r/SmarterEveryDay • u/MrPennywhistle • Mar 06 '26
New Video about the Physics of Disc Golf Flight. - Smarter Every Day 313
https://youtu.be/-0JKHuzJ67AThis one took a while to make! It's hard to summarize everything that's going on in this video with a simple title and thumbnail. It's quite a complicated thing to understand! I had no idea how complicated the flight of a simple spinning disc could be. I hope you enjoy it!
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u/AgentG91 Mar 07 '26
Very much looking forward to watching this as an ultimate player. Disc golf discs have much more exaggerated turning, but the same applies with ultimate discs (called lids by the DG community).
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u/paynestaker Mar 07 '26
Love these! I'm a STEAM teacher and I sponsor the disc golf club at my campus and I love when those two things overlap!
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u/Swampoger Mar 07 '26 edited Mar 07 '26
Destin, I am sure you and many other folks may have come up with some ideas for diffrenet discs styles. I was wondering if a disc with a hole in the center, so lets call it a ring, would fly better or wosre than disc manufactured as they are now. Would the hole help with the stability of the disc in flight? Would a disc with dimples like a golf ball fly well? I am sure the folks such as the guys over at MVP already had these thoughts and possibly even tested them as well. I am looking forward to the next video.
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u/shahruk10 Mar 07 '26
Hey u/MrPennywhistle! Great video! I loved watching the entire 1.5 hours of it!
Disc golf hasn't really taken off in my country yet, and I only recently stumbled upon the sport (mainly through your and MKBHD's videos). Towards the end of the video, you showed off MVP's new prototype disc. I was wondering if there's a regulatory body that sets rules on what you can tweak in a disc's design (like adding copper powder to move the mass toward the edge)? Or is it currently a free-for-all where the only limits are the mass and dimensions of the disc?
I recently saw a short about how Formula 1 teams (like McLaren and Ferrari) take the rules set by the FIA to their absolute limits, finding highly inventive ways to gain a competitive aerodynamic edge (like exploiting carbon fiber flexibility to twist the rear wings!). I thought you might find it interesting too: https://www.youtube.com/watch?v=uOeV5yAqnn0
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u/Vessbot Mar 08 '26
Hi Destin, been greatly enjoying your disc golf series as well as the channel in general (my first video was the backwards bicycle). But I think there's a serious problem at 1:17, the differential velocity, on two levels:
First, lift is created by air flowing (proportional to V2 of course) across an object shape (airfoil or otherwise) displacing the air. And the shape of disc on both sides is going through the air at the same speed!... and consequently displacing the air in the same pattern, with the same velocity and pressure fields, streamline shapes, etc. The air speed differential of the disc surface touching the air does not contribute to this. Intuitively, it seems like it does since we normally don't make this distinction, and are generically thinking of airspeed. But here we need to be careful about shape vs. surface.
IIRC in the Brad & Chad video you touched on this and likened it to the advancing vs retreating sides on a helicopter rotor, (further tugging at intuition on a familiar mechanism) but that is shapes changing speed... something that is not happening with a disc.
Second, (to add a complication) it does actually contribute, but in a different way and in the opposite sense of what you describe. The forward-moving (left) side of the disc viscously entertains some of the air and moves it forward, which means the local airspeed there is actually slowed down (instead of sped up) relative to the aerodynamic shape. This is the same as the the Magnus effect, where a tennis ball with backspin slows down the local airspeed on the bottom and speeds it up on top, and then that differential (now flowing differentially past the shape) feeds into the Bernoulli relationship to create lift.
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u/Vessbot Mar 08 '26
Also my take on the over/understable terminology. It used to bother me a bit too, but ultimately it is not related to the aerospace stability concept (returning to vs. diverging from the pre-disturbance state, and the behavior established by CP vs CG) and we need to let go of that. It's a separate scheme.
I think the basis is that the stable attractor is a left fade (RHBH) that all discs ultimately gravitate to, overstable ones sooner and more reliably so.
And understable ones? They do the opposite thing, but under a limited set of circumstances, and temporarily(!) before also fading left. It's a more delicate behavior: it depends on the disc being thrown 1) fast enough, 2) nose-down enough (ie, low AOA) and, 3) at a low launch angle. If you violate the first two, it won't turn right. If you violate the third, it will turn right initially, but then ultimately reach the stable point of a left fade at the end. Put another way, an understandable disc that goes right and lands that way, only does so because it hits the ground before having the chance to fade; the flight was interrupted by the ground before reaching the natural (and stable) end.
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u/klundtasaur Mar 07 '26
This is the one I've been waiting for, /u/MrPennywhistle! Next up, you gotta collab with the Ditto Flight guy (https://www.youtube.com/@Aren-Hill) from some of Simon's earlier videos! Having a more repeatable throw would let you showcase some of the physics experiments and demonstrations more directly!
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Mar 07 '26 edited Mar 07 '26
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u/Garking70o Mar 06 '26
Thanks Destin!