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Calculating the "spot"

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

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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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.

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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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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Quote:
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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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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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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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
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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

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.

DaVinciflies

Jun 11, 2012, 11:19 AM
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Were you RGJ?

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

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)
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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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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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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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Quote:
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.

Dave-Dornan  (C 110107)

Jun 11, 2012, 9:25 PM
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Since your profile says you are a uk student you will have to do a low and high spot for your JM1 and B cert.

You will get a brief from your instructors when you get to that stage.

Dave

nigel99  (D 1)

Jun 11, 2012, 9:33 PM
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Quote:
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.

Dave I understand why on a turbine it is a pain and that is why few modern jumpers learn to properly spot. But doesn't the lack of skill end up with incidents like Lake Tahoe? Also it seems to me that as a D license holder it would be a good skill to have.

davelepka  (D 21448)

Jun 11, 2012, 9:42 PM
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I wasn't suggesting that jumpers not learn to spot, I was suggesting that making a WDI toss a part of any modern skydiving training is a waste of time and energy. Should we also require jumpers to learn how to pleat their gores?

I'm a huge supporter of situational awareness among jumpers, and that includes the spot, weather, exit orders, aircraft loading etc, all things that do get lost in the mix at bigger DZs where those things are 'done for you'. Much like canopy control, those are things that jumpers should really take more of an interest in, as those are areas that are directly related to their safety and well-being. Sadly, many jumpers are content to take the minimum level of training required in those areas, and won't persue any further study on their own.

mjosparky  (D 5476)

Jun 11, 2012, 10:12 PM
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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.

WDI’s were dropped at 2,500 feet directly over the target. The plane would circle until the WDI landed. The spot is the same distance up wind from the target as the WDI is down wind. They only work for low level jumps; they do not give you any indication of upper winds.

Sparky
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Jun 11, 2012, 10:13 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.

Very nice (spot calculator)

http://www.skydivemidwest.com/...one/spot-calculator/

erdnarob  (D 364)

Jun 12, 2012, 10:51 AM
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Hi Rifleman

You mention you are a student...maybe in sciences or applied sciences ! Anyway, few years ago I have made a program to calculate the spot using a Graphing calculator HP 48 GX. If you are interested by it, I will send you the program and a sample of calculation which validates it. On my program every step is explained.

To summarize, my program results is an addition of distance vectors.

I also made a grid on a Google Map aerial picture of my DZ with the center being the landing area. Concentric circles are drawn every 500 ft and radials every 10 degrees. Therefore when you calculate the spot (given in distance and direction) you can easily find it on the picture.

(This post was edited by erdnarob on Jun 12, 2012, 10:55 AM)

hillson  (D 33134)

Jun 12, 2012, 2:53 PM
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I've found that is easier to figure out where you don't want to get out / land and go from there. With wind data and an aerial photo of your DZ it is pretty easy to figure out where you want to be and more importantly where you don't.

cavscout73  (C 40414)

Jun 12, 2012, 3:46 PM
Post #33 of 58 (1195 views)
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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
Not sure if its text book or good for all but i was told right after i came off student status to get the winds aloft for the given altitude and use 1/4 mile for every 10 mph of wind. Its gotten me back every time..

nigel99  (D 1)

Jun 12, 2012, 6:02 PM
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I wasn't suggesting that jumpers not learn to spot, I was suggesting that making a WDI toss a part of any modern skydiving training is a waste of time and energy. Should we also require jumpers to learn how to pleat their gores?

I'm a huge supporter of situational awareness among jumpers, and that includes the spot, weather, exit orders, aircraft loading etc, all things that do get lost in the mix at bigger DZs where those things are 'done for you'. Much like canopy control, those are things that jumpers should really take more of an interest in, as those are areas that are directly related to their safety and well-being. Sadly, many jumpers are content to take the minimum level of training required in those areas, and won't persue any further study on their own.
Thanks for clarifying. It is tough because we all 'learn' to spot for our A license. But with big planes and GPS all you are really doing is popping your head out the door for a few seconds. At some point in the sport you should be required to do a non gps spot.

dninness  (D 19617)

Jun 12, 2012, 6:03 PM
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http://www.skyjump.com/thespot

(Thats is for Pepperell. Matt Veno, the wizard code monkey behind it, has made it available to any DZ that wants to put it on their website: http://www.flyingchipmunk.com/...generally-available/)

Speaking from experience, it takes the forecasted winds aloft, so as per usual, "no plan survives first contact with the enemy." All the usual disclaimers apply.

EDIT: Sorry, now with clicky goodness

(This post was edited by dninness on Jun 12, 2012, 6:35 PM)

SansSuit  (D 21554)

Jun 12, 2012, 6:20 PM
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The spot is only important if you care where you land.

skyjumpenfool  (Student)

Jun 12, 2012, 7:27 PM
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Landing on the DZ is highly over rated!

and, their not called "wind drift indicators" any more. The PC term these days is "students".

