Ellipticity

[ZigZag 0]

I'll be happy to take advice and move this post to a different forum if suggested, but I'd like see if there is anything to be gained by comparing canopies of these two similar sports.

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[VectorBoy 0]

Are you getting airtime Ziggy? Glen

[ZigZag 0]

[crazy 0]

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Many threads deal with the issue of what kind of canopies novices should jump, and how best to define performance parameters of canopies, in order to match them with any given skill level.

Why not stick to the relevant and useful parameters? For instance, for a given canopy, with a given size, and a given wingloading:
- vertical and horizontal speed at full glide;
- minimum vertical speed (and associated horizontal speed);
- stalling point;
- length of the toggle stroke, from full glide to stall;
- turn rate and speeds (vertical & horizontal) with 1, 2 and 3 feet of input;
- speeds (vertical & horizontal) and recovery arcs (natural & minimum) after a radical 180 toggle hook turn;
- minimum altitude loss in a 360.

All of these are easy to measure. How many manufacturers provide this? Why don't they publish this kind of objective performance parameters?

--
Come
Skydive Asia

[AggieDave 6]

Paragliding students don't have to deal with the very fast turning spinning malfunctions on opening that a skydiver could have under an elliptical canopy, though.

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

[ibellis 0]

Well. I'll "chime in" since we are producing canopies at each end of the performance spectrum (student to high performance) in both disciplines (skydiving and paragliding).

Firstly, while both the paraglider and the skydiving canopy are both wings constructed from "non-rigid" materials, they differ greatly in aerodynamic design, construction and characteristics.

Our competition paraglider for example, has 60 cells is approximately 270 square feet and is constructed from 400 individually computer cut parts. It has an incredibly high aspect ratio and planform factor. It is trimmed to enable very high glide ratios, as well as its suspension line construction and configuration differences. Many other design characteristics are different as well.

The bottom line is they are incredible wings, are extremely fun to fly, and have some amazing capabilities, (as you mentioned) but I wouldn't pack one into my rig and go try to delpoy it, or fly it on a turbulent day, or enter a speed swoop event with it, etc. etc.

The skydiving canopy on the other hand uses aerodynamics and construction criteria that suit its purpose very well. High speed deployment, stability, etc.

Within the scope of each discipline, there are obviously multiple designs (models) specifically tailored to certain types of pilots (students, tandem, intermediates, experts/competitors, etc.)

In the final analysis they have many similarities and many differences. I can say that the design and testing process for each helps the other, i.e. we are able to test some pretty radical aerodynamics in the paragliders that you wouldn't want to get near in a skydiving canopy. What we learn from one trickles over to the other and makes them (in my opinion) that much better. They also share the use of some really nice three dimensional design tools that we use during the concept phase of development.

The handling characteristics are very different whether close to the ground or at altitude, remember your wing doesn't know what altitude it is at. Certain maneuvers you could perform with a skydiving canopy might collapse a paraglider, while the speed and descent rate of a skydiving canopy during a landing might be something a paraglider pilot will never see.

Instruction in paragliding focuses on take offs, piloting, weather conditions, etc (more similar to hang gliding I would guess, although I am not a hang glider pilot) while most instruction in skydiving focuses on other survival skills, outside of canopy control/flight/landing. That is not to say paragliding pilots do not get injured or are less prone to problems, but remember, the wings they are flying are more susceptible in many ways to conditions and radical response to pilot input.

Wing loading is a factor to be sure but less so in paragliding since the canopies you see are never going to be as small as skydiving canopies.

I hope this answers some of the questions. I am sure others can provide additional info to this topic.

Blue skies,

Ian Bellis
President
Aerodyne Research Corporation

[ZigZag 0]

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That is not to say paragliding pilots do not get injured or are less prone to problems, but remember, the wings they are flying are more susceptible in many ways to conditions and radical response to pilot input.

