Disc Physics

[Blake_T1]

The angle must be referenced and I suggest a relation to horizon at the rip. What I meant was that perhaps it's beneficial to pick an angle available to even amateurs without too much trouble and still not nose up.

newbies or ams? ams i know are capable of generating enough nose down to throw most drivers. newbies are the ones who struggle with nose down.

decent rec players are capable of finding a way to throw contemporary drivers of the era. this is the way it has always been and always will be. that doesn't mean they have good form, but there's guys who can find a way to make a destroyer land in the fairway quite often even though they don't have near the power for it.

however, each disc has an idealized flight and that flight is nose down.

On the nose angle/cruise speed topic: It sounds as if the ideal nose angle is one that is low enough to account for the lift generated?

there's 2 critical nose angles.
-enough nose down to allow the flight characteristics of the disc.
-not too much nose down so that there's no lift and it burns into the ground.

a "good" nose angle falls in between those angles. the more nose down within the range of those angles, the less stable the disc will be.

Nose down orientation can be achieved simply through a proper grip. It was taught to me (either by reading what Blake wrote or Dave D., I can't remember) by describing a cocked wrist position similar to when you are pouring coffee from a coffee pot.

there's 2 other factors:
-weight forward.
-tight to the body during the pull.

more wrist extension = more potential nose down.

 

[Jeronimo]

On the nose angle/cruise speed topic: It sounds as if the ideal nose angle is one that is low enough to account for the lift generated?

there's 2 critical nose angles.
-enough nose down to allow the flight characteristics of the disc.
-not too much nose down so that there's no lift and it burns into the ground.

a "good" nose angle falls in between those angles. the more nose down within the range of those angles, the less stable the disc will be.

Looking for a more quantitative response than this.

 

[JHern]

OK, Nose Angle/Angle of Attack...

Definition of Nose Angle: Look at the figure I posted at the beginning of this thread. Imagine the disc is flying over flat, level ground beneath it and the schematic perspective is not tilted relative to the ground. In the top left graphic, the nose is up (pitched upward relative to the plane of the ground, in the direction of motion). In the middle left graphic, the nose angle is flat. In the bottom left figure the nose is down (pitched downward relative to the plane of the ground, in the direction of motion).

Definition of Angle of Attack: Look again at the figure I posted at the beginning of this thread. In the top left graphic, the nose is pitched up relative to the velocity vector, yielding a positive angle of attack. In the middle left graphic, the velocity is in the plane of the disc, and it has zero angle of attack. In the bottom left figure the nose is pitched down relative to the velocity vector, yielding a negative angle of attack.

The difference: the nose angle is defined relative to the horizontal plane of the ground (flat ground assumed), while the angle of attack is defined relative to the velocity vector. Only if the disc is flying level and straight with no ascent or descent, are the nose angle and angle of attack the same thing. Because the velocity vector changes during flight, but the ground level stays fixed, the angle of attack can vary during a flight even if the nose angle stays exactly fixed throughout the flight (which is does, for the most part, except under extreme conditions).

Note that in assessing aerodynamic forces, the velocity of the disc should be defined relative to the velocity of the air, not the ground. The aerodynamic lift force on a disc depends on the Angle of Attack, not the Nose Angle, although a small or negative nose angle sets the disc up for a flight that will have a small or negative angle of attack.

In wind tunnel experiments with lid-like discs, the lift force was found to vary linearly with the Angle of Attack. The lift increases as the Angle of Attack increases. The lift forcegoes to zero at some critical negative angle of attack (it was around -4 degrees for a standard catch Frisbee), and for angles less than this critical angle the lift force is actually negative and pushes the disc down.

 

[George1]

Those are wise definitions and, at least in terms of the physics, it is necessary to keep clear the distinction. Is there a need to define similar angles for the perpendicular axis? I'm guessing that hyzer angle would measured with respect to the ground. What would be the analogous angle measured with respect to the air? (Roll angle? I suspect such a quantity would be needed in a simulation, but maybe it doesn't need a name, just a letter.)

If I can be of any help on your simulation project, please let me know.

George

 

[JHern]

They say a picture is worth a thousand words...

