Why the 45 degree method does not work (long)

[billvon 2,380]

Summary - the 45 degree method does not work. If you try to use it, and you really can tell where 45 degrees is, your separation will be suicidally short.

I've heard the 45 degree angle thing for a while now. For those of you who have never heard of it, basically you look out the door and wait until the group ahead of you makes a 45 degree angle with the door, then you exit. There are many problems with this:

1. Groups with more "throw" (i.e. headdowners) get to that angle either faster or instantaneously, and those are the people you have to leave _more_ time after.

2. You leave less time with lower airspeed aircraft, which is the opposite of what you want.

3. The separation you get has nothing to do with the difference between aircraft speed and opening-altitude windspeed, which is the important thing.

This can all be shown mathematically, but people have held on stubbornly to the 45 degree angle thing, I think because it's easy to do and it makes some sort of intuitive sense. Unfortunately, not many of us are born with good intuition about physics in moving frames of reference, and this is one time that our intuition fails us.

To prove this I took some pictures. I had a shop bend up a bracket that would hold two cameras at exactly 45 degrees and put stiffeners on it so the wind wouldn't mess with the angle. Then I mounted a still and video camera to the bracket and mounted that on the end of a boom made of 1" x 4" oak (which is pretty stiff.) I stuck that out the door of our otter and stood on the inside part of the boom to anchor it. The camera ends up in the front bottom corner of the door shooting down at a 45 degree angle; when the group passes the center of the frame it's at a 45 degree angle. The still camera has its standard (35mm equiv) lens and the video camera is a PC-9 with a .42 lens.

Conditions:

Winds aloft 30kts out of the west; winds at 3000 feet 12kts out of the west. Aircraft airspeed 85kts. Six groups:
-7 way belly
-3 way belly w/camera
-3 way head down
-2 way belly
-2 way sit pulling a little high
-solo

Based on those numbers, if I were planning the exit separation, I'd say a minimum of 8 seconds between groups, perhaps a little more after the 7-way.

I started the cameras and levered them out the door on the red light. The video camera runs continuously, the still camera fires about twice a second. It does not have reliable timing since a "complicated" picture takes longer to store than a simple one, so all timing came from reviewing the videotape and estimating with a digital clock (I don't have a frame counter on my video player.)

The first group has a stable launch and "sails" backwards a bit. They drop in the frame and cross the center of the frame after 1 second. The second group is completely unstable and crosses the 45 degree line .5 seconds out the door. The third group has a good head-down launch and _never_ crosses the 45 degree line; they start out below the camera and stay there. If the camera had a wider angle lens it might have picked them up in the door, in which case the timing would be ~.1 seconds.

Group 4 is .4 seconds, group 5 is .3 seconds. Group 6 (solo belly) really sails and takes almost a second to cross the center line.

On this load, people counted to separate themselves. Exit separations were:

1-2 16sec
2-3 11sec
3-4 10sec
4-5 12sec
5-6 8sec

If jumpers had relied on the 45 degree method separations would have been:

1-2 1sec
2-3 .5sec
3-4 .1sec
4-5 .4sec
5-6 .3sec

If people had really used those separations, only luck would have allowed people to avoid collisions on opening.

Attached are some still pictures of each group. Again, they are taken approximately .5 seconds apart, but the still camera is not super accurate when it comes to time between frames. I have the video if anyone wants to see that, too.

[stuffit 0]

This is a good observation/study but I dont think that the 45 degree angle (which i have heard many instructors tell students to use and no, I will not pm you any names) is meant to be taken exactly as it is said. I think it is meant more as a way to get the students used to looking out of the plane at the group in front of them and at the ground rather than counting to some number of seconds and jumping out without looking.

[AggieDave 6]

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I think it is meant more as a way to get the students used to looking out of the plane at the group in front of them and at the ground rather than counting to some number of seconds and jumping out without looking.

I've heard many instructors use it that way..."today we're taking X seconds between groups due to the uppers doing X, also I want you to watch for the group to fall away from the plane before you climb out..."

--"When I die, may I be surrounded by scattered chrome and burning gasoline."

[billvon 2,380]

>I think it is meant more as a way to get the students used to looking
> out of the plane at the group in front of them and at the ground
> rather than counting to some number of seconds and jumping out
> without looking.

That's fine, but why not tell people "check the spot, count to eight then go?" I would worry if I told someone to use a method that, if they did exactly what I told them to do, could kill them, and is only safe if they screw it up.

