Canopy design questions

[Professor 0]

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in testing the ability to land a cobalt tapers off at 5:1. the onyx will definately extend that range.

sincerely,

dan<><>

Damn! Who landed that?!? Are you defining "ablitity to land" as a complete stop, as zero decent, or as something else?

Ted

Ted
Like a giddy school girl.

[franck102 0]

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Would it be correct to restate Dan's claim as, "The center of gravity hangs below the center of lift"?

And would it be correct to restate Chris's reply as, "The angle between the chord and the CG-CL line is determined by the line set"?

Mark

Both essentially correct -) That angle is the angle of incidence (+90 degrees). And the CL moves along the chord as the angle of attack changes, so the angle of incidence changes with it. The CG is actually slightly behind the CP due to drag.

Franck

[markbaur 0]

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Differences can be seen in how long a canopy will remain in a dive (recovery arc), differences in riser pressures, differences in airfoil efficiency (how far it will surf), differences in neutral flight speed, and very importantly, differences in stability.

You don't say what the differences are, so I'm guessing:

Loading farther forward, in general: longer dive, heavier front riser pressure, less surf, more stable.

Loading farther aft, in general: shorter dive, lighter front riser pressure, more surf, less stable.

How am I doing?

Mark

[cobaltdan 0]

"cobaltdan claims: "but basically where you 'hang' under the canopy is a function of the airfoil chosen and its pressure distribution."

groundzero replies: the point where one "hangs" is determined by the designers lineset. Angles determined by the b and d cascades and their insertion point in the a and c lines will determine where the mass will be located under the airfoil, whether it be a "pd" airfoil, an atair airfoil or any other airfoil.

must run to play!

Chris xox "

chris: your statement is incorrect. if you draw a vertical line from the jumper up to the canopy you will see that where the jumper is suspended under that canopy is not determined by your line lengths and cascades as you refer. where that line intersects your canopy is dependent on the angle of attack the canopy flies with. this is influenced within a small range by the geometry of your lines, but mainly the pressure distribution of your chosen airfoil. different airfoils with identical line trims can fly at different angles of attack and consequently where you "hang" under each canopy is different.

for clarity i will resate: for a given airfoil there is a limited range of angle of attack where the canopy will have desirable performance. chosing an airfoil with a different pressure distribution allows the designer to change where a jumper is loaded under the canopy with a similar range of angle of attack. i.e. the difference between a fore loaded canopy (any canopy with a pd airfoil: xaos, fx, vx, stilletto, etc) and a center loaded canopy: cobalt.


sincerely,

dan<><>

Daniel Preston <><>
atairaerodynamics.com (sport)
atairaerospace.com (military)

[Spy38W 0]

This is something I've been thinking about lately. I was wondering what would happen if I (hypothetically) put an extra connector link between the lines and the rear risers (increasing the length of the rear lines.)

--
Hook high, flare on time

[VivaHeadDown 0]

The line set is the tool used to position the person, but not what determines the ideal cg. It's like the chicken and the egg, only in this case you know which gets designed first. Dan said that is a function of the pressure distribution, which means that once that is known you can design the line lengths to put the person where you want him/her to achieve the most efficient use of that airfoil.

[franck102 0]

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This is something I've been thinking about lately. I was wondering what would happen if I (hypothetically) put an extra connector link between the lines and the rear risers (increasing the length of the rear lines.)

We used to do that on early paragliders (which were very similar to today's high-performance 9 cell canopies). We added up to 5 french links (1+ inch each) on the rears to change the incidence and improve penetration.
Later models had adjustable rears - you could pull them in several inches and keep them there. Another popular system is to have the linesesets go all the way down to the bottom of the harness seat (instead of being grouped above your shoulders), and you can adjust the incidence by sitting back or forward.
Many paragliders today use foot-controlled "accelerator bars", which not only alter the incidence but also the camber of the canopy by pulling in different sets of lines by different amounts.
Don't try any of this on your canopy of course, let the manufacturer try it first... Although I have toyed with the idea of asking my rigger to install adjusters on my rears, to make it easier to come back from long spots...
Franck

[PhreeZone 20]

Most CRW jumpers have extra links on the rears to steepen the angle of attack. Just be warned... its going to change the openings a lot.

Yesterday is history
And tomorrow is a mystery

Parachutemanuals.com

[Spy38W 0]

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Most CRW jumpers have extra links on the rears to steepen the angle of attack. Just be warned... its going to change the openings a lot.

Hrm, change them a lot as in, make them harder?

-

My thinking is that this will make the canopy act as though I'm pulling on the front risers by the amount I'm (hypothetically again) adding to the rears.

And just to bring up a point for whoever might take this past hypothesis stage, I *believe* that metal to metal (additional hard links) is bad...

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If you're going to be stupid you better be tough... and have medical insurance

I think this may apply...

--
Hook high, flare on time

[GroundZero 0]

Links can make lines (entire riser groups) longer... if you want to try shorter, tie knots in the lines at the lower surface of the canopy.. there they won't interfere with the slider on opening... those are quick and easy line trim techniques we do in the field (away from a bartacker)

Chris

[SkymonkeyONE 4]

For small changes, some swoopers will use slinks on the front or rear and rapides on the other end. Fives are longer than fours, etc. The difference between slinks and number fives is about a half inch. It's amazing what that little difference can make.

Chuck

[Spy38W 0]

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For small changes, some swoopers will use slinks on the front or rear and rapides on the other end. Fives are longer than fours, etc. The difference between slinks and number fives is about a half inch. It's amazing what that little difference can make.

Thanks Chuck and Chris, I was thinking my ideas would get a lot more criticism and pretty much just end up as ideas. Now I'm starting to think about playing around a bit.

--
Hook high, flare on time

[dskydave 0]

I SAID THERE ARE SEVERAL AND DIDNT ATTRIBUTE THE CHANGE TO 1 PARAMETER.LINE LENGTH IS A MAJOR CONTRIBUTING FACTOR.SIMPLE PHYSICS

[Ron 10]

Back when the Batwing was new, Charlie Mullins had a 98 that we had at one time I think 2 links on the back line set...

The problem is that while it does change the angle of the wing, it is not uniform, and there will be a "Step" that can be seen on the top of the wing between the B and C line sets.

This disrupts the airfoil and reduces lift. The tests went well, and the "Speed Kit" was developed.

It was very interesting to pack and jump the canopy...On opening you could hear the links hitting each other.

These test jumps were done for a reason.....For the most part I would NOT mess with anything on your canopy....

BAD things can happen. And unless you are able to tell, you can get very hurt.

Charlie always jumped anything new before I did....He is one of the best canopy pilots in the world....And I have seen him biff a test canopy more than once.

Ron

"No free man shall ever be debarred the use of arms." -- Thomas Jefferson, Thomas Jefferson Papers, 334