How does a canopy turn?

[markbaur 0]

I observe that pulling down on both brake lines increases both lift and drag.
I also observe that pulling down one brake line, even a little bit, results in that side of the canopy being lower than the other.
Why does pulling down on both brake lines make more lift, and pulling down just one make less?
I understand stuff like drag coefficient, adverse yaw, pendulum stability, Vno, Va, etc., as they apply to airplanes, helicopters, and gliders, so I'm looking for an explanation in those terms.

[freeflir29 0]

It's much the same as putting down flaps on an airplane.....you have increased lift and drag. A better example would be some Kit Planes IE Kitfox, that has "Flaperons"
"Carb Heat On....Carb Heat On.....Carb Heat On..."-Phil Polstra Clay

[Jimbo 0]

Somewhere in this book is the answer to your question. And probably the answer to a lot more questions you don't know you have yet.
http://www.skydiveaz.com/resources/book_canopy.htm
-
Jim
Help with cancer research here.

[riggerrob 643]

Pulling down on a toggle creates far more drag than lift.
Pulling down on one toggle creates far more drag on one side of the canopy, the resultant yaw forces the canopy to turn.
Banking is just a by product of the process.
Or think of it as a glider with spoilers that can be deployed asymetrically.

[markbaur 0]

Actually, it's not at all like a Kitfox. In a Kitfox, if the left flaperon is deflected down, the left wing goes up and the aircraft banks right. On my parachute, when I deflect the left side of the trailing edge down, the left side of the canopy goes down, and I turn left.
I looked at the Skydive Arizona canopy book, but I didn't see an explanation for this apparent contradiction in performance: pull down both sides to increase lift, pull down one side to decrease lift on that side.

[markbaur 0]

I'm still not sure this is the explanation. If pulling down a toggle produces far more drag than lift, then why does my canopy glide farther in brakes than in full glide?

[PhreeZone 20]

Bacuse you are altering the AOA in brakes then in full glide. When you pull on the brakes its just not like putting on flaps, you are altering the entire shape of the wing and the new shape becomes more or less efficient at any AOA then the old airfoil shape. The increase or decrease in effecientcy is why a Stiletto will glide further then a Sabre at the same loading, the Stiletto is trimmed different and has a different airfoil shape.
I want to touch the sky, I want to fly so high ~ Sonique

[prost 0]

Your canopy only glides farther in brakes if you are going down wind. Try this going into the wind and you will see you glide less.

[Jimbo 0]

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Try this going into the wind and you will see you glide less.

What are you talking about? You'll _always_ glide less going into the wind, brakes stowed, brakes released, whatever. Am I missing something here?
-
Jim
Help with cancer research here.

[freeflir29 0]

"What are you talking about?"
He was speaking of the increase in total distance over the ground gained when using rear risers or even toggle when travelling down wind. The drag created when travelling into the wind cancels any of the advantages.......
"Carb Heat On....Carb Heat On.....Carb Heat On..."-Phil Polstra Clay

[quade 4]

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Why does pulling down on both brake lines make more lift, and pulling down just one make less?

It doesn't.
What's very different in a ram air parachute wing than on most airplane wings during a turn is that on the ram air you're only reshaping the camber and changing the angle of attack on one side. On an airplane, not only do the ailerons move down, but they also move up on the opposite side. It's this difference of having force being applied asymmetrically and the pendulum effect that makes the two types of wings behave a bit differently.
In the case of a left toggle turn, pulling down on the toggle does reshape the camber of the wing and change the angle of attack on that side. This creates more lift and, AS A RESULT, also more drag on the left side on the canopy. Since the force is being applied asymmetrically, the inertia of your body underneath wants to keep you going in a straight line, but the increased drag of the left part of the wing slows it down. Your body swings out, even if only a little, creating less tension of the right side and more tension on the left side, pulling the left side even further down. Once the wing is banked to the left, it can't really help itself from turning left as a result of the horizontal component of lift.
Fabric, lines and tension are slightly different animals when it comes to how they interact with each other -- especially if you're used to rigid wings with CGs that are fairly close them.
That said, the B-2 Stealth Bomber uses asymmetric drag to yaw/turn in a very similar fashion.
Paul
http://futurecam.com/skydive.html

[freeflir29 0]

Well said Quade.....I did think of a better rigid wing analogy. Let's look at a B-52 (Very strange bird) It has no aileron. It uses spoilers (creates massive drag) in place of ailerons to turn the aircraft. Create drag on the left.....you turn left.....right.....turn right......There is no opposing force generated on the other side of the aircraft. Of course.....these aircraft are also junk. They were designed in the 40's and early 50's. Not exactly "modern"
"Carb Heat On....Carb Heat On.....Carb Heat On..."-Phil Polstra Clay

[quade 4]

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Of course.....these aircraft are also junk. They were designed in the 40's and early 50's. Not exactly "modern"

Yeah, I was thinking about it and while you were typing your responce to my responce I thought of a better example -- the B-2.
Paul
http://futurecam.com/skydive.html

[freeflir29 0]

"the B-2"
Don't know a lot about those......I spent 3 and a half years as "Tin Bender and paint splaterer" on the Buff though. It's amazing those things still fly. They are a credit to those who maintain them.....LOL. It takes 3 times the per hour maintenance for a Buff compared to a KC-135 (707) That whole no aileron thing always struck me as strange.......
"Carb Heat On....Carb Heat On.....Carb Heat On..."-Phil Polstra Clay

[quade 4]

HERE is a pretty good picture that shows the split-flap control of the B-2.
Paul
http://futurecam.com/skydive.html

[freeflir29 0]

Man is that weird looking......It doesn't even look like it would work with them being so far off the direction of flight????
"Carb Heat On....Carb Heat On.....Carb Heat On..."-Phil Polstra Clay

[riggerrob 643]

If you are facing downwind and you pull down on toggles or the rear risers, you will travel farther because your canopy will be exposed to the winds aloft for more minutes.
By the same logic, if you face into the wind and apply brakes, your canopy will cover less ground because the upper winds are trying to push it backwards.
Think of your canopy as flying in a giant block of air. The canopy has no clue that it's block of air is sliding across the surface of a planet.

