!!!!!!USPA vs. SPOTTING
Glen Baker
nobody@nowhere wrote:
> I read the "Off the Mark" with some alarm. Everybody seems to think
> that since the airplane moves at a constant rate, airspeed, not ground
> speed, creates separation. Dead wrong, although it seems to make sense
> initially. Let's look at it from the exit timing with a typical Otter
> load. Assuming five exit groups taking a little over a minute on jump
> run, on a calm day they will be strung out over a corridor about two
> miles long. With strong uppers (and 50 mile an hour uppers do happen)
> in that same 65 seconds the
> airplane is only covering about half that distance in the same elapsed
> time, compressing everyone into a smaller area.
Sigh. As a staunch proponent of the "groundspeed doesn't matter!" camp I
have offered the following reductio-ad-absurdum several times and never
seen the "groundspeed matters" camp post a response:
If you really believe that groundspeed matters then consider the following.
In both cases the "groundspeed" is measured by an observer standing on
the dropzone.
Case 1: Airplane is travelling at 100 KIAS. Winds are calm. Jumpers exit
with 5 seconds between groups. Observers see the groundspeed of
the aircraft as 100 knots. Observers note the spacing between
groups at opening.
Case 2: I hook my Catapillar D-2000 tractor up to the entire 2000 acre
drop zone and start towing it at 100 knots along the jump run.
Airplane still travels at 100 KIAS. Jumpers exit at 5 second
intervals. Observers now note the "groundspeed" of the aircraft
as zero knots and note the spacing between groups at opening.
Does anybody really believe that the spacing between groups at opening
changes just because I hitched up the dropzone and started moving it??
The answer is "yes", but not because of any groundspeed arguments. What
changes is the actions of the jumpers...if they're downwind then when
they all start flying toward the DZ they'll be flying along the jump line
and will thereby reduce the horizontal separation.
..glen
nobody@nowhere
I have been monitoring the spotting issue closely, and I am sure that
you may have noticed that Jason Bell has done nothing to address the
confusion among skydivers regarding spotting. I had a telephone
conversation with Jason last week and he told me that he had no
intention of making an official USPA position. If the issue were taken
more seriously by USPA, a safety bulletin would have been released long
ago, or at least an article from the S&TA.
According to the Editor of Parachutist - Jason Bell, "everyone has
their opinions on spotting, formulas have been submitted and letters to
the editor have been published;" unfortunately, USPA has fallen short.
Additionally, the following post (of many) from a major DZ S&TA was sent to USPA.
What did USPA do regarding the subject? Nothing. For those of you out
there who believe this is some sort of trivial subject of conversation, please
take care of yourself. The life you save will be another jumper and yourself.
Jason Bell, editor
Parachutist Magazine
fax 703-836-2843
Hi Jason;
I read the "Off the Mark" with some alarm. Everybody seems to think
that since the airplane moves at a constant rate, airspeed, not ground
speed, creates separation. Dead wrong, although it seems to make sense
initially. Let's look at it from the exit timing with a typical Otter
load. Assuming five exit groups taking a little over a minute on jump
run, on a calm day they will be strung out over a corridor about two
miles long. With strong uppers (and 50 mile an hour uppers do happen)
in that same 65 seconds the
airplane is only covering about half that distance in the same elapsed
time, compressing everyone into a smaller area.
Now assume the winds aloft are 90 knots, typical jump run air speed on
an Otter. The airplane would stay over one spot, essentially causing
everyone to leave over the same point. Some groups might drift a little
more than others due to different fall rates (length of time they are
pushed by the winds) but that is the sole horizontal factor. The only
separation would be vertical. Mr. Fournier's suggestion that objects
released into a flowing stream from a fixed point would retain
separation is correct - if you assume an infinitely long river.
Interrupt the flow, and those objects would all wash up at the same
spot. One way or another we do that on every skydive.
This brings up the related question of exit order. Because of the
freefall drift/fall rate relationship, lots of people think
freestylists should go first because they fall faster. Actually,
whoever has the longest climb out should go first. Why? If a four way
team has a 20 second climb out, the pilot can give them the exit signal
(get GPS if you haven't already, and out landings will go down by at
least 75%) well before they
are actually leaving the airplane. This takes 20 seconds off of the
overall exit corridor, allowing everyone a chance to get back.
Bryan Burke
S&TA, Skydive Arizona
Unfortunately for the skydiving community as a whole, the organization
representing the entire body has let you down. Don't kid yourself, USPA
has let you down.
I have been a loyal dues paying member of USPA for 12 years. I have
always supported the USPA and believed in the fundamental guidelines
of what the USPA stands for, however, until the Editor of USPA, or the
S&TA of USPA, or the USPA Board, or someone who has the ability
to influence USPA to take a position, the issue will go unresolved.
Time is against USPA; time is against you. It is just a matter of time until
the issues raised in my article regarding spotting and the failure to follow
the basic principles of spotting will lead to a death.
Eric Bernstein
Author of "Off the Mark."
The following is a copy of the article as it was sent to Parachutist before editing.
Note: The emphasis in the original article was not on horizontal separation, but
more on technique. The emphasis should have been on how far apart you are
from others during deployment; my error. Believe me, I had no idea that so much
controversy would follow are article written for the express desire of passing on
life saving information. To my amazement and alarm, I and others discovered
a widespread misunderstanding on the subject. Maybe the information will help
spark question into some of the line of thinking I have seen some people take
regarding the subject.
Who's Going to Spot?
Author: Eric Bernstein
How often have you been in the situation where someone has asked, "Who's going
to spot?", and at that point you made sure eye contact was avoided with the
person asking the question? Sound familiar? Knowing how to determine the exit
point of an aircraft is the responsibility of every skydiver. If you are not
comfortable with the thought of looking out and determining where to exit, I
suggest you try it and make yourself learn the art of spotting. Spotting is a
skill that must be developed. Reading about spotting takes care of the theory,
but does not replace the practical application.
The following are guidelines to take into consideration when determining where
and when to exit any aircraft. Taking the time to follow these steps will lend
itself to building self-confidence about your spotting abilities, as you and
others on the plane trust your judgment.
There are several very important factors that need careful consideration when
determining where to exit an aircraft.
1. Preparation Time (Prep Time): Very important and too often the maker of a
bad spot. All too often the point of exit for your group, and the groups that
follow, take longer than anticipated. Guess what? You are walking. When you
think the exit point is too short, and feel you should wait that extra ten to
fifteen seconds, begin your climb out. The time taken here is exactly what
Prep Time is. Waiting the additional time lends itself to a long spot.
Climb out usually takes longer than you think. You may be surprised when you
realize how far the aircraft travels across the ground in ten seconds. The
next time you are in a DC-3 look out the door and make sure you are looking
straight down. Find a heading on the ground and count to ten seconds. See
how far the aircraft has traveled. Use this mental picture when calculating
Prep Time. A DC-3 will cover a considerable distance across the ground in
ten seconds traveling at a speed of 80KTS or 92MPH.
Compare the distance traveled when you repeat the same exercise the next time
you are in a Twin Otter, Cessna or local DZ aircraft. Use the mental picture
of the distance traveled across the ground when determining the point of exit.
Using this technique on high upper wind days could prevent a potentially
dangerous situation when jumpers from two groups cross into each others
airspace during a track.
A skilled spotter will take Prep Time into consideration for all groups on the
pass. Load the aircraft in such a way as to allow easy exit for each of the
groups on a pass. Determine the experience level of each group on the aircraft
so you can take into consideration the time necessary for climb out and exit.
Lower experienced groups will take longer to climb out. Each group on a pass
should, without exception, allow a minimum of 10 seconds before exiting the
aircraft to allow for adequate separation between groups. Always put the highest
opening jumper out last.
Remember:
a) When arriving at the DZ watch other groups exit to give yourself a mental picture
as to where the exit point should be.
b) Find out who the spotter was on a load that recently landed and ask them
what the upper winds are doing, and where the spot is.
c) Communicate with the pilot. Don't expect the pilot to know how you want
jump run flown.
2. Upper Winds (Free-Fall Drift): While climbing to altitude ask the pilot
how fast the upper winds are blowing at altitude, and from which direction the
upper winds are coming. The information is easily obtained from Flight
Services. *(See Footnote) Depending on the pilot, you could get a couple of
different responses. For example you may be told, "The winds are 25 out of
36," or in a less cryptic tone, "The winds are blowing at 25KTS from the north."
The former is a compass heading. 0 degrees or 360 or 36 all indicate the winds
are from the north, and 18 or 180 indicate the winds are from the south.
