Crosswind jumpruns

[Phillip Artweger]

Chris, you say in your Spotting page:

[q]Uppers at 3K are light and variable and winds at 12k are 270 at 45 knots. A jump run directly into the uppers would be possible, but if the first group delays getting out because they haven't gotten directly over the landing area, then the last people out might have difficulty getting back because there is really no wind to push them back. So, make a run so that everyone ends up the same distance west of the landing area by running due north or south offset three-tenths west.[/q]

Ok now why the 0.3 offset? if it's a 270/45 isn't that more like 45/6 = approx. 0.7 ? to get them over the landing area ?

And now that we are coming in offset, we need to think slant range, so where do you give the Green light?
(Also using a Garmin 3 so flying the offset is easy enough )

Cheers

Phillip Artweger
Vienna - Austria

[Chris Schindler]

Not sure where the 45/6 comes in.  But....if the winds are at 45 and almost zero at 3,000 feet AGL then the average wind during freefall is roughly 23 mph.  Assume that 23mph wind is steady and you will get a drift of about 1,800 feet.  So, offset the run by .3 nm and everyone will open up on a line going north and south over the landing area.  I believe the example talks about having a hazard just east of the landing area.  So flying the offset going north or south then the groups will all have the same chance at landing away from the obstacle.

The example is based on what we do here at Skydive Chicago.  We have a river running north to south on the east side of the river about .3 from the center of the landing area.  If you get stuck and can't make it over the river then you have a two hour hike to the east to get to a road.

You are correct, if we ran it just into the wind then we could start people out early and not worry about them landing out.  But you try and tell people to trust you to go on the green light when they are directly over the landing area and they will worry about drifting over the river.  So paralleling it gets them out the door.

Slant range:  well, if the winds are essentially zero under canopy then they should be able to make it to the main landing area if they are within .8 miles at 2,500 feet.  So, I would time their climbout (give the green light) so that when they actually launch they are .8 or closer.  Launching at .8 (which is the slant range) should have them opening at .7 or .6  

Actually, what I've done several times (when I had too much time on my hands) I've made a temporary waypoint .3 west of the landing area so I don't have to fly the offset and then I made a second temporary waypoint south .....drum roll... 8 tenths south.  Ok, way too much work I know, but it does work.

I know this sounds like I'm way too anal about spotting but I really see it as my job to get people to jump more and spend more money if I get them close to the airport AND make only one pass to get everyone out.  More and more we have 23 people on the otter and they are all two way free fliers with the tiniest, fastest canopies that all want their perfect swoop.  I take it as a challenge to get them all on.

I know I should get diagrams on here to explain my examples better.  English is my first language and sometimes I don't show much mastery of it.

Chris Schindler
D-19012
ATP/CFII

[hubija kokov]

Just use TLAR - That Looks About Right!!

You know where you are landing!!

Rockin Ricky

:0-:

[Hypoxic Muppet]

We have a similiar method.  The GPS has the following.
PEN (the cross itself)
PEN N3 (0.3 of a mile north of the DZ)
PEN S3 (0.3 "       " south "       ")
PEN N6 (0.6 "       " north "       ")

Etc. Etc.

The uppers just about always come from a direction of 200-330 degrees and we run in on a track of 270 degrees.

A typical day with strong (40kts +) uppers south westerly will have the spot being say, PEN S6, 0.5 after.  In other words, run it on 270, and they start getting out 0.5 of a mile pass the cross.

A nor-easter would have them getting out typically like PEN N3, 1 mile before.

         

[PilotBB]

i always do either a north or south jump run. if the winds are out of the east or west i will side step a little into the wind, but still doing either north or south jump run.