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Spot Calculator (HARP Program)

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One of our Instructors wrote a Spot calculator program, we tested it last season and it was spot on (pun intended)

The calculator if free to use at the link below feel free to link it to your websites or mail to your friends.

www.skydivemidwest.com/spot_calculator/

Big thanks to Bas Kuis for creating the program, please let me know if you have any issues with using it.

KG

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I plugged in some numbers for direction and speed and it returned info that was waaaaay off what it should have been.

Plug in some simple numbers that you know should generate a specific result and see.

I'm trying to figure out what it is that putting me out on a downwind and sometimes crosswind jump run.

I may be wrong here....I'm just using simple numbers.

12000 - Direction 270, Speed 15
9000 - Direction 90, Speed 15
6000 - Direction 270, Speed 15
3000 - Direction 90, Speed 15
ground - Direction 270, Speed 15

Results:
The ideal spot is 0.023 miles at heading 92 degrees

The Green (go) light should be switched on -0.877 miles at heading 92 degrees
My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

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I plugged in some numbers for direction and speed and it returned info that was waaaaay off what it should have been.

Plug in some simple numbers that you know should generate a specific result and see.

I'm trying to figure out what it is that putting me out on a downwind and sometimes crosswind jump run.

I may be wrong here....I'm just using simple numbers.

12000 - Direction 270, Speed 15
9000 - Direction 90, Speed 15
6000 - Direction 270, Speed 15
3000 - Direction 90, Speed 15
ground - Direction 270, Speed 15

Results:
The ideal spot is 0.023 miles at heading 92 degrees

The Green (go) light should be switched on -0.877 miles at heading 92 degrees




This ties into what I was saying in the other thread about using an excel calculator type sheet to do wind calcs. What you have in your example is known as erroneous winds. When you have erroneous winds and or doglegs, the excel calculator sheet method will not give you a correct answer.

Definition of erroneous winds: Erroneous winds are defined as one ninety (90) degree or greater change in a single altitude. (Erroneous winds will be disregarded for wind drift averaging but the altitude will be used in the DKAV formula)


Definition of a dogleg:Dog Legs are wind phenomena which can occur in HALO and HAHO operations.
A dog leg is a situation when the wind direction changes ninety (90) degrees or more for any two consecutive altitudes.
Two or more ninety (90) degree changes will require a separate computation and plot for the recorded wind data at a given altitude. With a Dog Leg computation, a separate plot is required for each computation.


EDIT: it is also worth noting that using the excel calculator method for computing the spot also assumes that your jump run will always be into the wind.
"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

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I'll disagree in principle with LouDiamond's saying that with big changes in direction, the spreadsheet method will result in errors. (B.S.!) But in PRACTICE, I'll agree. (Good point!)

It isn't that the math is fundamentally and magically wrong when there's a shift of over 90 degrees. But the solution can become very, very sensitive to the assumptions made. And many assumptions have to be made when designing the software.

At small distances, a predicted direction may not make sense. If the spot is calculated to be 10 feet from directly overhead (or something like"0.023 miles" = 120 ft), it isn't that useful to have the computer spit out a jump run direction which could be north, south, east, or west.

The jumper is exposed to the wind at different altitudes for different times, depending on rate of descent in freefall and under canopy. Does the calculation include extra sub-terminal time, or for simplicity just assume terminal speed? Belly terminal, right?

And for the longer period when the jumper is under canopy, at some assumed descent rate, does one assume the jumper is open at 3000', 2700', 2500', or what? That becomes critical in this example with wildly varying winds at different altitudes.

Aren't wind forecasts feet MSL? So does the software assume the DZ is at sea level or is its MSL altitude taken into account?

The software likely assumes the perfectly spotted jumper should drift to the target as he touches down. Who knows, someone else might decide to write software so that a jumper would drift above the target when they reach 1000', so there's still time to set up a proper circuit at a busy DZ.

One also needs to know if the calculation simply uses blocks of air at a constant speed, or averages between the reported heights. E.g., is the 3000' value assumed to take place everywhere between 3000' and 5999', or 1500' to 4499', or only at 3000' -- with it linearly averaging up and down to the ground and 6000' values.

To get ridiculously fancy, one could vary the wind speed from the ground up using an exponential curve to better simulate actual wind shear profiles in a viscous fluid, for which one must also take into account the height over ground that the "ground" reading was taken, and the degree of turbulent mixing of the air in that day's weather conditions.

The calculator in this case doesn't seem to deal with minor changes in forward throws for the three different aircraft types at the DZ, but presumably does take into account different speeds and number of jumpers, as the spots end up the same but the green light location differs.

The calculator also assumes the 182 drop height is the same as the King Air and Twin Otter, as the spot results are the same. (i.e., the 12000' winds influenced the jumpers for exactly the same length of time.)

