Disc Golf Course Review Spin rate measurements?
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#51
08-24-2019, 06:46 PM
 armiller * Ace Member * Join Date: Jun 2015 Location: West Virginia Years Playing: 4.6 Courses Played: 183 Throwing Style: RHBH Posts: 3,170 Niced 683 Times in 452 Posts

The main effect that spin has on a disc's flight is to increase its angular momentum and thus to cause it to resist both turn and fade.

There are quite a few interesting papers out there, both Masters and PhD theses, reporting on disc flight, some using wind tunnels and disc golf discs. If I recall correctly, they report that the Magnus effect is negligible in disc flight. The effect of aerodynamic moments caused by lift/drag is much more important than the Magnus effect, if those MS/PhDs are to be trusted.

As for headwinds, it is quite simple. Headwinds increase the velocity of air flowing over the disc, and this directly increases the magnitude of the lift force. This higher magnitude makes the disc turn more, regardless of spin. That's because it increases the moment (torque) causes about the disc's center of mass, which moment is perpendicular to its current angular momentum. As a matter of fact, a disc with higher spin will resist the turn more (i.e. turn less), but that's beside the point.

As for spin, I've said all this before somewhere. I think it's like throwing a football or baseball. Throwing it properly and efficiently (far and accurately) will naturally impart spin onto the ball. There are plenty of great NFL throws made which gain yards and score touchdowns without being perfect spirals. Likewise, I think you could gain something in disc golf by learning to control spin, but it's far more important to generate velocity while controlling trajectory, nose angle, and hyzer angle. If you do that, I bet you have also generated a the perfect amount of spin.

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Last edited by armiller; 08-24-2019 at 06:49 PM.
#52
08-24-2019, 08:36 PM
 Putt for D'oh Double Eagle Member Join Date: Sep 2015 Location: Santa Rosa, CA Years Playing: 4.6 Courses Played: 24 Throwing Style: RHBH Posts: 1,177 Niced 523 Times in 298 Posts

Quote:
 Originally Posted by cjman A disc will fade left when the lift created by the spin +
This fallacy is pretty important to a lot of the thoughts you are posting.

A disc is a single wing not a helicopter. The spin does not create lift.

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#53
08-26-2019, 06:58 PM
 sidewinder22 * Ace Member * Join Date: Nov 2008 Location: Creeping Creek DGC Years Playing: 13.4 Courses Played: 220 Posts: 15,165 Niced 2,900 Times in 1,771 Posts

Quote:
 Originally Posted by armiller There are quite a few interesting papers out there, both Masters and PhD theses, reporting on disc flight, some using wind tunnels and disc golf discs. If I recall correctly, they report that the Magnus effect is negligible in disc flight. As for headwinds, it is quite simple. Headwinds increase the velocity of air flowing over the disc, and this directly increases the magnitude of the lift force. This higher magnitude makes the disc turn more, regardless of spin. That's because it increases the moment (torque) causes about the disc's center of mass, which moment is perpendicular to its current angular momentum. As a matter of fact, a disc with higher spin will resist the turn more (i.e. turn less), but that's beside the point.
They actually recorded a Reverse Magnus Effect although not in those words. They stated the disc rolled slightly in the opposite direction of what Magnus Effect should be. Smooth objects with laminar flow reverse Magnus. IMO why discs start out of the box so overstable is because of the laminar flow, compared to just a couple throws in adding some surface roughness to make the boundary layer airflow turbulent/energetic.

Headwinds along with increasing lift magnitude as the relative airspeed increases, will also move the Center of Pressure further back on the disc which causes the disc to behave less stable. When you get the nose down into a headwind it typically exaggerates the turning effect, although not always depending on the disc and airspeed. When you get the nose up into a headwind it typically exaggerates the fade because the CoP will never get behind the CoM.

Quote:
 Originally Posted by Hummel Often considerable influence on the aerodynamics of the Frisbee has been mistakenly attributed to the effect of the spin about the axis of symmetry. Consider the motion of the left and right sides of a Frisbee due to spin in a right hand backhand throw rotating clockwise viewed from above. The motion of the left side of the Frisbee (viewed from behind) is in the direction of the velocity while that of the right side opposes velocity. Consequently the total velocity on the left (due to spin and linear velocity of the COM) will be greater than that on the right. Since lift is quadratic in velocity (eq. 2.6), the distribution of the lift might consequently be thought to be greater on the left side than the right side. The COP would be expected to shift left of the midline of the disc to the side with the higher velocity. Such a shift would cause a positive roll moment. However, data collected from Potts and Crowther (2002) shows the roll moment to be negative, not positive. Thus the mistaken rationale presented above does not even calculate the sign of the rolling moment, much less its magnitude, illustrating the complex nature of the flow around the Frisbee. Also, it is important to understand that in the lift calculation (eq. 2.6), CL applies only to the Frisbee as a whole and the relative velocity must be the velocity of the COM, not a left or right side velocity. In any case, the roll moment is very small and does not play a large role in the flight dynamics.

#54
08-27-2019, 01:55 PM
 dorseymatt Birdie Member Join Date: Sep 2011 Location: Baltimore, MD Courses Played: 13 Posts: 487 Niced 416 Times in 162 Posts

I bet Albert Tamm has the most spin relative to speed of any forehand on the planet.