Definition of 'Slightly Elliptical'

[regulator 0]

So I've been hearing alot of canopy manufacturers have been touting the 'slightly elliptical' design for some while. My question is this...In my humble opinion slightly elliptical means the shape of the wing itself is slightly curved more than an actual rectangular shape. But why is it that many of these canopies have more fabric covering the inlets of the cells? Does this factor into the 'slightly elliptical' definition as well? I know when I look at a pic of a Sabre 2 there isn't any fabric covering the inlets of the cells. Does this help with the flight characteristics? I just wanted some clarification because this has been bugging me for a while.

[AggieDave 6]

Slightly elliptical and tapered, you'll hear both of those terms quite a bit.

Typically when a manufacture uses "slightly" then they're talking about the rear edge of the canopy, instead of the leading edge. As opposed to elliptical canopies where the leading and trailing edge aren't square.

As for the formed nose of the canopy. That has nothing to do with being an elliptical. The reason why you see it on some elliptical canopies is that most elliptical canopies are higher performance canopies and the covered nose is also on higher performance canopies.

Clear as mud?

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

[regulator 0]

OK I get it...they are two entirely different animals. But then what gain do you have by covering part of the cell openings...does it make the canopy fly faster or more responsive...or both?

[AggieDave 6]

Quote

does it make the canopy fly faster or more responsive...or both

Yes and no and yes and a little no.

The higher performance canopies typically have a longer recovery arc, they are "faster" but some of that is from a higher wingloading. They are more responsive, but its not just a function of having a covered nose. The quick and dirty answer is that an elliptical canopy turns more sharply then a "square" canopy. Some people consider that more responsive.

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

[Gene03 0]

Quote

OK I get it...they are two entirely different animals. But then what gain do you have by covering part of the cell openings...does it make the canopy fly faster or more responsive...or both?

The nose baffles are there so the opening doesn't put your dick in your watch pocket.

“The only fool bigger than the person who knows it all is the person who argues with him.

Stanislaw Jerzy Lec quotes (Polish writer, poet and satirist 1906-1966)

[regulator 0]

I do that all the time. Oh wait doesn't everyone have a dickwatch?

[pilotdave 0]

I think terms like elliptical, slightly elliptical, semi-elliptical, tapered, etc. are more descriptive of the performance of the canopy than the shape of the canopy. They're basically marketing terms. A canopy described as slightly elliptical is probably not as fast and responsive as a "fully elliptical" canopy, regardless of their actual shapes. Of course the ultimate canopy is the super elliptical, or "round" canopy. Only used by expert jumpers.

Dave

[billvon 3,110]

> But why is it that many of these canopies have more fabric covering
>the inlets of the cells?

The two are not all that related. Inlet design has a lot to do with opening speed, canopy stability, efficiency (and thus glide angle) etc. "Slightly elliptical" "tapered" "moderately elliptical" etc don't mean all that much, other than the canopy isn't completely rectangular. Most canopies out there are slightly elliptical.

[regulator 0]

I have had enough of 'rounds' to last a lifetime. I was in the army and I have 17 jumps on round canopies. They suck donkey balls and PLF is the only option for landing these POS's. I was completely stoked the first time I landed a Ram Air canopy and understood what a difference it was to flair!

[d123 4]

from the theoretical point of view:
Semantics. One manufacturer use semi-elliptical/slightly elliptical the other one use slightly tapper. One says elliptical the other one says highly tapper. Aerodyne tried to introduce planform factor to describe how elliptical a wing is but it didn't click because some characteristics are depending on how elliptical the LE is and other on TE.

John LeBlanc from PD has a pretty nice explanation of what is elliptical and how it f*X*s you up if you're not ready for it.

I've never knew that Stiletto and Sabre1 share the same Airfoil, trim and almost aspect ratio until I've read this paper. clicky

from the practice point of view:
I would stick with manufacturer recommendation for each canopy and build the necessary experience before going *elliptical*.

Lock, Dock and Two Smoking Barrelrolls!

[hackish 8]

Since an elliptical canopy is more efficient, I expect it will fly faster than the same square footage that is perfectly square. If so then I would expect smaller openings on the nose would be needed to maintain canopy pressurisation. With smaller openings the wing should be more efficient with less drag.

I don't really know, just making an educated guess.

-Michael

[pilotdave 0]

Everything else being equal, maybe. But theres obviously a lot more to canopy design than planform. Elliptical wings, on airplanes, produce an elliptical lift distribution across the wing. Lift at the wingtips is basically reduced to nothing (on a purely elliptical wing), which reduces induced drag. Tapered wings basically have the same affect but are easier to produce. That's why they're so common and elliptical wings have rarely been used at all.

I'm only guessing, but I'd think for a canopy that induced drag is small compared to parasite drag. And how much is induced drag really reduced?

"Elliptical" canopies are going to have a lot more features that make them faster and more responsive than the shape of the wing as seen from above. The trim, the wing thickness, etc, etc, etc. Those are going to have far more effect, I'm guessing, than the fact that the wing is elliptical or tapered or whatever.

Dave

[riggerrob 643]

Now you are getting close.
Nose openings are completely separate from "elliptical."

Different sized nose openings can be tailored to change openings and the top speed.

