using an aviation winds aloft forecast,

[azureriders 0]

select the correct exit and opening point.


Working backwards from where you would want to land, you should open up wind and on the wind line.

Q. How far up the wind line. Ft per mile per hour of wind???


Working backwards from the opening point you would want to exit up the average wind line from the point of open. Average all the aloft wind speeds and headings and assuming a 60sec freefall from 14000ft....(any corrections welcome)

Q. How far up the wind line. Ft per mile per hour of wind???


I like to research my next lesson before I reach the lesson but I have not found much info on this one. It is one of the last things left on my A card and I would appreciate any info.

[LouDiamond 1]

This might be more information than your looking for but it will answer your question and then some. There are several DOC and PPT files attached to different posts I made in THIS thread that you should look at. If you have any questions just let me know

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[azureriders 0]

Thanks alot. That was exactly what I was looking for.

Why do some people insist on deriving formulas that require imperial unit input and produce a metric unit answer

[JohnMitchell 14]

I looked through some of the presentations. I know that there are a lot of formulas for figuring all that out. Sometimes a WAG, wild ass guess, can be pretty effective. Figure 60 seconds of freefall gives you one minute to drift. (Duh.) 60 mph winds will drift you one mile in one minute. 30 mph will drift you half as far. I actually reduce that estimate by 1/3, since winds aloft tend to slow as you get lower. In 30 mph uppers, I'll exit 1500 feet or so upwind, allowing a little time for climbout and exit.

One mile is a little over 5000 feet. How long is the runway at your DZ? Ours is 2500 feet, 1/2 mile, giving me a handy "yardstick' to visualize how far is far enough.

You got the basic idea, though, get out upwind ot the target. I've been really hosed by people who didn't seem to grasp that idea.

[azureriders 0]

Quote

How long is the runway at your DZ?

It varies. Just all depends on where the gypsy DZ is dropping that day

[billvon 2,435]

Basically start with feet per second; that's the most useful unit.

Get winds at opening altitude (in feet per second) and winds at exit altitude (in FPS.) Average the two. Multiply by seconds of freefall. That's how far you will drift. Subtract about 1000 feet for forward throw and you have your exit vs opening point. (This assumes jump run into the wind, wind same direction.)

Example:

Uppers north at 40kts, wind at 3000 feet 10kts. Average is 25kts. In feet per second that's 42 feet per second. For a 50 second freefall that's 2100 feet. With throw taken into account that's about 1100 feet.

[mark 104]

Here's a quick method that gets a similar answer:

Average the wind speed to the nearest 10 knots.
Go upwind a quarter-mile for every 10 knots.
(Subtract a quarter-mile for forward throw.)

Because of the limitations of winds-aloft forecasts, I don't think it's worth making a more accurate estimate than that.

The winds aloft forecasts are derived from radar tracks of weather balloons released twice in each 24-hour period at selected locations. The nearest one to any particular dropzone may be 50 to 100 miles away, and the winds do not change magically at 8, noon, and 4. The forecast is most accurate in between fronts, least accurate when there is a frontal passage occuring between the forecast station and the dz, and least useful when the winds aloft are opposite the surface winds.

Mark

[JohnMitchell 14]

The winds aloft are a lot more accurate now due to ACARS readouts from the planes in flight to the National Weather Service. It's like having hundreds of weather balloons aloft constantly. The forecast, or observation would be more accurate, is updated every two hours. This is relatively recent stuff, and very accurate.

I agree about the old forecasts. It would be frustrating to have the Otter pilot insist on jumprun in one direction when any one could see the clouds were blowing differently than forecasted. When in doubt, trust your eyes.

[skysurfcam 0]

Average the wind speed (in knots) and direction (in degrees) for the sectors you need.
ie: Freefall, canopy ride. You may need to build two freefall sectors if the winds change radically at a particular height.

Estimate the time in freefall and under canopy.

Estimate the distance for each of your sectors/vectors using the following:

"Half the seconds times the knots, equals the yards (or meters)"

Calculate backwards from your landing point to get your optimal opening point, and backwards from there t get your exit point.

It's a little rough and ready, but it's served me well on some pressure demo's into tight spots, including one time we were planning on using drifters, but couldn't get clearance to throw them. ATC gave us the winds, and we were able to use the formula, the pilots map and wizz wheel to plot an exit point.

These days, I also use it to calculate exit point on the way to height by checking winds on the way to height on the GPS (thankyou America/NASA!) and doing the artimetic in my head.

