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So we went out to the local stick the other day to make a jump. The winds were perfect during the entire climb up. But once we got to exit point at 1800 feet, we realized that the shadow from the antenna was right down the wire so we decided to climb down. Has this happened to anyone else? What would you do in this situation? See the attached photo.

As far as I know there has never been an incident involving shadowed-wire visibility and depth perception. But the ability to see the wires, as well as the ability to distiguish from the shadow and the wires while flying a wingsuit can make for a bad day. The good idea is to either climb down, or wait for the possibility for the shadow to move far enough away from the wires so they can be identified.


i was in that situation a month or so ago. I made the decision to climb down from 1600' but after I got to about 900' I looked at the shadow again and it had moved about 3 degrees off the wires, so I climbed back up to about 1300 and flew. weirded me out though.

... Plus there's photon pressure to think about.

Consider the analogous situation of a freefall jump in a crosswind, where any relative wind from the side at opening will cause an off-heading toward the upwind side. The effect is more pronounced on short freefalls, where the jumper hasn't had time to come to rest (sideways, anyway) relative to the air mass -- the magnitude of the effect is proportional to the relative speed of the wind (again, sideways) at deployment time.

Now, with light the problem is even more serious. Not only does light travel much faster than wind (imagine a 1.08 billion km/h crosswind), but Maxwell's equations tell us that its speed is actually independent of the jumper's velocity, with the consequence not only that neither space nor time can be considered in isolation from the other, but also that its effect on your canopy's heading performance is actually independent of delay. Furthermore, your off-heading will be toward the sun (ie, toward the other wires) and in calm winds you'll be closing quickly.

Photon pressure is going to be particularly significant on brightly-coloured fabrics, and (due to atmospheric absorption and photon momentum) for green and blue canopies. If you've chosen a rainbow colour scheme, clearly things are more complex.

Climbing down in good conditions due to a shadow wouldn't cross my mind so I'd jump it. In fact the shadow marks one set of wires quite nicely. Don't track toward the shadow.

That's what I'd do.

Edit:: I must edit because 736 makes a great point. Colors are important.

I feel this is not covered enough in FJC's or mentor/apprenticeships across the board. I think everyone should add at least general electromagnetic physics to the syllabus of their courses. I am glad this was brought to light.

Brought to light....no pun intended I am sure.

don't be obtuse. we are talking about safety here. of course no pun intended.

Forgive my possible exposure of ignorance, but what does a shadow have to do with anything at all? Are some people using the shadow as some kind of directional on this A?

Personally, I think our crew would have jumped that fucker and not given the shadow a second thought other than it would have made a good picture.

For that sake, we've all jumped in near total darkness and had no visiblity let alone a shadow.

i would never climb down from an antenna because of shadow placement. it doesnt make any sense at all to me.

Please tell me this is some horrible joke....

What would you do at night....?

That's fucking funny. You didn't jump because of a shadow:)

I was just going to ask Ian if he's being serious?

Ian, did you really climb down or are you messing with us? Either way it's funny.

What if I jumped shirtless or nakid and I have a lot of tattoo's with many colors...?

If they were not equal on both sides of the body... that could make you have am offset exit dependant on if it was before or after 12 noon?

Seriously? Even with a purple pilot chute? I'll shoot video.

don't be ignorant. there can be extremely negative visual interference from linear electromagnetic blockage.

anyone who jumps at night is asking for it. dangerous. quit being sketchy people.

that is what is wrong with all the old schoolers. (BASE #'s below 987)

you can't see the newly discovered possible safety issues, get with the times bra.

jump with slambo : )

Does he cast a shadow?

what would i do?
i could honestly say that this whole shadow thing would never cross my mind in a million years! i had to re-read the post because i didnt even understand what the hell you were talking about.
im guessing this is a joke or you only jump a's in the daytime. even then...
ITS A FUCKING SHADOW!
however if this is serious and you didnt feel good about the jump then you did the right thing by climbing down

i guess.

P.S. read your bio. DO YOU REALLY JUMP A WONDERHOG? you must see the irony of jumping a wonderhog but not jumping because of a shadow!!!!

the irony...
jumping a wonderhog
but not jumping because of a shadow!!

Ha ha ha

you cant be serious...

you climbed down 1800 feet? from 1800 feet i dont really care what the winds are doing. much less where the shadow is..

you should be stoked your jumoing an antenna in the daytime. fuck the shadow.

Thanks everyone for the information, especially 736. I have a few more questions for you; now that you brought up the photon pressure effects in regards to canopy colors. I have different top and bottom skin colors so what kinds of effects can I expect to happen on deployment? Since my center cell is an opposite color will it have minimal effect because it is in the middle and mot off-set? Also my ribs are different in color. Is this going to cause greater atmospheric absorption? Further more, will the photon momentum differences cause issues in the deployment and pressurization sequence. Thanks for your knowledge, these topics were never covered in my FJC and I am glad these issues are starting to be cleared up.