 

[Nothaz]

They say a picture is worth a thousand words...

It would take much less than a thousand for me to explain what I see there...

 

[JHern]

Those are wise definitions and, at least in terms of the physics, it is necessary to keep clear the distinction. Is there a need to define similar angles for the perpendicular axis? I'm guessing that hyzer angle would measured with respect to the ground. What would be the analogous angle measured with respect to the air? (Roll angle? I suspect such a quantity would be needed in a simulation, but maybe it doesn't need a name, just a letter.)

Sarah Hummel's thesis describes how this is typically done, by defining a coordinate system oriented by the plane of the disc and the velocity vector. That's what I'm following.

If I can be of any help on your simulation project, please let me know.
George

Cool. I'll find a way to post the PDF file when it is more readable, and then I'll start taking comments...it would be very nice to here from you at that point.

I had a nice discussion with Blake last night about disc flight, throwing, and all sorts of other stuff. It seems like it should be possible to use the simulations to map the flight chart into simulated flight characteristics for the various disc/molds by calibrating real physical values to the subjective scales already in use. On the other hand, Blake has also seen some very strange flights (albeit mostly under extreme conditions that won't apply to most throwers) that will be more difficult to analyze, and raise questions about some typical assumptions under various conditions.

 

[Blake_T1]

Looking for a more quantitative response than this.

heh...

you realize that it varies for every single disc on the market right?

it also varies depending upon your definition of the nose. some treat nose down as below the plane as if the disc was sitting on a flat surface (e.g. referencing the bottom rim or flat part of the top as the "level" point) while others will treat nose down as the below the angle of slope coming off the top of the disc near its edge.

using the first definition, a disc like an aviar will basically perform "nose down" well between say 0.1 degrees and 5 degrees. a disc like an orc needs more like 5-12 degrees.

there's ways to cheat nose angles a bit artificially by lining up your body in one direction and forcing a push/pull on the disc to force it slightly off line of center. pushing the disc left of center with a hyzer throw will behave more nose down than throwing it straight ahead. pulling a disc to the right of center with an anhyzer throw will behave more nose down than throwing it straight ahead. this is why you find people who throw with the disc too far away from the body entering the power zone generally only get nose down throws when they throw slight anhyzer.

it's also possible to OAT a disc nose down (or more nose down).

JHern and i discussed a bunch of stuff in regards to this with distance throws and how during the mega push sections of a distance toss (in the turn or fade portions) have the disc 30+ degrees nose down.

 

[JHern]

Looking for a more quantitative response than this.

heh...

you realize that it varies for every single disc on the market right?

It would be good to catalog the attack angle for zero lift for the various molds. It is an essential parameter.

there's ways to cheat nose angles a bit artificially by lining up your body in one direction and forcing a push/pull on the disc to force it slightly off line of center. pushing the disc left of center with a hyzer throw will behave more nose down than throwing it straight ahead. pulling a disc to the right of center with an anhyzer throw will behave more nose down than throwing it straight ahead. this is why you find people who throw with the disc too far away from the body entering the power zone generally only get nose down throws when they throw slight anhyzer.

I'm trying to visualize this, and it seems like it would be the other way around? I.e., right of center for hyzer and left of center for anhyzer? Or maybe I'm missing something.

it's also possible to OAT a disc nose down (or more nose down).

That's the only explanation I can think of for the crazy throws you were describing (e.g., Rico's Magnet throw). In principle OAT could give the disc a roll moment that precesses the disc to a nose down orientation. But of course this is hard to do in a reproducible, consistent way. And OAT surely loses velocity as well.

JHern and i discussed a bunch of stuff in regards to this with distance throws and how during the mega push sections of a distance toss (in the turn or fade portions) have the disc 30+ degrees nose down.

There are probably less than 1000 people in the world who could perform the kinds of extreme distance throws we were discussing...those with both big snap and exquisite ability to shape lines have mastered a very difficult pair of skills.

