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I wrote parts 1 and 2 in parallel hoping to make part 1 more readable by sticking to words and ideas and putting diagrams and calculations in part 2. I didn't think many people would feel moved to read part 2 so in order to make part 1 stand on its own there is some copy and paste of words from part 2 to part 1.
Dealing with Uppers part 1 - version 9,746,211 2004-2-2
---------------------------------------------- --------
This is not about spotting .. It's not about dealing drugs either.
In low to medium uppers it's about leaving separation, and in medium
to strong uppers it's about accepting that we are in a new environment
and changing the way we jump.
It's a confusing question because our intuitions have developed for
simple situations like jumping off of a chair where everything is
holding still and the ground is right there just a fraction of a
second away.
In skydiving we have fast moving airplanes, strong upper winds,
60 seconds worth of winds blowing us around in freefall, and fast
moving canopies, and our untrained intuitions give us wrong answers.
------------------------------------------------
Uppers are not a single, monolithic situation, and no
one size fits all approach is going to work.
What to do when we have strong uppers, long waits and
fast canopies is difficult to figure out.
Flying canopies away from jumprun instead of up under
the next group is very important.
We have to jump the conditions and not pretend that
we can do whatever we want no matter what.
------------------------------------------------
In zero to low uppers our intuitive idea of going when the previous
group has fallen far enough behind the plane works.
----
In low to medium uppers we have to expand our idea of separation
to mean separation of exit points, and we can separate exit points
using a chart of ground speed vs seconds between groups posted
on the wall back by the door.
In this low to medium region canopy speed becomes important
(canopy ground speed could be as much as half the airplane
ground speed), and the people on the up jumprun side of the
breakup should not fly their canopies up jumprun until they
know the following group is not on top of them.
----
In the medium to medium strong region this separation of exit
points approach breaks down.
The waits between exits become so long that the canopies of
the previous group are getting down out of the kill zone,
and the original motivation, horizontal separation at opening,
is losing its meaning.
It's hard to know how long to wait, it's hard to count that
many seconds accurately, and it's very unclear how to handle
this medium to medium strong region.
----
In the region of really strong uppers, like the day last year
at Brush when the King Air was showing a ground speed of 12 knots,
it is clearer what to do.
Stop treating these kinds of uppers as business as usual and only
do jumps with lots of room designed into them for looking down,
so we can check the spot and watch for canopies of previous groups
that we may be drifting over.
Maybe in these kinds of winds we should just go several miles up
wind and track back the dropzone.
------------------------------------------------------------------------
The Zero to Low Region
----------------------
These days the exit order:
UPPERS ----------------- > < ------------------- AIRPLANE
\ \ \ | | | \ \ \
\ \ \ | | | \ \ \
\ \ \ | | | \ \ \
\ \ \ | | | \ \ \
Openings ---> O O O | | | \ \ \
| | | \ \ \
O O O O O O
AFF's, Tandems Fast Falling Slow Falling
High Pullers Groups Groups
seems to be pretty well accepted, and the remaining confusion centers
around how to leave adequate separation from the group in front of us.
The most natural way is to watch the previous group fall away, and when
they have fallen far enough behind the plane, go.
Our intuition about jumping off of chairs tells us that with a little
training and experience in what "far enough behind" looks like that
ought to work.
And on no wind days it does work.
The Low to Medium Region
------------------------
With stronger uppers we watch the same initial separation happen,
jump out, and 60 seconds later go screaming by open canopies.
Our separation disappeared.
Why is that?
----
If we stand in the peas and watch the same jump it's easy to see
what happened.
The first group goes.
The plane isn't moving very much but the first group is swept away
from the plane by the relative wind just like it always is in the
first few seconds.
That initial separation is there just like it always is.
Then from a small distance upwind the second group goes.
They also get swept away from the plane by the relative wind
and now we can see what happened:
The freefall trajectory of the second group looks just like
the first group's but displaced upwind by the distance the
plane has moved.
The short distance the plane has moved is how far apart the
groups are on the bottom end.
The breakup tracks, and especially the canopy motion of
the first group while the second group is still in freefall,
have them opening in the same area.
We are saved from disaster by Bryan Burke's big sky theory.
The mistake (from our jumping off of a chair intuition) is thinking
that the separation we see in the first few seconds will still be
there 60 seconds later.
