exit space on windy days
JRWSKYDIVE
there was no reason to leave extra space between exits on windy days. This
is not correct. IMHO. What does everyone else think?
Gregory Layton Reid
: There were two letters in the most recent Parachutist that stated that
: there was no reason to leave extra space between exits on windy days. This
: is not correct. IMHO. What does everyone else think?
The only possible reason I could come up with would be radio controled
students. What did the letters in Parachutist say?
--
\\||// ----------------------------------------------
(_ _) / Greg Reid ac...@cfn.cs.dal.ca /
{(o)(o)} / Halifax Nova Scotia _________________/
( [] ) / Canada C1290 /
-------oOO-\<>/-OOo-------------------------------
Jeff Hauser
Suppose the winds are blowing at 80 kts on jump run and we are in a Cessna doing 80.
The plane is essentially playing helicopter with respect to the ground. I bail
out first and drift about a half mile downwind and at 2500' I open right over the
landing area. Down here, the wind is near zero. Since I am right over the landing
area, I am just going to do a slow turn and bleed off altitude until I have to
set up for landing. Meanwhile, the next jumper(s) get out of the plane. So,
about 10 seconds after I open, I look up and see somebody in freefall right above me.
Now, what if there is significant wind under canopy? For example, it is doing about
30. Otherwise, the uppers are the same as previous. Therefore, all jumpers are
going to go through the same path to the same opening point. If there is 10 seconds
between exits, how far will I drift under a round in the 10 seconds after I open?
I calculate 440 feet. And if it was a x-way and people were tracking away, odds
are that one of them will track back upwind and open such that when those 10
seconds are up, another freefaller is over them.
If the plane was doing 60 relative to the ground, and with 10 seconds between exits,
each group would hit an opening point about 880 feet from the previous group.
I therefore conclude that the higher the winds, the higher the separation time
that is needed between groups.
I don't have my parachutist in front of me, but I remember seeing an argument that
the wind would take care of the separation problem by itself. However, that argument
is valid only if the wind speed is constant from exit altitude all the way down.
I don't feel like doing the math, but given a jump run of a given speed,
and constant winds all the way down, I expect that it would reveal the horizontal
separation on opening will be a linear function of the time between exits.
--
Jeff Hauser
4A8/030-2/C213
3-3056 / (507) 253-3056 / 8/553-3056
vnet: hauser@rchland hauser@rchvmv2
internet: jha...@vnet.ibm.com
We are measured by the amount of work we get done,
not by the amount of work we eliminate.
--Jeff Bechdol
Cindy Pirkkala
: There were two letters in the most recent Parachutist that stated that
: there was no reason to leave extra space between exits on windy days. This
: is not correct. IMHO. What does everyone else think?
Just my opinion, but I think that this IS correct. You must understand
that groundspeed is not the important thing here. The analogy of a
boat anchored in a river dispatching "floats" should make it easier to
understand. If the river is flowing say 30mph.(wind blowing) The boat
is anchored (groundspeed = zero) if you put out a float ,say once each
3 to 5 seconds, the floats will have plenty of separation. In fact, it
may even be that on windy days, you could safely leave LESS space
between jumpers because they will "float" away faster.
JRWSKYDIVE
skydiver. In the airplane, ground speed is irrelevant to the flight of
the plane, air speed is what counts. Once you exit the plane, that is no
longer the frame of reference that pertains to you. Ground speed is what
determines separation across the ground.
Gary Allman
>
>I therefore conclude that the higher the winds, the higher the separation time
>that is needed between groups.
>
>I don't have my parachutist in front of me, but I remember seeing an
>argument that the wind would take care of the separation problem by
>itself. However, that argument is valid only if the wind speed is
>constant from exit altitude all the way down.
This is correct. The real reason for the need to increase time separation is
that wind are almost always lower at lower altitudes. When the winds are
high, it is likely that a significant difference in wind at 12k than at 3k.
--
Gary
gal...@netcom.com
Philip Yzarn de Louraille
I agree with the letters. A windy day will not change the way gravity works
so vertically speaking, nothing will have changed.
So unless people corkscrew themselves toward the ground *without* looking
there should no added problem, in any case, everyone should be paying
attention at the traffic under canopy whether they jumped first or last.
--
Philip Yzarn de Louraille Internet: yz...@chevron.com
UN*X Systems Specialist PROFS: ZARN(SMTP)
Chevron Information & Technology Co. Tel: (310) 694-9232
P.O. Box 446, La Habra, CA 90633 Fax: (310) 694-7709
SkyCalls
There were two letters in the most recent Parachutist that stated that
there was no reason to leave extra space between exits on windy days. This
is not correct. IMHO. What does everyone else think?
>>
I think they have a desire to freefall into someone elses opening main.
Martin
Tim Reynolds
Cindy Pirkkala <pirk...@freenet3.scri.fsu.edu> wrote:
[correct idead deleted]
>Just my opinion, but I think that this IS correct. You must understand
>that groundspeed is not the important thing here. The analogy of a
>boat anchored in a river dispatching "floats" should make it easier to
>understand. If the river is flowing say 30mph.(wind blowing) The boat
>is anchored (groundspeed = zero) if you put out a float ,say once each
>3 to 5 seconds, the floats will have plenty of separation. In fact, it
>may even be that on windy days, you could safely leave LESS space
>between jumpers because they will "float" away faster.
This argument came up before and I held your position, which is wrong.
Consider this:
Two groups exit a stationary helicopter in no wind. Group 2 kills group 1.
(and group 2!). Obvious?
Add 80 MPH winds and plane flying 80 MPH directly into the wind. Same as a
stationary helicopter, yes? Yes. Group 1 is blown away. 5 seconds later,
group 2 gets blown away to exactly the same place as group 1 (the plane has
not moved over the ground). Obvious?
If you intend to open 1,000' upwind of group 1, you must exit 1,000' upwind
of group 1.
If the point over the ground at which you exit the plane doesn't matter, you
wouldn't bother to spot the plane. Obvious? Yes.
I as appalled that USPA merely asked for more comments rather than spit out
the correct answer (which, admittedly, isn't as obvious as it seems).
How USPA could let someone earn a license without knowing this imperative
fact is beyond me. I'll tell you first hand that when someone doesn't know
the relevance of high winds and tracks past you in the opposite direction,
things get scary FAST.
Tim
Tim Reynolds
that make this a real consideration, you probably shouldn't be jumping
anyway.
Tim
I have to add some crap here as if I had a sig, because my newsreader is stupid
and etc etc etc gee, letsee, I actually got a Parachutist in the mail on the
last day of the month of the issue. My 3rd issue this year. That should do it.
Cindy Pirkkala
between airspeed and groundspeed. I don't doubt that there are some
people out there who believe that you spot longer on a windy day
because the stronger wind will BLOW YOU back farther than a light wind.
And even though that's not so, it's probably a good thing since you
may be last out behind several people who were allowing 30 seconds in
between exits since it was Really Windy. ha ha.
(sorry I'm being bad again eric, I must be bored)
JRWSKYDIVE
you want to know how long it will take to get where you are going, you
look at ground speed. For any two groups exiting on the same pass the
effects of inertia, deceleration, exceleration,and wind speed are the
same. Each group will appear ,to an observer in the door, to open the same
distance behind the airplane. The distance between the groups will be
equal to the distance that the plane travelled between exits. This is
equal to the ground speed of the airplane times the time between exits. A
plane flying at 90kts. in 0 wind has twice the ground speed of the same
plane flying into a 45 kt. headwind. For equal spacing you require twice
the time between exit groups.
J.R.Woody D-7295
RobertC539
You and your buddies are out skydiving. The winds are a constant 100
feet/sec from 2000 ft up to 12,500 ft. The aircraft is flying directly
upwind on jump run at 50 ft/sec (relative to the ground). The spot is
directly above a MacDonalds burger joint. A Burger King lies 6000 ft
downwind of the MacDonalds. You exit over Big Mac's Supper Club and your
buddies exit five seconds later. Assuming a 60 second freefall and
ignoring the time required to accelerate to the current wind velocity
after exit, where will you open relative to the Burger King? Where will
your buddies land relative to the Burger King?
Answer: Upon exit and ignoring the forward throw effects of the aircraft,
you are now traveling across the ground, blown with the wind, at 100
ft/sec. After 60 seconds, you have traveled 100 ft/sec * 60 sec = 6000 ft.
Since the Burger King is 6000 ft downwind of the MacDonalds, you find
yourself staring straight down at the Burger King. Your buddies remained
in the aircraft for five seconds after you left. They have traveled
50 ft/sec * 5 seconds = 2500 ft upwind of the MacDonalds during that time
and now exit. Upon exit, your buddies are "blown with the wind" the
exact same distance you have (that is, 6000 ft). However, since they
started 2500 ft upwind of your exit point, their opening point is also
2500 ft upwind of your opening point (that is, 2500 ft upwind of the
Burger King).
I leave it as a homework assignment to repeat the above calculation,
except this time with the aircraft flying at zero ft/sec relative to
the ground.
Moral - Horizontal separation between groups of jumpers = Ground Speed
of the aircraft times exit delay between groups.
Bob C - D-9437
Gregory Layton Reid
: When you want to know if its safe to rotate, you look at air speed. When
You had better recalculate and I am glad your not spotting my load.
