Let's talk about ellipticals

[Jessica 0]

I'm pulling this out 'cause I think it's an important subject. I, personally, don't know anything about the difference between squares and ellipticals other than obvious disparity in physical shape.
But why is an elliptical more difficult to fly? Why do some dropzones think it's ok to put students on lightly loaded ellipticals? What exactly are the characteristics of a semi-elliptical, anyway?
I just realized I'm completely ignorant on this, and it bothers me.
Walk a mile in your enemy's shoes. Then you're a mile away and have his shoes.

[PhreeZone 20]

Jess.... Start by looking here, and this one.
I want to touch the sky, I want to fly so high ~ Sonique

[riggerrob 643]

We covered this question a few weeks ago, but here we go again.
"Elliptical" is a fancy term introduced by the guys in marketing.
I have never seen a parachute that matched the geometrical definition of "elliptical." What I have seen are a variety of tapered canopies. Some are tapered only on the leading edge (Swept Wing Jedi). Some are only tapered on the trailing edge (Diablo). Some are tapered on both the leading and trailing edges (most other "elliptical" canopies).
Tapering a canopy does two things. First of all, the smaller end ribs produce smaller wing tip votices, which produce less drag, allowing the canopy to fly faster, or glide flatter at the same forward speed. Jumpers who are smooth on the toggles can translate this extra speed into extra lift and/or a longer turf surf.
Secondly, tapered canopies have smaller end cells that require less muscle to steer and the smaller end cells are easier to drag around the outside of a turn, equalling quicker turns.
A para-glider manufacturer named John Bouchard - from New Hampshire - claims to have built the first tapered canopy in the mid 1980s.
Back in the late 1980s, Parachutes de France introduced the Blue Track series of parachutes. BTs were the first tapered parachutes and the first built from zero porousity fabric. Skydivers soon found out well BTs landed and started the whole down-sizing craze.
Performance Design's "Stiletto" or Air Time's "Jonathan" (sorry, I cannot remember which was first) was the first tapered parachute built in North America.
Stilettos soon developed a reputation for violently spinning openings that caused such nasty line twists that the only cure was cutting away. Funny, most of those problems have disappeared after people learned how to pack neatly and open in stable body positions.
There are dozens of different ways to taper canopies depending upon how you want it to glide, turn and flare. Manufacturers are also experimenting with some sophisticated variations of line trim to further fine tune flying characteristics.
Nowadays, everyone from tandems (most manufacturers), first jump students (PD Navigator), recreational jumpers (too many models to mention) to blade running competitors jump "elliptical" parahcutes.
If you look closely at the steering lines on a Strong SET 400 tandem or PD Navigator student canopy you can see how the steering lines have been de-tuned. Both canopies have a few steering lines sewn to the end cells, but the flare lines are much farther inboard.
Most of the people who are afraid of "elliptical" canopies are afraid of small, heavily-loaded "elliptical" canopies.
Hint, wing loading is far more important than taper in determining how quickly you arrive at the scene of the accident.

[skyhawk 2]

so how would a true eliptical fly ????
(o)(o)

[skymedic 0]

Isn't a paraglider the only "true" eliptical??
marc
"...a mind stretched with new idea's will never regain its shape"

[skyhawk 2]

so it would fly like a paraglider ????
(o)(o)

[freeflir29 0]

"so it would fly like a paraglider ????"
But smaller...."Houston? That place is full of Crack heads and debutantes."- Hank Hill
Clay

[AndyMan 7]

Quote

So it will fly like a paraglider

Sort of. Paragliders have a very slim angle of attack. They're very floaty. This slim angle of attack means that theyll fly very slowly.
Because paragliders fly slowly, they can do very tight turns. Much tighter then elipticals. Elipticals fly faster, but do the turns aren't as tight.
Is there such thing as a "true" eliptical? Perfectly rounded end-cells, etc?
_Am

[PhreeZone 20]

Closest I've seen is the CAD drawings Atair put on here about their new prototype canopy. It is a TOTAL Elliptical. THe end cells form a point almost.
I want to touch the sky, I want to fly so high ~ Sonique

[Geoff 0]

An interesting question (well I think so!) for any aerodynamicists out there - is there any theoretical sense in which a truly geometrically elliptical planform (constant sum of the distances from the edge to each of two foci) would be optimum? - in terms of lowest drag or whatever.
I doubt it simply based on the fact that rigid airplane wings are not even remotely elliptical in shape.
If not, then why did the term elliptical start being used to described tapered planforms? Was it just a fancy-sounding word that bore some resemblance to the planforms being developed?
Any opinions?