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One thing they do have in common is that eventually you have to land with the airfoil. Is it, that paragliding students get better training in the limits of performance and the handling characteristics of paragliders, maybe because they start off with canopies that have high aspect ratios and planform factors. Is there a gap in training when jumpers come off of student status? The entire industry has responded to some extent, but I feel that in some way it is still lacking a structured training program for canopy control skills. The few professional programs that are available do not cover the entire community, so it seems that many jumpers will go out and try maneuvers based solely on what they see.
I have passed the scope of your response, but want to use this opportunity to widen the discussion. Maybe this is the point were this thread should be moved to a different forum.

[VectorBoy 0]

No Ziggy I'm talking about Para-gliders. Glen

[ZigZag 0]

Ziggy

[crazy 0]

Thanks for your input. As you are involved in many ways in this topic, maybe you can give us more information about the policy of manufacturers (at least your policy), regarding the publication of the flight characteristics.
Do you know why it is so difficult (or impossible) to get the basic flight characteristics and performance parameters of skydiving canopies? Why is there such a gap with the paragliding industry (it's much easier to get useful info about the performances of a paraglider)?

I personally think it's quite disapointing to get lots of not very useful info about the geometry of a canopy (aspect ratio, span, min & max chord) up to the 3rd digit, while it's impossible to get any info about it's performances, not even the most basic info, such as the speed. It's not only disapointing, it becomes worrying when i consider it at the light of the initial question of this thread:

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the issue of what kind of canopies novices should jump, and how best to define performance parameters of canopies, in order to match them with any given skill level

As there is no information available about the performances of the canopies, the match between a given skill level and a canopy is done in the shadow of 2 powerfull blindfolds: wing loading and geometry.
Wing loading is a powerful blindfold because two canopies at the same wing loading can have extremely different flight characteristics. Even though it's quite a fuzzy notion (there is not even a standard for the measurements), skydivers still happily discuss wingloadings up to the 3rd decimal while comparing canopies from two different manufacturers (like if there were so many common points between a stiletto at 1.25 and a Xfire2 at 1.22). Same thing for the geometry of the canopy: most modern main canopies are not rectangular, even beginners canopies. Comparing the degree of taper, ellipticity, or whatever planform factor, doesn't help much to figure out the actual performances.
The regulation about canopies is in terms of wing loading and canopy geometry. This is really odd because these are very abstract numbers, extremely remotely related to the meaningful information: speed and acceleration. Taper doesn't kill skydivers. High speed impact into the ground does.

So, which manufacturer is willing to publish meaningful (quantified) flight characteristics for their products?

--
Come
Skydive Asia

[ibellis 0]

Some good questions. I will try to explain the reasons (in my opinion) why the type of data you describe is not generally released.

Firstly, it is only in recent years that obtaining meaningful data acquisitions in flight has been technologically available in a cost effective system.

As a matter of fact I was just speaking with a friend about obtaining a new GPS/guidance computer that will give us a simpler system for collecting a greater amount of flight data.

I can tell you that not too long ago, we had to fly the canopy while trying to take airspeed readings and time rates of decent with stopwatches and altis.

The technology is finally getting there. The data acquisition is only part of it though, as you must qualify the conditions. While Aerodyne and others have been acquiring this sort of data for some time, the conditions for acquisition become very specific. For example you would typically convert all conditions to "standard day" conditions (temperature, air density, etc.)

Once you have done this, now you must look at the test pilot (suspended weight, drag on the system, etc.

If you are looking at turn rate you must measure toggle deflection vs. rate of turn using a specific length riser, altitude loss, toggle force, etc. Riser inputs the same. You must do all of this measurement objectively of course.

Now that we (the manufacturer) have done this, we can tell the end user exactly how this particular parachute behaved under standard day conditions with suspended weight of X (lbs/kg) using the exact set up (equipment for the tests)

Question: How many pilots will fit this criteria?
Answer: Probably none as some variable (probably many) will change from the test to real world use.