 

[Blake_T1]

I'm trying to visualize this, and it seems like it would be the other way around? I.e., right of center for hyzer and left of center for anhyzer? Or maybe I'm missing something.

no, especially if the focus is on a nose down launch rather than a nose down finish. when you swing a hyzer wide right it (in 95% of cases) immediately exposes nose up since you are throwing it slightly towards the bottom of the disc. the wider you pull the hyzer the more extreme this is. these will finish nose down but start nose up.

if you PUSH an anhyzer to the left you are also exposing flight plate. there's ways to aim left and PULL an anhyzer that will still start out to the left, but this is a completely different shot entirely.

That's the only explanation I can think of for the crazy throws you were describing (e.g., Rico's Magnet throw). In principle OAT could give the disc a roll moment that precesses the disc to a nose down orientation. But of course this is hard to do in a reproducible, consistent way. And OAT surely loses velocity as well.

not all OAT removes velocity. anytime someone is throwing a distance line hyzer flip s-curve they are putting OAT on it without decreasing their launch velocity.

there's two types of OAT. hyzer/anhyzer and nose angle.
there's several body motions that will deliver one or both types of OAT.
-changing the shoulder plane (hyzer/anhyzer)
-separating the elbow plane from the shoulder plane (hyzer/anhyzer)
-separating the wrist plane from the elbow plane (hyzer/anhyzer)
-changing the elbow plane and wrist plane (hyzer/anhyzer and nose angle)
-forcing weight forward or weight back (nose angle)
-forcing an abrupt weight shift forward/back after the initial weight shift (nose angle)
-rolling the wrist over/under (nose angle and hyzer/anhyzer)

There are probably less than 1000 people in the world who could perform the kinds of extreme distance throws we were discussing...those with both big snap and exquisite ability to shape lines have mastered a very difficult pair of skills.

sure, but there's likely less than 1000 people in the world who can consistently generate the power to throw 500'. however, it doesn't take big snap to be able to shape lines. most people do OAT unconsciously. guys who shape lines well do OAT consciously on a lot of throws.

the nice thing about consciously OATing to shape a line is that it requires much less precision than trying to pure a throw with a perfect angle, velocity, and disc selection given the wind conditions, etc.

 

[Gator]

While I will never stop reading these posts on here, sometimes I just have to back out of a thread and let my head stop spinning.

 

[Timko]

Blake, that's one of the best posts I've read by you.

 

[JHern]

I'm trying to visualize this, and it seems like it would be the other way around? I.e., right of center for hyzer and left of center for anhyzer? Or maybe I'm missing something.

no, especially if the focus is on a nose down launch rather than a nose down finish. when you swing a hyzer wide right it (in 95% of cases) immediately exposes nose up since you are throwing it slightly towards the bottom of the disc. the wider you pull the hyzer the more extreme this is. these will finish nose down but start nose up.

if you PUSH an anhyzer to the left you are also exposing flight plate. there's ways to aim left and PULL an anhyzer that will still start out to the left, but this is a completely different shot entirely.

OK, I think I get it now, but I will have to try and do this myself to really get it.

That's the only explanation I can think of for the crazy throws you were describing (e.g., Rico's Magnet throw). In principle OAT could give the disc a roll moment that precesses the disc to a nose down orientation. But of course this is hard to do in a reproducible, consistent way. And OAT surely loses velocity as well.

not all OAT removes velocity.

What I meant by OAT reducing velocity was not that you lose launch speed at release, but rather that the drag is increased while the disc is wobbling because the disc gathers a bunch of turbulent air around it like a coat of whirls that it drags along with it, effectively increasing the cross-section relative to the air this whole thing is passing through (and drag increases in proportion to cross-sectional area).

anytime someone is throwing a distance line hyzer flip s-curve they are putting OAT on it without decreasing their launch velocity.

there's two types of OAT. hyzer/anhyzer and nose angle.
there's several body motions that will deliver one or both types of OAT.
-changing the shoulder plane (hyzer/anhyzer)
-separating the elbow plane from the shoulder plane (hyzer/anhyzer)
-separating the wrist plane from the elbow plane (hyzer/anhyzer)
-changing the elbow plane and wrist plane (hyzer/anhyzer and nose angle)
-forcing weight forward or weight back (nose angle)
-forcing an abrupt weight shift forward/back after the initial weight shift (nose angle)
-rolling the wrist over/under (nose angle and hyzer/anhyzer)

It seems like any way you can shift the shoulders, elbows, wrist, weight, off plane will give some OAT. When you are specifying nose vs hyzer OAT, the essence is that the torque added to the disc before release is pitch or roll, respectively, right? However, it seems like during flight the disc inevitably ends up wobbling equally around the roll and pitch axes...this wobble dissipates relatively quickly, but during that time frame the overall pitch moment increases, making the disc turn over.