[billvon 2,991]

Quote

Tapering a canopy does two things. First of all, the smaller end ribs produce smaller wing tip votices, which produce less drag, allowing the canopy to fly faster, or glide flatter at the same forward speed. Jumpers who are smooth on the toggles can translate this extra speed into extra lift and/or a longer turf surf.
Secondly, tapered canopies have smaller end cells that require less muscle to steer and the smaller end cells are easier to drag around the outside of a turn, equalling quicker turns.

I'm not sure I believe either of those things. At a given weight, with a given wingspan, you're generally going to have to deflect the same mass of air to achieve a given amount of lift, and deflection of air is what causes vortices. While speed greatly affects vortex formation (faster speed = more air, deflected less) I don't think planform has a huge effect.
Also, I think that 99% of the effort needed to deflect the tail is effort working against aerodynamic forces, not effort needed to bend the fabric.
The main reason I think that elliptical canopies are more efficient is that, if you look at the pressures above and below the canopy, the greatest pressure differential is in the center, and the lowest is at the tips. You would have difficulty reducing the chord at the center, due to that high pressure, but it's easy to do at the wingtips because the pressure differential is less. Smaller wingtips = less drag, and a more efficient canopy. Also, since you change a larger percentage of the airfoil shape with toggles once you make the tips smaller, control inputs have a greater effect.
Just my theory.
-bill von

[billvon 2,991]

>Because paragliders fly slowly, they can do very tight turns. Much tighter then elipticals.
>Elipticals fly faster, but do the turns aren't as tight.
True of airplanes as well. The slower you go the less energy you have to redirect to make the turn.
>Is there such thing as a "true" eliptical? Perfectly rounded end-cells, etc?
I have a SuperSpace II that's pretty close to a true elliptical. The end cells are tiny, and have no opening in the nose. It inflates via crossports.
-bill von

[Strynx 0]

What's a crossports. Can i get a mental picture plz!P.L.U.R.

[SkydiveMonkey 0]

A crossport is a hole in the rib of the canopy which allows equilisation of pressure between cells.
my mind is like a canopy - 9 cells and I'm happy

[Strynx 0]

Thanx! How does this affects the opening i.e. Is the constancy of onheading.......
P.L.U.R.

[Pammi 0]

Phew...quite some complicated scientific reading. I'm glad you asked that question, Jessica, although I would have actually preferred more 'layman's terms' as to the basics of flight differences and why they are considered so 'scary'.
I got the opportunity purely by chance to jump an elliptical this last weekend when I borrowed the DZ's rig. My first thought was "Woa shit..elliptical!" but decided to give it a shot as it was a Heatwave 150, one size up from my Sabre 135 so didn't seem too 'daring'.
It was fantastic! Nice opening, a little faster on the turns, but not overwhelming by any means. To top it off, I don't know if it was luck or the canopy, but I landed them both on my feet - one time with a little wind, about 12 mph, and the next time without any! Landings are a bit sketchy for me on Sabre sometimes.
I don't know...but it wasn't nearly the experience that I expected. I'm sure it would've been different had it been a 135...same size and all, but I liked it. I've jumped a Manta, Triathlon, Sabre, Chute Shop (sp?) and now a Heatwave..the Heatwave is my fav so far, but keeping in mind I only jumped it twice.
Closing pin jewelry

[DanG 1]

If I remember my basic aerodynamics correctly, an eliptical planform does indeed affect the wingtip vorticies. If you look at a plot of pressure differential (difference between pressure above and pressure below the wing) across the wing, it will actually be an elipse with the largest differential in the center. The smallest pressure differential is at the tips. This pressure differential causes the vortices at the wing tips as the high pressure air underneath sneaks around the outside of the wing to hook up with the low pressure air on top. Wing tip drag is a significant drag contributer, and an eliptical planform reduces this effect.
Theoretically the eliptical planform has the highest Oswald efficiency factor (again this is from memory, I'm sure Quade can eloborate) which is an important factor in efficiency.
Also, I believe the only airplane to ever sport a truly eliptical wing was the WWII era Spitfire (I think). It, like eliptical canopies, was very efficient and maneuverable. However, the manufacturing costs to make the wing were huge. Straight edge wings are much easier to make. Some airplanes have strainght wings which simulate the eliptical shape. Next time you're at the DZ look at the trailing edge of a C-182.
- Dan G

[billvon 2,991]