Or maybe our real mistake is our untrained idea of what separation
is and how to see it.
With our feet in the peas we can see that a better idea of separation
is how far the plane has actually moved between exits, how far through
the sky, how far across the ground, how far between exit points.
----
With practice we can teach ourselves to stand in the door and see that
on a no wind day, we, the second group, are moving away from the first
group's exit point, while on a stronger wind day we are moving only a
little and they are being swept down wind from their exit point.
With stronger uppers it will take us longer to separate our exit points.
----
Here we run into a practical difficulty: it takes a fair amount of
training and practice to guage position and change of position over
the ground, and these days, with large turbines and GPS, people are
not taught to spot and rarely need to.
( Actually in the mythical old days a lot of people couldn't
( spot very well either, but you're not supposed to know that.
( It would ruin a lot of good jump stories.
----
Since we are still after horizontal separation that lasts all the
way down to breakup and opening altitude even in stronger uppers,
the logical thing to do in this age of cheap GPS units is to put
one back by the door and use that to get separation.
Need 1,500 ft? Watch the distance across the ground unroll on the
digital readout, estimate when to start the climb out, and go.
Better yet is the GPS readout on the heads up display in everybody's
helmet. That way everybody can check the separation.
----
While we're waiting for that to happen we can achieve the same effect
by knowing the ground speed on jumprun and posting a little table
of ground speed vs seconds between groups for some common cases and
light to medium uppers back by the door.
If we assume that the people on the up jumprun side of the breakup
turn away from jumprun after opening, or at least go into brakes for
a while, instead of flying up jumprun towards the following group,
we can use a ground speed vs distance table that accounts for a bit
of sliding around in freefall, the breakup track, and a buffer
between nearest neighbors of adjacent groups.
On the top row we put the aircraft ground speed on the left and
on the right we put the time between two eight ways (8-8), two
four ways (4-4) and two 1 ways (1-1). See part 2 of this writeup
for where these tables come from.
|-------|----------| |-------|-------|-------|
| AGS | AGS | | T | T | T |
| knots | ft/sec | | sec | sec | sec |
| | | | 8-8 | 4-4 | 1-1 |
|=======|==========| |=======|=======|=======|
| 100 | 168.8 | | 9.4 | 7.3 | 5.9 |
|-------|----------| |-------|-------|-------|
| 90 | 151.9 | | 10.4 | 8.1 | 6.6 |
|-------|----------| |-------|-------|-------|
| 80 | 135.0 | | 11.7 | 9.1 | 7.4 |
|-------|----------| |-------|-------|-------|
| 70 | 118.2 | | 13.4 | 10.4 | 8.5 |
|-------|----------| |-------|-------|-------|
| 60 | 101.3 | | 15.6 | 12.1 | 9.9 |
|-------|----------| |-------|-------|-------|
| 50 | 84.4 | | 18.8 | 14.5 | 11.8 |
|-------|----------| |-------|-------|-------|
| 40 | 67.5 | | 23.5 | 18.1 | 14.8 |
|-------|----------| |-------|-------|-------|
| 30 | 50.6 | | 31.3 | 24.2 | 19.8 |
|-------|----------| |-------|-------|-------|
| 20 | 33.8 | | 46.9 | 36.2 | 29.6 |
|-------|----------| |-------|-------|-------|
| 10 | 16.9 | | 93.7 | 72.4 | 59.2 |
|=======|==========| |=======|=======|=======|
|Exit Separation ft| |1584 ft|1224 ft|1000 ft|
| | | | | |
| slide + track + | | | | |
| buffer | | | | |
| | | | | |
| lower winds = 0 | | | | |
| CGS = 0 | | | | |
|-------|----------| |-------|-------|-------|
If you're some other combination, say a 5 way following a 7 way (7-5),
then just wing it. Pick a time between the two columns closest to your
combination.
The top few rows look plausible but the bottom ones aren't so clear.
People in the early groups can't face 90 degrees away from the dropzone
for too long or they won't make it back, and who on top can count that
many seconds accurately? Indeed, who on top is even going to try?
