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Calculating the "spot"

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rifleman  (Student)

Jun 9, 2012, 5:13 PM
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Is there some kind of formula for calculating the spot from wind charts/forecasts? If so, could someone please tell me what it is, as I'd like to be able to figure it out for myself.

Many Thanks

5.samadhi

Jun 9, 2012, 7:04 PM
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I just stay on the plane until the pilot looks at me nervously then I figure its time to go and fly my wingsuit back to the dropzone

nigel99  (D 1)

Jun 9, 2012, 7:12 PM
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In reply to:
Is there some kind of formula for calculating the spot from wind charts/forecasts? If so, could someone please tell me what it is, as I'd like to be able to figure it out for myself.

Many Thanks

From memory the USPA sim has the details. The sim is available for free on the USPA website. If I get a chance I'll post the section number but it should be fairly easy to find.

edited to add.

http://www.uspa.org/...242/Default.aspx#951

(This post was edited by nigel99 on Jun 9, 2012, 8:19 PM)

Rover  (D 241)

Jun 9, 2012, 8:11 PM
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In reply to:
Is there some kind of formula for calculating the spot from wind charts/forecasts? If so, could someone please tell me what it is, as I'd like to be able to figure it out for myself.

Many Thanks

It's the pilots job

BIGUN  (D 23385)

Jun 9, 2012, 9:24 PM
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Hope this helps...

http://library.enlisted.info/...s-1/FM31_19/APPB.PDF

JohnMitchell  (D 6462)

Jun 10, 2012, 9:29 AM
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Here's the other way to calculate. Go to the DZ and see which way the wind is blowing and how strongly. Watch the clouds and see which way the winds aloft are blowing and how quickly. Watch where the other loads are letting out and watch what they do under canopy. Watch to see if they get huge amounts of drift in freefall.

Figure on flying over the landing area, straight into the wind, and getting out up wind of your LZ. The harder the wind is blowing, the farther upwind you need go. Ask the pilot and others who've jumped that day how far upwind you should go.

If this sounds tongue-in-cheek, I assure you that this is what I used to do long before everyone had access to all the info in the world. I've used the winds aloft forecasts as guidelines, but since we were only jumping from 10-13K, I never bothered with all the arithmetic. I just estimated it.

dragon2  (D 101989)

Jun 10, 2012, 10:11 AM
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Ask the pilot and others who've jumped that day how far upwind you should go

That.

I can look up all the info on the internet to check winds aloft, and I do that. A number of times a day.
I still like to watch a couple of loads if I can, to see where people are exiting and where they end up opening, and how much forward speed they have on various altitudes under canopy. This helps me when spotting for myself/tandemrun and for any student or solo jumpers that go out lower or go before the tandems.
While in those cases I usually spot (although the pilot has gps and we do have a "green light = go" sort of system), I really appreciate it if those students/solos can tell me where they expect to exit, themselves

theplummeter  (D 34357)

Jun 10, 2012, 10:24 AM
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In reply to:
Here's the other way to calculate. Go to the DZ and see which way the wind is blowing and how strongly. Watch the clouds and see which way the winds aloft are blowing and how quickly. Watch where the other loads are letting out and watch what they do under canopy. Watch to see if they get huge amounts of drift in freefall.

Figure on flying over the landing area, straight into the wind, and getting out up wind of your LZ. The harder the wind is blowing, the farther upwind you need go. Ask the pilot and others who've jumped that day how far upwind you should go.

If this sounds tongue-in-cheek, I assure you that this is what I used to do long before everyone had access to all the info in the world. I've used the winds aloft forecasts as guidelines, but since we were only jumping from 10-13K, I never bothered with all the arithmetic. I just estimated it.

I've flown several hundred loads of static line students, tandems, and fun jumpers ranging from 3500 to 10500 feet. I have never calculated the exit point and I have never had anyone land off.

Low groundspeed means higher winds aloft. I fly the jumprun into the wind and tell the jumpers to wait a second after crossing over center, two seconds if we're over 8000.

JohnMitchell  (D 6462)

Jun 10, 2012, 10:42 AM
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It's not very hard to estimate a good spot if you take in information from many sources, such as watching the speed and direction of cloud shadows, how slow you're moving across the ground on jump run, etc. More than once I've observed us crawling across the ground on jump run and taken the spot out another quarter mile or so. I don't mind having the winds aloft forecasts available, but there are many other sources of info for your spot estimates.

Back when we all jumped rounds you got immediate and obvious feedback on every spot. Now with square canopies it's really not as critical unless you're the guy who has to go find cutaway canopies in the woods.

