Forums: Skydiving: Safety and Training:
Calculating the "spot"

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nigel99  (D 1)

Jun 15, 2012, 3:31 PM
Post #51 of 58 (525 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 (518 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 (515 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 (488 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 (483 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 (462 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 (410 views)
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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 (379 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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