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Off Headings

This page is a chapter in 'BASE Wiki Malfunctions and Problems'

Off Headings: Of all problems in BASE, the off heading is the most dangerous one. Granted, a total malfunction with no canopy coming out of the container is potentially more deadly, but a lot easier to avoid.


Offheadings are not entirely avoidable. Many famous BASE jumpers have said there are two types of jumpers; those who have hit an object, and those who will.

Effect

An offheading happens any time your canopy opens up and ends up flying in a different direction than you intended. Worst case scenario you find yourself flying directly towards a solid object, often when you have the dreaded one-eighty.


However, even offheadings of lesser degrees (nineties, or hundred-twenties) can cause significant problems if not corrected quickly. The key is to avoid obstacle collision at all cost. Given a choice between hitting an object and then the ground, or hitting just the ground, the latter option is usually a better choice.

This is a good time to remind everyone, that base is a VERY dangerous Sport. I also wanted to give a video about an off-heading jump that resulted in an object strike, which ended up in a very hard landing that caused serious injury to the jumper:

[youtube]F9Pk8P4u44c[/youtube]

Cause

There are five major factors involved in an offheading:

  1. Packing
  2. Body Position
  3. Winds
  4. Pilotchute Dynamics
  5. Bad Luck
Different people attach different levels of importance to these factors. It is generally accepted that the first three factors are the most important, with body position being a strong leader.

Packing

Avoiding an offheading starts with your packjob. Make sure you keep everything symmetric while you pack. Whatever you do on the left side, do it on the right side too. One area to pay extra attention is the dressing of your risers. If one riser is loaded before the other one, you will induce a turn in that direction. More importantly, be careful when closing your rig. Many beginning jumpers pack perfectly symmetrical and then completely distort their symmetry during the closing sequence of the container. Especially on hard-to-close pin rigs, you can see people yank hard on the pull-up cord, distorting the packjob on the inside.


If you find yourself getting consistent offheadings in a particular direction, it is a good idea to consider what you do when you are closing your container.

Body Position

Body position is by many considered the greatest factor in heading control. Many jumpers that go off unstable, drop-a-shoulder, go head-low or come out of an aerial with assymetrical rotation end up getting a canopy that is not flying on heading.


There are two main factors that cause an unstable body position to result in an offheading. First, the canopy comes out of your container the way you put it in. That means that you may very well get an onheading opening relative to your container, but since you presented the container in an unintentional direction, your canopy will open that way. Secondly, if you load your risers unevenly, the riser that gets loaded sooner will initiate a turn in that direction.

Winds

Winds contribute greatly to the chance of getting an off heading. Generally, a canopy has a tendency to open into the wind. However, it can also give your inflating canopy momentum in a certain direction. This is especially deadly in crosswinds. If you find yourself on top of a solid object with a strong crosswind, reconsider your desire to jump. Admittedly the same goes for winds from other directions. A general rule of thumb is that solid objects should be only be jumped in zero wind conditions.


When jumping from an antenna, the wind can actually help you. By making sure you jump with a tailwind and in between the wires, you will be pushed away from the wires. This is discussed in more detail in the section on Site Analysis.


Theoretically, a strong headwind can actually improve your heading performance. The wind will blow into the exposed center cell and the canopy will have a tendency to open into the wind. This knowledge is rarely useful since the drawbacks of a headwind if you do get an offheading are too great (the headwind will push you back into the object).


BASE WIKI dedicates an entire section to wind considerations.

Pilot Chute Dynamics

The pilot chute is what extracts your canopy out of the container towards line-stretch. A moving pilot chute will transfer its movement to the canopy it’s attached to, at least to a certain extent.

This problem is often referred to as the ‘oscillating pilot chute. Imagine a stowed pilot chute tossed out to your side. It will inflate and extend and come from the side towards the center. It carries momentum, continues to the other side and then bounces back. Essentially you see a pilot chute bouncing back and forth above the jumper. This movement is transferred to the canopy contributing to an off heading opening.
There are two major causes for pilot chute oscillations:
  1. An asymmetrical pilot chute, either because it’s manufactured that way or because it’s attached to the bridle that way. An asymmetrical pilot chute will spill more air on one side than on the other and start tipping over, until the other side spills more and tips to the other side, never quite finding an equilibrium. See the section on pilot chutes for more information on how to detect and avoid this.
  2. A pilot chute throw that is too strong to the side. Note that the force with which you throw your pilot chute is a delicate one. You want to make sure the pilot chute clears a potential burble and has a chance to inflate and do its work. At the same time, a throw that is too strong can contribute to off headings. When in doubt, err on the side of throwing too hard. It is better to have an off heading canopy than no canopy at all.
To combat pilot chute oscillations, manufacturers came up with vented pilot chutes that reduce oscillations. These vents let some amount of air spill through the top of the pilot chute, allowing the low pressure point above the pilot chute to be filled. Supposedly this results in pilotchutes that are more stable.
[YOUTUBE]dCvkU_N5Vho[/YOUTUBE]

Practice has shown vented pilot chutes to offer some advantage over non-vented pilot chutes, but the science of it is too fuzzy to come to strong conclusions. Some people prefer non-vented F-111 over vented ZP pilot chutes arguing that the F-111 is permeable over its entire surface, achieving what vents try to do more effectively.

Bad Luck

Remedy

Todo, talk about avoiding, factors (body position, winds, packing, magic), dealing with.

Turning around “quickly” needs to be qualified, look at three criteria:
  1. Altitude used
  2. Distance covered
  3. Time taken


04:03 by fabien.

As far as I could experience it:
Inducing factors: -opening position: launching slightly on one side, on a 3 delay, induced a 150°. Nailing an exit and pitching frankly on one side induced a 270° twisted opening ( no slider jump…). -Being stowed on a short delay: pitching involves a lot of body movement, which may destabilize the body during the opening sequence. Once experienced a full 180°, probably due to that. Pitching hard also launches the PC far from the body, creating a asymmetrical force when airspeed is low and PC is big. -Too small a PC, not creating enough drag and thus giving a looooong opening. The longer the opening is, the more likely it is to open off heading. -Using a slider on short delays (<4)doesn’t seem to be a direct factor, but makes the canopy way more sensitive to the other ones, by making the opening longer. -crosswind may also be a factor on short delays, the PC being swept laterally by the wind, and thus pulling the PC on the side.
There is a whole lot of factors that I didn’t explain, just take into consideration that this is only the result of my ( somewhat limited ) experience.



Dealing with an off heading: -First off all,

TURN THE CANOPY OFF THE OBJECT!

If there are line twists, the first thing to do is to determine whether it’s flying toward the object or not. I can tell you that it is really hard to figure it out, when having a line twist behind one’s neck… If the canopy is flying away from the object, then you have some time for removing the twist. If not… do what you can, including turning the canopy away by pulling on a line above the line twists, the hardest thing being finding out on which line to pull… If no line twists: Two methods are commonly used: rear riser turns, and toggle turns. I personally always used the riser method, because it’s quicker to locate and pull. It’s common to see people, whilst reacting really quick, beginning to turn the canopy with a toggle 3 to 4 after deployment, which is too much!. Grabbing a toggle would also give the canopy more forward speed, and this is something you don’t want, when flying toward an object. The riser method worked successfully for full 180°’s, on 1 to 12 delays, on any type of object. But others would argue for the toggle method…


This must have been the most controversial topic in the history of BASE jumping…





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