antenna wind direction

[guest]

Low timer. havent done antennas, but im a child of Blinc, so im not clueless. Only question remaining is how perfect wind direction needs to be. Have found an antenna but wind is often a bit off. Jumping off with the wind at my back, the wind bisecting the wires is optimal I know, but what if the wind is not perfectly bisecting the arc defined by the wires? How much crosswind should i consider acceptable? I know this will depend on the wind speed--stronger the wind the higher necessity for the wind to perfectly bisect the wires, and I know not to jump if the wind is running down the wires. Is there a formula here or are we back to testosterone levels? thx

[guest]

What delay are planning to do?

If you're opening relatively shortly after exit, you're going to be closer to the tower and the wires. Wind direction will be more critical here. Cross-winds can affect the canopy opening direction and your reaction to any off-heading openings will need to be faster. So, for short delays off a tower with wires 120 degrees apart, you probably want the winds to be in the middle 30-40 degrees somewhere. As you gain experience, you can widen that some.

Now for wind speed. Too strong of a wind, even a direct tail wind, isn't a good thing. Consider a windsock - it has a tail which creates drag causing the opening or "nose" of the windsock to turn into the wind. Your canopy's tail also creates drag (more so with the DBS you should be using). The last thing I want is the nose of my canopy turning into the wind after a short delay off of a tower, so I personally prefer lighter winds on low towers. That way, no matter what direction the wind is coming from (as long as it is inside my acceptable range), it is less of a factor.

If you're going higher and going to be taking a bit of a delay, you should have better separation from the tower. Wind direction and strength will be a bit less of a concern here. That "acceptable range" quickly widens. On tall towers, I personally don't mind the winds too much as long as they are in a jumpable sector. Down the wire is even acceptable for me as long as they are fairly steady and are not shifting direction. I think of it this way: Winds blowing directly down a wire don't hurt you - They just don't help you. In stronger winds near a wire, I track a bit toward the "upwind" wire - perpendicular to the wind line. The result is an opening in the center of the sector.

To hit an object, you must first be near it. Climb high, track far, open low...

Mark

[guest]

The big issue here is: Can you deal with an offheading?

In general, as long as the wind isn't straight down a wire, you'll be ok. Also, the stronger the wind, the more off-center is acceptable.

So, if the wind is howling at opening, and blows halfway between the wire and the "optimum wind direction", you'll be fine. If the wind is very light, then you ought to make sure you can track away from the antenna.

Basically, the wind makes antenna jumps safer--once the wind is dead, you've lost your best friend. If the wind would blow you into the wires (or structure), then your friend has become your enemy.

Bottom line: A bit of variance is ok. More variance is ok with more experience and comfort. If you aren't happy with the wind on any particular jump, climb down.

Let me know if this is all confusing, and I'll try to elaborate.

--Tom Aiello
tbaiello@ucdavis.edu

[guest]

For short delays, you can try to position yourself to open between a pair of guy wires.

One of the worst case scenarios is jumping with the wind down the wire, which requires more skill and knowledge to do safely. For example, if you jump with the wind down the right wire and you have a 90 degree off-heading to the right, it's easy to make a couple mistakes. If you correct to the left (if the winds are strong), you can easily hit the wire with the turn elongated by the wind. A better choice would be to correct right and face the tower, back up if needed, and continue to turn right.

That's all for now. I've gotta get back to work.

[Yuri]

Yo !

>"stronger the wind the higher necessity for the wind to perfectly bisect the wires"

This is a very common misunderstanding about antennas. Let's have a look:

The most dangerous condition is no wind at all (just when it feels so peaceful and safe...). After an off-heading opening you will be flying towards either of the wire sets at your canopy's speed in brakes.

Any wind down the wire is a much better case. If you open facing the downwind wire, you speed vector towards it is still your canopy's forward speed. If you open facing the upwind wire you are flying roughly at your canopy's speed minus the wind speed. Stronger the wind, safer you are. In a strong wind (at or above you canopy's speed) exiting almost parallel with the upwind wire (0..30 degrees off) gives you the most safety margin: 90..120 degrees free sector on the downwind side. The upwind off-heading is safe because you have no penetration and/or your canopy will be backing up. You will also open a bit further away from the downwind wire.

Obviously, the safest situation is a strong wind exactly between the wires.

Draw yourself a little picture with 3 lines at 120' angles representing the wires and 2 vectors representing speeds and directions of your canopy and the wind. Add these 2 vectors and everything will suddenly make sense. If their sum is pointing away from both wires no matter what direction is your canopy, you can throw a monkey off safely. Otherwise some prompt steering response will be required in case of an off-heading opening.

You must consider the wind at your opening altitude - NOT at your exit point. The wind will frequently turn as you climb up (usually to the right in the Northern hemisphere and to the left in Oz). Sometimes it turns enough to cross into another sector, and will be a big mistake to follow the wind and exit on the wrong side of the wire.

bsbd!

Yuri.

[guest]

thanks yuri for your explaination. i've had a friend tell me the same thing for years, but until now, i've never had a second opinion that i trust like yours. he has over 1000 base jumps most all from towers and i've never known him to climb down just because the wind was blowing down the wire. on the other hand, i've climbed down more than i've jumped which is why i only have 200 jumps. what you say makes perfect sense but it seems that the rule of thumb from the teachers of the sport has always been to climb down if the winds are more than 30* off center. maybe i'll get my nerve up and try it your way.
p.s. i got to see the video of your record breaking wing suit dive from the tower, AWSOME DUDE!!
base rigger