(This post was edited by JohnMitchell on Jun 10, 2012, 10:44 AM)

Croc  (D 29552)

Jun 10, 2012, 10:50 AM
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I jump at a Cessna DZ, so I can look at the GPS groundspeed and subtract that from the airspeed, which, if you are flying into the wind, gives you the wind speed. You can also get a pretty good idea of the windspeed by hanging your head out the door and determining how fast or slow your ground speed is. Slower ground speed means take it out farther and take more time between jumps. Not scientific, but it works very well, even for CRW.

I also ask people and pilots on the previous loads what their experience has been. John's advice to look at the clouds is a very good one if you can remember to do it!

(This post was edited by Croc on Jun 10, 2012, 10:53 AM)

skyjumpenfool  (Student)

Jun 10, 2012, 10:52 AM
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In reply to:
It's the pilots job

Really? Is the art of spotting that far gone? It may be the pilots "job", but when you exit the aircraft, it becomes your responsibility! Period.

OP... Great question! Check the weather. Check the winds aloft. Look at the clouds. Watch whats going on with previous loads. Ask the more experienced jumpers. Some of it's just guesswork. You might make a mistake, but with practice comes experience.

Even on loads where I'm not spotting, I'm spotting.

mjosparky  (D 5476)

Jun 10, 2012, 6:58 PM
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In reply to:
Even on loads where I'm not spotting, I'm spotting.

The “green” light means you have the pilot’s permission to jump. After that it is up to you to call the spot.

Sparky

kallend  (D 23151)

Jun 11, 2012, 7:38 AM
Post #13 of 58 (4497 views)
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In reply to:
Is there some kind of formula for calculating the spot from wind charts/forecasts? If so, could someone please tell me what it is, as I'd like to be able to figure it out for myself.

Many Thanks

If someone tells you, then you haven't figured it out for yourself.

JohnMitchell  (D 6462)

Jun 11, 2012, 9:37 AM
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I noticed your screen name "Rifleman." It's a lot like "Kentucky windage".

rifleman  (Student)

Jun 11, 2012, 10:34 AM
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What I meant was that I'd like to be able to calculate the spot for myself even though atm I'm having to trust my instructors to put me out at the right point.

How will I know if the spot is right if I have no idea how to figure it out? (6 years in the military have taught me that mistakes can and do happen, even with qualified personnel)

davelepka  (D 21448)

Jun 11, 2012, 10:46 AM
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Quote:
How will I know if the spot is right if I have no idea how to figure it out?

There is no hard and fast formula for coming up with the spot.

Look at the winds on a given day. Figure out all the places you could open at your pull altitude, and still make it back to the DZ.

If there are no winds at all, the area will be a perfect circle around the DZ, let's say 1.5 miles in diameter. If you open up anywhere in that circle, you can make it back to the DZ, so the 'spot' for you is anywhere in that circle.

Now say there are 10mph winds blowing out of the north. If you were south of the DZ, those winds would stop you from gliding very far, so you won't want to open up very far south of the DZ, let's say less than 1/4 mile.

On that same day, you could get out much further upwind (north) of the DZ, and have the winds puch you back to the DZ, let's say you could be 2 miles upwind.

So now if you use the point 1/4 south and 2 miles north as the tips of an ovel shaped area around the DZ, if you open anywhere in that oval, you can make it back to the DZ, so anywhere in there is your 'spot'.

What you do now is just start paying attention to all of these factors on your jumps. Take advatnage of the more experienced people helping you out, and then remember the wind speed and direction, and where the spot was for that day. Consider your canopy flight, and how it went, and if you could have been closer or further away. Store all of this info in your memory banks and use to figure out future spots.

On thing you can do is sit down and figure out what you think it should be on a given day, and then compare that to what the 'experts' are saying for that day.

In the end, it's a bunch of educated guesswork. It's not uncommon for there to be an informal morning 'meeting' between the pilot and a senior jumper/staff memeber where they guess at the spot. It also not uncommon for there to be a follow-up meeting after the first load to make 'adjustments'.

rifleman  (Student)

Jun 11, 2012, 10:48 AM
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The name 'rifleman' was originally my job description when I joined the Army (rifleman = private in some infantry battalions in the UK) and historically denoted a soldier trained to use a Baker rifle as opposed to a smoothbore musket. Riflemen operated in pairs ahead of the line infantry as skirmishers, taking advantage of the longer ranged weapon to target officers, artillery etc.

ufk22  (D 16168)

Jun 11, 2012, 11:18 AM
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OK, per the SIM, Cat E, page 70 in mine.