Now I am not by any means suggesting we not provide this info anyway, but the simple fact is that, as you mentioned, the manufacturers have not even been able to standardize on measurement methods for the physical characteristics of the wing, let alone the flight standards for testing.

In recent discussions with other (manufacturers) we discussed the supposition that, given the data acquisition was available to all manufacturers and standardized, some manufacturers might publish certain values while others could publish different ones, in an effort to put their own particular products in the best light.

Remember in all of this we are getting into the danger of "data overload" as well.

My personal experience is that most canopy pilots are not that interested in the degrees per second or bank angle generated, but more in how the canopy "feels" to fly.
They really couldn't care less if we (Aerodyne) or others gave them the exact specs describing the flight data of the canopy.

Our discussion of planform was a simple attempt to include an important physical characteristic of the design of the wing into the common vernacular of describing canopies and do so in an objective method that could be applied to all canopies.

I guess the bottom line is that most people I have spoken to over the years (and this is thousands of jumpers) are not that "into" the details, that we as designers and manufacturers get involved with. They trust us (the manufacturers) to do our "homework", test our products and provide a diverse product line with canopies that meet the needs of each type of pilot. The fact that we would tell customers that a Vision has a 73.5% faster turn rate (hypothetical numbers) than the same sized Pilot canopy, really wouldn't make much difference since this difference is described by us in general terms and anyone inquiring knows the Vision is a much faster turning canopy than a Pilot.

If we (the manufacturers) could standardize on a method and for example manufacturer X's canopy has a higher turn rate than manufacturer Y's, then manufacturer Y would come back and say theirs reaches a greater bank angle in less rotaion, etc. Which one is better? Neither really, just different, but one would feel better to some people and vice versa.

I know as a manufacturer, and many of my fellow manufacturers have told me as well, that we do not want to "spew out" volumes of data, that would only serve to confuse most (not all) customers, that are already overwhelmed with the number of choices they have out there. Especially considering the fact that we could not, at this point, guarantee that all manufacturers would use the same test equipment, protocols, etc.

One interesting example: for many years we (myself and others) have explained to people that the airspeed along the glidepath of a particular sized canopy, does not have much variance from model to model. That is to say that a 120 square foot model X canopy has approximately (say +/- 3mph at full glide) the same speed as 120 square foot model Y. Turn rate, decent rate, etc vary but airspeed at full glide is about the same. Most people would not believe us! Funny but absolutely true.

It may get to a point in the future wher all manufacturers will agree on a standard system for providing objective data. I personally would love to see it, but I think it will be some time (IMHO) before we can get all manufacturers on board with the idea and implementation.

Blue skies,
Ian Bellis
President
Aerodyne Research Corporation

[crazy 0]

I agree, many relevant parameters are quite difficult do define and measure in a standard way, particularly turns. However, the speeds (vertical and horizontal) at full glide and at the minimum sink point and at the stalling point can easily be provided in standard conditions at different wing loadings (no need to be accurate to 0.1%). For most paragliders this kind of info is available:

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- Wing loading during test: 3.15kg/m2 (for 27.55m2 and 87-8 kg)
- Max speed hands high (trim speed): 36km/h
- Max speed accelerated: 48km/h stabilised.
- Max glide: 7.9 (Sink rate 1.19m/s at 34.3km/h)
- Min Sink rate: 1.1m/s (glide angle 7.3 at 29km/h)
- Stall Point: 23km/h
(Measurements taken at 1000m ASL, with Skywatch Pro and Flytec 4030 GPS.
Access. Logiciel (Logisky) Flychart pro 4.0)

And i guess that this info is also available for the paragliders that you manufacture, right? Anyway, paragliders want to know this information; many of them wouldn't consider buying a canopy without knowing these characteristics.

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My personal experience is that most canopy pilots are not that interested in the degrees per second or bank angle generated, but more in how the canopy "feels" to fly.

