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Donít PLF on a downwinder?

 

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Divalent  (C 40494)

Apr 24, 2011, 7:06 PM
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Donít PLF on a downwinder? Can't Post

I ran across this article recently in the Canopy Control section of this website (in the Safety section), entitled ďAn Inconvenient Truth Regarding PLF'sĒ: (http://www.dropzone.com/...tail_page.cgi?ID=729). I searched to see if this article (published in March of last year) generated any discussion, but didnít find any.

In one section of the article, the author argues that PLFs on downwind landings are dangerous, and he proposes (and apparently has taught for many years) an alternative. Hereís a quote of the gist this. ďThere is a solution to this downwind landing possibility. It is easy to train and easily understood by newcomers and experienced skydivers alike. The simplest way to prepare for as many landing scenarios as possible is to assume the PLF position, fly the parachute and slide on one hip in the event of a forward motion, high speed landing

So, if I interpret this correctly, itís not exactly a butt slide, more of a hip slide (like sliding into second base?).

Anyway, Iíd be interested in hearing other peoples view of (and experience with, if any) this technique.


jwynne  (D License)

Apr 24, 2011, 8:12 PM
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Re: [Divalent] Donít PLF on a downwinder? [In reply to] Can't Post

Toally disagree. As a newbie, PLF is the safest way to go. Downwind landings just mean you're coming in faster. PLF for all your worth. With thousands of skydives and a bad knee, I slide in a lot of landings I can't run them out any more. It's not the way to start. There's timing and experience involved and you can break a leg or hurt you back if your timings off or the grounds uneven. Stick to a PLF. It's the more reliable way to walk away.


JohnMitchell  (D 6462)

Apr 24, 2011, 10:40 PM
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Re: [jwynne] Donít PLF on a downwinder? [In reply to] Can't Post

Haven't people died from broken necks PLF-ing on downwinders?

Here's my rule.

If you have a high rate of descent, PLF.
If you have a high forward speed, slide.
If you have a high rate of descent and a high forward speed, kiss your ass goodbye. Unsure


velvetjo  (D License)

Apr 24, 2011, 10:53 PM
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Re: [jwynne] Donít PLF on a downwinder? [In reply to] Can't Post

I've seen a student program firsthand that has very good success with teaching a modified baseball slide for downwind landings. They have students tuck one foot up under their butt and extend the other leg forward. It protects the spine / tailbone somewhat and there's less chance of damage to the extremities than a tumbling "PLF" with fast horizontal speed. Since most jumpers can't do a PLF to Airborne standards even under good conditions, there's a pretty significant risk of head or neck injury from a bad tumble.

PLF's convert vertical motion to horizontal by design, but that's not as much of a concern if you're moving downwind fast. After seeing both teaching methods in practice over periods of years, I'm sold on the modified baseball slide for fast downwinders. Even for students.

You claim the PLF is safer in this situation, but that contradicts my direct experience. I'm curious: what incidents or injuries have you seen from actually teaching students the slide method that formed this opinion?

Lance


kuai43  (C License)

Apr 25, 2011, 1:34 AM
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Re: [velvetjo] Donít PLF on a downwinder? [In reply to] Can't Post

I'm going to have to go with John & Lance on this one. Having taught rolls and falls in martial arts for many years, a great number of people (typically more physically-inclined than the avg. populace) don't have a natural ability to do it smoothly until they've accomplished a lot of repetitions. This is in a controlled environment, on mats, and with a coach.

Put in an adrenaline-charged, visually-intimidating unusual situation such as a parachute landing and the chances of a smooth rolling fall are going to significantly diminish.

PLFs were designed in the days when round canopies ruled. If you're sinking steeply, they still apply. However, as John said - high forward speed... slide.


JackC1

Apr 25, 2011, 2:04 AM
Post #6 of 73 (2390 views)
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Re: [JohnMitchell] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
Haven't people died from broken necks PLF-ing on downwinders?

Here's my rule.

