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Rule 808.D: the score for a hole is the total number of throws, including penalty throws. Best round so far: -.
Every disc below is on the PDGA Approved Disc List and carries the dimensions the PDGA measured for it. Speed, Glide, Turn and Fade are the manufacturer's published flight rating. a* is the incidence at which this model's centre of pressure crosses the disc centre and the roll reverses, and v des is the airspeed at which the disc flies level at that incidence. Both are computed from the measured geometry alone — neither is fitted to the published rating.
A golf disc does not curve for the reason a boomerang does. A boomerang curves because the advancing blade meets a higher airspeed than the retreating one. A golf disc curves because the centre of pressure moves along the chord as the angle of attack changes.
At release the disc is fast and nearly flat to the airflow, and the load sits behind the centre: the pitching moment is nose-down. A spinning disc cannot simply pitch — the moment is precessed a quarter turn by the spin and appears as roll. For a right-handed backhand that roll is to the right, and the disc turns.
Then it slows. The gyroscope holds the spin axis where it is while gravity swings the flight path downwards beneath it, so the angle of attack climbs all by itself. Past a critical incidence the leading-edge suction strengthens and the load migrates forward of the centre. The pitching moment changes sign, the roll reverses, and the disc fades back to the left. That is the S-curve, and nothing in this engine scripts it: the centre of pressure is integrated as a function of incidence and the reversal is the moment it crosses the disc centre. The readout after each throw prints the time it happened.
Turn the hyzer / anhyzer slider to see what a thrower really controls. Bank the disc one way and the turn is cancelled before it starts; bank it the other and the turn runs away into a roller. The straight line is the narrow path between them.
Several rules defer to the Tournament Director. Here is what this one decided:
Aerodynamic coefficients for a disc-golf disc section are not published by anyone. The PDGA measures geometry and flexibility, not pressure distributions. So the form of the model is taken from the literature — lift and drag linear and quadratic in incidence, and a pitching moment from the fore-and-aft imbalance of the load — while every number is derived here from the PDGA's measured geometry through a stated mapping. Three constants are calibrated, one of them against a published figure (the 118 m Gold drive) and two against stated statements about the shape of a flight. None of them is fitted to any Turn or Fade rating. The ground skip, the chains' ability to hold a disc — the PDGA says plainly that "how well a target catches discs is not tested" — the wind and the thrower's scatter are all reconstructed too.
The flight is integrated with a fixed step of 1/2000 s on an absolute clock, the whole coupled state at one order.
Disc golf was shaped into its modern form by Ed Headrick (1924–2002), who patented the pole hole catching basket in 1975 and founded the Professional Disc Golf Association. This is an independent reimplementation — an original course, an original engine and original art, with no code, assets or data from any commercial disc golf game. The rules, target dimensions, disc specifications and par tables are quoted from the PDGA's own published documents; the flight ratings are the manufacturer's published numbers. See CREDITS.txt for every source URL and for a full list of what differs from the real sport.
Space or Enter throws (and moves to the next hole once you have holed out). P toggles the plan view. Escape closes a panel.