Basejumper.com - archive

Hey all, I got carried away while analyzing a new site on google earth the other day, and came up with the following attachment. It's basically a schematic of an antenna, with the red lines representing the wires, the solid blue lines representing the approximate sectors appropriate for jumping on that side, and the dotted blue lines representing the corresponding wind direction. Obviously the numbers represent the range of wind directions that is appropriate for jumping. I find it quite helpful when glancing at aviation METAR reports near objects.

Method for construction: I took a screen shot of the site from Google earth, and put it in to Keynote (a slideshow program got Mac for those that aren't familiar). I then overlayed red lines over top of where the wires were, and green lines originating at the base of the tower and extending to true north and true east to help with alignment with the compass rose. I then selected all red and green lines, copied them, and pasted them in to a document with a picture of a compass rose. Once the north and east lines are aligned properly, I shortened all the lines to constrain them within the circle of the compass, then added the blue lines, text, etc... Just make sure that true north on the photo is aligned straight up to it's kosher with true north on the image of the compass. If someone was a little more motivated they could make the compass have a transparent background and lay it right on top of the google earth image. Merry Christmas to all those that would like to use...

Edited: Oops, forgot to hit the "upload attachment" button...

What attachment?

Assuming landing areas aren't a factor what's wrong with all the other wind directions?

I'm really only comfortable with a wind that's within a certain degree range of up the wire, so this helps to visualize that when looking at digits from an METAR. If you're OK with jumping an A in any wind then it's really of no help...

In SA our big A's are all 4 guy wires, so 90 degrees between wires...
I don't think you would like it here

I don't think I understand your diagram.

The solid blue lines indicate the exit direction?

Yeah, a friend of mine that lived over there for a few years told me that. Gross...

Yeah, the solid blue lines represent the exit direction, and the dotted blue lines are there simply to make it easier to read the opposite side of the compass where the wind direction is read.

I did the same thing, but with radial, or polar plot paper it has all the degrees on the paler already for easy reference. I think I got it from here http://www.printfreegraphpaper.com/. If not just google radial or polar plot paper for free and it will come up. Written from iPhone....

So, you are exiting in the direction exactly opposite the wind? Or the other line, at an angle to the wind?

Not that those are the only 2 directions, but those are the boundaries of where I would like the wind to originate, some variation of up the wire, but off perfect by a couple degrees.

In an ideal world where winds stay one direction all the way to altitude, or the weather man is actually even close to correct that thing might be useful.

I've found BASE to be way more fluid than that would allow. I get to the tower with a plan, then nearly always have to adjust the plan with the climb as i check winds on the ground, at approx opening and exit.

The attached diagram is probably
a little clearer communication of
the exact same idea, I think.

The attached spreadsheet might
help those who are challenged
by numbers & mathematics.
_______________________________

Scary Fucking Side Note

How long will it be till we run into
young newbies using APPs at an
object to determine their delays

Do you exit with the wind directly at your back?

This is how I roll, but then again thats probably why i flew through the wires

Green is safe, stay away from red, black is wires.

Yeah, the attachments seem to be a little more colourful version of what I was trying to get at. And yes, I was taught to (and prefer) jumping A's with the wind at my back.

Twice? Oh yeah, story time

What happened?

If the wind is only 30 degrees off the wire (one of the extremes of your "safe sector"), you need the wind at least twice as fast as the speed of your canopy to guarantee you won't hit the wires in the event of massive linetwists and inability to steer (1/sin(30) = 1/0.5). Even if the wind is perfectly between the wires, the safe windspeed is 15% faster than the canopy (1/sin(60) = 1.15) for 3 wires and 41% for 4 wires.

Wow... That's pretty technical, I'm envious of your ability

And vice versa, given the windspeed W at opening altitude and the speed of canopy V, the safety sector (from which the canopy cannot fly out not matter the direction it is flying) is 2*arcsin(V/W) wide (assuming wind is faster than the canopy; if this is not the case, wire strike is always possible). If you can fit this safety sector (centered around the wind direction) between the wires, you're 100% safe, object-strike-wise.

Suppose, canopy's speed in shallow brakes is 15mph. Then the safety sector size and the safe deviation of wind direction from the bisecting line of a 3-wire antenna for different windspeeds is:

Code

Now you're just trying to impress me... Thanks for the outstanding information.

If winds are blowing directly down the wire, the ground speed of the canopy toward the wire isn't effected by the wind. If two guys you Jump the same tower. one in 0 winds compared to one in 5mph winds down the wire and both jumpers open toward the wires they will hit at the same time, only one will be farther from the tower. In other words, a tail wind helps, but a wind down a wire isn't hurting you anymore than a no wind situation.

wouldn't the wind in that case push you to the wire?
I mean if the wind is blowing from almost the opposite direction that one of the guywire is, and you jump with wind in the back, you jump straight to the wire...