Squeak  (E 1313)

Jun 12, 2012, 11:15 PM
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Landing on the DZ is highly over rated!

and, their not called "wind drift indicators" any more. The PC term these days is "students".

JackC1

Jun 13, 2012, 12:59 AM
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I always watch a WiDI load before manifesting.

erdnarob  (D 364)

Jun 13, 2012, 9:36 AM
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I disagree completely with you that landing at the right place is over rated. Landing at the right place is safer. Anywhere outside the landing area can be hazardous. Any objects can be found on the ground and often hidden by high grass : piece of concrete with steel bars protruding, gap, irrigation channel, rusted pieces of metal...not counting roads, hydrolines, fences, houses...anything...name it.
You never know when you can be caught off gard by high winds and when the spot can be missed for various reasons.

Now about wind drift indicators. It seems old fashion but throwing wind rift indicators is the sure way to evaluate where the spot is.
No wonder why it is still a requirement or should be for the A license. People rely too much on their canopy performances but soon or later found themselves in a situation where they cannot make it back.
On a recent school football field parachute demo, the winds were marginal blowing at near 15 knots which is about the limit for a parachute demo. Fortunately, I had two wind drifts (red and gold). They landed, as expected, quite far away but from 2000 ft in the air I could easily evaluate the spot. People at the ground told me later that when they saw me leaving the airplane, they never thought I could come back. But the spot is the spot and I was back over the football field relatively fast and had the time to prepare for a nice landing in front of the spectators. Imagine a sec that I have missed the football field. The spectators would consider me as a zero instead of hero. Hundred of pictures have been taken. But because of the use of wind drift indicators, people on the ground will have a good opinion of skydivers and skydiving in general.

Knowing how to drop a wind drift indicator is important for any unusual winds situation and is a must for a parachute demo. But if you want always to rely on other people, never be on the first load of the day by high winds and decide to never get your PRO rating you are almost right.

(This post was edited by erdnarob on Jun 13, 2012, 12:27 PM)

JohnMitchell  (D 6462)

Jun 13, 2012, 11:32 AM
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You, Dave and I are all very experienced and we've all thrown our share of WDI's. With that said, I'll go with Dave's assessment that all square rigs have made starting the day with a WDI unnecessary.

Maybe for a tight demo, extreme weather or tight DZ with students, maybe, but I don't think I'll be hucking one at my present DZ.

popsjumper  (D 999999999)

Jun 13, 2012, 12:15 PM
Post #42 of 58 (1061 views)
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 Re: [rifleman] Calculating the "spot" [In reply to] Can't Post
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)

You are all over it, rifleman. Learn to do the math.
It could mean the difference some time.

Keep in mind that the example in the SIM is very basic. Learn that and then if you really want to be better at it, insert some changes in
-wind directions and speeds at different altitudes,
-jump run into the wind or some degrees of crosswind or even with the wind
-other.

By looking at varying conditions, you'll discover some very important issues regarding determining exit point, opening point AND separation at opening.

popsjumper  (D 999999999)

Jun 13, 2012, 12:28 PM
Post #43 of 58 (1055 views)
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 Re: [davelepka] Calculating the "spot" [In reply to] Can't Post
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.
And we can calculate that. We don't have to guess.

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.
And we can calculate that. We don't have to guess.

....so anywhere in there is your 'spot'.

Store all of this info in your memory banks and use to....
adjust for the inaccuracies of winds aloft charts and changes in wind direction and speed as the day goes on.

In the end, it's a bunch of educated guesswork.
Ummmm, for clarification:
Yes, we can only get good data out if we out good data in...and that goes for guesswork, too.

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.
Would you agree that doing the calculations would be a better start than "guessing"?

Sometimes students only see us doing the mental work in our heads, using previous experiences, and think we are "guessing".

Jun 13, 2012, 2:28 PM
Post #44 of 58 (1036 views)
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 Re: [JohnMitchell] Calculating the "spot" [In reply to] Can't Post
The value of developing the ability (art) of observing the weather conditions, displaying a thoughtful gaze for several seconds, and then confidently pronouncing where the spot should be cannot be underestimated!

JohnMitchell  (D 6462)

Jun 13, 2012, 7:24 PM
Post #45 of 58 (1008 views)
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 Re: [sundevil777] Calculating the "spot" [In reply to] Can't Post
You and I go way back. I know you know how to spot.

skyjumpenfool  (Student)

Jun 14, 2012, 11:25 AM
Post #46 of 58 (939 views)
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 Re: [JohnMitchell] Calculating the "spot" [In reply to] Can't Post
What Jon and Pops said above... start by studying, observing, calculating, etc? With that comes experience, with experience comes the ability to "guess/know" where the spot should be.