Knowing what the winds aloft are is critical. The technique in knowing how far
to take the aircraft upwind to allow for Free-Fall Drift takes time and
repetition. If in doubt ask a more experienced skydiver, who you know can be
trusted, to look over your shoulder. When you arrive at the DZ watch another
group exiting to see how much 'Free-Fall Drift' or push they get. Upper winds
blowing at >50KTS can cause drift of up to a mile or more if exit altitude is
13,000'.
Look at the following example:
The rate of speed at which an aircraft travels across the ground is known as
the Ground-speed. The speed at which an aircraft travels relative to the air
is called the Air-speed. Ground-speed and Air-speed are two factors not to be
confused. The discussion here focuses on the speed the aircraft travels across
the ground as rated in knots. The distance across the ground for one knot is
approx. 6080'.
Suppose an aircraft is traveling at 75KTS. With no upper winds, the aircraft's
ground speed is 75KTS, or 126.7 feet/per/second across the ground. The aircraft
is carrying three groups. Group 1A is a 10-Way, Group 1B is a 6-Way and Group
1C is a 4-Way. The upper winds are minimal; under 10KTS. If Group 1B takes
a 6 second delay before exit the horizontal distance between Groups 1A and 1B
will be approximately 760'. Sounds like a lot, doesn't it?
Now assume the upper winds are blowing at 30KTS. The aircraft is flying
directly into the upper winds. The ground-speed of the aircraft is reduced to
45KTS, or 76 feet/per/second. Horizontal separation between groups is reduced
from 126.7 feet/per/second to 76 feet/per/second. Group 1B only allows 5
seconds for separation time after Group 1A has exited the aircraft. Using the
factor of 76 feet/per/second, the horizontal distance between Groups 1A and
Group 1B is approximately 380'. Horizontal separation of 380' is dangerous,
especially when you take into consideration the distance covered across the
ground during a track.
For this example, lets assume Group 1A's break-off altitude is 3,500'. A
skydiver in a max-track position can achieve horizontal speeds up to 60MPH, or
52KTS. If a skydiver were to start tracking between 3,800'-3,500' and hold the
track until 2,500' (approximately 6 seconds), then flair, waveoff and pull, the
skydiver could achieve an average of almost 88 feet/per/second, or
approximately 528'. The result would be the potentially dangerous situation
whereby one or more skydivers from different groups on the same pass could
possibly cross each others airspace.
Taking this example a step further, assume the upper winds are now 65KTS. The
air-speed of the aircraft remains constant at 75KTS, however, the ground-speed
(distance the aircraft travels across the ground) has been reduced to 10KTS, or
16.9 feet/per/second. Based on this example, taking up to 45 seconds before
Group 1B exits is not excessive in an effort to gain adequate separation and
avoid a potentially dangerous situation. Canopy collisions can and do kill
skydivers.
3. Body Position: Face forward and look towards the front of the aircraft.
If you are new at spotting do not sit sideways to the door; sit facing forward.
Pitch your head sideways and look straight down. Now look up toward the wing
tips followed by scanning the horizon. Doing this will help you determine
whether or not you are looking straight down and if the aircraft is flying
level. Continue to do this motion of looking down, wing tips, scanning horizon
and looking down. Compare the horizontal axis of the wing to the horizontal axis
of the horizon. Are they horizontally relative to each other? Are they at an equal
plane? A couple of degrees off can be a mile or more, especially when the upper
winds are blowing. Know if you are looking straight down.
4. Forward Throw: Depending upon aircraft type, Forward Throw carries a group
a considerable distance. Take Forward Throw distance into consideration when
exiting aircraft such as a DC-3, C-130 or higher airspeed type of aircraft.
Although the transition sweep from horizontal throw to vertical decent is a
short distance in time, the distance across the ground can add up.
5. Ground Winds: There are times when ground winds exceed the upper winds.
Factor into consideration the ground winds in addition to the upper winds for
determining the spot. Maybe you will have to take some additional Prep Time
allowing the groups to remain up wind of the target. For student and novice
jumpers recently off of student status, and depending upon the exit altitude, throwing
a Wind Drift Indicator (WDI) may be necessary to help determine the push of the
ground winds. Spot for the ground winds when they exceed the uppers.
6. Type of Reserve: Never overlook the skydiver having a round reserve. If
you are spotting make sure you take into consideration the person with the
round reserve.
Learning to spot takes time and repetition. The next time someone asks,
"Who is going to spot?" say, "I will."
(Footnote) *In many geographic areas Flight Services can be contacted directly
for upper wind conditions. Contacting Flight Services directly is not
inappropriate for determining upper winds prior to the first load of the day.
Robert Bonitz
>
> Sigh. As a staunch proponent of the "groundspeed doesn't matter!" camp I
> have offered the following reductio-ad-absurdum several times and never
> seen the "groundspeed matters" camp post a response:
>
> If you really believe that groundspeed matters then consider the following.
> In both cases the "groundspeed" is measured by an observer standing on
> the dropzone.
>
> Case 1: Airplane is travelling at 100 KIAS. Winds are calm. Jumpers exit
> with 5 seconds between groups. Observers see the groundspeed of
> the aircraft as 100 knots. Observers note the spacing between
> groups at opening.
>
> Case 2: I hook my Catapillar D-2000 tractor up to the entire 2000 acre
> drop zone and start towing it at 100 knots along the jump run.
> Airplane still travels at 100 KIAS. Jumpers exit at 5 second
> intervals. Observers now note the "groundspeed" of the aircraft
> as zero knots and note the spacing between groups at opening.
>
> Does anybody really believe that the spacing between groups at opening
> changes just because I hitched up the dropzone and started moving it??
>
> The answer is "yes", but not because of any groundspeed arguments. What
> changes is the actions of the jumpers...if they're downwind then when
> they all start flying toward the DZ they'll be flying along the jump line
> and will thereby reduce the horizontal separation.
OK, i'll bite. The purpose for using ground speed is to have a fixed frame
of reference from which to measure aircraft speed and jumper separation.
Everything you said is true, but when you hook up your tractor to the DZ,
you no longer have a fixed frame of reference. Using the distance the plane
travels across the ground, gives one and accurate measure of the separation
between the nominal opening points. Note that I said opening points. They
should be far enough apart to compensate for tracking and canopy movement
after opening.
mARK bLOORE
> Case 1: Airplane is travelling at 100 KIAS. Winds are calm. Jumpers exit
> with 5 seconds between groups. Observers see the groundspeed of
> the aircraft as 100 knots. Observers note the spacing between
> groups at opening.
>
> Case 2: I hook my Catapillar D-2000 tractor up to the entire 2000 acre
> drop zone and start towing it at 100 knots along the jump run.
> Airplane still travels at 100 KIAS. Jumpers exit at 5 second
> intervals. Observers now note the "groundspeed" of the aircraft
> as zero knots and note the spacing between groups at opening.
notice where the separation comes from in case 2: the wind speed generated
by the motion of the drop zone. a much more realistic case is high uppers
and low lowers. so consider these two cases:
case A: winds are zero all the way to altitude. jumpers exit 5 seconds
apart, which gives about 800 feet horizontal separation between exit
points and between opening points.
case B: winds are zero below 2500 feet, and 100 knots at altitude. this gives
zero horizontal separation between exit points and between opening
points. the only separation between groups on opening is 5 seconds
flight under canopy.
when you are actually in the plane spotting, think like this: if the first
group exits over that house and opens over the road, then if the second group
exits over the house too, they will open over the road too.
the wind makes exit point and opening point different, but it is the same
difference for each group. this means that exit points should be as far
apart as you want the opening points to be.
--
mARK bLOORE (ma...@arachnae.com)
mARK bLOORE
> Sigh. As a staunch proponent of the "groundspeed doesn't matter!" camp I
> have offered the following reductio-ad-absurdum several times and never
> seen the "groundspeed matters" camp post a response:
ok, lets take a really absurd example: the upper winds are equal to the
plane's exit speed (say 80 mph). the first group gets out over a certain
house. the second group waits half an hour, and gets out over the same house.
if airspeed is all that counts, they should open 40 miles from where the
first group opened. if groundspeed matters, the second group should open
over the same point that the first group did. what do you think would
happen if you tried this?
--
mARK bLOORE (ma...@arachnae.com)
Arachnae Mgmt.
Barry Brumitt
>
> The answer is "yes", but not because of any groundspeed arguments.
First, you're wrong. Second, here's why:
Your argument is flawed in that the "wind" at all alitudes is the same. The
groundspeed is important because the uppers are often much faster than the
winds at openning altitiude. If you put an otter travelling at 80knots into an
80 knot headwind (groundspeed = 0), with 0 wind at 2000ft, and drop two groups
of jumpers 10 seconds apart, they will open in the same place, except the
first group will have had 10 seconds to decend at their canopy decent
rate. If, instead, the headwind was 40 knots, they would open with some
distance between them.
