High/Gusty Winds

[skykittykat 0]

I wandered down to the dz today with no intention of jumping as the winds were over 25.

When I got there, the winds were gusting around 8- 25.

I did notice several people turn very low to the ground on final. It scared me as these guys were turning low in high winds, but what if the winds suddenly had dropped whilst in that turn?

A friend of mine was jumping back to backs and on the first of their sequence, the winds were 25 - when they landed on their 2nd jump, the winds suddelnly dropped to 8 adn my friend, who normally lands in the same spot every time (20,000+ jumps) got caught out and landed on the concrete.

I asked him for his thoughts on turning low in high winds and he agreed with me, what are your thoughts?

I posted this as it may be a good learning curve....

Liz

[DShiznit 0]

25 steady winds - jumpable

17mph gusts - hell no

just my little low time jumper opinion

[riggerrob 643]

Strong, gusty winds provide great entertainment for grumpy old tandem instructors who sit them out.
It is way more fun to watch young guys drag through cactus!

[nicknitro71 0]

The heigth of your hook does not depend on wind speed. If you do a 270 at 500' with no wind then you do a 270 at 500' with 25kts wind.

The only thing that varies is the horizontal set up hence more up wind relative to the target in high winds, that's all.

Memento Audere Semper

903

[billvon 2,991]

> The heigth of your hook does not depend on wind speed. If you do a
>270 at 500' with no wind then you do a 270 at 500' with 25kts wind.

This is true if (and only if) the wind is 25kts at the surface and 25kts at 500 feet. This is often not the case. In most places, the last 200-300 feet see a significant decrease in wind, especially if there are trees/powerlines/hills/crops etc around. I'm not talking about turbulence; I'm talking about plain old friction between the wind and the surface of the earth. That's why winds are almost universally stronger the higher you get, and why windmills have to be as high as possible to be effective. The rule is that the rotor had to be at least 30 feet above the tallest object around.

Dennis Pagen's book "Understanding the sky" is a great reference for this sort of stuff.

What does this mean to a swooper? It means that if he starts a 180 in high winds, he will get to his normal planeout altitude with less airspeed than he expected, since the winds have dropped with altitude. If he does not anticipate this he could end up without enough airspeed to pull himself out of the corner.

[nicknitro71 0]

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What does this mean to a swooper? It means that if he starts a 180 in high winds, he will get to his normal planeout altitude with less airspeed than he expected, since the winds have dropped with altitude. If he does not anticipate this he could end up without enough airspeed to pull himself out of the corner.

This is not true. The air speed is going to be the same; the ground speed is going to be different. A canopy that flies at 20kts will fly at the same air speed downwind, upwind, and crosswind regardless of the speed of th.e wind. The only thing that changes is ground speed.

Memento Audere Semper

903

[tsisson 0]

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This is not true. The air speed is going to be the same; the ground speed is going to be different. A canopy that flies at 20kts will fly at the same air speed downwind, upwind, and crosswind regardless of the speed of th.e wind. The only thing that changes is ground speed.

Incorrect...abrubt changes in wind speed will affect the speed at which the air encounters the nose and leading edge of the canopy.

To visualize hypothetically: Imagine if there was a 20 mph wind coming directly from the north above 100 feet, and 20 mph wind coming out of the south below 100 feet and you flew your canopy through this shear zone. Flying to the north...the airspeed of the canopy above 100 feet is approx 20 mph, below 100 feet it is instantly zero and the canopy is no longer flying rather falling.

This is the concept of Windshear that has taken down airliners on final (remember Delta Airlines DC9 in Dallas, TX...or the Eastern Airlines flight that crashed in Denver).

Your wing will not instantly maintain airspeed through turbulence or changing wind directions.

[billvon 2,991]

>The air speed is going to be the same . . .

Incorrect. The air speed is going to be _less_ because the airspeed changes with altitude. It's like landing just behind a massive wall facing into a 5 kt wind. When you get below the lip of the wall, you're going to lose the wind and drop. How fast/hard you drop depends on how your canopy reacts to the loss of airspeed. While your canopy does not care about wind, it cares very much about sudden changes in wind, because that means sudden changes to the airspeed it sees.

