Originally published at: https://discgolf.ultiworld.com/2021/06/18/how-utahs-high-altitude-will-affect-discs-flight-at-worlds/
Ultiworld Disc Golf’s coverage of the 2021 PDGA Pro World Championships is presented by Skybreed Discs, a top online retailer and preferred vendor of the 2021 Ledgestone Insurance Open, and Aria Discs, a new disc golf brand making discs designed for beginners.
It has been two full years since the last PDGA Pro World Championships, where Paul McBeth and Paige Pierce won their fifth World titles in Peoria, Illinois. However, the tides (well, more like the winds) have changed for this year’s event, which is being held in Ogden, Utah, at Mulligans Creekside and The Fort disc golf courses over five rounds of play.
Ogden stands high above most other Worlds locales at 4,300 feet above sea level, nestled in the valley below the Wasatch Range. It is easily the highest altitude players have competed at this season, and it’s set to shake up a lot of bags: discs fly differently at altitude.
That’s due to the change in air density, the mass per unit of volume of the Earth’s atmosphere, or, in other words, how many air molecules are in a given volume of space.
Air density is affected by three factors: temperature, humidity, and pressure. Temperature, aside from its common definition of how hot or cold something is, is also a measure of how fast the particles of a given substance are moving. As these particles move faster and faster (temperature increasing), these “pieces” of air move further and further away from each other, which leads to lower air density.
Humidity affects air density the least of the three factors, but it still has the ability to make a noticeable difference. Humidity is a measure of how much water vapor is in a given volume of atmosphere. Despite how it can feel outside on a humid day, water vapor is actually less dense than other air contents (mainly nitrogen and oxygen molecules). As the water vapor replaces these particles in a given volume of air, the air becomes less dense. High humidity, then, decreases air density.
Lastly, pressure is the measure of force that air exerts on any surface in contact with it. Pressure is most greatly affected by changes in altitude — the higher you go above sea level, the lower the air pressure. It is the most significant factor in changing the flight path of a disc.
2021 Worlds is sure to bring the challenges of low air density to the players. With temperatures in Utah slated to be in the mid-90s Fahrenheit, as well as the substantial altitude increase from previous tour stops, both players and their discs are going to feel the effects.
Primarily, discs tend to become more stable at higher altitudes (and consequently lower air pressure): they turn less in the initial part of their flight and fade more late. But why?
Ultiworld Disc Golf spoke with UCF assistant professor of mechanical and aerospace engineering Dr. Michael Kinzel, who explained that the lower air pressure reduces the lift generated at a given speed, as there are fewer air molecules for the disc to come in contact with.
Dr. William Crowther, an aerospace engineering professor at the University of Manchester who has co-authored multiple papers on the flight of flying discs, said, “Flight speeds have to go up by about 10% for a flying object to generate the same amount of lift [at 4600’, Ogden’s altitude] … If you throw [a disc] the same way as before, it will have a different flight path.”
The reduced lift translates into diminished turn. Kinzel explained that because a disc spins, one half of the disc (the right side for a right-handed backhand) has a lower effective airspeed while the other side is moving faster. That causes a pressure imbalance that creates what disc golfers call turn. “The side going into the wind is getting significantly more lift than the side going out of the wind,” he said. “That can cause that teetering effect, that roll.” At higher altitudes, though, lower overall lift means less turn.
That’s likely to mean that players will put less stable plastic in their bags, as the low air density will negate some of the turn and glide that discs have. Perhaps that could be an advantage for players who compete often at high altitude, like Colorado’s Eagle McMahon.
Regardless of the disc selection decision, the obstacle of, ironically, less air adds an extra layer of intrigue to next week’s world championship competition.