You *ARE* wrong. I promise. Tell me the flaw in the *very* simple example
above. I've named your flaw, you tell me mine.
Barry
ps. Besides, tractors can't fly! :)
--
Barry L. Brumitt | bel...@frc2.frc.ri.cmu.edu |99.9%|Disclaimer: Opinions
Robotics GradStudent| Skydive! D-15427,SL/AFF I'95 | PGP |given herein may not
Carnegie Mellon | My 15kilobytes of fame: |Savvy| be the opinions of
"Who is John Galt?" | http://www.frc.ri.cmu.edu/~belboz/ |FRC, SCS, RI, or CMU
Bill Von Novak
when skratch and i were talking about this issue. no tractors pulling
DZ's, no 100 mph headwinds, just some everyday examples. hope it
helps.
=========================================================================
A few spotting examples (with just a little math.) I am just
considering distance from group 1's canopies to group 2 as they open -
I'm not considering if the spot is a practical one or if the winds are
safe to land in. I'm also assuming that 500 feet is the minimum safe
separation at opening time.
CASE 1: no wind, 1000 feet separation (skratch rules)
Exit spacing = (airplane speed - wind speed) * time, so ~6 seconds
gives you 1000 feet. Jumpers follow the same trajectory. Separation is
decreased by tracking (assumed to be 100 feet per jumper) and canopy flight
in the first group (assumed to be 25 mph * 6 seconds, or 220 feet.) We have
to assume a worst-case of canopy flight out from the center, since that's
what the jumper should be doing for the first few seconds. We look at the
point in time when the second group has broken off and is about to pull.
We started with 1000 feet, minus 220 feet for canopy flight of the
first group, and 100 (x2) feet for tracking. We're left with 580 feet.
Looks good. Diagram below:
note: group spreads out as jumpers track off, then deploy.
also note: vertical scale at bottom end is greatly exaggerated - the two
groups would actually be at almost the same altitude.
AIRCRAFT SPEED:120 MPH
MAX TRACK:100 FEET
CANOPY SPEED:25 MPH
group 1 group 2 |\
-----------------------------------------------[=0==>------------> JUMP RUN
* <- 1000 FEET -> * | 12000
* (6 SECONDS) * |
* * | NO WIND
* * |
* * |
* * |
* * |6000
* * |
* * |
* * | NO WIND
* * |
* * |
* * |BREAKOFF ALT
where group * * * * |3000
1 will be * * 222 <-opening alt, group 2 |
when group 2 * * |OPENING ALT
opens ---> 111111111 |
|
MIN HORIZ SEP |
|<-580 FEET->| |
------------------------------------------------------------------
=========================================================================
CASE 2: 30 mph wind, 1000 feet separation
Again, Exit spacing = (airplane speed - wind speed) * time, so ~7.5 secs
gives you 1000 feet. Jumpers all follow the same trajectory. Separation is
decreased by tracking (assumed to be 100 feet per jumper) and canopy flight
(assumed to be 25 mph * 7.5 seconds, or 275 feet.) However, winds blow the
first group away from the second group, so we add (30 mph * 7.5 sec) or 330
feet.
We started with 1000 feet. Subtract 275 feet for canopy flight of the
first group, add 330 feet for wind induced separation, and subtract 200 feet
for tracking again. We're left with 850 feet. Looks even better now.
AIRCRAFT SPEED:120 MPH
MAX TRACK:100 FEET
CANOPY SPEED:25 MPH
---------------------------------------------------------------> JUMP RUN
* <- 1000 FEET -> * | 12000
* (7.5 SECONDS) * |
* * |
* * |
* * |
* * |
* * |6000
* * |
* * | WIND
* * | <-- 30 MPH
* * |
* * |BREAKOFF ALT
* * * * |3000
* * 222 |
* * |OPENING ALT
11111111 |
|
MIN HORIZ SEP |
| <- 850 FEET -> | |
-----------------------------------------------------------------
===========================================================================
CASE 3: 30 mph wind at altitude, 0 mph at opening, 1000 feet separation
Again, Exit spacing = (airplane speed - wind speed) * time, so ~7.5 secs
gives you 1000 feet. Jumpers all follow the same trajectory. Separation is
decreased by tracking (assumed to be 100 feet per jumper) and canopy flight
(assumed to be 25 mph * 7.5 seconds, or 275 feet.) There is no wind at
opening, so the group is not moved in any direction
We started with 1000 feet, subtract 275 feet for canopy flight of the
first group and 200 feet for tracking again. We're left with 525 feet.
Uh oh. Getting closer.
Why is this jump different from the first one? The groups are waiting
longer between exits, so the canopies have more time to wander away from
the center of the group. (and no, we can't assume they're going to do
any differently. They SHOULD be moving away from the center for the
first few seconds, which is the worst case.)
AIRCRAFT SPEED:120 MPH
MAX TRACK:100 FEET
CANOPY SPEED:25 MPH
---------------------------------------------------------------> JUMP RUN
* <- 1000 FEET -> * | 12000
* (7.5 SECONDS)* | WIND
* * | <-- 30 MPH
* * |
* * |
* * |
* * |6000
* * |
* * |
* * | WIND 0 MPH
* * |
* * |BREAKOFF ALT
* * * * |3000
* * 222 |
* * |OPENING ALT
111111111 |
|
MIN HORIZ SEP |
|<-525 FEET->| |
-----------------------------------------------------------------
===========================================================================
CASE 4: 30 mph wind at altitude, -15 mph at opening, 1000 feet separation
(i.e. wind at opening altitude is 180 degrees different.)
Exit spacing = (airplane speed - wind speed) * time, so ~7.5 secs
gives you 1000 feet. Jumpers all follow the same trajectory. Separation is
decreased by tracking (assumed to be 100 feet per jumper) and canopy flight
(assumed to be 25 mph * 7.5 seconds, or 275 feet.) Separation is also
decreased by winds blowing the first group back towards the second one.
Since the second group hasn't traversed this space yet, the winds have
not yet blown them anywhere. so we have to subtract an additional
(15 mph * 7.5 seconds, or 165 feet.)
We started with 1000 feet, subtract 275 feet for canopy flight of the
first group, 165 feet for wind drift, and 200 feet for tracking again.
We're left with 360 feet. Too close.
AIRCRAFT SPEED:120 MPH
MAX TRACK:100 FEET
CANOPY SPEED:25 MPH
---------------------------------------------------------------> JUMP RUN
* <- 1000 FEET -> * | 12000
* (7.5 SEC) * |
* * |WIND
* * | <-- 30 MPH
* * |
* * |
* * |WIND
* * | --- 0 MPH
* * |
* * |6000
* * |WIND
* * | --> 15 MPH
* * |
* * |BREAKOFF ALT
* * * * |3000
* * 222 |
* * |OPENING ALT
111111111 |
|
MIN HORIZ SEP |
|<360 F>| |
-----------------------------------------------------------------
TSW
> Case 2: I hook my Catapillar D-2000 tractor up to the entire 2000 acre
> drop zone and start towing it at 100 knots along the jump run.
Please quit moving the DZ...I have to drive there every wkend and it can
be a real pain when its never in the same place twice.....
tsw 'a staunch proponent of the "moving the dropzone does matter!" camp'
d-16909
--
...And once you have tasted flight, you will walk the earth with your eyes turned skyward, for there you have been and there you long to return ...
eri...@oz.net
has to take a position on the subject. There is no excuse for negligence.
From "hooking up tractors" to a total "lack of training," the skydiving community needs the support
of USPA before someone is killed; we will all suffer in the end. USPA must validate the potential
lifesaving information regarding horizontal separation during deployment as outlined in the "Off the
Mark" article.
I am not certain why the USPA has not taken any action to validate this safety issue. I can only
guess that:
1) Lack of technical experience/knowledge on the part of USPA staff.
2) Lacking the leadership.
If USPA fails to take action, precognition may just dictate the following:
FAA Investigates USPA---
WASHINGTON, DC. - The Federal Aviation Administration is reported to
have initiated an investigation into the safety practices of the United
States Parachute Association (USPA). Investigator reports alleges USPA
has failed to provide life saving information to its members regarding
skydiver exit distances and traffic congestion.
The United States Parachute Association is an organization representing
skydivers throughout the United States supported by membership dues.
