tail wind on 0-1 second delays?

[rfarris 2]

I may be way off base here, (no pun intended), but is there such thing as too much tail wind on short delays. And I'm not talking about hurricane force winds here, but maybe something in the range of 20-30 mph tail winds.

Just curious as to what are other people's limits on winds , and why?


Rod

[CrazyThomas 0]

A more specific scenario may be helpful. Tail wind on a short delay, with how much height?
Off what type of object (letter only please)?
And, what else are factors?

For instance, an "S" jump, it may work to jump with a 20-30 mph tail wind. Now, here is the tricky part. Can you be comfortable handling a 20-30mph down wind landing? and can avoid obstacles? or pull a quick 180 turn into the wind?
I have heard that tail wind decreases canopy inflation time. So, if you are considering ULTRA LOW objects,....YES, TAIL WIND is a big factor.
Maybe someone with more knowledge or experience can add to this discussion.
I would just say that a tail wind of 20-30mph is always a factor. Consider this type of jump carefully, many times, and be not afraid to walk away.
Tiz easier to walk away wishing you had, than to limp away wishing you hadn't.
Peace,
Thomas

oh, and on wind limits:
Tokemon says:
"If it's too windy to smoke, it's too windy to jump."

[rfarris 2]

Thanks for your response Thomas.

More specifically, my object is a 320' freestanding "A", with open landing areas on three of the four sides . The possible downwind landing I'm aware of, and have done. But then again, the times I've jumped it, the grounds winds have been next to none. but I was curious if a high tail wind at the platform has an effect on canopy inflation, heading, or PC entanglement?

Rod

[Faber 0]

I normaly jump 400ft A.I have noticed that too much wind on slider off/deepbreak can course that the tail of the canopi can break(so it looks like an u layingdown)That mean that the tail goes under the the chute.This is dangereus near ground,Take the togles and near stall it(beaware of the object behind),then if you are lucky you can safe your self.
I have never tryed it where the canopi are half under half but have tryed that it were starting to get under.

Please be aware that im a newbie and it migth be wrong what im writing now(while it based on my few jumps).Pleace Tom and D-Dog say your oppinion to this subject.

Stay safe
Stefan Faber

[mickknutson 0]

Quote

I may be way off base here, (no pun intended), but is there such thing as too much tail wind on short delays. And I'm not talking about hurricane force winds here, but maybe something in the range of 20-30 mph tail winds.

Just curious as to what are other people's limits on winds , and why?


Rod

You really should be asking these advanced questions to the audience at BLiNC.

Mick Knutson
* BLiNC Magazine "Everything you ever wanted to know about Parachuting, but didn't know whom to ask."

[460 0]

I've done these jumps many times, from 400' or less from antennas. There are a couple issues:

use a tailgate, especially since 1) you canopy opens tailfirst 2) the tail will inflate quite uncontrolled way with such a strong tailwind, leading to a possible lineover.

be careful about going stowed. handheld has always been reliable for me in these situations, despite the danger of working with a pilot chute in high winds.

note your landing area: power lines, other hazards. I did one jump and the canopy opened in a downplane because of the severe tailwind. it also opened 90 to the right, toward the landing area covered in power lines. i lost a lot of altitude in the downplane and turn, but still made it fine. any uncertainty on my part though could have been a real problem.

you can minimize the effect of the tailwind just by taking a slightly longer delay. at 1 second, your going 20mph. at 2 seconds, almost 40mph. (the charts posted by Vertigo, Basic Research, are incorrect for delay vs speed [I'm a physicist]).

If your landing area is cake, no worries. if not, imagine all scenarios and memorize your actions thoroughly beforehand.

Good luck.

Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174

[TomAiello 26]

I've added a few thoughts on deployment stall, which can be responsible for the downplane-on-opening phenomenon, to the discussion on BLiNC.

A deeply braked canopy deployed in a tailwind may stall immediately, and dive to recover relative airspeed. While disconcerting, this is only really dangerous on low and/or advanced objects.

-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

[460 0]

Tom, I'm not sure I understand what your saying.

In a stall, the canopy should just fall out of control. I don't know why it would dive forward despite the action of the tailwind on the fully inflated canopy.

From watching other people, it looks more like the pilot chute goes so far in front of the jumper when pitched in high winds, so that the canopy is just deployed sideways and not vertically, leading to a downplane.

Looks like a death sandwich without the bread - Steve Deadman Morrell, BASE 174

[TomAiello 26]

Quote

Tom, I'm not sure I understand what your saying.

Here's the phenomenon I've seen. Adam (CR) described it to me as "deployment stall" when I discussed it with him.

The brakes are quite deep. You are deploying in a tailwind.

As the canopy deploys, it "sees" the relative tailwind, and this reduces it's forward speed during inflation. The canopy's speed, relative to the (tail)wind is below the stall speed of the wing.

The wing stalls, and becomes a "jellyfish", essentially sinking.

The tailwind pushes the (partially inflated due to pressure on the bottomskin) canopy forward.

Once the "jellyfish" begins moving forward, the relative tailwind is decreased (i.e. speed of the canopy relative to the airspeed increases).

With increased airspeed, the canopy inflates, and begins to fly.

Basically, the wind pushes the stalling canopy forward (and it falls), inducing a dive, which re-inflates the canopy.

I've only seen this happen between five and ten times, so my knowledge of it is relatively thin. It is my understanding that a canopy with overly deep brakes (but not too deep) deployed in calm air can behave in a similar fashion.

-- Tom Aiello

Tom@SnakeRiverBASE.com
SnakeRiverBASE.com

[DJL 235]

Like a hop and pop (extreme example) except w/ head towards ground vs. towards sky while still on the hill? In engineering terms, the normal force has magnitude along the X axis (horizontal) until all mass has reached equilibrium with the wind relative to the launch point.

"I encourage all awesome dangerous behavior." - Jeffro Fincher