewhat, giving them something other than a circular cross section, something the is probably a key in creating decent glide performance.

There are some subtleties in their body angle though, somewhat angled down early in the flight while dropping more steeply (not totally flat to the horizon!), later flatter with just the head angled down (for vision?), forebody flat to the horizon (angle of attack 20-40 deg.), and aft body angled downwards. Without trying to figure it all out, it is complex and not always clearly seen especially in that one video looking from the front and slightly below.

That's my serious answer to your less serious post!


Edit:
There goes my Sunday morning as I start to read the research lab's other papers. The snakes flatten out their bodies much more than I thought -- turning them cross sectionally into quite an airfoil (and almost a sort of staggered biplane when S curved side to side.) Attached pic shows the flattening in a snake.

We should stick with human RW jump tracking in this thread, though, because snakes don't take grips!

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Generating "lift" requires something that in some way resembles an airfoil moving through the air parallel to the direction of travel ( lift being perpendicular to the direction of travel). The implication of lift that I was reponding to was that by using a diving track initially that the extra downward speed would generate lift (slower verticle speed) as the track became more horizontal.
In free fall, our verticle speed is always so much higher than our horizontal speed that any potential lift (which could only be generated by flying head down or in a standup, not with belly or but into the relative wind) would be so small as to be inconsequential and would always be horizontal.
Mainly, we develope a high pressure "bubble" underneath us and move by directing some of that pressure (or airflow) in the opposite direction we wish to move, more like a surfer riding a wave.
This is the paradox of skydiving. We do something very dangerous, expose ourselves to a totally unnecesary risk, and then spend our time trying to make it safer.

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Ufk22:

You're fine with your general understanding of forces, but I am pointing out that according to the proper use of the term lift (scientifically, aerodynamically, technically, whatever), we as skydivers are creating lift as soon as we deviate off a straight down flight path.

So you are right that a skydiver may be creating a crappy little amount of lift that is not created like that of an airplane wing which would have smooth attached airflow accelerating over the upper surface of the wing, and where the high pressure underneath is a lesser part of the overall lifting force. Something blunt and stubby will indeed be relying to a greater extent on that high pressure underneath.

Also, the forces will indeed be directed largely horizontally and not very much upwards -- so it isn't 'lifting us upwards' much at all.

But I'm trying to teach that according to the way the terms are defined, it is still LIFT, whether or not pointed upwards, whether or not created largely by high pressure on the underside of a blunt object.

Feel free to call it crappy, inefficient, non-airplane-like lift that is hardly pointed upwards much at all - but it is still called lift.

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The steep track then flatten out path is the 'least time' path (as you know from physics or math classes).



How did you make this conclusion?



Because of all the stuff I learned in math and physics and knowing first hand that a dive and flatten out track can get to a point faster than a flat track.

.
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Make It Happen
Parachute History
DiveMaker

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I find it hard to wrap my head around the physics

...

for maximum horizontal separation, the physics seems to suggest



I think you've got it here. You say 'physics' when you mean 'my intuition'.

It's all right for your intuition to be wrong, it happens to everyone - it's happened to me plenty, especially about skydving, and I fully expect it to happen again.

Bigway is instructive, not because it has some magical technique, but because it gives you an opportunity to see a lot of trackers at once, and compare how they go.

The very, very furthest trackers at deploy time, all other things (technique) being equal, are the lankiest and skinniest (I'm looking at you Spider Monkey Girl, scarer of camera flyers at breakoff). That's simply because they can get their fall rate down quicker, and keep it down.

[edit: on the other hand, I can safely say I have never seen someone be lower than me early in the track, then further away at deploy time. Never ever.]
--
"I'll tell you how all skydivers are judged, . They are judged by the laws of physics." - kkeenan

"You jump out, pull the string and either live or die. What's there to be good at?

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The steep track then flatten out path is the 'least time' path (as you know from physics or math classes).



How did you make this conclusion?