If you have a high rate of descent, PLF.
If you have a high forward speed, slide.
If you have a high rate of descent and a high forward speed, kiss your ass goodbye. Unsure

Yup, that's my rule too.

When you have a lot of forward speed, quite often the first thing that will hit the floor after your feet is your knee and that's how femurs get broken. Then you get thrown forwards onto your head, and that's how necks get broken. A slide is safer IMHO.


popsjumper  (D 999999999)

Apr 25, 2011, 3:06 AM
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Re: [JackC1] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
In reply to:
Haven't people died from broken necks PLF-ing on downwinders?

Here's my rule.

If you have a high rate of descent, PLF.
If you have a high forward speed, slide.
If you have a high rate of descent and a high forward speed, kiss your ass goodbye. Unsure

Yup, that's my rule too.

When you have a lot of forward speed, quite often the first thing that will hit the floor after your feet is your knee and that's how femurs get broken. Then you get thrown forwards onto your head, and that's how necks get broken. A slide is safer IMHO.

I agree with John, too...to a point.

What you describe is not a PLF...it's a faceplant.
If you don't do the PLF properly, you negate the benefits of the PLF entirely. Upwind, downwind, whatever...a proper PLF will save your butt. A faceplant is NOT a PLF.

"Haven't people died from broken necks PLF-ing on downwinders? "
No. Barring other contributing factors, they probably died because what they did WASN'T a proper PLF.

Downwind PLF:
With a "high" rate of horizontal speed you're not going to get the final roll with feet and knees together. What you will get though is a nice slide on your calf-thigh-hip-side. Picture a "superman" on your side with your arms down in flare position instead of your belly with your arms extended.

I am extremely against teaching students to slide and here's why...
- Students have no frame of reference for what constitutes a high rate of descent or high forward speed. This causes the "ground rush" we're all familiar with. Teaching them two different methods (PLF/slide) only confuses things for them. It gives them an option that often leads to making the wrong choice.

A proper PLF is best for either up- or down-wind.

If you're going to mess up the PLF, you're going to do it regardless of landing direction.

- Sliding for students doesn't work well because again, they have no frame of reference for speed and decent rate. Get it wrong and you're going to hit hard on your spine whether is flat out on the butt of offset towards a hip. I've seen too any back injuries from student butt/slide landings and I don't want to see any more.

Now, having said that, I agree that yes, a good "baseball" slide is a valid technique for landing. It would be a good idea to have some feel for descent rate and forward speed before attempting it.

In summary, you PLF until you get some experience under your belt and only then go for the slide.

Oh, and yes, those with some experience with sliding such as baseball players do have a large advantage over others when it comes to learning the slide technique.


(This post was edited by popsjumper on Apr 25, 2011, 3:10 AM)


popsjumper  (D 999999999)

Apr 25, 2011, 3:52 AM
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Re: [Divalent] Donít PLF on a downwinder? [In reply to] Can't Post

I read your reference. Please take note:

- "With a square parachute our hands are down at our sides (hopefully) controlling the flare."
This is not (hopefully) what is being taught these days for proper PLF body position. Hands are in at the crotch, not out to the sides.

- "...impact with the ground, more than once, as the roll proceeds. What one hopes for is the best case scenario where the jumper is rolling from shoulder to shoulder across the ground."
This assumes that the jumper is going to roll multiple times on a side-to-side roll and that is not, by far and away, the case. Usually it's only a slide on the side with the feet back towards the direction the landing is coming from with the canopy pulling the head and shoulders (by way of the risers) in the direction of landing.

- "At touch down the jumper should try to absorb as much as possible of the downward impact with their feet but lean back in the harness."
Well, injuries are caused by resistance to force. You bones can only take so much force in any direction before they break. Absorbing "as much as possible...with their feet" exposes those bones of the feet, ankles and legs to breakage.

The whole purpose of the PLF is to MINIMIZE forces on the bones.

