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Old 07-17-2014, 12:47 PM
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Toro71 Toro71 is offline
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Disc Physics...???

I still have a question that's been addressed variously in multiple threads, like:

From http://www.dgcoursereview.com/forums...hlight=physics

"Because the velocity on the port (left) wing of the disc is higher, the air must flow faster over its dorsal surface on that side, causing its pressure to decrease. On the flipside, air is travelling much slower over the dorsal side of the starboard (right) wing, meaning the pressure is much higher. This pressure gradient causes the disc to tilt to the right, which is what we know as turn. Because turn is velocity-based, it is easy to see why it is dominant only during the initial part of a disc's flight."

And from http://www.dgcoursereview.com/forums...ht=moment+lift

which links to

http://www.discgolfreview.com/forums...p?f=17&t=14825

which seems to agree with "sarah":

"Turn is defined here as the disc's natural tendency to decrease its hyzer angle while in flight through precession (right for RHBH). Turn is caused by a center-of-pressure/lift that is behind the center of the disc. I.e., lifting the trailing edge of the disc more than the leading edge causes the disc to precess in a manner that makes it turn."

So, basically, there seems to be two theories on "turn," one looks at the disc as analogous to both wings on a plane (more or less,) the other looks at it as one wing (more or less.) Interesting to me, is that both theories seem to consider spin a factor in turn, and not just as a stablizing effect.

Do we have a consensus here? Both ideas have merits from a layman's POV, just wondering if any of the supernerds here can shed light?
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  #2  
Old 07-17-2014, 12:55 PM
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bradharris bradharris is offline
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Turn is generally caused by the Magnus Effect

Fade is the result of precession.
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Old 07-17-2014, 01:09 PM
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I've always thought more spin=more turn, but could be wrong.
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Old 07-17-2014, 01:12 PM
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Well, spin stabilizes an object generally (think a top) but there seems to be some differing ideas about how that factors in with forward velocity.

@ bradharris: so like a curveball...?

Last edited by Toro71; 07-17-2014 at 01:17 PM.
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Old 07-17-2014, 01:15 PM
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Olorin Olorin is offline
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Quote:
Originally Posted by Toro71 View Post
"Because the velocity on the port (left) wing of the disc is higher,
I think that this fundamental premise is incorrect, therefore the conclusions are flawed. It would probably take too much verbiage to explain why I think this, but I will make a brief attempt. This idea is very widely held myth that has reached the status of becoming "true" merely through constant repetition.

Here's what I think:
1) Start by using a sharpie to mark a point on the outer rim of a disc. We will call this point "1".
2) IF there was a point on the left side of highest velocity, call this "A".
3) Then IF there is also a point somewhere of lower, and thus lowest, velocity, somewhere on the right side call this "B".
4) How can point 1 be faster at point A than at point B? That would mean that by some unknown force point 1 speeds up until it reaches A then it slows back down when it reaches B then it speeds back up to get to A... This speeding up and slowing down makes no sense; it is illogical, therefore the assertion is false.

Does that make sense to you? Do you agree?

I think this idea started by looking at pressure differntials on fixed wing aircraft and working backward to postulate that the left side must be slower. But a rotating disc cannot be compared to an airplane.

So I think that the shifted Center of Pressure explanation is much more plausible.

The rotation of a disc makes it incredibly complex, and I have not seen any information on DGR, DGCR, or the internet that satisfactorily explain all of the observed phenomena. But it is still fun to discuss and learn about!
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Old 07-17-2014, 01:21 PM
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jrawk jrawk is offline
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Quote:
Originally Posted by Toro71 View Post
So, basically, there seems to be two theories on "turn," one looks at the disc as analogous to both wings on a plane (more or less,) the other looks at it as one wing (more or less.) Interesting to me, is that both theories seem to consider spin a factor in turn, and not just as a stablizing effect.

Do we have a consensus here? Both ideas have merits from a layman's POV, just wondering if any of the supernerds here can shed light?
A disc is an unstable wing which uses spin/gyroscopic effect for it act as a stable wing. The rate of rotation is a constant variable, which makes the flight direction of disc a constant variable as well. Any slight variance in rate of rotation will cause the disc to pitch/yaw in a different direction.

