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# Exit separation calculator

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sorry, I suck at using computers...

Methane Freefly - got stink?

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Unfortunately, the 45 degree rule is out there and needs to be addressed. It DOES work if there is no wind at all, and that needs to be understood.

Not so.

As Prof Kallend has already pointed out, as long as the airplane TAS is less than a skydiver's descent rate, the 45-degree angle cannot be reached.

It takes a jumper about a minute to travel the 2 vertical miles from altitude to opening. During that same minute, an 80-knot jumprun will take the jump plane about 1-1/2 miles horizontally. Draw a picture or do the math: the angle between the airplane and the jumper at pull time is less than 45 degrees.

If you were serious about using the 45-degree angle method, you would allow as little time as possible between groups; it is only immediately after exit that a jumper's vertical speed is less than the aircraft horizontal speed.

I'm so disappointed.

Mark

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Unfortunately, the 45 degree rule is out there and needs to be addressed. It DOES work if there is no wind at all, and that needs to be understood.

Not so.

As Prof Kallend has already pointed out, as long as the airplane TAS is less than a skydiver's descent rate, the 45-degree angle cannot be reached.

It takes a jumper about a minute to travel the 2 vertical miles from altitude to opening. During that same minute, an 80-knot jumprun will take the jump plane about 1-1/2 miles horizontally. Draw a picture or do the math: the angle between the airplane and the jumper at pull time is less than 45 degrees.

If you were serious about using the 45-degree angle method, you would allow as little time as possible between groups; it is only immediately after exit that a jumper's vertical speed is less than the aircraft horizontal speed.

I'm so disappointed.

Mark

I am looking forward to seeing Billvon's videos of exit angles measured with a protractor.
...

The only sure way to survive a canopy collision is not to have one.

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Unfortunately, the 45 degree rule is out there and needs to be addressed. It DOES work if ...

No it doesn't. The "45 degree rule" is patent horseshit and should never be treated as anything but.

If your watch (analog, with hands) breaks, it tells the exact time twice a day. If you then say that it's 100% accurate under certain conditions, there is a grain of truth to the contention.

To use a stopped watch to tell time because it's occasionally right is as useful as using exit angle to determine exit spacing.

To give any lip service to the "45 degree rule" at all is unconscionable. If you think it has any merit whatsoever, you really don't understand the subject.

Blue skies,

Winsor

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I've attached my version of the separation calculator spreadsheet.

This one is quite simple. You will see that it doesn't take wind direction or speed into consideration. But, I think that is okay for a general calculation to give a ball park look at exit delay to achieve a desired amount of separation.

If everyone on the airplane fell at the same rate (say 120 mph) then I don't think wind speed or direction would have much bearing on the results. Everyone would be falling through the same mass and their 'drift' due to the wind would be the same relative to each other. Separation distance at opening point relative to exit point would be about the same for each group of jumpers. You just need to know the distance of separation that you want in advance and then determine/calculate the number of seconds of delay needed to give you the desired distance.

It seems to me that if you have someone jumping head down doing 200 mph, and the next group of belly flyers doing 120, then wind direction and speed will play a bigger role in the difference in drift between a fast falling group and a slow falling group. I think the impact is greater if the jumprun is on the windline.

It seems that the impact of wind direction and speed would be diminished on a cross wind jump run as drift along the line of flight would be attributable to the 'throw' of the airplane. This should not be too different for different styles of jumping. The amount of 'drift' attributable to the direction and speed of the wind would be perpendicular to the line of flight of the jump plane. So, the amount of separation would be roughly the same between head down or belly flyers on a cross wind jump run.

In fact, as I think about it now, on a cross wind jumprun, the stronger the wind is, the greater the amount of separation that would be obtained because the belly flyers would be 'pushed' by the wind for a longer period of time than the head down jumpers.

However, it is too late for me to think about the wind blowing in two different directions at different altitudes.

Let me know if there is any merit to these ideas.

-mh.

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sorry, I suck at using computers...

A suggestion. Don't output times like 7.44047619 seconds. It makes the answer look stupid. You'd need an atomic clock on board to time it. Round it off to the nearest second above.
...

The only sure way to survive a canopy collision is not to have one.

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The Elsinore website has a simple separation rule on its page of procedures. For reported uppers of 0-10 knots, they use 5 - 7 sec between groups. For uppers of 15 knots and up, they recommend using a simple knots/2=seconds formula, with a few examples, like 20 knot uppers/2=10 sec. of separation. You do need to find out what the uppers are (try asking somebody). It's definitely simple, sounds valid, and you don't need a Ph.D. to figure it out. It also probably helps that a lot of people count and wait before even climbing out and doing their exit count.

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I have put together an Excel spreadsheet to compare the results of considering groundspeed (such as you'd get from a GPS readout) alone or adding the headwind component at opening altitude in the calculation.

The delay using both groundspeed and headwind at opening altitude is that which will give you the desired separation between groups at opening altitude. The final column, "Separation at opening altitude, groundspeed calc.," is the actual separation between groups that results if treating the headwind at opening altitude as zero.

I have picked 1,000 feet as the fixed distance between group centers as a basis. In the time between breakoff and pitching, it is quite possible to track 500 feet from the center of the formation, so people from formations 1,000 feet apart would just reach each other by pull time. Thus, I consider this to be a bare minimum between groups.

The values in the first three columns can be changed; feel free to plug in different numbers to see what is the result.

Blue skies,

Winsor

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Here's a revised version of the spreadsheet for suggested separation based on group size.
...

The only sure way to survive a canopy collision is not to have one.

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You guys kick butt. All this math is great brain food, and great learning, all the while addressing a most valid topic.

Rox.

________________________________________

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Here's a revised version of the spreadsheet for suggested separation based on group size.

Of course once you have used this nifty little exit seperation calculator you then need to work out a few others things. Like,

1. How far does each skydiver need to track to get the required separation.
2. Knowing the answer to 1. helps you decide the break off altitude. After all you need a certain amount of time to track a certain distance.
3. When the groups get larger the suggested separation may involve someone pulling in place without tracking (if they don't have a video man)

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Quote

Here's a revised version of the spreadsheet for suggested separation based on group size.

Of course once you have used this nifty little exit seperation calculator you then need to work out a few others things. Like,

1. How far does each skydiver need to track to get the required separation.
2. Knowing the answer to 1. helps you decide the break off altitude. After all you need a certain amount of time to track a certain distance.
3. When the groups get larger the suggested separation may involve someone pulling in place without tracking (if they don't have a video man)

Yes, yes and yes (except I padded the numbers so the third "yes" is more of a "maybe". And most of the jumps I've been on of 16 or more seem to have had a staged breakoff plan).
...

The only sure way to survive a canopy collision is not to have one.

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why? It doesn't surprise me that a lot of us out there - myself included - still don't fully understand not only HOW to successfully calculate exit separation (i'm still a watch the ground/count sort of person) but don't seem to care about the significance of doing so properly either.
It's still one of the scariest parts of the jump for me (thinking that the person/group leaving after me won't have left enough separation between my exit and theirs). Does anyone else on a solo jumps sometimes look up to see the next person out to see how long they have left for separataion, or is that just me?

"Skydiving is a door"
Happythoughts

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