Why front riser turns the canopy the way it does?

[sjc 0]

Hello,

The common explanation for a toggle turn is that one side of the canopy slows down while the other maintains the speed. The result is that the faster side goes around the slower one. So left toggle down -> left side is slow -> left turn happens.

Trying to use the same logic for front risers results in the confusion for me. Front risers increase the speed of the canopy. So pulling down left front riser should increase the speed of the left side, so the RIGHT turn should happen. It does not :)

What am I missing there?

Thanks.

Regards, Alexander. http://staticlineinteractive.com

[drudchen 0]

Think of the speed in terms of a vector quantity (magnitude and direction). During the left front riser turn the left side does speed up (in magnitude) as you pointed out, but the direction of the vector becomes more steep (angled towards the ground). So if you look just at the horizontal component of the speed, it slows down.

[BrianSGermain 1]

When you pull on a front riser, you are reducing the angle of attack on that side of the wing. This alters the spanwise distribution of lift, causing a change to the bank or "roll" angle. This results in an increased horizontal component of lift, which pulls the wing into a mostly coordinated turn toward the low side of the wing.

There may be another explanation that makes more sense, but I haven't run into it just yet.

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[sjc 0]

Quote

When you pull on a front riser, you are reducing the angle of attack on that side of the wing. This alters the spanwise distribution of lift, causing a change to the bank or "roll" angle.

Given that the "roll" happens towards the input side, then vertical (perpendicular to the canopy surface) component of the lift should go down, hence the side drops down creating "roll". This roll helps sliding of the canopy to the side. That's clear. In order for the "roll" to happen increase angle of attack should reduce lift coefficient enough to compensate for the increased speed of the side. This says that the lift coefficient curve must have a decline steeper than quadratic (lift changes depends on the square of the speed).

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This results in an increased horizontal component of lift, which pulls the wing into a mostly coordinated turn toward the low side of the wing.

What side of the canopy has increased horizontal component of lift? It looks to me, as drudchen said, the input side must experience the drop in horizontal component, so that yaw can happen in the correct direction.

Thanks.

Regards, Alexander. http://staticlineinteractive.com

[deadbug 0]

The input side experiences a decreased vertical component of lift and a increased horizontal component of lift due to the warping of the input side front of the canopy. This is a direct result of the warping of the canopy on the input side and a decreasing of the angle of attack on the input side. To put the process on a time line. Lets assume a left front riser turn. Left front riser pulled down resulting in a decreased angle of attack on the left side of the canopy resulting in a decrease in vertical component of lift on the left side resulting in a roll to the left resulting in a increased horizontal component of lift across the entire wing.

Doug

[BrianSGermain 1]

I said:
"This results in an increased horizontal component of lift, which pulls the wing into a mostly coordinated turn toward the low side of the wing."
You said:
"What side of the canopy has increased horizontal component of lift?"

My thoughts:
"The entire wing changes in its attitude on the roll axis, so the horizontal lift energy is increased across the board. In a coordinated turn, the tip speeds are not that different, inboard compared to outboard, unless the radius of the turn is really tight, which is hard to accomplish on a front riser turn. Therefore is is unlikely that the unbalanced spawise distribution of lift is the dominant factor here. It is far more likely that the tilted lift vector is what drives the turn, due to the pitching energy created for the forward-skewed lift of the airfoil. In other words, the center of lift is near the "A-B" section of the wing, so the tilted roll axis allows the forward-skew of the lift to "hinge" the wing into the turn, pitch energy creating yaw.

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Canopies and Courses:www.BIGAIRSPORTZ.com

[sjc 0]

I'm confused about "increased horizontal component of lift across the entire wing" and how roll affects it. It's clear that roll affects the direction of the lift. Lift can be affected by velocity of the relative wind, angle of attack, area of the wing (the rest are parameters are properties which stay constant with or without roll, I think). So for lift to change, roll must change some of these. I can see that as the roll increases the lift drops down, because wind does not move along the surface of the wing, but across it. This means horizontal component should decrease as well.