I agree with most of that; however:
>Wing tip drag is a significant drag contributer, and an eliptical planform reduces this effect.
Agreed, but increased drag does not contribute directly to a wake vortex. I have not seen anything that indicates that an elliptical planform changes the pressure differential curve, and that's the primary contributor to wake vortices.
-bill von

[skyhawk 2]

so if i jumped out with a pariglider (for arguments sake) what would the dif be between it and an eliptical canopy
(o)(o)

[billvon 2,991]

>so if i jumped out with a pariglider (for arguments sake) what would the dif be between it and an eliptical canopy
Give it a try! They are incredibly slow and floaty, and they feel dangerously unstable. Just go find some place that will give you an introductory lesson for $50 or something.
The problem with jumping them is getting them to deploy. The only person I've known who has had any success with that has been Christian Wehrfritz, a german paraglider designer who basically designed a paraglider out of parachute material (normal paraglider material can't really be packed.)
-bill von

[Pammi 0]

Quote

To top it off, I don't know if it was luck or the canopy, but I landed them both on my feet - one time with a little wind, about 12 mph, and the next time without any! Landings are a bit sketchy for me on my Sabre 135 sometimes.

So...does anyone have a thought on this? I'm really curious whether it could've actually been the canopy that helped with my landing. Does it fly that differently then a Sabre on landing that it's actually easier to land? I'm still trying to figure out if it was pure luck or perhaps not..?
Closing pin jewelry

[PhreeZone 20]

I know I said I'd avoid posting here but.....
Fact is accourding to John LeBlanc like 75% of the sabres flying today have thier brakes set too short. These short brakes translate to less flare power since the canopy is already flyign in brakes. The Heatwave probally had the brakes set at the proper length and that allowed for more flare power to let you stand up a landing.
The larger canopy probally had some to do with it too. A larger canopy is more forgiving of mistimed, misinput on the flare then a smaller canopy is.
Murphy's Laws of Love - If the person isn't taken, there's a reason for that...

[skycat 0]

Quote

Does it fly that differently then a Sabre on landing that it's actually easier to land?

Yes and no, Like Phree sayed the large canopy is definately more forgiving, and Saber brake lines usually are to short, look at your canopy in full flight next time you jump it, is there any bowing, pull down your toggles and see how far before you start to pull on the tail, you should have to pull it a few inches.
Now I did experience the same thing when I went from a saber 135 to a crossfire 116, the crossfire was way easier to land. On the other hand it was not very forgiving to mis-timed flares. Now are you flaring the saber a bit late which would cause you to have to run your butt off, under say my crossfire it actually wants to be flared later, that was the hardest thing for me to relearn.
One other thing that could have made it easier to land is the fact that you know the dangers of ellipticals and were paying 200% more attention to what you were doing and flying it than say thinking about how your jump went.
Kelli

[diverdriver 5]

Quote

One other thing that could have made it easier to land is the fact that you know the dangers of ellipticals and were paying 200% more attention to what you were doing and flying it than say thinking about how your jump went.

Ok, I would not say ellipticals are more dangerous because they are elliptical. What makes them dangerous is the general lack of training anyone gets before jumping one. I compare canopy training and skydiving in general to aircraft pilot training. Without the proper initial training ANY canopy will be dangerous. As an industry/sport we have been failing. Many new programs have been started to try and change that and we are headed in the right direction.
Ok, I think I'm digressing from the topic of the thread.
Chris Schindler
D-19012
ATP/CFII
www.DiverDriver.com

[Spectrejumper 0]

Quote

Ok, I would not say ellipticals are more dangerous because they are elliptical. What makes them dangerous is the general lack of training anyone gets before jumping one. I compare canopy training and skydiving in general to aircraft pilot training. Without the proper initial training ANY canopy will be dangerous.

I said this before in a different thread, but I'll say it again here: all the training in the world doesn't make up for lack of experience. Ellipticals are much more dangerous to inexperienced jumpers due to one of their major selling points: their responsiveness. Give a good yank on the toggle and an elliptical TURNS NOW, perhaps even spinning you into line twists. The same input on a pure square or semi-elliptical will not have such dire consequences. To use your aircraft analogy: you start pilots out in Cessna 172's or something similar, not Citabria's or fighter jets. Even the most basic canopy instruction program will tell students not to make radical control inputs close to the ground, but in a moment of panic (getting cut off on final for instance) a low time jumper is more likely to yank down a toggle than a more experienced jumper. Less aggressive canopies=more forgiveness for the inevitable mistakes.
Mike D-23312
"It's such a shame to spend your time away like this...existing." JMH