Winds on an 'A' jump

[rendezvous 0]

last evening my buddy and I went up an 'A' that is 315 ft high. The winds on the ground were not more than 0-4mph. At 100ft it was still about 4mph but past 200ft it started picking up. At the top it was probably in the 18-20mph range. The landing area on this jump is huge enough not be to an issue. If we had jumped we would have had the winds coming from directly behind us hence pushing us away from the 'A'. We were going to do a 1 sec delay, hand held, tail gate, slider down, 47"PC. Our concern centered more around the effect of 18-20mph winds on the pilot chute throw, the pack job extraction on opening, canopy inflation, turbulance due to wind shear around 200 ft where the winds seemed to start picking up.

Since we were not certain about the impact of such a wind condition we decided to climb down and try and get a better understanding of it first. I would love to hear from the more experienced on the affect of 18mph winds on such a jump. Is 18mph considered strong, border line or not a concern for an 'A' (it was coming from the right direction) Again, the landing area is a big open field so being carried out over it due to the strong wind wouldn't be much of an issue.

[JaapSuter 0]

I've heard stories about Dwain doing floaters off an antenna in 30 mph winds. He opened facing the antenna and was just blown backwards away from the antenna.

As long as the landing area still allows a nice setup, preferably landing into the wind, I would imagine jumping in 18 mph is fine.

See BASE WIKI on antennas.

[TomAiello 25]

Quote

I've heard stories about Dwain doing floaters off an antenna in 30 mph winds. He opened facing the antenna and was just blown backwards away from the antenna.

This is actually very commonly done on one of the regular Northern California objects.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[TomAiello 25]

Quote

...effect of 18-20mph winds on the pilot chute throw...

I don't think that 18-20 is enough to do this, but;

I've had strong tailwinds at exit (30+) blow a stowed PC in front of me, under my arm, resulting in a bridle wrapped around my arm. Under these conditions, you might want to go hand held, and pitch in an upward direction, to reduce this concern.

Quote

...the pack job extraction on opening, canopy inflation...

With very low airspeed, it's likely that the wind will govern your opening heading. I've been on loads in 35+ tailwinds where every jumper had exactly the same offheading opening--directly into the wind. If you have a strong tailwind, and a short delay, be prepared for a 180 (or whatever opening is directly into the wind). A longer delay will generally help avoid this. As a rule of thumb, if your fall rate (relative wind) is less than the absolute tailwind, expect the absolute wind to be the governing factor on your opening. Of course, with a tailwind that strong, a 180 isn't usually a big deal, because you are being blown away from the object quite quickly.

Quote

...turbulance due to wind shear around 200 ft where the winds seemed to start picking up.

That's a big point that many people miss out on. Good on you for thinking about it. Any time the wind changes, there is turbulence. The greater the magnitude of the change, the greater the turbulence. If there is a sharp boundary (as in your case) expect greater turbulence. One strategy for dealing with this is to take a deeper delay (and hence open below the turbulence). That's psychologically easier, but in reality, I don't think it matters much. BASE canopies recover from turbulence so fast that the only turbulence that's really dangerous is too low to open underneath anyway. In this case, my guess is that you would have passed through the turbulence and had time to recover before landing.

Quote

Is 18mph considered strong, border line or not a concern for an 'A' (it was coming from the right direction) Again, the landing area is a big open field so being carried out over it due to the strong wind wouldn't be much of an issue.

18 mph probably isn't too much of a concern on a site like that. I can't say for sure without actually seeing it, though.

I think you made the right choice. You're both still walking around without crutches, and the 'A' will still be there the next time you go.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[TomAiello 25]

Quote

See BASE WIKI on antennas.

I'm pretty sure the BASE Wiki article you are referring him to has no information about his specific questions, at this point.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[JaapSuter 0]

Quote

I'm pretty sure the BASE Wiki article you are referring him to has no information about his specific questions, at this point.

To all; nudge nudge...

[rendezvous 0]

Thanks. This really helps.

[VictorSuvorov 0]

how about a side wind, 15-30 MPH, 1-2 sec delay?
that would be applicable to an A with 120 sector guidewires with the wing blowing exactly down the wire. IMHO the optimal exit direction is 90 degrees to the wind direction into either downwind sector. any thoughts on that?

[TomAiello 25]

Quote

how about a side wind, 15-30 MPH, 1-2 sec delay?

15-30 is a pretty big range. So is 1-2. I'd say that a 2 second delay with 15 mph wind is a whole lot better than a 1 second delay with 30.

1 second delay with 30 mph wind, I'd guess you're going to get an offheading into the wind.

