BrianSGermain

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I have been thinking about the effects of volume on size more since I wrote this article. I believe that that balance of power between D1 and D2 as it relates to scale has a profound effect on the flight characteristics. Given the fact that canopy drag changes while body drag does not, large canopies; even with an adjusted airfoil height, will never have as long a recovery arc as their smaller counterparts. Likewise, large canopies will always have a higher pitch angle in full flight due to their higher drag value, and will consequently have a flatter glide ratio. That said; the non-linear scale effects are still something to be considered, as are the differences between canopy designs. We need to consider all of the variables if we are to accurately predict a parachutes flight characteristics, and any single metric will be insufficient.

To clarify the method I used for calculating internal volume:
Span x Chord x [*Rib height]
Rib height = maximum rib height divide by two, averaged value of all ribs
This is not an exact figure, however it is an expedient way to make the calculations. If the math takes too long, other manufacturers are not likely to measure their volumes. If all the manufacturers use this method, we will level to playing field and make volume comparisons across products a quite valuable number.
That said, the total number of ribs alters the inflated volume of the canopy, a fact which must be taken into account. In other words, a standard seven cell will have a larger inflated volume than a nine cell with the exact same ribs. I am not yet clear on how we will factor this into the equation, but acknowledge the necessary of this amendment.
Again, the goal of the use of this number is to help parachute customers to have another metric to predict a parachutes performance beyond just 2-D area. There is no doubt that other variables have a huge impact on parachute performance beyond area and volume alone. These variable include: (elliptical taper, line trim, line length, location and duration of max rib height, line attachment displacement, fabric type, line type and diameter, number of stitch rows and thread type, and undoubtably several others that I have not thought of in this moment. Nevertheless, volume is a significant feature, and the customers should be able to compare differences between designs.

If, as you say, 8-10 lbs of line stow extraction force is necessary to prevent a hard opening, why do the thousands of semi-stowless bags open softly and beautifully? It seems to me that the issue is bag dump. In my experience, elastics that are too tight (other than the closing stows), cause off heading openings and line twists.
From what I understand, out of sequence line deployment is the focus of the "double stow" religion, as the belief is that lines that come off the bag out of sequence will cause tension knots. I have not seen this in the field very often, and the risks posed by double stowing seem to out weight the need for this paranoia-driven panic to double stow everything.

Corey, I think that fear of mistakes on the students part is the fundamental to being a caring instructor. It is just like being a parent, in that the desire to prevent harm is often so strong that we prevent learning through direct experience. It is true that the paradigm from which instructors come creates a tendency to continue in that direction, nevertheless evolution is part of the quest for higher levels of safety. If we find a balance between the two ends of the spectrum, and say, have radios but only use them to serious situations, true safety can be achieved. We can use the radio to teach, through asking good questions of the student under canopy that lead to understanding, rather than just giving them the answers, we will be on the road to an expanded model. That, I believe, is where we are headed.

It is interesting to me that in the US and other countries where radios are always used, the case is made why we absolutely need them. The idea that a first or second jump student is emotionally incapable of flying a pattern to a safe landing is unthinkable in this cultural context.
In countries such as Norway and Sweden, places that tend to have the most favorable incident statistics, radios are rarely used at all. Is it possible that we are using radios in the States to mask our hidden agenda of not wanting to spend the time to teach our students how to fly their parachutes? Is it possible that the human factors argument, for most people, is not valid, and has merely been a mechanism of a litigious society once again impinging on human freedom?
Philosophical discussion aside, it is my agenda to make sure that everyone who flies a parachute knows how to do it safety. It is through articles like this one that we can get skydivers thinking about HOW to teach safe parachuting methods. We need to create responsible canopy pilots who understand the dynamics of the situation on a very deep level, and your article is another part of that puzzle. Thank you for writing it.

Evan: This a a good point if someone does not have stainless steel hardware, and is planning in swinging around wildly in the harness. However, at just one "G", under normal circumstances, I have never seen a problem with metal on metal for this practice, and I have been doing it for many years. However, if it really concerns you, try a climbing sewn "quick draw" to prevent metal on metal contact.

It is quite obvious that the term "prop blast penetration" doesn't work for most people. I liked the alliterative quality, it is kinda fun to say, but I am willing to let it go. I think that "forward throw" is a great term that I have heard as well, or perhaps "relative wind penetration", "jumprun penetration" or even "horizontal distance traveled". How about we put it to a vote and have Sangiro change the article based on the people's choice?