JRWSKYDIVE
learned in school. For example: At work you tell a non jumper, that thinks
you are crazy, that after 11sec. you don't fall any faster. He looks at
you funny. He's pretty sure that the acelleration of gravity keeps right
on working till you hit the ground. Then you tell him that heavy people
fall faster than light people. Now he's pretty sure that somebody got
burned at the stake in the middle ages proving that everything falls at
the same speed regardless of how much it weighs. Now he knows youre not to
be trusted with anything breakable. We all (know) that in aviation its all
airspeed. Think carefully.
J.R.Woody D-7295
Michael Masterov
winds at altitude on separation. I don't really know I'f I'm going to make
a dent in this or not, but I'm going to try to explain the source of the
disagreements.
They have to do with choosing a frame of reference and then using it
improperly, as well as with failing to choose realistic examples.
For purposes of this explanation, I'm going to pick a fixed frame of
reference (the ground, with special emphasis on the 'spot' or point
on the ground over which the first group exits the aircraft) and do
three examples.
Let's take a realistic example. The winds at opening altitude (2000 AGL)
are 12 kts (about 14 mph). The winds at exit altitude (11,500 AGL) are
also 12kts. The aircraft on jumprun has an airspeed of 72 kts (about 82 mph).
Let's ignore the forward throw of the aircraft and the time it takes to
accelerate to the wind speed - these will affect all groups about equally
and will thus not increase nor decrease the separation at altitude.
First, do it as a groundspeed calculation. Assume that the first group
exits over some arbitrary point 0. Groundspeed is 60 kts. That's
about 100 ft/sec. Allowing a time spacing of 5 seconds (typical spacing
for small groups) means that the second group exits about 500 ft forward
of point 0. So we have 500 ft of horizontal separation. Right? Wrong.
In those 5 seconds, the first group is moving backwards (relative to
the jumprun) at 12 kts. That's 20 ft/sec, or 100 ft. So the horizontal
separation is 600 ft.
Freefall takes about 60 seconds. During that time, each group will be moving
over the ground at 12 kts. That's 20 ft/sec, or 1200 ft in 60 seconds.
60 seconds after the 2nd group exits, it has moved 1200 ft back (to 700 ft
behind pt 0). They are now opening. The 1st group is already open for 5
seconds (and thus at about the same altitude as the 2nd group - you don't
lose much altitude in 5 seconds of canopy time) so, neglecting any forward
speed of the canopies, they have also been blown back 1200 ft in these 60
seconds. They started out 100 ft behind 0, and are now 1300 ft behind 0.
Separation is 600 ft (1300-700) just like it was at exit.
Try a different example. The winds are 60 kts at all altitudes. This
makes jumprun have a ground speed of 12 kts. 5 second separation puts
the 2nd group 100 ft forward of 0, but in the same 5 seconds the 1st
group is blown back 500 ft - separation at exit is still 600 ft.
In freefall, 60 seconds blows the 2nd group back 6000 ft. In the same
60 seconds (again, 55 sec of freefall and 5 sec of canopy time for the
1 st group) the 1st group is also blown back 6000 ft. So the 1st
group is now at -6500 ft (6500 ft behind pt 0) and the 2nd is at -5900
ft. Sepration remains 600 ft.
Incidentally, at an airspeed of 72 kts in still air, 5 seconds of
separation gives you (120 ft/sec * 5 sec) 600 ft. Airspeed is all.
But what about a more realistic example? Suppose winds aloft (at 11,500)
are 60 kts while winds at opening altitude (2000 ft) are 12 kts? This
makes jumprun have a ground speed of 12 kts. 5 second separation puts
the 2nd group 100 ft forward of 0, but in the same 5 seconds the 1st
group is blown back 500 ft - separation at exit is still 600 ft.
So far so good. But (assuming winds decay linearly with altitude) the
average windspeed in freefall is going to be 36 kts. That's 60 ft/sec.
Since little altitude is lost in the first 5 seconds of freefall, we'll
assume that during the first 5 seconds of freefall the wind speed is
60 kts.
So what happens in the next 60 seconds? The 2nd group is blown back 500
ft in the first 5 seconds (100 ft/sec * 5 sec) and 3300 ft in the next
55 (60 ft/sec * 55 sec) to a final position of -3700. The 1st group is
blown back 3300 ft in the 55 sec of freefall and 100 ft in the 5 seconds
of canopy time in 12 kt winds, for a final position of -3900. Oh SHIT!
Separation at opening is only 200 ft, 1/3 of what it was at exit!
Conclusion: When the winds are high but constant, separation is not
adversely affected. But when they are high aloft and low at opening
altitude (NOT an uncommon situation) separation is adversely affected.
600 ft is probably more distance than is going to be closed by two
people tracking towards one another at breakoff. 200 ft? It could
happen. When the winds aloft are really cooking, and the ground
winds are low enough to jump, 5 second separation between groups
exiting a slow aircraft just isn't enough.
I hope this clears up the confusion.
Michael Masterov C-24473
Philip Yzarn de Louraille
Enough mathematical modellings! Real life is not modelled so. Winds do vary
in direction and strength from the ground up. If you want to be safe then you need
to watch several passes from the time they exit to the time they open,
then you can make you judgement and it will be valid if nothing else change
which is wrong, of course.
5 seconds between groups of jumpers on the same pass should be enough most of the time. You should still look down from time
to time as you freefall to make sure the path is clear, regardless of the winds,
and especially if you are jumping after somebody (sharing a pass).
PS: those people with the modellings forgot to take into account that most
skydiving groups do slide! Tsssk, tsk, tsk....
Tim Reynolds
Cindy Pirkkala <pirk...@freenet3.scri.fsu.edu> wrote:
>People seem to be having a real problem understanding the difference
>between airspeed and groundspeed. I don't doubt that there are some
>people out there who believe that you spot longer on a windy day
>because the stronger wind will BLOW YOU back farther than a light wind.
>
From this, I think *you* must have the understanding problem. Do you
really believe we fall straight down in high winds? If that were the case,
why would we bother landing into the wind? Have you never seen people
drift in freefall? Have you ever seen things (say, tumbleweeds, or maybe
18-wheelers) get blown across the ground? Things in wind move with the wind.
Surely you understand this.
Consider this:
You exit the plane at the same spot over the ground as some group of people,
perhaps because you are part of the group. You fall in the same column of
air, of course. If the plane has not moved over the spot on the ground for
5, 10, or 30 seconds, you fall in the same column of air. You open at the
same place as the group ahead. Yea, they got blown away. You too get blown
away. To the same place.
As has been said, the winds aloft are probably not the same as the winds at
opening altitude. This changes nothing. In the extreme case of an airplane
on jumprun, stationary with respect to the point on the ground, everything
that falls from the plane ends up at the same place.
If you dispatch floats from an anchored boat in a moving stream of water,
the floats are separated until they arrive at the pond where the water is
no longer moving. The floats swirl around like open canopies. In the same
place.
>And even though that's not so, it's probably a good thing since you
>may be last out behind several people who were allowing 30 seconds in
>between exits since it was Really Windy. ha ha.
>
Tim
JRWSKYDIVE
together. The main reason is that climb outs for RW take longer than most
people realize. Ten to twenty seconds at least. This leaves pleanty of
space even when the next climb out starts right after the previous exit.
Not everyone is doing traditional RW these days. People who are doing
freestyle or sitosis may not always use a climb out, but just go right out
the door. The few seconds they leave may not be enough without the delay
of the climbout.
I happen to have had a personal experience along these lines recently at
Eloy. A sitosis jumper fell right through our four way breakoff. The
formula is reduced exit time, reduced ground speed, and unequal drift ,
and a track toward the other group equals overlap. No harm done but we
can't always depend on luck, or the extra separation we have been used to.
(Due to typically time consuming RW climb outs.) Thanks.
J.R.Woody D-7295
Rick Lemons
In article <20...@lhdsy1.lahabra.chevron.com>,
<yz...@lhdsy1.lahabra.chevron.com> writes:
The problem on windy days has to do with horizontal separation
between groups. On real windy days (at exit altitude) you need to
leave more time between exits to allow for separation between the
groups. Think of it this way. Once a group leaves the aircraft, we
can forget about everything because the same forces acting on the 1st
group will be acting on the second group. So the only consideration
is the distance covered between the exit points of the 2 groups. And
this depends on ground speed NOT airspeed. In a higher head wind
condition, the aircraft will not put as much distance between the
exit points of 2 groups as in a no wind condition (because the ground
speed is lower). So if you want the same horizontal separation
between groups, you must wait longer between exits on high wind days
at altitude.
John Luke Mills
: 600 ft is probably more distance than is going to be closed by two
: people tracking towards one another at breakoff.
This is pretty pathetic tracking performance. If you break at 3.5 and
open at 2.5 or lower, any competent tracker should be able to cover at
least 500 feet. A pair tracking toward each other should easily be
able to close 1000 feet.
Onwards to the main issue:
The situation we are talking about is when the forward airspeed of the
plane and the exit altitude wind speed are very close. Nothing else
matters in this situation. Think about the case were the plane's
ground speed is zero. This case is equivalent to jumping off a tower.
Every group going off such a tower (I want one to 13.5 with a fast
elevator) is going to move thru the air in pretty much the same path
and open in pretty much the same place. If you were jumping off this
tower, how long would you wait before your group followed the previous
group. Remember, you would be right over them in the same path and
they will be opening before you!
Fortunately, the plane's airspeed and the windspeed rarely match
exactly. When they are close, you definitely want to give extra time
to provide more vertical separation and to allow what little ground
speed there is to provide some horizontal separation.
