Canopy measuring methods - different manufacturers

[Quagmirian 40]

Does anybody know what measuring methods all the manufacturers use? Does anyone use the PIA method? Performance designs say on their website that they use the bottom skin by chord measurement, but they don't specify whether this is cut or finished. I emailed Precision asking them about how they measure their wings and they didn't entertain me with an answer. Icarus have switched to PD's method, right? I just thought it would be nice to know how much canopy we are getting from each company.

[JohnSherman 1]

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Does anybody know what measuring methods all the manufacturers use? Does anyone use the PIA method?

The correct engineering method is "inflated plan form".
This entails drawing the canopy in its inflated form and measuring the sq. footage as viewed from above. This shortens the physical span because of the perspective from above foreshortening it. The cord is additionally foreshortened by the attack angle being involved. If the canopy was designed in CAD 3D it is easy to measure the perimeter. However, early canopies were not designed this way 'cause CAD wasn't readily available.
Other methods require different approaches to measuring the cord. If the airfoil is not cambered then it is tip to tip. If it is cambered then it is the “X” or horizontal axis is used.
We use this method (inflated plan form) as it is the way we were taught. It does put us at a slight disadvantage when being compared to canopies from other manufacturers as our canopies will look smaller.

[pchapman 261]

JohnSherman

We use this method (inflated plan form) as it is the way we were taught. It does put us at a slight disadvantage when being compared to canopies from other manufacturers as our canopies will look smaller.

So it is projected area, as used more commonly in the paragliding world?

Is that mentioned in Jump Shack info?

Maybe I missed it! In any case, that is a huge, huge change in comparison to how other canopies are measured in skydiving. (e.g., the old debate about PIA vs PD measurrment style).

So the measurement is still based on the physical dimensions of everything stretched out fully (as in a 3-D CAD drawing), but not with aeroelastic effects modelled (ie, spanwise shrinkage as cells inflate), correct?

Using inflated plan form would create a smaller number than other companies have, for the same canopy. So for the same number, a Jump Shack canopy would tend (all else being equal, which it is not) to pack bigger and fly bigger.

Please correct me or clarify as needed!

[sundevil777 93]

pchapman

***
We use this method (inflated plan form) as it is the way we were taught. It does put us at a slight disadvantage when being compared to canopies from other manufacturers as our canopies will look smaller.

So it is projected area, as used more commonly in the paragliding world?

Is that mentioned in Jump Shack info?

Maybe I missed it! In any case, that is a huge, huge change in comparison to how other canopies are measured in skydiving. (e.g., the old debate about PIA vs PD measurrment style).

So the measurement is still based on the physical dimensions of everything stretched out fully (as in a 3-D CAD drawing), but not with aeroelastic effects modelled (ie, spanwise shrinkage as cells inflate), correct?

Using inflated plan form would create a smaller number than other companies have, for the same canopy. So for the same number, a Jump Shack canopy would tend (all else being equal, which it is not) to pack bigger and fly bigger.

Please correct me or clarify as needed!

It would seem that canopy mfgs would want to make it clear how their products compare to the competition. I understand that there might not be easy agreement on which way is "best", or as JS put it, "the way we were taught", but it wouldn't take much effort for a mfg to have info available about how the other methods (maybe 3 methods total?) would change the 'size' of what we buy.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[Quagmirian 40]

So Jumpshack measures by projected area? Doesn't this mean that your canopies will measure tiny, as in several sizes smaller? Won't it also give you very low aspect ratios too?

[RiggerLee 61]

When it inflates and it bulges and the ribs shift and every thing else, all canopies shrink from side to side. You might say that it gives you the true aspect ratio. I'm not sure it's really important. Even in the simplest modeling of this there is another number in there. It's one of the fudge factor coeficents that we use. It basically relates to the eficentcy of the plane form. Basicly it's how close the lift distribution comes to the ideal of an elips. It's like drag or lift coefecents. It just get's absorbed into the fudge numbers. So eaven if you measure things a little weird it all still works out as long as you do it the same way EVERY time.

On the other question What do they care if the numbers compare. No one has ever been perticuarly eager to be compared to there compediters on an even playing field. They just want to be perceived as having some advantage. Example: Clothing. Ask your girl friend how big is a size 8 dress is?

Lee

Lee
[email protected]
www.velocitysportswear.com