What are possible standards for measuring sqf of a HP canopy?

[Falko 0]

I'm trying to collect all possible measurement "standards" of how to measure the square footage of a high performance elliptical canopy.

So if both manufacturers and riggers would answer here about the different ways they measure, that'd be great!

What I've found so far:

1) On the PIA website I found the old TS-104 document (from 1987) which describes measuring a rectangular canopy.

2) The FAQ on the PD website says:

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How do manufacturers calculate the sq. footage of a canopy?
There are several methods used. We take the length of the rib from the tip of the nose to tip of tail in a straight line. We then measure the width of all the cells across the bottom skins. Multiplying the two gives us the wing area. This is slightly different from the official PIA method, which differs only in that the width of all the cells is measured across the top surfaces 6" behind the nose, before multipying by the length. (Our canopies measure slightly larger using this method.) Other manufacturers may use an estimated inflated shape, which yields a measurement similar to our method. At least one manufacturer measures the total area of the top surface. Our canopies would measure huge using this method. There are advantages and disadvantages to each method. For example, the total top surface method would result in a canopy packing very small for its advertised size, and would infact be smaller when inflated than the same advertised size coming from most other manufacturers. None of this was done intentionally to confuse people, it was just that in the beginning of ram air parachutes, each manufacturer did what made sense to them. In reality, the most important thing is how "big" the canopy flies and lands.
There are no manufacturers that add up the top and bottom areas, or the total fabric used.

3) Aerodyne offers a document worth reading about the Planform factor, but doesn't tell how exactly the sqf is measured on Aerodyne canopies. I will email them these days.

Question to the riggers: What else is possible, and what's your preference and why?
Any info is appreciated!

PS:
I also found a few old threads which deal with the topic but didn't help me much:
Anyone actually measured a Safire? (Oct 11, 2001)
"True" Canopy Area (Apr 3, 2002)
How to measure a canopy? (Feb 13, 2003)

Ich betrachte die Religion als Krankheit, als Quelle unnennbaren Elends für die menschliche Rasse.
(Bertrand Russell, engl. Philosoph, 1872-1970)

[FrogNog 1]

* You could inflate the canopy at a specified loading-speed in a wind tunnel (i.e. at the speed it would glide with either brakes set or full flight with a specific weight under it) and find the area of its true shadow.

* You could do the same wind-tunnel thing and identify the left or right angle from vertical of the normal vector of the topskin at every point, and use the cosine of this value as a "lift factor"; multiply the lift factor by every area of the actual topskin size. This would attempt to address canopies with more "cell bulge" flying smaller than canopies with more rigid shapes.

Of course, not every part of the chord from nose to tail produces lift at all, so this measurement method still contains misleading assumptions when producing a size number. (Specifically, it assumes that a 150 sq ft canopy has 150 sq ft of topskin or effective topskin that is producing lift.)

-=-=-=-=-
Pull.

[Professor 0]

I believe Performance Variable (of Germany) use the inflated area of the canopy, to measure their canopies. A demon 110 demo I had a while ago was noticably bigger than my stiletto 120.

Ted
Like a giddy school girl.

[mr2mk1g 10]

two of the differences I know of are:

1: top skin measurement vs. bottom skin measurement.
2: projected area vs. planform area

See this post for a pretty concise explanation: http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=161421#161421

[riggerrob 558]

Sandy Reid used to measure new canopies for PIA.
PIA's methods worked great for rectangular canopies, but got to labor-intensive on tapered canopies.
Para-Flite and PISA used PIA's method, however when PISA was absorbed by Aerodyne, they switched to a method similar to PD, ergo Aerodyne insists that their Solo 270 has the same surface area as PISA's Skymaster 290.
To further muddy the waters, Icarus switched from PIA's method to PD's method in 2001.
Don't waste your time asking Atair: "We just ask the computer!"

[Falko 0]

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Para-Flite and PISA used PIA's method, however when PISA was absorbed by Aerodyne, they switched to a method similar to PD, ergo Aerodyne insists that their Solo 270 has the same surface area as PISA's Skymaster 290.

Sounds logical to me, since PIA measures span at the top skin vs PD measuring span at the bottom skin.

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To further muddy the waters, Icarus switched from PIA's method to PD's method in 2001.

In response to my request on the Icarus Website I received a call yesterday from Martin in Barcelona, briefly describing the measuring method of Icarus. It sounded similar as what is described on the PD Homepage. (mean chord multiplied with span of bottom skin)

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Don't waste your time asking Atair: "We just ask the computer!"