There are probably less than 1000 people in the world who could perform the kinds of extreme distance throws we were discussing...those with both big snap and exquisite ability to shape lines have mastered a very difficult pair of skills.

sure, but there's likely less than 1000 people in the world who can consistently generate the power to throw 500'. however, it doesn't take big snap to be able to shape lines. most people do OAT unconsciously. guys who shape lines well do OAT consciously on a lot of throws.

the nice thing about consciously OATing to shape a line is that it requires much less precision than trying to pure a throw with a perfect angle, velocity, and disc selection given the wind conditions, etc.

Interesting. It looks like I'll have to account for OAT a bit more in my model, if I'm going to reproduce the disc flights we all know and love (even if we don't always know why).

 

[Blake_T1]

What I meant by OAT reducing velocity was not that you lose launch speed at release, but rather that the drag is increased while the disc is wobbling because the disc gathers a bunch of turbulent air around it like a coat of whirls that it drags along with it, effectively increasing the cross-section relative to the air this whole thing is passing through (and drag increases in proportion to cross-sectional area).

you can do it without wobble though. wobble is indicative of OAT, but OAT doesn't mean it wobbles.

It seems like any way you can shift the shoulders, elbows, wrist, weight, off plane will give some OAT. When you are specifying nose vs hyzer OAT, the essence is that the torque added to the disc before release is pitch or roll, respectively, right? However, it seems like during flight the disc inevitably ends up wobbling equally around the roll and pitch axes...this wobble dissipates relatively quickly, but during that time frame the overall pitch moment increases, making the disc turn over.

"good" OAT happens very late in the throw. i think of it more as english in pool.

i'm too tired to write about this in depth right now heh.

 

[JHern]

After discussing with Blake last night, about the force balances and equilibriums that a disc seeks to achieve throughout its flight, I decided to put together the following figure to illustrate some key concepts. I have derived this from the equations of motion alone, so this is from exact math.

Here's the brief explanation of the figure below. The disc is trying to achieve the equilibriums shown on this plot. It might over/under-shoot equilibrium, but the equilibrium is stable and restoring forces bring it back to equilbrium when it drifts away. This leads to oscillatory behavior, however, the oscillations are damped by viscous dissipation of the surrounding air. Because it is a high dissipation system, the system will rapidly approach equilibrium conditions. A disc's flight follows the paths shown by the arrowheads, from high speed to low speed. When ascending, working against gravity as well as drag slow the disc down. When descending, gravity helps add energy to the disc's flight, but dissipation is ever present. An equilibrium between work done by gravity and drag dissipation is attained at the "Glide" points.

I'm sure there are going to be loads of questions now. This will hopefully ignite this discussion.

(Figure updated with some more details...)

 

[Jeronimo]

Awesome.

 

[erb]

