Winds/Spotting - beginnings of faq
Ben Daniels
Theme: Safe separation between groups at opening
comes directly from adequate separation of groups at exit.
Sub theme: When flying into high uppers
leave more time between exits.
We will first look at two jumpers and their exit and opening points.
Then we will look at the effect of
1. Tracking
2. Canopy motion of group 1 while group 2 is still in freefall
3. Uppers in one direction and lowers in the opposite direction
Now, using the ground as the frame of reference, imagine many layers of
wind blowing every which way and a jump run in some arbitrary direction.
Jumper 1 exits at X1 and opens at O1.
Jumper 2 exits at X2 and opens at O2.
The separation between exit points is ground speed times exit interval.
Jumper 2 Jumper 1
X2 <---- S = GS * EI -----> X1 <-- airplane
\ \
. \ . \
. \ . \
. \ . \
. / . /
. / . /
. \ . \
. \ . \
. \ . \
. \ . \
. \ . \
. \ . \
. O2 <---- S = GS * EI -----> O1
. . . .
. . . .
------x-------x-------------------x-------x----------- ground
X2 O2 X1 O1
The two paths are exactly the same shape separated by S = GS * EI at
all points top to bottom.
We may achieve this separation S = GS * EI of opening points by either
Dividing ground speed into separation distance to get exit interval
EI = S/GS.
or
Looking out the door and gauging the separation of exit points by eye
(spotting).
This is our basic picture. Separation of opening points comes directly
from separation of exit points. Flying into high uppers causes slower
ground speed and requires greater exit interval.
Other frames of reference are possible - the airplane, the air itself.
Imagine we are standing on the tailgate. The outside air is moving past
at airspeed AS, the ground is moving past at ground speed GS. Jumper 1
exits and EI seconds later jumper 2 exits. What do we see?
airplane air --> AS = air speed
*
* ground --> GS = ground speed
*
*
*
*
*
*
O2 <- S = GS * EI -> O1
. .
. .
-------------------x--------------------x------------- ground
O1 ----------------> O1
Jumper 1 falls away on some trajectory, jumper 2 falls away on the
same trajectory EI seconds later. Jumper 1 opens. While jumper 2 falls
the remaining EI seconds, jumper 1's opening point moves a distance
S = GS * EI and their opening points are separated by S = GS * EI.
Now imagine we are a wind molecule hanging out at the drop zone on a
typical day. An airplane flies by, drops jumper 1 right next to us,
and EI seconds later drops jumper 2. What do we see?
<--- airplane AS = airspeed
<--- ground WS = windspeed (not ground speed)
Jumper 2 Jumper 1 wind molecule
<----------- AS * EI ---------------> @#@
X2 <- GS * EI -> X1 <- WS * EI --> X1
* . *
* . *
* . *
* . *
* . *
* . *
* . *
* . *
* . *
O2 <- GS * EI -> O1 <- WS * EI -> O1
. . .
. . .
-x----------------x----------------x------------------ ground
O2 O1 <------------ O1
What we don't see is two airplanes in formation, one dropping jumper 1
right next to us and the other simultaneously dropping jumper 2 at a
distance AS * EI from us. We all know that hanging out with the wind
molecules changes our view of things, but this is not that change.
What we do see is that while jumper 2 is flying the distance AS * EI
through the air to his exit point, jumper 1 starts down his trajectory
and his exit point moves a distance WS * EI. When jumper 2 exits the
exit points are separated by S = GS * EI.
And on the bottom end, while jumper 2 falls his final EI seconds,
jumper 1's opening point moves a distance WS * EI. When jumper 2 opens
the opening points are separated by S = GS * EI.
So this is our basic picture. Separation of opening points comes directly
from separation of exit points. Flying into high uppers causes slower
ground speed and requires greater exit interval.
Now as a math major I would be happy to stop right here, but since we
have a ***practical application*** in mind we should do some numbers and
find out what we are actually talking about.
Let's take an airspeed of 80 kts, fly into various uppers and see
what exit interval is required for various separations.
AS = 80 kts 6076 ft = nautical mile EI = S/GS
uppers kts | 0 30 45 60
|
GS kts | 80 50 35 20
|
GS ft/sec | 135 84.4 59.1 33.8
----------------------------------------------
S = 1,000 ft | 7.4 11.9 16.9 30 <-- EI = exit interval
|
S = 1,500 ft | 11.2 17.8 25.4 44.4
|
S = 2,000 ft | 14.8 23.7 33.9 59.3
Now let's do the same thing for an air speed of 100 kts.
