Tech disc test driven development

[Brychanus]

Yes, I have data from -90 to 90 degrees. You see +4 in the graphs I posted. The drag increases exponentially with the angle, and increases by roughly 50 % from 0 to 4 degrees.

Can you help me understand the scale of the Y-axis lift coefficient and drag coefficient?

E.g., it stands out right away that the proportional effect is and that it is quite large over just a few degrees.

Just curious if there is an intuitive way to understand the raw effect sizes (if they're meaningful).

 

[Eric_T]

Can you help me understand the scale of the Y-axis lift coefficient and drag coefficient?

E.g., it stands out right away that the proportional effect is and that it is quite large over just a few degrees.

Just curious if there is an intuitive way to understand the raw effect sizes (if they're meaningful).

Not sure I fully understand what you're asking here. But in general I am a bit wary of using my intuition in complex problems like this, because it has turned out to be wrong so many times fluid dynamics is highly non-linear, which makes it difficult to reason about. The variables of the flight are also tightly coupled, increasing the lift affects turn/fade and so on.

Lift will vary more or less linearly, because as the angle increases, more of the air is deflected downwards. Drag is more complex, as it depends on how the flow separates over the disc and the wake that develops behind it. The disc is a lot more complex than e.g. an airfoil, as the flow is three-dimensional and you have the sharp edges creating separation and turbulence. Still, you can see very similar behavior as for for airfoils, see e.g. the plots for lift and drag here:

NACA 0012 AIRFOILS (n0012-il)

Details of airfoil (aerofoil)(n0012-il) NACA 0012 AIRFOILS NACA 0012 airfoil

airfoiltools.com

 

[BenjiHeywood]

Thanks for all your input here, Eric, it's hugely valuable.

Do you have any thoughts on the classic 'why do beat-in discs turn more' question? I'm guessing you're better placed than most of us to understand all that.

Lots of people seem convinced that the disc gets bent downwards on impact with things, and this lowers the PLH. This seems wildly unlikely to me - surely the disc gets bent in random directions each time it hits something. Often a single dent will both raise AND lower the rim at that specific point of impact!

I see the solution as more to do with turbulence at the rim, as the spinning, dented disc means that the nose is effectively oscillating wildly, albeit over only a millimetre or so. I find it interesting that a wobbling disc (with it's oscillating rim) also gets more turn. But i haven't got anything like your level of fluid dynamics knowledge to back that up.

Any thoughts?

 

[disc-golf-neil]

I updated the grip alignment labels btw since some people here were mention spots that weren't labelled.

Going to use these new labels going forward when comparing grips in tech disc tests. It should be detailed enough to not need to change it again.

@OverthrowJosh tagging you since I showed you the old one just in case you were tempted to reference it.

The pictures are too big to upload here in HD. HD versions are on drive
Without explanation text:


With explanation text:


I show an example in the video below of how the grip appears to change when closing the hand but doesn't actually change (for my standard F1P0). Sometimes it does change a decent amount depending on how extreme the alignment is before closing the hand.

 

[disc-golf-neil]

Another test. Comparing grip alignment F1P0 to F1P-3 with pour the tea on both.

 

[Brychanus]

Not sure I fully understand what you're asking here. But in general I am a bit wary of using my intuition in complex problems like this, because it has turned out to be wrong so many times fluid dynamics is highly non-linear, which makes it difficult to reason about. The variables of the flight are also tightly coupled, increasing the lift affects turn/fade and so on.

Lift will vary more or less linearly, because as the angle increases, more of the air is deflected downwards. Drag is more complex, as it depends on how the flow separates over the disc and the wake that develops behind it. The disc is a lot more complex than e.g. an airfoil, as the flow is three-dimensional and you have the sharp edges creating separation and turbulence. Still, you can see very similar behavior as for for airfoils, see e.g. the plots for lift and drag here:

NACA 0012 AIRFOILS (n0012-il)

Details of airfoil (aerofoil)(n0012-il) NACA 0012 AIRFOILS NACA 0012 airfoil

airfoiltools.com

Was just meaning to ask what the units on the Y-axis mean - in some areas of science the units are arbitrary or scaled to some reference point. I was trying to figure out if the exact values mattered, or only their relationship 0 or to the x-axis or other variables.

Since I know exactly nothing about these models I was suddenly confronted with how little I actually knew lol

 

[seedlings]

Even more grip adjustments are available.

 

[Nick481]

Was just meaning to ask what the units on the Y-axis mean - in some areas of science the units are arbitrary or scaled to some reference point. I was trying to figure out if the exact values mattered, or only their relationship 0 or to the x-axis or other variables.