I don't have the time right now to read this whole post, but thought I would just throw in one of my thoughts on fade/spin/shape.
I believe that much of the fade is due to the discs friction with the the air and the direction of spin on the disc. By overtaking the forward velocity (and maybe a small bit of glide) of the disc, after drag slows it down a bit, and then becoming the main force controlling the discs movement. Much like how spin affects a baseball pitches motion, and I think also bending a soccer ball kick (but I don't know that much about soccer). I think that when the disc slows down enough and the spin force is greater it fades because the nose and the front half or front semicircle of the disc start to "bite" or "grip" the air. And it rolls/moves in the direction that the spin makes it. Almost like if a disc thrown at a wall sticks then rolls left or right based on its spin. This is shown in throws with opposite spins and the direction of the discs fade (RHBH fades left, LHBH fades right). What also supports this theory is the strength of fade you see in two discs with similar glide but with different nose thickness. The thick noised disc will have a stronger fade. Dave D. knows this also, if you look at his products the Max, Firebird, Monster all have a fairly thick nose and have a strong fade. Also remember when he tried to make a more overstable Wraith (talking about the first Teerex) he just made the nose thicker, it had similar HSS but more LSS.
What also contributes to fade by friction is the angled top and bottom of the disc, that make up the front semicircle of the disc. This is a combination of how steep or sloped the sides are and how much effective area the disc has. What I mean by "how much effective area the disc has" is this formula:
Effective area of the disc = 2*(to the area of a semicircle of the disc) - the area of the discs semicircular flat part on top - the area of the inside part of the disc where your fingers go into to throw it.
You subtract the Semicircular flat part on top and inside of the bottom since the friction developed there is negligible.
Then you use some calculus to find just how much a discs effective area and slope contribute and add that to the thickness of the nose to see how the shape of the disc will effect it's fade.
But after all that glide and slow cruising speed are the the fade killer. This is shown in discs that are closer to ultimate style discs. the Fade is much more forward dominated and not just hard left or right.

One more thought since I brought up spin.
I also believe that more spin to speed helps with distance and accuracy (and maybe overall straighter flight). This is coming from how rifling effects a bullet's flight. Rifles before the invention of rifling where very inaccurate with the ball flying all over the place, Similar to a knuckle ball in baseball. Then with the help of rifling the bullet flew in a straighter line, meaning it would go where you pointed it. This straighter flight would also direct more of the energy in a forward direction and less energy would be wasted moving the ball side to side, thus achieving a longer range with the same amount of gun powder. But the main difference is that with a disc the axis of which it spins around is more perpendicular to the line of flight and in the bullet it's tangent to the line. So how much that fact changes things, I'm not really sure.

But, hope that gave you some ideas to think about.

 

[Blake_T1]

I believe that much of the fade is due to the discs friction with the the air and the direction of spin on the disc. By overtaking the forward velocity (and maybe a small bit of glide) of the disc, after drag slows it down a bit, and then becoming the main force controlling the discs movement. Much like how spin affects a baseball pitches motion, and I think also bending a soccer ball kick (but I don't know that much about soccer)

There was a time when I believed that disc surface friction had something to do with it but fluid boundary dynamics disproved that. the effects that spin has upon disc flight are not based upon air friction as it is with something like a curveball/slider in baseball.

What also contributes to fade by friction is the angled top and bottom of the disc, that make up the front semicircle of the disc. This is a combination of how steep or sloped the sides are and how much effective area the disc has. What I mean by "how much effective area the disc has"

this is true, but it's based more upon aerodynamics.

 

[JHern]

I don't have the time right now to read this whole post, but thought I would just throw in one of my thoughts on fade/spin/shape.
I believe that much of the fade is due to the discs friction with the the air and the direction of spin on the disc. By overtaking the forward velocity (and maybe a small bit of glide) of the disc, after drag slows it down a bit, and then becoming the main force controlling the discs movement. Much like how spin affects a baseball pitches motion, and I think also bending a soccer ball kick (but I don't know that much about soccer). I think that when the disc slows down enough and the spin force is greater it fades because the nose and the front half or front semicircle of the disc start to "bite" or "grip" the air. And it rolls/moves in the direction that the spin makes it. Almost like if a disc thrown at a wall sticks then rolls left or right based on its spin. This is shown in throws with opposite spins and the direction of the discs fade (RHBH fades left, LHBH fades right). What also supports this theory is the strength of fade you see in two discs with similar glide but with different nose thickness. The thick noised disc will have a stronger fade. Dave D. knows this also, if you look at his products the Max, Firebird, Monster all have a fairly thick nose and have a strong fade. Also remember when he tried to make a more overstable Wraith (talking about the first Teerex) he just made the nose thicker, it had similar HSS but more LSS.

