Disc flight science

[Brychanus]

This thread is intended to focus discussion on disc flight modeling and mechanics from a scientific perspective. In that case, I want to link directly to peer-reviewed sources on modeling, controlled studies, and simulations.


Frisbee aerodynamics
Associated images boiling it down

The physics of frisbees

Disc golf trajectory modelling
related scripts
social media source

Optimal disc design using modeling and machine learning

One topic I remain interested in is the "dimple tech" hypothesis and other potential sources of variance as discs get beat up.

It's also potentially fun to list available public tools like thedisclab that involve some simulations or data sources here.

Obligatory "science-y" picture from the Optimal Disc Design paper:

 

[seedlings]

All I know is I have a Loft Bohrium, and it's decent - I hope they continue this high tech route and make a really great disc. IMHO they could make the rim diameter the absolute widest permitted, increase the depth a bit, and dome it more to get a bit more LSS, and even more lofty glide.

 

[txmxer]

There are some good threads that have discussed disc physics previously. You might want to check those out for reference.

 

[Doofenshmirtz]

One topic I remain interested in is the "dimple tech" hypothesis and other potential sources of variance as discs get beat up.

This is sort of the flat earth theory of disc golf. The Magnus effect as a explanation for turn has some basic problems that you can see in the video.

First, the shape of the two discs, when shown edge to edge, is obviously not the same. It almost looks like on disc is tilted to make the two edges meet where they do.

Next, the comparable PLH is only shown at one location on the discs; but if one of the reasons for a beat in disc becoming more understable is the change of shape from things like tree hits, you would really want to confirm both that the shape of the disc is the same and that the PLH is uniformly the same as the comparison disc all the way around the edge.

If the Magnus effect is responsible for turn, then it should be causing a flat turn and not causing the disc to flip up and turn over. In other words, the Magnus effect, if substantial enough to affect the flight path of the disc, shoudn't change the roll angle of the spinning disc because the force causing the direction change would be applied at an angle that is perpendicular to the spin axis of the disc. That the disc rolls and changes direction tends to suggest that the roll is caused by gyroscopic preception, in turn caused by a change of disc shape and not some kind of "dimple effect."

The comparison of cups, earlier in the video, is also telling. The relative surface area of a lightweight cup that makes up its leading edge when thrown as shown is utterly different than the surface area of a disc when compared to the disc's weight. The use of that comparison really tells you that the person who is using it really doesn't seem to understand the Magnus effect and why it likely has exceedingly little if any impact on the flight path of a disc.

Also, using a person throwing the disc and claiming that the "angle is the same" and the effort was the same, etc., is really asking for a suspension of disbelief.

 

[BogeyNoMore]

Many of the folks who posted in the linked thread are no longer active on these boards, abd I'm not saying everything in this thread is correct, but...

There's a lot of good info and discussion on the topic.

https://www.dgcoursereview.com/forums/showthread.php?t=2250

 

[txmxer]

Also, using a person throwing the disc and claiming that the "angle is the same" and the effort was the same, etc., is really asking for a suspension of disbelief.

Isn't repeatability a fundamental skill for disc golfers?

 

[hawgdriver]

Also, using a person throwing the disc and claiming that the "angle is the same" and the effort was the same, etc., is really asking for a suspension of disbelief.

What if....

"a person"

was actually

a Throwbot?

 

[sidewinder22]

This is sort of the flat earth theory of disc golf. The Magnus effect as a explanation for turn has some basic problems that you can see in the video.

First, the shape of the two discs, when shown edge to edge, is obviously not the same. It almost looks like on disc is tilted to make the two edges meet where they do.

Next, the comparable PLH is only shown at one location on the discs; but if one of the reasons for a beat in disc becoming more understable is the change of shape from things like tree hits, you would really want to confirm both that the shape of the disc is the same and that the PLH is uniformly the same as the comparison disc all the way around the edge.

If the Magnus effect is responsible for turn, then it should be causing a flat turn and not causing the disc to flip up and turn over. In other words, the Magnus effect, if substantial enough to affect the flight path of the disc, shoudn't change the roll angle of the spinning disc because the force causing the direction change would be applied at an angle that is perpendicular to the spin axis of the disc. That the disc rolls and changes direction tends to suggest that the roll is caused by gyroscopic preception, in turn caused by a change of disc shape and not some kind of "dimple effect."

The comparison of cups, earlier in the video, is also telling. The relative surface area of a lightweight cup that makes up its leading edge when thrown as shown is utterly different than the surface area of a disc when compared to the disc's weight. The use of that comparison really tells you that the person who is using it really doesn't seem to understand the Magnus effect and why it likely has exceedingly little if any impact on the flight path of a disc.