According to investigators, USPA has a published document entitled
Basic Safety Regulations (BSR's) which provide fundamental guidelines
for individuals entering the sport and for safety concerns of
experienced skydivers as well. Investigators have uncovered evidence
to suggest USPA is aware of a wide spread misunderstanding among its
members that could lead to a fatality, but has failed to take action .
FAA officials are considering an injuction directed against USPA for
negligence, and considering legislation that would force USPA to fall
under the FAA umbrella and regulate safety considerations.
Glen Baker
> First, you're wrong. Second, here's why:
> Your argument is flawed in that the "wind" at all alitudes is the same.
I will freely admit to this flaw. In fact, that's why my reductio-ad-absurdum
is a bit absurd. However I will *still* maintain that groundspeed doesn't
matter a hoot....it's the relative windspeeds that matter. There's nothing
special about the ground that makes it the one-and-only proper reference.
My point is that to a first degree you don't care one bit what the ground
is doing until you step on it...then you care a whole heck of a lot!
> You *ARE* wrong. I promise. Tell me the flaw in the *very* simple example
> above. I've named your flaw, you tell me mine.
Actually I think my flaw was in not stating my case very clearly.
> ps. Besides, tractors can't fly! :)
You've never seen 'em clearing the snow in the parking lot at Squaw Valley.
Scary.
..glen
Charles Thomas
writes:
> Case 1: Airplane is travelling at 100 KIAS. Winds are calm. Jumpers
exit
> with 5 seconds between groups. Observers see the groundspeed of
> the aircraft as 100 knots. Observers note the spacing between
> groups at opening.
>
> drop zone and start towing it at 100 knots along the jump run.
> intervals. Observers now note the "groundspeed" of the aircraft
> as zero knots and note the spacing between groups at opening.
>
Man. Thanks a lot.
Now I'm more confused than ever.
I had thought this issue settled, but your argument makes sense to me.
However let's say it this way.
Case 1: Airplane is travelling at 100 KIAS. Winds are calm. Jumpers exit
with 5 seconds between groups. Observers see the groundspeed of
the aircraft as 100 knots. Observers note the spacing between
groups at opening.
Case 2: I hook the King Air to a large tower. Winds are blowing at 100
knots.
Jumpers exit at 5 second intervals. Observers now note the
"groundspeed"
of the aircraft as zero knots and note the spacing between groups
at opening.
Wouldn't they all pile up in a pile on the ground together regardless of
exit spacing?
RobertC539
kind of scary. I can't believe (1) we are dragging this up again and (2)
so many people (that is - the ground speed doesn't matter crowd) can be
absolutely wrong. USPA needs to get off of there ass and get the correct
word out (it is not making policy to clarify the laws of physics!). This
is a sport were not knowing the correct theory of freefall and wind
effects on jumper separation can get people killed.
The moral of this mess - on windy days, make sure that whoever is spotting
knows what there doing and allows extra time between exits.
Bob C D-9437
Patrick
White...@semail.jsc.nasa.gov wrote:
>Glen Baker wrote:
>
>> Case 2: I hook my Catapillar D-2000 tractor up to the entire 2000 acre
>> drop zone and start towing it at 100 knots along the jump run.
>
>be a real pain when its never in the same place twice.....
Actually, I don't mind just so long as I get to drive the tractor.
Although, if I did get to drive the tractor I would prefer to crush
stuff with it rather than moving the DZ on everyone. I mean, why waste
perfectly good construction equipment pulling a DZ around? Yeah, that's
definitely the ticket. Crushing stuff. Heck, that would even be worth
the price of a jump ticket or two.
Firmly in the camp of crushing stuff with heavy equipment,
Pat
--
Patrick Sugent
Robert Bonitz
>Barry Brumitt (bel...@frc2.frc.ri.cmu.edu) wrote:
>
>> First, you're wrong. Second, here's why:
>> Your argument is flawed in that the "wind" at all alitudes is the same.
>
> I will freely admit to this flaw. In fact, that's why my reductio-ad-absurdum
> is a bit absurd. However I will *still* maintain that groundspeed doesn't
> matter a hoot....it's the relative windspeeds that matter. There's nothing
> special about the ground that makes it the one-and-only proper reference.
No, but it is easiest (IMHO) to visualize the problem from a fixed ground-based
reference frame.
> My point is that to a first degree you don't care one bit what the ground
> is doing until you step on it...then you care a whole heck of a lot!
>
>> You *ARE* wrong. I promise. Tell me the flaw in the *very* simple example
>> above. I've named your flaw, you tell me mine.
>
> Actually I think my flaw was in not stating my case very clearly.
Both are right. It is just a matter of perspective. What counts is
separation between jumpers. They are a variety of ways of expressing
the situation and a variety of assumptions one can make.
eri...@oz.net
Trying2Fly
try again?
Buzz Fink
USPA. Without beating a dead skydiving horse into the ground, ground
speed does matter and USPA needs to address this.
I understand your total frustration with USPA. It seems they have grown
to a size and a mentality unrivaled by City, State and Federal
Burocracies. With the exception of the licenses and awards department,
which have done a great job, the rest of USPA, in this DZO's humble
opinion, have lost sight of the mission-SERVICE.
Suggestion - Write an article and or letter to the editor of SKYDIVING
magazine. The are more forthright and willing to print what needs to be
printed with less concern for political correctness or of hurting
someones feelings. Also, write Sherry Schrimsher a letter along with all
National and Regional Directors. Have them put the pressure on. Have
all the jumpers at your DZ sign a letter to them and BE BLUNT! Tell them
they are @#$%^ing up and they need to straighten up and do their job.
Keep up your fight until you hit your goal-anything less would allow them
to win and allows them to continue with their slapshot service.
Sincerely,
The Buzzman, Dissappointed Group Member DZO
Allen Erickson
the following.
> In both cases the "groundspeed" is measured by an observer standing on
> the dropzone.
>
> with 5 seconds between groups. Observers see the groundspeed of
> the aircraft as 100 knots. Observers note the spacing between
> groups at opening.
>
> drop zone and start towing it at 100 knots along the jump run.
> intervals. Observers now note the "groundspeed" of the aircraft
> as zero knots and note the spacing between groups at opening.
>
> changes just because I hitched up the dropzone and started moving it??
>
> The answer is "yes", but not because of any groundspeed arguments. What
> changes is the actions of the jumpers...if they're downwind then when
> they all start flying toward the DZ they'll be flying along the jump line
> and will thereby reduce the horizontal separation.
>
I hate to do a "this is your brain on drugs" (no I don't) but...
If an airplane has zero ground speed, then for all practical
purposes it is just like a tower. If you drop skydivers off a
tower, there will be no separation (except verticle) with any wind
speed. The only thing that changes is the actual shape of the
descent path, but they will overlay. Post opening maneuvers by the
skydivers are irrevlevant for this discussion. After thinking
about that for awhile, realize that the same ananlysis would apply
for variing amounts of airspeed. (If you disagree, explain to me
where the separation occurs in my example.}
Allen
___________________________________________________________________
Allen R. Erickson Internet: al...@skydiver.win.net
Cal-Asia Truss Engineering
1747 Galindo St. Compuserve: 73727,2471
Concord, CA 94520 (510) 680-7701
Barry Brumitt
> With the exception of the licenses and awards department,
> which have done a great job, the rest of USPA, in this DZO's humble
> opinion, have lost sight of the mission-SERVICE.
Careful. I passed my AFF FJC on March 6th. It is now July 6. I have not yet
seen my new rating card. I can still use the rating since the logbook is
signed, but come on, 4 months delay?!!?
Barry
Glen Baker
> If an airplane has zero ground speed, then for all practical
> purposes it is just like a tower.
Yep.
> If you drop skydivers off a
> tower, there will be no separation (except verticle) with any wind
> speed.
Absolutely positively incorrect! Consider the case of a tower and 100
knots of wind. Jumper 1 exits, then jumper 2 exits 6 seconds later. Now
while it is true that jumper 2's opening point is identical to jumper
1's opening point *with respect to the ground* it is NOT true that there
is no horizontal separation. In the 6 seconds between opening times jumper
1 has been blown downwind 880 feet (minus whatever canopy velocity he
manages to achieve toward the tower).
The opening points with respect to the ground don't matter one single bit!
What matters is the distance between jumpers.
> (If you disagree, explain to me where the separation occurs in my example.
It comes from the fact that skydivers don't suddenly stop moving with the
airmass at the time when their parachutes open.
..glen
eri...@oz.net
I would suggest discussing your theory over with your local S&TA, or a USPA Rated Instructor. What you
are attempting to describe is natural from a pilot's perspective, however, in skydiving ground speed
is the variable used to determine horizontal separation between groups during deployment. I like you,
was confused at first. In time, I do hope you become clear on the subject. Many skydivers are confused
on the theory at first, however, time seems to strighten this out.