Give it a whirl...

Cheers,

Craig

Brother Wayward's rule of the day...
"Never ever ever go skydiving without going parachuting immediately afterwards."
100% PURE ADRENALENS

[skysurfcam 0]

Because aviation the world over still uses the nautical imperial system, cos aviation distances make complete sense that way.

Not ever country is still using imperial on the ground though. Many of us can think in either imperial, metric, or a combination of both.

Having grown up using both imperial then metric, I'll take metric on the ground any day. It makes things so easy to be able to count on my fingers...

Cheers,

Craig.

Brother Wayward's rule of the day...
"Never ever ever go skydiving without going parachuting immediately afterwards."
100% PURE ADRENALENS

[LouDiamond 1]

Quote

It's a little rough and ready, but it's served me well on some pressure demo's into tight spots,

Hey Craig, take a look at the PPT presentation I linked to in my post above. I think you will find that it works exceptionaly well when you have tight spots to get into and the formula accounts for incompatibale winds and or doglegs,etc. It's what I use "at work"
However, if your using a Garmin GPS with the jumpmaster feature/software on it, it uses the same formula only it does all the number crunching, you just input the numbers.Very handy tool.

"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

[skysurfcam 0]

Scott,


Jeeze, it's half 12 in the am here. I got started, but that's way too complex for me, both at this time of night, and if I get stuck with the first tandem of the day, or if I cant throw drifters on a tight demo. I almost bought an e-trex vistafor that, but I've shucked out the bucks for a foretrex 201 instead to play with on the wingsuits

Given the following winds from ground patry/GPS/Area forecast, I'd get this with "1/2 the sec X the knots = the distance" I'm not including throw foward, cos I'm assuming the 182 I'll be stuck in this weekend

SFC 030/10, 1000 055/15, 2000 060/15, 4000 080/20, 6000 090/15, 8000 110/25, 10000 105/30, 12000 115/35

So the tandem will be out at 12K and open at 4. Call it 45 seconds of freefall. Rough average 25 knots

So, 45 x 0.5 x 25 = 562.5 mtrs freefall drift at (say) 100.

4 mins under canopy = 240 sec, wind ave say 070/15, 240/2 * 15 = 1800 mtrs 070.

So adjust for magnetic, go 1800 mtrs at 070, then 550mtrs at 100, and get out.

Lemme know how that stack up, I'd be curious to see how well it works against your system.

The formula was actually taught to me by an old time paratroop JM. It assumes 0 canopy foward speed.

(I sould point out that my maths may be shakey due to the time of night/ My BAC.)

Cheers,

Craig.

Brother Wayward's rule of the day...
"Never ever ever go skydiving without going parachuting immediately afterwards."
100% PURE ADRENALENS

[matthewcline 0]

loudiamonds info is the way to go.

I use the same HARP/CARP methods and I too put canopies in very tight spots (although not usually under fire like lou does)

I have used it for over 300 "blind" spots and I haven't missed the landing ao yet. (knocking the hell out of my real wood desk!).

I even use it when I can use WDI's. It never hurts to stay practiced at it.

An Instructors first concern is student safety.
So, start being safe, first!!!

[Eule 0]

Quote

The winds aloft are a lot more accurate now due to ACARS readouts from the planes in flight to the
National Weather Service.

Sometimes you can even do better than that. NWS operates several "wind profilers" which are special
radars that sit on the ground and look up. The Midwest US (IA-NE-MO-KS-OK-TX) and California have
pretty good coverage, but there are lots of them around. Check it out:
http://www.profiler.noaa.gov/npn/profiler.jsp

Note that if you take all the default options, the newest observations are on the LEFT SIDE of the graph.
I typically switch the defaults to "Left to Right", "1000x750", and "PNG (Best)". Also, the wind barbs
are in 5 m/s increments and the height is kilometers MSL. If you click on "Advanced Display Options",
you can get the wind in knots, the height in feet AGL, and set the max height to something reasonable
like 15,000 feet. I've attached a sample plot from a nearby profiler.

In Dallas, I've jumped and watched loads coming down after looking at the profiler data, and the profiler
data usually matches what's happening pretty well. Disclaimer: I've only got about 40 jumps, and about
5 or 6 in Dallas. When the weather is relatively calm, any nearby site is probably OK. As has been
mentioned, if a front is coming through, you have to pay more attention, like maybe preferring sites
west of you.

Eule

PLF does not stand for Please Land on Face.