[stuffit 0]

Quick off topic question: I know you jump in san diego but I dont think i have met you. Which guy are you(nothing bad, just curious).

Back to topic: I am not saying that anyone should use the 45 degree method but I have seen a bunch of students at Otay jump without looking or counting long enough. It scared the shit out of me. Actually happened on Saturday the 28th. I saw a solo belly go out ahead of us after a 4 way belly. He didnt even look out the door and he only counted for about four seconds. I dont know if this is due to teaching methods or not but I have also seen people there look out at the group ahead of them and still not give enough separation.

[billvon 2,380]

> I know you jump in san diego but I dont think i have met you.
> Which guy are you(nothing bad, just curious).

I'm the guy who's always in the power room fixing things. I jump mostly at Perris nowadays.

[Scrumpot 1]

Looking at these pictures Bill, even jumpers who adamantly believed in "the 45' rule" I think, would NOT just automatically GO at these points, even if they actually did recognize these AS 45' (which I doubt they would in the 1st place) and this quickly, as illustrated. ...At least I would hope not.

Funny though, how it was precisely the last time I was out THERE at Perris in Nov. that I happened to hear somebody on jumprun invoke this mystical "make sure we are 45' out the door before you go". Hmmmmm....

Personally, I think what we have here is something which has evolved from some instructor somewhere, probably dealing with some just off AFF soloists who, as we know sometimes haven't yet learned to manage that open-door adrenaline surge who were having difficulty in accurately counting, so this was 'suggested'. Somehow it has just proliferated from there, but never meant to be LITERAL. Just an aid in slowing some of those nubes down. How or why it has now somehow gotten picked up by some as "gospel"? Kinda like the urban legend phenomenon maybe, methinks.

Nice work & actual, real-world illustrations put forth here.
-Grant

coitus non circum - Moab Stone

[nightjumps 1]

I admit to being one of those who "learned" the 45 degree rule back in the early 80's. It was meant as a measure for validating the seconds of separation, not as the primary factor. For example, you're the first load of the day... assume its "X" number of seconds based on the winds aloft forecast and "assumed" ground speed.

It was taught as count to "X" seconds (for separation) AND make sure the previous group is at least 45 degrees from the plane.

Bottom line - about two years ago, I downloaded and played with Kallend's model for a few hours over a period of days and the 45 degree method just doesn't work. Not as a primary, nor even "validating" method.

[markbaur 0]

It is clear to me, but may not be so clear to 45*-angle proponents, that the jumpers start above the 45-line then descend below it (almost immediately), instead of being "blown back" from below the line to above it, as the 45-degree method mistakenly asserts.

That's a point worth emphasizing.

Mark

[The111 0]

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...haven't yet learned to manage that open-door adrenaline surge who were having difficulty in accurately counting

This is a very good point. Even now with almost 200 jumps I still wonder how accurate my counting is in the door... my adrenaline definitely still flows. But I know for a fact that when I had 20 jumps my counting was VERY rushed,, what I thought was 8 seconds was sometimes 2-3, seriously.

So how do we teach people to count accurately? Should the green light flash one time per second?

www.WingsuitPhotos.com

[crazy 0]

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It is clear to me, but may not be so clear to 45*-angle proponents, that the jumpers start above the 45-line then descend below it (almost immediately), instead of being "blown back" from below the line to above it, as the 45-degree method mistakenly asserts.

Right, the minimum angle can be a few seconds after the exit.

It all depends on the speed of the aircraft and the type of exit. The faster the aircraft, the higher the angle. Belly flyers are seen at an higher angle than freeflyers. Besides, the perceived angle during the first second doesn't really matter because the angle depends mainly on the position of the observer (a camera on the floor shows a higher angle than someone standing at the door).

Attachement is a graph giving the theoretical angles for different aircraft speeds (red=50kts, green=70kts, blue=90kts), both for bellyflyers (lines) and freeflyers (dots). Clearly shows that the 45 degrees rule is really safe :-)

--
Come
Skydive Asia

[kallend 1,621]

Can I use your pictures (with due credit)?

It looks to me as if the camera was set fairly low or forward, and looking below or in front of the jumpers as they set up in the door, so that they dropped through the center of the frame. Is this correct?

Is there any way of seeing the video?

...

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

[billvon 2,380]

>Can I use your pictures (with due credit)?

Of course.

>It looks to me as if the camera was set fairly low or forward, and
> looking below or in front of the jumpers as they set up in the door,
> so that they dropped through the center of the frame. Is this correct?