--
)
o /
> / )__ __
/ / / ) )
/ ( / ( (
(__/
Robert Bonitz
>the horizontal seperation between groups is equal to
>
> (amount of time between exits) multiplied by (airspeed of the aircraft)
>
>and has exactly nothing to do with how fast the airplane is travelling
>over the ground. All groups exiting the aircraft are affected, for all
>practical purposes, the same in relation to the ground.
>
>Period.
Please don't exit behind me. Period.
Pete Shew
> high
> winds at altitude on separation. I don't really know I'f I'm going to
> make
> a dent in this or not, but I'm going to try to explain the source of the
> disagreements.
>
>
> Let's take a realistic example. The winds at opening altitude (2000
> AGL)
> are 12 kts (about 14 mph). The winds at exit altitude (11,500 AGL) are
> also 12kts. The aircraft on jumprun has an airspeed of 72 kts (about
> 82 mph).
> Let's ignore the forward throw of the aircraft and the time it takes to
> accelerate to the wind speed - these will affect all groups about
> equally
> and will thus not increase nor decrease the separation at altitude.
>
> First, do it as a groundspeed calculation. Assume that the first group
> exits over some arbitrary point 0. Groundspeed is 60 kts. That's
> about 100 ft/sec. Allowing a time spacing of 5 seconds (typical spacing
> for small groups) means that the second group exits about 500 ft forward
> of point 0. So we have 500 ft of horizontal separation. Right? Wrong.
> In those 5 seconds, the first group is moving backwards (relative to
> the jumprun) at 12 kts. That's 20 ft/sec, or 100 ft. So the horizontal
> separation is 600 ft.
Yes, but what you forgot to figure in was that in the five seconds
between group 1 opening and group 2 opening, group 2 would have closed up
that extra 100ft to make the separation once again 500ft.
The frame of reference is only important in that a consistent one must be
used. However, some are easier to visualise. Using a ground based frame
of reference, and postulating unvarying (though possibly complex) winds,
any groups exiting above the same point on the ground will end up opening
at the same place as each other - regardless of the time between exits.
(From a plane with zero ground speed you therefore need to leave enough
time for the earlier group to have descended a thousand feet under canopy
to be safe - at least a minute).
If the plane is moving over the ground, the entire path of the jump will
be displaced in the direction of motion of the plane at the speed the
plane is moving over the ground; that is the eventual opening point is
moving at the same speed and in the same direction as the exit point -
i.e. with the planes ground speed. To get 500ft separation, it is
necessary wait until the plane has covered 500ft across the ground.
Cessna into a headwind maybe 40 seconds, TurboLet on a downwind run-in
around 3 seconds (I have jumped both).
So ground speed is all that matters - figure both upper wind speed and
the planes performance (or check the GPS) and leave longer times if the
groundspeed is lower (i.e. on windy days).
Pete Shew D10029
pete...@cix.compulink.co.uk
Bill Von Novak
>The situation we are talking about is when the forward airspeed of the
>plane and the exit altitude wind speed are very close. Nothing else
>matters in this situation. Think about the case were the plane's
>ground speed is zero. This case is equivalent to jumping off a tower.
>
>Every group going off such a tower (I want one to 13.5 with a fast
>elevator) is going to move thru the air in pretty much the same path
>and open in pretty much the same place. If you were jumping off this
>tower, how long would you wait before your group followed the previous
>group. Remember, you would be right over them in the same path and
>they will be opening before you!
yes - but on a very windy day that's not a problem.
most aircraft fly at around 80 knots. if winds at altitude are
80 knots and ground winds are also 80 knots, the plane will hover. in
this contrived case, if all the groups use their 'standard' spacing
(8 seconds or whatever) they will all open at the same spot over the
ground. however, the 80 knot ground winds will guarantee adequate
separation by blowing the opening group back as soon as they open. this
case is identical to jumping on a no-wind day but over a big conveyor
belt moving at 80 knots under the plane. the spacing at opening will be
fine, even though the opening points are over the same point on the belt,
since it's moving at the same speed as the plane.
so tower jumps on a day with 80 knot winds won't present a
problem. however, in the real world, winds at lower altitudes are less.
now you have groups opening at the same point, but without the 80 knot
wind to blow the lower group clear of the next group - hence the problem
with keeping the standard 8-second-or-whatever separation.
-bill von novak D16479 AFF/SL JM94
Barry Brumitt
Ah.... Why do we bother? This *has* been the subject of this group
before. Is it in the FAQ, btw? It should be... :-)
As soon as my thesis proposal is done (1 week, 1 day from now!) I will start
working on that experienced jumper FAQ. Things like this make it clear we need
one.
And if no one her volunteers to do it, I'm going to write an article on
seperation on windy days... lots of simulations with graphics and such... I'l
even add forward throw of the airplane. However, I need somsone to discuss
other aspects of load organzing w.r.t. exit order and the like... Proably
would get into parachutist w/o a problem, since there is SO MUCH confusion on
this subject.
Finally, I left 5 seconds after a 4-way on a 20knt uppers day to do some
freestyle. I transitioned to a standup shortly after exit, and watched the
fourway from afar. It was quit neat to watch them go "up" well above me even
though they'd had quite a good head start :)
Anyone out there working on using a standup for a long swoop instead of a
dive? Seems like you might be able to get better visibility in a more
vertical swoop... however, I don't think I want to try it on a large
load... particularly if there's video...
Barry
--
Barry L. Brumitt | bel...@frc2.frc.ri.cmu.edu | Disclaimer: Opinions
Robotics GradStudent | PGP Available Upon Request | given herein may not
Carnegie Mellon |http://frc2.frc.ri.cmu.edu/~belboz/| be the opinions of
"Who is John Galt?" | *Skydive!* (D-15427,SL JM/I95) | FRC, SCS, RI, or CMU
Ben Daniels
I've been trying to post this for several days from my usual place (csn.org)
but there's some problem there so I'll do it here where I'm doing a
short job.
----------------------
Forget all the wind velocities and times between groups and look
out the door at where the previous group got out.
If I want 1,000 ft of horizontal separation on the bottom, then I
need 1,000 ft of horizontal separation on the top, because my trajectory
is the same shape as theirs - just displaced 1,000 ft up the jumprun line.
If the uppers are strong it will take longer to cover that 1,000
horizontal feet. I know a lot of jumpers carry a sly drool around and can
probably figure all this out in the heat of the action but I feel better
looking out the door.
Now, in fact, I do think about the strength of the uppers, and I count
between all the exits because I'm curious about what people are
doing. And the count is kind of a background check on what I'm doing,
but mostly it's based on looking out the door.
Another thing is that I incorporate ground reference and altitude as
an active ingredient in the dive design (Oreo Cookie) and the breakup
is a full fledged part of the plan so on the track apart we fan out
perpendicular to the jump run line to avoid people following us out
who might think that 5 seconds or so is really enough separation.
This whole issue seems clearer to me when I think in terms of horizontal
spatial separation instead of wind velocities and time separation. Heck,
I just want to skydive ... I don't want to have to think too :-) :-)
Skratch
----------------
bdan...@csn.org
BADutile
Being a novice I have no opinion...except....When in dought....take the
safe route.
PEACE and Blue Skies!
Bonnie
Bill Von Novak
>The way I see it, you are either ignorant or you're deliberately
>spreading erroneous information. . . .you obviously haven't understood a
>shit of the explanations . . .
>Making unqualified statements the way you do only makes you look more
>stupid than you are. Probably.
whoah! this is getting kind of personal. slamming people like
this just encourages people to stay out of the discussions we're having.
posting a correction is enough. i mean - someone could slam you for
talking about horizontal separation without even being able to spell it.
but we'd never do that. . .
-bill von novak D16479 AFF/SL JM94 ASELS
Gregory Layton Reid
windy days" camp. Maybe part of the problem is that separation on exit is
not necessarily the same as separation at opening as was most clearly
demonstrated in the case of 0mph groundspeed senario.
--
TSW
(JRWSKYDIVE) wrote:
Due to all the confusing dissertations on this subject, which all seem to
say the same thing in different ways just to confuse me, destroy my mind
and ruin my life....I have decided to remove this problem from my personal
experience.
Solution as follows assuming only 1 aircraft flying upwind:
I insist on spotting, I make everyone other than my group stay seated with
there seatbelts on, I spot for my group appropriatly, and just as my group
leaves for no-show exit yell GO AROUND!!!!
Granted no-show exits can get a little boring, and the pilots will
probably string me up....but at least I'm safe!
<sarcasm off>
tsw
--
...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 ...
Michael Masterov
>> First, do it as a groundspeed calculation. Assume that the first group
>> exits over some arbitrary point 0. Groundspeed is 60 kts. That's
>> about 100 ft/sec. Allowing a time spacing of 5 seconds (typical spacing
>> for small groups) means that the second group exits about 500 ft forward
>> of point 0. So we have 500 ft of horizontal separation. Right? Wrong.
>> In those 5 seconds, the first group is moving backwards (relative to
>> the jumprun) at 12 kts. That's 20 ft/sec, or 100 ft. So the horizontal
>> separation is 600 ft.
>
>Yes, but what you forgot to figure in was that in the five seconds
>between group 1 opening and group 2 opening, group 2 would have closed up
>that extra 100ft to make the separation once again 500ft.