@ erdnarob ... Um, that was an attempt at sarcasm. However, I am in no way afraid of landing off. Partly because I jump where there is an abundance of open space, partly because I've been there - done that. The ability (or at least the lack of fear) to land off can make some decisions much easier. And, decision fear = indecision = late decision = bad decision.

JohnMitchell  (D 6462)

Jun 14, 2012, 11:50 AM
Post #47 of 58 (929 views)
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 Re: [skyjumpenfool] Calculating the "spot" [In reply to] Can't Post
Good point.

Sooner or later every jumper will land off. How you prepare yourself mentally and practice for that day will determine the outcome.

popsjumper  (D 999999999)

Jun 14, 2012, 10:16 PM
Post #48 of 58 (899 views)
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 Re: [skyjumpenfool] Calculating the "spot" [In reply to] Can't Post
The ability (or at least the lack of fear) to land off can make some decisions much easier. And, decision fear = indecision = late decision = bad decision.

Worth repeating...several times

Lack of knowledge = decision fear....

MikeJD  (D 10605)

Jun 15, 2012, 5:20 AM
Post #49 of 58 (881 views)
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 Re: [JohnMitchell] Calculating the "spot" [In reply to] Can't Post
I'll go with Dave's assessment that all square rigs have made starting the day with a WDI unnecessary.

Not to mention the fact that in general we're exiting higher than we used to. Winds upstairs can be howling and can be completely at odds with those on the ground. Combine that with the improved range of square canopies and I'd guess that freefall drift is at least as significant now as canopy drift.

And you're not going to learn anything much about freefall drift by throwing a WDI from opening height. :)

popsjumper  (D 999999999)

Jun 15, 2012, 2:41 PM
Post #50 of 58 (852 views)
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 Re: [nigel99] Calculating the "spot" [In reply to] Can't Post
Thanks for clarifying. It is tough because we all 'learn' to spot for our A license. But with big planes and GPS all you are really doing is popping your head out the door for a few seconds. .
...and THAT is not spotting. It's only a small part of the process.

nigel99  (D 1)

Jun 15, 2012, 3:31 PM
Post #51 of 58 (658 views)
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 Re: [popsjumper] Calculating the "spot" [In reply to] Can't Post
Thanks for clarifying. It is tough because we all 'learn' to spot for our A license. But with big planes and GPS all you are really doing is popping your head out the door for a few seconds. .
...and THAT is not spotting. It's only a small part of the process.

But it is the reality of an Otter spot isn't it?

rifleman  (Student)

Jun 15, 2012, 4:12 PM
Post #52 of 58 (651 views)
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 Re: [nigel99] Calculating the "spot" [In reply to] Can't Post
So, if you jump from from 15,000 ft you take the wind speed and direction from the winds aloft table for 3,6,9,12 and 15,000 ft and divide by 5 to get the average.

What do you do if you're only jumping from 10,000. Do you only use the wind speeds and directions from 3,6 and 9,000 and divide by 3?

skyjumpenfool  (Student)

Jun 15, 2012, 4:30 PM
Post #53 of 58 (648 views)
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 Re: [rifleman] Calculating the "spot" [In reply to] Can't Post
So, if you jump from from 15,000 ft you take the wind speed and direction from the winds aloft table for 3,6,9,12 and 15,000 ft and divide by 5 to get the average.

What do you do if you're only jumping from 10,000. Do you only use the wind speeds and directions from 3,6 and 9,000 and divide by 3?

That'd probly work, keeping in mind there is no magic bullet here. Squares give you great range and landing off won't necesarily kill you. Each time you spot you're building that experience/skill.

T-10's got us back most of the time... back in the day. Technology has only gotten better.

JohnMitchell  (D 6462)

Jun 16, 2012, 8:53 AM
Post #54 of 58 (621 views)
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 Re: [rifleman] Calculating the "spot" [In reply to] Can't Post
So, if you jump from from 15,000 ft you take the wind speed and direction from the winds aloft table for 3,6,9,12 and 15,000 ft and divide by 5 to get the average.

What do you do if you're only jumping from 10,000. Do you only use the wind speeds and directions from 3,6 and 9,000 and divide by 3?
Sure. But realize that wind direction also can change with altitude, often a little, sometimes a lot. That's when it gets complicated. You can calculate a vector for your time spent in each altitude block and add the vectors together. I think they get into all that for HALO/HAHO jumps. Winds at 25K can easily be 50kts. I've seen them in the 100's at 30,000'.

ufk22  (D 16168)

Jun 16, 2012, 9:51 AM
Post #55 of 58 (616 views)
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 Re: [rifleman] Calculating the "spot" [In reply to] Can't Post
So, if you jump from from 15,000 ft you take the wind speed and direction from the winds aloft table for 3,6,9,12 and 15,000 ft and divide by 5 to get the average.

