Why the 45 degree method does not work (long)

[tombuch 0]

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Well, it just goes to show you all that there is no perfect method. I happen to use the 45, have been teaching the sport for almost 15 yrs and teach my students the same. So far, there hasn't been any problems. Tom has a good point that I have been trying to get across to jumpers for awhile.

Welcome to the forums. I hope you will reconsider teaching of the 45 degree method. It really isn't effective at higher speeds, with larger groups, longer jumpruns, or when applied literally. Your experience suggests that it can work under very limited circumstances, but not when it matters.

I was originally taught the 45 degree method when I was a student at a Cessna DZ 20+ years ago. I think what happens at Cessna DZ's is that a spotter watches for 45 degrees, and then starts the exit process, thus adding extra seconds.Too, the groups are small and since there are so few groups there isn't the pressure to get everybody out fast. At a bigger or more active DZ there is a stronger "Go NOW" pressure so users of the 45 degree rule tend to bunch up.

Anyway, my point was that the 45 degree method really doesn't work, but that there are plenty of experienced jumpers who believe it does. When discussing spotting with experienced jumpers we need to acknowledge anecdotal experience that suggests the method does work, then disprove it technically before we can apply a time/distance based method that really does work.

I got grief for even acknowledging the 45 degree method a while back, and I suspect that can of worms has been opened again, but oh well. If you missed my S&TA feature about the topic on The Ranch web site, it is available at http://ranchskydive.com/safety/tb_article15.htm

Tom Buchanan
Instructor (AFF, SL, IAD, Tandem)
S&TA
Author JUMP! Skydiving Made Fun and Easy

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

[markbaur 0]

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I hope you will reconsider teaching of the 45 degree method. It really isn't effective at higher speeds, with larger groups, longer jumpruns, or when applied literally.

Let's be more specific. The 45-degree method isn't effective at any speed, with any size group, or with any length jump run. And whether you apply it literally or not, no angle-based method works.

Mark

[kallend 1,621]

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Well, it just goes to show you all that there is no perfect method. I happen to use the 45, have been teaching the sport for almost 15 yrs and teach my students the same. So far, there hasn't been any problems. Tom has a good point that I have been trying to get across to jumpers for awhile. Having over 2100 hrs myself flying jumpers, groundspeed and time isn't that bad of a method if you really know how to count accurately and do the basic math. As I said there is no perfect solution, I feel that you should use the method that seems to work best for you and your DZ. You don't have to go to MIT to realize that you really should leave more than a couple of seconds between groups Bill. And I really have a hard time with the fact that your otter pilot was flying in a level attitude!! How much separation do you really need? Where is it most important? I kind of think it is at the opening point. Have a great day Y'all.

How can you justify using and teaching a method that has no basis whatsoever in physics, can be proven to be insensitive to winds, preaches using an angle that can't be measured accurately by eye and which is never reached anyway under normal circumstances, and for which Bill has now produced a beautiful video showing that in practice all the bad things that the theoreticians warned us about this so-called method are true.

The physics is clear, and the experimental results are clear. The angle method does not work and can not work.

...

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

[pilotdave 0]

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And I really have a hard time with the fact that your otter pilot was flying in a level attitude!!

Even more reason NOT to use the 45 degree method. Assuming the camera was angled down at 45 degrees from the aircraft's longitudinal axis, any positive angle of attack would cause the 45 degree line in the video or pictures to actually be greater than 45 degrees down from the horizon. Factoring in angle of attack, the jumpers were even farther from reaching 45 degrees than they appear to in the pictures.

Your reasoning for using it would be just like a pilot that never checks the oil before flying because it's never been a problem before. You know it doesn't work, so why teach it?

Dave

[riddler 0]

Safety Day, March 13th. One instructor stood up in front of about 70 people and reiterated about not getting enough separation between groups. I was happy to hear him say that this dropzone was always willing to make a second pass if there wasn't enough time for proper separation. Not many dropzones I've been to want to do that.

Then I heard him say "before you get out, make sure you have 45 degrees of separation". Rrrgh! I respect this person - he has more experience and knowledge than I do, but I think we still have work to do to educate people (even instructors!) about this. If instructors and DZOs tell this to students, it will be much harder to correct.

