Disc Flight Mechanics

DISC FLIGHT

A modern disc golf disc has been engineered to give the beginner as well as the expert disc golfer a wide range of options with varied disc performance to meet their skill and expertise.  Understanding the design aspects of the disc and how these factors are manipulated, gives the player the opportunity to choose the disc best suited to their skill, experience level and the course’s conditions to improve the players experience and enjoyment of the round.

On Disc Design

The four-number flight rating system was introduced by INNOVA 3 decades ago and has become the standard adopted by most manufacturers today to give players an impression of how different disc molds will fly.  The 4 numbers constitute the four aspects of disc flight: Speed, Glide, Turn, and Fade (i.e. 7/7/-1/1). 

The four numbers are always listed in the same order Speed/Glide/Turn/Fade.
For example, consider a disc with 8/4/-3/1 flight numbers.  For a Right-Handed Back Hand* (RHBH) thrower, releasing this disc flat and at a appropriately fast speed, the disc will initially move 3 to the right soon after release and at the end of the flight Fade back 1 to the left. 

These numbers describe the flight tendencies of a disc assuming it is thrown flat and at an appropriate speed for that disc.  When the disc is released with an angle or at an inappropriate speed for that disc, the numbers don’t really apply. Throwing the disc with angle is a means of shaping your shot and you will learn how the disc flies in these circumstances with experience.

Disc Flight (continued)

The first number (Speed) is mainly the result of aerodynamics.  Generally, the higher the speed the higher the potential for more distance.  But a high speed rated disc comes with a cost.  The higher speed discs require more arm speed and a more precise angle of release, or they may not even fly as far as slower rates discs.  Speed should be matched to the players form and control, as well as release stength.  It is generally recommended that new players choose drivers in the 9 speed or less range (until they can consistently throw 300’ with accuracy).

The second number (Glide) is highly related to the last two numbers (Turn and Fade). But it is the last two that are the most important.  These numbers show the gyroscopic behaviors the disc will exhibit. Disc designers noticed that by varying the distribution of weight in the rim and the flight plate caused the disc to rotate differently on its axis.  Placing more weight in the rim caused the disc to tilt in the opposite direction of rotation.  For a RHBH thrower (having a natural clockwise rotation) the disc with a heavier rim would try to tilt left on a disc making it overstable, for example (10/5/-1/3).  The reverse is true for an understable disc with numbers like (7/4/-2/1). The less weight in the rim causes it to tilt in the direction of its spin or to the right for a RHBH thrower.  And finally, when the distribution of weight reaches a happy medium as with a stable disc, the numbers might be (7/4/-1/1). The rotation remains relatively flat until the very end of the flight were the disc usually fades proportionally to the difference between the Turn and Fade flight numbers.

Overstable – An overstable disc has a higher Fade rating than Turn rating. For RHBH* thrower, the disc has high tendency to fly to the Left.  For example, a disc with flight numbers 13/5/-1/3 would be considered overstable.  A short cut method for determining whether a disc is over or under stable is to add the last two numbers in the flight numbers, in this case: -1+3=+2.  If the resulting number is positive the disc is said to be overstable.  If it’s negative it is understable, and those resulting in 0 would be considered stable or straight.

Overstable discs are usually recommended for the power throwers with considerable experience.  In the hands of an inexperienced player the results will usually be disappointing because the disc will fade so early in flight it doesn’t glide a worthwhile distance.

Understand – An understable disc has a Turn rating that is greater than its Fade rating.  For example, a disc with flight numbers 13/5/-3/1 would be considered understable.  A short cut method for determining whether this disc is over or under stable is to add the last two numbers in the flight numbers, in this case: -3+1=-2.  If the resulting number is positive the disc is said to be overstable, if its negative it is understable, and those resulting in 0 would be considered stable or straight.

Generally, newer players, players with lower arm speed or less leverage (shorter arms) usually find understable discs easier to throw.  These discs require less power and a less perfect angle of release to fly well.  You might say these are the most forgiving discs for players still working on their form. 

Stable – A stable disc has a Turn rating that is equal and opposite its Fade rating.  For example, a disc with flight numbers 9/5/-2/2 would be considered Stable.  A short cut method for determining whether this disc is over or understable is to add the last two numbers in the flight numbers, in this case: -2+2=0.  If the resulting number is positive the disc is said to be overstable.  If its negative it is understable, but since in this case it’s 0 the disc would be considered stable or straight. 

DISC WEIGHT - There are some considerations regarding the appropriate weight for a player’s discs.  A heavier disc is potentially more accurate and less affected by the wind.  The heavier disc flies better than a lighter disc into a head wind.  However, a heavier disc requires more power to accelerate its weight to reach the necessary speed to fly correctly.  A lighter disc on the other hand requires less power to reach proper launch speeds.  For this reason, players with lower arm speed, less leverage (shorter arms), or imperfect form can usually get greater distance with lighter discs, but this comes with some costs.  The lighter discs are more affected by the wind and don’t do well into head winds.  The greater glide achieved through their lighter weight negatively affects their accuracy.  The lighter disc has less torque resistance and if thrown too hard may flip over (in the direction of the spin) and glide off out of control.

CHOOSING A DISC WEIGHT - Disc weights are usually stamped or stickered on the bottom of the disc by the manufacturer.  The Professional Disc Golf Association (PDGA) regulates all the rules for Disc Golf, including allowable disc weights. And for a manufacturer to print “PDGA Approved” on their discs they must agree to abide by these regulations.  The PDGA regulations mainly limit the maximum weight for a disc, limiting it to 8.3 grams per centimeter of diameter.  The common weight range is from around 135 grams to 180 grams, but there are discs legal up to 200 grams!

There are no hard and fast rules for determining the right weight range for an individual.  This will take some experimentation to determine what’s right for you.  Your first considerations will probably change as your skill develops.  Our recommendation is to choose putters and midranges near or at max weight since these discs are thrown for accuracy and the heavier discs perform better in more playing condition than their lighter counter parts.  Drivers are a place we encourage you to experiment.  Find the weight that goes the farthest and that is most accurate for you.  Maybe carry a variety in your bag for different shots and playing conditions.

*All examples are for a right-handed backhand or left-handed forearm thrower (RHBH, LHFA), right-handed forearm or left-handed backhand throwers are the mirror image regarding direction of flight paths and disc behaviors.