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Disc Review

Disc Qualities and Their Effects On Flight

by Blake Takkunen

Originally Posted: 2-28-06
Revised: 7-01-06

Table of Contents


I. Dome Height – “Domey” vs. Flat

II. Rim Width and Density – The Gyroscopic Characteristics of Mass Distribution

III. Disc Size – The Disc's Diameter and Flight

IV. Rim Stabilizers – Rim Characteristics and Flight

V. Air Friction – The Effects of Plastic on Disc Flight


There are a lot of generalizations about the physical characteristics of discs and how those characteristics dictate and affect the disc's flight. While some of these views are true, some are not quite the complete truth. With this article I hope to help shed some light on the topic of discs and disc shape.

I. Dome Height – “Domey” vs. Flat

While there is a common belief that discs that have higher domes are more “flippy” than flatter discs (especially when they are variations of the same model), this is only partially true. Discs with a higher dome will generally be less high-speed stable than a flatter version of the same disc, but the high-domed disc will also be more apt to flex out if it gets turned. A flatter disc is more difficult to turn but is more likely to keep turning after the turn begins. This is due to the gyroscopic effect and can be illustrated by the physics example of a spinning bicycle wheel with handles.

If you equate the spinning wheel to the flat disc, you will see it is hard to turn the wheel off of its axis, but once it gets turning it will continue to turn farther in that direction. If you picture the spinning bicycle wheel where one side of the spokes is conical/triangular in shape, it will be easy to turn in one direction up to a point (and it will exert less gyroscopic forces) but it is also easier to turn back in the opposite direction. Late in a disc's flight it has lost a lot of its initial rotation and velocity and as the disc slows, a disc with a high dome will be more apt to stay in the air and fade back left. Wind will affect a disc with a higher dome more than a flatter version since the taller profile will be more affected by the wind.

II. Rim Width and Density – The Gyroscopic Characteristics of Mass Distribution

Discs with wider rims have greater mass distribution on the outer edge of the disc and will have greater gyroscopic tendencies than discs with narrower rims and more mass towards the center of the disc. That is, a wider disc will be more difficult to turn over, but will be more apt to continue to turn once it has been turned. A wide disc will also be more likely have a strong fade at the end of its flight as the disc slows down. Also, the wider the rim, the more the disc will change its flight characteristics due to changes in disc mass.

A wide rim disc holds a large percentage of its mass on the rim. If you take two discs of the same wide rim mold, one heavy and one light, they will have roughly equal mass on the flight plate (it can only get so thin without collapsing) and the majority of the mass difference will occur on the rim. A disc with more mass on the rim exerts greater gyroscopic forces than a disc with less mass on the rim (assuming they are thrown the same). Discs with narrower rims carry less mass on the rim and more on the flight plate so the effects of mass changes will have smaller effects on disc stability between different discs in that mold.

Higher end plastics have greater density than lower grade plastics. The result is that a disc of a particular mold run in high grade plastic will have a greater percentage of mass on the rim than a disc run in low grade plastic. Thus, higher-grade plastic discs will hold stronger gyroscopic properties and will yield increased high-speed stability and more low speed fade than their lower grade plastic counterparts.

III. Disc Size – The Disc's Diameter and Flight

While stability and flight speed are mainly dictated by the disc's shape, there are a handful of disc flight characteristics that are emphasized by the size of the disc. Larger diameter discs will have more natural gyroscopic fade than smaller diameter discs. Larger discs also generally fly slower than smaller discs. With more surface area, a larger disc will have more potential glide at low speeds than a smaller disc that covers less surface area.

Without taking rim shape into consideration, larger diameter discs will generally be easier to turn over (since they have relatively low stable air speeds which can easily be exceeded) and will be more apt to stay turned over once they get turned (due to increased gyroscopics).

IV. Rim Stabilizers – Rim Characteristics and Flight
While the overall shape and contour of the rim will determine the disc's overall flight, there are a few design factors that make the disc fly more high speed stable and fade more predictably at the end of their flight. The two most noticeable of these design factors can take the form of a bead (either prominently rounded or a very abrupt slope change) at the bottom of the rim or a notch (flat spot) at the very edge of the wing. Both of these characteristics will aid in the structural rigidity and overall durability of the disc but also affect its flight.

As a general rule of thumb, a bead on the rim will yield a slight increase in high-speed stability and in some cases (mainly those with a prominently rounded bead) it helps delay low speed fade. While it has been debated whether or not a bead does affect disc flight, my experiences with beaded and non-beaded versions of the same model discs as well as factored discs that have had the bead removed have generally yielded these results.

A “notch” (for lack of a better term) on the wing can vary greatly from a 1-2mm flat spot to a very noticeable flat area as the rim contour approaches the edge of the disc. Discs with a “notch” generally fly more high-speed stable and are more likely to fade at the end of their flight and will fade slightly earlier than versions of the disc that have had the notch smoothed off or if the notch has worn off due to wear. This fade characteristic is especially noticeable if a disc has been turned over.

V. Air Friction and Disc Shape – The Effects of Plastic on Disc Flight
Disc plastic has a great affect on disc flight characteristics due to the varying amounts of air friction between plastic types. Lower priced standard plastics will have the most air friction when new and will build additional air friction more quickly as they break in. Higher priced premium plastics have the least air friction and also build friction more slowly through their aging process. While disc stability is dominated by the disc's shape, two discs of the same mold produced in different grades of plastic will have noticeable differences in their flight characteristics.

The disc's ability to move in the direction of the spin will increase when there is greater air friction on the disc. The characteristics of plastic that help a disc flatten from a hyzer and/or turn over is similar to throwing a curveball with a baseball. The greater the air friction on the baseball, the more the ball will “bite” and help the ball to move in the direction of the spin, in this case, top spin causing the ball to drop. It is easier to flatten a hyzer and/or turn over a high friction disc since the disc's rotation will help pull/hold the disc in the direction of the spin.

Gyroscopic fade occurs as the disc slows down and causes the disc to fall in an opposite direction from the spin. Low friction discs will fade earlier than high friction discs since the air friction will help the disc hold the line longer by the greater pull of the rotation in the direction of the spin (and away from the gyroscopic fade). The difference in air friction coupled with the rim density of discs run in separate plastics explains the often striking differences in flight between plastic lines of the same disc mold.

An additional factor comes into play when comparing discs across plastics. Discs in higher grades of plastic are more "true" to the mold shape. That is, in lower grade plastics the discs lose some of the shape of the disc mold during cooling and end up with less distinct rim contours. The more true to shape that a disc is, the more affect the rim contours will have on its flight. Since most discs released before 2003 were designed in standard or mid-grade plastics, discs in premium plastics tend to fly more overstable than their less-defined counterparts. Similarly, for premium plastic discs, it takes until the overly-defined areas of the rim to smooth down due to wear before it will fly similarly to a lower-grade plastic version of the same model.

I would like to give Bradley Walker credit for bringing the shape differences across plastics to my attention.

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