Nope. Wrong. In the five seconds after group 1 opens, they are under
canopy and are descending at about 15-20 ft/sec. They are also still in
the windstream and still being moved at 20 ft/sec horizontally. Group
2 is still frefalling at 180 ft/sec and being moved horizontally at
20 ft/sec. You can't close the separation under those conditions. An
easy way of visualizing what happens is to break up the 65 seconds from
Group 1 exiting to Group 2 opening as follows:
Segment 1 - 5 seconds:
Group 1 has just exited, and will freefall about 350 ft while moving
horizontally at 12 kts opposed to jumprun. This moves them -100 ft.
Group 2 is still in the airplane, moving at 60 kts forward; this
moves them +500 ft. So on exit, there is 350 ft of vertical separation
and 600 ft of horizontal separation.
Segment 2 - 55 seconds
Group 1 is freefalling to 2000 AGL. They are moving at 12 kts opposed to
jumprun; this moves them -1100 ft to a new position of -1200 ft. Group 2
is freefalling to about 3000 AGL (they won't make 2000 AGL for another 5
seconds or so). They, too, are moving at 12 kts opposed to jumprun, thus
moving -1100 ft to a new position of -600 ft. Thus when the 1st group
opens there is a horizontal separation of 600 ft and a vertical separation
of 1000 ft.
Segment 3 - 5 seconds
Group 1 is under canopy, descending at 15 ft/sec. They are STILL moving
at 12 kts horizontally, opposed to jumprun, neglecting whatever forward
speed their canopies may have. This puts them at about 1925 AGL and
another -100 ft, for a final position of -1300 ft (that's 1300 ft away
from their exit point, in the direction opposite to jumprun). Group 2
is freefalling to 2000 AGL, also being blown by the 12 kt winds, also
moving another -100 ft, for a final position of -700 ft. Separation
is still 600 ft. So now, at the critical point (Group 2 opening) the
vertical separation is GONE for all practical purposes (75 ft is essentially
zero in this situation) while the horizontal separation is 600 ft, just
like it was the moment Group 2 exited and at all points since.
>The frame of reference is only important in that a consistent one must be
>used. However, some are easier to visualise. Using a ground based frame
>of reference, and postulating unvarying (though possibly complex) winds,
>any groups exiting above the same point on the ground will end up opening
>at the same place as each other - regardless of the time between exits.
Yes, that is entirely correct. The extreme case of this is where the
jumprun speed is equal to the windspeed, and thus the aircraft is truly
hovering. All the groups that exit that aircraft will open over the
same point. You can still ensure adequate horizontal separation, though.
It's very easy. All you need to do is plan an opening point upwind of the
target. Neglecting forward speed of the canopies (after all, someone may
have to use a round reserve, which is why we plan the opening point upwind
of the target) the group, once it opens, will be moving downwind at the
windspeed. Knowing the windspeed at opening altitude will allow you to
calculate the required separation time. For example, if winds at opening
altitude are 12 kts and the aircraft is hovering at exit altitude, you
will need to allow 5 seconds for every 100 ft of horizontal separation
you want.
>(From a plane with zero ground speed you therefore need to leave enough
>time for the earlier group to have descended a thousand feet under canopy
>to be safe - at least a minute).
No - see the above. This would only be true if the winds at opening
altitude were zero.
This brings to mind another consideration, though. On days when the
winds at exit altitude are REALLY high, the winds at 2000 AGL tend to
be close to the forward speed of the canopy. So if you spot a little
short, people will mostly be holding into the wind. This will make
the groundspeed of the first group to exit approximately ZERO. The
guy with the round reserve is just going to land out, but the others
will be holding to make the landing area. In that case, your simplified
analysis suddenly becomes the correct one and you really
will have to allow at least a minute for vertical separation.
>If the plane is moving over the ground, the entire path of the jump will
>be displaced in the direction of motion of the plane at the speed the
>plane is moving over the ground; that is the eventual opening point is
>moving at the same speed and in the same direction as the exit point -
>i.e. with the planes ground speed. To get 500ft separation, it is
>necessary wait until the plane has covered 500ft across the ground.
Again - true only if there is no wind at opening altitude. Usually, if
the winds are really cooking at altitude, they will still be significant
at 2000 AGL. But since the jumpers may be holding into the wind on
opening, you have to take that as the worst case scenario for a standard
jump run.
For a dwonwind jumprun, the worst case scenario is a jumper running with
the wind in full flight immediately after opening. This suggests a
simple rule of thumb for computing minimum separation:
For an into-the-wind jumprun, compute the separation based on the ground
speed of the aircraft. For a downwind jumprun, compute the separation
based on the groundspeed minus 50 kts (that's about as fast as the
groundspeed of a canopy running downwind on a windy but jumpable day
is going to be). These rules will give you a worst-case separation.
>So ground speed is all that matters
Almost. At least on an into-the-wind jumprun. For a downwinder, the
rules change (but a downwind jumprun on a windy day will almost
certainly give you adequate separation since the winds aloft will
most likely be faster than the combined windspeed of the winds at
opening altitude and forward speed of the canopy - giving you the
airspeed of the aircraft for separation).
Michael Masterov C-24473
Philip Yzarn de Louraille
>Someone just pointed out in email that what I said before wasn't clear.
Geee that is funny, I thought you had made the clearest posting of them
all.
>
>Maybe this is a better way to say it:
>
>If I want my opening point to be 1,000 ft up the jumprun line from the
>group in front of me, then I have to make my exit point be 1,000 ft up
^^^^^^^behind, perhaps?
>the jump run line from their exit point.
>
>Our trajectories through the air are the same shape, just 1,000 ft
>apart at all points.
>
>Skratch
>
>----------------
>bdan...@csn.org
Glen Baker
> Are you trying to tell me that if an airplane is travelling at 90kts
> into a 90kt head wind and 2 groups exit with 10 sec between them that
> they won't fall through the same track? If you are, then please don't
> follow me out of an aircraft in those conditions. Airspeed has
> nothing to do with it. It is GROUND speed that counts.
Why is it that everybody seems to think that once the parachute opens the
effects of the wind suddenly go away??? In the above example it is true
that the two skydivers open in the exact same spot with respect to the
ground. However, the second group opens 10 seconds later during which
time the original group has traveled downwind somewhat (the absolute
distance depends on which way they fly after opening).
Assumptions are everything in this discussion. As others have pointed out,
in the trivial (and unlikely case) of surface winds == upper winds == W
a given delay should give the identical horizontal separation regardless
of the value of W.
..glen
Ben Daniels
Maybe this is a better way to say it:
If I want my opening point to be 1,000 ft up the jumprun line from the
group in front of me, then I have to make my exit point be 1,000 ft up
Rick Lemons
>Why is it that everybody seems to think that once the parachute
>opens the effects of the wind suddenly go away??? In the above
>example it is true that the two skydivers open in the exact same
>spot with respect to the ground. However, the second group opens 10
>seconds later during which time the original group has traveled
>downwind somewhat (the absolute distance depends on which way they
>fly after opening).
>Assumptions are everything in this discussion. As others have
>pointed out, in the trivial (and unlikely case) of surface winds ==
upper winds == W a given delay should give the identical horizontal
>separation regardless of the value of W.
Consider tracking in your estimates. That could put the groups over
each other at opening even allowing for your wind drift under canopy.
Not everyone gets to track at 90 deg to line of flight. And that
assumes all jumpers were upwind at opening. I still think you need
the separation without consideration of wind drift under canopy.
scru...@ac.dal.ca
> In article <D1v34...@news.cis.umn.edu> Will Forshay <wil...@awd.cdc.com> writes:
> |> [Will's theory that it is. Period.]
>
> [some rude inflammatory crap and Baard's theory that it is]
"Two men say they're Jesus..." I've seen lots of convincing arguments on
both sides of the fence "...one of them must be wrong."
This contest requires the wiener to explain the correct answer in 50 words
or less so that it could be explained to a child. The winner will be hard
pressed to include the words "rubber duck", "boat", "period" or phrase
"flatulent low-timer scum" in 50 words but bonus points are available.
First prize will consist of (with Barry's sponsorship) a credit in the FAQ,
a three week supply of good Karma, and the holy grail of Enigma Publius.
Meanwhile, concerned netizens should avoid the problem by:
- only doing big-ways or downwind jump-runs
- jumping 727's at 200+ knots and giving everyone 15 seconds.
- staying in the plane with their UPS backed cellular slip IRC linux
[Ed: 1.1.79 suggested] palmtop box and awaiting the death of this
thread so that they can start jumping again.
I, low-timer newbie scum in a rotten climate, will have to be content with
my new SGI VR skydiving simulator - 60 Hz refresh rate! I've put a desk fan
on top of my Indigo2 monitor and painted alternating blades blue and green,
ahhh, feel the wind... oh sorry - smells like 7'5
-Jeff Scrutton
scru...@ac.dal.ca
> "flatulent low-timer scum" in 50 words but bonus points are available.
^^^^^^^^^^^^^^^^^^^^^^^^^
I have blasphemed, forgive me, I am not worthy. Sometime I forget the lessons
of the masters, yes, achieving true god-like flatulence can only come with
years of dedication, sacrifice, and the abuse of the intestinal tract found
only in the path to becoming one with the DZ. And yes if we study the teachings
and the word of Dangerous Ed closely we learn that this is what is wrong with
accuracy jumpers, they never rise above the clouds to the glorious world of
7'5, never learn to endure, enjoy, and take part in the creation of a primal
incense so thick you can taste it. I am ready for my penance, yes, to regain
my humility I must fly with a load of women.