Yes. It was in the far forward bottom corner of the door about 6" outboard. I'll try to take a picture of the setup next weekend.

>Is there any way of seeing the video?

I have an .AVI of it; if you know of an FTP site I can put it on that would work.

[mr2mk1g 10]

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I have an .AVI of it; if you know of an FTP site I can put it on that would work.

skydivingmovies.com hehehe.

No seriously, please post to that site with an appropriate commentary when its back up and running. Its an amazingly popular site and just as good a way of spreading the word as any.

[kallend 1,621]

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>Can I use your pictures (with due credit)?

Of course.

>It looks to me as if the camera was set fairly low or forward, and
> looking below or in front of the jumpers as they set up in the door,
> so that they dropped through the center of the frame. Is this correct?

Yes. It was in the far forward bottom corner of the door about 6" outboard. I'll try to take a picture of the setup next weekend.

>Is there any way of seeing the video?

I have an .AVI of it; if you know of an FTP site I can put it on that would work.

How big is it? .avi's are usually pretty big, can you compress it any? I can find somewhere for it if it's not too big (say =<5MB)

...

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

[JohnMitchell 14]

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...haven't yet learned to manage that open-door adrenaline surge who were having difficulty in accurately counting

This is a very good point. Even now with almost 200 jumps I still wonder how accurate my counting is in the door... my adrenaline definitely still flows. But I know for a fact that when I had 20 jumps my counting was VERY rushed,, what I thought was 8 seconds was sometimes 2-3, seriously.

So how do we teach people to count accurately? Should the green light flash one time per second?

Count out loud, One one thousand, two one thousand . . ., just like a student jump. I'll count out on my fingers if I have a student in the door, just to emphasize counting. Seems to work.

• Quote

[PhreeZone 14]

I've sent Bill a message with a place to upload a file up to about 50 megs to.
I'm looking forward to seeing how you use the video and stills.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[bbarnhouse 0]

45 Degrees Before You Leave?
Bryan Burke, Safety and Training Advisor

Lots of skydivers talk about using a 45 degree angle rule for exit separation, which means that on jump run you watch the group before you to make sure they are at a 45 degree angle behind the plane before you go. The 45 rule is attractive because it simplifies a complex problem. That’s exactly why it shouldn’t be relied upon.

Freefall speed and aircraft speed actually are fairly close. 90 knots indicated airspeed at 13,000 feet is about 133 miles per hour. So, in theory, after the freefaller has lost all forward throw from the airplane (about six to eight seconds out the door) the airplane and freefaller will maintain close to a 45 degree angle from each other.

Unfortunately the 45 degree rule is just another incarnation of the old “airspeed vs. groundspeed” argument. We see this as soon as we add wind aloft to the equation. If there is a 33 mile per hour wind on jump run, now the plane is only going 100 miles per hour over the ground while the freefaller is still going 133 down, give or take a few depending on the activity. A 45 degree angle will never be achieved. The windier it gets the steeper the angle will be. About the only thing the 45 degree rule does is get people to wait a little extra time while they puzzle over the angle.

There are more variables, all of which apply to any discussion of exit separation and none of which are solved by the 45 rule.

As any group leaves the plane, there will be an exit picture that will vary with the type of exit. A well launched RW chunk will appear much higher than a well launched head down exit. It will take several seconds, until the group has lost all forward throw, before the picture becomes useful. Then, it is only useful if you know what kind of ground speed you have, as noted above. And then, it is time to get going anyway, at least for smaller groups.

The 45 rule implies that someone can watch the previous group the whole time. This is fine for a solo but isn’t practical when you need to pick up grips.

Exit separation only works if the fast fallers leave after the slow fallers. If you change this order, you still have the problem of freefall drift affecting separation.

If the angle is exactly the same between each group, that means the separation is the same for a solo and a 10-way. The 45 rule makes no allowance for group size, fall rate, or freefall activity.

Ultimately it comes down to this: groups and individuals need to be far enough apart at deployment that they are unlikely to collide. The only way to do this is horizontal separation, and the only accurate reference is the ground. The airplane will never be a useful reference point. Forget about 45 degrees. Get accurate information about winds aloft and learn how to use it.

[lug 4]

The 45-degree method is by no means 100% accurate. When there are not head winds affecting the aircraft, which is not realistic 100% of the time, the 45-degree does work. Although when head winds are encountered the 45 become less reliable, and more so, as winds increase.