So I'm thinking that just because we can do arithmetic doesn't mean
we have solved the problem, and maybe we should change the bottom few
rows like this to avoid misleading people into thinking there is some
scientific, four out of five leading doctors, official answer here:
|-------|----------| |-------|-------|-------|
| AGS | AGS | | T | T | T |
| knots | ft/sec | | sec | sec | sec |
| | | | 8-8 | 4-4 | 1-1 |
|=======|==========| |=======|=======|=======|
| 100 | 168.8 | | 9.4 | 7.3 | 5.9 |
|-------|----------| |-------|-------|-------|
| 90 | 151.9 | | 10.4 | 8.1 | 6.6 |
|-------|----------| |-------|-------|-------|
| 80 | 135.0 | | 11.7 | 9.1 | 7.4 |
|-------|----------| |-------|-------|-------|
| 70 | 118.2 | | 13.4 | 10.4 | 8.5 |
|-------|----------| |-------|-------|-------|
| 60 | 101.3 | | 15.6 | 12.1 | 9.9 |
|-------|----------| |-------|-------|-------|
| 50 | 84.4 | | 18.8 | 14.5 | 11.8 |
|-------|----------| |-------|-------|-------|
|-------|----------| |-------|-------|-------|
| 40 | 67.5 | | Not business as usual |
|-------|----------| |-------|-------|-------|
| 30 | 50.6 | | Look down |
|-------|----------| |-------|-------|-------|
| 20 | 33.8 | | Check for canopies |
|-------|----------| |-------|-------|-------|
| 10 | 16.9 | | Check the spot |
|=======|==========| |=======|=======|=======|
|Exit Separation ft| |1584 ft|1224 ft|1000 ft|
| | | | | |
| slide + track + | | | | |
| buffer | | | | |
| | | | | |
| lower winds = 0 | | | | |
| CGS = 0 | | | | |
|-------|----------| |-------|-------|-------|
------------------------------------------------------------------------
If we let people fly up jumprun towards the following group the
time between groups gets larger, especially as the uppers increase.
The longer we wait on top for separation, the more that canopy moves.
And we see in the bottom rows of AGS - CGS (aircraft ground speed -
canopy ground speed) that the canopies are covering ground faster
than the plane is.
This separation of exit points approach only works in low to medium
uppers, and we should chop off the bottom few rows of this table too.
See part 2 for further discussion of these points.
|-------|----------|-----------| |-------|-------|-------|
| AGS | AGS | AGS - CGS | | T | T | T |
| knots | ft/sec | ft/sec | | sec | sec | sec |
| | | | | 8-8 | 4-4 | 1-1 |
|=======|==========|===========| |=======|=======|=======|
| 100 | 168.8 | 124.8 | | 12.7 | 9.8 | 8.0 |
|-------|----------|-----------| |-------|-------|-------|
| 90 | 151.9 | 107.9 | | 14.7 | 11.3 | 9.3 |
|-------|----------|-----------| |-------|-------|-------|
| 80 | 135.0 | 91.0 | | 17.4 | 13.5 | 11.0 |
|-------|----------|-----------| |-------|-------|-------|
| 70 | 118.2 | 74.2 | | 21.3 | 16.5 | 13.5 |
|-------|----------|-----------| |-------|-------|-------|
| 60 | 101.3 | 57.3 | | 27.6 | 21.4 | 17.5 |
|-------|----------|-----------| |-------|-------|-------|
| 50 | 84.4 | 40.4 | | 39.2 | 30.3 | 24.8 |
|-------|----------|-----------| |-------|-------|-------|
| 40 | 67.5 | 23.5 | | 67.4 | 52.1 | 42.6 |
|-------|----------|-----------| |-------|-------|-------|
| 30 | 50.6 | 6.6 | | 240.0 | 185.5 | 151.5 |
|-------|----------|-----------| |-------|-------|-------|
| 20 | 33.8 | -10.2 | | xx.x | xx.x | xx.x |
|-------|----------|-----------| |-------|-------|-------|
| 10 | 16.9 | -27.1 | | xx.x | xx.x | xx.x |
|=======|==========|===========| |=======|=======|=======|
| Exit Separation ft | |1584 ft|1224 ft|1000 ft|
| lower winds = 0 | | + | + | + |
| | | CGS*T | CGS*T | CGS*T |
|-------|----------|-----------| |-------|-------|-------|
So far we have taken the winds at opening altitude to be zero.
If they are from the same direction as the uppers the separation at
opening gets better. If they are opposite the uppers it gets worse.
But, we don't have to do a whole separate table. We can just notice
that a 10 knot opposite lower wind is equivalent to a 10 knot slower
aircraft ground speed and look at the next row down for the answer.
