Tech disc test driven development

[disc-golf-neil]

I can appreciate exploring this stuff, but...wind drag caused by moving the disc into the power pocket?!

Have you every done a practice throw with the disc pronated and heard the WOOSH from the wind while it's still in your hand? That is wind drag, isn't it? Or is wind drag technically only after it leaves your hand? Whatever the semantics are, you can feel the effect of the air on the disc when it is oriented certain ways while it's still in your hand.

Similarly, during a headwind, swinging a pickleball paddle very hard has A LOT more resistance than a stringed racquet.

 

[RowingBoats]

Have you every done a practice throw with the disc pronated and heard the WOOSH from the wind while it's still in your hand? That is wind drag, isn't it? Or is wind drag technically only after it leaves your hand? Whatever the semantics are, you can feel the effect of the air on the disc when it is oriented certain ways while it's still in your hand.

I know what the concept of wind drag is, but the speed the disc is moving at that particular time...is not fast lol.

It feels, in fact, painfully glacial and this is one of the number one things people get wrong.

 

[Brychanus]

Have you every done a practice throw with the disc pronated and heard the WOOSH from the wind while it's still in your hand? That is wind drag, isn't it? Or is wind drag technically only after it leaves your hand? Whatever the semantics are, you can feel the effect of the air on the disc when it is oriented certain ways while it's still in your hand.

Oh, that's true.

I generally thought you will want to avoid wind drag in the move leading up to the release.

Are we all on the same page about that, or no?

 

[disc-golf-neil]

Oh, that's true.

I generally thought you will want to avoid wind drag in the move leading up to the release.

Are we all on the same page about that, or no?

Yes, that's why I was speculating it's hard to maintain some of these awkward positions such as radial deviation or over-supination because they are orienting the disc to catch more wind at different points causing additional force to oppose maintaining that position.

However, I do think the weight of the disc under the momentum is a much bigger factor at that point, but I was just trying to point out how many things are stacking up against it making it hard to fully implement potentially explaining some of the surprising (to me) results.

 

[Sewer bill]

I don't have a tech disc but I do experience the audible whoosh on hard high anhyzer shots.

 

[BenjiHeywood]

I think we often overlook stability when talking about nose angle. What we want (i think?) is for the glide phase to be stable, so that we maximise efficiency as we fall from peak height down to flare-out at the end.

In that glide phase, we want gravity to perfectly cancel drag, so the disc stays at the same speed for a long time. And we also want the lift force to be acting at the centre of gravity so that there's no twisting forces causing precession - we don't want the disc turning or fading too much, since a vertical disc does not glide.

But different disc designs will be 'balanced' (i.e. lift will be acting at the center of gravity) at different nose angles - a flippy disc can fly straight with the nose up, whereas something more overstable might need significant nose-down to fly straight.

So the 'correct' nose angle for a Force is not the same as for a Bolt.

A little bit of nose down is (from what I've read) the lowest-drag scenario, so being able to throw something slightly more overstable, that flies straight and balanced with that negative nose angle, will maximise efficiency. That's what most pros do. But an amateur, throwing a Bolt, with lowish spin, will often maximise distance with slight nose-up, since that is the way it will glide straight for longest. The techdisc simulator, for what it's worth, does seem to suggest that a couple of degrees of nose up works well for very flippy drivers.

 

[BenjiHeywood]

Actually i just looked at the tech disc numbers. I've sometimes played around with different settings for the flight numbers, not chasing any particular angles, just seeing what happens. Then i can sort all those throws by simulated distance, and see what nose and launch angles resulted in that maximum distance. Again, to be clear, these reps were done chasing mph and/or rpm, not caring about angles, so any preconceptions about nose angle didn't matter much.

My longest simulations with Rive flight numbers are about +6.5 launch with -3 nose. My longest simulations with something flippier like a Destiny are more like +3 launch with +2 nose. Apparently i can even airbounce a flippy disc (significantly positive nose angle, slightly negative launch angle) nearly as far as i can throw the Rive.

I'm not saying the simulator is perfect or anything, but that's interesting nonetheless.

