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Definition Square elliptical?

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Any policy on what defines a airfoil as square or elliptical?
Is it up to the manufacturer to decide, seeing that nobody wants to market square canopies, semi-elliptical sounds so much cooler..
On aspect ratio: at what aspect ratio does a square become semi-elliptical, and where does a semi-elliptical become a square?

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Square = a rectangle, it either is or it isnt. The only currently sold square sports canopy off the top off my head is a triathlon.Where it gets more arbitrary is the difference between semi-elliptical and elliptical, this sometimes refers more to the performance rather that the shape of a particular model.

ciel bleu,
Saskia

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If we want to be exact there are no elliptical parachutes but there are tapered parachutes (or semi tapered).

On a so called fully "elliptical" parachute, generally there are 5 cells in the middle having the same chord length then the 2 ends cells each side are tapered which means their chord length decreases.
For instance on my Katana 170 which is a fully tapered canopy the chord of the middle cell is 8.50 ft while the chord of the ouside cells is 5.78 ft which almost 3 ft less that the middle one. Moreover a fully tapered canopy is tapered on the leading edge and on the tail. Have a look at the sketches I made of a Katana and a Nitro showing the line attachment points (38 on the Katana and 36 on the Nitro).
Note. Some canopy are sligthly elliptical or tapered while other (the Katana) are highly elliptical or tapered.
1) sketch 1 the Katana (black dots are the 38 line attachment points and in green the secondary steering line attachment points (4 each side)).
2) sketch 2 the Nitro ( black dots are the 36 line attachment points and in green the secondary steering line attachment points (4 each side)). I hope that answers your question.
Learn from others mistakes, you will never live long enough to make them all.

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I will bite on this one.... Keep in mind I know next to nothing about canopies but I have a great deal of knowledge about flight in general...

Square is just that.. square.. right angle ends..

Elliptical is sort of a tapered end, where the end cells have a shorter chord than the middle cells, giving it a rounded off appearance from the top down view. These are generally much more maneuverable...

An example is the ww2 spitfire with an elliptical wing, and the german FW190 with a square wing. (The fw190 is tapered at the end, but not elliptical)
Also the eliptical canopy is PROBABLY not near as rounded off as my example of the spitfire..
There is a trade off though.. more agile, but a higher stall speed.

My example used are aircraft wings, which probably are completely different, but I hope I gave you a general idea..

I welcome others to correct any misinformation.
Millions of my potential children died on your daughters' face last night.

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an elliptical canopy has the leading and trailing edge dimensions the same. As Rob said, the center cell longest then tapering off towards the edges, but the same dimensions front and back. A semi- elliptical may have a straight leading edge and a tapered tail.

"An ellipse is a smooth closed curve which is symmetric about its center."

if the leading edge is tapered differently to the trailing edge it is elliptical like, or semi-elliptical, but a truly elliptical design has (by definition) to be the same front and back.
Pete Draper,

Just because my life plan is written on the back of a Hooter's Napkin, it's still a life plan.... right?

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Cheers Sid..
A person with 80 jumps, loads a wing, 1:1...we reccomend that he jump a square desighn.
Is'nt there more variables in the equation to what canopies are suited for beginners than just the aspect ratio of the canopy?
eg. trim, handeling of terbulance..

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Trim is a big issue when chosing canopies for junior jumpers.
For example, Solo 270 is trimmed very flat and has a short recovery arch. Which means that students can do toggle hook turns ridiculously low to the ground and - most of the time - still have a canopy over head for touch-down.
If you try to same toggle hook turn with a Katana (long recovery arch) the canopy will still be diving hundreds fo feet after the Solo planed out and you meet lots of ambulance drivers, nurses, orthopedic surgeons, etc.

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Trim for sure is very important for the canopy behavior. Here is a comparative study I made for some common canopies (in attachment). You can see that the Katana has the highest "pitch or depression" angle with 18 degrees while the Nitro has the lowest angle with about 13 degrees. That's why the Katana has a long recovery arc I guess and is a "diver" as well (ground hungry). The Nitro would be a "glider".
In my study I associate the triangle ADF to a right triangle, this approximation makes the calculation easier. Since I use the same method for all canopies that gives a comparison for the concerned angle.
This is very easy to do.
When somebody lands, I measure the length AD with tension on the stitch (on the same cell stitch in the middle) and using the same attachment points (A and D) with tension on the lines this time I measure the difference in length of the 2 lines and that's it. The rest is made by the formula.
Learn from others mistakes, you will never live long enough to make them all.

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A fully tapered (elliptical) canopy is reacting and turning faster than a rectangular canopy (just like the SPITFIRE airplane was more agile than the german Messerschmitt in dogfight during the WWII) this is why a beginner doesn't start with a fully "elliptical" one. Half sligthly tapered like the Sabre 2 or the Safire 2 are often use for intermediate student. Tapered canopies also open in a softer way than rectangular ones.
Learn from others mistakes, you will never live long enough to make them all.

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Quote


if the leading edge is tapered differently to the trailing edge it is elliptical like, or semi-elliptical, but a truly elliptical design has (by definition) to be the same front and back.



It's a marketting term. Any non-rectangular canopy (tapered or curved on leading and/or trailing edge) that meets market expectations regarding canopy responsiveness to control input is elliptical.

Non-squares with less aggressive handling characteristics are tapered or semi-elliptical according to their makers.

Brian Germain defines "Fully Elliptical" as a canopy with more than 20% of taper which I'd assume means the difference between center and tip chord. Such canopies are forbidden to skydivers with fewer than 300 jumps and add one size to the smallest recomended and allowed canopies.

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Thanks for the details: Just for the benefit of the readers:
Then my Katana 170 has a chord of 8.50 ft on the middle cell and a chord of 5.78 ft on the end cells. Therefore the percentage of taper is:
(8.50 - 5.78) / 8.50 = 0.32 or 32 % and since it's more than 20% the Katana 170 according Brian Germain is a fully "elliptical" canopy. Remember the pitch angle is 18 degrees (no canopy I have measured have more pitch angle than the Katana even the cross braced ones).
Learn from others mistakes, you will never live long enough to make them all.

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