Unless we measure that lower wind on the way up we are guessing
based on previous loads, but if it's there we should try to take
it into account.
----
When I first ran into the exit separation discussion on rec.skydiving
in the early 90s my intuition from round canopy days was that airplanes
are fast, freefall is even faster, canopy motion and lower winds are
small and can be ignored.
My intuitive mental model of skydiving was that the airplane and freefall
were way up there in one world, and canopy flight was down here in a
totally separate and unrelated world.
In today's world of high altitudes, strong uppers and fast canopies
that is not true. I may be a couple miles below and behind but I'm
flying my canopy in the same world that airplane is.
To put it another way:
If I saw an airplane flying along dropping stuff, would I
fly over and get below and behind it?
That's what flying up jumprun right after opening amounts to.
----
Some people say the ground is irrelevant, you could be hauling the
dropzone around with a giant tractor and it wouldn't change anything
but the spot. It's the uppers and the plane's air speed plus the lowers
and the canopy speeds plus a bit of tracking at breakup that determine
the separation.
As a physics problem about spherical, isotropic skydivers falling
through an ideal atmosphere they are right.
But for the person in the door trying to leave separation they are
wrong. You can't see the layers of air but you can see the ground.
You can only guess how the layers are moving, but with GPS you can
measure the speed across the ground.
We also know from physics that choosing a good coordinate system
can really help us understand a problem.
And for me that's a big advantage in using the ground as the frame
of reference: I can understand what's going on in these separation
discussions.
----
Another advantage of using the ground and ground speeds is that the
same tables apply to any airplane, whereas if you based it all on,
for example, the speed of the uppers you would need a different
set of tables for every plane with a different air speed, or even
the same plane flying a different air speed.
----
This low to medium region is common and I think that trying this tables
approach would remove some of the uncertainty in how to handle it.
Even students doing solos just off of AFF could leave separation.
Right now it is difficult to explain to them and there is a lot
of chaos and misinformation even among experienced jumpers.
----
These tables are my best estimate of a starting point to be field
tested for a season or two and adjusted based on experience.
For actual use I would round the seconds to whole numbers and put
some kind of "change your activity" words in the bottom rows.
Perhaps someday we will settle on some commonly accepted recommendations
and they will end up in the SIM.
(Hey, look mom! There's an optimistic idealist! :-) :-)
The Medium to Medium Strong Region
----------------------------------
and
The Really Strong Region
------------------------
I'm not sure what to do for these cases. The canopies of the previous
groups could be outrunning the plane or even on the ground and the
original motivation of horizontal separation at opening wouldn't apply.
It is tempting to invoke Bryan's big sky theory as an active part of
the strategy except that these days a lot of people are pulling while
still in low earth orbit so you can't really be sure that they will
be down out of the way.
We also need to emphasize that there is more to separation than
mechanical tables of ground speed vs whatever.
If someone can't fall straight down they need to get some coaching,
and that's a social question.
Only doing jumps with lots of look down time built in in really
strong uppers would be another change of social behaviour.
When people are tracking away they need to watch where they are going
and watch for people or canopies below them.
I know from experience that when I'm tracking away I can not accurately
judge my trajectory relative to fast moving canopies below.
Hawks and falcons can do that, but I can't.
People on the up jumprun side of the breakup not flying up jumprun
right after opening needs to become standard lore.
And yet for the people in the front of the load you can't face
90 degrees away from the dropzone for too long or you won't make
it back.
This interplay between strong uppers, long waits and fast canopies
is an area rich in opportunity for some new thinking and new ideas.
I have heard of pilots doing cross wind jumpruns which seems like
a partial answer.
On a crosswind jumprun in high uppers there will have to be a large
crab angle to maintain a course across the ground perpendicular to
the uppers, so the ground speed of the plane will be greater than
flying into the uppers but still small enough to require more thought.
Even with tables of official seconds for low to medium uppers people
still need to look out the door, check the spot, look for planes and
so on.
So I don't really know what to do for these extreme cases. I do know
that we're all jumpers, so we're going to go anyway whether we know
what we're doing or not, but we should not treat strong uppers like
business as usual.
This whole upper wind question is filled with estimates and rules of
thumb, but we only have to do it well enough to be safe and not cause
too many go arounds.
Revised 2004-3-29
Skr
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