[Help] Comprehensive Explanation of Disc Golf Physics

[PMantle]

Also, I cannot follow the statement, that removing a part of the lower edge of the wing, would lower the PLH. Removing the lower edge of the wing makes the wing definitely higher and thus the PLH higher.

You're just not visualizing this properly. I don't even come close to understanding how you think this way. Removing something under something makes that something lower.

 

[armiller]

This is the post I reference in my original. I think that a lot of the effects it talks about are too minor to have significant effects on the flight of discs, and some effects are simply not accurate at all the way they are explained. I'd gladly listen to supporting evidence, though.

You definitely have to read through a lot of nonsense to get to the people who actually know what's up. But the good stuff is pretty good. I'm curious exactly what you mean or what you are referencing (still haven't had a chance to read your entire initial post)...

 

[Meillo]

You're just not visualizing this properly. I don't even come close to understanding how you think this way. Removing something under something makes that something lower.

I think we misunderstood each other: I don't mean the part that touches the table if you put the disc on the table. I rather mean the wing tip, i.e. the outermost part of the disc, and there the lower edge. This is what gets scratched if my discs skip off roads.

 

[Meillo]

I think because of the flight plate on top is structural not allowing the disc to bend that way, so the weak point (bottom) is going to bend down. Think of the entire disc folding like a hard shell taco. It's going to fold at the point of least resistance so the flight plate is like the bottom outer shell of the taco.

Now the disc doesn't fold that much of course unless it;s supper floppy, but I think the flight plate is creating the impact downward into the wing.

Thinking about it too is the point that joins the flight plate and wing will act like a hinge, so it will bend down from the hinge point. The center of gravity for the wing even on a FB is lower then the hinge.

I understand what you mean, but if I think of a puddletop Zone, I have difficulties to believe that this kind of force, which in case of a Zone goes almost into the flight plate, not below it, would bend the wing down enough that it would explain the change in flight. For some molds I can think that it does, but for some like a Zone it does not.

I'm pretty sure that there are multiple factors. If there would only be bending the wing down, how would you then explain the different beating-in schemes of Teebird and Eagle? They would have to beat in the same, which would be, lowering the PLH and thus losing HSS. But Teebirds lose their fade first, staying pretty HSS. Thus there's another kind of beating-in happening.

If bending the wing down does develop turn (i.e. losing HSS), I could follow that. But losing fade would need a different explanation then.

 

[txmxer]

Ha ha, I knew someone would get me for that. You're right, it's not as simple as that. However, I sacrificed exact calculations here for intuitive understanding, and the effect I describe is still accurate and easily testable.

To be fair, I don't think that's the only thing that is inaccurate. Some more egregious.

 

[armiller]

Warning: it's about to get technical.

I've been looking around for a comprehensive and technical explanation of why discs fly the way they do and everything I've found has been either outright incorrect or not as technical as I wanted. Even if there is another good explanation out there, I want to make a good explanation easier to find on Google.

Therefore, I've compiled an explanation that to my knowledge shows technically how discs work. If any physicists out there catch any errors, please let me know, the last thing I want to do is look like a buffoon claiming that my wrong answer is right.

I should note that there is another post on this website about this topic, but 1) I want to use slightly more technical language and 2) I'm not confident that the effects it describes are entirely responsible for disc flight.

...

There are a few things here I haven't mentioned. First, what determines the speed of a disc. I imagine this is simply a measure of its wind resistance, but I don't know.

Second, what determines the glide of a disc and why the bottom rim of some discs is curved. I imagine this is something to do with fluid dynamics, which I know very little about.

Third, the other post about physics on this website. Frankly, I didn't follow it very well because I couldn't see the figures. However, the parts I did understand were more or less based in good science, but would not create enough force to significantly affect the flight of a disc.

The merit of your post is that you hit the high points. In other words, disc flight comes down to the fact that a disc is 1) an airfoil or wing as well as 2) a gyroscope. The forces (weight plus lift and drag) and the rotational factors such as angular velocity/momentum and changes therein (secondary to torques from lift and drag) are what govern disc flight.

