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Side drift

 

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fonz

Oct 4, 2001, 5:16 AM
Post #1 of 28 (1683 views)
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Side drift Can't Post

Hi,

On my last jump, I turned into the wind for final, but as I went down, I
caught a lot of sideways drift and ended up with a crosswind touchdown.

Where do drifts like this come from?

Blue skies,

Alphons



3fLiEr

Oct 4, 2001, 5:45 AM
Post #2 of 28 (1676 views)
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Re: Side drift [In reply to] Can't Post

This is a common mis-perception - The side gusts many people experience at touchdown are pilot induced by unknowningly rising the opposite toggle and sometimes pulling the same side toggle down further to the leading foot.

You wanna get out of this bad habit before you get onto faster and less unforgiving canopies.

HTH

BSBD

"Go hard, fast & way low"



fonz

Oct 4, 2001, 5:51 AM
Post #3 of 28 (1673 views)
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Re: Side drift [In reply to] Can't Post

> will also pull the same side toggle down slightly

I'll definately make sure not to do that. Thanks!
But ehm, in this case I'm pretty sure it wasn't the case.
I'm positive that I had both toggles all the way up.
I turned in excess of 90 degrees!

Alphons



3fLiEr

Oct 4, 2001, 6:27 AM
Post #4 of 28 (1669 views)
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Re: Side drift [In reply to] Can't Post

Oh i thought this was on touchdown............... did this happen on full drive after your turn? - are you jumping an eliptical?



Premier SkymonkeyONE  (D 12501)

Oct 4, 2001, 6:58 AM
Post #5 of 28 (1662 views)
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Re: Side drift [In reply to] Can't Post

What happened here is that you "thought" you were going straight into the wind. Never get complacent under canopy; keep flying that thing until you come to a complete stop. If a breeze causes you to "drift" in one direction, then compensate slightly with the opposite toggle just enough to keep your parachute flying straight. Your final flare might be slightly uneven, but that is fine in this instance. Remember, you are the pilot, not just a passenger under canopy.

Chuck

"I'd rather have a bottle in front of me than a frontal lobotomy"


geoff

Oct 4, 2001, 7:32 AM
Post #6 of 28 (1654 views)
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Re: Side drift [In reply to] Can't Post

In reply to:
I turned in excess of 90 degrees!
If you turned, then something about you or the rig made it happen - one toggle lower, uneven weight in harness, leg straps not even, bad trim, or whatever. Not the wind.

If you're off the wind line, you'll get pushed sideways, but not turned.

Geoff



Premier billvon  (D 16479)
Moderator
Oct 4, 2001, 1:20 PM
Post #7 of 28 (1634 views)
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Re: Side drift [In reply to] Can't Post

>I'll definately make sure not to do that. Thanks!
> But ehm, in this case I'm pretty sure it wasn't the case.
> I'm positive that I had both toggles all the way up.
> I turned in excess of 90 degrees!

I have never jumped a canopy that responded to wind so strongly that it turned more than about 10 degrees before I could stop it. It is very unlikely that this is happening to you. I can almost guarantee you that the canopy is doing exactly what you tell it to do. You flare, get a slight drift off to one side, then "stick out your hand to break your fall" thus turning the canopy in that direction. We had one jumper who did this on every single jump and swore that a side gust at the last minute always knocked him over.

To overcome this, learn to flare turn. As you are flaring, turn 10 degrees before you come to a stop. Make sure you can do that in both directions. Next time you feel a side gust, use that skill to keep the canopy going straight. This will likely break you of the "sticking out your hand to break your fall" habit.

-bill von


fonz

Oct 10, 2001, 7:42 AM
Post #8 of 28 (1547 views)
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Re: Side drift [In reply to] Can't Post

billvon> You flare, get a slight drift off to one side

Actually, it happened way before the flare, only seconds
after turning onto final.

Sorry for the confusion,

Alphons



fonz

Oct 10, 2001, 7:52 AM
Post #9 of 28 (1545 views)
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Re: Side drift [In reply to] Can't Post

3fLiEr> did this happen on full drive after your turn?

Yup.

3fLiEr> are you jumping an eliptical?

Not exactly. A Sabre 170 loaded at approx. 1.0

I know that you might need to make minor course corrections
on final, but this time I found it quite radical.

