Skydiving separation patern

1. EXIT SAFETY
Spotting, Winds, and Separation
John Kallend
Department of Mechanical, Materials and Aerospace
Engineering
Illinois Institute of Technology
2004 Spring Skydiving Expo

2. ISSUES
Large jump planes with many groups
Multiple planes on jump run
Mixed disciplines with different fall
rates
High exit altitudes (and higher winds,
windshears)
GPS spotting
High performance canopies

3. RESOURCES
http://www.iit.edu/~kallend for
download of the 2-d Freefall
Separation program, relevant links and
a copy of these slides.

4. AVOIDING THE BAD STUFF
Out-landings in snake filled swamps
Freefall collisions
Canopy collisions
Each DZ has unique circumstances.
There is no single solution that fits all
DZs on all occasions.

5. THE MESSAGE WILL BE:
Check the spot and look for traffic below.
The “45 degree method” doesn’t work.
Belly fliers should go first.
Groundspeed methods are OK in most
circumstances; learn the exception.
There’s no hurry

6. SPOTTING
Most DZs now use GPS for
spotting.
It works very well, BUT

7. EACH SKYDIVER IS RESPONSIBLE
FOR HIS/HER OWN SAFETY.
Don’t be a “wind dummy”.
Look out the door!
Check that no planes etc. are below (GPS
doesn’t see these). Other pilots are under no
obligation to avoid DZs.
Do a visual check on groundspeed.
Be sure you can get back.

8. LZ
SPOTTING: NO WIND
On a no-wind day,
canopies opening within
the shaded area make it
back to the LZ. Outside
this area will land off.
The boundaries of the
shaded area extend about
a mile beyond the LZ
(depends on opening
altitude). OK
OK
Off
Off
Off
OK
OK
OK

9. LZ
SPOTTING: STEADY WIND
On a windy day, the area
from which a canopy can
reach the LZ is shifted
upwind, but its size stays
the about the same.
If making low hop’n’pop
from a helicopter or
balloon, you want to exit
over this area.
OK
OK
Off
Off
Off
Wind
OK
OK

10. LZ
SPOTTING: STEADY WIND
From altitude, freefall
drift will displace the
exit area from which you
can make it back to the
LZ. You will need to
exit inside the red line to
make it back. The exact
displacement depends on
jumprun airspeed, fall
rate, upper winds, and
direction of jump run.
The SIZE of the safe
area to exit is unchanged
Wind
Drift

11. SPOTTING: GREEN LIGHT
Consider an area for a safe
exit and a satisfactory spot
that is 2.5 miles across.
With 100kt true airspeed and
40kt uppers, jumprun will
take:
Downwind, 56 seconds
Upwind, 2 mins 10 sec.
(no need to rush). That’s 11
2-ways with 13 second
separation)
Crosswind, 1 min 22 sec.
wind

12. SPOTTING
LZ
X marks the spot.
First group out
cannot wait for the
perfect spot, or the
last out will be
HOSED.
WIND

13. GETTING BACK FROM A BAD SPOT
Learn the “accuracy trick”
Get “small” to reduce drag.
If upwind of the DZ, use rear risers or brakes
to flatten the glide.
If downwind of the DZ, rear risers may still
help in light winds. Otherwise use full flight.
Front risers only help in very strong
headwinds.

14. GETTING BACK FROM A BAD SPOT
Forward speed depends mostly on wing
loading. Risers and brakes mostly affect
descent rate.
Have a safe landing spot selected while still
above 1000’agl
It is better to walk a mile than to be carried a
few yards.

15. Separation
(Collisions are No Fun)

16. “Now lets talk about separation from other jumpers. First
of all, anyone who counts on vertical separation for safety
is out of touch with reality. I see people in freefall at 1,500
feet and lower routinely, so just because someone plans to
open at 2,500 doesn't mean you should bet your life on it.
Everyone needs to open in their own column of air.
Horizontal separation is the only guarantee of
security.”
Bryan Burke
Skydive Arizona
SEPARATION

17. HOW MUCH SEPARATION IS NEEDED?
A modern canopy flies at around 30mph = 44ft/sec
(some are notorious for off-heading openings)
It takes about 3 seconds to recognize a
collision hazard and take action
Two canopies on a head on course cover
around 300 feet in this time
Let’s take 300 feet as the absolute
minimum acceptable separation.