What am I missing in the rolling action?

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It is far more likely that the tilted lift vector is what drives the turn, due to the pitching energy created for the forward-skewed lift of the airfoil.

I can understand the tilt of the lift, due to the change of the trim on one side of the canopy. My confusion can be explained as following: imagine that the canopy has lifts straight up (let's imagine it) as I pull left front riser I can see that the left side lift tilts forward, which should create a motion down and forward relative to the other side, given that the magnitude of the lift stays the same. Well this means that the right hand turn should happen. But we all know it does not. So my understanding of tilt is wrong in one (or all) of the following: it tilts the other way (hard to connect with the trim change, though), the magnitude of the lift changes to make sure that horizontal component is less than of the other side (most likely, but I do not see increase in the horizontal component). Of course once in the turn, the speed increases including horizontal component, but I'm trying to understand the transition.

Thanks.

Regards, Alexander. http://staticlineinteractive.com

[Pendragon 1]

What most people don't realise when you gently pull on your right control toggle is that, initially, you turn left slightly as more lift is generated on the right side. Further control input subsequently slows that side down, and the canopy yaws and banks to the right.

Right front riser doesn't really accelerate the wing on that side as much as deform it; such a deformation actually creates less lift on that side as it reduces the efficiency of the wing, and also induces bank. Hence you turn right.

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[za_skydiver 0]

If pulling the left front riser.

Wouldnt it just be easier to say that the left side dives more to the ground, therefore increasing in speed on the left side resulting in less lift while dragging the right side after it, which is creating more lift?

Some dream of flying, i live the dream...

[Guinness_fr 0]

Quote

When you pull on a front riser, you are reducing the angle of attack on that side of the wing. This alters the spanwise distribution of lift, causing a change to the bank or "roll" angle. This results in an increased horizontal component of lift, which pulls the wing into a mostly coordinated turn toward the low side of the wing.

I think this explanation makes perfect sense.

[schmit.paul 0]

To elaborate just a bit more on the vector interpretation of what's going on. Any time you have a system with a force acting upon it that is always perpendicular to the instantaneous direction of motion, a curved trajectory will result. This is, for instance, why objects in the solar system like planets, comets, and meteors orbit the sun in elliptical, circular, or hyperbolic trajectories (the gravitational pull is straight toward the center of the sun, even though most objects are inclined to move around it). This is also why when you tie a weight at the end of the string and swing it around above your head in circles, the harder and faster you oscillate your wrist the faster around the weight goes in a circle (rather than pushing the weight forward, the string tugs the weight in a new direction harder and harder). The concept is called "centripetal acceleration," and a similar effect results on a canopy any time there is a horizontal lift component directed perpendicular to the instantaneous horizontal flight path. This can be achieved by initiating a tilt about the roll axis, either via manual deformation of the wing through riser input/harness turns, or by establishing a spanwise vertical lift gradient along the wing through toggle application (causing the low-lift side of the wing to drop). While vertical motion may affect the magnitude of the lift vector, the curved horizontal motion is essentially an independent phenomenon...as long as that lift vector is tilted so that a component of it resides perpendicular to the flight path, a curved trajectory (turn) will always result.

Curiously, Brian comments in his book on how a jumper can actually temporarily speed up a toggle turn by first initiating a toggle turn, and then in mid-turn applying more brakes evenly to each side. This is because once the parachute is turning, an even application of brakes (maintaining the offset between the left and right toggles) temporarily increases the magnitude of the lift vector without changing its direction, and thus the centripetal force increases, speeding up the turn (as if the artificial "sun" pulling us in orbit suddenly gained more mass). Of course, as the airspeed slows down this effect decreases, but initially it seems like the effect could be pretty profound.

"Ignorance more frequently begets confidence than knowledge." ---Charles Darwin