Canopies

[skydude2000 3]

Hey all. Another stupid newbie question. What's the difference between elliptical and non-elliptical canopies? I should know already, but a detailed explanation would be appreciated.

Thanks,

Skydude

PULL!! or DIE!!

[PhreeZone 20]

Elliptical canopies have different widths per cell. The end cells are narrower then the center cells. This leads to the canopy providing slightly more lift, but it also allows for faster turns and opening issues.

Do a search for elliptical and you'll have enough reading material for weeks

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[phoenixlpr 0]

Quote

providing slightly more lift

AFAK Elliptical canopies are more efficient as a wing, but more lift? Where is that more lift coming from?

[mnealtx 0]

Because a more efficient wing can develop more lift at a given speed?

Mike
I love you, Shannon and Jim.
POPS 9708 , SCR 14706

[riggerrob 643]

Elliptical canopies differ from rectangular canopies in that every rib is a different size in an elliptical canopy. This means smaller wing tips and smaller wing tip vortexes, ergo less drag.
So an elliptical canopy probably produces the same amount of lift as a - similar sized - rectangular canopy, but less drag, ergo a flatter glide angle, or the same rate of descent with greater forward speed, or a dozen variations on that theme.
Performance Designs tested Sabres (rectangular) and Stilettos (elliptical) side-by-side and found maybe one knot difference in forward speed. However, Stilettos have a reputation for gliding flatter.
The big difference is in roll rate, which translates to quicker turns and more "responsive" handling for ellipticals.
Also note that the term "elliptical" has been reduced to marketing jargon. I have never seen a canopy that resembled at,canopy planforms are all combinations of straight lines.
"Tapered" is a more accurate term as you can taper the leading edge, trailing edge or both for a bewildering variety of handling, opening, landing, etc. characteristics.

[amir1967 0]

``Performance Designs tested Sabres (rectangular) and Stilettos (elliptical) side-by-side and found maybe one knot difference in forward speed. However, Stilettos have a reputation for gliding flatter``

was that tested with the same line trim ?
I´ve thoght that the Sabre was trim much stipper

AM67

[PhreeZone 20]

Thats part of the reason the Stiletto glides further

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[billvon 3,111]

>This leads to the canopy providing slightly more lift . . .

Just a clarification -

All canopies a given person might jump generate EXACTLY the same amount of lift when they're flying in normal flight. The lift they generate is equal to their exit weight. If it wasn't they'd either accelerate upwards or downwards until they reached absurdly high speeds. But when you disturb that normal flight (say, by flaring) different canopies react in different ways. Some provide a lot of lift for a certain amount of toggle deflection, some provide less. These are the differences people talk about when they say "canopy X has more lift than canopy Y."

[larsrulz 0]

Fundamentally, a more elliptical wing produces less drag. Google "oswald's efficiency factor" sometime if you are bored...a perfectly elliptical wing (the british WWII spitfire had a {nearly} elliptical wing) has a oswald's efficiency factor, e, of 1. They actually misdefine it in those pages you'll find, but it is the same basic idea.

The bonus this has with parachutes is that full flight drag compared with drag when a single toggle is dropped half way is that the difference is much much larger between elliptical parachutes than non-elliptical. This means that an elliptical parachute can respond very aggressively to a relatively small toggle inputs.

Also, Bill...saying "the lift they generate is equal to their exit weight" is not exactly correct, otherwise a parachute could enter steady, level flight, which obviously they can't. In fact, Lift*cos(x)=Weight where x is the angle of flight with respect to the ground. In the end, the forces of lift, drag, and weight sum up to be zero (which is basically what you were getting at), but part of the lift is taken away to overcome the drag force.

I got a strong urge to fly, but I got no where to fly to. -PF