Truth be known, this is the real cause that keeps many women away from
skydiving. From an early age women are taught not to outperform men but
it becomes clear at 7'5 that they can not help but be regarded as god
like in their natural excellence. Many women take part in first jump
courses but quickly drop out of this nobel pursuit because they realize
that all gods shine at altitude and they are not happy to be put on a
pedestal of flatulence. You JM's, in your shaolin like pursuit of truth
and excellence, know this to be true. I will not mention names, a true
master's reward is in making the pilot blow chunks, but I am told that
there are gods among us on the net.
PS: I fully expect to be shot by an evangalist for stuff like this some
day but the truth must be told and the pills are starting to work.
Shine on blue skies,
-Jeff Scrutton
Will Forshay
jrwsk...@aol.com writes:
>There were two letters in the most recent Parachutist that stated that
>there was no reason to leave extra space between exits on windy days.
This
>is not correct. IMHO. What does everyone else think?
the horizontal seperation between groups is equal to
(amount of time between exits) multiplied by (airspeed of the aircraft)
and has exactly nothing to do with how fast the airplane is travelling
over the ground. All groups exiting the aircraft are affected, for all
practical purposes, the same in relation to the ground.
Period.
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)
*celebrating the Year of the Pig*
Will Forshay
baar...@idt.unit.no writes:
>Making unqualified statements the way you do only makes you look more
>stupid than you are. Probably.
>
>particular case.
whheeeee..........
(at the risk of sounding pig-headed)
let's make sure we're talking about the same thing. am I correctly
assuming that the we are desiring to have the same distance between
groups, on opening, on a windy day as on a no wind day? otherwise, if we
desire greater seperation on opening, the time between exits SHOULD be
greater. and I caution those that challange my credentials, as it's
obvious that SOMEBODY'S incorrect, even those with greater credentials
then me, because there are people on both sides of the issue. yes, I had
math through calculus, but that isn't necessary here. I'm simply one of
the few, the proud, the ones who aren't afraid to post to USENET.
an airplane on jump run at, say, 80 MPH through the air, is travelling
117 ft/second through the air. if solo jumpers exit, for the sake of
discussion, exactly 5 seconds apart, the jumpers will exit 585 feet
apart. assuming no odd variables like geeks who backslide, they will
open 585 feet apart. this is the same whether the mass of air through
which they are travelling is totally motionless or roaring at 100MPH
across the ground. the point is that the jumper's frame of reference is
the jumpship and the air. doesn't matter that the air is moving up down
backwards forwards sideway. that is, UNTIL THE JUMPER TOUCHES THE
GROUND. only then is there "wind". during the skydive, all freefall is
RELATIVE TO THE JUMPSHIP.
all jumpers will be affected approximately equally by changing "winds" as
they descend. the wind doesn't "bunch people up" any more than it
"spreads them apart", because there is no "wind" until one touches the
ground.
like I stated in my first paragraph, if you desired to have greater than
the exampled 585' upon opening, you simply wait longer, which perhaps you
wish to do, in which case I didn't understand the problem and we don't
disagree. if you desire to have less than 585' apart than just have less
than 5 seconds between exits.
in conclusion, the airplane will fly, at 80MPH, in 5 seconds through 585
feet of air. now, compared to the ground the airplane may be going
forward, staying the same, or even BACKWARD if it's super-howlin', but if
jumpers exit with 585 feet THROUGH THE AIR difference, they will, with
some caos errors, open 585 feet apart whether they each do hop 'n pops,
each do 5 second delays, each do 10 second, each do 50 second, or
whatever. if the airplane is 80MPH into a 75MPH headwind and a jumper
does a hop 'n pop, the airplane doesn't move away from that jumper at
only 5 MPH. if they all take the same delay they will all be open 585'
apart, just the same as when they left. there is some "wind" relative to
the jumpship, but all jumpers will be affected approximately equally.
during the skydive, all freefall is RELATIVE TO THE JUMPSHIP.
with all due and considerate respect (boy those skydivers really go up
when there parachutes open!),
dso...@uoft02.utoledo.edu
bel...@frc2.frc.ri.cmu.edu (Barry Brumitt) writes:
>In article <BAARDKJO.9...@drue.idt.unit.no> baar...@idt.unit.no (Baard Kjos) writes:
>
>
> Ah.... Why do we bother? This *has* been the subject of this group
> before. Is it in the FAQ, btw? It should be... :-)
>
>As soon as my thesis proposal is done (1 week, 1 day from now!) I will start
>working on that experienced jumper FAQ. Things like this make it clear we need
>one.
How about this, if opening separation really does depend on airspeed,
I can quite worrying about separation on BASE jumps. As long
as there is 20 mph of wind I will blow away from the other jumper
at 29.33 feet per second regardless of the wind at opening altitude.
So if I wait a minute, our *opening points* will be seperated by 1760
feet.
Gosh Will must use an awfully long lens when he does that
bridge day video since after 4 hours the jumpers have opening points
80 miles apart.
And here I thought math was difficult....
/* Dale Southard Jr. Sr. Rigger VectorTM */
/* Sr. System Administrator, C of Engineering AFF/I SL/I */
/* College Computing, University of Toledo S&TA D-11216 */
/* dso...@uoft02.utoledo.edu 419/537-3596 "I'd rather be skydiving" */
Baard Kjos
|> In article <BAARDKJO.9...@drue.idt.unit.no>,
|> baar...@idt.unit.no (Baard Kjos) says:
|>
|> >The way I see it, you are either ignorant or you're deliberately
|> >spreading erroneous information. . . .you obviously haven't understood a
|> >shit of the explanations . . .
|>
|> >Making unqualified statements the way you do only makes you look more
|> >stupid than you are. Probably.
|>
|> whoah! this is getting kind of personal.
Ooops, sorry about that. I think perhaps "...a shit" sounds more harsh
in the US than I meant it to be... I could probably also have written
"..look unneccessarily stupid", meaning that he wasn't neccessarily
stupid at all, but perhaps too dogmatic relative his factual level of
knowledge.
|> slamming people like
|> this just encourages people to stay out of the discussions we're having.
What triggered my reaction was probably that this, like a few other
threads on rec.skydiving, actually leaves very little room for
*discussions*. It is, in this particular case, more a matter of
presenting correct or erroneous information, the correct information
typically consisting of short and concise answers followed by precise
explanations of *why* the particular answer is correct.
I mean, you can't *discuss* whether groups exiting at the same point
will follow the same trajectory, can you? You can merely state that
they *will*, and then explain why, and also what implications this has
wrt horizontal (note the "z"!) separation at different altitudes. Am I
wrong?
Nah! I'm probably just bored (yepp, that's my name: Baard) with those
quasi-intellectual threads that sometimes (quite often wouldn't you
agree?) pop up in this forum, and I took it all out on this poor guy.
Sorry. Perhaps it's my periods coming a few days early this time. I
always try to avoid posting when I'm having my periods.
Eeek! Periods???
|> i mean - someone could slam you for
|> talking about horizontal separation without even being able to spell it.
|> but we'd never do that. . .
I know. But then again, I wouldn't slam *you* for your Norwegian
spelling either. :-)
Period!
--
Baard Kjos | http://www.idt.unit.no/~baardkjo/
Div. of Comp. Sci. and Telematics | ____
The Norwegian Institute of Technology | \ / The heart is a small
N-7034 Trondheim, NORWAY | \/ indomitable muscle...
MIKE MEYER
-> with there seatbelts on, I spot for my group appropriatly, and just
-> as my group leaves for no-show exit yell GO AROUND!!!!
...which explains that parahiking I saw at the DZ last weekend... 8^>
Rick Lemons
In article <D1v34...@news.cis.umn.edu>, <wil...@awd.cdc.com>
writes:
> the horizontal seperation between groups is equal to (amount of
>time between exits) multiplied by (airspeed of the aircraft) and has
>exactly nothing to do with how fast the airplane is travelling
>over the ground. All groups exiting the aircraft are affected, for
>all practical purposes, the same in relation to the ground.
>
> Period.
>
Baard Kjos
|>
|> (amount of time between exits) multiplied by (airspeed of the aircraft)
|>
|> and has exactly nothing to do with how fast the airplane is travelling
|> over the ground. All groups exiting the aircraft are affected, for all
|> practical purposes, the same in relation to the ground.
|>
|> Period.
The way I see it, you are either ignorant or you're deliberately
spreading erroneous information. Considering the proportionally large
crowd of inexperienced skydivers reading this news group (you are
perhaps one yourself?), both is harmful. The very least you could have
done, since you obviously haven't understood a shit of the
explanations that has been given, was to indicate your lacking
knowledge by using expressions like "I always thought that..." or "The
way I see it...".
Making unqualified statements the way you do only makes you look more
stupid than you are. Probably.
The very least you can do now is to admit your ignorance in this
particular case.
The horisontal separation *measured in seconds* is the same at exit
altuitude and at opening altitude, e.g. 8 seconds. The distance in
feet depends on wind speed at the two altitudes, since the falling and
suspended bodies are subject to the same horisontal wind forces all
the way. At exit altitude, horisontal separation is equal to aircraft
airspeed times seconds between each group. At opening altitude, the
separation in feet (before accounting for tracking and/or sliding
effects) is equal to the wind at that point times seconds between each
group. If it blows 80 knots all the way, separation is ok, but you're
probably not jumping due to high winds. If it's 0 knots e.g. below
3000' you're probably jumping, and horisontal separation below 3000'
is close to zero, assuming an aircraft airspeed of appr. 80 kts. Add
tracking and sliding effects to this, and you have the greatest of all
messes. Try it, if you dare.