I think that your organization and separating into straight-flying, falling, and rising is somewhat arbitrary. It doesn't really change any of the forces or moments on the disc, just changes the direction and magnitude. But I like most of your figures, and I agree that it would be helpful for new folks to have good photos to grasp these concepts.

The thread that is stickied, which you referenced, is there because it's the longest and most complete, even though it also has the most INCORRECT information. You have to sift through some bad stuff to find the good.

Here is another thread, called "Disc Golf / Frisbee Physics 101" which has very good information (the user, john63, very briefly hopped onto DGCR here and added some very good info). In particular, you will sound like a doofus if you talk about this stuff without having read Hummel's thesis (a Masters thesis from UC Davis around 2005 related to ultimate discs). The Potts & Crowther lab in the UK is also excellent, and I remember one particularly good paper (5-10 years ago) that compared some molds, such as the Aviar, Buzzz, Flick, and Wraith. Some of your discussion on the PLH or OS/US discs is confusing to me. I think it's easy to fall into a trap where you try to make the strict/technical physics stuff apply to the geometry of discs. It's commendable, but I've read lots of posts that try to connect all the physics things to more practical aspects of disc design... and I don't think anyone has quite gotten it right. Or maybe it's just not worth trying to get right?

Glide and Speed are artificial values, somewhat arbitrary, assigned by golfers and designers. Glide tries to quantify lift, and speed tries to quantify drag. But since all these things are velocity dependent (and angle of attack), they're imperfect even if they can be helpful sometimes (i.e. in describing how a disc flies to someone who has never thrown the disc).

 

[IronIceandFire]

"It doesn't really change any of the forces or moments on the disc, just changes the direction and magnitude."

I might be misunderstanding this, but from my perspective, the forces on the disc are vectors, which have direction and magnitude. When you change those, you by definition change the forces.

Thank you for the complements, and thank you VERY much for linking more scholarly stuff! The more scholarly sources we have attached to this thread the better, IMO.

 

[PMantle]

I think we misunderstood each other: I don't mean the part that touches the table if you put the disc on the table. I rather mean the wing tip, i.e. the outermost part of the disc, and there the lower edge. This is what gets scratched if my discs skip off roads.

That still will not raise the parting line.

 

[oldmandiscer]

I understand what you mean, but if I think of a puddletop Zone, I have difficulties to believe that this kind of force, which in case of a Zone goes almost into the flight plate, not below it, would bend the wing down enough that it would explain the change in flight. For some molds I can think that it does, but for some like a Zone it does not.

I'm pretty sure that there are multiple factors. If there would only be bending the wing down, how would you then explain the different beating-in schemes of Teebird and Eagle? They would have to beat in the same, which would be, lowering the PLH and thus losing HSS. But Teebirds lose their fade first, staying pretty HSS. Thus there's another kind of beating-in happening.

If bending the wing down does develop turn (i.e. losing HSS), I could follow that. But losing fade would need a different explanation then.

The Teebird is just a perception or illusion (Star or Champ especially). It is losing both at the same time but since the disc had so much HSS to being with you are only visually seeing it fade less or later (losing LSS). It didn't turn to being with and still isn't after some beating so you just don't notice it. So it just flies straighter.

The Zone is a narrow rim so it's going to take a ton of wear. Maybe mostly from the bottom from skipping off rocks, pavement, or just general sticks and ground. The bending of the rim itself is going to be minor but I could see the bottom edge wearing in quicker overall, like wearing off any flash or simply wearing the bottom edge to lower the PLH overtime.

That was the original reason for the bead, to prevent the bottom edge from wearing out quickly (especially with the base plastics) and the disc losing stability so it lasts longer.

 

[txmxer]

"It doesn't really change any of the forces or moments on the disc, just changes the direction and magnitude."

I might be misunderstanding this, but from my perspective, the forces on the disc are vectors, which have direction and magnitude. When you change those, you by definition change the forces.

Thank you for the complements, and thank you VERY much for linking more scholarly stuff! The more scholarly sources we have attached to this thread the better, IMO.

You should read those sources then provide a correction to your flawed "comprehensive explanation ".