-"Öyou should have done a PLFĒ. This is not always the case, particularly with todayís parachutes. A PLF is no longer a panacea for all conditions. "
Today's parachutes make it easier to do PLFs in the big scheme of things. Forward motion helps initiate a good PLF. Anyone that has landed a parachute, regardless of shape, has probably landed one coming straight down. They know it tougher to do a good PLF coming straight down because it probably ends up in a small pile on the ground as opposed to getting a a stretched-out PLF roll.
Panacea? Nope, never was and never will be since there are no panaceas for anything. It is, however, IMO, the best option for students.



Side note:
Jack, your mileage may vary. If you've been doing things that way for "decades" with success, my hat's off to you. OTOH, proper PLFs have the great track record too. Most landing injuries come from NOT doing proper PLFs so anyone blaming the PLF technique for that should redirect their blame to the real cause.


dragon2  (D 101989)

Apr 25, 2011, 5:12 AM
Post #9 of 73 (2334 views)
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Re: [Divalent] Donít PLF on a downwinder? [In reply to] Can't Post

As a student, I once came in hot downwind @ <300 ft and couldn't turn anymore due to trees/barn on one side and the runway on the other. I PLFed, rolled 2 or 3 times and didn't even have a bruise to show for it (and I bruise VERY easily).

I do however still have a tailbone problem due to a slide I did 1 1/5 yrs ago.

Guess where my vote goes?


BETO74  (D License)

Apr 25, 2011, 5:31 AM
Post #10 of 73 (2318 views)
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Re: [JohnMitchell] Donít PLF on a downwinder? [In reply to] Can't Post

Quote:
If you have a high rate of descent, PLF.
If you have a high forward speed, slide.
If you have a high rate of descent and a high forward speed, kiss your ass goodbye.

Agree!


JackC1

Apr 25, 2011, 5:51 AM
Post #11 of 73 (2304 views)
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Re: [popsjumper] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
What you describe is not a PLF...it's a faceplant.

Absolutely. If you fail to perfectly perform your PLF, a faceplant is the common outcome.

It's just that the mechanics of performing a PLF under a fast square canopy make them easy to screw up. With a lot of forward speed it all happens very quickly. This can mean that you end up going where momentum takes you rather than directing the momentum with a PLF. Unless you put the effort in to change the situation, you are invariably going to be facing forward as you approach the landing. In actual fact you need to be slightly sideways for the safest PLF. If you pile in too straight with a lot of forward movement, it's really easy to go down hard on your knee which I reckon is a very good way to get your femur broken.

But I also agree that for students who are generally on large canopies with a lower decent rate and lower forward speed, the best bang for the buck is probably still a PLF, provided they can do it properly.


(This post was edited by JackC1 on Apr 25, 2011, 5:53 AM)


JohnMitchell  (D 6462)

Apr 25, 2011, 8:07 AM
Post #12 of 73 (2237 views)
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Re: [popsjumper] Donít PLF on a downwinder? [In reply to] Can't Post

And I did get a nice PM from a jumper who said a PLF probably saved his life on a bad swoop. Pretty badly injured, he healed to jump again. I've been in similar crappy situations and attempting to PLF as best as I could probably limited my injuries.

So I have to say that in Situation #3, high rate of descent, high forward speed, put your feet and knees together and take the impact with your legs, not your vital organs, your spine or your skull. Yes, it's going to suck, but it's going to suck less with a broken leg than with a broken back. Prevention is the best solution to that situation.

So I guess I'd like to modify#3 to be "you're screwed, but get your feet and knees together anyway. It's probably gonna hurt less that way."


Premier billvon  (D 16479)
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Apr 25, 2011, 8:08 AM
Post #13 of 73 (2234 views)
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Re: [Divalent] Donít PLF on a downwinder? [In reply to] Can't Post

I recommend doing a PLF on any "bad" landing, downwind or not. However, the PLF changes with speed.

On a standard PLF, you get your feet and knees together and bend your knees, with your knees angled in some direction or the other. This protects your knees and ankles. When you hit, you let yourself collapse, so that your feet, sides of calves, sides of thighs, back and then shoulder hit in sequence, making it as much of a rolling motion as possible.

