How a golf disc flies

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bruce
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How a golf disc flies

Post by bruce » Tue Feb 23, 2010 4:35 pm

Or Fluid Dynamics 101*

All new players (and probably quite a few old ones) should read this, as understanding the basic principles of how a disc flies will save you masses of time learning to throw the things!

For the purposes of this description, I'm assuming a right-handed backhand throw (RHBH), effects are reversed for LHBH or RHFH (forehand)

A flying disc is a wing and as such has many characteristics that it is helpful to understand in order to throw them properly. Just like an aeroplane wing a disc generates lift when it is flying fast, and stalls when it slows down too much. Unlike an aeroplane however, the disc is spinning. What this means is that lift is not generated straight up, it's generated in the direction of the spin, i.e. to the right. Likewise when it stalls it stalls against the spin, to the left.

This explains the natural flight of a golf disc, at high speeds they 'turn over' to the right, at low speeds they 'fade out' to the left.

Armed with this knowledge, you can now understand a bit more about your discs. All discs will have two important speed characteristics. The first is how fast they have to be going to generate lift. This is often called 'high speed stability' or 'Turn' in Innova's rating system. The second is how slow they need to be going to stall, or 'low speed stability'. Innova call this 'Fade'.

Image

It's worth noting at this point that these speeds are relative airspeeds, and have a real world value. Say for example that a disc needs to be travelling at 40mph to turn over and 20mph to fade out. If you throw it flat at 30mph it will fly straight for a while, then fade out once it drops below 20mph. If you do exactly the same 30mph throw into a 15mph headwind it will be travelling through the air at 45mph and therefore will turn over until it loses 5mph. At this point it will fly in the direction it is now heading (to the right) until it slows down below 20mph airspeed, which is just 5mph actual speed. It should be obvious that these two flights will have very different shapes!

The distance between these two speed values can vary greatly. Some discs, such as the Teebird, have a very high HSS, so are hard to turn over, but also have a low LSS so don't fade out until very late. The result is that the flight is very straight; it doesn't deviate much from how you threw it. The benefit of this is that the flight is very predictable in a lot of different wind conditions. The downside is that it will go exactly where you throw it, so no excuses!
Other discs, including most of the newer high speed drivers, have a very narrow gap between their HSS and LSS, meaning that the disc is either turning over or fading out for nearly all of its flight. The downside here is that if you don't get it up to speed, the disc simply won't fly properly for you.

Hopefully this will help you understand why the discs are doing what they're doing!

*Disclaimer: The descriptions contained in this are not 100% accurate, certain effects have not been discussed to make the article understandable to the masses. If you want the full in depth understanding of gyroscopic precession and the physics of a rotating wing, they can be found at http://www.discwing.com/research/aerodynamics.html
[Standard post disclaimer] My posts are never intended to undermine the work of the Board or individuals putting in effort to grow the sport, they are my honest thoughts on the best ways to grow the game

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