In this particular example with crazy winds from 090 and 270, I'd make a judgment call (other than staying on the ground!) about how far up the ground winds extend compared to the 3000' MSL winds. That's the critical thing here, the region under canopy where most of the drift will occur.

So there are many assumptions that go into calculating the spot, each of which might result in answers different than 0.023 miles at 92 degrees.

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I'll disagree in principle with LouDiamond's saying that with big changes in direction, the spreadsheet method will result in errors. (B.S.!) But in PRACTICE, I'll agree. (Good point!)



If you use the excel calculator, which simply performs the arithmetic according to the formula that is usually done by hand, with wind data that is incompatible, you will get a wrong answer period. UNLESS, you realize that the winds you are entering into the calculator are either erroneous and or contain a dogleg and figure for them accordingly. It's simple trash in, trash out. The user has to be able to identify when the winds are not suitable for use in the calculator and even when doing it by hand and make the proper adjustments in order to get a correct solution. On the calculator commonly used in the military community there are several notes on the sheet to remind the jumpmaster of several important considerations.

** Note: If using wind directions from 315 degrees to 045 degrees to calculate average wind direction, erroneous averages may result. To compensate, the Jumpmaster adds 360 degrees to directions of 001 to 045 degrees.

** Note: Don't forget to convert direction of winds and drift from Magnetic or True to Grid.

** Note: Don't forget to figure forward throw of the A/C in the opposite direction of flight.


The only other way you could possibly get away with being able to input wind data that contained erroneous and or dogleg winds in it is if the software was written so that it could recognize that wind data being input contained incompatible winds. It would then have to automatically execute another calculation and merge that data with the first calculation and or make the needed numerical changes as explained in the first note above BEFORE spitting out an answer. To the best of my knowledge, an excel sheet that is capable of doing that does not exist.

A complete and in depth explanation on this can be found in the power point presentation(post #30) and in the word docs(post #28) that I posted in an old thread HERE and will address many of the other questions you posed in your post.
"It's just skydiving..additional drama is not required"
Some people dream about flying, I live my dream
SKYMONKEY PUBLISHING

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I plugged in some numbers for direction and speed and it returned info that was waaaaay off what it should have been.

Plug in some simple numbers that you know should generate a specific result and see.

I'm trying to figure out what it is that putting me out on a downwind and sometimes crosswind jump run.

I may be wrong here....I'm just using simple numbers.

12000 - Direction 270, Speed 15
9000 - Direction 90, Speed 15
6000 - Direction 270, Speed 15
3000 - Direction 90, Speed 15
ground - Direction 270, Speed 15

Results:
The ideal spot is 0.023 miles at heading 92 degrees

The Green (go) light should be switched on -0.877 miles at heading 92 degrees



Alright ... I figured I'd give some insight into the spot calculator ... the way it works ... the psychological part of spotting etc.

First of all ... the winds you entered don't make much sense as far as a realistic scenario ... and hence it is not very interesting do discuss it in detail ... but since you use this result as evidence that the calculator is flawed I will take some time to explain the results and why they are unsymmetrical.

This is the principle the calculator is based upon.

Adding up 'air-layer' displacements vectors described below:
*(13500-10500) using 12000ft data and 15sec affecting displacement
*(10500-7500) using 9000ft data and 15sec affecting displacement
*(7500-4500) using 6000ft data and 15sec affecting displacement
*(4500-1500) using 3000ft data and 110sec affecting displacement (110sec because part of this descent will be under canopy)
*(1500-00) using ground wind data an 90sec affecting displacement (90sec is a good average for the time period spend under parachute under 1500ft)

This data will determine the jumprun dead center. Meaning the middle jumper on the load should get out at this displacement.

We are not done yet....

Next we have to take into account some other factors:
* The delay from green light to actual exit ... and its associated displacement. This depends on what aircraft you use ... faster aircraft have a greater displacement because they travel further in a shorter amount of time.
For a king-air this is approximately 0.15 miles.
* The airplane forward speed drift after exiting the aircraft. The kinetic energy your body has opposed to air layer you transition to will make you travel an additional 0.15 miles after exit - in the case of a king-air.
* The length of a complete jump-run. This is different for many aircraft ... and load sizes ... but a full load in the king-air is between 1 mile and 1.4 miles long. Smaller loads are obviously shorter.

So lets say we have no wind ... meaning no additional displacement aside from the three major factors listed above ... a spot would look something like this

Greenlightdistance = 0 - greentodoordelay - freefalldrift - (lenghtofjumprun / 2)

A spot with no wind in the King Air therefore should be about 0.9 Miles prior ... and understand that the first jumper under parachute will in fact be under paracute 0.6 miles prior to the center of the airfield and the last jumper will be under canopy 0.6 miles after.