Duh! Well, I sent cobaltdan a PM yesterday with a link to this thread. Maybe he'll chime in...

Ich betrachte die Religion als Krankheit, als Quelle unnennbaren Elends für die menschliche Rasse.
(Bertrand Russell, engl. Philosoph, 1872-1970)

[aubsmell 0]

Aerodyne uses the “Bottom Skin” Method.

The PIA use the Span of the Top Skin
We use the Span of the Bottom Skin

The PIA measures the Span of the Top Skin 6” back from the
This is not the Max Span or the Min Span.

Using the Bottom skin Span measurement represents an exact value, In Aerodynes case this is the Maximum Span. The PIA method does not take the new designs of canopy into account.

BTW this is the way I understand it from our Tech Dirctor, I won't comment on other methods or techniques, everyone has an opinion as to what is best and why.

You have to understand that also, some companies with some models use numbers like names in marketing as well. To be a bit generic what I mean is this:

A company may have a canopy: the "X Warrior 300" may and it may actually only measure out to 293 or it may be 317 but they decide on the name 300 because of it's marketing value. So when you are busting out your calculator to get your wing loading down to the ninth decimal point, you may have no idea what you are talking about.

I have to admit that I didn't read all the above posts, I just clicked in from your PM and posted.

Regards.

Aubrey

"Those who say it cannot be done, should not interrupt those who are doing it"

[Falko 0]

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So when you are busting out your calculator to get your wing loading down to the ninth decimal point, you may have no idea what you are talking about.

... that's what I'm trying to show with this thread.

Thanks a lot for the info!

Ich betrachte die Religion als Krankheit, als Quelle unnennbaren Elends für die menschliche Rasse.
(Bertrand Russell, engl. Philosoph, 1872-1970)

[mattjw916 2]

...and when you are done, can you solve that whole mid-east peace thing, they need a bit of help over there too.

NSCR-2376, SCR-15080

[Falko 0]

Thanks for the constructive input. We need more one-liners like that in Gear&Rigging, really helps put things into perspective

Ich betrachte die Religion als Krankheit, als Quelle unnennbaren Elends für die menschliche Rasse.
(Bertrand Russell, engl. Philosoph, 1872-1970)

[Zoter 0]

Would be nice for some kind soul to actually put something together for all the 'modern' canopies as a comparison ...
I dont care what method is used as long as its used the same way across all the canopies so at least its comparable
I saw the PIA one....but its a little dated now I think....
What have the canopy manufactuers got to hide here by not all subscibing to a uniform measurement system..??

[mattjw916 2]

A couple of points, this has been tried over and over again. No one seems inclined to alter their methods. Secondly, does it really matter??? Take two canopies, both "semi-elliptical" 9 cells, one is a 148 using one method and one is a 150 using another. Which one is "faster" or "higher-performance"? This is a largely subjective impression based on the degree of taper in the wing, the trim of the canopy in full flight, and the physical amount of fabric overhead. Even riser length can significantly affect recovery arc length, etc.

Some people, especially on this forum, seem obsessed with hundredths of a point in wingloading as was alluded to earlier in the thread, i.e if you have 100 jumps and fly a canopy loaded at 1.09 you are "safe" and if you load at 1.12 you are "dangerous". I would hazard to guess that most people cannot feel such minute changes in loading hence differences in measuring methods are really not of critical importance. The only way to prove or disprove that would be some ludicrous double-blind experiment.

That said, demoing and coaching should lead people to the correct size canopy for them, not high-precision mathematical equations or marketing hype.

That's just my opinion (subject to revision at any time) and I didn't even stay at a Holiday Inn Express last night... so flame on...

NSCR-2376, SCR-15080

[Falko 0]

I totally agree and just for the record: We're on the same side, what you write is my point exactly. Seems you read some "intention" of mine into the subject line that is not there? I am NOT trying to have mfgs alter their measuring methods or pushing a dead discussion. Just learning here.

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I would hazard to guess that most people cannot feel such minute changes in loading hence differences in measuring methods are really not of critical importance.

How do you know when you don't know in which way these methods differ? From what I've learned these differences may result in 10%-20% (or even more?) of size difference, resulting in WL value that has no significance.

Would like to paste a part of a recent email conversation with John LeBlanc that does fit in here. I asked him a few detailled question regarding their measuring methods & why's. A quote of my answer:
Now there's 2 things bothering me about the whole WL regulation discussion:
1) One calculation base of WL is square footage, but noone seems to be interested in where that value comes from and what it actually describes. People compare apples and oranges from different manufacturers here but still get hysterical about WL differences in the 0.1 range!
2) Noone talks about the other factors that determine responsiveness/agility etc of a canopy, like ellipticity, line trim etc.