Blue Skies,
Eric
Barry Chase-D9545/AFF I'94/Tandem Instructor
= ps. Besides, tractors can't fly! :)
This entire debate has taken a bcakseat to my desire for one of
those tractors!
WHERE DO I GET ONE!!!
= --
= Barry L. Brumitt | bel...@frc2.frc.ri.cmu.edu |99.9%|Disclaimer: Opinions
= Robotics GradStudent| Skydive! D-15427,SL/AFF I'95 | PGP |given herein may not
= Carnegie Mellon | My 15kilobytes of fame: |Savvy| be the opinions of
= "Who is John Galt?" | http://www.frc.ri.cmu.edu/~belboz/ |FRC, SCS, RI, or CMU
--
If it wasn't for us skydivers having so much fun,
the rest of the people wouldn't know
how much their lives sucked.
-----
_..-'( ba...@gate.net )`-.._
./'. '||\\. (\_/) .//||` .`\.
./'.|'.'||||\\|.. )o o( ..|//||||`.`|.`\.
./'..|'.|| |||||\`````` '`"'` ''''''/||||| ||.`|..`\.
./'.||'.|||| ||||||||||||. .|||||||||||| ||||.`||.`\.
/'|||'.|||||| ||||||||||||{ }|||||||||||| ||||||.`|||`\
'.|||'.||||||| ||||||||||||{ }|||||||||||| |||||||.`|||.`
'.||| ||||||||| |/' ``\||`` ''||/'' `\| ||||||||| |||.`
|/' \./' `\./ \!|\ /|!/ \./' `\./ `\|
V V V }' `\ /' `{ V V V
` ` ` V ' ' '
.....
Barry Chase-D9545/AFF I'94/Tandem Instructor
= Absolutely positively incorrect! Consider the case of a tower and 100
= knots of wind. Jumper 1 exits, then jumper 2 exits 6 seconds later. Now
= while it is true that jumper 2's opening point is identical to jumper
= 1's opening point *with respect to the ground* it is NOT true that there
= is no horizontal separation. In the 6 seconds between opening times jumper
= 1 has been blown downwind 880 feet (minus whatever canopy velocity he
= manages to achieve toward the tower).
True. But while we may realistically jumps in 100 knot uppers, we
don't jump in winds that high at projected opening altitude. What is
important to us is to be sure we have the separation from the peolple
coming behind us, and in a max of about 20-30 knots, a collision is possible.
Your example seems to be replacing hurricane force winds with the
ground spped of the aircraft.
Michael Masterov
>Allen Erickson (al...@skydiver.win.net) wrote:
>
>> If an airplane has zero ground speed, then for all practical
>> purposes it is just like a tower.
>
> Yep.
Ooooh, we're getting closer to a consensus! Understanding is beginning
to shine through...
>> If you drop skydivers off a
>> tower, there will be no separation (except verticle) with any wind
>> speed.
>
> Absolutely positively incorrect! Consider the case of a tower and 100
> knots of wind. Jumper 1 exits, then jumper 2 exits 6 seconds later. Now
> while it is true that jumper 2's opening point is identical to jumper
> 1's opening point *with respect to the ground* it is NOT true that there
> is no horizontal separation. In the 6 seconds between opening times jumper
> 1 has been blown downwind 880 feet (minus whatever canopy velocity he
> manages to achieve toward the tower).
>
> The opening points with respect to the ground don't matter one single bit!
> What matters is the distance between jumpers.
OK, great. As long as the winds are 100 kts all the way from exit
altitude to the ground, this is exactly correct. But what if they are
not? What if the winds at altitude are much higher?
A fairly typical scenario where I jump (Indiana) are winds at about 15 kts
on the ground, 20 kts at 3000 MSL (which is about 2150 AGL here, opening
altitude), and 65 kts at 12000 MSL (about 11150 AGL).
Suppose we have our clunky C-206, which flies jumprun at about 90 kts,
dropping 2 groups at 11,000 ft. On a no-wind day, 6 seconds of separation
gives us 800 ft, minus tracking (say 100 ft) and whatever the canopy can
muster (maybe 200 ft at about 25 mph).
On the 15/20/65 kt day, groundspeed is 25 kts. 6 seconds gets you just over
200 ft. If the winds were 65 kts at 2000 ft, you would pick up the other
600 ft then - but you don't. The winds at 2000 ft are about as fast as the
canopy can fly, so if the first group holds into the wind all you get is
200 ft separation minus whatever you lost to tracking.
Person in first group tracks 100 ft up the jumprun, person in 2nd group
tracks 100 ft down jumprun, has a slow opening or hums it a little, and
separation is ZERO - he falls through a canopy.
NOW is it clear?
>> (If you disagree, explain to me where the separation occurs in my example.
>
> It comes from the fact that skydivers don't suddenly stop moving with the
> airmass at the time when their parachutes open.
No, they don't. But the airmass is not at a constant speed. That's what
is wrong with using the air as a reference frame - it's not all moving
at the same speed so it's not really all the same reference frame. If
you want to use the air as a reference frame, you have to decide at what
altitude, and then you have loads of corrections to make at other altitudes.
Didn't we go through all this once before?
Michael Masterov, C-24473
eri...@oz.net
Peoples lives, and yours, are at stake. Being an instructor, you should understand
the fundamental principles of horizontal separation. Please, pass this information
along in an effort to educate and not humiliate.
Thank You
eri...@oz.net
trying to educate skydivers as to what is important. The missing element here
is that USPA has not taken a stand on the Safety concern. USPA knows ground
winds are the factor, and they know what is correct, however, they must
communicate this to the skydiving community. I have heard every excuse from
USPA, however, they are disappointing many for not publishing a position based
solely on fact and safety.
Please send your post(s) to, and attention it to the Board of Directors:
Thank You
mARK bLOORE
> Allen Erickson (al...@skydiver.win.net) wrote:
>
> > If you drop skydivers off a
> > tower, there will be no separation (except vertical) with any wind
> > speed.
>
> Absolutely positively incorrect! Consider the case of a tower and 100
> knots of wind...
[snip]
> In the 6 seconds between opening times jumper
> 1 has been blown downwind 880 feet...
[snip]
> The opening points with respect to the ground don't matter one single bit!
> What matters is the distance between jumpers.
>
> > (If you disagree, explain to me where the separation occurs in my example.
>
> It comes from the fact that skydivers don't suddenly stop moving with the
> airmass at the time when their parachutes open.
>
> ..glen
if wind speed at altitude is 100 kts, and at opening it is 0 kts, then
successive groups will NOT have 880 feet of horizontal separation.
that number depends on the wind at opening altitude alone.
it looks like what matters is not airspeed alone, and not groundspeed alone,
but rather a combination of airspeed, groundspeed, and *wind speed profile*,
i.e., the wind speed at all altitudes from exit to opening.
rules of thumb for some extreme cases:
1) if the wind is very high from exit to below opening, then you should separate
groups by time. there is no point in hanging around waiting for the plane to
move if the previous group will blow away after opening.
2) if the wind is very high at exit and very low at opening, then you should
separate groups by ground reference. in this case the previous group will
*not* blow away after opening.
freefall drift can complicate things, which is why the whole wind speed profile
matters, rather than just the wind at exit and opening. consider a strong 180
degree wind shear; it is possible for the open canopies to be carried along
with the same groundspeed as the aircraft, and successive groups would open
in the same airspace however long their spacing!
since the most common situation is high upper winds and low lower winds,
without much shear, the simplest, usually safest thing to do is to spot by
looking at the ground.
--
mARK bLOORE (ma...@arachnae.com)
Chris Hunter
exit
> with 5 seconds between groups. Observers see the groundspeed
of
> the aircraft as 100 knots. Observers note the spacing between
> groups at opening.
>
> Case 2: I hook my Catapillar D-2000 tractor up to the entire 2000
acre
> drop zone and start towing it at 100 knots along the jump run.
> Airplane still travels at 100 KIAS. Jumpers exit at 5 second
> intervals. Observers now note the "groundspeed" of the
aircraft
> as zero knots and note the spacing between groups at opening.
>
I'm sorry....but.....spotting's hard enough without somebody moving the
Drop Zone around.....so.....in theory....if the DZ is never in the same
place at one time.....and the uppers are at ...say....200 knots out of
the northwest.....and you allow 3 minutes between groups....and there are
dust devils.....doesn't that mean the second group lands in Oz????......
or maybe even.....Hollywood??
Just Wondering...