The same thing will happen if you start a hook at 500 feet and the wind is less at the surface. If the wind is 25kts at 500 feet and 20kts at the surface, and you are hooking downwind to upwind (which is normal) you are going to lose that same 5 knots of airspeed. If you have left yourself enough margin you'll probably be OK. If your usual swoop leaves you deep in the brakes as you pull out, you may not have enough recovery power to save yourself from injury.

>A canopy that flies at 20kts will fly at the same air speed downwind,
>upwind, and crosswind regardless of the speed of the wind.

That is true only if the wind does not change with altitude. If it does, all bets are off.

[nicknitro71 0]

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To visualize hypothetically: Imagine if there was a 20 mph wind coming directly from the north above 100 feet, and 20 mph wind coming out of the south below 100 feet and you flew your canopy through this shear zone. Flying to the north...the airspeed of the canopy above 100 feet is approx 20 mph, below 100 feet it is instantly zero and the canopy is no longer flying rather falling.

I still don't agree

If we assumed the canopy flies at 20 mph heading north here is what we have: above 100' the airspeed is 20 mph and the ground speed zero. Below 100' the airspeed is still 20 mph and the ground speed 40 mph.

Memento Audere Semper

903

[billvon 2,991]

>above 100' the airspeed is 20 mph and the ground speed zero.
>Below 100' the airspeed is still 20 mph and the ground speed 40 mph.

How do you accelerate to 40mph in a fraction of a second?

[nicknitro71 0]

I am with you that at the windshear (the space between the two moving masses) you will encounter turbolance but this is due to updrafts and downdrafts caused by the friction between the two air masses. The drop of the canopy is related, in part, to the height of the windshear and that unfortunately can vary quite a bit.

If the windshear was a fine line (like you are trying to picture it) then the drop of the canopy would be minimal.

The bottom line here is that nobody should hook lower in high winds.

Edited to add:
Few months ago I was going through a windshear with my S3. We had 35kts NW upper and 5-10 Kts S ground. The windshear was at about 5k. Upon entering my S3 dropped down and stalled. It took me about 2k to regain control and pull.

Memento Audere Semper

903

[ianmdrennan 2]

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The bottom line here is that nobody should hook lower in high winds.

Absolutely, 100% positively true.

High wind, low wind, I start my hook at the same height. Granted a SUDDEN decrease or increase in airspeed will cause either a high or low approach but I don't jump in conditions like that intentionally.

Blues,
Ian

Performance Designs Factory Team

[billvon 2,991]

>The bottom line here is that nobody should hook lower in high winds.

So I guess we disagree on the details but agree on the big picture.

[tsisson 0]

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I still don't agree

If we assumed the canopy flies at 20 mph heading north here is what we have: above 100' the airspeed is 20 mph and the ground speed zero. Below 100' the airspeed is still 20 mph and the ground speed 40 mph.

The problem is that the transition isn't instantaneous...the canopy needs time to accelerate back to it's normal flight speed as related to the relative wind. At 100 feet, the transition time is greater than the altitude available and you will impact the ground under a canopy that is not producing lift.

Again, the point should be clear that hooking in adverse conditions can set you up for catastrophic canopy collapse at an unrecoverable altitude. Please don't do this...

Where's John LeBlanc and Brian Germain when we need them?

[teason 0]

The change in airspeed will affect the lift on the wing until the wing can accelerate and that will sometimes require the canopy to dive.
The ammount of lift is directly proportional to windspeed and in gusty conditions, the airspeed can change (dangerous on the landing).
Example; We had a beautiful day at the DZ, winds were 7 mph out of the north and it was getting close to lunch, it started to get quite hot.
A 180lbs student under a ZP 290 was faced into the northwind. at about 10-15' the student flared at the same instant a thermally genrated wind gust hit him from the south (behind) at about 5 mph. The resulting change in canopy airspeed caused the flare to be totally useless and the canopy dropped out of the sky. The student suffered a broken back.