Blue skies,

Alphons



freeflir29  (D 10000000)

Oct 10, 2001, 12:14 PM
Post #10 of 28 (1538 views)
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Re: Side drift [In reply to] Can't Post

My opinion? Most canopies will try and run with the wind. I.E. If they are not perfectly lined up on the wind line they will want to turn and run down wind. This happens a lot when you have "No pilot input" during your final. You will have to do some small corrections to keep the canopy going into the wind. I personally like to use the front risers. I'm not talking about huge inputs. Just little ones to keep you on the wind line. This allows you to correct without "slowing the canopy" as using the toggles causes much more drag and can cause some very poor flaring performance due to the lost speed. Please, make sure you know what you are doing. Don't pull the risers into your chest at 30 ft less you want a trip to the hospital or morgue. Learning to land at Raeford does have it's advantages...Smile


"The sky resembles a back lit canopy...with holes punched through it"- Incubus
Clay


fonz

Oct 11, 2001, 4:28 AM
Post #11 of 28 (1512 views)
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Re: Side drift [In reply to] Can't Post

freeflir29> If they are not perfectly lined up on the wind line
freeflir29> they will want to turn and run down wind.

That might be the answer to my question. Thanks!

I will try the front riser technique, but no sooner than I'm perfectly capable of making decent (i.e. stand-up) landings.
I have only jumped the Sabre twice and so far I screwed up both landings. Not dangerously or something, but I just look bloody silly, tumbling across the grass.




RemiAndKaren  (C 2328)

Oct 11, 2001, 5:01 AM
Post #12 of 28 (1508 views)
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Re: Side drift [In reply to] Can't Post

another way to make small changes in the direction of the canopy is to use the harness: just shift your weight on the side you want to turn into.

Remi
Muff 914


geoff

Oct 11, 2001, 5:13 AM
Post #13 of 28 (1508 views)
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Re: Side drift [In reply to] Can't Post

In reply to:
freeflir29> If they are not perfectly lined up on the wind line
freeflir29> they will want to turn and run down wind.

That might be the answer to my question. Thanks!
It might be, but it isn't.

A straight-line steady-speed wind can't affect the direction the canopy is pointing. The canopy can be pushed forwards, backwards, or sideways by the wind, but not turned, unless there's turbulence, or a different wind speed hitting one end of the canopy to the other.

Imagine this - you're flying your canopy in a straight line in still air inside a huge closed container. You look out the window of the container (while still flying your canopy) and realise that the container is actually on wheels and is moving sideways at constant speed compared to the way you're flying. Does the steady motion of the container (and hence the body of air you're flying in) cause your canopy to turn? - no. In fact, unless you refer to something outside the container, it's impossible to tell that the air is actually moving at all (this is actually the basis of Relativity theory)

Now take the motorised container away, and assume the masss of air is just moving along of it's own accord. In other words, it's just plain windy. Same story. You'll be pushed sideways, sure, but you'll keep the same heading.

Geoff



fonz

Oct 11, 2001, 5:49 AM
Post #14 of 28 (1502 views)
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Re: Side drift [In reply to] Can't Post

RemiAndKaren> use the harness: just shift your weight on the side you want to turn into.

Now that's something I will try on my next jump. Thanks!

Alphons



fonz

Oct 11, 2001, 5:53 AM
Post #15 of 28 (1501 views)
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Re: Side drift [In reply to] Can't Post

geoff> unless there's turbulence,

The landing area is grass only. In fact, even the runway is grass.
Wouldn't that make turbulence an unlikely event?

> or a different wind speed hitting one end of the canopy to the other.

Now what could cause such a thing to happen?

Alphons



Premier billvon  (D 16479)
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Oct 11, 2001, 6:09 AM
Post #16 of 28 (1496 views)
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Re: Side drift [In reply to] Can't Post

>The landing area is grass only. In fact, even the runway is grass.
>Wouldn't that make turbulence an unlikely event?

The landing area at Perris is grass and dirt, but there is tremendous turbulence there in the summer. Thermal differences can easily cause turbulence from rising hot air. Dust devils are an extreme example of this, but ordinary thermals can bump you around as well.

>>or a different wind speed hitting one end of the canopy to the other.

>Now what could cause such a thing to happen?

-A thermal, where one side of the canopy hits rising air and the other doesn't. (This is one way sailplane pilots look for thermals, BTW.)
-A wingtip vortex from a landing aircraft or another canopy.
-Wind shear (sudden change in wind direction.)