I kind of think your post was mostly trolling. A new member first post. Here is the physics of flight. Gonna get technical up in here.

But most of it is wrong. Errors and illogical presentation.

 

[armiller]

You should read those sources then provide a correction to your flawed "comprehensive explanation ".

I kind of think your post was mostly trolling. A new member first post. Here is the physics of flight. Gonna get technical up in here.

But most of it is wrong. Errors and illogical presentation.

That's a little strong...

I do think you touch on the fundamental issue with all these physics discussions. Some of us, in the course of our disc golf obsession, become obsessed with the physics of disc flight. However, it's usually just one time, close to our initial disc golf exposure. So this is what we see: someone comes along and asks all these questions, posits some explanations, and then there's a decent discussion which seems to reach some kind of consensus. Then things get quiet for 6 months or so, and then someone else comes along, resurrects the discussion, asks/answers the same questions, and then everyone forgets about physics for a while. We should commission one of these labs to write a "Disc Physics for Dummies" authoritative document that we can rely on.

 

[armiller]

"It doesn't really change any of the forces or moments on the disc, just changes the direction and magnitude."

I might be misunderstanding this, but from my perspective, the forces on the disc are vectors, which have direction and magnitude. When you change those, you by definition change the forces.

Thank you for the complements, and thank you VERY much for linking more scholarly stuff! The more scholarly sources we have attached to this thread the better, IMO.

That's kind of nitpicking... I mean it doesn't fundamentally change the forces involved. They're the same fundamental forces in any situation, but those different magnitudes and directions change the flight significantly.

I keep wanting to draw my own diagrams and make a similar post to yours with my own explanation of things, but I just haven't ever done it and don't have the desire to make images or scan drawings.

 

[txmxer]

That's a little strong...

I do think you touch on the fundamental issue with all these physics discussions. Some of us, in the course of our disc golf obsession, become obsessed with the physics of disc flight. However, it's usually just one time, close to our initial disc golf exposure. So this is what we see: someone comes along and asks all these questions, posits some explanations, and then there's a decent discussion which seems to reach some kind of consensus. Then things get quiet for 6 months or so, and then someone else comes along, resurrects the discussion, asks/answers the same questions, and then everyone forgets about physics for a while. We should commission one of these labs to write a "Disc Physics for Dummies" authoritative document that we can rely on.

I agree that a simplified qualitative discussion is useful.

The presentation here was presented as if we were about to get schooled in the physics of flight , but then the OP proceeds to bumble through some basic Newtonian physics and overlook some more critical aspects of flight plus throw in a few errant factoids.

When some newb shows up and reads this, they will be misinformed if not for the responses that direct them to more accurate information.

The "physics of flight " YouTube videos would be a much better resource than what was given here.

 

[IronIceandFire]

I agree that a simplified qualitative discussion is useful.

The presentation here was presented as if we were about to get schooled in the physics of flight , but then the OP proceeds to bumble through some basic Newtonian physics and overlook some more critical aspects of flight plus throw in a few errant factoids.

When some newb shows up and reads this, they will be misinformed if not for the responses that direct them to more accurate information.

The "physics of flight " YouTube videos would be a much better resource than what was given here.

I was really hoping that we could keep to scholarly discussion here. Which phenomena specifically do I describe incorrectly?

 

[IronIceandFire]

I do agree that comprehensive was the wrong word entirely, however. At the very least I hope that the aspects I didn't cover will be covered or at least linked in the thread, though. So maybe in that sense the thread can be called comprehensive.

 

[txmxer]

I was really hoping that we could keep to scholarly discussion here. Which phenomena specifically do I describe incorrectly?

Sorry not here to educate you—id be guilty of repeating others information that is in the referenced links.

Your use of CCW right off the bat makes your presentation hard to follow as most throw RHBH, and virtually all discussions are based on CW rotation. I know it doesn't matter from physics standpoint, but you immediately ask the reader to reverse all traditional thought. Plus I think you referenced RHBH at one point.

Pretty sure the whole stability section is garbage. Question for you to answer: Disc air speed determines stability. Why?