That's my subject, and this thread is about point 1)

Ich betrachte die Religion als Krankheit, als Quelle unnennbaren Elends für die menschliche Rasse.
(Bertrand Russell, engl. Philosoph, 1872-1970)

[Falko 0]

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Would be nice for some kind soul to actually put something together for all the 'modern' canopies as a comparison ...

I've played with that thought. That is of course not putting that together (impossible for a single person) but inviting people to measure their canopies by the same standard. It would have to be a joint effort and it must be easy to accomplish. The compromise is having a fool-proof way of measuring while getting exact values that describe something meaningful. The more detailed you'd get, the more useful the values would be. But more detailed also means less fool-proof.

Anyway, without detailed manufacturers input I suspect the measured values could be moot.

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What have the canopy manufactuers got to hide here by not all subscibing to a uniform measurement system..??

Don't think they have anything to hide. I think it's just different philosophies, different technical backgrounds and design histories. No conspiracy there.

Ich betrachte die Religion als Krankheit, als Quelle unnennbaren Elends für die menschliche Rasse.
(Bertrand Russell, engl. Philosoph, 1872-1970)

[phoenixlpr 0]

What is the sqf of a HP canopy ?

Do you mean area? What kind of area?

What is a HP canopy by definition?

[Falko 0]

>What is the sqf of a HP canopy ?
>Do you mean area?

Yes, Planform area or Projected area as defined in this document:
PIA TS100 - Standardized Nomenclature for Ram-Air Inflated Gliding Parachutes

>What kind of area?

Depends on the measuring method. I've learned about quite a few different ones now. For example Paratec Germany measures both top and bottom area and calculates the square footage by using a relation of 2 (top) to 1 (bottom) to describe the "effective area". Thus they account for the amount of lift that is generated by each side of the parachute. I remember some aerodynamics class where the rule of thumb was "the top of an airfoil creates 2/3 of the lift, the bottom of an airfoil creates 1/3 of the lift" (aviators correct me there?).

Simple example: 100sqf top, 90 sqf bottom = (2x100 + 1x90) / 3 = 96,7sqf

They also measure the projected area instead of the planform area, thus coming closer to describing the "effective surface" rather than the size of the fabric. I've never seen any numbers but it makes sense to me.

edit: hp statement deleted

Ich betrachte die Religion als Krankheit, als Quelle unnennbaren Elends für die menschliche Rasse.
(Bertrand Russell, engl. Philosoph, 1872-1970)

[phoenixlpr 0]

Sorry. Those were not real questions.

Its hard to make a standard if there are any answer like "it depends".

I don't know why the term of wing area is so simple in aviation.

AFAK Spectre is not rectangular.

[Falko 0]

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Sorry. Those were not real questions.

Well I was tempted for a second to just answer "are you kidding me" but then I remembered that we need to be "nice" in the forums and answer questions to the best of our knowledge so the moderators don't have to chew our asses...

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Its hard to make a standard if there are any answer like "it depends".

Agreed, but learning from the mfgs about the different standards and why they use them can't be bad. At least it gives food for thought the next time someone get's bashed for having a 1.4 instead of 1.3 wingloading.

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AFAK Spectre is not rectangular.

Uh well, yes it's slightly tapered.
I own a Spectre150 as a second canopy and it does look () rectangular from below. Since I never actually measured it (har har ) I didn't know it was tapered until I read the ad just now.

Ich betrachte die Religion als Krankheit, als Quelle unnennbaren Elends für die menschliche Rasse.
(Bertrand Russell, engl. Philosoph, 1872-1970)

[phoenixlpr 0]

I'm still surprised why is it so simple to specify the wing area for aircrafts.

[Falko 0]

OK here's a few quotes from emails I received from John at Performance Designs. I asked a few detail questions on their measuring method. But the most interesting is part 2 where he goes on about the factors that make up the performance of a canopy.

Published with permission, his one concern is that the context not be lost so I haven't cut out anything.

John LeBlanc on the measuring methods of PD canopies:

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Thanks for your inquiry. For question 1, we measure the chord of each rib when determining area. On question 2, we measure the width (span) of each cell individually, as many of our designs have varying cell widths in a single canopy. I have heard from an Icarus representative that they do measure using our method, as they consider it to be the real "industry standard." However, I was told by that same representative that the Icarus canopies build by Precision (in the early days of the company) were sized using the Precision method, which results in a much smaller canopy and pack volume that the number may indicate. I am not sure how Aerodyne measures.