For example, if you want fast openings, make large nose openings, like reserves.
Similarly, if you want a canopy to re-inflate quickly after a stall, then sew in huge - underhung - nose openings like Para-Foils.
BASE canopies even use extra bottom skin vents to scoop more air and speed openings.

However, large nose openings can be a disadvantage at the top end of the speed range. At terminal velocities, large nose openings can scoop too much air and create hard openings. That is why Sabre 1 started with over-hung top skin, that reduces the size of nose openings. Crossfire carries tiny nose openings to an extreme, by over-lapping the top and bottom skins.

There is a second motivation for tiny nose openings. At faster canopy speeds (eg. screaming around that last corner into the pond swooping gates) large nose openings can scoop too much air. When that excess (to opening and canopy pressurization) air starts backing out the nose, it disrupts airflow and increases drag.
To that end, some paragliders even use mesh across the nose to reduce the amount of air allowed to enter the nose.

[riggerrob 643]

"Elliptical" or "tapered" canopies have two motivations.
The first is to flatten the glide and the second relates to handling.

By tapering the wing tips/end cells, you create smaller wing tip vortices. Smaller wing tip vortices produce less induced drag, which results in a flatter glide.

The other issue is handling (distinct from performance).
Smaller end cells have less resistance to rolling, so they turn faster.
The other reason for tapering end cells is that smaller end cells require less muscle to pull down.
For example, most modern student canopies (Navigator, Solo, etc.) have tapered end cells to reduce the amount of muscle required to flare, so students are less tired by the time they reach the ground.

[erdnarob 1]

AS PD people mentioned it, there are not really any elliptical canopies but we should rather use the expression "tapered" because this is what they are. Then there is several types:
1) half tapered: generally the front of the canopy (starting at the 2nd cell from the edge) becomes tapered or has the chord decreasing while the tail stays straight (ex. the Sabre 2)
2) fully tapered: the front and the rear of the canopy are tapered (starting from the 2nd cell from the edge) ex. the Katana, the Nitro, the Nitron...

NOTE.
1) Some canopy are slightly tapered which mean the difference between the chord at the end cell and the middle cell is not important (3-5 inches).Highly tapered canopies have a more important difference (1-3 feet)
2) Some fully tapered canopies are more tapered at the front than at the rear while other are more tapered at the rear than at the front.
3) the Sabre 2 has some material covering the nose but the Crossfire has more material covering the nose

The taper or "ellipticality" of a canopy has nothing to do with the amount of material covering the nose but has to do with its geometrical shape only

Have a look at the 2 drawings included in attachment (sorry but the text is in French) this is the shape and attachment points (line junctions) of the Nitro 150 and the Katana 170.

Learn from others mistakes, you will never live long enough to make them all.

[d123 4]

define efficient
Smaller sizes with the same weight underneath, flies faster because they are *less* efficient. They need more speed to generate the same lift (your weight). A more efficient wing, for the same weight, will fly slower.

I think that decreasing the drag affects more the glide ratio (L/D) and less the speed. Same thing with the collapsible PC. You shouldn't go faster just flatter.

Lock, Dock and Two Smoking Barrelrolls!

[billvon 3,110]

>Since an elliptical canopy is more efficient, I expect it will fly faster than
>the same square footage that is perfectly square.

All things being equal, often efficiency translates to a better L/D (which translates to better glide) rather than higher speed. But speed is so dependent on trim angle, chord etc etc that it's hard to draw any firm conclusions.

>If so then I would expect smaller openings on the nose would be needed to
>maintain canopy pressurisation.

In steady flight you only need a large enough opening to compensate for leakage out of the canopy; most canopies have nose openings far, far in excess of what you need to make up for losses through the canopy (i.e. holes from the sewing process.)

[regulator 0]

Thanks to all that posted regarding this issue. You have now educated me on this and I know the difference now.

I appreciate it

Paul

[SethInMI 174]

That article by John LeBlanc was a great read. He basically has a whole canopy course in that 13 pages. I was inspired to do a comparison of two canopies, a Pulse and a Katana from data on PD's website.

Using a cad program, I created shapes from the chord (length) and span (width) off the website for the both canopies, and while holding the span and chord (for the Katana both chord measurements) to the published numbers, I adjusted both shapes until the cad program said they were 120 sq ft in area. I barely had to tweak the Pulse shape.

Pulse 120
Chord: 6.81ft
Span : 17.65ft
Katana 120
Chord:7.14/4.86ft
Span: 18.13ft

So you can see from the numbers above and the pic that the Katana is longer and fatter for the exact same square footage. I always had this idea that ellipticals were both longer and skinnier that squares, but that is not the case.

It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".

[d123 4]

Glad you've like it. We should have more articles like that one !

Shouldn't Pulse have a more tapper shaped? clicky

Lock, Dock and Two Smoking Barrelrolls!

[SethInMI 174]

Hmm. Well if that shape is correct, and the span and chord for a Pulse 120 are correct in the PD website, then a Pulse 120 would actually have a little less than 120 sq ft of surface area.

I think the picture i created is still valid, basically showing how the span and chord for a Katana varies from a Pulse by being "fatter" and "longer" but coming out with roughly the same square footage.

It's flare not flair, brakes not breaks, bridle not bridal, "could NOT care less" not "could care less".