Get surface winds and winds aloft, 3k, 6, 9k, 12k, in mph and head degree.
Add the surface and 3k numbers together, devide by 2 to get the average wind speed and average wind direction for canopy flight. Assume average canopy ride of 3 minutes=1/20th of an hour. 1/20th of the average wind MPH=distance upwind from target (at opposite heading of the average of the two wind headings) on opening.This is where you want to end up after freefall is over.
To go from there to the exit point, add and average wind velocities (and headings) in mph at 3, 6, 9, and 12K. Divide the average speed by 60 (assuming 1 minute of freefall) and this will give you the distance in miles you will drift in freefall at the average of the wind headings.
Take the opening spot, move the distance you got for drift in the opposite direction of the average wind direction, and you have the exit point.

The answer to most beginners skydiving questions are in the SIM. It's even a FREE download.

DaVinciflies

Jun 11, 2012, 11:19 AM
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Were you RGJ?

("If you can't hack it....")

wildWilly  (B License)

Jun 11, 2012, 1:59 PM
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I started at a Cessna DZ and learned from the beginning how to get the pilot to do rate 1 turns ( 360 degree turn that takes 2 min.) from this I can figure the drift of the lower winds ( opening point) then do it again up higher 7K to figure out the upper winds ( exit point) and never landed off.
This is a little hard to do with a bigger plane ( Otters etc.)
That is why I hardly ever get on the first load of the day.

Blue Skies,

Willy

faulknerwn  (D 17441)
Moderator
Jun 11, 2012, 5:48 PM
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If you go to skydive midwests website they have an app which lets you enter the winds aloft and ground winds and it will do the math. We've been using it for a couple years now and it works quite well.

jverley  (D 16677)

Jun 11, 2012, 6:21 PM
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The ONLY way to get it right is to throw a Wind Drift Indicator. It the old days this was a weighted sheet of crepe paper that would be thrown over the target and watched to see where it landed relative to the target. The spot was then adjusted the same distance upwind.

It requires multiple passes of the plane and many DZ's are loathe to make the extra pass.

The modern approach is to see where the first group on the first load got out and how far off they land and then adjust the spot accordingly.

dthames  (D 34390)

Jun 11, 2012, 6:43 PM
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In reply to:
The ONLY way to get it right is to throw a Wind Drift Indicator. It the old days this was a weighted sheet of crepe paper that would be thrown over the target and watched to see where it landed relative to the target. The spot was then adjusted the same distance upwind.

It requires multiple passes of the plane and many DZ's are loathe to make the extra pass.

The modern approach is to see where the first group on the first load got out and how far off they land and then adjust the spot accordingly.

Some DZs still use WDIs. I got a chance to jump at one of them and observe. Dropped the WDI right over the field at the height the tethered SL students would exit. Then saw the offset of where it landed, and made the offset to the jump run so the students would drift right to the landing area. Low tech, but effective.

nigel99  (D 1)

Jun 11, 2012, 9:01 PM
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In reply to:
In reply to:
The ONLY way to get it right is to throw a Wind Drift Indicator. It the old days this was a weighted sheet of crepe paper that would be thrown over the target and watched to see where it landed relative to the target. The spot was then adjusted the same distance upwind.

It requires multiple passes of the plane and many DZ's are loathe to make the extra pass.

The modern approach is to see where the first group on the first load got out and how far off they land and then adjust the spot accordingly.
Some DZs still use WDIs. I got a chance to jump at one of them and observe. Dropped the WDI right over the field at the height the tethered SL students would exit. Then saw the offset of where it landed, and made the offset to the jump run so the students would drift right to the landing area. Low tech, but effective.

I've never done it myself, but would love to give it a nshot (wdi). It should be a prerequisite to C or D license.

davelepka  (D 21448)

Jun 11, 2012, 9:25 PM
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It should be a prerequisite to C or D license.

Negative ghostrider. WDIs were of use in the days of round canopies when drift could mean the difference between landing on the DZ or not. With a very narrow window of manuverablity, a round canopy needs to be spotted accurately to get the students home.

Squares, on the other hand, can get home from a wide swath of sky, and if you can drop the jumpers anywhere in that area, they can make it back to the DZ. The precision you can gain with a WDI is far more than is needed for modern, steerable canopies.

Consider than an average Otter load might cover a mile or more between the first and last exits, and it's rare for anyone to land off these days. If you want to jump a round, pull out a WDI and give it a shot. Otherwise, when jumping a square, simply look at the wind speed and direction, make your best guess, and then pilot yourself back to the DZ.

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