I honestly think the 45-degree farce gets repeated because there is no simple answer to this problem. I say there is no simple answer because the correct answer is to check ground distance covered. And that involves spotting. New jumpers don't know how to spot. I can't even say that I'm good at spotting. It isn't taught to students anymore. It isn't encouraged by dropzones anymore. It's hard to take time to practice spotting when you have 15 people behind you in a King Air that either want the door shut because it's too cold, or want you to get out because the green light is on.

I fully intend to bug skr about attending his Cessna Playground because I want to practice spotting. But what happens when you have an entire group of new skydivers that don't know how to spot? I can show them how to spot when they ask me for coaching, but can I make a difference when so many instructors still say 45-degrees of separation?

Best answer I heard was from one of the CReW dogs. He said every dropzone has a ruler on the ground called the runway. You can use the runway to measure how far you've gone over the ground. If the runway is a mile long, divide it into thirds and that is how much distance you need to cover before you jump.

Trapped on the surface of a sphere. XKCD

[mnischalke 0]

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I say there is no simple answer because the correct answer is to check ground distance covered.

The ground has nothing to do with it. It's just as bad as the "45-degree rule." What gives true physics-based separation between groups is the differential between exit altitude airspeed and opening altitude airspeed.

If you really want to know how many seconds of separation to give, plug the variables into Billvon's excel separation calculator and go. If you want to know how much horizontal separation you'll need at opening altitude for group size, use Kallend's spreadsheet.

Edit: To add an illustration to why watching the ground doesn't work, I want to add Windsor's spreadsheet and the post explaining it:

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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.

mike

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

[bmcd308 0]

>>The ground has nothing to do with it. It's just as bad as the "45-degree rule." <<

You and I have talked about this before, and I think you will recall that while I absolutely agree with your (and my - they are the same) physics, distance over the ground IN MOST CASES is a good rule to use. It is important to understand when it does not work (i.e. opening altitude winds opposite direction from jump run), but in the general case, distance over the ground is a good rule of thumb, and any error due to ignoring opening altitude winds serves to increase, rather than decrease, separation.

I disagree that distance over the ground is as bad as the 45 degree rule, since in most cases using distance over the ground results in a calculation of separation TIME that is at least adequate to provide necessary separation DISTANCE at opening.

EDITED to add: You will note in the exit separation thread that I said that I would ignore a headwind at opening altitude but DEDUCT a tailwind from groundspeed in the calculation of separation time.


YMM(and probably does)V

Brent

----------------------------------
www.jumpelvis.com

[riddler 0]

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It's just as bad as the "45-degree rule."

I should say that I feel that distance covered over the ground is the correct answer, given the limited information that you have. No, I don't think it's just as bad as the 45 degree rule. I think it's much better.

There's no perfect answer. Even with a lot of separation, if two groups spend the whole sydive tracking towards each other, they can still hit each other. Distance covered over the ground is the best answer I can think of. If you find a way to use the Excel spreadsheets and on-line calculators on jump run, and get accurate wind indication at the different altitudes on jump run, then let me know.

Trapped on the surface of a sphere. XKCD

[Scrumpot 1]

Interesting Bill, that I was just at "YOUR" dropzone over this past weekend (Perris Valley). On Sunday, they were handing out to every jumper out of manifest, presumably as a follow-up to Safety Day, Perris' (presumed) "official" safety guidelines.

Take a look at page 2 (the back page ...double-sided copied) under EXIT SEPARATION:

and I quote:
"Exiting groups should wait until the previous group has achieved a 45' angle from the aircraft before making their exit." This is apparently, the Perris now PUBLISHED policy!

Like I've said before, it is interesting to me how the only place I have aver actively heard this was there. -Perris! Now again, just coincidentally during my only maybe 1 - 2 times per yr actual visit there yet again. Hmmmm.....

So, what gives?
I'll presume you had no input into what was just being put out there yet again just this weekend too, eh? And you wonder how this MYTH seems to get perpetuated.

Blue Skies,
-Grant

coitus non circum - Moab Stone

[billvon 2,380]

>Interesting Bill, that I was just at "YOUR" dropzone over this past
> weekend (Perris Valley) . . .

