How the Disc Flight Lab works — and where it doesn't
A physics simulation, not a curve-fit animation. Here's the model, the
decisions behind it, and the honest limits.
The physics
It's a full rigid-body (6-DOF) model of a spinning disc — the canonical
Hubbard–Hummel aerodynamics. Lift, drag and a pitching moment are functions of the
angle of attack (the angle between the disc plane and the oncoming air).
The engine integrates angular momentum directly (dL/dt = M) and recovers spin
from it, so gyroscopic precession is emergent: a pitching moment doesn't pitch the
disc, it makes it bank — which is exactly why discs turn and fade. At high speed
(low AoA) the moment is nose-down → the disc turns (right, for RHBH); as it slows the AoA
rises, the moment flips, and it fades (left). Forehand / left-handed mirror this.
Wind enters in exactly one place: aerodynamic forces use the airspeed
(velocity − wind). So a headwind adds lift (understable discs flip more), a tailwind robs
lift (the disc "falls out of the air"), and crosswinds push downwind — all emergent.
How discs differ
Every disc carries real mass, diameter, both moments of inertia, and a full
coefficient set — so a putter, a driver, a frisbee and a discus differ for physical
reasons, not a label.
Frisbee (Ultrastar) uses Hummel's coefficients, fit to filmed flights — the
trustworthy quantitative anchor.
Disc-golf discs are built from their flight numbers (Speed / Glide / Turn /
Fade). There is no published formula mapping flight numbers to aerodynamic
coefficients, so this is a documented heuristic, anchored to the per-class wind-tunnel
data of Kamaruddin, Potts & Crowther (putter / mid / driver).
Calibration decisions (and why)
Distance is tuned to launch-monitor / radar data: ~7–10 ft per mph; roughly
50 mph → 300 ft, 60 → 390, 70 → 510, elite ~600+ (Pozzy radar study; TechDisc).
Lift is set so each disc flies ~flat at its design speed — fast discs need
little lift coefficient (so they don't balloon); slow discs keep more (so they glide).
Over-power a disc and it balloons and flips over, as in real life.
Turn is scaled by design speed, because the aero moment grows with v² while
gyroscopic stability is roughly fixed; without this a "−1" speed-12 driver would flip
violently the moment you threw it hard.
Spin = stability, not propulsion. Wind-tunnel work finds lift/drag are unaffected
by spin; TechDisc measures only ~3 ft per 100 rpm (vs ~10 ft per mph). The sim matches
this — spin's real job is keeping a fast disc from rolling over.
Wobble: an under-spun throw (low advance ratio) gets a drag/lift penalty, so too
little spin makes the disc "die" and lose distance.
Weight rescales mass and inertia: lighter = more understable, heavier = more
overstable. At a fixed speed the distance change is small — the real gain from light discs
is that you can throw them faster.
Limits & caveats (the haters' section)
Per-model disc-golf numbers are estimates. Trust the flight shapes and
relative comparisons; treat absolute distances as indicative. Every coefficient is
tunable to match a real flight chart.
Coefficients are constant — no variation with Reynolds number or advance ratio.
Wobble is an empirical penalty, not a real off-axis nutation simulation; the disc
is otherwise released perfectly clean.
The ground is a single flat plane — elevation is downhill/flat only; uphill and
real terrain aren't modeled.
Catalog flight numbers are manufacturer-published, gathered via automated
research — some are approximate and a few may be wrong. Override them freely.
Discus is qualitatively right (a lifting body with a steep optimum), but the
subtle "flies farther into a headwind" effect isn't reproduced.
No ground interaction (skip / roll / fade-out on landing), no disc flex, no vertical
wind or gusts. The 3D release view uses a painter's-algorithm renderer (no true depth
buffer), so the disc/plane intersection is approximate.
Sources
Hummel, Frisbee Flight Simulation and Throw Biomechanics (UC Davis, 2003) —
thesis PDF
Hubbard & Hummel, Simulation of Frisbee Flight (2000)
Crowther & Potts, Simulation of a spin-stabilised sports disc (2007)
Kamaruddin, Potts & Crowther, flying-disc aerodynamics (2018) —
PDF