Thanks for contributing, erb. Many people have the same impression about fade, but it's actually not true...I'll explain:

What you speak of is called the "Magnus Force," which due to rotation causes the total aerodynamic lift force to point sideways from the velocity, making the object veer sideways. This is indeed what makes a spinning ball curve in its flight (its important in all ball sports...baseball, soccer, tennis, cricket, etc.). It is not, however, what make the disc turn or fade (see below for a possible exception). The reason why the disc is not strongly affected by the Magnus force is that the lateral surface area of the disc is very small, i.e., it has a low profile in the direction in which the force is supposed to act. (The drag force also acts on the same small profile, which is why a disc can fly far without significantly slowing down.) This is different for a ball/sphere, which shows the same cross-section area in every direction. But anyways, due to the small side profile of the disc, there is very little aerodynamic forcing generated because the area to act on is small in comparison to the area of the flight plate.

Possible exception: what Blake calls Hyper-Spin (or something similar). This is when the disc is spun ridiculously fast; where the velocity at the edge of the disc due to spin is very fast in comparison to the translational speed of the disc through the air. Then you might detect the very slightest side force. But this is not at all typical, and I personally have never seen this phenomenon unambiguously occur.

What really causes turn/fade is the lift force, and the center of lift/pressure on the disc. At slow speeds the lift torques the nose up, but due to the gyroscopic stability of the spinning disc, it rolls left (for RHBH) instead of pushing the nose up or down. This is a bit tricky, so I'll give an analogy that might help you understand how the disc responds to pitching moments...

Try to imagine a steering wheel on a car that works not by turning the wheel about its axis, but rather turns the car when you tilt the steering wheel up or down (in the same sense as the tilt position adjustment). If the car follows the same convention as that of a right-hand backhand thrower (i.e., downward angular velocity), then tilting the steering wheel forward causes the wheels to turn to the right, while tilting the wheel back makes the car steer to the left. This is the same sense as the manner in which a spinning disc turns in flight: if you try to push the nose down/lift the tail up, the disc will execute a turn that decreases the hyzer angle (right for RHBH). If you lift the nose up/push the tail down, the disc will execute a negative turn (fade) that increases the hyzer angle (left for RHBH).

More later...

 

[George1]

JHern,

I've finally had time to think about your last figure. Treating the problem in terms of energy instead of forces certainly clarifies some things. Since you posted to get some discussion going, here are a few questions:

How does the potential energy fit in to your three different throws? I can see that the nose-down throw reaches an equilibrium point sooner than the level throw or the nose-up throw. I would assume that means that the latter portion of the flight is more energy efficient for the nose-down throw. (Or rather, that the nose-down flight makes efficient use of the gravitational energy sooner.) However, does the nose-down throw have more or less potential energy when it reaches that point? In other words, if the nose-down throw follows a very flat trajectory, it might be very energy efficient at the end but not have as much height and therefore as much potential energy to work with.

Also, how significant is the potential energy? Is it a large or small fraction of the kinetic energy? I can see the drop in kinetic energy as the disc ascends, but how much of that is work against gravity and how much is it work against drag forces? (I tried a back of the envelope calculation, guessed a flight speed of 20 m/s and an apex height of 5m, and came up with about a 1:4 potential to kinetic ratio, but I'm not sure how realistic my assumptions are.)

How does the rotational kinetic energy relate to the drag energy loss and to the linear kinetic energy? In other words, as the angular velocity of the disc gets smaller, where does the rotational kinetic energy go? My guess would be that most of the loss is to drag and to (slight) sideways motion of the disc caused by a Magnus force. I would also guess that the disc only loses a small fraction of its rotational kinetic energy during the flight. (I assumed that the kinetic energy on your vertical axis was the linear part of kinetic energy.)

Overall, it seems to me that there are four relevant energy terms in the problem--linear kinetic, rotational kinetic, potential, and loss to drag. It would be interesting to see all four of those plotted as a function of time. Alternatively, if you could replot your figure with the potential plus kinetic energy on the vertical axis that would give different and helpful information as well.

I don't mean to be critical--your work and your figure are both outstanding and very helpful and I'm quite impressed. They just raise lots of interesting questions! Thanks for posting it!

George