Actually, I still consider San Diego to be my home DZ, small as they are. But I jump at Perris a lot.

>I'll presume you had no input into what was just being put out there
> yet again just this weekend too, eh?

Nope; they did not ask my input before publishing that flyer. On the "rules" board by manifest, one item says "Allow at least 10 seconds between groups." I think you are seeing the usual difference of opinion between skydivers.

[kallend 1,621]

Maybe this would make a good topic for USPA's S&TA forum?

...

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

[feuergnom 22]

BUMP

last week at skydive dubai during the DZ-briefing instructor told me to use the 45-dregree-rule to get the exit separation right. couldn't believe what I heard and was to stunned to get into an arguement.
Info is out for over a decade know and there's still instructors telling BS

guess I'll send them just the link to all the threads

The universal aptitude for ineptitude makes any human accomplishment an incredible miracle

dudeist skydiver # 666

[Scrumpot 1]

coitus non circum - Moab Stone

[Speed-Flyer 0]

who was it? That is not protocol.

[Divalent 89]

USPA really should explicitly note in the relevant section of the SIM that this method does not work. I have also heard a number of instructors endorse this technique, and if it's been known for 15+ plus years that it doesn't work, perhaps something besides episodic DZ.com discussion threads is needed to stamp it out.

[sammielu 3]

Remember who is in the sky with you. Bigger groups often had higher break off altitudes, and some of those fliers may be very experienced at tracking away and can cover a lot of ground.
Example: break off at 6k because the group includes newer jumpers - I can cover a lot of distance in the 10-15 seconds it takes to get to pull altitude of 3k. Definitely more than the 500' normally given in the 1000' separation rule. Do you really trust everyone to avoid tracking up/down jump run?

My point: there are other factors to consider when thinking about separation. Pull altitude and break off altitude, for example.

[Di0 1]

I was mentioned the "45 degrees rule" a couple of times. Sadly, as an "alternative" to the proper "count X seconds and look" separation.
I honestly brushed it off as seemed too empiric, i.e. technically you could LEAVE the aircraft and reach 45 degrees from exit very quickly, anyway it doesn't make sense because 45 degrees is a perspective thing, you could have 45 degrees even when you are very close horizontally and vertically so, that alone doesn't work. It means you are as far horizontally as you are vertically, which only works AFTER waiting a certain number of seconds.
That's why I somewhat "recycled" the 45 degrees as a visual reference AFTER counting the X seconds: if after X seconds the group doesn't look well behind the AC but it's still well inside the quadrant (octant?) between the "nadir" and 45deg then I wait a little bit more to make sure they clear some extra airspace as it might mean the wind up top were stronger than expected, separation should have been longer or go figure where the group is drifting about.
In this case, 45 degress is more of an help to me to have a reference point to make sure the picture looks about right after giving the separation count. Separation count is what matters, but it's a way to not follow it blindly either.
You do, generally speaking, see the group "approach the 45 deg line" as the count goes on. Which is neat.

When, as a coach, I teach or mention or practice spotting, I make absolutely no reference of it though, the SIM teaches to calculate the exit order separation based on winds, group size, drift, etc. and then count, so I relay that message because it's what makes sense and starting to quote "magic numbers" that have no solid validity will only create dangerous confusion.
I will tell, however, that the whole point of counting is to ensure separation, so it's always good to not only count but also visually make sure the previous group is "moving away horizontally" and everything looks good as you are spotting.

I'm standing on the edge
With a vision in my head
My body screams release me
My dreams they must be fed... You're in flight.

[billvon 2,380]

>You do, generally speaking, see the group "approach the 45 deg line" as the
>count goes on. Which is neat.

No, you don't. See pictures above. They go below the 45 degree line and generally just get farther and farther away from it.

[Di0 1]

Mh. Mh.

You're actually right.

Considering a vertical speed of ~120mph and an horizontal speed of ~80mph (plus or better: minus whatever the winds are), they should get away from 45 degrees as they cover more vertical distance than they do horizontally.
If, unrealistically, the plane has a relative horizontal speed bigger than their vertical speed, then they would approach and surpass 45 degrees.
At this point I guess it's more of an "optical illusion" than anything else. We think we see it at 45 degrees because we think that's what should happen and that's what 45 degrees look like. But in reality, that's dead wrong. Makes sense?
Oh well, as said, the 45 degrees thing has really no proven validity. One more reason to say it.
Next time I'll spot from an otter, I'll try to see what that angle is more carefully, but yes, I bet it's nowhere near 45 degs, that wouldn't make sense for normal conditions.