On a high speed PLF, you get your feet and knees together and bend your knees, with your knees angled in some direction or the other. This protects your knees and ankles. When you hit, you let yourself collapse, so that your feet, sides of calves and the sides of your thighs hit. Then you stop and let yourself slide feet-first through the landing area. Your ankles and knees are protecting themselves, your feet are in front to protect against impacts, and you're taking the bumps on the side of your thigh, rather than your chest or your coccyx.


Divalent  (C 40494)

Apr 25, 2011, 10:51 AM
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Re: [billvon] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
...On a high speed PLF, you get your feet and knees together and bend your knees, with your knees angled in some direction or the other. This protects your knees and ankles. When you hit, you let yourself collapse, so that your feet, sides of calves and the sides of your thighs hit. Then you stop and let yourself slide feet-first through the landing area. Your ankles and knees are protecting themselves, your feet are in front to protect against impacts, and you're taking the bumps on the side of your thigh, rather than your chest or your coccyx.

Just to clarify, it sounds like what you are describing is similar to the baseball slide into second base, similar to what the author was suggesting. That is, in the high speed version, you are attempting to keep your feet moving ahead of you (aimed in the direction of landing) as the rest of your body (feet, ankle-knees, hips, torso) touch down in succession behind them. To do that, feet have to be sliding downwind after touch, and I think one would have to be leaning back to keep from doing a face plant or forward head-over-heals.

Otherwise, I don't see how you can keep your feet in front of you: standard PDF is feet touch down, then the rest of the body in succession (with body angled a bit), leaving the head somewhat downwind of the feet. (Unless the final position you described is achieved after a roll on the back, allowing the person to swing their feet forward again).


voilsb  (D 30581)

Apr 25, 2011, 11:02 AM
Post #15 of 73 (2162 views)
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Re: [popsjumper] Donít PLF on a downwinder? [In reply to] Can't Post

Having done thousands of PLFs, I tend to agree with Pops. A properly executed PLF automatically slides in on a fast landing. I remember thinking this when that article came out, too.


nigel99  (D 1)

Apr 25, 2011, 11:11 AM
Post #16 of 73 (2157 views)
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Re: [voilsb] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
Having done thousands of PLFs, I tend to agree with Pops. A properly executed PLF automatically slides in on a fast landing. I remember thinking this when that article came out, too.

With the importance of landing correctly, I must admit that I am surprised that modern training has done away with practicing PLF's to the extent that it has. Our training was carried out over more than 1 day and involved falling off of bales of hay for about 8 hours. Admittedly they were rounds and so for many people it was critical to avoid injury.


popsjumper  (D 999999999)

Apr 25, 2011, 12:46 PM
Post #17 of 73 (2119 views)
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Re: [JackC1] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
With a lot of forward speed it all happens very quickly. This can mean that you end up going where momentum takes you rather than directing the momentum with a PLF. Unless you put the effort in to change the situation,
This is where we are slightly off of each other.

Again, the whole idea of a PLF is to minimize forces on bones. Any resistance you put into it (you put the effort in to change the situation) increases the point-of contact forces. I read your initial note and this response to say that one should put some pressure into it somehow to change the direction of momentum. That is what increases the forces on that point-of-contact. Not good.

Let it roll. Let it happen. Do not try to stop it

In reply to:
...you are invariably going to be facing forward as you approach the landing. In actual fact you need to be slightly sideways for the safest PLF.
Absolutely! Hopefully, that's the way it's being taught!

In reply to:
If you pile in too straight with a lot of forward movement, it's really easy to go down hard on your knee which I reckon is a very good way to get your femur broken.
Agreed...because it wasn't a proper PLF. You see? Putting that knee down induced that resistance to the forces generated on landing and whack! something gets broken.

