Why do discs beat in?

[jupiterboy]

What's gong on on a molecular level? Seems to happen with most plastics, but what is going on? I've asked before if discs get more understable over time just sitting, the premise being that some sort of off-gassing would change the molecular structure over time. That doesn't seem to be the case, so what is happening with the shock of hitting a tree or the ground, or is it the spin? IDK, but maybe someone does.

 

[Brychanus]

What's gong on on a molecular level? Seems to happen with most plastics, but what is going on? I've asked before if discs get more understable over time just sitting, the premise being that some sort of off-gassing would change the molecular structure over time. That doesn't seem to be the case, so what is happening with the shock of hitting a tree or the ground, or is it the spin? IDK, but maybe someone does.

I don't know that I've ever encountered a fully satisfying explanation, but one of the more convincing ones is the changes in turbulence interacting with the disc as it gains divots and scratches. Think golf ball dimples, but incurred by wear and tear:

https://www.scientificamerican.com/article/how-do-dimples-in-golf-ba/

That helps explain why e.g., soft baseline plastics that gouge seem to beat in so quickly. Like golf balls, relatively small changes in surface texture can have outsize impacts on flight. There's way more money in golf ball engineering/science but I'd love to see turbulence models for discs.

I also speculate that maybe as the polymer chains in the plastic break down over time the plastics tend to get softer, more or less domey, and maybe the gyroscopic stability changes.

Curious if there are any good data out there.

 

[thatdirtykid]

Parting line also seems to slowly beat lower with most discs.

The general consensus is that PLH change and texture/resistance from scrapes are the two main factors

 

[Angelo_Troiola]

Hmm, I never really thought about why it happened, just figured that chips in the plastic and such made the disc less predictable.

Second question though. I have heard that it's actually the bottom of the rim that makes the real difference when it comes to a disc getting beat in and becoming understable, not the edge of the rim. Has anyone heard this? Can you confirm or deny?

 

[@CD-]

I agree with the flashing removal/smoothing of the parting lines (outer rim + bottom of the disc) being the main reason premium discs flight change. Usually they are not taking a lot of damage to the rim (lowering the average PLH) like a base/midgrade plastic will.

Also a player's grip/pivot point might change with discs as they get scraped up/oxidized and the flight plate becomes more flexible, producing slightly more RPMs.

 

[chevis]

Hmm, I never really thought about why it happened, just figured that chips in the plastic and such made the disc less predictable.

Second question though. I have heard that it's actually the bottom of the rim that makes the real difference when it comes to a disc getting beat in and becoming understable, not the edge of the rim. Has anyone heard this? Can you confirm or deny?

for sure. if you take a beaded disc & sand that beading off it will fly less stable.
i hate sharp edged discs (flashing); sometimes i test a disc with the flashing still on & then take that flashing off and notice a change in flight (less stable).

 

[jupiterboy]

I suspect that, as suggested, changes in the parting line, particularly the height as the plastic relaxes, contributes more than anything.

 

[BillFleming]

I've heard lots of reasons, like those posted above, but one other reason is the disc 'distorting'. Hitting the disc against objects causes a slight distortion in them that isn't noticeable to the naked eye. And softer plastics beat in faster because they distort easier. I guess if you took exact measurements of a disc prior to throwing it at an object, depending on the exactness of your measurements, you might be able to detect the distortion.

 

[Rastnav]

Here is a nice video comparing new discs and beat in discs, as well as some new overstable and understable discs.

He refers to "nose angle". People here prefer "parting line height".

 

[ThrowBot]

The surface roughness does cause more turbulent air flow on the top of the disc, and importantly: this effect is not uniform across the surface!

The front of the disc sees more laminar flow because there's a transition zone before fully turbulent flow develops.

The air pressure observed at the disc surface under the turbulent zone is LESS than the pressure under the laminar flow. So the front of the disc is getting pushed down harder than the back of the disc. This contributes to the torque that makes the disc want to precess in the understable/high-speed-turn direction.

In other words: the disc acts more flippy.

 

[tomsdiscs]

I don't know that I've ever encountered a fully satisfying explanation, but one of the more convincing ones is the changes in turbulence interacting with the disc as it gains divots and scratches. Think golf ball dimples, but incurred by wear and tear:

https://www.scientificamerican.com/article/how-do-dimples-in-golf-ba/

That helps explain why e.g., soft baseline plastics that gouge seem to beat in so quickly. Like golf balls, relatively small changes in surface texture can have outsize impacts on flight. There's way more money in golf ball engineering/science but I'd love to see turbulence models for discs.

I also speculate that maybe as the polymer chains in the plastic break down over time the plastics tend to get softer, more or less domey, and maybe the gyroscopic stability changes.

Curious if there are any good data out there.

I agree with everything Brychanus posted, and add, plastic discs get stretched out and more limber, so better and faster rotation potential is enabled.

In addition to throwing the discs 100+ times, you can stretch them with your hands to help accelerate the breaking in, I like to fold them into tacos, rotate a little, fold into a taco again, etc.

 

[jenb]

Because in is naughty. Ba dump bump tish

 

[DeanMoriarty]

How exactly is a rainbow made? How exactly does a sun set? How exactly does a posi-trac rear-end on a Plymouth work?

It just does.

 

[jupiterboy]

How exactly is a rainbow made? How exactly does a sun set? How exactly does a posi-trac rear-end on a Plymouth work?

It just does.

How does your mom hold her breath that long?

 

[BogeyNoMore]

That's just being rude...

 

[GripEnemy]

How exactly is a rainbow made? How exactly does a sun set? How exactly does a posi-trac rear-end on a Plymouth work?

It just does.

Aaaaaand I'm watching Joe Dirte' tonight.

 

[ThrowaEnvy]

Hmm, I never really thought about why it happened, just figured that chips in the plastic and such made the disc less predictable.

Second question though. I have heard that it's actually the bottom of the rim that makes the real difference when it comes to a disc getting beat in and becoming understable, not the edge of the rim. Has anyone heard this? Can you confirm or deny?

Well in my disc modification experience I found that removing the bottom plastic made it less stable with the most effect being the fade or LSS

By sanding the bottom of the nose it affected it's HSS more.

A large rim gouge affects the HSS the most.
When it's beat to squirrelly it turns faster and generally fades with more of a knife hyzer losing both hss and glide.

Warm weather makes my discs softer and less stable. I assume because of dome changes like a little mild puddle topping creating a divot of turbulence. Dome means extra glide but also added stability (as a broad generalization).

 

[DeanMoriarty]

How does your mom hold her breath that long?

I don't know, why don't you come ask us in person?

 

[jenb]

When it's beat to squirrelly it turns faster and generally fades with more of a knife hyzer losing both hss and glide.

What is a "knife hyzer?"

 

[ThrowaEnvy]

What is a "knife hyzer?"

Kinda like the action you get with a tilt or something stupid OS.. it just knifes back, kinda like a spike hyzer. Maybe it's a term I made up but I think some folks found here have used it.