#21  
Old 05-02-2017, 04:19 PM
thirtydirtybirds thirtydirtybirds is offline
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Originally Posted by Nenja View Post
At this speed the sharpest knife doesn't cut wind most efficient?
Good analogy actually. Believe it or not the sharpest knife isn't dead smooth. The blade is sharpest when it has millions of micro abrasions on its edge. Think serrations but really really really small.
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  #22  
Old 05-02-2017, 05:26 PM
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sidewinder22 sidewinder22 is offline
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Originally Posted by Doofenshmirtz View Post
Are you making this up or do you have some evidence that points to change in the surface of the disc as the source of the change in stability?
It's theory based on observational evidence and aerodynamic and gyroscopic principals. You may have noticed I used the word "may" in there on parts that I'm less sure of.
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Old 05-02-2017, 05:37 PM
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Originally Posted by sidewinder22 View Post
It's theory based on observational evidence and aerodynamic and gyroscopic principals. You may have noticed I used the word "may" in there on parts that I'm less sure of.
LOL, I see what you did there!
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Old 05-02-2017, 05:42 PM
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Originally Posted by Nenja View Post
Wow seriously? I assumed that a smooth and new disc would have the least drag dye to being aerodynamic... So the increaseed air resistance of the uneven edge is increased but it decrease the drag over the disc more by creating a air tunnel?

At this speed the sharpest knife doesn't cut wind most efficient?
Correct. Think of it as "shark skin technology" to decrease drag: http://www.popularmechanics.com/scie...anes-16792156/

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Old 05-02-2017, 06:09 PM
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Originally Posted by sidewinder22 View Post
It's theory based on observational evidence and aerodynamic and gyroscopic principals. You may have noticed I used the word "may" in there on parts that I'm less sure of.
What observational evidence are your referring to? Also, who are these aerodynamic and gyroscopic principals you rely on? Are their some aerodynamic and gyroscopic high schools out there that I don't know about?
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Old 05-02-2017, 06:16 PM
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Originally Posted by FlipFlat View Post
I agreed with all of what posted except i don't think the "Magnus Effect" can effect a disc. It does effect ball shaped objects and even Barrel shaped objects. I could be (wrong) though but everything i have ever read about disc physics has dismissed the Magnus effect.
IIRC the scholarly articles written have stated that Magnus effect was measured as non-zero, but negligible in their calculations. IIRC they were also only tested a frisbee at like 45mph with low spin rates, so the speed and spin would be significantly below what pro disc golfer actually throw. The Magnus effect would "push or pull" the sidewall/wing of the disc sideways. This is a much smaller effect than a ball or cylinder would experience due to the height of the disc wing not being very tall like 2cm and relatively heavy compared to a basketball that has a much larger side spinning surface and relatively lighter mass for its overall size.

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Old 05-02-2017, 06:18 PM
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Quote:
Originally Posted by sidewinder22 View Post
Correct. Think of it as "shark skin technology" to decrease drag: http://www.popularmechanics.com/scie...anes-16792156/
These are my favorite kinds of disc golf discussions!

Sidewinder, while I agree the roughening of the surface of a disc may cause a minor reduction in drag, I still think that mostly affects the distance/speed one might get out of a throw. I would estimate 90-99% of the effect on stability comes from the wing's edge being bent down from tree hits, general use, etc. Also, since a disc is much more aerodynamic than a sphere, I would say the drag/wake would be smaller, thereby decreasing the noticeable effect of roughening the surface.

This kind of makes me want to get one of my champion plastic discs I never use, throw it in a field a bunch, then rub the topside on gravel, then see if it flies noticeably different. Without the wing having much of a chance to get beat in, this should be a fairly accurate test.
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Old 05-02-2017, 06:40 PM
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Originally Posted by Doofenshmirtz View Post
What observational evidence are your referring to? Also, who are these aerodynamic and gyroscopic principals you rely on? Are their some aerodynamic and gyroscopic high schools out there that I don't know about?
This might help...

https://www.facebook.com/DefinitiveGuidetoDiscGolf/ Ch 7 "Dynamics of Disc Flight" gets pretty deep in the weeds regarding the physics.

I have also heard good things about Spinning Flight: Dynamics of Frisbees, Boomerangs, Samaras, and Skipping Stones - Ralph D. Lorenz, though I have yet to read this one.
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Old 05-02-2017, 07:27 PM
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Breaking in a disc makes it feel and fly better!
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  #30  
Old 05-02-2017, 08:05 PM
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Quote:
Originally Posted by atison View Post
Golf balls fly farther with dimples because of the backspin imparted on them at impact. The dimples give the air something to "grab onto" and help create negative net pressure on the top of the ball versus the bottom of the ball resulting in it staying aloft longer (until the inertia of the initial impact slows down to the point that the air moving over it isn't strong enough to create the differential). Without dimples, a golfball simply knuckes through the air with no consistent net negative pressure on any side of the ball regardless of spin.

There is a great video of a guy dropping two basketballs off a damn. One he drops with no spin. The other he drops with backspin. Great video explaining why golf drives need spin to fly far (optimal amount of backspin is a whole other discussion).

There is a great video of a guy dropping two basketballs off a damn. One he drops with no spin. The other he drops with backspin. Great video explaining why golf drives need spin to fly far.
I think you are misconceived about a couple things.

A golf ball that is struck with a normal swing will spin regardless of dimples or not. A smooth golf ball will fly more like a ping pong ball with a lot of spin and quickly veer off in the direction of the retreating spin side, it will not knuckle ball around like a basketball without spin. The dimples actually reduce drag so they fly straighter/truer, and will reach higher peak trajectory heights due to the reduced drag and increased speed/efficiency.

Spin is not required for dimple tech to work - see Mythbuster dimple car video below.




Quote:
Originally Posted by atison View Post
A disc stays aloft primarily because of the airfoil design of the leading edge of the wing. 2 things bring it down out of the air. 1) loss of inertia, 2) it slowing down past its point of continuing a stable and level flight. Roughing up a disc makes it less stable because there is more negative pressure on the wing that is spinning forward (left edge on a RHBH throw).

The part of this that makes the disc fly farther is the decreased stability (resistance to fading) at low speeds. When the disc is slowing down, the outside edge is being held up longer by increased negative net pressure on the top side of the outside edge due to the increased turbulence.
Not sure that is entirely correct. Magnus effect would be more pronounced at higher airspeed than low airspeed. The retreating spin side(right-side RHBH) carries or drags the airflow along with the spin and deflects the air around the back, while the advancing spin side separates the airflow and there is no deflection causing the disc or ball to veer to the right as the separated air pressure pushes back.

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