AS = 100 kts 6076 ft = nautical mile EI = S/GS
uppers kts | 0 30 45 60
|
GS kts | 100 70 55 40
|
GS ft/sec | 168.8 118.1 92.8 67.5
----------------------------------------------
S = 1,000 ft | 5.9 8.5 10.8 14.8 <-- EI = exit interval
|
S = 1,500 ft | 8.9 12.7 16.2 22.2
|
S = 2,000 ft | 11.8 16.9 21.5 29.6
With the free plummet case in hand we can handle tracking and canopy
motion by setting our free plummet exit and opening points far enough
apart.
--------------------- <-- There .. I just drew the line :-) :-)
This is as far as I can go with this right now.
How much do people track? 300 ft each? Would free plummet opening points
300 + 300 + 600 = 1200 ft be enough?
What if the lowers are opposite the uppers and jumper 1 flies his canopy
500 ft toward jumper 2's opening point - and they each track 300 ft
toward each other? Is 300 + 300 + 500 + 600 = 1700 ft enough?
And on another subject how can we get all this happening in practice?
Being an idealist my favorite way would be for everybody to read the
FAQ when it finally gets written, think deeply about it, and then do
the right thing on jump run.
Right.
More feasible would be some kind of load master on each plane load who
knows (estimates/guesses) what the separation should be and helps / ensures
that people do it.
Other ways would be that oreo cookie stuff - seeing the breakup as a full
fledged maneuver in its own right. Tracking perpendicular to the jump
run, using vertical separation , .. stuff like that.
So let's thrash out some of these remaining quesions here in rec.skydiving
and then someone can write a FAQ and Bob Bonitz can make a formal proposal
to USPA :-) :-)
Skratch
----------------
bdan...@csn.org
Robert Bonitz
>Winds, Exit Intervals, Separation of Groups
>
>Theme: Safe separation between groups at opening
> comes directly from adequate separation of groups at exit.
>How much do people track? 300 ft each? Would free plummet opening points
>300 + 300 + 600 = 1200 ft be enough?
>
>What if the lowers are opposite the uppers and jumper 1 flies his canopy
>500 ft toward jumper 2's opening point - and they each track 300 ft
>toward each other? Is 300 + 300 + 500 + 600 = 1700 ft enough?
>Other ways would be that oreo cookie stuff - seeing the breakup as a full
>fledged maneuver in its own right. Tracking perpendicular to the jump
>run, using vertical separation , .. stuff like that.
At breakoff if my tracking lane is up/down the line of the jump run,
I don't do a full-out track, but a rather weak one just to get a bit more
separation from the subsequent/previous group. Nor do I fly my canopy
towards the subsequent/previous group after opening. Your oreo cookie
stuff is right on the money and should be part of the package.
>So let's thrash out some of these remaining quesions here in rec.skydiving
>and then someone can write a FAQ and Bob Bonitz can make a formal proposal
>to USPA :-) :-)
Say who?
--
Question with boldness even the existence of God; because if there be one,
He must more approve of the homage of reason, than that of blindfold fear.
Thomas Jefferson (1743-1826)
Bill Von Novak
>At breakoff if my tracking lane is up/down the line of the jump run,
>I don't do a full-out track, but a rather weak one just to get a bit more
>separation from the subsequent/previous group. Nor do I fly my canopy
>towards the subsequent/previous group after opening.
your best prevention against canopy collisions after opening is
a good track after breakoff. a weak track is asking for trouble,
especially if someone else on the load has the same idea. if the
spacing is going to be a problem, leave more time between groups or
take a second pass. breakoff isn't the place to be dealing with group
separation problems.
-bill von novak D16479 AFF/SL JM95
Robert Bonitz
Unfortunately, you can't always count on the group behind you; especially,
considering the ignorance of many on how to achieve proper separation. I
have had numerous close calls because the next group did not allow enough
time. Now ideally I would like to be able to go full out on my track at
break off, but the goal here is separation and that includes separation
from people from the subsequent or previous group as well. Remember that
a full-out track doesn't guarantee adequate separation anyway if someone
else is tracking right next to you. I know where the people in my own
group are and I can check them out before dumping so I can get adequate
separation from them. I don't know how much separation I have from another
group so by not going full out up or down the jump run line, I give myself
a bit more of a margin from them.
Glen Baker
> Theme: Safe separation between groups at opening
> comes directly from adequate separation of groups at exit.
Agreed.
> Sub theme: When flying into high uppers
> leave more time between exits.