Chris(hmmmm....maybe
there's a new
skydiving movie in this)
Hunter, A-20428
eri...@oz.net
FROM: Will Forshay <wil...@awd.cdc.com>
SUBJECT: Re: USPA & SPOTTING
DATE: Fri, 7 Jul 1995 15:59:12 GMT
ORGANIZATION: Skydivers From Hell, Baldwin, Wisconsin
iamr...@aol.com (I am Rhyno) wrote:
>speed. It's nice to discuss a subject but keep it in prospective and don't
>expect USPA to knee jerk react to every controversial posting.
no. but we do expect a followup to editor Jason Bell's call (in "Letters" in PARACHUTIST) for a more technical analysis. indeed, R=
hyno, your opinion would be valuable input as well as the technical answers to the debate.
--------------------------------------------
The word "BASE" is censored from PARACHUTIST.
Please let your feeling about this be known to your Regional Director and any National Directors that you know.
--------------------------------------------
Will Forshay There's no sensation to compare with this
D-12167, S/L-I Suspended animation, A state of bliss...
Vector T/M, Sr. Rigger
CFI, A-SEL; Com & I: MEL (USPA, AOPA)
Florian Rieger
we will all suffer in the end.
Thats wrong! Theres no collective bouncing.
Do you believe in THE BIG BROTHER?
1) Lack of technical experience/knowledge on the part of USPA staff.
2) Lacking the leadership.
Ah! The whale! Thar she blows! Lacking the leadership!
Watch out, take care of yourself, thats enough.
No Cry Babies!
*************ITS SPRUNGVERGNUEGEN!**************
Green Skies
Flo
- via BulkRate 2.0
Ben Daniels
(deleted)
>the wind makes exit point and opening point different, but it is the same
>difference for each group. this means that exit points should be as far
>apart as you want the opening points to be.
Right .. And we just need to separate the opening points enough to account
for tracking and the canopy motion of the first group while the second one
is finishing their free fall.
Is 200-400 horizontal ft reasonable for a breakup track?
Is 20-30 mph reasonable for today's canopies?
I'm trying to arrive at a formulation of all this so that if I get a wind
check on the ride up and everything has changed, I have a
simple_as_possible procedure to tell me how much to separate the exits.
And it has to be simple. I don't integrate those equations in my head
as fast as I used to. I never did. (Thanks Bob, good line :-) :-)
Skratch
----------------
bdan...@csn.net
eri...@oz.net
Charles Thomas <Char...@macc.wisc.edu> wrote:
>In article <3thflo$k...@emerald.oz.net> , eri...@oz.net writes:
>>Wake up USPA. Read the responses on the internet. Common sense will
>tell you
>>that the USPA S&TA
>>has to take a position on the subject. There is no excuse for
>negligence.
>
>
>
>I'm not sure we've all seen it five times yet.
>
>Sheesh.
Charles:
I apologize if my multiple posting have offended you. Unfortunately,
sometimes becoming proficient at a skill takes times and mistakes are made. I
am sure you can understand.
On a more positive note, I believe it would be more productive of you to take
the time as you did in this post and send a post to us...@pia.com, attentioning
it to the BOD, and ask why USPA has not taken a position on this as Jason Bell
promised he would.
The issue is no longer how far the plane travels, or how fast is it going, but
rather an issue of safety and USPA has failed to follow through on what they
said they were going to do. The life saved may be your own.
Thank you, and have safe skydives.
Blue Skies
Allen Erickson
In article <3tjjil$j...@canyon.sr.hp.com>, Glen Baker (gl...@sr.hp.com) writes:
>
> Absolutely positively incorrect! Consider the case of a tower and 100
> while it is true that jumper 2's opening point is identical to jumper
> 1's opening point *with respect to the ground* it is NOT true that there
> is no horizontal separation. In the 6 seconds between opening times jumper
> 1 has been blown downwind 880 feet (minus whatever canopy velocity he
> manages to achieve toward the tower).
1. The jumper in freefal and the open canopy all move with the wind
at the same speed. (Ignore direction of flight as unpredictable)
2. what if the ealier jumper ends his freefall with six seconds
less elapsed time? oops. You cannot presume anything with regard
to relative opening times.
Allen Erickson
>freefall drift can complicate things, which is why the whole wind speed profile
>matters, rather than just the wind at exit and opening. consider a strong 180
>degree wind shear; it is possible for the open canopies to be carried along
>with the same groundspeed as the aircraft, and successive groups would open
>in the same airspace however long their spacing!
>
>since the most common situation is high upper winds and low lower winds,
>without much shear, the simplest, usually safest thing to do is to spot by
>looking at the ground.
>
>--
>mARK bLOORE (ma...@arachnae.com)
What you are not taking in to consideration is the winds effect on
an open canopy is the same as it is on a body in freefall. Both
objects drift over the ground at the wind speed. (The media is
moving). Ignore canopy flight characteristics, as they are not
predictable in this determination.
Buzz Fink
here goes!
Uppers are 100 Knots, jump run is into this wind at 100 KIAS. After the
first jumper exits, a solid steel pole pertrudes from the back of the
aircraft connecting the airplane and the opening point.
The next jumper leaves 5 seconds later, and opens at the same place.
The next jumper leaves 5 hours later (oh yeah, this plane has buko fuel)
and provided the winds have not changed at all, the jumper opens at the
same point.
Lets say the wind dies down to 80 Knots-watch the end of the pole at the
opening point slowly move. Once enough seperation has been atained, that
is the opening point end of this magic pole has moved sufficiently, then
the second group could safely exit.
The lesser the winds, the sooner the seperation is attained and the less
time between groups.
Morals to this story:
1. with zero ground speed, all groups exit and open at about the same
point.
2. With slow ground speed, you need extra time between groups in order
to have adequate seperation.
3. Planes with 5 hours of fuel climb slow.
4. 10,000 poles pertruding from aircraft should not fly under 10,000
feet.
5. Ground speed matters.
The Buzzman
Buzz Fink
Morals to this story:
4. 10,000 ft poles pertruding from aircraft should not fly under 10,000
eri...@oz.net
XQM...@prodigy.com (Buzz Fink) wrote:
>I just got off the phone with Jack Gregory, USPA Director of Safety &
>Training, about an admin question. When I was finished, I enlightened
>him on all the ruckus on the net about this ground speed issue. I let
>him know that it has become a sore subject that needs immediate action by
>USPA. Also that USPA was coming off looking like shi%$# again (imagine
>that) and that he needed to step in and make sure an article was
>published, one that clarifies this issue once and for all. He told me he
>wrote an article quite a while ago and sent it to Jason but it has not
>been printed. In the strongest of words, I "politely" suggested he get
>involved and take action now! He said he would.
>
>By the way, I find it hard to believe a Regional Director would take the
>stand that was written on an earlier post. I've heard of singing the
>company song, but this went far beyond.
>
>The Buzzman
>
Mr. Buzzman:
I would like to thank you for your support. As a point of interest, and in
case you were not aware, one of the two gentlemen lack is not being honest
with you. According to Jason Bell (per 'one' of my phone conversations with
him) he could not take any action, and that the S&TA was going to make a
statement. When no statement was published the story changed. The latest
story from USPA was that no statement was going to be made and that it was a
Board decision. I tend to believe a statement was given for publication, but
never made it.
After viewing and living all the facts regarding this issue, if anyone can
honestly say the USPA has acted with integrity, then I believe they need to
take another look. USPA is supposed to be the voice of the skydiving
community. However, since creditability seems to be going by the wayside, I
would call on the Board and members of USPA to rethink the actions of the
force behind its publication and decide if a change is not in order.
Blue Skies...
Jeff Scrutton
: The opening points with respect to the ground don't matter one single bit!
: What matters is the distance between jumpers.
Glen,
You are right that opening point with respect to the ground doesn't matter,
however, let's consider that winds have dropped off to next to nothing at
opening altitude on that tower -- not atypical right? Let's say the first
load off the tower simply orbits under canopy, the next group will be
falling right into the first group.
The reason for mentioning the ground is:
a) Wind at opening altitude often bear a closer relationship to
winds on the ground than winds at exit altitude.
b) The ground is our only reference point when spotting. Sometimes
we get lucky and can watch the ground track/speed of a cloud's
shadow to help in spotting but it takes a lot more experience and
mental judgement -- and they are not _always_ there (except here).
Point (a) has a large influence in relating events happening at opening
altitude to the ground.
Forget the plane for a second. Soon after exit both groups will accelerate
with the wind mass and start into a wicked freefall drift across the ground
but one group has a five second lead, as we get lower the winds generally
drop off and our freefall drift will slow down.
A high ground speed scenario shifting down to a low ground speed one. High
uppers, slow lowers.