Another example:
Consider a number of helicopters with one group in each, hoovering at
exit altitude with 500' horisontal separation between them. In this
example you can afford *zero* seconds of separation between the
groups, even in no-wind conditions. What normally happens in light
winds is that the airplane move from one "helicopter position" to the
other, giving each group their own path downwards. In high winds, the
plane isn't able to move from one position to the other, thereby
giving each group the same path. See? It isn't horisontal airspeed or
seconds that counts, but vertical sepration in feet.
Ah.... Why do we bother? This *has* been the subject of this group
before. Is it in the FAQ, btw? It should be... :-)
Jim Milstead
is traveling at the speed of light, I jumped out into winds
traveling at the speed if light, would time go backwards
and I actually never made the jump so who gives a shit where
I spotted? How far would I go up when I pulled the string??
Do aliens jump at the speed of light? Would booties help??
Can a Porter nose over and actually go up? Would Tim jump
a D-18? Would Will be elected? What would Barry video??
These are just some of the questions I have for the masters.
Grasshopper
But much to my surprise when I opened my eyes jmil...@spd.dsccc.com
I was a victim of the Great Compromise """ DSC Communications Corp
John Prine @(o o)@ Plano, Tx.
--------------------------------------------000---U---000----------------------
Pete Shew
> >between group 1 opening and group 2 opening, group 2 would have closed
> up >that extra 100ft to make the separation once again 500ft.
>
> Nope. Wrong. In the five seconds after group 1 opens, they are under
> canopy and are descending at about 15-20 ft/sec. They are also still in
> the windstream and still being moved at 20 ft/sec horizontally. Group
> 2 is still frefalling at 180 ft/sec and being moved horizontally at
> 20 ft/sec. You can't close the separation under those conditions.
Lots of good stuff omitted
> Michael Masterov C-24473
Sh*t, you spotted it (so did I after posting). What a dumb mistake to
assume that everything stopped when the canopy opened. I think I'm
changing sides.
Pete Shew D10029
pete...@cix.compulink.co.uk
Glen Baker
> How about this, if opening separation really does depend on airspeed,
> I can quite worrying about separation on BASE jumps. As long
> as there is 20 mph of wind I will blow away from the other jumper
> at 29.33 feet per second regardless of the wind at opening altitude.
> So if I wait a minute, our *opening points* will be seperated by 1760
> feet.
Why the heck does anybody care if the *opening points* are at the same
place? What *I* care about is our horizontal separation. As long as the
opening *times* are different the *points* can be identical.
Time to write a simulation program....
..glen
Michael Masterov
>> >between group 1 opening and group 2 opening, group 2 would have closed
>> up >that extra 100ft to make the separation once again 500ft.
>>
>> Nope. Wrong. In the five seconds after group 1 opens, they are under
>> canopy and are descending at about 15-20 ft/sec. They are also still in
>> the windstream and still being moved at 20 ft/sec horizontally. Group
>> 2 is still frefalling at 180 ft/sec and being moved horizontally at
>> 20 ft/sec. You can't close the separation under those conditions.
>
>assume that everything stopped when the canopy opened. I think I'm
>changing sides.
Well, don't do that yet. I shouldn't have posted as quickly as I did -
what I posted was not entirely correct and very confusing. If we all
used non-steerable rounds, it would have been entirely correct - but
still confusing. I'm going to try to make up for that.
Because people are going to fly their canopies non-randomly (they'll
all run with the wind if the spot was long, and they'll all hold into
the wind if the spot was short) we may have to account for that
effect in it's worst case instance.
For a jumprun into the wind, the worst-case separation occurs on a short
spot. The total separation will be defined by the ground speed of the
aircraft minus the ground speed of the canopies holding into the wind.
(Assuming the aircraft is not backing up).
For a downwind jumprun, it's the aircraft groundspeed minus the ground speed
of the canopies running downwind. That creates an interesting situation.
If the winds aloft are something like 50 mph (seen them faster) and the
winds at opening are 10 mph, and your jumpship has a cut speed of 80 mph,
You are only getting separation at about 20 mph (about 30 ft/sec) since
the canopies can probably do at least 10 mph ground speed into the wind.
If you want 1000 ft separation, you're looking at 30+ sec spacing. But
going downwind, you're getting separation at 100 mph, so 6 second spacing
will be fine.
It's not just about airspeed, and it's not just about groundspeed - it is,
unfortunately, more complex than that.
Michael Masterov C-24473
Glen Baker
> It's not just about airspeed, and it's not just about groundspeed - it is,
> unfortunately, more complex than that.
Hmm...seems to me that it's 100% about airspeed and the actions of the
skydivers relative to the air-mass. I would contend that groundspeed
has zero effect.
For all those folks who think that groundspeed matters I propose the
following reductio-ad-absurdum:
Zero winds aloft. Zero winds on the ground. 5 second exit separation. The
two skydivers have *some* horizontal separation at the time the second
skydiver opens (doesn't matter what the absolute value is).
Send the plane back up. Same conditions except that this time I pull out my
Catapillar D5000 tractor, hook up the entire 3000 acre drop zone to the
trailer hitch, and start pulling the entire DZ at 20 mph. Does anybody
believe for one instant that the horizontal separation at opening changes
one bit??
What *does* change is the actions of the skydivers. Depending on the spot
the individuals may choose to track and/or fly (after opening) along the
jump run. Bad idea...
..glen
Baard Kjos
In article <D1x1t...@news.cis.umn.edu> Will Forshay
<wil...@awd.cdc.com> writes:
|> am I correctly
|> assuming that the we are desiring to have the same distance between
|> groups, on opening, on a windy day as on a no wind day?
Yepp. The same horizontal distance in space, not in time.
It is necessary to assure a *ground relative* horizontal spacing at
exit altitude because the winds at opening altitude very well may be
(almost) zero RELATIVE TO THE GROUND. This very typical condition will
lead to a situation where jumpers from an early group practically
doesn't move horizontally at all the 8 or so seconds it takes before
the second group shows up in the same area RELATIVE TO THE GROUND.
Some jumpers in the first group probably haven't even touched their
brakes when the second group shows up, e.g. because of line twists.
The second group will indeed end up in the same area RELATIVE TO THE
GROUND, since they have exited from the same spot RELATIVE TO THE
GROUND due to 80 mph winds RELATIVE TO THE GROUND at exit altitude,
and have been subject to the same horizontal wind forces as the first
group. Since the second group hasn't moved much RELATIVE TO THE GROUND
(little or no wind, and only 8 seconds of canopy ride), the second
group will end up with almost zero distance RELATIVE TO THE FIRST
GROUP.
Tracking and sliding effects makes the situation worse, since this
may allow for jumpers to close distances up to 1000'.
It is the definition of "a windy day" that is the clue. Your assuption
is that the bodies fall through *uniform* air masses, which is a big
mistake in this case. We all know that winds vary with altitude, and
in particular on a windy day. Since winds at exit altitude is 80+ mph
(the aircraft stands still) and winds at landing is below, say, 25 mph
(we feel comfortable with the current landing conditions) we *must*
have a situation with a non-uniform airflow.
|> an airplane on jump run at, say, 80 MPH through the air, is travelling
|> 117 ft/second through the air. if solo jumpers exit, for the sake of
|> discussion, exactly 5 seconds apart, the jumpers will exit 585 feet
|> apart. assuming no odd variables like geeks who backslide, they will
|> open 585 feet apart.
Only if they are falling through uniform air.
|> all jumpers will be affected approximately equally by changing "winds" as
|> they descend.
Yes.
|> the wind doesn't "bunch people up" any more than it
|> "spreads them apart", because there is no "wind" until one touches the
|> ground.
Non-uniform air does. Look at cars at a highway with reduced speed
ahead (e.g. beacuse of road consruction). Even if every driver does
*identical* maneuvers (decelerating and accelerating, mimicking the
effect of different wind conditions at different altitudes) along
their *identical* trajectories, horizontal distances will vary. Flow
theory is the key, I guess.
An extreme example, just to point out the principle clearer:
If winds are 80 mph above 10,000' and zero below (heavy turbulence at
10,000), all groups exiting will be falling through exactly the same
vertical column of air from 10,000' to opening altitude, one group 8
seconds below or ahead of the other. With the first group opening e.g.
at 2500' and the next at 2000', the two groups will *definately* pose
a problem for each other....
|> during the skydive, all freefall is RELATIVE TO THE JUMPSHIP.
During the skydive, all freefall is RELATIVE TO THE AIR ONE FALLS
THROGH. When the air is a bit wicked, computing the path and
accounting for sufficient safety becomes a bit tricky.
|> 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)
I can't even decipher this.
|> *celebrating the Year of the Pig*
Hence, the comment about you being pig-headed? I guess I'll join you
in your celebration then.
Baard Kjos
|> Why is it that everybody seems to think that once the parachute opens the
|> effects of the wind suddenly go away???
We *know* that we have 80+ mph at exit altitude (the aircraft stands
still) and less than 25 mph at the ground (we feel comfortable with
the current landing conditions).
|> Assumptions are everything in this discussion.
Indeed.
BADutile
>been blowing lately and not from 12500 either....
I second that motion!
Tim Reynolds
Michael Masterov <mast...@atom.ecn.purdue.edu> wrote:
>
>It's not just about airspeed, and it's not just about groundspeed - it is,
>unfortunately, more complex than that.