Also, using a person throwing the disc and claiming that the "angle is the same" and the effort was the same, etc., is really asking for a suspension of disbelief.

I think you misunderstood the point of this video which was a look out how "Surface Roughness" affects discs. This video was never intended to explain the Gyroscopic or Inertial effect on discs, which is why it is labelled "Viscous". A video explaining the full disc flight theory would also involve different wing shapes(under-stable vs over-stable wing design), weight distribution, lift, CoP, etc.

That is why this video only involved two discs of the same weight and wing design - with the main difference being the Surface Roughness. Any other differences between these two discs should be fairly negligible for this experiment. There are no camera tricks or disc tilting, they are virtually the same PLH all the way around the discs, no warp. I'd be happy to test any discs you can provide me that you approve of for this experiment of surface roughness.

I noted in the video that Magnus effect is not the only thing changing between the two discs, the dimples affects the Reynolds and boundary layer/drag/velocity. I also noted in the video that the sidewall height changes the magnitude of the Magnus effect that occurs.

If you want to buy me a radar gun I'd be happy to prove the release speed was consistent. The frames in video never matched up to actually prove the angle at moment of release, but I threw multiple shots with both discs with very little variation in results.

I have not seen any peer reviewed data on the effects of Surface Roughness on golf discs, but my conclusions are not incompatible with those from Potts & Crowther.

The effect of spin on the side force, pitching moment and rolling moment is small but measurable. The side force for higher AdvR(Advance Ratio >0.69) becomes positive. The aerodynamic moments exhibit similar characteristics, the pitching and rolling moments for higher AdvR both moments become more negative for typical flight angles of attack, 0° to 10°. The higher advance ratios provide a greater nose down pitching moment and a higher trim AoA just above 10°. The rolling moment for higher AdvR becomes negative.

The (precessional) pitch divergence is therefore caused by the spin-dependent Magnus rolling moment and has been shown to be zero for all typical flight AoA except for higher advance ratios. At this speed 20m/s(45mph/72kmph) the rotation rate would have to be 480rpm or above to start generating a non-zero rolling moment.

The aerodynamic Robins-Magnus side force and Magnus rolling moment act on the spinning disc-wing due to the interaction of near surface fluid structures. The resultant side force in this eventuality the disc may drift sideways in level flight or sideslip towards ground when flying with non-zero bank angle.

The lowest AdvR from Erin Hemmings results was about 0.85 which is well above the 0.69 from Potts and Crowther.

 

[Doofenshmirtz]

That is why this video only involved two discs of the same weight and wing design - with the main difference being the Surface Roughness. Any other differences between these two discs should be fairly negligible for this experiment. There are no camera tricks or disc tilting, they are virtually the same PLH all the way around the discs, no warp. I'd be happy to test any discs you can provide me that you approve of for this experiment of surface roughness.

I noted in the video that Magnus effect is not the only thing changing between the two discs, the dimples affects the Reynolds and boundary layer/drag/velocity. I also noted in the video that the sidewall height changes the magnitude of the Magnus effect that occurs.

What is "changing" between te two discs is that they are two different discs, in addtion to whatever differrences there are between the throws. It would seem much, much easier and far more persuasive to simply use one disc instead of two different ones. The throws don't show anything othern than that the two discs are different. That isn't exactly news or anything that supports the conclusions you seem to draw. It seems designed to give you license to simply interpret it to support the conclusion that you were trying to prove.

How hard could it possibly to buy a new disc, throw it, then go over that outer edge with a little sandpaper and throw it again?

 

[Sheep]

I got some links to add someplace. I'll have to find them.

And ... What you're kinda saying here is I need to move the disc golf wind tunnel higher on the priority of my projects right now so we can try and test any of this data?

 

[seedlings]

What is "changing" between te two discs is that they are two different discs, in addtion to whatever differrences there are between the throws. It would seem much, much easier and far more persuasive to simply use one disc instead of two different ones. The throws don't show anything othern than that the two discs are different. That isn't exactly news or anything that supports the conclusions you seem to draw. It seems designed to give you license to simply interpret it to support the conclusion that you were trying to prove.

How hard could it possibly to buy a new disc, throw it, then go over that outer edge with a little sandpaper and throw it again?

Sandpaper isn't the mechanism - it's dented crevices where the dirt collects, which are difficult to replicate in a short period of time. Say someone bought three Cloudbreakers of the same weight, wing height and dome; and they were more overstable than desired for a given form. Say that person took one of the three Cloudbreakers and threw it hard into the chains every single hole for a month of rounds… that's the kind of dimples talked about- not sandpaper removing bits of plastic.