What do you do if you're only jumping from 10,000. Do you only use the wind speeds and directions from 3,6 and 9,000 and divide by 3?
That'll be close enough, just remember to also adjust for the change in freefall time. You divide by 60 because 60 secs=1/60 of an hour. If your going out at 15k your freefall time is more like 75 seconds, so you would divide your average wind speed in MPH by 48 (3600 seconds in an hour/75 seconds of freefall=48=1/48 of an hour) With modern canopies, the spot is not near as critical as it once was, but I admire you for wanting to actually know what's going on and why rather than just being a "green light" skydiver.

popsjumper  (D 999999999)

Jun 16, 2012, 6:35 PM
Post #56 of 58 (595 views)
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 Re: [ufk22] Calculating the "spot" [In reply to] Can't Post
So, if you jump from from 15,000 ft you take the wind speed and direction from the winds aloft table for 3,6,9,12 and 15,000 ft and divide by 5 to get the average.

What do you do if you're only jumping from 10,000. Do you only use the wind speeds and directions from 3,6 and 9,000 and divide by 3?
That'll be close enough, just remember to also adjust for the change in freefall time. You divide by 60 because 60 secs=1/60 of an hour. If your going out at 15k your freefall time is more like 75 seconds, so you would divide your average wind speed in MPH by 48 (3600 seconds in an hour/75 seconds of freefall=48=1/48 of an hour) With modern canopies, the spot is not near as critical as it once was, but I admire you for wanting to actually know what's going on and why rather than just being a "green light" skydiver.

Thank you, UFK22...that's what it's all about.

dninness  (D 19617)

Jun 23, 2012, 4:48 PM
Post #57 of 58 (543 views)
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 Re: Calculating the "spot" [In reply to] Can't Post
Many years ago, I got pretty adept at tossing things out of moving helicopters and hitting targets on the ground from 1000-1500ft (long story). When I started jumping, spotting the 182 was actually not that big of a mental exercise for me, I just had to learn how to adjust for parachute & freefall drift, etc.

One day we're doing 4-way out of the Cessna, and I wind up in the slot that puts me in "jumpmaster" in the plane. I hear one of the guys groan "Great, newb spotting.."

So we get to altitude, pilot opens the door and I lean out. I'm giving him corrections and waiting for us to get the right distance upwind and I can hear "Ok, lets go.. ok, lets go.." from behind me. Finally, I signal for the cut, we climb out and go on about our 4-way business.

After we land, I'm walking in and one of the very experienced jumpers is standing in front of the building and bellows "WHO THE FUCK SPOTTED THAT LOAD?"

I'm thinking "Oh, shit. What did I do?" as I meekly say "I did."

"Well, that was about an outfuckingstanding spot!"

One of my co-conspirators had a cutaway (I didn't even notice.. I saw traffic in the air, but I still wasn't quite to the point of recognizing who was who) and his trash landed about 3/4 of the way down the sidewalk between the main building and the aircraft loading area.

From then on, I was considered the "master spotter" or something.

The really funny thing is that when the ISP and all that came along, suddenly there was an actual "spotting lesson" in the syllabus. I became a coach about the time my girlfriend started jumping, and one day we're at the DZ kind of early and she says "OK, teach me... Where is the spot today?"

I looked up at the sky, over at the wind sock on the hangar, back up at the sky, pointed off to the northwest and said "Uh, over thataway, I guess."

You'd have thought I told her that airplanes fly by "pure fucking magic." She goes "No! How do you calculate the spot?"

(my student learning of spot calculation did not involve using the forecast winds and math. It involved educated guesstimation and a WDI, and not always both)

So I (honestly) said "Well, I look at the ground winds, and if there are clouds I'll see what the uppers are doing, and, you know, its kinda upwind of the DZ a little ways" and waved my hand in the direction I thought the spot was in.

I thought she was gonna pop a cork. Come to find out, she'd read the spotting bit in the SIM and wanted me to walk her thru it. I was a fairly new coach, didn't realize there was a lesson in the SIM, and since I was sure I knew how to spot, I probably wouldn't have followed it anyway. (LOL) I used experience and intuition, not the forecast and math.

Made her crazy. It was actually pretty funny later.

popsjumper  (D 999999999)

Jun 24, 2012, 4:09 AM
Post #58 of 58 (512 views)
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 Re: [dninness] Calculating the "spot" [In reply to] Can't Post
I thought she was gonna pop a cork. Come to find out, she'd read the spotting bit in the SIM and wanted me to walk her thru it. I was a fairly new coach, didn't realize there was a lesson in the SIM, and since I was sure I knew how to spot, I probably wouldn't have followed it anyway. (LOL) I used experience and intuition, not the forecast and math.

Made her crazy. It was actually pretty funny later.

I applaud her for wanting to learn proper spotting.

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