Seperation - knots to seconds

[eightate8at8 0]

Is anyone able to post a small table or some sorts with some general guidelines?

__knots = ~__seconds etc..

[billvon 3,119]

Some easy tricks:

For most airplanes flying into the wind (Otters etc) - if the upper winds are low leave at least 7 seconds between groups. If they are above about 20kts at altitude then divide them by 3 and leave that number of seconds. (i.e. 42 kts = 14 seconds.) This works 95% of the time. The one time it does not is if winds at opening altitude are OPPOSITE of winds at altitude; then you have to leave even more time.

If you want to do the math it's:

(Ground speed of the airplane + windspeed at opening altitude) * seconds between groups = distance.

An example:

Ground speed of plane is 60kts per the GPS. Windspeed at opening altitude is 10kts. So ground speed is 100 feet per second, opening winds are 17 feet per second. Waiting five seconds would give you (117*5)= 585 feet; probably not enough for most groups. Waiting nine seconds would give you (117*9)= 1053 feet, probably enough.

Using this formula you could come up with as detailed a chart as you like.

[eightate8at8 0]

Awesome info, thanks man

[strop45 0]

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If you want to do the math it's:

(Ground speed of the airplane + windspeed at opening altitude) * seconds between groups = distance.

So is this formula only when winds at opening altitude are in opposite direction to winds at exit??

If the wind is the same at opening as exit (same direction and speed), then seperation is same regardless of actual wind speed?

The difference between stupidity and genius is that genius has its limits." -- Albert Einstein

[lippy 918]

When there's no (or negligible) difference between exit and opening winds, and jumprun is heading into the wind, then separation time should be increased as winds increase (as Bill said in his initial post).

The higher the winds, the less ground the plane is going to cover and therefore you need to wait more time to ensure that you're not getting out 'over top' of the group that exited before you.

Winds affect a plane on jumprun a lot more than they'll affect jumpers in FF.

I got nuthin

[SethInMI 174]

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When there's no (or negligible) difference between exit and opening winds, and jumprun is heading into the wind, then separation time should be increased as winds increase (as Bill said in his initial post)..

No, Bill's formula shows that if there is no difference between opening and exit winds, then the winds cancel each other out, and seperation time is independent of wind speed.

Bill's formula:
(Ground speed of the airplane + windspeed at opening altitude) * seconds between groups = distance.

Groudspeed of airplane is airspeed of airplane - wind at exit altitude (flying into the wind), so we can make Bill's formula:

(airspeed of airplane - windspeed at exit altitude + windspeed at opening altitude) * seconds between groups = distance.

So if exit and opening windspeeds are the same, they cancel out and then Bills formula becomes:

airspeed of the airplane * seconds between groups = distance.

So if the winds are the same they don't matter at all.

What most people forget is that after they open, the canopy is carried out of the way by the wind at opening altitude, so the stronger the wind is, the less separation time is required.

It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

[JohnMitchell 16]

I need a formula to know how many degrees to subtract from 45 for each knot of winds aloft.


>>>

[SethInMI 174]

Since you jump at 47 degrees latitude, I would subtract 2 degrees for everything. Since you are half way between the pole and the equator, the Coriolis force cancels out the winds aloft and you can take any delay you want.

It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

[billvon 3,119]

>So is this formula only when winds at opening altitude are in opposite direction
>to winds at exit?

No, that assumes that the winds are the SAME direction from exit to opening. This is the case 95% of the time. The only exceptions I've seen have been :

San Diego during a building El Nino, where you can have strong easterlies at altitude while the surface winds are out of the west and

San Francisco near the coast on windy days.

If the winds are from opposite directions then the formula is (groundspeed - windspeed at opening) * seconds. If the opening winds are at 90 degrees to uppers then the formula is groundspeed * seconds.

[JohnDeere 0]

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I need a formula to know how many degrees to subtract from 45 for each knot of winds aloft.


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Damnit John! It's 52.5 deg.

