How "breaking in" effects flight characturistics

[thirtydirtybirds]

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.

 

[sidewinder22]

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.

 

[Puckstopper]

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!

 

[sidewinder22]

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/sci...pire-faster-swimsuits-and-airplanes-16792156/

 

[Doofenshmirtz]

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?

 

[sidewinder22]

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.

 

[knettles]

Correct. Think of it as "shark skin technology" to decrease drag: http://www.popularmechanics.com/sci...pire-faster-swimsuits-and-airplanes-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.

 

[PBokor]

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.

 

[Aim For The Chains]

Breaking in a disc makes it feel and fly better!

 

[sidewinder22]

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.

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.

 

[sidewinder22]

It may also increase sideways lift/Magnus effect.

This is wrong, it would decrease Magnus effect as demonstrated by the golf ball.

 

[sidewinder22]

What observational evidence are your referring to?

The relationship between the dings in my discs and how they fly.

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?

Izak Neuton.

 

[sidewinder22]

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.

Do putter wings get bent down?

PLH is NOT affected in any measureable way by beating a disc up. I have had this argument with people before - and it took a week of experimenting, and a lot of ink to show it was BS.

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.

The underside of the wing is where most of the dings occur or get a Diablo DT which would seem likely to translate to a change in the center of pressure/lift resulting in gyroscopic turn(or less fade) as it reduces drag and pushes the CoP/L further back.

Some interesting stuff:

 

[DG_player]

You can't directly take effects from golf ball flight and apply it to a disc.

Spheres are pretty un-aerodynamic, more aerodynamic than a cube say, but way worse than a disc or wing. Because of this the primary cause of drag is pressure drag. A large volume of air piles up in front of the ball and flows towards the back. At some point, approximately half way back, the air separates and a low pressure wake is formed behind the ball. This pressure differential causes a huge amount of drag.

When you add dimples to a ball, it causes turbulent flow, which does a couple of things. First off, it actually increases surface drag, there is more friction along the ball's surface than with a laminar flow. However, the turbulent flow causes the air moving around the ball to adhere to it longer. So instead of the airflow shearing off halfway back, it stays connected to the ball longer. This causes the low pressure wake to be much smaller. Since a ball is un-aerodynamic and it's pressure drag is much large than surface drag, the overall drag drops significantly and the ball travels further.

A wing on the other hand is a different story. #1 they generate lift totally different than a golf ball, all of a balls lift comes from the magnus effect, whereas a wing generates lift by creating a pressure differential between the top and bottom. Additionally a wing is aerodynamic, so pressure drag has a much smaller effect compared to surface drag. A laminar flow does a much better job of generating lift and reducing drag because the air is moving smoother and faster over the top of the wing. This is why aircraft wings are designed to maintain laminar flow as far along the wing as possible. This is also why pilots are terrified of wing icing, because it disrupts laminar flow and causes a significant loss of lift and increase in drag.

As far as why does this make a disc more under stable, I would say Sidewinder's theory is probably the most likely. As you increase angle of attack, the separation point moves forward, which in turn causes the center of pressure to move forward. If there was enough wear on the disc to create turbulent flow, the separation point should be further back at any given AoA and thus the COP further back. However, while it makes your disc more under stable, it's unlikely it would improve it's lift/drag performance. I suspect if you found an expert on wing icing, they could shed some serious light on airflow over a beat in disc.

As an aside, since it hasn't been mentioned yet, there's also the possibility that repeated impacts actually change the shape of the disc. This could also have some effect, although I suspect it would be minor compared to the turbulent flow effects.

 

[Dr.Smooth]

In gerneral discs break in more understable. To which degree will be depended too on plastic and mold. DX or baseline plastic gets beat in very fast and is almost "chewed" away, the clear style plastics, champion and such, are more durable and usually more overstable than other plastics, breaks in slowly, higher end like star, 400g, s-line are more towards mold flight characteristics i.e. break in understable then clear style but will keep flight character longer than dx.

Whichever one works best for you is mostly dictated on personal preference, though I usually have a mix of plastics so I can use whichever feels best for the shot.


Sent from my iPhone using Tapatalk

Right on....I would add that if a disc smashes a tree at a very close range assuming its not dx that you introduce wobble. An out of balance flight plate. That was what we used to call tacos back in the days of dx. Tacos well meant by a new disc. The oustanding new champ like plastic handles most whacks. But not all.