If a 180lbs jumper can can break his back under a ZP 290 Manta, then obviously jumping in high wind gusts and performing high performance landing is lunacy.

Yeah, I'm one of those grumpy old guys. It's one thing to know how to do high performance landings, it's another to know when not to do them.

I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet.

[nicknitro71 0]

I am very well aware of wind gusts: I broke my ankle and two vertebrae due to one.

The points I am tying to make are very simple actually:

-Don't hook lower in high winds because your canopy will lose the same altitude not less

-Windshear is not a fine line, it's a space that can be as high as few thousand feet.

-The main cause of turbolance in a windshear are the up and downdrafts

That's all.

Memento Audere Semper

903

[Jeth 0]

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What does this mean to a swooper? It means that if he starts a 180 in high winds, he will get to his normal planeout altitude with less airspeed than he expected, since the winds have dropped with altitude. If he does not anticipate this he could end up without enough airspeed to pull himself out of the corner.

This is not true. The air speed is going to be the same; the ground speed is going to be different. A canopy that flies at 20kts will fly at the same air speed downwind, upwind, and crosswind regardless of the speed of th.e wind. The only thing that changes is ground speed.

I saw the debate on this point about air speed vs. ground speed. As an FYI -- I was just at a Scott Miller seminar on Saturday and he said EXACTLY the statement above. That air speed stays the same, and only ground speed changes with the wind.

"At 13,000 feet nothing else matters."
PFRX!!!!!
Team Funnel #174, Sunshine kisspass #109
My Jump Site

[billvon 2,991]

>I was just at a Scott Miller seminar on Saturday and he said EXACTLY the
>statement above. That air speed stays the same, and only ground speed
>changes with the wind.

People are confusing ground speed/airspeed and wind shear. Wind shear is real; it has caused 747's to crash, and it can cause a heck of a lot more trouble for us.

If you turn from downwind to upwind in a _steady_ 20kt wind, your canopy does not know the difference. If you do the same thing, but the wind started out at 20kts and ended up at 10kts because you are close to the ground and got that friction-induced shear, you are going to lose a lot more altitude in the turn, and come out of it with less airspeed. If you don't leave yourself sufficient margin, that can prove to be a painful or deadly mistake.

[klafollette 0]

I think the thing we are all forgetting is that we and our parachute have mass, and thus take time to accelerate/decelerate when a force (the wind) acts upon us. With wind in a steady-state as we turn, our body/canopy have time to accelerate (relative to the ground) as the wind shifts from headwind, to crosswind, to tailwind. If that turn is made gradually enough, you will experience pretty much a constant airspeed regardless of the wind speed/direction (ignoring for the moment all the lift vector stuff that causes us to accelerate in a turn).

Now consider that you are flying in a 10 mph headwind (groundspeed), and your canopy has a normal gliding airspeed of 20 mph (airspeed). Your ground speed will then be 10mph. Now you fly into a wind shear with a 10 mph tailwind (groundspeed). Under the right conditions, you could encounter that wind change in less than a second as you drop through it. As the wind changes 180-degrees, you aren't going to instantly accelerate to a 30mph ground-speed, maintaining the 20mph airspeed. Until you and your canopy have a chance to accelerate, your canopy will, for a few moments, continue to have a ground speed of 10mph, but now with a 10mph tail wind (ground speed) and actually experience an airspeed of 0 (zero) mph until you start to accelerate. That could potentially stall your canopy or cause an end-cell to collapse, until it accelerates to the normal 20mph windspeed.

Same principle would apply with gusty winds. Air can accelerate/decelerate very quickly (compared to us) and a 10-15 mph change can hit in an instant, while your canopy takes time to react to that wind. for that instant a portion of your canopy can have a dramatic change in the relative airspeed, causing a stall, lift imbalance, turning moment, all sorts of bad stuff, and usually at the most inopportune time