18. 300 150
300 ft separation means each jumper has a
“column of air” 150ft in radius, with
himself or herself at the center. These
columns of air should not overlap.
VIEW FROM ABOVE

19. SEPARATION WITHIN THE
GROUP

20. TRACKING
A survival skill that is fun.
A breakoff track should be flat and
fast.
Tony Hathaway

21. To obtain 300’ separation between jumpers in a 4-
way, need to track 212 ft from the center so the
individuals’ columns of air don’t overlap.
3 seconds after
opening there
could be canopies
anywhere in an
area 724 ft in
diameter. Each
group needs its
own column of air.
The corresponding area for an 8-way is more than
1,000 ft. across. These numbers are minima.
724ft

22. How Far to Track, and What Size is the Group’s Air Column?
Group Size Tracking Distance (ft) Radius of Group’s Space (ft)
1 0 150
2 150 300
3 173 323
4 212 362
6 300 450
*7 345 (300) 495 (450)
*8 391 (345) 541 (495)
*10 485 (438) 635 (588)
Note: this table gives the absolute minimum distance to track and the absolute
minimum radius of the group’s space for 300’ separation, assuming efficient tracking
and equally spaced tracks. In reality, more space will be needed.
* For groups larger than a 6-way, the smaller values in parentheses are for when one
jumper deploys in place and the others track.

23. AND
Make sure the first wave doesn’t stop too soon.
A staged breakoff gives better separation for any
group of 12 or more skydivers.
BUT
The “first wave” needs to go 300’ (or more) farther
than the next wave.
SO
Make sure the second wave waits long enough
before turning and tracking.

24. SEPARATION BETWEEN
GROUPS

25. Centers of groups should be separated by > sum of their
radii to minimize chance of collisions between groups.
Group 1 Group 2
R1 + R2
R1 R2
Example: Group 1 is 8-way, radius 541; group 2 is 4-way,
radius 362. Separation should be > 541 + 362 (= 903ft).
Since these are absolute minima, you should space more
conservatively. Plan on, say, 1,200ft to allow for long
tracks, sliding, etc.

26. How much spacing is needed?
Group
Sizes
1 2 4 6 8 10
1 6-800 800 1000 1000 1000 1000
2 1000 1000 1000 1100 1100
4 1000 1200 1200 1300
6 1200 1350 1500
8 1450 1500
10 1600

27. HOW DO WE ACHIEVE THIS?
People do the strangest things
(like tracking up the line of flight)
SO
We won’t try to predict what they
will do

28. Computer model will use virtual “Spaceballs” with
fall rate adjusted for the discipline, to remove human
factor. Freefly spaceball falls 11,000ft in 50 seconds.
RW spaceball takes 65 seconds to fall the same
vertical distance. Spaceballs define the “perfect”
trajectory, no backsliding or tracking.

29. ACHIEVING SEPARATION
1. Watch angle from vertical to previous
group.
2. Look down and watch until 1,200 ft have
passed. (Skratch’s method).
3. Count to 5, then jump (Otter covers about
750 ft in this time on jump run at
13,000ft, no wind)
4. Wait for time taken to cover 1,200ft across
ground (groundspeed method)
Question: Do these methods work?

30. First we’ll take a look at the “angle”
method.
“Wait until the group in front of you
makes an angle of 45 degrees behind
the plane, then exit.”

31. 45o ?
1. Can you judge 45 degrees ?
2. If you can, does the method work anyway ?
Computer model Freefall does the math.
Uh-Oh

32. Conclusion 1
The angle made between the vertical and the previous group
varies very little after the first two or three seconds. It does
not depend on wind speed. It rarely reaches 45 degrees.
There is no physical or mathematical basis for this method.
DON’T USE IT.
Video by Bill von
Novak

33. From 13,000 feet, a  2.75
degree error in judging the
vertical leads to a 1,200 foot
error on the ground!
How well can you judge the
vertical from a moving
aircraft?
2. Look at the
ground.

34. Ask the pilot the groundspeed and you
do the math. 1 knot is roughly 1.5
ft/second, or 100kt = 150ft/sec
Example: groundspeed = 100ft/sec
and you want 800ft separation. Then
you wait 800/100= 8 seconds between
exits. Does this work?
3. GROUNDSPEED METHOD

35. Case 1. Groundspeed = 40kt
Wind at 3000ft = 30kt
Exit delay = 8 seconds
How Groundspeed Can Mislead
(Unless you deploy on the ground)
Click on the link Freefall Simulation

36. Case 2: Same groundspeed = 40kt
Wind at 3000ft = 30 kt tailwind
Exit delay same (8 seconds)
Use Freefall Simulation again
Observations:
1. Groundspeed calculation works if winds are in same
direction at all altitudes
2. Separation also depends on wind at opening altitude,
if in opposite direction to uppers, BEWARE.