-bill von


geoff

Oct 11, 2001, 6:13 AM
Post #17 of 28 (1495 views)
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Re: Side drift [In reply to] Can't Post

By turbulence, I mean turbulent enough that part of the canopy is collapsed or distorted enough to cause a turn. This can certainly happen, and can be very nasty. I don't see how this could happen gently or consistently, though. So yes, it's unlikely that you'll often observe a turn due to this during landing, unless the canopy is bucking, buffeting, or concertina-ing. In which case, you probably shouldn't be jumping anyway.

As for different wind speeds on different ends of the canopy. Again, this could be turbulence off trees, buildings or whatever, or even a rotating wind like a dust devil. Again, this would be really nasty, and you probably shouldn't be jumping in such conditions.

As someone said previously, the most likely cause is something you're doing without realising - not balanced in the harness, reaching with a hand or foot, or whatever. It could possibly also be a trim problem or your leg straps are not even.

Hope this helps,

Geoff



Premier billvon  (D 16479)
Moderator
Oct 11, 2001, 6:17 AM
Post #18 of 28 (1492 views)
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Re: Side drift [In reply to] Can't Post

>My opinion? Most canopies will try and run with the wind.

Canopies don't know which direction the wind is coming from, so they can't turn away from it, any more than any aircraft knows which direction the wind is coming from. (Pilots don't have to fight a 747's tendency to "run downwind" with the jet stream when they are flying east to west.)

However, two factors conspire to make it seem this way. One, when you are closer to the ground, you become much more aware of your speed and direction, because we perceive a higher relative speed when we're closer to the ground. Two, turbulence generally increases as you get closer to the ground, and any turbulence when you're facing exactly into the wind will try to turn you away from the wind.

-bill von


Premier billvon  (D 16479)
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Oct 11, 2001, 6:18 AM
Post #19 of 28 (1492 views)
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billvon> You flare, get a slight drift off to one side

> Actually, it happened way before the flare, only seconds after turning onto final.

Now I really don't understand. You turned onto final, there was a sudden something that caused a 90 degree turn, and you did not have time to fix this before landing? Are you turning to final at 40 feet? Why couldn't you turn back into the wind before landing?

-bill von


freeflir29  (D 10000000)

Oct 11, 2001, 11:08 AM
Post #20 of 28 (1474 views)
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Re: Side drift [In reply to] Can't Post

"Canopies don't know which direction the wind is coming from"

Well, I was mostly speaking from my experience on round canopies. I can tell you for sure that if you are jumping a -1C and do absolutely nothing after opening the canopy WILL turn and "run with the wind." I have seen many an Army grunt with no experience on a steerable rig fly off into the woods. Smile
Now, with square canopies I have watched countless students, especially the last couple very windy weekends, turn to final and not stay "on top" of their canopy. They aren't lined up perfectly and their canopy will easily make a 90 deg turn with no pilot input. I'm not going to get into a physics or aerodynamics argument as I don't have a degree in either but I know what happens. I have always assumed it was due to uneven wind speed due to not being lined up perfectly straight on the wind line. Am I wrong?

"The sky resembles a back lit canopy...with holes punched through it"- Incubus
Clay


Premier billvon  (D 16479)
Moderator
Oct 11, 2001, 1:51 PM
Post #21 of 28 (1466 views)
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Re: Side drift [In reply to] Can't Post

Now, with square canopies I have watched countless students, especially the last couple very windy weekends, turn to final and not stay
"on top" of their canopy. They aren't lined up perfectly and their canopy will easily make a 90 deg turn with no pilot input. I'm not going to
get into a physics or aerodynamics argument as I don't have a degree in either but I know what happens. I have always assumed it was
due to uneven wind speed due to not being lined up perfectly straight on the wind line. Am I wrong?

I've seen exactly the same thing, but not for that reason, I believe. When I'm landing a student, I often notice the canopy turning because 1) they are not sitting straight in the harness and/or the legstraps are uneven, 2) they are loading one toggle more than the other, 3) there is turbulence bouncing them every which way and 4) there is a built in turn in the canopy. When they are at 1000 feet, it's a non-issue - I'll just overturn them to the left if they have a built in right turn (for example.) When they are on short final, suddenly I'm a lot more concerned about their heading, and it seems like some malevolent force is trying to turn the canopy away from the wind. Of course, there's no new force at work, I'm just worrying more over the same sort of behavior the canopy was displaying before.