Because of all the stuff I learned in math and physics and knowing first hand that a dive and flatten out track can get to a point faster than a flat track.

.



What stuff that you learned supports that?

How do you know diving first gets you to a point faster?
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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Because of all the stuff I learned in math and physics and knowing first hand that a dive and flatten out track can get to a point faster than a flat track



Exactly, and the point of flat tracking is to reduce the vertical speed to allow for a longer duration of track. One of the points you will reach faster with a diving mauver is the vertical point (altitude) where you intend to pull, thus reducing the amount of time you have to track.

You might be able to dive down and scoot over to the horizontal point 'x' in the sky faster than a flat tracker, but you'll reach the vertical point 'y' (pull altitude) quicker as well. The flat tracker, on the other hand, may take longer to get to point 'x', but when they do wil still be above point 'y', and thus be able to continue tracking past point 'x', reaching point 'y' at the further out point 'z'.

Let's say it's a wash, and you more or less get the same result. The deciding factor now is if you would rather dive down below the others in your group and pull sooner, or float above them and pull later. Based on the idea that I don't want someone crashing through my canopy, I vote for floating above and pulling later.

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well Dave my point is that you scoot down vertical point X faster and end up at horizontal point Z (instead of horizontal point Y with a flat mushy slow track where Z is further from the origin of the track than Y).

but I have already acknowledged that this might not be good for big formations...I study and practice tracking because I hope someday to be blessed with the opportunity to track off of a big wall. Different technique.

I have learned the maximum technique is not always the best (because there are subtleties to be very very careful about).

edit - I have also talked with a few people that have done a lot of tracking off of large antennaes and cliffs and they all say categorically a steeper track is what I want to refine. I trust them because they have proximity to ground to determine distance (where we skydivers do not have this luxury we only really have relativity to other skydivers and vague proximity to ground). They have the luxury of being able to track off an antennae over and over again and determine what AoA is best for distance...so I tend to trust them!

If I want to do a bigway though I am trusting Bill and other skydivers!!!!!

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Looks to me like more photographic evidence that diving below and then attempting to glide out, is not the ideal method.

The sport evolves and we old timers would do well to evolve with it. (not directed at you Spot)

Tracking methods have changed, improved even, and those who wish to ignore it will be the ones creating a sky hazard and causing an incident report in which i read of another friends death.

Matt
An Instructors first concern is student safety.
So, start being safe, first!!!

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>If we truly could generate lift, then we could fall at a slower rate than normal coming
>out of a dive.

We can. You can fall more slowly in a very good track than you can in slow-fall position (which is drag only.)

>A glider can pull out of a dive and climb.

Well, the Space Shuttle can't; at best it could get its descent rate to close to zero for landing. But we still consider that a glider that uses lift.

We are far worse gliders than even the Space Shuttle, which is one of the worst gliders ever built. But we can still generate lift; create low and high pressure areas near us and use those pressures to move around the sky. That's why we can track away from a formation while descending _more_ slowly than we did before.

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edit - I have also talked with a few people that have done a lot of tracking off of large antennaes and cliffs and they all say categorically a steeper track is what I want to refine. I trust them because they have proximity to ground to determine distance (where we skydivers do not have this luxury we only really have relativity to other skydivers and vague proximity to ground). They have the luxury of being able to track off an antennae over and over again and determine what AoA is best for distance...so I tend to trust them!



Some rather major differences: In a skydiving track (I'll say it again) you start with at least 120mph vertical speed to use. In a max performance BASE track you will never reach 120mph vert, so this idea of diving at the start of a track to gain speed (which I assume you are transferring over from what you have heard about BASE exits) is simply not applicable. You've already got all the speed you need.

Also, most guys doing much BASE tracking will be using a tracking suit. Tracking suits love to be flown steep and it's a very different flight mode to tracking in an RW suit.
Do you want to have an ideagasm?

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The steep track then flatten out path is the 'least time' path (as you know from physics or math classes).