Quote:
Originally Posted by sandman365 View Post
I've always thought more spin=more turn, but could be wrong.
in a vacuum constant spin would have zero effect on flight direction. However outside a vacuum, the friction of the disc turning through air will push it toward the direction of it's rotation. i.e. clockwise rotation will push it right, where counter clockwise rotation will push it left.

Just my thoughts.

Edit: and I totally agree with Olorin
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Old 07-17-2014, 01:22 PM
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Quote:
Originally Posted by Olorin View Post
I think that this fundamental premise is incorrect, therefore the conclusions are flawed. It would probably take too much verbiage to explain why I think this, but I will make a brief attempt. This idea is very widely held myth that has reached the status of becoming "true" merely through constant repetition.

Here's what I think:
1) Start by using a sharpie to mark a point on the outer rim of a disc. We will call this point "1".
2) IF there was a point on the left side of highest velocity, call this "A".
3) Then IF there is also a point somewhere of lower, and thus lowest, velocity, somewhere on the right side call this "B".
4) How can point 1 be faster at point A than at point B? That would mean that by some unknown force point 1 speeds up until it reaches A then it slows back down when it reaches B then it speeds back up to get to A... This speeding up and slowing down makes no sense; it is illogical, therefore the assertion is false.

Does that make sense to you? Do you agree?

I think this idea started by looking at pressure differntials on fixed wing aircraft and working backward to postulate that the left side must be slower. But a rotating disc cannot be compared to an airplane.

So I think that the shifted Center of Pressure explanation is much more plausible.

The rotation of a disc makes it incredibly complex, and I have not seen any information on DGR, DGCR, or the internet that satisfactorily explain all of the observed phenomena. But it is still fun to discuss and learn about!
I'm not sure. In a vaccuum, I see where you're coming from. Rotational velocity can't be different on one side of the disc or another. But I can't seem to make up my mind if that spin causes differences in relative air speed between the side of the disc spinning into the direction of travel vs. the side spinning away...in other words making separate moments of lift, one "greater" than the other.

bradharris' point about the "curveball" effect would seem to make sense in conjunction with the single moment of lift forward/behind the axis of spin.
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Old 07-17-2014, 01:25 PM
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....except that "turn" doesn't necessarly = moving to the right off line for a rhbh. Think hyzerflip into a shallow hyzer. Or, am I just trying to make something more complicated than it is?
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Old 07-17-2014, 01:35 PM
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Quote:
Originally Posted by Olorin View Post
I think that this fundamental premise is incorrect, therefore the conclusions are flawed. It would probably take too much verbiage to explain why I think this, but I will make a brief attempt. This idea is very widely held myth that has reached the status of becoming "true" merely through constant repetition.

Here's what I think:
1) Start by using a sharpie to mark a point on the outer rim of a disc. We will call this point "1".
2) IF there was a point on the left side of highest velocity, call this "A".
3) Then IF there is also a point somewhere of lower, and thus lowest, velocity, somewhere on the right side call this "B".
4) How can point 1 be faster at point A than at point B? That would mean that by some unknown force point 1 speeds up until it reaches A then it slows back down when it reaches B then it speeds back up to get to A... This speeding up and slowing down makes no sense; it is illogical, therefore the assertion is false.

Does that make sense to you? Do you agree?

I think this idea started by looking at pressure differntials on fixed wing aircraft and working backward to postulate that the left side must be slower. But a rotating disc cannot be compared to an airplane.

So I think that the shifted Center of Pressure explanation is much more plausible.

The rotation of a disc makes it incredibly complex, and I have not seen any information on DGR, DGCR, or the internet that satisfactorily explain all of the observed phenomena. But it is still fun to discuss and learn about!
If you're watching the disc fly from above, you'll see your sharpie point speed up on the left side and slow down on the right (for a RHBH throw).

Imagine the path it would trace as it travels. It will not be a straight zig-zag back and forth. It will be a curve where it covers far more distance on the left side than it does on the right.
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  #10  
Old 07-17-2014, 01:47 PM
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Stop all this math mumbo-jumbo, you are sucking all the fun out of it
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