EXIT SAFETY

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2004 Spring Skydiving Expo
EXIT SAFETY Spotting, Winds, and Separation John
Kallend Department of Mechanical, Materials and
Aerospace Engineering Illinois Institute of
Technology
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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
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RESOURCES
http//www.iit.edu/kallend for download of the
2-d Freefall Separation program, relevant links
and a copy of these slides.
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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.
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THE MESSAGE WILL BE
Check the spot and look for traffic below. The
45 degree method doesnt work. Belly fliers
should go first. Groundspeed methods are OK in
most circumstances learn the exception. Theres
no hurry
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SPOTTING
Most DZs now use GPS for spotting. It works very
well, BUT
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EACH SKYDIVER IS RESPONSIBLE FOR HIS/HER OWN
SAFETY. Dont be a wind dummy. Look out the
door! Check that no planes etc. are below (GPS
doesnt see these). Other pilots are under no
obligation to avoid DZs. Do a visual check on
groundspeed. Be sure you can get back.
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SPOTTING NO WIND
Off
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
LZ
OK
OK
OK
Off
Off
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SPOTTING STEADY WIND
Off
OK
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
hopnpop from a helicopter or balloon, you want
to exit over this area.
OK
LZ
Wind
OK
OK
Off
Off
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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
LZ
Wind
Drift
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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). Thats 11 2-ways with 13
second separation) Crosswind, 1 min 22 sec.
wind
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SPOTTING
X marks the spot. First group out cannot wait
for the perfect spot, or the last out will be
HOSED.
LZ
X
WIND
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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.
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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 1000agl It is better to walk a mile than
to be carried a few yards.
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Separation (Collisions are No Fun)
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SEPARATION
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
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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
Lets take 300 feet as the absolute minimum
acceptable separation.
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VIEW FROM ABOVE
150
300
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.
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SEPARATION WITHIN THE GROUP
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TRACKING
A survival skill that is fun. A breakoff track
should be flat and fast.
Tony Hathaway
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To obtain 300 separation between jumpers in a
4-way, need to track 212 ft from the center so
the individuals columns of air dont 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.
724ft
The corresponding area for an 8-way is more than
1,000 ft. across. These numbers are minima.
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How Far to Track, and What Size is the Groups
Air Column?
Group Size Tracking Distance (ft) Radius of
Groups 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 groups 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.
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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.
AND Make sure the first wave doesnt stop too
soon.
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SEPARATION BETWEEN GROUPS
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Centers of groups should be separated by gt sum
of their radii to minimize chance of collisions
between groups.
R1 R2
R1
R2
Group 2
Group 1
Example Group 1 is 8-way, radius 541 group 2 is
4-way, radius 362. Separation should be gt 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.
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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
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HOW DO WE ACHIEVE THIS? People do the strangest
things (like tracking up the line of
flight) SO We wont try to predict what they will
do
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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.
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ACHIEVING SEPARATION
1. Watch angle from vertical to previous
group. 2. Look down and watch until 1,200 ft
have passed. (Skratchs 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?
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First well 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.
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45o ?
Uh-Oh

• Can you judge 45 degrees ?
• If you can, does the method work anyway ?
• Computer model Freefall does the math.

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Conclusion 1
Video by Bill von Novak
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.
DONT USE IT.
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2. Look at the ground.
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?
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3. GROUNDSPEED METHOD
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?
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Case 1. Groundspeed 40ktWind at 3000ft
30ktExit delay 8 seconds
How Groundspeed Can Mislead (Unless you deploy on
the ground)
Click on the link Freefall Simulation
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Case 2 Same groundspeed 40kt
Wind at 3000ft 30 kt tailwind Exit delay same
(8 seconds) Use Freefall Simulation again

• Observations
• 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.

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CONCLUSION 2
Its not the speed over the ground that
counts. Its 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.
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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.
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HOW TO GET WINDS ALOFT
Ask the pilot, or Call 1-800-WX BRIEF, or Point
your browser at aviationweather.gov/products/nws/
fdwinds/
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TO GET 1000FT OF SEPARATIONJumprun 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.
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Next well look at
Fall Rate Differences Forward throw Freefall
drift due to upper winds
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For Forward Throw Click on Freefall.exe
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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.
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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?
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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.
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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
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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.

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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.
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IF FREEFLIERS EXIT BEFORE RW GROUPS extra spacing
is needed to achieve adequate horizontal
separation, maybe tens of seconds.
But it is not always a bad idea
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.
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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, uppers30kts. Normal
spacing 9 seconds. Now require 9 4 (3 x
2) 19 seconds between exits.
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THE MESSAGE WAS
Check the spot and look for traffic below. The
45 degree method doesnt work. Belly fliers
should go first. Groundspeed based methods are OK
in most circumstances learn the
exception. Theres no hurry
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ACKNOWLEDGEMENTS
Discussions with Winsor Naugler III Skratch
Garrison Tamara Koyn Tim Wagner Articles Bryan
Burke Bill von Novak Video Bill von Novak