37. CONCLUSION 2
It’s not the speed over the ground
that counts.
It’s the speed relative to the air at
opening altitude.
Usually groundspeed methods work
because the winds at 2,500’ are light
and/or in the same direction as the upper
winds.

38. CONCLUSION 2 (cont.)
To achieve separation between groups that have
the same fall rate, methods based on
groundspeed work and have margin for error
UNLESS
the lower winds are opposite the uppers,
IF THAT IS THE CASE THEN
extra spacing is needed. ADD the lower wind
speed to the jumprun headwind, or SUBTRACT
the lower wind speed from the groundspeed.

39. HOW TO GET WINDS ALOFT
Ask the pilot, or
Call 1-800-WX BRIEF, or
Point your browser at:
aviationweather.gov/products/nws/fdwinds/

40. TO GET 1000FT OF SEPARATION
Jumprun indicated airspeed= 80kt
Headwind
(kt)
Delay between
exits (sec).
0 6
10 6.5
20 7.5
30 8.5
40 10
50 12
This assumes
lower winds are
light and/or in
same direction as
uppers.

41. Next we’ll look at:
Fall Rate Differences
Forward throw
Freefall drift due to upper
winds

42. For Forward Throw
Click on Freefall.exe

43. CONCLUSION 3
In no-wind conditions, a freeflier
will have a forward throw down
the line of flight of about 1,800 ft.
A belly flier will have a forward
throw of around 1,200 ft.

44. CONCLUSION 3 (cont)
For any jumprun airspeed, Freefliers
will have a forward throw down the
line of flight that is greater than that
of belly fliers by a distance
approximately equal to the distance
covered by the jump plane in 4
seconds. For 80kts IAS this is around
600 feet.
What About Winds?

45. WIND DRIFT
Even in freefall you “blow along” with the
winds, which may be quite strong at
altitude. Freefliers spend less time in the
upper winds.
Compare wind drift for freefliers and
bellyfliers: Freefall.exe for winds.

46. CONCLUSION 4
In headwind, freefliers have a steeper
trajectory than belly fliers.
For each knot of average upper wind, a
belly flier will drift 20 feet farther than a
freeflier (so a 40kt average wind will
result in 800 feet more drift for the slow
faller).
This adds to the forward throw
difference if the jumprun is into the
wind

47. CROSSWIND AND DOWNWIND
JUMPRUNS
Forward throw is unaffected.
Wind drift effects on separation go
away on crosswind jumpruns
Wind drift effects are reversed on
downwind jump runs.

48. CONCLUSION 5
Separation can be achieved with any exit
order.
BUT
If the freefliers go first, adjacent groups
CONVERGE. This is not fail-safe!
If RW groups go first, groups DIVERGE, a
fail-safe situation. It is easier and takes less
thought to achieve horizontal separation if
freefliers exit after RW groups.

49. IF FREEFLIERS EXIT BEFORE RW
GROUPS
extra spacing is needed to achieve adequate
horizontal separation, maybe tens of
seconds.
For example, if a freefly 2-way is followed
by a large RW group (like a 16-way) that
will take a lot of time to climb out, it may be
easy to get the required separation.
But it is not always a bad idea…

50. IF FREEFLIERS EXIT FIRST
Use your usual method to calculate spacing.
Add 4 seconds to account for extra forward
throw.
Add 2 seconds for every 10kt of upper winds
Example: Want 1000ft spacing, no anomalous winds,
groundspeed =70kts, uppers=30kts. Normal spacing = 9
seconds.
Now require 9 + 4 + (3 x 2) = 19 seconds between exits.

51. THE MESSAGE WAS:
Check the spot and look for traffic below.
The “45 degree method” doesn’t work.
Belly fliers should go first.
Groundspeed based methods are OK in most
circumstances; learn the exception.
There’s no hurry

52. Discussions with:
Winsor Naugler III
Skratch Garrison
Tamara Koyn
Tim Wagner
Articles:
Bryan Burke
Bill von Novak
Video: Bill von Novak
ACKNOWLEDGEMENTS