 

[Eric_T]

This is an interesting discussion. I am not sure where the idea that approximately -4 degree nose angle is somehow optimal originated. I saw Brodie Smith mentioned it in one of his TechDisc videos, but without any justification. The wind will not flip a disc up or down during the flight. Since the disc is spinning, any torque is translated into turn/fade instead. However, the change of direction of the lift and drag caused by the nose angle will make the disc change its trajectory. The extreme version of this is an air bounce, where throwing the disc on a downward trajectory with very high nose angle eventually will change the trajectory to go upwards (or vice versa, the reverse air bounce, as @sidewinder22 mentioned )

To add some quantitative data to the discussion, here is how the aerodynamic coefficients for a disc typically change around 0 degrees angle of attack (nose angle at the point of release). This data is taken from computational fluid dynamics simulations I have performed, and the trends are similar across a large range of discs.



So having nose down makes the disc behave more understable (lower moment coefficient) and reduces the lift, while the drag more or less stays the same (even a slight reduction here, but it varies between discs).

If we plug this into a trajectory simulator we can compare the flights. This is not perfect, of course, but the benefit of a simulator is that you are able to really isolate the effect of a single parameter. Here are two simulated throws, where the one with nose angle down also has a higher hyzer angle to compensate for the lower initial moment coefficient:



So why does the lower nose angle go further, even though we have reduced the lift? The answer is that by reducing the lift while maintaining the momentum and not increasing drag, we allow the disc to push more forward instead of rising up. This also makes the fade towards the end of the flight less pronounced, as you don't get as severe angle of attack towards the end of the flight. So I believe a slightly negative nose angle is beneficial, maybe especially when throwing faster, overstable discs.

 

[Nick Carroll]

To add some quantitative data to the discussion...

Love it! This makes a lot of sense to me.

 

[Eric_T]

Just for fun, here is an example from the computational fluid dynamics simulations. The top image has nose angle 0, the bottom nose angle -4, and the disc travels from right to left. The blue regions are low pressure and the yellow regions are high pressure.



It's maybe hard to extract something meaningful from this without digging more into the details, but we can clearly see how the pressure is higher along the top with a negative nose angle, which is reducing the lift. We also see that the wake at the back is smaller for the negative nose angle, reducing the drag, which maybe helps explain why drag stays the same overall.

 

[BenjiHeywood]

Just for fun, here is an example from the computational fluid dynamics simulations. The top image has nose angle 0, the bottom nose angle -4, and the disc travels from right to left. The blue regions are low pressure and the yellow regions are high pressure.

Is that (low drag at negative nose angle) the same for both understable and overstable discs? Obviously they have to be thrown differently due to the turn and fade differences, but a separate question is: does a very understable or overstable disc experience minimum drag at the same nose angle, or does it depend on the PLH?

If, for example, it were true that understable discs fly straightest nose up but fly most efficiently when nose down, that would be a clear indication that learning to throw something overstable more nose down is going to be best. But it seems to me unlikely that PLH has no bearing on the optimal low-drag nose angle. I'd love to know if you can answer that one!

 

[BenjiHeywood]

Also: "The wind will not flip a disc up or down during the flight."

Head and tail wind, or simply still air that the disc passes through, will affect turn and fade and won't move the nose. But a meaningful crosswind might. I've certainly witnessed this in ultrastars, which can stall or nose dive due to the crosswind.

I guess it depends on how we define the nose - logically i suppose it's always the bit the air is hitting, in which case it's trivially true that the nose won't move up and down because there's no such thing as a crosswind, but in more casual language we'd refer to the nose as the bit pointing in the direction of travel (relative to the ground), and that can move up and down.

 

[Nick481]

This is an interesting discussion. I am not sure where the idea that approximately -4 degree nose angle is somehow optimal originated. I saw Brodie Smith mentioned it in one of his TechDisc videos, but without any justification. The wind will not flip a disc up or down during the flight. Since the disc is spinning, any torque is translated into turn/fade instead. However, the change of direction of the lift and drag caused by the nose angle will make the disc change its trajectory. The extreme version of this is an air bounce, where throwing the disc on a downward trajectory with very high nose angle eventually will change the trajectory to go upwards (or vice versa, the reverse air bounce, as @sidewinder22 mentioned )

To add some quantitative data to the discussion, here is how the aerodynamic coefficients for a disc typically change around 0 degrees angle of attack (nose angle at the point of release). This data is taken from computational fluid dynamics simulations I have performed, and the trends are similar across a large range of discs.

View attachment 336192

So having nose down makes the disc behave more understable (lower moment coefficient) and reduces the lift, while the drag more or less stays the same (even a slight reduction here, but it varies between discs).