In reply to:
...the best bang for the buck is probably still a PLF, provided they can do it properly.
And there's the key!


popsjumper  (D 999999999)

Apr 25, 2011, 1:05 PM
Post #18 of 73 (2102 views)
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Re: [billvon] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
I recommend doing a PLF on any "bad" landing, downwind or not. However, the PLF changes with speed.

And for Bill,
This is one point of difference we have on this topic. IMO, speed is the only change. All techniques are the same as slow landings.

In reply to:
On a high speed PLF, you get your feet and knees together and bend your knees, with your knees angled in some direction or the other. This protects your knees and ankles. When you hit, you let yourself collapse, so that your feet, sides of calves and the sides of your thighs hit.
...so far, so good...

In reply to:
Then you stop and let yourself slide feet-first through the landing area.
This not a PLF procedure nor does it happen on a PLF of any speed. You're describing something different. It appears, as Divalent noted, that you're describing a feet-first slide.

In reply to:
{ in a feet first slide... }...Your ankles and knees are protecting themselves, your feet are in front to protect against impacts, and you're taking the bumps on the side of your thigh, rather than your chest or your coccyx.
Yep, the baseball slide. Totally different from PLF.

Students. Please keep in mind (besides the dammit-don't-do-it butt slide exposing your tailbone) that sliding feet-first exposes ankles to severe damage should you put your feet down to stop the slide.

Any time you're sliding with your feet in front of you, you are exposing tailbones and ankles to damage.

If we are going to advise baseball slides, then we really should address the probability of broken ankles caused by putting the feet down trying to stop the slide or getting the feet caught on a clump, a rut or rock or something. Had one ever actually played competitive baseball, one would remember getting the slide training re-inforced with the idea of keeping spikes up or behind....never down in front.

Now, with experience, a slider learns when it's safe to put the feet down and use the momentum to rise to a standing position.


JackC1

Apr 25, 2011, 1:41 PM
Post #19 of 73 (2074 views)
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Re: [popsjumper] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
I read your initial note and this response to say that one should put some pressure into it somehow to change the direction of momentum. That is what increases the forces on that point-of-contact. Not good.

That's not what I mean, fighting the roll will do no good at all. Relaxing and going with it is far better. What I meant was when you approach the landing, you are probably going to be facing directly forward, and like you say, you are taught to turn slightly sideways, that's what I meant by putting some effort into changing your situation. I think botching a PLF in this way is one of the reasons why the word femur gets used as a verb in this sport. But generally, I think we agree on all the important parts. Smile


(This post was edited by JackC1 on Apr 25, 2011, 1:48 PM)


yeyo  (D 32048)

Apr 25, 2011, 1:51 PM
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Re: Donít PLF on a downwinder? [In reply to] Can't Post

I see you all talking bout 3 different kinds of slides, and I dont recommend 2 of those.

-2 feet forward sliding on butt. You gonna hurt your tailbone.Pirate
-2 feet forward, body sideways, sliding on hip? I dont see how that can be done hanging on a harness.Crazy
-1 leg forward, other leg bent under butt. This is how I do it all the time when is too fast to run it out. Slide and keep flying the canopy until you are going slow enough, finish your flare and stand it up. Dont do it wearing shorts Tongue


megamalfunction  (B 35178)

Apr 25, 2011, 2:16 PM
Post #21 of 73 (2012 views)
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Re: [Divalent] Donít PLF on a downwinder? [In reply to] Can't Post

Watch the last skydiving scene in 'Point Break.' PLF like Keanu and you'll be fine.


megamalfunction  (B 35178)

Apr 25, 2011, 2:18 PM
Post #22 of 73 (2009 views)
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Re: [Divalent] Donít PLF on a downwinder? [In reply to] Can't Post

Tuck & Roll!


MakeItHappen

Apr 25, 2011, 3:08 PM
Post #23 of 73 (1970 views)
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Re: [Divalent] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
I ran across this article recently in the Canopy Control section of this website (in the Safety section), entitled ďAn Inconvenient Truth Regarding PLF'sĒ: (http://www.dropzone.com/...tail_page.cgi?ID=729). I searched to see if this article (published in March of last year) generated any discussion, but didnít find any.