[alan 1]

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the Stiletto is trimmed different and has a different airfoil shape.

You were doing pretty well until here. The Stiletto uses the same airfoil as the Sabre, but it is trimmed different and is not a constant aspect ratio plan form.
alan

[quade 4]

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The Stiletto uses the same airfoil as the Sabre.

John LeBlanc wrote me today and confirmed that the Stiletto and Spectre airfoils are the same and also said the old Sabre was the same as well.
However, he also said that the Sabre2 is a different airfoil and more efficient. He didn't say in what way it was more efficient, only that it was.
He didn't have NACA numbers for any of them.
Paul
http://futurecam.com/skydive.html

[markbaur 0]

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Your canopy only glides farther in brakes if you are going down wind. Try this going into the wind and you will see you glide less.

Not quite.
The folks in the soaring community have made a fine art of calculating best cross-country speeds, that is, the speed to fly to achieve maximum range. As a starting point, the two important speeds are the best glide speed (the speed which results from minimizing combined drag, given assuming no-wind conditions), and the minimum sink speed (the speed which gives you the most time aloft, what the airplane pilots call maximum endurance speed).
With a tailwind, you'd like to reduce your airspeed from best glide to something closer to minimum sink. With a headwind, you need more speed to get more range. So far, this corresponds with our canopy experience.
We use airspeed as a proxy for angle of attack, and for our canopies the angle of attack (the angle between the mean chord line and the relative wind) is in large part built in by the suspension line lengths (although some posters have pointed out that the mean chord line, and thus the angle of attack, changes when you pull on a riser or brake line). Many -- but not all -- canopies are rigged for best glide.
I jump an Icarus 93, which is rigged for a speed faster than best glide, so in some light headwind conditions slowing down results in better range.
Mark

[markbaur 0]

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What's very different in a ram air parachute wing than on most airplane wings during a turn is that on the ram air you're only reshaping the camber and changing the angle of attack on one side. On an airplane, not only do the ailerons move down, but they also move up on the opposite side. It's this difference of having force being applied asymmetrically and the pendulum effect that makes the two types of wings behave a bit differently.

And yet asymmetrical flap extension also causes a roll away from the more extended flap.

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In the case of a left toggle turn, pulling down on the toggle does reshape the camber of the wing and change the angle of attack on that side. This creates more lift and, AS A RESULT, also more drag on the left side on the canopy.

Let me propose this explanation instead: pulling down on one brake line increases lift on both sides of the canopy. The side that is pulled down experiences an increase in induced drag, but the other side accelerates (a result of inertia), and therefore produces more lift with less induced drag.
Mark

[quade 4]

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And yet asymmetrical flap extension also causes a roll away from the more extended flap.

Depends on the specifics of the aircraft and the size of the lever arm you're talking about, but for the most part you're correct. In the case of a C-172 for example you're VERY correct, They are fairly powerful flaps but located very near the CG compared to the rudder. The rudder is still able to keep the aircraft from yawing too much and keep it pointed (somewhat) forward so most of the split flap energy can go into banking the aircraft. It's a nasty (and thank goodness very rare) control problem in a C-172, but it's still usually landable. But I digress.

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The side that is pulled down experiences an increase in induced drag, but the other side accelerates (a result of inertia), and therefore produces more lift with less induced drag.

I see what you're trying to say but the only problem with that is that there is no -acceleration- due to -inertia-. Think about it.
What there -is- is acceleration at the opposite wing tip as a result of the entire canopy wanting to pivot around the increased drag being produced by the side being pulled down with the toggle.
(There -has- to be a better way of saying that, but my head is spinning right now.) ;^)
Functionally, this is the same thing, but the cause is way different.
Paul
http://futurecam.com/skydive.html

[quade 4]

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Many -- but not all -- canopies are rigged for best glide.
I jump an Icarus 93, which is rigged for a speed faster than best glide, so in some light headwind conditions slowing down results in better range.

I believe that -most- canopies are trimmed at a speed slightly faster than Vg.
Paul
http://futurecam.com/skydive.html

[quade 4]

One more . . . I can't resist.

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The folks in the soaring community have made a fine art of calculating best cross-country speeds . . .

(fine art?)
Isn't that what a Vario is for? ;^)
Paul
http://futurecam.com/skydive.html

[freeflyguy 0]

Nice thread
One thing nobody has mentioned, is how a front riser turns the parachute.
When you pull a front, that side isn't changeing the shape of the wing (camber or planform). Only angle of attack. You are not reshapeing it to have more lift, or drag. But it has less lift because you decreased the angle of attack. It speeds up, as it starts down. Of course the other side of the parachute follows. But it will have more lift, as compared to the other side, so it will be above the risered side, and turn you. Your body follows along as well. But doesn't swing you out as much as the toggle turn.