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Inspired by a comment Tom made on the accident thread.

The only B jumps I've not done so are those in which I got to see previous jumpers. Even then, I usually did so (the most notable exception being organized events where there was a large string of jumpers to observe).

Not ever being in any particular hurry I've always thought that for buildings;

The best wind is no wind . . .

You can throw all the WDIs you want that show the wind in your favor as you launch, but if you have a (who knows what) problem after deployment, that wind can then conspire against you.


NickD
BASE 194

Rule of thumb in Ohio: Let the person with the least jumps go first!

no thanks.

I usually wait to see if NCjumpjunkie's roll over goes well.

And when that first guy is up there looking over the edge, pc in hand, keep whispering "I'd have gone then, You coulda gone, Go now."

hence the name "space monkey"
hahaha

In paragliding (yes that again) we call the first person to launch... wind dummy!

I agree. Usually when I jump the B's I have (9 jumps off of 3 different, so bear with my inexperience), it was dead calm, no wind at all. On two occasions, at one of the less congested buildings (no surrounding buildings being a factor), I have jumped in probably 6 mph once, and about 8 mph another. What I was checking for (with WDI) was anything but a clean constant wind, no swirls, updrafts, downdrafts. I know SO little about it, that this is also meant for some critique/insight by anyone who can enlighten me on the subject. Could I be setting myself up by my false comfort in thinking a little push from behind (300 degrees from exit on a corner, so pretty much a tailwind) would actually push me away from the object in case of an off heading? Am i even making sense? hhmmm...
A

If you are on the far downwind side or corner of the building, and there is sufficient wind, the downwind rotor (think of it as the buildings "burble") can actually create a push back against the building at opening altitude. In these (general--I can't speak to any specific case without knowing a lot more about it) conditions, it's better to jump the side corner, so that your deployment happens in cleaner air (i.e. not in the buildings "burble").

Hey can you give the definition of WDI. I've seen it in videos but don't know the name.

So your saying on a "B" I would think on a far down wind side of a B you would have a cross wind + burble from wind wraping around and comming from over top. I'll stick with the no wind. but a responce would be cool. wich side corner? Prevailing winds from the East light an variable.

And for you guys in Ohio be nice to the new guy.

Just curious... For those who have said they only jump in calm conditions, do you know this because you drop a WDI, or just because it's calm at the exit point?

Michael

Wind Drift Indicator

I have 5 jumps from a 200' object that is solid concrete and 4 square corners. Very similar to a building. The exit point however, is in the middle of one of the sides (not a corner). I have dropped wind drift on all sides of the object just to see what happens. The down wind side was the most intresting. WDI went away fom he object, then down and twards the object, then hit the object and came right back up the wall to the top and started over agian. Wind was light, 5 mph on ground and less then 10 on top. My thought is no wind seems best, 90 deg cross wind is the best option if there is light wind, tail wind is a gamble and maybe your best shot for a jump that is anything but ordanary. How do some of you feel about crosswinds and B's.

We are very nice to the up and commers in Ohio. We advise them not to jump these types objects until they demonstrate the approiate skills nessary for a safe outcome. Most of us have around the same jump numbers and we usualy (let) the lower number go first.

he he... 6 mph. weeeee.

Yep. Pretty much.

Unfortunately, you can't answer this question without actually seeing the object, and it's surroundings.

Postulating a theoretical building, which is a perfect cube, 300' on a side, situated on a perfect north-south axis, with no other obstructions or turbulence generators of any kind (i.e. this building sits alone in a flat field that extends to infinity in all directions)? With wind coming exactly from the east, you'd want to exit either the northwest or southwest corner, exiting toward the northwest (or southwest) at approximately a 45 degree angle.

Obviously, there are way too many variables involved in evaluating a real building for us to try to do such a thing via internet postings.

If you're really interested in sorting through these kinds of winds, I'd recommend two things.

First, read a couple textbooks on fluid dynamics--especially the kinds with pictures.

Second, go find a real building, and bring a long a pack of helium balloons and a couple bottles of talcum powder. Stand on the roof and have a friend release the balloons at intervals from a series of locations below you, and watch them. When this gets dull, start squeezing the talcum powder over the edge from a variety of locations, in a steady stream.

Even the people who have Ph.D.'s in this kind of stuff, and work in turbulence laboratories, don't have an exact handle on it. The best we can hope for, at this point, is to develop a good feel for the general principles.

White water kayaking is another great way to learn about reading eddies and rotors. It's not quite like moving air, but there is significant overlap.

Also, there is a neat little application on this website. A direct download to the executable is here. It allows you to draw obstacles and see how they affect the fluid flow. It seems to handle eddies and rotors pretty decent.

Obviously there is no way this comes close to what happens in three dimensions, or reality for that matter, but it's still fun to play with for a bit.

I've been meaning to write something like this myself so it allows you to remove obstacles and set wind direction and strength, but I'm too caught up in jumping.

Cheers,

Jaap

Consider of course the shape of the building. A round building won't have as severe of a turbulent zone. Also consider the presence of other nearby buildings, which can be a dominant factor. Additionally, consider the presence of small building(s) upwind of the building to be jumped. The 'wind shadow' of a building can be unique to the object and to the wind direction and wind speed. There are some buildings where you will experience a direct headwind given a perfect on heading opening when jumping on the downwind side. The downwind side is not necessarily the best or optimal jumping side or corner.

There are a lot of indicators around said B that suffice, flags and such. Never dropped paper though, not on one, have every time on another, described earlier.

Great toy... someone needs to write a more complex one(and still generally accurate for any given reynolds number) asap......