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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. ISSUES Large jump planes with many groups Multiple planes on jump run

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Exit safety spotting winds and separation john kallend

2004 Spring Skydiving Expo

EXIT SAFETY

Spotting, Winds, and Separation

John Kallend

Department of Mechanical, Materials and Aerospace Engineering

Illinois Institute of Technology


Exit safety spotting winds and separation john kallend

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


Resources
RESOURCES

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


Exit safety spotting winds and separation john kallend

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.


The message will be
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


Spotting
SPOTTING

Most DZs now use GPS for spotting.

It works very well, BUT


Exit safety spotting winds and separation john kallend

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.


Spotting no wind
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


Spotting steady wind
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 hop’n’pop from a helicopter or balloon, you want to exit over this area.

OK

LZ

Wind

OK

OK

Off

Off


Spotting steady wind1
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


Spotting green light
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


Spotting1
SPOTTING

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

LZ

X

WIND


Getting back from a bad spot
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.


Getting back from a bad spot1
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.


Exit safety spotting winds and separation john kallend

Separation

(Collisions are No Fun)


Exit safety spotting winds and separation john kallend

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


Exit safety spotting winds and separation john kallend

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.


View from above
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.



Exit safety spotting winds and separation john kallend

TRACKING

A survival skill that is fun.

A breakoff track should be flat and fast.

Tony Hathaway


Exit safety spotting winds and separation john kallend

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.

724ft

The corresponding area for an 8-way is more than 1,000 ft. across. These numbers are minima.


Exit safety spotting winds and separation john kallend

How Far to Track, and What Size is the Group’s Air Column? to track 212 ft from the center so the individuals’ columns of air don’t overlap.

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.


Exit safety spotting winds and separation john kallend

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 doesn’t stop too soon.


Separation between groups
SEPARATION BETWEEN GROUPS 12 or more skydivers.


Exit safety spotting winds and separation john kallend

Centers of groups should be separated by > 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 > 541 + 362 (= 903ft).

Since these are absoluteminima, you should space more conservatively. Plan on, say, 1,200ft to allow for long tracks, sliding, etc.


How much spacing is needed
How much spacing is needed? radii to minimize chance of collisions between groups.


Exit safety spotting winds and separation john kallend

HOW DO WE ACHIEVE THIS? radii to minimize chance of collisions between groups.

People do the strangest things

(like tracking up the line of flight)

SO

We won’t try to predict what they will do


Exit safety spotting winds and separation john kallend

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.


Achieving separation
ACHIEVING SEPARATION 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.

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?


Exit safety spotting winds and separation john kallend

First we’ll take a look at the “angle” method. 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.

“Wait until the group in front of you makes an angle of 45 degrees behind the plane, then exit.”


Exit safety spotting winds and separation john kallend

45 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.o ?

Uh-Oh

  • Can you judge 45 degrees ?

  • If you can, does the method work anyway ?

  • Computer model Freefall does the math.


Conclusion 1
Conclusion 1 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.

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. DON’T USE IT.


Exit safety spotting winds and separation john kallend

2. Look at the ground. 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.

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?


Exit safety spotting winds and separation john kallend

3. GROUNDSPEED METHOD 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.

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?


Case 1 groundspeed 40kt wind at 3000ft 30kt exit delay 8 seconds
Case 1. Groundspeed = 40kt 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.Wind at 3000ft = 30ktExit delay = 8 seconds

How Groundspeed Can Mislead

(Unless you deploy on the ground)

Click on the link Freefall Simulation


Case 2 same groundspeed 40kt
Case 2: Same groundspeed = 40kt 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.

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.


Conclusion 2
CONCLUSION 2 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.

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.


Conclusion 2 cont
CONCLUSION 2 (cont.) 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.

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.


How to get winds aloft
HOW TO GET WINDS ALOFT 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.

Ask the pilot, or

Call 1-800-WX BRIEF, or

Point your browser at:

aviationweather.gov/products/nws/fdwinds/


To get 1000ft of separation jumprun indicated airspeed 80kt
TO GET 1000FT OF SEPARATION 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.Jumprun indicated airspeed= 80kt

This assumes lower winds are light and/or in same direction as uppers.


Next we ll look at
Next we’ll look at: 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.

Fall Rate Differences

Forward throw

Freefall drift due to upper winds


Exit safety spotting winds and separation john kallend

For Forward Throw 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.

Click on Freefall.exe


Conclusion 3
CONCLUSION 3 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.

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.


Conclusion 3 cont
CONCLUSION 3 (cont) 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.

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?


Wind drift
WIND DRIFT 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.

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.exefor winds.


Conclusion 4
CONCLUSION 4 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.

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


Crosswind and downwind jumpruns
CROSSWIND AND DOWNWIND JUMPRUNS 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.

Forward throw is unaffected.

Wind drift effects on separation go away on crosswind jumpruns

Wind drift effects are reversed on downwind jump runs.


Conclusion 5
CONCLUSION 5 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.

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.


Exit safety spotting winds and separation john kallend

IF FREEFLIERS EXIT 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.BEFORE RW GROUPS

extra spacing is needed to achieve adequate horizontal separation, maybetens 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.


If freefliers exit first
IF FREEFLIERS EXIT FIRST 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.

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.


The message was
THE MESSAGE WAS: 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.

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


Acknowledgements
ACKNOWLEDGEMENTS 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.

Discussions with:

Winsor Naugler III

Skratch Garrison

Tamara Koyn

Tim Wagner

Articles:

Bryan Burke

Bill von Novak

Video: Bill von Novak