If a person filmed that Cloudbreaker on day 1, and then filmed again a month or two later of chain dimpling, the weather, barometric pressure, humidity, temperature, wind, etc, could similarly void the comparison.

IOW, there is no practical way to eliminate ALL variables. SW22 demonstrated in his video a significant variation in flight - not a slight variation.

Sidenote: I know a guy with a flippy Cloudbreaker.

 

[timothy42b]

I got some links to add someplace. I'll have to find them.

And ... What you're kinda saying here is I need to move the disc golf wind tunnel higher on the priority of my projects right now so we can try and test any of this data?

Or throw in a pool.

Just keep the dimensionless numbers the same.

 

[Sheep]

One topic I remain interested in is the "dimple tech" hypothesis and other potential sources of variance as discs get beat up.

There was a dimple disc made, like golf ball dimples on the wing. It wasn't very good.

I wish I could use my words right now to explain all of this better.
But basically beat up discs create unstable drag on the wing. But there is a correct word for it that's not coming at 4am.

Oh it will come to me in the middle of filming later today when I dont have time to get on here and bump it in.

grrrr.

 

[BogeyNoMore]

Now defunct Quest Advanced Technologies made some discs with dimples for aerodynamics:
Raging Inferno DT and Defender (not to be confused with Dynamic Discs Defender) come to mind.

They each featured dimples along the wing. You should be able to google images of them.

 

[Doofenshmirtz]

Sandpaper isn't the mechanism - it's dented crevices where the dirt collects, which are difficult to replicate in a short period of time.

Right. So what you are saying is that this "theory" isn't replicable? Is it the dirt causing the discs to become flippy or the "crevices"?

It isn't the mechanism of putting the dimples on the disc that should matter, it is simply whether the texture of that surface causes the differences seen in the flight of the discs. Using two different discs to show significant differences in the flight between them only shows that the two different discs are, in fact, different.

 

[seedlings]

Right. So what you are saying is that this "theory" isn't replicable? Is it the dirt causing the discs to become flippy or the "crevices"?

It isn't the mechanism of putting the dimples on the disc that should matter, it is simply whether the texture of that surface causes the differences seen in the flight of the discs. Using two different discs to show significant differences in the flight between them only shows that the two different discs are, in fact, different.

Of course it's replicable. Everyone who's beat in a disc knows it flys differently than new. Washing the dirt off doesn't restore the flight characteristics. It's the dents and crevices. There may even be some sciency term that talks about the effects of dents and crevices?

 

[txmxer]

Of course it's replicable. Everyone who's beat in a disc knows it flys differently than new. Washing the dirt off doesn't restore the flight characteristics. It's the dents and crevices. There may even be some sciency term that talks about the effects of dents and crevices?

He has a point. While players have experience with "beat in" discs, whatever the effect is, cannot be un-reproducible through intentional modifications to the disc.

 

[Sheep]

He has a point. While players have experience with "beat in" discs, whatever the effect is, cannot be un-reproducible through intentional modifications to the disc.

This is what makes beat in discs good and bad.

A beat in disc ends up with an overtime flight we've learned and we like.

Then trying to season in another disc to fly like it doesn't always work.

Examples.

I had an electron soft envy that gave me the most beautiful controlled turnovers.
It went swimming to not be found when fishing.
I got another one. It flies nowhere near like the other one. Because they dont beat the same.

Example 2.
I got an Orange Fission Tesla. 158g.
That disc was my cherry. It used to fly SO straight, and it held this for months and months, then one day it was like "i'm flippy now"
And its a hyzer flip monster.
Watching online, its twin brother came up, same color/weight/run.
It's slightly seasoned. Like 10 rounds seasoned.
Fly straight? hahaha.
no, its barely seasoned and its almost as flippy as the other tesla.

Point being, that there are a lot of factors in disc flight in general from how the weight is balanced around the whole disc. chunks missing causing weird weight issues. Turbulence in the air of the flight.
And that other thing I said earlier that I still cannot think of.

I don't think its necessarily "micro dimples" that give these flights.
But anything that changes how the air pushes on the disc in flight is going to cause flight changes.

But this also has to do with spin of the disc, as. I can put the discs in a wind tunnel and we'll probably not see a huge difference in a stationary disc from new to seasoned, we'll see some. But not a lot.
But if the disc was spinning the micro turbulence the disc will see as those spaces move around the disc in flight will show us different results i'd suspect.

 

[Doofenshmirtz]

But this also has to do with spin of the disc, as. I can put the discs in a wind tunnel and we'll probably not see a huge difference in a stationary disc from new to seasoned, we'll see some. But not a lot.
But if the disc was spinning the micro turbulence the disc will see as those spaces move around the disc in flight will show us different results i'd suspect.