Now compare that to an airial view of a Forumla one grand prix race. On the
high speed straightaways a 5 second lead translates to a very long distance,
as the (relative) racers brake and slow down for entry into a (lower ground
speed) tight hairpin the distance between them compresses very quickly but
the leader still has a 5 second lead. This reduction in distance between
the two things is the dangerous part.
--
-Jeff scru...@predator.ocean.dal.ca
Oceanography Department, Dalhousie University
Halifax, Nova Scotia, Canada, B3H 4J1
Jeff Scrutton
proving this to non-believers :) One key view of the problem is looking
at the skydiver's ground speed.
I wrote:
: Forget the plane for a second. Soon after exit both groups will accelerate
: with the wind mass and start into a wicked freefall drift across the ground
: but one group has a five second lead, as we get lower the winds generally
: drop off and our freefall drift will slow down.
: A high ground speed scenario shifting down to a low ground speed one. High
: uppers, slow lowers.
: Now compare that to an airial view of a Forumla one grand prix race. On the
: high speed straightaways a 5 second lead translates to a very long distance,
: as the (relative) racers brake and slow down for entry into a (lower ground
: speed) tight hairpin the distance between them compresses very quickly but
: the leader still has a 5 second lead. This reduction in distance between
: the two things is the dangerous part.
While I'm into the spotting subject, people have mentioned the extreme case
of 180 shear: uppers from the north and lowers from the south for example.
For me the case doesn't work out badly... How do you folks pick a jump run?
We normally take jump run onto the windline as felt on the ground, if that
means crabbing the plane up jump run it happens, if that means a cooking
jump run it happens. If we find people crabbing back from the spot then
we swing or offset the jump run to compensate for freefall drift or a
different wind line at opening altitude. How are you folks doing it so
that the case of reversed uppers and lowers cause difficulty?
I guess I should add we do a no-cut 80 knot jump run in the 182.
Rick Lemons
In article <5...@skydiver.win.net>, <al...@skydiver.win.net> writes:
> What you are not taking in to consideration is the winds effect on
> an open canopy is the same as it is on a body in freefall. Both
> objects drift over the ground at the wind speed.
This is NOT true. A body in freefall will be affected less by winds than
one under canopy. A freefall body has much more momentum and less surface
area for the winds to act on.
Rick Lemons
In article <3tjjil$j...@canyon.sr.hp.com>, <gl...@sr.hp.com> writes:
> > (If you disagree, explain to me where the separation occurs in my example.
>
> It comes from the fact that skydivers don't suddenly stop moving with the
> airmass at the time when their parachutes open.
>
> ..glen
>
This is true. But, during spotting you can not take all the variables for this
into account. You don't generally know the winds a 2,000'. You don't know the
airspeed of the jumper's canopy. You don't know which direction he will be
flying after openning. How long he will take to stow his slider while
travelling which direction without looking, etc. Play it safe and separate the
opening points between groups with enough distance to provide a safety margin.
mARK bLOORE
> What you are not taking in to consideration is the winds effect on
> an open canopy is the same as it is on a body in freefall. Both
> objects drift over the ground at the wind speed. (The media is
> moving). Ignore canopy flight characteristics, as they are not
> predictable in this determination.
it takes a while for a body to match the windspeed around it,
but it doesn't take a canopy long, since it has far greater drag.
if a freefaller's horizontal speed instantly matched the windspeed, then
style competitions would not be run with downwind jumpruns, since the
jumper's path relative to the judges would be the same as for an upwind
jumprun. and you wouldn't have to consider forward throw when spotting,
either.
--
mARK bLOORE (ma...@arachnae.com)
Allen Erickson
In article <NEWTNews.21166.8...@ICR.ibm.net>, Rick Lemons (rle...@ibm.net) writes:
>
>In article <5...@skydiver.win.net>, <al...@skydiver.win.net> writes:
>> What you are not taking in to consideration is the winds effect on
>> an open canopy is the same as it is on a body in freefall. Both
>> objects drift over the ground at the wind speed.
>
>one under canopy. A freefall body has much more momentum and less surface
>area for the winds to act on.
>
A body's (or canopy's) motion with the wind is not caused because
the wind is blowing it but because the medium of suspension (air)
is moving. (Remember the boat in a stream example?)
The body in freefall moves with the moving air (wind) the same as
the open canopy. (Ignoring differences in acceleration caused by
wind speed changes)
mARK bLOORE
> A body's (or canopy's) motion with the wind is not caused because
> the wind is blowing it but because the medium of suspension (air)
> is moving. (Remember the boat in a stream example?)
what is the difference between air moving and wind blowing?
an object's motion with the medium it moves through depends on its initial
velocity relative to the medium, its drag in the medium, and its mass.
a boat in a stream has a lot of drag, relative to its mass. a body in
air does not.
> The body in freefall moves with the moving air (wind) the same as
> the open canopy. (Ignoring differences in acceleration caused by
> wind speed changes)
you can't ignore these differences, because they are very large. a jumper
under an open canopy has far more area, and thus drag, than when
in freefall, but the same mass, and so will be accelerated (horizontally)
by the wind much more quickly.
actually, it strikes me as a bad idea to spot groups so closely that such
considerations are important.
--
mARK bLOORE (ma...@arachnae.com)
Rick Lemons
In article <6...@skydiver.win.net>, <al...@skydiver.win.net> writes:
> A body's (or canopy's) motion with the wind is not caused because
> the wind is blowing it but because the medium of suspension (air)
> is moving. (Remember the boat in a stream example?)
>
> the open canopy. (Ignoring differences in acceleration caused by
> wind speed changes)
Has everyone forgotten about gravity here? The stream example does not
apply because it ignores the forces of gravity. There really is gravity,
the Earth does not suck.
Rick Lemons
In article <mark-11079...@algor.arachnae.com>, <ma...@arachnae.com>
writes:
> actually, it strikes me as a bad idea to spot groups so closely that
such
> considerations are important.
At last. A man that know the difference between a Mathematician and an
Engineer. If you put a mathematician on the other side of the room from a
pile of money, he figures he can never get to the money. To get to the
money he must first get half way there. Since, theoretically, there are an
infinite number of half ways, he can never get to the money. The engineer
says, "I may not be able to get to the money, but I can get close enough
to get my hands on it!".
Mark has just pointed out that while all these factors of wind drift under
canopy could be analyzed to assure the exact time to exit, it doesn't make
sense to do so. There are too many ways to be wrong. Leave extra time.
Tom Loebach
>
> In article <6...@skydiver.win.net>, al...@skydiver.win.net (Allen Erickson) wrote:
>
> > A body's (or canopy's) motion with the wind is not caused because
> > the wind is blowing it but because the medium of suspension (air)
> > is moving. (Remember the boat in a stream example?)
>
> an object's motion with the medium it moves through depends on its initial
> velocity relative to the medium, its drag in the medium, and its mass.
> a boat in a stream has a lot of drag, relative to its mass. a body in
> air does not.
>
> > the open canopy. (Ignoring differences in acceleration caused by
> > wind speed changes)
>
> under an open canopy has far more area, and thus drag, than when
> in freefall, but the same mass, and so will be accelerated (horizontally)
> by the wind much more quickly.
> considerations are important.
>
> mARK bLOORE (ma...@arachnae.com)
This has been a confusing thread. There is not nor can ever be a
hard and fast rule for group seperations on the same pass. Wind,
backsliding formations, long tracks etc. all play a part. I
guess only experience counts. We use a slow 5 count. Others 10.
Who really knows.
D3331
ENOUGH ALREADY!!!
Everybody take a chill.
Open the door and get out.
Steve Noonan SCS-567
*****************************************************************
...."I take the fear and I visualize it into a big question mark
and I embrace the uncertainty"....
Gilda Radner
*****************************************************************
Bill Von Novak
> . . .
>Mark has just pointed out that while all these factors of wind drift under
>canopy could be analyzed to assure the exact time to exit, it doesn't make
>sense to do so. There are too many ways to be wrong. Leave extra time.
we could come up with a worst-case number (say, 15 seconds) that
gives you enough clearance 99% of the time. that way no one has to
think. but are people willing to shell out the extra money for that?
(on an otter, two passes on every load are going to drive prices up by
$1 to 2 per jumper.)
or maybe the DZ could have a regular (higher) price, then offer
a discount for jumpers who understand the separation thing . . .
-bill von novak D16479 AFF/SL JM95 TM95
mARK bLOORE
> STOP, STOP, PLEASE STOP!!!
>
> ENOUGH ALREADY!!!
>
> Everybody take a chill.