If we plug this into a trajectory simulator we can compare the flights. This is not perfect, of course, but the benefit of a simulator is that you are able to really isolate the effect of a single parameter. Here are two simulated throws, where the one with nose angle down also has a higher hyzer angle to compensate for the lower initial moment coefficient:

View attachment 336193

So why does the lower nose angle go further, even though we have reduced the lift? The answer is that by reducing the lift while maintaining the momentum and not increasing drag, we allow the disc to push more forward instead of rising up. This also makes the fade towards the end of the flight less pronounced, as you don't get as severe angle of attack towards the end of the flight. So I believe a slightly negative nose angle is beneficial, maybe especially when throwing faster, overstable discs.

Extremely well said and thank you for posting your CFD data! Super nice to see the Aoa vs. drag especially. I was dreading having to relearn ANSYS to do a golf disc CFD in the future haha (probably just wouldn't have ever gotten around to it).

 

[Eric_T]

Is that (low drag at negative nose angle) the same for both understable and overstable discs? Obviously they have to be thrown differently due to the turn and fade differences, but a separate question is: does a very understable or overstable disc experience minimum drag at the same nose angle, or does it depend on the PLH?

If, for example, it were true that understable discs fly straightest nose up but fly most efficiently when nose down, that would be a clear indication that learning to throw something overstable more nose down is going to be best. But it seems to me unlikely that PLH has no bearing on the optimal low-drag nose angle. I'd love to know if you can answer that one!

Yes, the plot I showed was actually for a pretty understable disc. Here is a comparison against an overstable one:



You see the drag behaves more or less the same way, but the overstable disc has lower lift and higher moment coefficients. You can probably design a disc that behaves differently, though. I would think that whether to throw understable or overstable depends more on the speed you throw at and what shape you want from your throw.

 

[Eric_T]

Also: "The wind will not flip a disc up or down during the flight."

Head and tail wind, or simply still air that the disc passes through, will affect turn and fade and won't move the nose. But a meaningful crosswind might. I've certainly witnessed this in ultrastars, which can stall or nose dive due to the crosswind.

I guess it depends on how we define the nose - logically i suppose it's always the bit the air is hitting, in which case it's trivially true that the nose won't move up and down because there's no such thing as a crosswind, but in more casual language we'd refer to the nose as the bit pointing in the direction of travel (relative to the ground), and that can move up and down.

Yes, you are right, and as you say it is just a matter of definition. If you have crosswind you slightly change the actual direction of the wind that the disc "sees" (this is typically called side-slip). That is the axis that the disc will turn and fade around.

 

[BenjiHeywood]

Yes, the plot I showed was actually for a pretty understable disc. Here is a comparison against an overstable one:

View attachment 336205

You see the drag behaves more or less the same way, but the overstable disc has lower lift and higher moment coefficients. You can probably design a disc that behaves differently, though. I would think that whether to throw understable or overstable depends more on the speed you throw at and what shape you want from your throw.

Fabulous stuff. Thank you.

 

[BenjiHeywood]

Yes, you are right, and as you say it is just a matter of definition. If you have crosswind you slightly change the actual direction of the wind that the disc "sees" (this is typically called side-slip). That is the axis that the disc will turn and fade around.

I dunno about 'slightly' lol - the 45mph crosswind i had the other day moved the nose at least 45 degrees

 

[CoachChris]

Just for fun, here is an example from the computational fluid dynamics simulations. The top image has nose angle 0, the bottom nose angle -4, and the disc travels from right to left. The blue regions are low pressure and the yellow regions are high pressure.

View attachment 336194

It's maybe hard to extract something meaningful from this without digging more into the details, but we can clearly see how the pressure is higher along the top with a negative nose angle, which is reducing the lift. We also see that the wake at the back is smaller for the negative nose angle, reducing the drag, which maybe helps explain why drag stays the same overall.

Eric, will you run another drag computation on a disc with a +4° nose angle? I'm curious to see drag is increased with more of the bottom flight plate exposed. Thanks

 

[Eric_T]

Extremely well said and thank you for posting your CFD data! Super nice to see the Aoa vs. drag especially. I was dreading having to relearn ANSYS to do a golf disc CFD in the future haha (probably just wouldn't have ever gotten around to it).

Thanks! I may have the theoretical tools, but you are a lot better than me at putting the theory into practice

 

[Eric_T]

Eric, will you run another drag computation on a disc with a +4° nose angle? I'm curious to see drag is increased with more of the bottom flight plate exposed. Thanks

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.