I think this is the problem with the Magnus effect as the proposed mechanism of increased turn in beat in discs. People know that beat in discs fly differently and when an explanation comes along that sounds sciency, they jump on it. The problem is that there is a known explanation for turn/flippiness/understability whether or not it happens in a disc that has been beat in and it isn't the Magnus effect.

The Magnus effect being responsible for the change in stability of a beat in disc is ostensibly being "proven" by showing how two different discs fly, which is evidence of nothing more than two different discs flying differently. So, so far, no evidence has been presented that the Magnus effect is causing a beat in disc to be flippier than it was when it was new. Oh, hey, and there's different disc, look how it flies differently.

Unlike Magnus, the only change that need happen to a disc in order for gyroscopic precesstion to fully explain a change in its stability is for its shape to change a little. This is the principle that disc tuning relies on. I still have an Epic whose stability I can change in a few seconds. In order to exclude this effect as the explanation for the change in stability of a beat in disc, you would need to show that the beat in disc hasn't changed shape. Comparing the flight of two different discs doesn't show that.

The other thing, about the video specifically, that caught my eye in this thread is the image with the caption about the PLH and weight being the same. Its at the point in the video showing the two discs (it's the point where the video is linked to in the "dimple tech" link above). Here's the image. Tell me that these two discs are basically the same shape and a good basis for the comparison that's being made:

I added a shadow reduction rectangle that gives a little basis for comparison. Notice the difference in slope of the top plate, amount of dome and somewhat different edge shape. I can't tell you how which of these things contributed to anything in the video, but I am very doubtful that the difference between the flights of these two discs is the "dimpling" on the beat in one.

If a disc's flight changes because of dimpling, then prove it by making that change happen by adding dimples to the disc and then compare the change in its flight to the same disc's original, pre-dimple flight without changing anything else. That is how this point could either be proven or debunked.

 

[sidewinder22]

I think this is the problem with the Magnus effect as the proposed mechanism of increased turn in beat in discs. People know that beat in discs fly differently and when an explanation comes along that sounds sciency, they jump on it. The problem is that there is a known explanation for turn/flippiness/understability whether or not it happens in a disc that has been beat in and it isn't the Magnus effect.

The Magnus effect being responsible for the change in stability of a beat in disc is ostensibly being "proven" by showing how two different discs fly, which is evidence of nothing more than two different discs flying differently. So, so far, no evidence has been presented that the Magnus effect is causing a beat in disc to be flippier than it was when it was new. Oh, hey, and there's different disc, look how it flies differently.

Unlike Magnus, the only change that need happen to a disc in order for gyroscopic precesstion to fully explain a change in its stability is for its shape to change a little. This is the principle that disc tuning relies on. I still have an Epic whose stability I can change in a few seconds. In order to exclude this effect as the explanation for the change in stability of a beat in disc, you would need to show that the beat in disc hasn't changed shape. Comparing the flight of two different discs doesn't show that.

The other thing, about the video specifically, that caught my eye in this thread is the image with the caption about the PLH and weight being the same. Its at the point in the video showing the two discs (it's the point where the video is linked to in the "dimple tech" link above). Here's the image. Tell me that these two discs are basically the same shape and a good basis for the comparison that's being made:

I added a shadow reduction rectangle that gives a little basis for comparison. Notice the difference in slope of the top plate, amount of dome and somewhat different edge shape. I can't tell you how which of these things contributed to anything in the video, but I am very doubtful that the difference between the flights of these two discs is the "dimpling" on the beat in one.

If a disc's flight changes because of dimpling, then prove it by making that change happen by adding dimples to the disc and then compare the change in its flight to the same disc's original, pre-dimple flight without changing anything else. That is how this point could either be proven or debunked.

Finally.... you brought some evidence, but doesn't really disprove anything.

I said that the dimples are the reason the disc behaves the way it does. I never claimed that Magnus was the main thing responsible for turning the discs over, or that this was the authoritative explain all of disc physics. I talked about Magnus effect during the cup demonstration. During the disc demonstration I talked about the dimples affecting drag and velocity(non Magnus things) - which would also affect CoP. The main point of the video was to demonstrate a fun drill/practice you can do inside and explain the physics on the cups, and to a lesser point the discs.

The iPhone I used to take this ultra-scientific experiment was handheld, so it's tilted and not centered and the discs are also not the same exact distance from the lens. You can see the bottom doesn't match exactly either. Regardless the PLH/wing tips are the same exact height, if anything the new disc has slightly lower PLH which should make it less stable. There was a slight dome on the new disc. The consensus seems to be that PLH is much greater indicator of stability than dome and there doesn't seem to be consensus on whether dome makes the disc more or less stable.