When you measure your canopies, keep in mind that the sewing of the seams tend to shrink the material somewhat. This may make a 1-2 foot difference in the total area measured.

and more detail:

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We measure the span between the bottom seams perpendicular to both. This assumes that the bottom surface edges are parallel, which they are on virtually all canopies. (We do have three obscure old canopies of ours that do not have parallel bottom surface edges.) I would suggest measuring halfway between the A and B lines on the longest of the two ribs you're measuring between, and go perpendicular outboard to the adjacent rib wherever that ends up. It really shouldn't matter, as I know of only one manufacturer who has any taper in the bottoms of their canopies, and its not much.

The PIA method says six inches behind the leading edge of the top skin, which means that you would be measuring span progressively slanted on on all the canopies with a leading edge taper. Pretty wierd. (ALL of our tapered/elliptical/semi-elliptical canopies have at least some taper on the leading edge, even the Spectre and the tandems.)

May I say that a detailled answer like that is great customer service!

John LeBlanc on the factors that make up the performance of a canopy:

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There are several things that make up the performance of a canopy, area being only one of them. The aspect ratio, planform, airfoil shape, and trim are the biggies. Airfoil shape is huge, and we've tried hundreds of them in different R&D canopies. the permutations are unbelieveable! Let me take an example outside of our sport:

I know of two high performance homebuilt aircraft that both carry the same two passengers and fuel load behind the same engine. I really love them both. They both cruise at an honest 240 mph, and land at about 70mph. One of them has 84 square feet of wing area and the other has 104 square feet, even though both weigh very close to the same amount. In all my time around the homebuilt movement, I have not heard one pilot/builder/designer ever attempt lay claim that the performance of one over the other based purely on wingarea.
To isolate wing area out from the rest as being the one all important thing, would seem very silly to the designers of these beautiful machines. They know that their beautiful machines are so much more than just wingarea, which is only important in the context of the other parameters. In this particular instance, the plane with the larger wing has a fairly low drag and high speed airfoil, which needs to be balanced by the larger wing.
The other plane has a pretty high lift airfoil which has more drag than is typical, but this is balanced by a smaller than normal wing.

I am not trying to minimize wing loading as being important for parachutes, as it is a huge thing. But the comparisons being attempted in our sport are pretty anal, compared to just getting a demo of a reasonable size, putting the thing on, and seeing what you think. Do I make sense?

So bottom line is that you have the wing area number to compare to other canopies of the same manufacturer. Comparing to other brands will result in different performance qualities for a similar advertised size. These differences may include more or less speed at the top end or bottom end of the speed range. In some cases you may get more at both ends.
Some of these differences, and others, may come from the different measuring methods, or perhaps other design aspects. You may find that one canopy "feels" smaller, possibly because it seems to not slow down as well as you expect, or perhaps it feels faster at the top end. Either way, it may be because a different inflated shape of the airfoil, or how efficient the canopy is, or what the designer was trying to emphasize, or maybe it shrinks a bit more spanwise when it inflates due to some reason, or perhaps it actually is measured differently. But does it really matter to you once you've made the comparison and you know what the differences are? Can any comparison really be made about performance that doesn't include flying them canopies in question?

Sorry for the long rant, but I hope my views from a design perspective helps.

John

... the do indeed. Thanks a lot

Ich betrachte die Religion als Krankheit, als Quelle unnennbaren Elends für die menschliche Rasse.
(Bertrand Russell, engl. Philosoph, 1872-1970)

[mjosparky 3]

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I'm still surprised why is it so simple to specify the wing area for aircrafts.

One is made of fabric and thread, it will stretch and distort to some degree when inflated. It has to be measured while on the ground not inflated.

An a/c wing is hare and ridged and has the same shape on the ground as in the air. It’s that simple.

Sparky

My idea of a fair fight is clubbing baby seals

[phoenixlpr 0]

Even an airfoil can be modelled with a computer system.
It should not be a problem.

[mjosparky 3]

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Even an airfoil can be modelled with a computer system.
It should not be a problem.

Ram Air canopies and airplane wings are airfoils.

Tell it to John Lablanc and others that design and manufacture canopies.

Sparky

My idea of a fair fight is clubbing baby seals

[phoenixlpr 0]

Thanks for your support .