Agreed, but not for the reasons Skratch gives.
> exit points are separated by S = GS * EI. [proven several ways]
Yes the ground referenced separation of opening points is GS * EI.
However, I don't give a rats ass about that! I'm perfectly happy putting
up an Otter full of skydivers in a 100 knot breeze and having every single
skydiver open over precisely the same spot *as long as they don't all do
it at the same time!*
Jumper #1 does *not* remain stationary after opening, but continues
merrily downwind (neglecting pilot input). The fact that the next skydiver
opens over the precise same spot is meaningless if he does it 20 seconds
later because during that time jumper #1 has been blown downwind (almost
3000 feet in my 100 mph winds!).
The observer on the ground will see every canopy open over the same point,
but he will *not* see a vertical line of canopies, but a diagonal one.
There are, however, compelling reasons to increase separation on days with
high uppers. Most of these reasons have to do with how people fly their
canopies after opening on windy days with short spots.
..glen
Rick Lemons
In article <3pdrmr$l...@canyon.sr.hp.com>, <gl...@sr.hp.com> writes:
> Ben Daniels (bdan...@aurora.esig.ucar.edu) wrote:
>
> > Sub theme: When flying into high uppers
> > leave more time between exits.
>
> Agreed, but not for the reasons Skratch gives.
>
As I said in my original post, one side of this argument will never convince
some of you. You continue to over think this thing with variable points of
reference and streams of water and such. The fact is that Skratch's FAQ was
perfectly written and correct. But let's stop spending so much effort trying to
convince each other and spend that effort in getting the USPA to address
this issue. This is a safety issue that needs an official answer. If the
official answer is wrong, then we know to whom to direct our arguments. Please
get on the USPA's case. I thought they handled the safety of skydiving.
Johan Conroy
>As I said in my original post, one side of this argument will never convince
>some of you. You continue to over think this thing with variable points of
>reference and streams of water and such. The fact is that Skratch's FAQ was
>perfectly written and correct. But let's stop spending so much effort trying
>to
>convince each other and spend that effort in getting the USPA to address
>this issue. This is a safety issue that needs an official answer. If the
>official answer is wrong, then we know to whom to direct our arguments.
>Please
>get on the USPA's case. I thought they handled the safety of skydiving.
I've decided to settle this thing once and for all. I'm writing a
simulation for this. I'll appreciate it if anyone can give me some
equations describing the dynamics involved in exiting, freefall, tracking,
opening and canopy flying. At the moment, I'm using a very simple model
with vertical speed following a limited exponential increase, horizontal
speed equal to wind speed and vertical speed going instantly from terminal
to canopy rate of descent after opening.
Preliminary results show that everything depends on the wind profile.
Depending on the wind, opening separation is a weighed function of airspeed,
groundspeed and fallrate.
I'm using some graphics, so it's only going to work under MS-DOG, but IF
anyone wants it, I can post the (quite messy) C source code once I've
finished.
Johan
Robert Bonitz
>As I said in my original post, one side of this argument will never convince
>some of you. You continue to over think this thing with variable points of
>reference and streams of water and such. The fact is that Skratch's FAQ was
>perfectly written and correct. But let's stop spending so much effort trying to
>convince each other and spend that effort in getting the USPA to address
>this issue. This is a safety issue that needs an official answer. If the
>official answer is wrong, then we know to whom to direct our arguments. Please
>get on the USPA's case.
A better approach than getting on somebody's case is for someone to put
together a proposed change to the SIM and send it to the Safety & Training
Committee.
>I thought they handled the safety of skydiving.
Hmmm. I thought we all did.
Stephen Creagh t2526
>with vertical speed following a limited exponential increase, horizontal
>speed equal to wind speed and vertical speed going instantly from terminal
>to canopy rate of descent after opening.
>
>Preliminary results show that everything depends on the wind profile.
>Depending on the wind, opening separation is a weighed function of airspeed,
>groundspeed and fallrate.
Um, I don't think you need to get so complicated about this. You can
solve differential equations up the wazoo, but if you do them right you will
just get the same result people have been posting for a while. Ie, the distance
between opening points is determined by groundspeed, but then you get a
little bit extra from the winds at opening altitude, maybe a lot extra if the
winds at opening altitude are large enough. This I think was the point of
the previous poster.
It seems to me that we need to get an expert to tell us what typical
wind profiles are like. Like
1. How often *do* the winds get up to 50 mph or so at altitude
(assuming they are 20mph or less on the ground)?