If you are playing on windy days and trying to get distance into a headwind broken in is not usually ideal. You want the disc fresh so it can penetrate. Scuffs, knicks causes friction against the wind.

 

[Dr.Smooth]

In gerneral discs break in more understable. To which degree will be depended too on plastic and mold. DX or baseline plastic gets beat in very fast and is almost "chewed" away, the clear style plastics, champion and such, are more durable and usually more overstable than other plastics, breaks in slowly, higher end like star, 400g, s-line are more towards mold flight characteristics i.e. break in understable then clear style but will keep flight character longer than dx.

Whichever one works best for you is mostly dictated on personal preference, though I usually have a mix of plastics so I can use whichever feels best for the shot.


Sent from my iPhone using Tapatalk

Right on....I would add that if a disc smashes a tree at a very close range assuming you introduce wobble. An out of balance flight plate. That was what we used to call a "taco" back in the days of dx. Taco, well meant by a new disc. The outstanding new champ like plastic handles most whacks. But not all.

If you are playing on windy days and trying to get distance into a headwind, broken in is not usually ideal. You want the disc fresh so it can penetrate. Scuffs, knicks causes friction against the wind.

 

[knettles]

Do putter wings get bent down?


The underside of the wing is where most of the dings occur or get a Diablo DT which would seem likely to translate to a change in the center of pressure/lift resulting in gyroscopic turn(or less fade) as it reduces drag and pushes the CoP/L further back.

Some interesting stuff:

I'm pretty sure putter wings get bent down. I'd say it's more the whole rim bending down slightly as opposed to just the tip of the wing bending down on a driver.

Also, you're right. I'd have to roughen up the rim of the disc as opposed to the flight plate.

P.S. - I find it hilarious that all this started from a new player asking what happens when a disc gets beat in.

 

[sidewinder22]

I'm pretty sure putter wings get bent down. I'd say it's more the whole rim bending down slightly as opposed to just the tip of the wing bending down on a driver.

Also, you're right. I'd have to roughen up the rim of the disc as opposed to the flight plate.

Dings from below - blow the nose/wing upward. How often do your discs land upside down?

P.S. - I find it hilarious that all this started from a new player asking what happens when a disc gets beat in.

 

[sidewinder22]

Of course we also have the Aerobie Epic which tunes the disc PLH for understable or overstable flight by bending the edges up or down.

 

[Doofenshmirtz]

The relationship between the dings in my discs and how they fly.


Izak Neuton.

Yeah, I figured that you are guessing on this. The problem with an explanation that involves the surface roughness of the disc causing, directly or indirectly, more lift, is that it would be asymmetrical due to the spin of the disc. The advancing side of the disc and the retreating side of the disc would be affected differently due to spin. If there were additional lift on the advancing side of a thrown disc, precession would cause the the disc to nose up, causing a more rapid onset of fade.

This is just something that would need to be explained away if, somehow, reduced friction drag is the mechanism by which beating in increases understability. Perversely, lift itself causes drag. Add lift, and you add drag. An additional wild card to be explained away.

Another thing that makes me question the skin friction theory is boating. Air is a much less dense fluid than water and surface treatments on boats generally just try to smooth the surface because the friction drag is such a small part of the equation that it generally doesn't merit any shark-skin-like treatment (though such things do exist). The vast majority of the drag comes from moving aside the water through which the boat must move. Discs, flying through air, experience even less drag from skin friction than boats.

You'll also notice that airplanes are simply smooth. Don't you think if the airlines could save fuel and gain added lift that they would scuff them up? The drag that a disc or airplane experiences is primarily, if not wholly, a result of the need to move air out of the way to let the disc/plane move through it.

Finally, it is generally understood that a disc can be tuned. Aerobie even touts this feature of the Epic and provides instructions on how to do it. This trick is clearly an attempt to change the shape of the disc and it also pretty clearly works. While I don't KNOW that beating in a disc changes the disc's shape, that seems to be the most ready and elegant explanation for the effect that it has. Additionally, maybe someone with knowledge of plastics can weigh in on whether the simple aging of plastics can cause the shape of the disc to subtly change over time.

It also seems that shape change hypothesis would be the easiest to disprove. If so many people carry around so many discs of the same mold in varying levels of beating in, certainly it would not be too difficult to photograph all of them next to a vertical ruler. Even better, would be to do this to one disc, say a DX Roc, by photographing it when new, noting the flight characteristics, then when those characteristics change, photograph it again (or even better, video the edge while it is spinning on a turntable next to that vertical ruler).