Spotting being more art than science, IMHO, the point I try to make to my
AFF students is with the extreme case of an aircraft stationary with respect
to the ground at exit, no wind at opening vs. a typical light winds at all
altitudes situation. If they can understand the difference, and explain to
me why I made them understand it, I let it go at a that.
Other abductees, those that fathom light-spped travel as i do, and certain
ones that nod knowingly at my booties I let slide.
Tim
Tim Reynolds
Philip Yzarn de Louraille <yz...@lhdsy1.lahabra.chevron.com> wrote:
>
>I don't know about you guys, but it seems to me that a lot of "wind" has
>been blowing lately and not from 12500 either....
Some flatulent low timer scum computer geek made an ascii drawing of a
fart and turned it into an Internet Virus. Articles with the topic of
Goot Times and something else distribute it. Don't read them!
Tim
RobertC539
based education" (:
One of my jobs in the Navy was to plan minefields to be planted with
aircraft. This task is similar to what we are discussing since both
involve
"spotting" and separation between mines when they hit the water (or
skydivers when they open there parachutes). Of primary importance in
minefield planning is placement of the mines relative to one another and
also where they wind up relative to a target.
Placement of a mine on a target (the "key" mine from which all other mines
are placed) is planned by "spotting". From the given wind velocity,
AIRSPEED of the aircraft (airspeed and wind velocity determines
"forward throw" of the mine when it leaves the aircraft), and aircraft
altitude, a suitable launch point ("spot") is chosen. From this spot, we
know the mine, when released, will impact the water at the chosen target.
Since one aircraft can drop several mines, the next critical parameter is
determining when to drop the second mine. The way this is planned we want
the second mine to land a fixed distance from the first mine. This is done
by choosing a ground speed for the aircraft to fly on the mining run. If
we want to drop mines 1000 yards apart, then we take GROUND SPEED divided
by SEPARATION DISTANCE to come up with a time in seconds. Wind velocity
never entered into our planning other than to calculate the release point
of the first mine.
But then, as they say, there are three ways of doing things, the
"right way, my way, and the Navy way"!
"If I was to jump from a hovering helicopter and, after opening, count on
the wind blowing me out of the way of the jumpers exiting after me, that
wind better be honking!" Bob C. D-9437
Cindy Pirkkala
: In article <BAARDKJO.9...@drue.idt.unit.no>, baar...@idt.unit.no (Baard Kjos) says:
: >The way I see it, you are either ignorant or you're deliberately
: >spreading erroneous information. . . .you obviously haven't understood a
: >shit of the explanations . . .
: >Making unqualified statements the way you do only makes you look more
: >stupid than you are. Probably.
: whoah! this is getting kind of personal. slamming people like
: this just encourages people to stay out of the discussions we're having.
: posting a correction is enough. i mean - someone could slam you for
: talking about horizontal separation without even being able to spell it.
: but we'd never do that. . .
: -bill von novak D16479 AFF/SL JM94 ASELS
Isn't there just One mathematical aeronautical meteorological
weather phenomenon expert specialist extraordinaire highest rated
pilot with every type-rating skydiver with a million jumps, all on
different canopies who can settle this for once & all. I thought I had
it figured out, but I've gone back & forth so many times on this
thread that now I'm not sure what to think. In fact I'm totally
convincedd out, but after reading this thread, my own thought
processes have become so confused that the only thing I know for sure
is that I have absolutely no idea what in the hell I think, so I'm
going to just stop jumping. (Not a chance)
Robert Bonitz
>
> Isn't there just One mathematical aeronautical meteorological
>weather phenomenon expert specialist extraordinaire highest rated
>pilot with every type-rating skydiver with a million jumps, all on
>different canopies who can settle this for once & all.
Hey, we're talking about skydivers here. There are thousands of mathematical
aeronautical meteorological weather phenomenon expert specialist extraordinaire
highest rated pilot with every type-rating skydivers with a million jumps, all
Tim Reynolds
Cindy Pirkkala <pirk...@freenet3.scri.fsu.edu> wrote:
>I thought I had
>it figured out, but I've gone back & forth so many times on this
>thread that now I'm not sure what to think. In fact I'm totally
>convincedd out, but after reading this thread, my own thought
>processes have become so confused that the only thing I know for sure
>is that I have absolutely no idea what in the hell I think, so I'm
>going to just stop jumping. (Not a chance)
I have the same problem, many of the arguments on both sides are compelling.
It might help to *literally* draw a picture of an airplane, stationary with
resepct to a point on the ground, and the path that the jumpers take as they
fall away. Draw the path that the next group takes. Try to figure out how
those paths might magically differ. That's the point.
Tim
Michael Masterov
>"Two men say they're Jesus..." I've seen lots of convincing arguments on
>both sides of the fence "...one of them must be wrong."
>
>This contest requires the wiener to explain the correct answer in 50 words
>or less so that it could be explained to a child.
I know I'm paraphrasing someone, and if I plagiarize I apologize but:
Some things can not be explained in 50 words, simplified, and popularized
for the masses. They still require thought, effort, skull sweat, and
rigor. Physical laws are not subject to debate, legislative amendment,
court review, referendum, or initiative. They are absolute, and the
punisment for ignoring them is often death - with no clemency and no
appeal.
You make a choice. You either take the time and trouble to understand the
physics and the math and work it out for yourself, or you decide to trust
someone and hope you've chosen the right person to trust.
Michael Masterov, C-24473
Will Forshay
I'm cooking, so step up for your piece.
In article <D1xvK...@utnetw.utoledo.edu> , dso...@uoft02.utoledo.edu
writes:
>How about this, if opening separation really does depend on airspeed,
>I can quite worrying about separation on BASE jumps. As long
>as there is 20 mph of wind I will blow away from the other jumper
>at 29.33 feet per second regardless of the wind at opening altitude.
>So if I wait a minute, our *opening points* will be seperated by 1760
>feet.
well, your opening points *will* be separated by 1760 feet relative to
the *air*, and here is where I was at fault.
The following mental roadblock has been removed: if jumpers wanted to
land relative to the airplane, what I said is true (for whatever
credibility I have left). however, when spotting, I seem to be looking
at the ground for where I want to exit and land. therefore, my desired
exit point, and separation from other groups, is relative to the ground.
thanks Dale for saying DO THE MATH. thanks Michael for doing it for me.
thanks Bill for the wind shear example. thanks Eric for the kahunas
award for my willingness to post.
I only ask that you leave this exchange with a respect for my quest for
the truth, whether I have to beat it into you or have to bake the
aforementioned pie.
should any of you find me at a boogie, step right up for a beer that'll
be on me. of course, since you've already paid your registration, it'll
once again prove that I'm a cheap ass who'll only have to pull the tapper
for you.
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)
*celebrating the Year of the Pig*
dso...@uoft02.utoledo.edu
Because winds vary at different altitudes. The 80 knot winds at 13,000'
may be 5 knots at 3000'. In that case the lack of canopy drift means
that groups will be doing CRW unless their opening points relative
to the ground have horizontal separation. The only way to do that
is have exit points with horizontal separation relative to the ground.
It is not a good idea to rely on canopy drift to provide your opening
seperation.
> Time to write a simulation program....
Go ahead. I problem most people have isn't the math, it deciding which
inertial frame is the important one.
Baard Kjos
|> brakes when the second group shows up, e.g. because of line twists.
Oooopps.
I guess this could be understood as if the second group shows up
because of line twists. Although some of the bravest among them may
have an intention of becoming the hero of the day, by giving the
fellow with line twists a helping hand, I don't think this will be
their major reason for suddenly entering the arena...
TSW
> In article <BAARDKJO.9...@drue.idt.unit.no>,
baar...@idt.unit.no (Baard Kjos) writes:
> > In article <D1v34...@news.cis.umn.edu> Will Forshay
<wil...@awd.cdc.com> writes:
>
> > |> [Will's theory that it is. Period.]
> >
> > [some rude inflammatory crap and Baard's theory that it is]
>
> "Two men say they're Jesus..." I've seen lots of convincing arguments on
> both sides of the fence "...one of them must be wrong."
>
"Everything I've read seems to say two things, one God is omnipotent, two
Satan was not a fool. There seems to be a contradiction there."
paraphrased from To Reign In Hell
by I can't remember his name
good fiction book about the beginning of the world/universe/God
tsw
--
...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 ...
Philip Yzarn de Louraille
I don't know about you guys, but it seems to me that a lot of "wind" has
been blowing lately and not from 12500 either....
--
Philip Yzarn de Louraille Internet: yz...@chevron.com
UN*X Systems Specialist PROFS: ZARN(SMTP)
Chevron Information & Technology Co. Tel: (310) 694-9232
P.O. Box 446, La Habra, CA 90633 Fax: (310) 694-7709
John Luke Mills
: Maybe this is a better way to say it:
: If I want my opening point to be 1,000 ft up the jumprun line from the
: group in front of me, then I have to make my exit point be 1,000 ft up
: the jump run line from their exit point.
: Our trajectories through the air are the same shape, just 1,000 ft
: apart at all points.
: Skratch
This is probably the best description yet, even better than my tower
example. At Pepperell the load organizers and spotters always say to
leave extra time between groups when there is not much airspeed.
It seems we are as unlikely to reach consensus on this issue, just like
last time. We seem to be split about 35% who say the ground speed
doesn't matter and %65 who say it does. Given the safety implications
of this, perhaps we should ask USPA's Safety and Training committee to
take a stab at it. Probably the only way to settle this is to
experiment with a hovering helicopter and video the paths and opening
points from the ground.