How did you make this conclusion?



Because of all the stuff I learned in math and physics and knowing first hand that a dive and flatten out track can get to a point faster than a flat track.

.



What stuff that you learned supports that?

How do you know diving first gets you to a point faster?



I am not going to list all the courses I've taken in math and physics.
Least time concepts are taught in both math and physics classes.
Perhaps, the most widely known one is Fermat's principle.
Stick a fork into a glass of water and learn what the index of refraction means.

Please see the attached figure to illustrate the point.

You want to go from point A to point B.

The least time solution is to do a steep dive and then flatten out ( path 2 ).
The speed along path 2 is faster such that you beat the speed along path 1.
The other path ( path 1 ) takes longer but it achieves the desired results of positioning jumpers such that they can see each other and ensure horizontal separation while reducing the possibility that one jumper is pulling underneath another jumper.


A flat track done by all jumpers in the group is safer for breakoff.

.
.
Make It Happen
Parachute History
DiveMaker

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Sure, you put a marble on the two different kind of tracks, and it will surely get to the end along the steeper track (track 2). They will arrive with the same kinetic energy (speed) when they do get there, but the steeper track will get the marble there first.

That result happens when there is almost no significant friction. The skydiving version of that is very different because there is so much friction, the friction increases greatly with the square of speed, and the acceleration along the steeper track is so much less than it would be without friction. If someone can do a real trial to show how a steep dive does work better, that would be interesting to see, but I don't think it would happen.

One of the best professors I had would ask us on a test what were the assumptions for a particular theory/equation. It is very good to remember that there are assumptions that come along with all that learning of theory.
People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

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Dan, learn to flat track well. That is the best thing to do.

Many try to re-invent the wheel. Many don't realize that their "new" ideas have already been thought of and tested and determined short on being "best practices".

In the case of tracking away from a formation, flat tracking is best practices. You learn it and perfect it while doing small groups so you'll be prepared to use it when you do larger groups.

It's not a matter of getting to the same point faster or slower. It's a matter of being able to see what's going on around you.

You tell me....

Would you rather be below those others in the group at pull time or above them?

Above them, of course.

Why? If for no other reason, because you can see them much better and easier when they are on level or below you. You can't see them as well when they are above you. You can't dodge what you can't see.

When your canopy comes out, you've eliminated at least two opportunities to dodge.
-when to pull
-tracking to avoid

Let's not get all confused by the talk about physics and all that.
My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

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I have also talked with a few people that have done a lot of tracking off of large antennaes and cliffs and they all say categorically a steeper track is what I want to refine. I trust them because they have proximity to ground to determine distance (where we skydivers do not have this luxury we only really have relativity to other skydivers and vague proximity to ground). They have the luxury of being able to track off an antennae over and over again and determine what AoA is best for distance...so I tend to trust them!



There you have it. You took a newbie jumper asking about tracking away from other skydivers on a skydive, and you gave him advice based on what you were told about BASE jumping. Sounds like a good fit.

As others have mentioned, BASE is a different animal, where you're starting with 0 airspeed, and have no hope of going anywhere until you build some airpseed. The sooner you can do that, the sooner you can begin to fly away from the object.

On a skydive, you're already starting with a full head of steam, so diving to gain even more airspeed is simply giving away altitude and putting yourself in the least advantageous for deployment, that being vertically lower than the other on your jump.

Truth be told, the flatter track is the harder skill to refine, so that's what you should be working on. Even on a BASE jump, once you get up to speed, you're going to want to flatten out and scoot. As previously mentioned, the flat track will have the slowest speed vertically, so you'll be able to reach your 'tracking speed' faster once you leave the object.

Beyond that, you can do solos or just get on tracking dives which are intentionally steeper than a flat track if that's what you want to practice. Just like there are times to give (or not give) certain adivce, there are also times to practice (or not practice) certain skills, and group jumps where you're tracking for utility is not the place to practice your steep tracks.

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