Nothing opens like a Deere!

You ignorant fool! Checks are for workers!

[tombuch 0]

I put together a piece on The Ranch S&TA site a bunch of years ago that covers the 45 degree rule and why to ignore that crazy concept, and then offers a couple of tables that show how the groundspeed of the aircraft can determine exit separation. You can find the story listed as "Article 15, Waiting Between Groups" at http://theblueskyranch.com/STA.php.

The last chart assumes no difference in direction between winds, and is based on exit winds and aircraft travel, rather than using winds at opening altitude. I find that approach is easier to manage, and removes some of the other variables. The last table gives some times for various wind speeds, and breaks separation times out for small, medium, and large groups. I wouldn't use the small numbers in real life...they were listed to make our pilots happy but are too quick for most jumpers. I'd wait a minimum of five seconds in almost all cases. You can easily use the math in other posts to produce a similar chart for your specific aircraft.

With experience you will be able to look out the door and determine ground travel and then know how much time to allow, but for many people a real number is needed to avoid conflict.

Tom Buchanan
Instructor Emeritus
Comm Pilot MSEL,G
Author: JUMP! Skydiving Made Fun and Easy

[lippy 918]

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When there's no (or negligible) difference between exit and opening winds, and jumprun is heading into the wind, then separation time should be increased as winds increase (as Bill said in his initial post)..

No, Bill's formula shows that if there is no difference between opening and exit winds, then the winds cancel each other out, and seperation time is independent of wind speed.

Bill's formula:
(Ground speed of the airplane + windspeed at opening altitude) * seconds between groups = distance.

Groudspeed of airplane is airspeed of airplane - wind at exit altitude (flying into the wind), so we can make Bill's formula:

(airspeed of airplane - windspeed at exit altitude + windspeed at opening altitude) * seconds between groups = distance.

So if exit and opening windspeeds are the same, they cancel out and then Bills formula becomes:

airspeed of the airplane * seconds between groups = distance.

So if the winds are the same they don't matter at all.

What most people forget is that after they open, the canopy is carried out of the way by the wind at opening altitude, so the stronger the wind is, the less separation time is required.

I stand corrected and really need to pay more attention before replying, and rethink exit separation

I got nuthin

[azureriders 0]

If you are indeed making a chart then the converstion factors that I am about to list should be easy to find on the internet and in conjunction with Bill's formula you should be set. I however tend to do this in my head and therefore need some easy to remember numbers, so:

1kt = 1.68667 ft/sec, I remember ~1.75 or rather ~1-3/4 ft/sec.
therefore an
80kt ground speed = 135 ft/sec, or ~140 ft/sec if done in my head.
the difference is fairly negligable.

I have found a pilot or two with his GPS set to MPH, so
1mph = 1.4667 ft/sec, I remember ~1-1/2 ft/sec.
again the difference is negligable.

Another one that I use a lot when calculating a spot:
1kt = 101.2 ft/min, so I obviously remember ~100 ft/min
so if have an average of a 15kt wind during free fall,
my FF drift will be ~1500 ft/min
or in my case, 1/2 a runway length during a 60 sec skydive

I am obviously one who likes numbers and the math behind what we do. However I think it is important to get a 'feel' for what is going on around you. In other words, no matter if you know the math and/or have a chart, you should know when to leave more time than normal in between groups. If you have learned that ~8 sec works for you in most cases, then you should also know that a slower plane, higher head winds, following larger groups, following groups that will be all over the sky, all require more time than you have been giving. Tom mentioned learning to gauge the ground speed of the plane with your eyes, this is very important as it will give you a sense of higher head winds and/or a slower plane, even if you did not already have that information.

How do you think all those using the 45d rule have not been killing us. Well, if they know when to leave more, and have built an internal clock (~8 sec probably) to tell them when they 'think' the group behind them is at that magical angle, then they should be able to make it work. Hopefully you know I am not trying to advocate the 45d rule, just that knowing when to leave more than 'normal' is a valuable tool.