2. When they are so high, do they really drop off to nothing by
2500ft? I realise it's safest to assume the worst case scenario--- that
they do --- but maybe this is overly pessimistic.
By they way, has there ever actually *been* a collision because people didn't
adjust for high windspeed? Seems like a large part of the jumping population
ignores this (iuncluding me until recently), and I don't hear much of
near accidents because of it.
Stephen Creagh
Robert Bonitz
>By they way, has there ever actually *been* a collision because people didn't
>adjust for high windspeed? Seems like a large part of the jumping population
>ignores this (iuncluding me until recently), and I don't hear much of
>near accidents because of it.
I don't know if there has ever been a collision, but I have had numerous
near misses. Every time the winds get high at jump altitude I become,
shall we say, concerned. Especially, considering the lack of understanding
that many jumpers have concerning this issue.
Rick Lemons
In article <conr-hj.4...@babel.ee.up.ac.za>, <con...@babel.ee.up.ac.za>
writes:
> I've decided to settle this thing once and for all. I'm writing a
> simulation for this.
Your simulation will prove exactly what you program it for. If you program in
the wrong assumptions, you will get the wrong results. Make sure you go into it
with all the factors accurate, not just someone's interpretation of the
factors.
dso...@uoft02.utoledo.edu
stephen...@rphs1.physik.uni-regensburg.de (Stephen Creagh t2526) writes:
>>opening and canopy flying. At the moment, I'm using a very simple model
>>Preliminary results show that everything depends on the wind profile.
>>Depending on the wind, opening separation is a weighed function of airspeed,
>>groundspeed and fallrate.
>
> Um, I don't think you need to get so complicated about this.
> It seems to me that we need to get an expert to tell us what typical
>wind profiles are like. Like
OK, I am not an expert. I am the S&TA at Napoleon Skydiving Center
in MI. We have a Twin Otter. I often spot the Twin Otter, expecially
on high wind days. I also (as S&TA) advise others how to spot. I
am also an AFF and SL I, so instruction of new jumpers sometimes falls
to me as well.
> 1. How often *do* the winds get up to 50 mph or so at altitude
>(assuming they are 20mph or less on the ground)?
The last two weekends at Napoleon had at least one day when then
uppers were in excess of 40 knots while the ground winds were under
20 knots and in a different direction. It happens fairly frequently,
especially with higher exit altitudes.
> 2. When they are so high, do they really drop off to nothing by
>2500ft? I realise it's safest to assume the worst case scenario--- that
>they do --- but maybe this is overly pessimistic.
Not generally. But there is often a significant shift in direction
by 2500'. I have seen "screaming" uppers with less than 5 mph ground
winds, but it is uncommon.
>By they way, has there ever actually *been* a collision because people didn't
>adjust for high windspeed? Seems like a large part of the jumping population
>ignores this (iuncluding me until recently), and I don't hear much of
>near accidents because of it.
You bet. Three weeks ago a jumper in a later group tracked through the
center of the 4 way that left just before him. As I looked into the
near miss, witnesses in the plane said there was a 5-second delay
between groups. On this particular day, the uppers were very strong, and
the resulting lack of exit seperation put the two groups within easy
tracking distance of one another. Incidently the group that was tracked
thru was led by a very experienced AFF I and evaluator. His classification
of "near miss at deployment time" is NOT an exaggeration (the jumper was
in freefall within 25 feet of a deploying canopy).
Keep in mind that, with today's high performance canopies, canopy drift
after opening cannot be counted on to provide adequate seperation. In
high winds most jumpers will immeadiately turn into the wind on opening
to prevent being blown downwind of the DZ. In this orientation, their
canopies are flying in the direction of the next group's opening point.
If the plane traveled an insufficient distance over the ground between exits,
there will be insufficient distance between openings. With rounds
or older, slower squares, things would be different, but with the advent
of canopies that glide at 35 mph, canopy drift is a non-issue -- the
canopies can hold or penetrate in almost any wind condition. In
today's world, opening point seperation relative to the ground is what
saves lives.
/* Dale Southard Jr. Sr. Rigger VectorTM */
/* Sr. System Administrator, C of Engineering AFF/I SL/I */
/* College Computing, University of Toledo S&TA D-11216 */
/* dso...@uoft02.utoledo.edu 419/537-3596 "I'd rather be skydiving" */
Stephen Creagh t2526
>>
>You bet. Three weeks ago a jumper in a later group tracked through the
>center of the 4 way that left just before him. As I looked into the
>
Stephen Creagh