In one section of the article, the author argues that PLFs on downwind landings are dangerous, and he proposes (and apparently has taught for many years) an alternative. Hereís a quote of the gist this. ďThere is a solution to this downwind landing possibility. It is easy to train and easily understood by newcomers and experienced skydivers alike. The simplest way to prepare for as many landing scenarios as possible is to assume the PLF position, fly the parachute and slide on one hip in the event of a forward motion, high speed landing

So, if I interpret this correctly, itís not exactly a butt slide, more of a hip slide (like sliding into second base?).

Anyway, Iíd be interested in hearing other peoples view of (and experience with, if any) this technique.

Please see
"Average Landing Force Dependence on Length and Direction of Landing, Parachute Velocity Components and Wind Speed"
AIAA 9th Aerodynamic Decelerator and Balloon Technology Conference, 1986
J. Meyer University of Arizona (yep that would be me)

In a nutshell, yeah sliding in as though you were stealing home would be a good thing if you were doing a downwinder in relatively high winds.

From personal experience, a wind shear hit Coolidge one day.
The sock showed winds out of the north.
The guy landing about 40 seconds before me (to the North) & slightly offset from the wind sock, had his canopy crash down in front of him (indicating a downwinder).
I was following him into the landing area. My ground speed was increasing even though the wind sock showed I was going into the wind.
I leaned back in the harness as far as I could, picked my legs up to do the best ever "stealing home in the bottom of the 9th winning run" and landed safely after a ~70ft slide across the 'grass/weeds'.
The guy before me broke his ankle & was helo out.

.


(This post was edited by MakeItHappen on Apr 25, 2011, 3:10 PM)


AllTheWay

Apr 25, 2011, 4:23 PM
Post #24 of 73 (1914 views)
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Re: [Divalent] Donít PLF on a downwinder? [In reply to] Can't Post

I have the paratrooper mentality that a proper PLF will always be the safest. I firmly believe that as long as you have your feet and knees together, with knees bent, that you will not break your legs. It seems to me that the slide not only separates your legs, but you will have one leg extended and another tucked under--either of which could catch and break the extended, or crack your knee on the tucked. PLF's, when performed properly, will displace the impact regardless of direction/speed. But as mentioned above, it takes many repetitions to get the hang of. At Airborne school, we did PLF's for two weeks, at AFF ground training, I think I did one. With all this being said, however, I am now dying to try the "slide"


pchapman  (D 1014)

Apr 25, 2011, 4:51 PM
Post #25 of 73 (1895 views)
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Re: [AllTheWay] Donít PLF on a downwinder? [In reply to] Can't Post

In reply to:
IIt seems to me that the slide not only separates your legs, but you will have one leg extended and another tucked under--either of which could catch and break the extended, or crack your knee on the tucked.

I'm thinking:

Yes with legs split they can't support each other, but that position would be used for only certain slides.

One leg forward and one leg under is more for a good-conditions slide, where you expect to slide along reasonably smooth grass, including cases where you even expect to remain standing at the end of the slide. Or, you think one leg in front is enough, and one leg under is there to guard against a possible drop on your ass due to turbulence or a poor flaring canopy or whatever.

For a more of an emergency conditions slide, as long as you don't expect to drop down on your spine, both legs would be out in front.

If you do expect both a lot of descent rate and forward speed, there's no easy answer, but you'd rather keep feet underneath against the descent rate to protect your spine, and take what comes in the high speed tumble.

Where to use the various versions of landing techniques all depends on how much vertical speed and horizontal speed one expects to arrive with (and smoothness of the terrain). To some degree one landing can transform into another. (Eg, sliding in rougher terrain but body kept high, so if the feet do dig in, you tumble into a PLF roll instead of crumpling up against the obstacle catching your feet). But to some degree, you just have to make a choice ahead of time as to what type of landing conditions to expect and how to position yourself.


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