Your effort is just, but your testing method is not sound. You can’t just nail a camera to an aircraft at the 45 degree. Who is to say that the mounting surface is vertical at the time each one of the sticks exited the plane. Using the camera is a good idea but it more important that it be used correctly.

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If jumpers had relied on the 45 degree method separations would have been:

1-2 1sec
2-3 .5sec
3-4 .1sec
4-5 .4sec
5-6 .3sec

I am supposed to use the 45-degree because I have to it’s the DZ policy but in using this method all the time I know how it works and what to look for, your not looking at the exit group correctly.


To illustrate this I need to ask a question. How many time will a group who exit an aircraft, appear to be at the 45 degree angle from vertical during the time they let go and through their fly away? (Once, Twice, or Three time) You might want to take a look out side the door on the next load your on before you answer.

Do I fallow the 45-degree rule all the time? Only when winds are vary light, on strong winds I watch the ground track of the aircraft it is the only thing I trust. I know how long the runway or hangers are and from that I can determine 1,000’ a good number for separation from say a four way, I'll add more distance the larger the group.

Memento Mori

[kallend 1,621]

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The 45-degree method is by no means 100% accurate. When there are not head winds affecting the aircraft, which is not realistic 100% of the time, the 45-degree does work.

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No it doesn't

Although when head winds are encountered the 45 become less reliable, and more so, as winds increase.

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How often are there zero winds at 13,000ft?

(Even if there are, it still doesn't work)

Your effort is just, but your testing method is not sound. You can’t just nail a camera to an aircraft at the 45 degree. Who is to say that the mounting surface is vertical at the time each one of the sticks exited the plane. Using the camera is a good idea but it more important that it be used correctly.

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Who is to say that your eyeball is more accurate in gauging 45 degrees than a camera fixed to an aircraft by a professional engineer using a protractor?

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If jumpers had relied on the 45 degree method separations would have been:

1-2 1sec
2-3 .5sec
3-4 .1sec
4-5 .4sec
5-6 .3sec

I am supposed to use the 45-degree because I have to it’s the DZ policy but in using this method all the time I know how it works and what to look for, your not looking at the exit group correctly.


To illustrate this I need to ask a question. How many time will a group who exit an aircraft, appear to be at the 45 degree angle from vertical during the time they let go and through their fly away? (Once, Twice, or Three time) You might want to take a look out side the door on the next load your on before you answer.

Do I fallow the 45-degree rule all the time? Only when winds are vary light, .

How do you measure it? With a protractor?

...

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

[billvon 2,380]

>the 45-degree does work.

No it doesn't. It works as well as rubbing a rabbit's foot and jumping.

>your not looking at the exit group correctly.

The cameras are looking at exactly a 45 degree angle to the deck of the plane. The artificial horizon showed the plane was level, therefore it's also a 45 degree angle from the horizon.

>To illustrate this I need to ask a question. How many time will a
>group who exit an aircraft, appear to be at the 45 degree angle from
> vertical during the time they let go and through their fly away?

Either zero or one time.

>You might want to take a look out side the door on the next load your on before you answer.

I did! I have done so on several thousand jumps, which is why I know the 45 degree angle thing doesn't work. And now I have pictures to prove it.

[ChasingBlueSky 0]

I love the fact that there are so many jumpers out there that believe they know better than the math and real proof. I've heard one too many JM's, S&TA, etc say you don't need to worry about how many seconds, just look for 45 degrees. I've had two close calls because of that.

These are often the same people that believe it is ok to put freeflyers out first

_________________________________________
you can burn the land and boil the sea, but you can't take the sky from me....
I WILL fly again.....

[mnischalke 0]

Sorry, but I had to say, I laughed out loud at this one, twice:

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No it doesn't. It works as well as rubbing a rabbit's foot and jumping.

Keep fighting the good fight. Someday, folks might actually open their minds and understand these concepts. I had an older, very experienced jumper give me a dirty look on the otter sunday when I mentioned that the 45 rule is bunk and that you can't judge separation by looking at the ground.

mike

Girls only want boyfriends who have great skills--You know, like nunchuk skills, bow-hunting skills, computer-hacking skills.

[foxyroxtail 0]

I heard it on the plane this weekend, too. From a very experienced jumper who's never been a JM. Of course I jump where the freeflyers leave first, so .... Maybe I shouldn't be surprised.

Rox

________________________________________

[base698 1]

This is probably opening another can of worms, but I was curious what people think of freeflyers exiting first when you allow double exit time between freefliers and flat flyers. This seems to be the easiest solution to the problem.