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Old 11-14-2019, 12:04 PM
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Join Date: Dec 2009
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From Noob questions or ask a stupid question thread: post 402

Originally Posted by LoPan12 View Post
Neither am I. I do however have a degree that involved a lot of fluid dynamics. And before you ask the question, air is a fluid. And ArcheType, you're sort of right. I'll try to make this as understandable as I can....but this will get REAL sciencey, so bear with me please, or feel free to just skip this post entirely. Or better yet, go hit the end. After finishing up, I realized the first couple paragraphs aren't directly about "Why do I get more glide as it beats in"

Since we're talking about glide here, we'll treat the disc, as a whole, like a wing, or airfoil, as seen here.

Okay. When the disc flies through the air, you get a distinct seperation of air flow. Now consider two particles that get split up be the disc, one goes on top, one goes on the bottom. They will meet up again, behind the disc, so, because the top one has to travel farther, it is going faster. As speed increases, pressure decreases. You are left with a lower pressure area above the disc, and a higher pressure area below the disc. This phenomenon is called "LIFT" and for a given speed, will overcome the weight of the disc, and push it up. And what about that empty space under the disc? Well in that space, you get all sorts of forces, and I'm not totally sure what the net effect'm not even gonna try.
When you now consider the rotation, think about relative speeds. For a RHBH, the left edge of the disc is moving faster than the right edge. So, due to the higher speed, the left edge will create MORE LIFT than the right side. This is shown in Fig. A below. The blue line is the amount of lift exterted on the disc. This is where you get the effect of flip, or HSS. The cant of the the disc then causes the overall lift force to steer the disc to the right.

AH! So why don't all my discs keep going right?'ve got a rotating mass. This causes gyroscopic forces having to do with angular momentum and pitch and roll and whatnot. In a nutshell, the rotating mass of the disc causes a sum of forces call gyroscopic procession. This is what causes LSS, same as HSS, just the opposite direction. Fig. B shows the this force on the disc.
When you first release the disc, it has the most spin it ever will in that flight, and the assymetrical lift forces will outweigh precessional roll. But as the disc slows down, the lift forces aren't as large, and the disc rolls to the left.

It slows down, because of DRAG! Drag is a force that opposes your disc. The friction between the disc and air rob energy and the spin reduces, and the forward speed declines! BTW, a driver has less drag than a putter, due to putters having a blunt edge. So a driver's flight is therefore less lift-driven, and more ballistic. But don't think about that for now.

NOW, those of you still reading (god-bless you) are asking, "Okay, neat...what's this s#$t have to do with beating in and more glide?"
Well, turbulence is our friend here. A turbulent boundary layer on the surfaces of the disc eventually result in less drag! There's more fluid dynamics involved here, but trust me when I say, you end up with less drag. This is why golf balls are dimpled, but the reasons are a bit different for a sphere.
So, as you beat in a disc, it gets all these micro abrasions, that cause little eddies and vortexes that add up to turbulent, chaotic flow. In some cases, while this turbulence increases surface friction drag, the overall effect is a reduction in drag forces. This has to do with boundary layers, seperation points, and changes in pressure fields. But I'm damned tired.
The beating in reduces drag (to a point, then you start to get screwed again) allowing a disc to maintain the various lift forces for longer, lettings it go longer before fading, letting it glide longer.
Yeah. I think. Good Night.

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