Since I know exactly nothing about these models I was suddenly confronted with how little I actually knew lol

The drag and lift coefficients are dimensionless quantities that get multiplied by values with dimensions (fluid density, fluid velocity, and reference area) to result in a force value in the drag and lift equations, respectively. When working in pure SI units the result would generally be in Newtons.

The drag force and drag coefficient can get especially weird though. The coefficient is derived from the physical measurements of fluid density, fluid velocity, and reference area (since it is a dimensionless coefficient). Luckily with airfoils, the reference area is usually the total wing area rather than the frontal area (as it would be in a car for example).

But, I'm not sure if @Eric_T calc used the total wing area or if it used the instantaneous frontal area to calculate the Cd. Since the frontal massively increases with increases in AoA, the real drag force could be either the same or worse than what the Cd is showing us. He will have to chime in to confirm which it used.

 

[disc-golf-neil]

Even more grip adjustments are available.

Thanks for the vid. The one on the thumb muscles is covered in the the alignment labels I believe here:

Tech disc test driven development

Yes, I have data from -90 to 90 degrees. You see +4 in the graphs I posted. The drag increases exponentially with the angle, and increases by roughly 50 % from 0 to 4 degrees. Can you help me understand the scale of the Y-axis lift coefficient and drag coefficient? E.g., it stands out right...

www.dgcoursereview.com

On the palm side you are showing P2 or P3 when putting the disc more on the thumb muscle, on the finger side it likes like F2 or F3, not sure. So F2P3 possibly.

I just tested in the vid a few replies back going more negative on the palm side and F1P-3 gave me more nose down than F1P0, so it would be super interesting if I also get more nose down with F2P3 compared to F1P0 or F1P-3. I'll test it soonish but as it looks like with you it's hard to keep the pinky on with F2P3 so I might have to do 3 fingers.

 

[disc-golf-neil]

Can't believe I forgot about this and didn't include it in the video, lol.

I got distracted trying to finalize the grip alignment notation to be able to make the video..



Of course it seems like it can't be true, so we'll see if it's reproducible. Exciting either way.

 

[seedlings]

Thanks for the vid. The one on the thumb muscles is covered in the the alignment labels I believe here:

Tech disc test driven development

Yes, I have data from -90 to 90 degrees. You see +4 in the graphs I posted. The drag increases exponentially with the angle, and increases by roughly 50 % from 0 to 4 degrees. Can you help me understand the scale of the Y-axis lift coefficient and drag coefficient? E.g., it stands out right...

www.dgcoursereview.com

On the palm side you are showing P2 or P3 when putting the disc more on the thumb muscle, on the finger side it likes like F2 or F3, not sure. So F2P3 possibly.

I just tested in the vid a few replies back going more negative on the palm side and F1P-3 gave me more nose down than F1P0, so it would be super interesting if I also get more nose down with F2P3 compared to F1P0 or F1P-3. I'll test it soonish but as it looks like with you it's hard to keep the pinky on with F2P3 so I might have to do 3 fingers.

I don't use the pinky. Have short fingers, which also sucks on guitar and keys… pinky sits on my ring finger. Same with putting. Usually I use more of a pinch grip, but demo'd power grip for that clip to eliminate confusion

 

[Eric_T]

Was just meaning to ask what the units on the Y-axis mean - in some areas of science the units are arbitrary or scaled to some reference point. I was trying to figure out if the exact values mattered, or only their relationship 0 or to the x-axis or other variables.

Since I know exactly nothing about these models I was suddenly confronted with how little I actually knew lol

Sure, @Nick481 explained it well. It's just the forces in Newton and Newton*meter (for the torque), but scaled with dynamic pressure and a representative area. This makes it possible to more easily compare results taken in different environments and also reduces the parameter space. Here, the reference area is taken as the planform area of the disc, similar as for airfoil analysis, so it's basically just scaling the forces by a constant value.

 

[Brychanus]

Sure, @Nick481 explained it well. It's just the forces in Newton and Newton*meter (for the torque), but scaled with dynamic pressure and a representative area. This makes it possible to more easily compare results taken in different environments and also reduces the parameter space. Here, the reference area is taken as the planform area of the disc, similar as for airfoil analysis, so it's basically just scaling the forces by a constant value.

Nice, thank you!

The drag and lift coefficients are dimensionless quantities that get multiplied by values with dimensions (fluid density, fluid velocity, and reference area) to result in a force value in the drag and lift equations, respectively. When working in pure SI units the result would generally be in Newtons.