You're right, most skydivers would say "demo". Now, take two average skydivers, let them demo two canopies and ask them to compare them, you'll likely get two very different answers, sometimes contradictory. Looks that how the canopy feels to fly is a very subjective thing. It's not surprising because when we fly a canopy we are really overloaded with inaccurate data.
This illustrates subjectivity quite well:

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One interesting example: for many years we (myself and others) have explained to people that the airspeed along the glidepath of a particular sized canopy, does not have much variance from model to model. That is to say that a 120 square foot model X canopy has approximately (say +/- 3mph at full glide) the same speed as 120 square foot model Y. Turn rate, decent rate, etc vary but airspeed at full glide is about the same. Most people would not believe us! Funny but absolutely true.

You're absolutely right, there are still many people believing that a stiletto 120 is way faster than a sabre 120.

Now, even though the airspeed at full glide doesn't change so much, it is still interesting to know which one is faster, which one is slower. It is even more interesting to know the vertical speeds (there there are significant differences) and the stalling point.

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It may get to a point in the future wher all manufacturers will agree on a standard system for providing objective data. I personally would love to see it, but I think it will be some time (IMHO) before we can get all manufacturers on board with the idea and implementation.

Maybe you could show the way to your competitors
Objective data is way cheaper and way more convenient than demo programs. In addition, without objective data, the skydiving community definitely misses a classification of canopies.
Objective data increased significantly the safety and the level of understanding in the paragliding community. Given the increasing number of landing injuries and fatalities among skydivers, it might be time to make the same move.

--
Come
Skydive Asia

[ZigZag 0]

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Remember in all of this we are getting into the danger of "data overload" as well.

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thank you for engaging in this discussion. I find it extremely informative and has compelled me to look at the literature in my library from a different perspective.
The problem with "data overload" might be attributed to a lack of understanding how to interpret the information given and how individuals can apply the data to specific situations. On the other hand there is no substitute for real experience, in other words jumping a canopy and putting it through its paces. Here are some performance parameters that I would like to see.
1. Forward speed in full flight, various brakes.
Alltough the speed difference for similar sized canopies may not be that great, they vary for different sizes and designs and most people that buy a new canopy do so with the intent on downsizing from a student canopy or a canopy that no longer provides the thrill and excitement. This parameter would provide a useful gauge before a purchase or demo. An additional concern is the ability of certain airfoils to remain stable and inflated at slow forward speeds(true air speed, not relative to the ground), as with designs that have partially closed leading edges. They still rely on the ram-air principle.
2. Descent rates.
Historically this/these value(s) were and still are of primary importance to round canopies as you cannot flare them and survivability on landing is the issue. Quoting from note 1. in a letter from the Department Of The Air Force (published in the PIA's Para Newsbrief dated Oct. 1994 Volume 94-4), that released the test results of some 35 canopy designs for a bailout rig: "The uncontrolled vertical velocity is important because the probability of a landing injury increases directly with the vertical velocity. "Uncontrolled" implies the most novice jumper (or even incapacitated).".
This parameter does apply to airfoils as well. Of further significance to modern airfoils is the ability to slow them down in a tight spot by applying brakes with a resultant change in vertical velocity. To me that would be some useful information.

I went through some old manuals published by Paraflite in the late 80's and thought it interesting that they made the effort to publish performance specifications for all their canopies.
Generally they referred to Rate of Descent, Forward Speed and Turn Rates at various control line inputs.

To be fair, I've done my share of studying the manuals for modern canopies and find much useful information, in some cases quite extensive. Neither can I fault the manuals for the warnings and explanation of risk that any given individual accepts by participating in this sport.
Acceleration during control input and recovery arcs are indeed very difficult to quantify and may remain subjective parameters for a long time to come. These two parameters will vex our collective psyche as we continue to witness bad decisions under a "perfectly good canopy".
In some respects I am warming to the idea of a "Planform Factor". It could be argued that "ellipticity" does give indication of how radical a canopy will be, now that I have acquired a bit more insight. But other easily quantifiable parameters should be included. It is a more complete picture I would like to see.