So I guess would make more sense to jump a bit sidewind (i.e in the first case if wind blows from 160, would be good to jump towards 40), and then the wind will push you between the guywires and you have a safe landing

That doesn't seem 100% correct to me. I'd think that they will fly toward the wires at the same speed, but the wind down the wire would actually help compared to zero wind, because it would add a component to the canopy's vector that would result in it being further away from the tower when the wires are reached, and thus have a higher likelihood of flying over top of them, no?

Yes very correct, I just meant the time in which you would reach them if you did hit one...and further more if your flying over the top of wires sets and not through them, your pulling way to high.

Wind down the wire is also better than no wind because you can jump towards the upwind wire and use the wind to your advantage.

Exactly, and it's helping with 180 scenarios as well where no wind isn't. I think the point we are trying to make is that a straight down the wire wind is actually better than a no wind situation which we all jump in all the time. There is an article on all this...http://www.basejumper.com/...is/Antennas_752.html

I think this article needs to be corrected.

"Note that, although the ground speed of the canopy is higher with winds down the wire, the worst-case closing speed in the quadrant shown is no faster than if there were no winds. The important thing to consider is the rate at which the wind will blow a canopy toward a wire (or tower) strike. Any wind that increases the rate at which you close on the tower or wire is dangerous. Any wind which blows you away from the tower is good. Both zero wind and wind down the wire have no effect on the rate at which you close toward object strike."



While it is true that the tangential speed that the canopy is approaching the wires is the same for no wind and wind down the wire, there are several factors that weigh against jumping in the wind down the wire:

- wind straight down the wire on exit point does not guarantee that from opening altitude to the ground it is in the same direction. A 20-30 degree fluctuation towards the wrong sector is no problem if the wind is bisecting the good sector, but can be disastrous if wind is down the wire.

- in 180 scenario, you'll be approaching wires sideways (crabbing), not straight-on; it is also harder to judge distance to wires (or see them at all in the darkness) than the tower

- with canopy moving faster, the strike will be more devastating

Of course wind splitting the wires is better than wind down the wire, that is an obvious given that I think everyone can agree on.


I don't see how this is relevant, as it would be equally hard to spot wires in no wind conditions as down the wire conditions.


If the wind down the wire is strong enough to significantly effect canopy speed then you should def be jumping toward the upwind wire to decrease the chance of wire strike. However, if wire strike happens anyhow, would a few mph faster necessarily be more dangerous considering that the extra speed would not be propelling you directly into the object?

A freefall deployment in a crosswind with fall rate less than windspeed is prone to open into the wind, which is the "safe" offheading direction in this situation.

Spot on, but this is why I hate smoke stacks.
Take care,
space

Prone, sometimes... but not guaranteed. (besides, jumping a guy wire A with a delay at which fall rate on opening is less than windspeed - let alone with the wind down the wire, too - is really, really not smart.)

I thought that articles published on blowjobs.com should advocate ultra-safe approach, as they are the resources that mostly beginners read. For guy wire antenna analysis, such an article should state outright that this object has this wonderful property that, like a large arch bridge, it can be jumped with 100% strike-free certainty if the wind is right, and here's how to chose the right wind, and jumping in any other wind is strongly advised against. And it does, in the first part of the wind chapter. But then it has this sketchy suggestion that wind down the wire is safe, too.

I don't know the history of this article, maybe it was written in its entirety by some young guy smoking some good Canadian stuff ;), or, as "Wiki" name suggests, some other guy smoking some other good stuff inserted this paragraph about the wind down the wire.

If you're teaching students and saying things like these about wind down the wire, I want to try your stuff.

Yuri

The articles database is user modifiable. Anyone can submit a change to it.

If you want to write an update, have at it.

If you've discovered any guarantees in BASE, I'm sure lots of people would love to know them.

Tom, one of those [multiple] guarantees is actually the topic of this thread.

You don't know any guarantees in BASE? Has you account been hijacked or what?

wow. this entire thread is retarded. you guys can over complicate and argue about anything.

climb the tower. if the winds feel good to you on the climb, jump. if not, climb down. the end.

all the math in the world is not going to mean shit when you're up there crapping your panties for an hour while contemplating all the "what ifs" you read on dipshit.com and "but the weather report said it was this!" while everything below you has changed.

fucking man up or go home.

smooches.

That bout sums it up folks.