The drag force and drag coefficient can get especially weird though. The coefficient is derived from the physical measurements of fluid density, fluid velocity, and reference area (since it is a dimensionless coefficient). Luckily with airfoils, the reference area is usually the total wing area rather than the frontal area (as it would be in a car for example).

But, I'm not sure if @Eric_T calc used the total wing area or if it used the instantaneous frontal area to calculate the Cd. Since the frontal massively increases with increases in AoA, the real drag force could be either the same or worse than what the Cd is showing us. He will have to chime in to confirm which it used.


View attachment 336504

View attachment 336505

Nice, this helps & I appreciate the equations! Thanks

 

[disc-golf-neil]

Some pics of pros where you can see the palm alignment.



Gannon, looks like P0 palm alignment, probably F1P0 because F1 is my default assumption if I cant see it since it seems most common when I've asked pros or see their vids explaining grip.


Eagle shows that he uses an F1P0 alignment in this vid


In this pic though, it looks like a P-3 alignment, probably F1P-3 like I just tested. Maybe it wasn't his final grip before throwing or maybe he switched it for a particular purpose:


AB's grip alignment looks like it's shifting here, possibly increased chance of the disc moving in the grip with the added wrist extension he does on the back swing. Looks like it starts around P0 so probably F1P0 and then ends up P1 or P2, but it might just be that it looks like the disc is closer to P1 or P2 but it's just a gap where the disc isn't touching P0 but is still aligned with P0.

 

[Brychanus]

Interesting, I had noticed the tall thin guys closer to F1 P0, and I guess we see some variability in the palm setting, action, wrist extension etc. heading into peak reachback.

And yeah, there's the disc line, then the disc plane, then the evolution of pressure along the move and as the forearm and fingers begin to get into it. Finger pressure data along the disc would be neat.

Gurthie (captain supinator) might be F1 -ish and P -2 or -3 -ish. Notice that as the slack comes out of his arm the disc probably gets yoked into a slightly different alignment due to the supination and probably the finger & thumb pressure as he commits the shot. There's a visible torque on his discs as they move into and out of the pocket, then it ends up exceptionally low-wobble upon release. Something like this style has always been more accessible to me with the square palm/short index finger.

 

[disc-golf-neil]

Interesting, I had noticed the tall thin guys closer to F1 P0, and I guess we see some variability in the palm setting, action, wrist extension etc. heading into peak reachback.

And yeah, there's the disc line, then the disc plane, then the evolution of pressure along the move and as the forearm and fingers begin to get into it. Finger pressure data along the disc would be neat.

Gurthie (captain supinator) might be F1 -ish and P -2 or -3 -ish. Notice that as the slack comes out of his arm the disc probably gets yoked into a slightly different alignment due to the supination and probably the finger & thumb pressure as he commits the shot. There's a visible torque on his discs as they move into and out of the pocket, then it ends up exceptionally low-wobble upon release. Something like this style has always been more accessible to me with the square palm/short index finger.

View attachment 336718

Interesting! In the last one on the right it does look like it's still a bit below the forearm which is was the difference I observed testing F1P0 vs F1P-3 and when turning the key, normally I get ~-5 nose with F1P0 but with F1P-3 I was getting -9 average and less wobble, so it seems they synergize together and perhaps that's another reason GG gets extra nose down.

 

[Brychanus]

Interesting! In the last one on the right it does look like it's still a bit below the forearm which is was the difference I observed testing F1P0 vs F1P-3 and when turning the key, normally I get ~-5 nose with F1P0 but with F1P-3 I was getting -9 average, so it seems they synergize together and perhaps that's another reason GG gets extra nose down.

Added a couple lines to forearm & disc in the rightmost image there to make sure my eye wasn't tricking me.

 

[itlnstln]

Reverse air bounce.

I suspect this is what I notice in James proctor's throws. His seem to hit some imaginary ceiling, drop a little, then ride flat. It also seems that he has some amount of supination evident in his follow through at times

 

[sidewinder22]

Some pics of pros where you can see the palm alignment.



Gannon, looks like P0 palm alignment, probably F1P0 because F1 is my default assumption if I cant see it since it seems most common when I've asked pros or see their vids explaining grip.
View attachment 336714

Eagle shows that he uses an F1P0 alignment in this vid


In this pic though, it looks like a P-3 alignment, probably F1P-3 like I just tested. Maybe it wasn't his final grip before throwing or maybe he switched it for a particular purpose:
View attachment 336715

Interesting how both of them appear to be backwards from what they say.

 

[Brychanus]

Possible dynamic alignment change as arm/disc/gravity interact through the move?