Quote

...that would be applicable to an A with 120 sector guidewires with the wing blowing exactly down the wire. IMHO the optimal exit direction is 90 degrees to the wind direction into either downwind sector. any thoughts on that?

If you know, for certain, that the wind speed exceeds your canopy's forward speed, I don't think you need to stop at 90. Maximum separation from the obstacle you might strike (the tower or the downwind wire) is the goal. If the wind guarantees that you will not strike the upwind wire, you can pretty much exit as close to it as you want.

Can you explain your reasoning on the 90 degrees? I'm thinking it through, and it looks like maximum separation is achieved by exiting as close to the upwind wire (120 degrees) as possible, but I might be missing something.

-- Tom Aiello

[email protected]
SnakeRiverBASE.com

[VictorSuvorov 0]

it is just like swimming through a current, there is no point in fighting it if you want is to get across. Exiting more into the wind will result in a wider safe sector of possible off-heading openings but the separation from the antenna and the downdwind wire will be less.

[jalisco 0]

I agree with the 90 degrees -- ref: this post (crayolas and all)

Basically, a) 90 deg puts you as far as possible from the down-wind wires -- 110 seems further from the down-wind wires, but it's really not, since the wind will be carying you past where they start in short order -- so an opening facing directly at the plane of the down-wind wires puts you closer to striking them with a 110 deg exit than with a 90 deg exit.
b) the diagram in the above post shows that with the right opening you can hit the up-wind wire even if the wind-speed equals (or even slightly exceeds) your canopy speed.

[Nathan601 0]

I used to have a good freestander that I would exit facing it and if the winds cut off I would just turn to whichever side it opened and fly past the side to landing but I jumped facing away and had it collapse on me at a 100' from the wind shear turbulance. And just like Tom, I've had a PC come back at me with the wind.
However, on higher jumps, I often exit normal and turn to track into the tower on high wind days. Almost every jump is like this in the fall for me, here.
SOmething to think about. Both floater exits on a low freestander and tracking up to the steal on a tall tower go against what you learn early and are a bit trippy at first but logically make sense. That is, if you're going to exit on a high wind day in the first place. That leaves some room for thought in itself. I commend the climbing down to ask.

Night Base 107

[Anvilbrother 0]

I was told that on high A's the wind changes direction just a bit from the ground winds due to some type of effect? I am not sure if it was (sp) corolioas(/sp?) or the spin of the earth or something else.

Postes r made from an iPad or iPhone. Spelling and gramhair mistakes guaranteed move along,

[truckerbase 0]

Quote

I was told that on high A's the wind changes direction just a bit from the ground winds due to some type of effect? I am not sure if it was (sp) corolioas(/sp?) or the spin of the earth or something else.

In terms of expectation of winds aloft, the coriollis effect can turn LIGHT winds from their ground heading. If they are borderline on the ground, they could be down the wire aloft...Strong winds carry too much momentum to be affected, in general coriollis doesnt play a major part in Antenna evaluation. Dropping little pieces of spit or paper at various altitudes as you climb, to be intimately aware of what the wind is doing, in order to form a mental wind profile of your antenna on a jump night, is a vastly more important tool. Be aware of the forecast, be very aware of what winds are doing on the ground and at expected opening altitude, and be mindful of whether a wind-line (or wind shear) exists. (Strong winds aloft dropping off sharply nearer the ground to light or calm winds; the canopy may dive to regain a speed necessary to fly if the canopy crosses a wind line, from strong wind to light wind. Your accuracy in landing in a given spot will be influenced by the existence of this effect, and if it occurs closer to the ground, you could lose significant altitude rapidly when you may not have it available. Particularly with you big guys





*******************************************************

[Anvilbrother 0]

Thanks I just needed a refresher on that...Hey what do you mean you big guys?

Postes r made from an iPad or iPhone. Spelling and gramhair mistakes guaranteed move along,

[truckerbase 0]

Quote

Thanks I just needed a refresher on that...Hey what do you mean you big guys?

Well, I thought Aiello probably needed a refresher. Im pretty sure he hasnt been on an antenna in years...


*********************************************

[fab777 0]

The change in direction is mostly due to the proximity of the ground, which slows the air down. Being slower, the air is less affected by the coriolis effect, and thus tends to drift in a more direct manner from high pressure to low pressure.

When observing the ground wind, one can theorically expect the wind aloft (~1000'/2000') to turn 30° to the right and increase by 50%.

This doesn't take local particularities in account.

Fabien
BASE#944

[peterk 0]

Also, tailwind openings will generally be slower, less on-heading, and have a higher incidence of line-overs...

---------------
Peter
BASE - The Ultimate Victimless Crime