BenjiHeywood
Par Member
- Joined
- Dec 17, 2023
- Messages
- 188
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.
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.
This is a very interesting question, and one I really want to study more in detail. Disc golf is really unique here, I think, in that the projectile we use wears over time and that this is a beneficial effect.
I believe it's a combined effect of many separate factors. The idea that the PLH is lowered actually seems reasonable to me. Since the overall shape of the flight plate typically has some dome, it makes sense that a direct hit will push the PLH downwards most of the time. And we can already demonstrate in the simulations that this would make the disc more understable. Similarly, shaving off some of the rim bottom will also make the PLH lower (which is why beads are used to mitigate this effect), so that's clearly a contributor.
The effect of roughness, though, seems poorly understood at the moment. Maybe it could lead to an effect as I've tried to illustrate below. If the roughness introduces enough instability to make the flow near the disc turbulent, you may reduce the size of the wake underneath the flight plate. This is somewhat what some older disc designs have tried to do, with textured/dimpled rims (Latitude Missilen, Quest AT Scream DT etc). What's interesting, though, is that this is a phenomenon that depends a lot on the velocity, so the behavior could change during the flight. This might be why people say that a beat-in disc keeps its low-speed stability but loses some of its high-speed stability. It's at least a hypothesis I think is worth testing out and getting some quantitative data on. I have most of the stuff ready to test this, so hopefully I will have some data soon. Would be happy to hear some other thought on this as well!
View attachment 336824
@Eric_T has chipped in with some really excellent quantitative content on @disc-golf-neil 's grip thread. I think this stuff is worthy of its own thread, as it contains a ton of interesting things that many of us have speculated about but Eric has actual data.