So aside from obvious variations on jump-run length - and other factors that are not taken into account ... this model fairly accurate.

Over the last summer we at Skydive Midwest have done our best to adjust variables to make the spot calculator more accurate - and have enjoyed very, very few off landings since.

Also ... keep in mind that the human mind tends to be drawn to spotting short on windy days ... and long on no-wind days.

Also ... offset jump-runs maybe something an experienced pilot can perform accurately ... but with a proper heading the gains are minimal. Therefore the calculator doesn't include an offset. If anybody would be interested in having an offset included let me know, I like a challenge. ;-)

_____________

In conclusion - people that want to can use this tool to help determine the first spot of the day - hopefully eliminating the dummy loads and the clash of egos over who knows best. Also I would love to make this tool better and more accurate so I invite suggestions and feedback.

Mainly we are looking for the following aircraft data:

jump-run speed
your delay from light till actual exit (use a stopwatch etc ... lets be scientific here :-))
the average length of jump-run (in miles - this has to be very accurate )

Alright everybody, have a great week!
...Its late ... I'm gonna hit the hay. ;)
Have fun!

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I plugged in some numbers for direction and speed and it returned info that was waaaaay off what it should have been.

Plug in some simple numbers that you know should generate a specific result and see.

I'm trying to figure out what it is that putting me out on a downwind and sometimes crosswind jump run.

I may be wrong here....I'm just using simple numbers.

12000 - Direction 270, Speed 15
9000 - Direction 90, Speed 15
6000 - Direction 270, Speed 15
3000 - Direction 90, Speed 15
ground - Direction 270, Speed 15

Results:
The ideal spot is 0.023 miles at heading 92 degrees

The Green (go) light should be switched on -0.877 miles at heading 92 degrees



12000 - Direction Speed 15
9000 - Direction Speed 15
6000 - Direction Speed 15
3000 - Direction Speed 15
ground - Direction Speed 15

The "center" of the spot is 0.023 miles at heading 92 degrees

Caution: Because of the difference in direction in upper winds and total displacement an inverted version is deplayed.

Inverted version: The Green (go) light should be switched on -0.9 miles at heading 270 degrees

Regular version: The Green (go) light should be switched on -0.9 miles at heading 90 degrees

-----------------------------------------

I made some changes to the spot calculator ... now when the angle of the displacement and the upper winds differ more than 90 degrees ... the sport will be inverted ... shortening the jumprun ... this makes the most sense

_____________________________________

The new and improved

http://www.skydivemidwest.com/spot_calculator/

More feedback is greatly appriciated - I want this thing to work well
Have fun!

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First, let me say that you are doing a great service to all of us by working on this....thank you.

For my edumacation, what do you mean by "Inverted" and "Inverted version"?

And, why is there a need to display both regular and inverted versions?

I'm still seeing displays telling us to do downwind jump runs which, considering ground speed, should have very different numbers for exit point.

As for the example being unrealistic...maybe so. But we need to have confidence that the calculator works for ALL conditions else we are wondering if the input we give is being considered "realistic" or not.
My reality and yours are quite different.
I think we're all Bozos on this bus.
Falcon5232, SCS8170, SCSA353, POPS9398, DS239

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By an inverted version I mean that the direction of jump-run is opposite to the sum of all wind vector displacements.

I believe that spotting according to the total displacement is the best way to spot.

However you raised the obvious question that the total displacement vector may be opposite to the upper winds ... making the jump-run longer ... Hence I added the inverted version of the spot ... the purpose of this is to decrease the total length of jump-run in an attempt to make the total spot more compact.

You will find that the spot ofter isn't directly into the upper wind ... nor the wind on the ground ... instead the spot will always be in line with the sum of all displacement vectors.

If you would like the calculator to give jump-run directly into the upper wind ... or ground wind ... jump-run offsets will have to be calculated. It is my understanding that not many pilots can accurately fly a jump-run with an offset. (The only benefit would be that jump-run could then be flown directly into the upper wind ... and therefore would most likely be shorter)

However ... before we should worry about this I would like to make sure that the quality of the data the model currently uses is good. I estimate the accuracy of the current model to be approx 20% ... You would only save an additional 10% or so from flying accurate offset jump-runs.

So when the model is perfected to be accurate to less than 10% ... I guess it would be really cool to improve it further ... and include offset jump-run recommendations.

I know this calculator isn't perfect ... but it has proven to be a great tool to help determine the first spot of the day. From then on ... the jump-masters can adjust it depending on how the spot came out.

Again, feedback is greatly appreciated.

Stay safe & have fun!
Have fun!

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