--
)
o /
> / )__ __
/ / / ) )
/ ( / ( (
(__/
Gregory Layton Reid
: GROUND. < > RELATIVE TO THE JUMPSHIP.
: Will Forshay There's no sensation to compare with this
: D-12167, S/L-I Suspended animation, A state of bl
--
Well put. Sounds plausible. But so do some of the other arguements. Boy
am I confused.
\\||// ----------------------------------------------
(_ _) / Greg Reid ac...@cfn.cs.dal.ca /
{(o)(o)} / Halifax Nova Scotia _________________/
( [] ) / Canada C1290 /
-------oOO-\<>/-OOo-------------------------------
Matthew Swinden
>
>Ben Daniels (bdan...@athena.esig.ucar.edu) wrote:
>
>: Maybe this is a better way to say it:
>
>: If I want my opening point to be 1,000 ft up the jumprun line from
the
>: group in front of me, then I have to make my exit point be 1,000 ft up
>: the jump run line from their exit point.
>
>: Our trajectories through the air are the same shape, just 1,000 ft
>: apart at all points.
>
>: Skratch
>
>This is probably the best description yet, even better than my tower
>example. At Pepperell the load organizers and spotters always say to
>leave extra time between groups when there is not much airspeed.
>
You are right, this is probably the best example, except it is the
GROUND SPEED not AIRSPEED since airspeed is the measurement of air
flowing over the wings. Ground speed is measured how fast you are moving
on the ground.
For my 2 cents worth is that alot of people have gotten off on the wrong
track with airspeed vs. groundspeed. It is basically the distance you
want between the groups and since the plane is covering LESS ground w/
higher winds at altitude the plane is going slower, if the plane is
flying into the wind. So you must wait longer between groups to gain
that spacing interval.
Now how about them Chargers...
BS MS
Robert Bonitz
scru...@ac.dal.ca
>
> [Michael says that he is unable to solve the problem without a calculator
> or explain it to "the common man" in 50 words, and uses a lot more than
> 50 words in the process.]
>
In six words: Phuck fysics, the winner is Skratch. Let's have a big round of
net.applause for Skratch.
--
-Jeff "Don't make me bring up the super conducting super collider!" Scrutton
Barry Chase D9545/AFF I'95/Tandem Instructor
>by choosing a ground speed for the aircraft to fly on the mining run. If
>we want to drop mines 1000 yards apart, then we take GROUND SPEED divided
>by SEPARATION DISTANCE to come up with a time in seconds. Wind velocity
>never entered into our planning other than to calculate the release point
>of the first mine.
>"If I was to jump from a hovering helicopter and, after opening, count on
>the wind blowing me out of the way of the jumpers exiting after me, that
>wind better be honking!" Bob C. D-9437
You are mentioning that point that seems to be missing, but are
leaving out the ability of the jumpers to fly their canopies and have the
wind help them get back.
If you want separation, and then you need airspeed combined with
time between exits, as you said above. Even if the wind is howling along
at 100 mph, it's all relative since EVERYONE is getting blown at 100mph.
--
-----
_..-'( ba...@gate.net )`-.._
./'. '||\\. (\_/) .//||` .`\.
./'.|'.'||||\\|.. )o o( ..|//||||`.`|.`\.
./'..|'.|| |||||\`````` '`"'` ''''''/||||| ||.`|..`\.
./'.||'.|||| ||||||||||||. .|||||||||||| ||||.`||.`\.
/'|||'.|||||| ||||||||||||{ }|||||||||||| ||||||.`|||`\
'.|||'.||||||| ||||||||||||{ }|||||||||||| |||||||.`|||.`
'.||| ||||||||| |/' ``\||`` ''||/'' `\| ||||||||| |||.`
|/' \./' `\./ \!|\ /|!/ \./' `\./ `\|
V V V }' `\ /' `{ V V V
` ` ` V ' ' '
.....
Barry Chase D9545/AFF I'95/Tandem Instructor
said:
>
> OK.. Let me see if I can get this straight. If the airplane
> is traveling at the speed of light, I jumped out into winds
> traveling at the speed if light, would time go backwards
> and I actually never made the jump so who gives a shit where
> I spotted? How far would I go up when I pulled the string??
> Do aliens jump at the speed of light? Would booties help??
> Can a Porter nose over and actually go up? Would Tim jump
> a D-18? Would Will be elected? What would Barry video??
The video would turn out to be a 60 secnd sequence of a
topless beach down here in Miami. It would probably confuse the
resulting windburn right off of all of us, but none of us would
complain. Except maybe Doug Sunda who would rather be at Fire Island
for the 'drag' races. *8->
Barry Chase D9545/AFF I'95/Tandem Instructor
>
>Michael Masterov (mast...@atom.ecn.purdue.edu) wrote:
> Send the plane back up. Same conditions except that this time I pull out my
> Catapillar D5000 tractor, hook up the entire 3000 acre drop zone to the
> trailer hitch, and start pulling the entire DZ at 20 mph. Does anybody
WOW!!!! Can I have one of those??? I need to haul my ex-wife out of
state soon, and that just might (maybe) do the trick!!
Tim Reynolds
>
>In six words: Phuck fysics, the winner is Skratch. Let's have a big round of
>net.applause for Skratch.
Yay Skratch! He won last time we had this argument, too.
D. Jan's a lucky girl.
Tim
Barry Chase D9545/AFF I'95/Tandem Instructor
said:
> Isn't there just One mathematical aeronautical meteorological
>weather phenomenon expert specialist extraordinaire highest rated
>pilot with every type-rating skydiver with a million jumps, all on
>different canopies who can settle this for once & all. I thought I had
Ivy league or technical Phd. gradute?
Brenton Faulkner Milner
> One of my jobs in the Navy was to plan minefields to be planted with
> aircraft. This task is similar to what we are discussing since both
> involve
> "spotting" and separation between mines when they hit the water (or
> skydivers when they open there parachutes).....
So, since when did the Navy start aiming mines so they hit skydivers
when they open their parachutes? I often jump at Saint Mary's
County, MD just up the road from PAX River. Is this something
we should be watching out for?
Blue Skies, Dark Beer
Brent
Jeff Buck
says...
am using a slip client that is being a pain in the butt..
I am not an expert anything.. I have had high school
physics, and that is all that the problem requires to find a
solution...
In short. The ground does not matter. You are not in
it's inertial frame of refrence, and it is not affecting yours
or the other jumpers...
Yes- If you drop rocks (or anything) from a building on
a windy day, if the wind is the same, the rocks follow the same
path..
On the other hand, if you drop people from a plane
without the wind dragging them away from one another, They all
still follow the same path... They will all hit the ground
directly below the airplane,..
The only thing seperating any two jumpers, is the amount
the wind seperates them between their exits. If you are going to
say that the ground speed is important, you will at least have
to point out how the "Earth" is relavent...The Earth could be
spinning backward, and it wouldn't effect the path of the
skydivers... They might have a ground speed of 1000 mph, and
their relative postitions would not be affected.. If you jumped
out of a plane that was going 1000 mph, you could expect some
serious seperation- ALL FROM THE WIND... Yes, it is possible for
the jumpers to follow the same path, if you are looking at ANY
jump from a particular frame of refernce then this is the case.
The important part.. Can they be in the same place at the same
time? Nope, not any more than they could have been any other
jump.
That said, I think it is still wise to leave extra time
between exits on windy days... When it gets windy, the wind's
interaction with the ground can cause a lot of unpredictability.
You all know that at different altitudes, you have different
wind situations (boxing currents like in Albequerque (sp?) could
cause someone canopy open to cross under someone still in
freefall.. I guess more time could be dangerous in this
situation... But only if canopies were deployed at different
altitudes..Oh well, you get the point).. More time doesn't hurt,
it just gives you more seperation.. If the wind is the same
speed all the way down (and the same for each jumper), then the
extra seperation isn't necessary.. It is better safe than sorry,
there is no way to predict what the wind will do.
As I said before, there is nothing special about the the
physics here.. I have no idea how exactly this relates to real
jumps.. I do know that only funky wierd wind things matter, but
I don't have the skydiving experience to know how realistic it
is to expect "funky wierd wind things"... I have been on exactly
three jumps (all tandem- no responsibility, no wind to speak
of)...
It is extremely late- almost 6am, and I have yet to go
to bed.. I hope that this message makes sense, but I really
doubt that it does :).. Nite folks..
Incoherently Yours,
Jeff Buck (jb...@eskimo.com)
RobertC539
>So, since when did the Navy start aiming mines so they hit skydivers
>when they open their parachutes? I often jump at Saint Mary's
>County, MD just up the road from PAX River. Is this something
>we should be watching out for?
Only if you are a Clinton fan and happen to be jumping in North Carolina.
Bob C. D-9437
PJ Perdue
JB> Organization: Eskimo North (206) Forever writes:
JB> to point out how the "Earth" is relavent...The Earth could be
JB> spinning backward, and it wouldn't effect the path of the
JB> skydivers...
My two cents' in the debate on calculation
Of windy-day exit points location:
You have to add, to your computation,
Winds-aloft and ground winds differentiation;
The Global Positioning System's indication;
The wind-drift indicator's final imputation;
The speed and direction of the Earth's rotation;
And whether Mars trines Venus in its constellation.
And when your friends have collision due to lack of separation,
And all land far from their original destination,
You'll STILL owe them all an explanation.
And beer.
-- PJ