I've often seen student canopies turn 45 from turbulence, although I don't think I've seen any sudden 90's. I've seen plenty of gradual 90's, when they just stop paying attention and the canopy's built in turn takes over and steers them away - which is why I don't teach "don't turn at all on final!" any more.

So I certainly believe that there are lots of reasons a student may experience a turn on final, but I don't believe that there's a force that makes them turn downwind and then stay facing downwind. (Other than wind shear, and there has to be a lot of wind for that to be a factor - and students don't jump when there's that much wind.)

-bill von


Premier SkymonkeyONE  (D 12501)

Oct 11, 2001, 2:45 PM
Post #22 of 28 (1464 views)
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Re: Side drift [In reply to] Can't Post

Bill,
just to let you know where Clay is coming from: We have a friend, Larry Sherling, who did not make it completely back into the wind on his final turn. It was a breezy day and his final turn put him at about a 45 degree angle into the wind before he stopped making his turn and prepared to land. The wind TURNED his parachute to the right and he flew right into one of the 6"x6" uprights of our covered packing pavilion at Raeford. If it would have simply PUSHED him sideways, he would have hit the pole sideways; he hit it head on. The wind had turned him about 60 degrees to the right. This all happened in less than 50 feet of altitude. There were a ton of people watching it happen. Larry broke 27 bones in 74 places and is VERY lucky to be alive (there was a surgeon sitting right there supporting some military MFF train-up jumping). This "accident" happened because Larry did not counter the turn with his left toggle on final and allowed his parachute to be driven into the post. Anyone want to talk to him about it? He works at SkyKat gear shop now.

Chuck Blue
D-12501

"I'd rather have a bottle in front of me than a frontal lobotomy"


fonz

Oct 11, 2001, 10:02 PM
Post #23 of 28 (1443 views)
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Re: Side drift [In reply to] Can't Post

billvon> there was a sudden something that caused a 90 degree turn

Not sudden. Continuously.

For clarity's sake, met me try to properly restate what happened.
I turn onto final, in the direction which I know is into the wind.
I know it's normal that one needs to make small corrections in order to keep going in the right direction.
But, for some reason which I don't understand (which is why I'm asking) my canopy started turning in such a way that a "minor" course correction would not suffice. Even though I had both toggles all the way up, I started turning steadily (yet not radically). Of course I tried minor corrections through subtle toggle input, but that didn't help. The amount of input required to stop the turning was more than I was willing to give/dare/risk.

Alphons



FallingMarc  (B 25542)

Oct 11, 2001, 10:29 PM
Post #24 of 28 (1440 views)
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Re: Side drift [In reply to] Can't Post

Please correct me if I'm wrong, but if your canopy is turning at a constant rate, there should be a toggle position that will counteract it. If you have to hold one toggle down by your head to keep the canopy flying in a straight line, but it does fly in a straight line with the toggle held there, it's better to land like that than to fly a curved final approach. This could be caused by you shifting in your harness, leg straps being tightened unevenly, etc...

If this is the case, then even if you're holding one toggle lower than the other, if your canopy is flying straight, it's flying straight, and that's what you want. Your goal is to fly a straight-line final approach. Ideally this means you get on your line, then fly with toggles all the way up, and no more control input until you flare. But, if it takes some constant input to keep from turning, that's better than landing while in a turn.

If you do have to hold your toggles slightly unevenly to keep from turning, just remember to flare with them similarly uneven--if a canopy turns with both toggles all the way up, it will turn with both toggles all the way down as well.

Marc



fonz

Oct 12, 2001, 7:28 AM
Post #25 of 28 (1426 views)
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Re: Side drift [In reply to] Can't Post

Thanks to all of you guys for trying to help me out with this.

If I understand it right, my turn was most likely caused by one (or more) of the following:
1) turbulence
2) not sitting straight in the harness, unevenly tightened legstraps or some other asymmetric thing I did
3) more input on one toggle than on the other
4) the canopy I jumped has a builtin turn

In this case, I doubt it was reason 3 or 4.

Another thing I learnt is to give more input if necessary.
No radical yanking on the toggles of course, but try to find a position that keeps the canopy flying straight.

Thanks,

Alphons



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