Actually, come think about it, the only point they might be at 45 degs is somewhere shortly after the hill, this thing makes no sense at all. LOL

I'm standing on the edge
With a vision in my head
My body screams release me
My dreams they must be fed... You're in flight.

[rehmwa 2]

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but also visually make sure the previous group is "moving away horizontally" and everything looks good as you are spotting

that's a placebo (perhaps some people 'claim' they can see if someone is tracking up the line of flight, I suppose)


talking watching the angle of the group at all is part of the same misconception. watching that 'angle' is a complete waste of time based on false reasoning. So once again, and again.....

two things -

1 - The AIRSPEED of the plane is the same regardless of how the uppers are blowing

2 - People leaving that plane are pretty much falling in the same airmass that the plane is flying in (for the first part of the freefall). again - regardless of how the uppers are blowing

so the relative position of the plane vs the jumpers just doesn't matter - it's essentially the same 'relative' profile every time - ie., it looks the same from someone positioned on the plane. windy day, or still day - it doesn't matter

what matters is the relative position of the jumpers at the end of the freefall - looking from the door at the previous exiting group doesn't give you any info on that

If the DZ won't do the calculations based on the wind vs altitude profile, then you are infinitely better off ignoring the previous group and watching the ground, at least that works in the 'typical' jump run/wind direction assumptions


people can watch the jumpers all you like - it gives zero useful info (unless one of them takes out the tail, then I'd recommend exiting quickly.)



the mental errors in the 45 degree discussions are analogous to people that claim flying downwind will collapse a canopy more readily than flying up wind. one needs to correctly recognize the difference between groundspeed vs airspeed, and reference frames fixed to the door of a plane vs fixed to the ground

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[Di0 1]

Yes, good point.
No matter how you look at it, it's hard to find any rational basis for this 45 degrees rule. I like the word placebo to sum up that sometimes "we see what we want/expect to see".

I'm standing on the edge
With a vision in my head
My body screams release me
My dreams they must be fed... You're in flight.

[pchapman 261]

Thanks remwha, that saved me some typing.
To reiterate somewhat:

Unless there's a massive wind change "just below the aircraft", lets say within 1000' below the aircraft, then every exit and the next 7-9 seconds will look the same as it usually does.

Every RW group presenting lots of drag to the wind will fall back more and fall slower, while every head downer will stay more forward and pick up vertical speed faster. All as normal.

(Naturally the ground in the background will move differently depending on the wind situation, and that is a sign that separation might not be normal.)

[rehmwa 2]

pchapman

Unless there's a massive wind change "just below the aircraft", lets say within 1000' below the aircraft, then every exit and the next 7-9 seconds will look the same as it usually does.

I'm not very pithy at it, but I sometimes ask the person what the 4way exit looks like from the plane if you couldn't see the ground for reference - cloud cover, night..... It doesn't matter what the winds are since the system is living inside the same moving mass of air - regardless of how fast that air is moving relative to the planet

But, we all like to think we can 'see' what we need. Not always. depends on what we are looking at, and where we are viewing it from.



(I really did have one guy argue that a canopy is more likely to stall when landing with a tail wind vs a headwind (this during the final leg, not after touchdown). He said the wind is more likely to blow the back of the canopy over the nose while flaring.)

...
Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants

[stayhigh 2]

It doesn't work because no one brings a protractor.

If you bring a protractor and start measuring the angles, by the time you figure it out you'll have plenty of separation.

Bernie Sanders for President 2016

[theplummeter 14]

stayhigh

It doesn't work because no one brings a protractor.

If you bring a protractor and start measuring the angles, by the time you figure it out you'll have plenty of separation.

I don't want to spend jump money on a protractor (wasted too much on a fancy compass for drawing perfect circles) but still want to do proper math. Do you know of any good protracting apps that work without data at altitude?