>
> Open the door and get out.
while i agree that this gets tiresome, i consider it very important.
i have had the experience of opening close beside the canopies of the group
that left before mine, after too short a wait on a day with high winds
at exit and none at opening.
--
mARK bLOORE (ma...@arachnae.com)
mARK bLOORE
> This has been a confusing thread. There is not nor can ever be a
> hard and fast rule for group seperations on the same pass. Wind,
> backsliding formations, long tracks etc. all play a part. I
> guess only experience counts. We use a slow 5 count. Others 10.
> Who really knows.
it is true that there can be no hard and fast rule (short of a quite impractical
calculation), there are rules of thumb that bear thinking out.
there are not uncommon conditions under which a slow five count could kill you.
--
mARK bLOORE (ma...@arachnae.com)
I am Rhyno
It's good to hear some sanity for a change. I can't believe all this talk
about spotting. These people have made a mountain out of a mole hill.
Where are the statistics that support all this "danager"?
Rhyno
David Zimmerman
A few weeks ago at a boogie, I was tracking away from our 4 way when
suddenly there were canopies opening all around me. I opened
immediately (opening a Stiletto in a track is no fun). I followed them
to the ground to find out why we happened to share air space at
opening, and it turns out they were the group *after* us. They had
given us a "good 2-3 seconbds". They didn't seem to notice that we had
all been very lucky. Canopies from different groups opening within a
few hundred feet of each other scares me a great deal. I was mindful of
who followed me out of the airplane for the rest of the weekend.
David P Zimmerman dz...@nando.net
916 Riderwood Ct 919 557 7692
WillowSpring NC 27592
eri...@oz.net
>A few weeks ago at a boogie, I was tracking away from our 4 way when
>suddenly there were canopies opening all around me. I opened
>immediately (opening a Stiletto in a track is no fun). I followed them
>to the ground to find out why we happened to share air space at
>opening, and it turns out they were the group *after* us. They had
>given us a "good 2-3 seconbds". They didn't seem to notice that we had
>all been very lucky. Canopies from different groups opening within a
>few hundred feet of each other scares me a great deal. I was mindful of
>who followed me out of the airplane for the rest of the weekend.
This is exactly what I have been attempting to pass on to the skydiving
community. The distance the aircraft covers across the ground determines the
amount of horizontal separation between groups at the time of deployment. The
longer you wait, depending upon the uppers, the greater the physical distance
between groups.
It doesn't take a physics major to figure that one out.
Blue Skies
eri...@oz.net
Statistics:
Accidents reports. Common sense. Broken Legs. Unexplained canopy
collisions between jumpers on different groups. etc.
Open your minds people, and give it some thought.
eri...@oz.net
gosc...@sunny.dab.ge.com (John Goscinski) wrote:
>In article h...@qualcomm.com, bil...@qualcomm.com (Bill Von Novak) writes:
>
>> we could come up with a worst-case number (say, 15 seconds) that
>> gives you enough clearance 99% of the time. that way no one has to
>> think. but are people willing to shell out the extra money for that?
>> (on an otter, two passes on every load are going to drive prices up by
>> $1 to 2 per jumper.)
>
2 passes on the otter. - It's just about hanging there in the air. I know this
is one of the big contentions here, but with extra-low groundspeed the plane
won't be moving off of the spot very fast.
>
>John
>
>
John:
You are exactly correct. This is why a 45 second wait is not inappropriate in
the example you reference. During the spring time in Perris, when the uppers
are >50, wait time between groups can be longer than a minute. This extra
long wait will allow for the minimal ground speed and give you adequate
horizontal separation between groups during deployment.
The distance the aircraft travels across the ground will determine the
horizontal separation between groups; ground speed. Airspeed is relative.
Ground speed is physical with respect to the aircraft and earth and you.
Blue Skies
John Goscinski
eri...@oz.net
several forums on rec.skydiving and it seems as though similar subject items, or responses
supporting a certain issue are being deleted discriminately. If what I suspect is correct,
it must stop.
I would like to know who has the authority, or power to delete messages from rec.skydiving.
Your input is appreciated.
Blue Skies
Timothy McMichael
: I would like to know who has the authority, or power to delete messages from rec.skydiving.
: Your input is appreciated.
: Blue Skies
I would have replied sooner, but your message got deleted ;-)
Actually, rec.skydiving is an unmoderated newsgroup, so nobody has the power to
censor any messages. In theory, but I guess anything is possible 8^O
The only thing I've noticed is messages out of sequence within a thread. But
that's perfectly normal. Keep in mind that the messages arrive at different
sites at different times.
Tim Mcmichael
alerma
was to pull out the pilot chute and wave it around,
so if some clown was above you he'd get out of the way..
Allen Vizzutti
--
Allen Vizzutti
:
: In article <NEWTNews.21166.8...@ICR.ibm.net>, Rick Lemons
: >> What you are not taking in to consideration is the winds effect on
: >> an open canopy is the same as it is on a body in freefall. Both
: >> objects drift over the ground at the wind speed.
: >
: >This is NOT true. A body in freefall will be affected less by winds than
: >one under canopy. A freefall body has much more momentum and less surface
: >area for the winds to act on.
: A body's (or canopy's) motion with the wind is not caused because
: the wind is blowing it but because the medium of suspension (air)
: is moving. (Remember the boat in a stream example?)
: The body in freefall moves with the moving air (wind) the same as
: the open canopy. (Ignoring differences in acceleration caused by
: wind speed changes)
: Allen
Sorry for the test. I've been having major trouble posting.
Rick is right. The wind affects the freefaller less than the person
under canopy for two reasons.
1) The freefaller is exposed to the force of the wind far less the
when he's under canopy. If he passes through the medium four times as
fast the total force applied to him will be one fourth of what it is
when under canopy.
2) The freefaller surface area perpendicular to the direction of force
is *much* smaller than when under canopy. Although the pressure of
the wind *is* constant, say 5 lbs/inch^2, the applied force is much
smaller for the freefaller because his surface area is much smaller.
If you want to use water as a medium consider this: Drop a rock in a
fast moving stream. Now drop a leaf. Which travels further?
If you don't like that example: Drop a deflated balloon on a windy
day. Now drop an inflated balloon. Which travels further?
I hope I'm not beating a dead horse. (I think I saw some movement
a minute ago!)
Anykindaskies,
Vizz
.
--
law...@fhi-berlin.mpg.de
> The routine I and many of my old friends used to use,
I hope this means you don't do this anymore...
> was to pull out the pilot chute and wave it around,
> so if some clown was above you he'd get out of the way..
--
The perfect way to get the bridle wrapped around your arm or hand.
Peter
-----
_|_ Sometimes you loose, sometimes the others win.
---*--O--*---
O O X Peter Lawrenz (DFV3772)
X X http://www2.rz-berlin.mpg.de/~lawrenz/
X law...@fhi-berlin.mpg.de irc: zaremba
FreeFall-> FreeBag-> FreeBeer
Charles Thomas
law...@fhi-berlin.mpg.de writes:
>The perfect way to get the bridle wrapped around your arm or hand.
>
>Peter
Some interesting little anecdotes from Southern Wisconsin:
Guy at our DZ yesterday deployed his pilot chute, but somehow got the
bridal wrapped around his arm. The bag came out and went by his head and
the lines started unstowing as he got the bridal off his arm. The pilot
chute wrapped around his slider as his canopy was opening and resulted in
a pretty weird mess which he subsequently cut away. Landing under his
reserve was uneventful. Please note that description of these events are
the jumper's and are to be taken as such. :)
Same day, tandem master cut away his main when the stabilizer fabric got
caught in the slider and kept the slider from coming down as well as
tucking the end cells under. The resulting canopy looked like an
umbrella. His reserve deployment went flawlessly. Tandem passenger was
completely unruffled by the experience.
Jumper on a night jump three days earlier experienced a malfunction and
cut away his main. Canopy was spotted a few days later (by air) in a
tree on the edge of a nearly impassable swamp. Several efforts to
retrieve it returned unsuccessful and muddy. As of Sunday it was seen
(from the Twin Otter) to be still in the same tree.
Robert Bonitz
>eri...@oz.net (eri...@oz.net) wrote:
>: I would like to know who has the authority, or power to delete messages from rec.skydiving.
>: Your input is appreciated.
>
>: Blue Skies
>
>I would have replied sooner, but your message got deleted ;-)
>
>Actually, rec.skydiving is an unmoderated newsgroup, so nobody has the power to
>censor any messages. In theory, but I guess anything is possible 8^O
If Senator Exon has his way, the Feds will be censoring the net and you
won't be able to say any of Carlin's "Seven Words You Can't Say on TV." So
post them cuss words now, folks, while you still can!