True that.

unless by shadow you mean ground, and the ground was covered in lions and tigers. then i probably wouldnt jump.

FJC's teach fundamental survival skills. they can't teach everything without totally confusing students. they basically hide the photon pressure under the concept of "know your canopy." if you do enough practice jumps on it, you sort it out.

Fully made the right decision. I mean wow!! That could've been a magnificent jump, instead it must have been a fabulous downclimb!! Thanks for bringing these safety issues to our attention! People like myself need this sort of guidance in our new found pursuit of joy

Again thank you, very wise decision indeed!!

Dude, turquoise stabilizers are black death.

So theoretically, If I were to jump a free stander the position of the shadow wouldn't matter as much since there are no wires for the shadow to intersect with?

I think I'd still be a little tempted.

Your first post in this thread was great stuff Ian. Keep it up!

are you scared of your own reflection too? why in the world would anyone climb down due to a shadow?

So they say. You'll "sort it out" about like you could be expected to sort out how many clamps to use on your packjob, or whether to use a 42" or a 44" pilot chute from 500'. That these things aren't stressed in every BASE course is negligence, plain and simple.

Regarding Ian's canopy colours... Your colour scheme looks mostly great. It's symmetrical -- first rule of jumping in the daylight -- so that you shouldn't see any heading issues due to photon pressure. The use of light-coloured fabric on the bottom and dark fabric up top is wise, as well. Light fabrics up top can cause excess topskin pressure in sunlight, leading to an early stall in daytime jumps and making the canopy generally handle a little like it hasn't fully pressurized. If you've been having hard openings on this, you might try a darker bottomskin. The green ribs will do a lot to promote pressurization, too, and shouldn't have an effect on opening shock (which is mostly a matter of bottomskin inflation).

To tell you the truth, I'm not sure what to make of the blue center cell. Have you jumped this in daylight yet? It's important to remember that just having your colours symmetrical is not enough. A contrasting center cell like this may cause a tendency to bowtie spontaneously, or it may promote center-first inflation. I'd definitely talk to the manufacturer about it.

Thanks for the valuable input 736. The reason I went with the blue center cell is because I was told by the manufacturer that it would increase the amount of pussy I received 3 to 1 over any other color combination.

... And how's that working out for you?

Can't complain.

I would have thought you realized that subtle truths exist in folklore. from "being afraid of your shadow," through the groundhog deal, there are plenty of allusions to photon pressure and shadows.

frankly, I'm kinda shocked you missed this one.

460 is a blonde....
386

lmao. Funny shit, Ian.

Ahhh, if I only had a dollar for every time I got shadowed of an antenna

+1

so wait, is this some sort of joke? haha jokes on me if it is.
if a shadow makes you climb down 1800 feet of ladder then truthfully i think you may be in the wrong sport.
if this was a joke you can laugh at me though.

I walked onto a building under construction at noon one time. No body said anything at first, but when I was in the elevator on the way up the guy asked me what I did there. I told him electrician, but he wasn't buying it cause I didn't have a hard hat, and I think the stash bag over my rig, and the leg straps that were totally visible seemed kind of weird to him. Luckily he didn't dive into the conversation until we had been in the elevator for a while, and the door opened at 40th floor as he was starting to realize I was full of it and probably shouldn't be there. I started ignoring him and walked out. He was saying wait a sec, you can't be here, I walked up the stairs and out on the roof. Other people were out there working on the roof and started watching the commotion he was making and then started moving in on me like they were going to help stop the criminal or something. As I got to the edge thinking, this is gonna trip them out, I looked down and realized there was a shadow in the landing area. Fuck! Bastards grabbed me and held me till the cops got there.

Dude, I am with you, the shadow shit seemed
like a joke to me too and then they started to
push it to colors affecting stuff then I know it
was either a joke or bullshit.

So Dave, you got pinched?

Funny, Exactly the same thing happened to me after reading this a few days ago. Jumped it anyway.

No. It was an elaborate story (like I'm sure most of this thread is) to joke about how stupid it is to not jump because of a shadow.

The shadow is only on the topside of the wire. One would be able to see the wire shortly before striking it.
Hope this helps.
Take care,
space

  i watched a program on pbs about solar sails.... so i understand u completely.

 
What about moving shadows cast by a bird or other such flying entity? What would the effect of this be if your canopy passes through the shadow path during descent? might there be momentary depressurization?

Yes, this exact situation happened to me once also....... I aimed away from it